Hungitons Disease
Hungitons Disease
Hungitons Disease
HUNTINGTON'S DISEASE:
ETIOLOGY AND SYMPTOMS,
DIAGNOSIS AND TREATMENT
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HUNTINGTON'S DISEASE:
ETIOLOGY AND SYMPTOMS,
DIAGNOSIS AND TREATMENT
THOMAS J. VISSER
EDITOR
Contents
Preface
Chapter I
Chapter II
vii
Molecular Mechanisms Involved in the Pathogenesis
of Huntington Disease
Claudia Perandones, Martn Radrizzani
and Federico Eduardo Micheli
Huntingtin Interacting Proteins: Involvement in Diverse
Molecular Functions, Biological Processes and Pathways
Nitai P. Bhattacharyya, Moumita Datta,
Manisha Banerjee, Srijit Das
and Saikat Mukhopadhyay
Chapter III
Chapter IV
Chapter V
Chapter VI
Chapter VII
39
61
75
87
99
127
vi
Chapter VIII
Index
Contents
The Control of Adult Neurogenesis
by the Microenvironment and How This May be Altered
in Huntingtons Disease
Wendy Phillips and Roger A. Barker
181
239
Preface
Huntington's disease, chorea or disorder (HD) is an incurable neurodegenerative genetic
disorder, which affects muscle coordination and some cognitive functions, typically becoming
noticeable in middle age. It is the most common genetic cause of abnormal involuntary
writhing movements called chorea and is much more common in people of Western European
descent than in those from Asia or Africa. The disease is caused by a dominant mutation on
either of the two copies of a gene called Huntington. This book gathers and presents current
research in the study of Huntington's Disease including the outlining effects of mutant htt in
the nucleus and cytoplasm and the role of cell-cell interactions in Huntington's Disease
pathology, as well as a review of the role of Huntington (HTT) interacting proteins.
Chapter I - Huntington's disease (HD) is an autosomal-dominant, progressive
neurodegenerative disorder with a distinct phenotype, including chorea, incoordination,
cognitive decline, and behavioral difficulties. The underlying genetic defect responsible for
the disease is the expansion of a CAG repeat in the gene coding for the HD protein,
huntingtin (htt). This CAG repeat is an unstable triplet repeat DNA sequence, and its length
inversely correlates with the age at onset of the disease. Expanded CAG repeats have been
found in 8 other inherited neurodegenerative diseases. Despite its widespread distribution,
mutant htt causes selective neurodegeneration, which occurs mainly and most prominently in
the striatum and deeper layers of the cortex.
Remarkable progress has been made since the discovery of HD gene in 1993. Animal
models to study the disease process, unraveling the expression and function of wild-type and
mutant huntingtin (htt) proteins in the central and peripheral nervous systems, and
understanding expanded CAG repeat containing mutant htt protein interactions with CNS
proteins in the disease process have been developed . Consequently, it has been concluded
that htt may cause toxicity via a wide range of different mechanisms. The primary
consequence of the mutation is to confer a toxic gain of function on the mutant htt protein,
and this may be modified by certain normal activities that are impaired by the mutation. It is
likely that the toxicity of mutant htt is only revealed after a series of cleavage events leading
to the production of N-terminal huntingtin fragment(s) containing the expanded
polyglutamine tract. Although aggregation of the mutant protein is the hallmark of the
disease, the role of aggregation is complex and the arguments for protective roles of
inclusions are discussed. HD progression has been found to involve several
pathomechanisms, including expanded CAG repeat protein interaction with other CNS
proteins, transcriptional dysregulation, calcium dyshomeostasis, defective mitochondrial
viii
Thomas J. Visser
bioenergetics and abnormal vesicle trafficking. Notably, not all the effects of mutant htt are
cell-autonomous, and it is possible for abnormalities in neighboring neurons and glia to also
have an impact on connected cells.
The present review focuses on HD, outlining the effects of mutant htt in the nucleus and
cytoplasm as well as the role of cell-cell interactions in the HD pathology. The widespread
expression and localization of mutant htt and its interactions with a variety of proteins suggest
that mutant htt is engaged in multiple pathogenic pathways. A better understanding of these
mechanisms will lead to the development of more effective therapeutic targets.
Chapter II - To gain insight into role of Huntingtin (HTT) interacting proteins in
pathogenesis of Huntingtons disease (HD), in the present review, using various databases
and published data we analyzed 141 validated HTT interacting proteins out of 311 proteins
identified as the interactors of HTT. Results revealed that (i) all 141 proteins express in brain,
(ii) fifty three HTT interacting proteins are down regulated and 36 proteins are increased in
caudate of HD patients (iii) 25 proteins preferentially interact with mutated HTT, 19 proteins
have higher affinity towards wild type HTT and 33 proteins interact equally and (iv) 120 HTT
interacting proteins interact with 1780 unique other proteins including 67 HTT interacting
proteins and having 2998 interactions altogether. Altered expressions of HTT interacting
proteins and their preferences for the wild type and mutated proteins are likely to alter the
network of HTT interacting proteins in HD resulting in cellular dysfunctions observed in HD.
Several interacting proteins are known to modulate HD pathogenesis in cell, animal models
and HD patients. Significantly enriched HTT interacting proteins in various functional
categories, biological processes and pathways compared to that coded by human genome
indicates that these functions, processes and pathways are altered in HD. All these data
presented and reviewed in this chapter indicate that in spite of being a monogenic disease, HD
is quite complex at molecular level. Understanding the molecular interactions and diverse
pathways these interacting proteins participate are expected to help in devising therapeutic
strategies to combat this devastating disease.
Chapter III - Huntington's disease (HD) is a progressive neurodegenerative disorder
resulting in cognitive impairment, choreiform movements and death which usually occurs 1520 years after the onset of the symptoms. A CAG repeat expansion within exon 1 of the gene
encoding for huntingtin (IT15) causes the disease. In the normal population the number of
CAG repeats is maintained below 35, while in individuals affected by HD it ranges from 35
to more than 100, resulting in an expanded polyglutamine segment in the protein. HD age at
onset is inversely correlated with the CAG repeat length; moreover the CAG repeat length
seems to be related to the rate of progression of neurological symptoms and motor
impairment. Somatic CAG repeat expansion in the huntingtin gene has been observed in
several tissues of HD patients, but particularly in the striatum, the region most affected by the
disease. An age-dependent somatic CAG repeat expansions was also observed in tissues of
HD transgenic mice. Recently, it was found that somatic CAG repeat expansion is induced by
oxidative stress in cultured HD fibroblasts and occurs during the repair of oxidized base
lesions, dependent on a single base excision repair (BER) enzyme, the DNA glycosylase
OGG1 which specifically removes oxidized guanine (8-oxo-G) from the DNA. It was
therefore hypothesized that an age-dependent increase in 8-oxo-G formation in post-mitotic
neurons could induce a DNA damage response mediated by OGG1 and give rise to a CAG
repeat expansion that likely contributes to the onset and the progression of the disease.
Further studies confirmed that somatic expansion of the CAG repeat tract in the brain is
Preface
ix
associated with an earlier HD age at onset. Preliminary results from our group suggest that a
common OGG1 Ser326Cys polymorphism could contribute to CAG repeat number and
disease age at onset. Several subsequent studies support a role for oxidative DNA damage and
BER to somatic instability of CAG repeats. There is also evidence that another DNA repair
pathway, the mismatch repair (MMR), is required for the active mutagenesis of expanded
CAG repeats. Since MMR is required for the repair of mismatched adenine opposite to 8-oxoG, it remains to be seen if both BER and MMR co-operate physically in the process of CAG
repeat expansion.
Chapter IV - Huntingtons Disease (HD) is a late onset autosomal dominant
neurodegenerative disease leading to movement disorders, dementia and psychiatric
manifestations. The management of these patients, for whom there is still no cure, has been
for long time neglected by clinicians.
The identification of HD mutation in 1993 has raised a new interest in research as well as
in clinical field and experimental data on patients care have begun to heap up. Among
pharmacological therapies, data have become available on management of motor disorders
with different types of neuroleptics or other classes of drugs while for the treatment of
psychiatric and parkinsonian symptoms the available evidence is not specific for HD.
Among non pharmacological therapies, rehabilitation has recently provided good results
supported by measurable outcomes.
Although these advances in management are encouraging, HD poses so many problems
on so many different levels, that the way to attain an evidence based best care is still long.
In this chapter we provide some discussion as to the best care in HD as well as to some
ethical problems posed by the disease. We take into consideration either the advances attained
in the different types of therapies or the knowledge acquired outside an experimental setting,
during many years clinical practice with HD patients.
Chapter V - With the many advances in medical care, the dentist will be quite likely to be
asked to treat patients with special health care needs. The dentist may be asked to recommend
preventive regimens to maintain good oral health or provide comprehensive treatment of
advanced dental disease. The patient with Huntingtons disease is but one example of the
debilitating effects systemic disease can have upon the oral cavity. There are no direct
adverse affects on the oral cavity due to Huntingtons disease; however complications
associated with the disease increase the risk for dental caries and periodontal disease. As
Huntingtons disease progress, the persons ability to cooperate will diminish as functional
and cognitive abilities decline. This will require the development of realistic treatment plans
and easily maintainable dental restorations. Caregivers will need to be involved throughout
the process as oral complications are likely throughout this long and difficult disease.
Chapter VI - Huntingtons Disease (HD) is an autosomal-dominant neuropsychiatric
disorder characterized by irreversible physical and mental deterioration, personality change,
mental disorder, and increased susceptibility to suicidal ideation and suicide. Typically the
disease has a very long course to run before death. There is little that the affected or HD
persons who find out their carrier status can do, although if they come early for genetic
testing, they can make reproductive choices. If the diagnosis or the predictive information has
little therapeutic value to the patient, especially if there is no family, one possible available
action is planning of a suicide. Higher suicide rates are reported for HD patients compared to
the general population. It is also well known that persons with HD have an increased
propensity to psychiatric dysfunction and elevated rates of catastrophic social events.
Thomas J. Visser
Furthermore, surveys of attitudes about likelihood of attempted suicide have indicated that 529% of at risk individuals would contemplate suicide if they received a result indicating a
carrier status. The prevalence of suicide and suicide attempts is difficult to estimate because
of methodological problems. Suicide rates of HD populations vary among countries, and they
are affected by factors such as socio-economic status, age, sex, and prevalence of HD. It
appears that cases of suicide vary from 1.6% to 13.8% in HD populations. In this chapter,
suicidal behaviour, psychological affect of predictive testing, suicidal ideation and behaviour
before and after predictive testing, and depression in HD, are discussed. At present, the
problems associated with suicidal ideation and suicide in HD populations, worldwide, are
much the same as two decades ago. The need for counselling, using a well designed protocol,
and the importance of focusing on suicide risk of participants in predictive testing programs is
emphasized.
Chapter VII - This chapter makes two contributions to the psychology of decision
making. It draws on empirical work to document how family members make and live with
reproductive decisions as they become aware of their risk for a serious late-onset genetic
disorder, Huntingtons disease (HD). Decision-making involves negotiating two dimensions
of reproductive risk that for any child which might be born and the uncertainty that arises
about the at-risk parents ability to sustain a parenting role should he or she become
symptomatic. A detailed account is given of how the model of responsibility was generated
from their narratives. This model encapsulates what families find important when making
reproductive decisions. It demonstrates that how people make decisions can become as
important as what they decide. Examples are given to show how the model provides a
framework for comparing how people deal with each dimension of risk, to compare different
peoples decision-making and to illuminate decision-making in the face of change. This
includes how they address new options generated by recent developments in molecular
genetics which can resolve uncertainty about, or avoid these risks. A detailed account is also
given of the process of their decision-making. These findings are used to evaluate claims
being made by naturalistic decision-making (NDM) initiatives to account for decision-making
in the real world. An outline of this initiative prefaces the research findings. Beachs (1990)
image theory, used to illustrate the NDM approach, emphasises the role that values play in
forming, negotiating, implementing and living with decisions that arise in everyday lives.
Participants accounts support this claim - revealing how values such as responsibility
become established and contribute to decision-making. This and other findings lend support
to the NDM claims. The chapter concludes with suggestions about how the model might be
used more generally to further our understanding of the psychology of decision-making in the
face of risk.
Chapter VIII - Neurogenesis is the processes whereby newborn neurons are formed and
occurs in mammals in adulthood in specialised areas, known as neurogenic niches. The
subventricular zone, and subgranular zone of the dentate gyrus of the hippocampus are such
specialised neurogenic niches and newborn neurons formed here contribute to learning and
memory, but neurogenesis may occur elsewhere in the brain to a more limited extent. The
neurogenic niche is composed of specialised glial cells, basal lamina, ependymal cells,
neurotransmitter complement and vasculature. Neurogenesis is a complex process, involving
many different cell types, and several stages of neuronal maturation; and each component
may be affected by many different microenvironmental perturbations. External perturbations,
like seizures and lesions alter the microenvironment and in turn, alter neurogenesis. Chronic
Preface
xi
disease can also affect neurogenesis and the inherited neurodegenerative condition
Huntingtons disease may do so through an alteration of the microenvironment. We will use
the example of Huntingtons disease to explore how changes in the microenvironment might
impact on neurogenesis and, thus identify potential therapeutic targets.
Chapter I
Abstract
Huntington's disease (HD) is an autosomal-dominant, progressive neurodegenerative
disorder with a distinct phenotype, including chorea, incoordination, cognitive decline,
and behavioral difficulties. The underlying genetic defect responsible for the disease is
the expansion of a CAG repeat in the gene coding for the HD protein, huntingtin (htt).
This CAG repeat is an unstable triplet repeat DNA sequence, and its length inversely
correlates with the age at onset of the disease. Expanded CAG repeats have been found in
8 other inherited neurodegenerative diseases. Despite its widespread distribution, mutant
htt causes selective neurodegeneration, which occurs mainly and most prominently in the
striatum and deeper layers of the cortex.
Remarkable progress has been made since the discovery of HD gene in 1993.
Animal models to study the disease process, unraveling the expression and function of
wild-type and mutant huntingtin (htt) proteins in the central and peripheral nervous
systems, and understanding expanded CAG repeat containing mutant htt protein
interactions with CNS proteins in the disease process have been developed .
Consequently, it has been concluded that htt may cause toxicity via a wide range of
different mechanisms. The primary consequence of the mutation is to confer a toxic gain
1. Huntingtons Disease
1.1. Introduction: Unstable Expanding Repeats as a Novel Cause of
Disease
Prior to this decade, the adage that goes like begets like fitted nicely with the dogma of
human genetics where the genetic material was considered stable upon transmission, and in
the rare instance of mutation, the new variant itself was stably inherited. Although there had
been clear instances when this did not hold true, the human genetics community did not
embrace the notion of dynamic mutations.
Clinical researchers had long suspected something was amiss when carefully examining
families with dominant Myotonic Dystrophy, where they found that off-springs of affected
individuals often had a more severe form of the disease.
The term anticipation was used to define this progressive increase in expressivity of the
identical mutation over a number of generations.
Since anticipation did not easily fit with the biological dogma of the genetics of that era,
the concept of anticipation was summarily dismissed as an ascertainment bias. Many years
later, the recognition of increasing penetrance through subsequent generations in Fragile X
syndrome, later known as the Sherman Paradox, resembled the genetic anticipation of
Myotonic Dystrophy.
While the observation in Fragile X syndrome -the Sherman paradox- was more easily
accepted by the scientific community, anticipation could not be readily explained at a
molecular level.
Even when proven true, the phenomenon represents one of the darkest black holes in
molecular genetics.
In 1991, the genes responsible for the Fragile X syndrome and Spinobulbar Muscular
Atrophy were found to contain unstable, expanded trinucleotide repeats. The following year,
Myotonic Dystrophy was also found to be the result of an expanded trinucleotide repeat.
These findings were soon followed by a remarkable number of neurological disorders, each
sharing the mutational mechanism of the unstable expansion of a repeat, most often a triplet
in form.
Soon, the behavior of these repeats in affected families clearly revealed a pattern where
the increasing penetrance (Sherman Paradox) or increasing expressivity (Anticipation),
through subsequent generations, correlated with increasing lengths of the triplet repeat. Thus,
a biological basis of anticipation was defined -the dynamic mutation.
polyglutamine tracts, constraints of the individual protein structures significantly modify this
range. This is most apparent in SCA 6 where the largest normal allele contains 18 repeats,
whereas the smallest abnormal allele contains 21 repeats. In all coding expansions, the
mechanism(s), while still poorly understood, appear to reflect a gain or change of function of
the abnormal protein, eventually leading to neurodegeneration.
Common features of the diseases caused by expansion of an unstable CAG repeat within
a gene include:
They are all late-onset neurodegenerative diseases, and except for Kennedy disease, they
are all dominantly inherited.
The expanded allele is transcribed and translated.
The trinucleotide repeat encodes a polyglutamine tract in the protein.
There is a critical threshold repeat size, below which the repeat is nonpathogenic and
above which it causes disease.
The larger the repeat above the threshold, the earlier the onset age (on average;
predictions cannot be made for individual patients, but there is a clear statistical
correlation).
The CAG repeat disease genes identified so far are widely expressed and encode proteins
of unknown function. When the polyglutamine tract exceeds the threshold length,
there is protein aggregation, forming an inclusion body that apparently kills the cell.
The different clinical features of each disease reflect killing of different cells, presumably
because of interactions with other cell-specific proteins.
Neuronal cell death caused by protein aggregates is a common thread in the pathology of
CAG repeat diseases, Alzheimer disease, Parkinson disease and prion diseases; the
mechanism and their general significance remain to be discovered.
MIM
number
309550
Repeat
Unit
(CGC)n
Gene
Product
FMRP
Normal
Repeat
6-60
Expanded
Repeat
>200 (full
mutation)
FRAXE
FRDA
309548
229300
(CCG)n
(GAA)n
FMR2
Frataxin
4-39
6-32
200-900
200-1700
B. RNA-mediated pathogenesis
Disease
DM1
MIM
number
160900
Repeat
Unit
(CTG)n
Gene
Product
DMPK
Normal
Repeat
5-37
Expanded
Repeat
50-10.000
DM2
602668
(CCTG)n
ZNF9
10-26
75-11.000
FXTAS
309550
(CGG)n
FMR1
RNA
6-60
60-200
Dr. Huntingtons treatise displayed such clarity that it was reprinted in prominent
neurology texts and termed Huntingtons Chorea. More recently, the observation that some
cases, and particularly those with a young onset, may present without chorea, has led to the
widespread adoption of the designation Huntingtons Disease (HD) to refer to this affliction.
HD is a midlife-onset disease which strikes at a mean age of 40 years, but onset may vary
from 4 to 80 years of age (Harper, 1992).
It is a progressive neurodegenerative disorder with primary neuropathological
involvement in the basal ganglia. HD is invariably fatal, without periods of remission, and the
course from onset to death averages 15 to 17 years (Myers, Sax et al. 1991). The disease is
characterized mainly by involuntary choreiform movements, cognitive impairment, and
personality disorder featuring depression, anger and temper outbursts, as well as cognitive
disorders.
Table 2. Unstable repeat disorders caused by unknown pathogenic mechanisms
Disease
SCA 8
MIM
number
608768
Repeat Unit
(CTG)n
SCA 10
603516
(ATTCT)n
SCA 12
604326
(CAG)n
EHL2
606438
(CTG)n
Gene
Product
SCA 8 RNA
Normal
Repeat
16-34
Expanded
Repeat
> 74
10-20
500-4500
PPP2R2B
7-45
55-78
Junctophilin
7-28
66-78
Main clinical
features
Ataxia, slurred
speech, nistagmus.
Ataxia, tremor,
dementia.
Ataxia and
seizures
Similar to HD.
MIM
number
143100
Gene
Product
Huntingtin
Normal
Repeat
6-34
Expanded
Repeat
36-121
164400
Ataxin 1
6-44
39-82
SCA 2
183090
Ataxin 2
15-24
32-200
SCA 3
109150
Ataxin 3
13-36
61-84
SCA 6
183086
CACNA1a
4-19
10-33
SCA7
164500
Ataxin 7
4-35
37-306
SCA 17
607136
TBP
25-42
47-63
SBMA
313200
Androgen
Receptor
9-36
38-62
DRPLA
125370
Atrophin
7-34
49-88
Huntington
disease
SCA 1
The cytogenetic bands of the short arm of chromosome 4 (4p) are depicted with the location of the HD
defect in 4p16.3 from the genetic linkage and physical mapping according to what studies indicate.
The map of 4p16.3 provides an expanded view of this telomeric cytogenetic band to illustrate the
location of the defect relative to polymorphic DNA markers used to sequentially narrow the
minimal HD genetic region by recombination analysis, linkage disequilibrium, and haplotype
analysis.
Figure 2. Huntingtin gene localization in Chromosome 4
The HD gene was genetically linked to an anonymous marker located in 4p16.3 (Figure
2) (Gusella, Wexler et al. 1983) and, following a 10-year long molecular genetic search, was
finally discovered to be an unstable CAG trinucleotide repeat (The Huntington's Disease
Collaborative Research Group, 1993). The mutation extends a polymorphic stretch of CAG
codons in the first exon of the HD gene, lengthening a segment of polyglutamine near the
amino terminus of the HD protein which has been named huntingtin. The mutation which
leads to the expression of HD is an approximate doubling in the number of the triplet repeats
from a normal number of about 18 to an expanded number of 40 or more.
1.4. Epidemiology of HD
The prevalence of HD is estimated at 5 to 10 affected persons per 100,000 among
individuals of European descent but is less common among other ethnic groups (Harper,
1992; Al-Jader, Harper et al., 2001; Bertram and Tanzi, 2005).
Indeed, the prevalence of HD among the native African population is so low as to make
an accurate estimate difficult, and its prevalence among Japanese and Asian populations is
approximately one-tenth of that observed in Caucasians. Since for each affected individual,
there is an estimate of two living carriers who are still too young to manifest symptoms, the
prevalence of HD gene carriers in the general Caucasian population may be estimated at 15 to
30 per 100,000, and there is an equal number of siblings at risk, who are the ones who have
not inherited the HD defect. Thus, approximately 1 in every 2,500 births is an individual born
at risk for the disease, making HD the most common of the CAG repeat expansion diseases.
Therefore, genotype-phenotype correlations in HD will most likely enable to describe
uncommon events such as new mutations or alleles with reduced penetrance, which may be
too rare to be observed in other triplet repeat diseases.
10
B. Age at onset
The age at onset of HD is highly variable. The earliest cases have been reported with
onset at 2 to 3 years of age, while the latest onsets approach 80 years of age or even older.
The average is at age 40 and is not gender related. Approximately 7% of all cases present
before the age of 20 and this group of individuals has traditionally been termed juvenile
onset HD.
The impact of the HD repeat upon phenotypic expression has been heavily researched.
The relationship between age at onset and repeat size is unequivocal and very strong but it is
not linear; most investigators have noted that the best fit is a model in which the repeat
predicts the log10 of onset age (Ranen, Stine, et al. 1995). For the 220 HD cases depicted in
Figure 3, the correlation between repeat size and log of onset age is r = - 0.84 and accounts
for about 70% of the variance in onset age.
Kremer et al (Kremer, Squitieri, et al. 1993), noted that for late-onset cases, with onset at
age 50 or older, the correlation of onset with repeat size is reduced (r=-0.29).
Relationship between the length of the expanded HD CAG repeat and age at neurological onset of
disease. The CAG repeat sizes for 220 individuals affected with HD diagnosed through the New
England Huntingtons Disease Research Center are presented in relation to the age at onset of
motor impairment. Repeat size is strongly related to age at onset. Onset age before age 20 is
usually associated with a repeat size of more than 60 CAG units. Among persons with adult onset,
the range in onset age for a given repeat is large and may vary by 35 years or more.
Figure 3. Relationship between length of CAG repeat and age at neurologic onset of disease
11
It has been noted that there is a +/- 18-year, 95% confidence interval around the estimated
onset age for a given repeat size. Although one group recently suggested that the confidence
interval may be smaller than this estimate, all published reports confirm that the range in
onset age for a given repeat size exceeds 30 years among persons with mid and late-life
disease.
Thus, for more than 90% of presymptomatic HD cases, the relationship of repeat size xxx
is not strong enough to predict the onset age.
C. Rate of disease progression
The course of disease in HD is remarkably variable, but there have been only a few
studies of factors related to progression (Myers, Sax, et al. 1991). There is evidence that age
at onset is related to rate of progression, and it has been suggested that a single mechanism
influences both the age at onset and the rate of disease progression. Although not strong
enough to predict onset pre-symptomatically, the HD repeat size appears to be the primary
determinant of onset age and thus it is reasonable to expect that the repeat size is related to the
rate of disease progression as mediated either by its effect upon onset age or by a direct effect
upon disease progression.
A study of a set of monozygotic twins raised apart suggested that progression is largely
determined by genetic factors and that the most likely determinant is the trinucleotide repeat
size (Sudarsky, Myers, et al., 1983).
Many authors have reported a significant association between repeat size and rate of
disease progression.
Another factor is the gender of the affected parent, with offspring of affected fathers
having a more rapid progression than offspring of affected mothers. In addition, lower body
mass index early in the disease is related to more rapid disease progression.
While the gender of the affected parent and paternal transmission is now known to be
related to the transmission of an expanded repeat, it is not known whether the repeat size
influences weight loss or lower body mass index (Marder, Zhao H, et al. 2009).
These studies are relevant when considering trials for therapeutic interventions, which
will need to consider the HD repeat in the randomization of study participants.
D. Neuropsychology
1. Cognitive function in HD
While language functioning remains relatively intact, the most striking cognitive deficits
involve areas of executive system functioning (e.g., strategies in problem solving and
cognitive flexibility), short-term memory, and visuospatial performance. The memory
disorder is characterized by inconsistent retrieval of information. In the early stages of the
disease, recognition memory for verbal information is robust, while spontaneous recall of
information may be more frequently impaired.
Early in the disease process, the cognitive deficits are relatively focal. A global,
progressive subcortical dementia does not evolve until the disease advances significantly.
Although this dementia is significant and debilitating in the late and final stages of the
disease, it is qualitatively different from the cortical dementia observed in Alzheimers
disease (Duff, Beglinger, et al. 2009).
12
13
14
15
Four CAG repeat size intervals are recognized as associated with varying disease risk in HD. These
ranges have been defined by the US HD Genetic Testing Group (USHDGTG) and are derived
from information gleaned from more than 1000 HD tests.
Figure 4. Repeat size and HD risk
However, despite having performed additional histochemical staining, the authors failed
to detect the presence of htt in the ubiquitin-positive neuronal intranuclear inclusions.
16
Although the detection of the htt stain is not absolutely necessary to establish the
neuropathological diagnosis of HD (Jean Paul Vonsattel, MD, personal communication),
arguably in this case it would be relevant to confirm the presence or absence of the mutated
protein in the nucleus, as the subcellular localization of mutant htt is critical for the pathology
of HD.
In agreement with this report, many recent experimental findings are shifting the focus
from the polyglutamine expanded tract to other domains of the protein for toxicity (Zoghbi
and Orr 2009). In other words, the notion that toxicity is simply a result of an expanded toxic
polyglutamine tract that might escape the cellular degradation and quality control machinery
becomes less likely.
The expansions of the polyglutamine tracts, although relevant, are not the only molecular
mechanisms to cause toxicity. Many studies in spinobulbar muscular atrophy and HD indicate
that protein domains outside the polyglutamine tract play a significant role in the selective
neurotoxicity observed in these diseases (Graham, Deng et al., 2006).
The possibility of having HD with 29 CAG repeats would entail significant changes in
genetic counselling of HD families, HD therapeutic trials and the current understanding of the
molecular pathogenesis of the disease.
17
For example, even in early to mid stages of the disease, structural magnetic resonance
imaging (MRI) studies reveal that regions other than the neocortex and striatum, notably
hippocampus, globus pallidus, amygdale and cerebellum, can also show morphometric
changes (Rosas, Koroshetz, et al., 2003). Pathology in the neocortex and hippocampus may
be of particular significance with regard to the cognitive deficits seen in HD.
Reactive microglia has been detected in the cortex and striatum of post-mortem human
HD brains. The density of activated microglia correlated with the degree of neuronal loss and
Vonsattel grading. Markers of increased inflammatory gliosis were also identified post
mortem in the putamen and frontal cortex, and together, these findings suggest that an
inflammatory process may possibly be contributing to HD, although it is not known whether
this has any impact on disease onset or progression.
The genetic expression of Huntingtin can be observed through a tridimensional approach using in situ
hybridizations performed with mRNAs in murine cerebral cortex slices (http://www.brainmap.org, Allen Institute for Brain Science. 2004). The results of these hybridization assays are
in concordance with the ones previously published in Nature (Site, Lein, E.S. et al., Genomewide atlas of gene expression in the adult mouse brain, Nature 445: 168-176 (2007),
doi:10.1038/nature05453). The bottom figure is a tridimensional reconstruction that highlights the
regions showing selective vulnerability in HD, namely the striatum and cerebral cortex.
Figure 5. Selective vulnerability of the striatum in HD.
18
Control
Affected
One characteristic neuropathological feature, present in both human HD patients and transgenic HD
mice, is the presence of protein aggregates, also known as neuronal inclusions, which are formed
from the aggregation of expanded polyglutamine-cointaining Htt fragments as well as numerous
other proteins.
Figure 6. Neuritic aggregates and perinuclear inclusions in HD
2. Molecular Pathogenesis of
Huntingtons Disease
2.1. HD Gene and Gene Product
The genetic defect responsible for HD is an expansion of a CAG repeat in the gene
coding for the HD protein. This CAG repeat is an unstable triplet repeat DNA sequence, and
its length is inversely correlated with the age at onset of disease, especially in juvenile HD
19
cases, in which the repeat length is often >60 CAG units (Andrew, Goldberg et al., 1993)
(Figure 7: A schematic diagram of human Huntingtin).
Expanded CAG repeats have been found in 10 other inherited neurodegenerative
diseases, as well, including spinocerebellar ataxia (SCA) and spinobulbar muscular atrophy
(SBMA) (Zohbi and Orr, 2000; Gatchel and Zoghbi 2005; Butler and Bates 2006) (see Tables
2 and 3). It is now clear that expansion of this repeat in various genes can cause distinct
neurodegenerative pathology leading to different disorders.
The CAG repeat is translated into a polyglutamine (polyQ) domain in the disease
proteins. Human htt is a large protein comprising 3144 amino acids. A normal polyQ domain,
which in htt begins at amino acid position 18, tipically contains 11-34 glutamine residues in
unaffected individuals, but this expands to more than 37 glutamines in HD patients. The
length of the polyQ repeat varies among species. For example, mouse htt has 7 glutamines,
whereas pufferfish htt contains only 4 (Harjes and Wanker 2003), which suggests that the
polyQ domain may not be essential, but that it can regulate protein function. Consistently,
deletion of the CAG repeat in the HD gene only results in subtle behavioral and motor
phenotypes in mice.
The diagram shows the structure of the gene, mRNA and htt protein.
Figure 7. A schematic diagram of human huntingtin
20
Htt is ubiquitously expressed in the brain and body and distributed in various subcellular
regions (Gutenkunst, Levey et al., 1995). Its sequences do not show homology to other
proteins of known function. One structural feature of htt, is the presence of HEAT repeats
(Takano and Gusella 2002), which are sequences of ~40 amino acids that occur several times
within a given protein and are found in a variety of proteins involved in intracellular transport
and chromosomal segregation (Neuwald and Hirano 2000).
Several lines of evidence also suggest that htt is involved in intracellular trafficking and
various cellular functions. As an example, htt is associated with a number of subcellular
organelles (DiFiglia, Sapp et al., 1995; Gutekunst, Levey, et al., 1995; Sharp, Love et al.,
1995; Gutekunst, Li et al., 1998).
In concordance with that, htt is known to interact with a variety of proteins that can be
grouped according to whether they are involved in gene transcription, intracellular signaling,
trafficking endocytosis, or metabolism (Harjes and Wanker 2003; Li and Li 2004).
Identification of these htt-interacting proteins suggests that htt may function as a scaffold
involved in coordinating sets of proteins for signaling processes and intracellular transport.
The essential role of htt has been established using HD gene knockout mice. In this
model, the absence of htt causes cell degeneration and embryonic lethality (Duyao, Auerbach
et al., 1995; Nasir, Floresco et al., 1995; Zeitlin, Liu et al., 1995). Conditional knockout mice
also show degeneration in adult cells (Dragatsis, Levine et al., 2000). These observations
have led to the theory that a loss of htt function may contribute to the neuropathology of HD
(Loss of function hypothesis) (Cattaneo, Rigamonti et al, 2001). However, there is more
evidence to support the theory wherein mutant htt gains a toxic function (gain of function
hypothesis). For example, heterozygous HD knock mice are known to live normally. Further,
identification of the HD gene has allowed the generation of various animal models in which
mutant htt is expressed in the presence of endogenous normal htt, and these transgenic mice
still develop neurological symptoms and die early, even when endogenous normal htt is
expressed at the normal levels (Davies, Turmaine et al., 1997; Schilling, Becher et al., 1999).
Moreover, mutant htt can rescue the embryonic lethal phenotype of htt-null mice
(Hodgson, Smith et al., 1996), which also suggests the HD mutation can lead to neuronal
toxicity, independent of the essential function of htt.
21
22
2000; Li, Li et al., 2001). Moreover, the neuropil aggregates are associated with axonal
degeneration in HD mouse brains (Li, Li et al., 2001; Yu, Li et al., 2003).
Taken together, the localization of htt aggregates in the nucleus and neuronal processes
reveals that mutant htt elicits toxicity in both the nucleus and cytoplasm.
23
Transgenic mice expressing polyglutamine expanded htt with a mutated caspase-6 cleavage
site did not manifest behavioral deficits or neurodegeneration, even when the expression level
of htt exceeded that in unmutated polyglutamine expanded htt transgenic mice. Also, htt
mutated at caspase-6 cleavages sites had a significant delay in its nuclear translocation.
Nuclear translocation is an early step in pathogenesis in an HD knock-in mouse model
(Wheeler, Gutekunst et al., 2002) and is known to be required for neurotoxicity of other
polyglutamine disease proteins.
These results demonstrate that sequences outside the polyglutamine tract are critical for
pathogenicity and are consistent with cleavage of htt by caspase-6 as a critical event for
pathology in HD. However, the importance of caspase-6 cleavage for HD needs to be
confirmed through manipulation of caspase-6 activity in transgenic mice expressing full
length mutant htt.
Most studies used transfected proteins to identify cleavage sites, and the nature of toxic
N-terminal fragments generated organically in the HD brain is still being explored. It is likely
that the proteolysis of full-length htt generates a number of N-terminal htt fragments. The
decreased activities of the proteasomes and chaperones, which are responsible for clearing out
misfolded and toxic peptides, promote the accumulation of htt fragments in aged neurons. In
the meantime, an expanded polyglutamine tract causes them to misfold and aggregate in the
nucleus and neuronal processes. The accumulation of mutant htt in the nucleus and neuronal
processes therefore suggests that these subcellular regions are the primary sites for mutant htt
to elicit its toxicity.
24
Studies of N-terminal htt fragments have failed to find whether these fragments contain
nuclear localizations sequences. Thus, N-terminal htt fragments may passively enter the
nucleus, but expanded polyQ repeats prevent their export from the nucleus (Cornett, Cao et
al., 2005). The presence of mutant htt fragments in the nucleus and various cleavage sites in
the N-terminal region of htt (Sun, Savanenin et al., 2001) also support the notion that
proteolysis of htt leads to the generation of toxic htt fragments. Consistently, smaller Nterminal htt fragments appear to be more toxic than large-sized fragments in both cultured
cells (Hackam, Singaraja et al., 1998) and transgenic animals (Davies, Turmaine et al., 1997;
Schilling, Becher et al., 1999; Yu, Li et al., 2003).
The aberrant nuclear accumulation of mutant htt is likely to cause gene transcriptional
dysregulations. Indeed, several nuclear transcription factors that bind htt have been found
(Sugars and Rubinsztein 2003; Li and Li 2004). Of these, the coactivators cAMP response
element-binding protein (CREB) and the specificity protein 1 (Sp1) are particularly important
for neuronal function. Deletion of CREB in the brain causes selective neurodegeneration in
the hippocampus and striatum (Mantamadiotis, Lemberger et al., 2002). Many neuronal genes
that lack a TATA box require Sp1 for their transcription (Myers, Dingledine et al., 1999).
Dysregulation of gene expression mediated by CBP (CREB-binding protein) and Sp1 have
been found in HD mouse brains (Luthi-Carter, Hanson et al., 2002).
The interactions of mutant htt with transcription factors may occur at various binding
sites. Many transcription factors contain a polyQ-rich domain. Since CBP is recruited into
aggregates formed by different polyQ proteins, such as the androgen receptor (McCampbell,
Taylor et al., 2000), the SCA3 (Chai, Wu et al., 2001), and the Dentatorubral-Pallidoluysian
atrophy (DRPLA) proteins (Nucifora, Sasaki et al., 2001), it has been thought that the polyQ
domain is the binding site to interact with other polyQ proteins. Supporting this idea, a
number of transcription factors containing polyQ or proline rich domains, including CBP
(Nucifora, Sasaki et al., 2001; Steffan, Bodai et al., 2001), TBP (Huang, Faber et al., 1998;
Perez, Paulson et al., 1998), and TAF130 (Shimohata, Nakajima et al., 2000), have been
found in nuclear polyQ inclusions.
However, subsequent studies showed that the acetyltransferase domain in CBP interacts
with htt (Chai, Wu et al., 2001; Steffan, Bodai et al., 2001), which led to the finding that
inhibition of histone deacetylase (HDAC) or promotion of histone acetylation ameliorates
neurodegeneration in cellular and fly models (Steffan, Bodai et al., 2001) and motor deficits
in a mouse model of HD (Hockly, Richon et al., 2003).
These observations prompted a hypothesis whereby the pathogenic process was linked to
the state of histone acetylation; specifically, mutant huntingtin induced a state of reduced
histone acetylation and as a result altered gene expression. Support for this idea was obtained
from the Drosophila HD model expressing an N-terminal fragment of huntingtin with an
expanded polyglutamine tract in the eye. Administration of inhibitors of histone deacetylation
(HDAC) arrested neurodegeneration and lethality (Steffan, Bodai et al., 2001). In 2002,
Hughes et al. reported protective effects of HDAC inhibitors for other polyglutamine
disorders, prompting the concept that at least some of the observed effects in polyglutaminedisorders are due to alterations in histone acetylation. This hypothesis has led to several
preclinical studies using HDAC inhibitors (Ferrante and Kubilus 2003, Gardian, Browne et
al., 2005).
Whether HDAC inhibitors, such as the FDA-approved SAHA, can be used in treating HD
and other polyglutamine disorders remains to be proven. The evidence linking histone
25
acetylation to polyglutamine pathogenesis is based, for the most part, on work performed
using a fragment of the mutant polyglutamine protein. Thus, the biological relevance of this
work depends on the extent to which the pathogenesis will prove to rest on the properties of
the polyglutamine tract.
The colocalization of some transcription factors in nuclear polyQ inclusions also led to
the idea that recruitment of transcription factors into polyQ inclusions reduces the level of
these transcription factors. However, after examining several HD mouse models, researchers
were unable to find decreased levels of CBP in symptomatic mouse brains (Yu, Li et al.,
2002; Tallaksen-Greene, Crouse et al., 2005). In addition, altered expression of a number of
genes was not necessarily associated with the formation of htt aggregates in HD mice (LuthiCarter, Hanson et al., 2002) and may occur in cell models in the absence of nuclear inclusions
(Kita, Carmichael et al., 2002; Sipione, Rigamonti et al., 2002). Thus, it is likely that soluble
or misfolded htt may interact with transcription factors to alter transcriptional activity. This
idea is further supported by the finding that soluble mutant htt reduces the binding of Sp1 to
DNA (Dunah, Jeong et al., 2002; Li, Cheng et al., 2002).
In conclusion, there is ample evidence that mutant htt acts in the nucleus to affect gene
transcription (Transcriptional dysregulation hypothesis)
26
(Sheng, Chang et al., 2006), and its dysfunction may contribute to hypothalamic pathology or
degeneration in HD (Kremer, Roos et al., 1990; Li, Yu et al., 2003; Petersen, Gil et al., 2005;
Sheng, Chang et al., 2006).
HIP1 is also important for assembly and function of the cytoskeleton and endocytosis
(Kalchman, Koide et al., 1997) and binds clathrin and alpha-adaptin subunit AP-2 (Mishra,
Agostinelli et al., 2001; Waelter, Scherzinger et al., 2001; Metzler, Li et al., 2003). The
interactions of HIP1 with these proteins may constitute a protein complex involved in
clathrin-mediated endocytosis. Unlike HAP1, HIP1 binds mutant htt weakly (Kalchman,
Koide et al., 1997). This finding suggests that HIP1 requires interaction with htt for normal
function, whereas dissociation from mutant htt may impair its function.
Although the interactions of htt with HAP1, HIP1, and other cytoplasmic proteins
suggests that htt is involved in intracellular trafficking, more compelling evidence has come
from the studies of trafficking function in cells that express mutant htt. Recent studies show
that normal Drosophila htt functions in the axonal transport pathway and that polyQ
expansion causes soluble htt to recruit more microtubule transporter proteins, thereby
reducing the soluble pool of these proteins in axons (Gunawardena, Her et al., 2003). In
cultured neurons, htt is involved in HAP1-associated axonal transport of brain-derived
neurotrophic factor (BDNF), both anterogradely and retrogradely, which is disrupted by
mutant htt (Gauthier, Charrin et al., 2004).
A hypothetical model of proposed molecular and cellular mechanisms involved in the pathogenesis of
HD. The expanded polyglutamine in the mutant HD protein is suggested to disrupt key processes
relating to cell signaling (4), gene transcription (1), protein trafficking (2, 5, 6), presynaptic and
postsynaptic signaling (7), mitochondrial dysfunction (3), and protein-protein interactions.
Figure 8. Molecular and cellular pathways involved in HD pathogenesis
27
28
from individuals with CAG repeats spanning in size from normal (9-34 repeats) to affected
(35-70 repeats), alleles revealed an inverse association between the length of the longest
repeat in an individual and the ATP/ADP ratio. This association extended throughout both the
normal and mutant alleles, indicating that the length of the polyglutamine tract in huntingtin
regulates in some fashion the energy status of a cell that may contribute to the increased
susceptibility of striatal neurons in HD.
Recent studies (Lee, Ivanova, et al. 2007) were performed to test the prevailing
hypothesis that huntingtin may directly affect the mitochondrion. By using comprehensive
gene expression analysis, it was investigated whether the HD mutation may replicate the
effects of 3-nitropropionic acid (3-NP), a compound known to inhibit mitochondria, with loss
of striatal neurons. They found that, while mutant huntingtin and 3-NP both elicited energy
starvation, the gene responses to the HD mutation, unlike the responses to 3-NP, did not
highlight damage to mitochondria, but revealed effects on huntingtin-dependent processes
instead. Thus, rather than direct inhibition, the polyglutamine tract size appears to modulate
some normal activity of huntingtin that indirectly influences the management of the
mitochondrion. Understanding the precise nature of this extra-mitochondrial process would
critically guide efforts to achieve effective energy-based therapeutics in HD.
3. Conclusion
Huntingtons disease appears to involve disruption of numerous molecular and cellular
processes, including protein-protein interactions, proteosomal actions, transcriptional
regulation, protein trafficking, inter and intraneuronal signaling and synaptic plasticity. This
disruption is expressed as an altered structure and function of networks of neurons, leading to
motor, cognitive and psychiatric symptoms, prior to cell death. The role of other specific
cellular processes, such as altered neurogenesis, may either be an epiphenomenon or a
causative component of pathogenesis, but this remains one of the many issues yet to be fully
elucidated. A key issue for further research is to distinguish cause and effect with respect to
mechanisms of pathogenesis.
Other important issue facing researchers is how to sort out the major pathogenic
pathways as targets for developing therapeutic strategies. For example, which is more critical
for neuronal dysfunction and neurodegeneration, the nuclear or cytoplasmic effect of mutant
htt? Answering this question would probably require a better understanding than what we
currently have of mutant htts effects in different types of cells and at different stages of the
disease.
Identification of molecular pathways altered by expanded repeats is beginning to reveal
potential therapeutic interventions that can be tested in the existing animal models in
preparation for eventual clinical investigations. The findings that motor, behavioral, and
pathological phenotypes can be reversed in mouse models of HD upon silencing of the mutant
transgene are quite exciting and provide hope that therapeutic interventions are likely to
benefit not only presymptomatic individuals, but potentially individuals in early and
midstages of the disease as well.
29
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36
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Chapter II
Abstract
To gain insight into role of Huntingtin (HTT) interacting proteins in pathogenesis of
Huntingtons disease (HD), in the present review, using various databases and published
data we analyzed 141 validated HTT interacting proteins out of 311 proteins identified as
the interactors of HTT. Results revealed that (i) all 141 proteins express in brain, (ii) fifty
three HTT interacting proteins are down regulated and 36 proteins are increased in
caudate of HD patients (iii) 25 proteins preferentially interact with mutated HTT, 19
proteins have higher affinity towards wild type HTT and 33 proteins interact equally and
(iv) 120 HTT interacting proteins interact with 1780 unique other proteins including 67
HTT interacting proteins and having 2998 interactions altogether. Altered expressions of
HTT interacting proteins and their preferences for the wild type and mutated proteins are
likely to alter the network of HTT interacting proteins in HD resulting in cellular
dysfunctions observed in HD. Several interacting proteins are known to modulate HD
pathogenesis in cell, animal models and HD patients. Significantly enriched HTT
interacting proteins in various functional categories, biological processes and pathways
compared to that coded by human genome indicates that these functions, processes and
*
Correspondence: Nitai P. Bhattacharyya, Ph.D; Professor, Crystallography and Molecular Biology Division and
Structural Genomics Section; 1/AF Bidhan Nagar, Kolkata 700 064, India; e.mail: nitaipada.bhattacharya@
saha.ac.in; nitai.bhattacharyya@gmail.com; Telephone: 091 033 23375345, extension 1301; Fax: 091 033
23374637
40
Introduction
Huntingtons disease (HD, OMIM ID 143100) is a devastating autosomal dominant
progressive neurodegenerative disorder named after George Huntington, who provided a
classic systematic account of the conditions in HD (Huntington, 1872). Motor dysfunctions
like involuntary purposeless motion, known as choreiform, cognitive impairment and
psychiatric disturbances like anxiety, depression, aggression and compulsive behavior are the
common symptoms in HD. The genetic basis of HD lies in the expansion of CAG repeats in
exon1 of the gene, initially called IT15 (interesting transcript 15), now designated as
huntingtin (HTT) at chromosome 4p16.3 (HDCRG, 1993). The HTT gene consists of 64
exons and codes for a protein of ~348kDa with unknown function(s). CAG repeat numbers
vary from 7-36 among normal individuals. Repeat numbers greater than 36 however give rise
to the disease. Appearance of the first symptoms, known as the age at onset, varies normally
between 30 to 40 years, although early and late onset is also reported. Clinical features of HD
progressively develop with an increase in choreic movements, dementia and other motor
deficits like dystonia and rigidity. The disease is terminated in death within 10-20 years after
the appearance of the initial symptoms. There is no cure for the disease at present. HD is
highly prevalent among Caucasian and less frequent among Japanese, Chinese, Finnish and
Indians (Harper, 1991). It has been proposed that prevalence of the disease is higher in
diverse Indian populations than that of in Japan and China, while lower than that of Caucasian
populations (Pramanik et al., 2000).
Extensive researches on the mechanism(s) by which mutant HTT exerts its toxicity to
specific region of brain provide a wealth of information but the exact cause remains largely
unknown. Autosomal dominant nature of the disease and other evidences indicate gain of
function of the mutant HTT. However, reports for loss of function of wild type HTT allele
together with other HTT interacting proteins (see the following sections) are also available. It
is now believed that neurodegeneration in HD could arise from both gain of function and loss
of function (reviewed by Ross, 2004). It is revealed that increased poly Q stretches alters the
conformation of the protein leading to cytoplasmic and nuclear aggregates, also known as
neuronal intranuclear inclusions (NII) through intermediate oligomers and finally results in
various cellular dysfunctions observed in HD. It is still debatable whether NII is toxic or
protective. Altered cellular and molecular abnormalities observed in various models of the
disease and post mortem brains of patients include apoptosis, autophagy, excitotoxicity,
dopamine toxicity, endocytosis, protein trafficking, oxidative stress, deregulation of
transcription, mitochondrial function, protein degradation and chaperone assisted folding (for
recent review see Imarisio et al., 2008). Various processes that are altered in HD are
pictorially shown in the Figure 1.
41
Figure 1 Various responses arising from the mutated HTT leading to neuronal death. Vertical bar represents
the expanded poly Q stretch at the N-terminal HTT coded by the exon1 of the gene HTT.
Large numbers of proteins interact with HTT, however role of such interactions in the
pathogenesis of the disease is not known fully. We cataloged 311 proteins from various
sources that interact with HTT. Among these 311 proteins, 141 proteins are validated either
by a second method than that initially used or shown to be involved in pathogenesis of HD.
We analyzed 141 validated HTT interacting proteins to gather comprehensive information on
(a) expressions of these interacting proteins in brain and other tissues, (b) altered expressions
of the HTT interacting proteins in the caudate of HD patients, (c) preferential interaction of
the proteins with wild type HTT or mutated HTT, (d) interacting partners of the HTT
interacting proteins and (e) participation of HTT interacting proteins in diverse molecular
functions, biological processes and pathways. Result of this analysis shows that the HTT
interacting proteins are involved in various biological processes and pathways indicating that
diverse cellular functions, processes and pathways are altered in HD.
42
pull down followed by mass spectrometry assay (reviewed in Li et al., 2007). In another
approach, aggregates of mutant HTT are isolated, separated on gel and aggregate associated
proteins are identified by mass spectrometry (Mitsui et al., 2002). Faber et al identified 13
proteins and named as huntingtin yeast two hybrid proteins (HYPs) in Y2H assay (Faber et al,
1998). Considering that Y2H predictions are subject to high rate of false positives (Von
Mering et al., 2002), it is essential to establish the physical interaction of the protein with
HTT. Some of these interactions are subsequently validated functionally to establish that the
proteins can modulate the HD pathology at least in cultured cells or by a second method like
immunoprecipitation (IP, for example see Raychaudhuri et al., 2008). In a similar Y2H assay,
Goehler et al. identify 19 HTT interacting proteins, 4 of them was identified earlier. Most of
theses new proteins were confirmed by additional IP assay (Goehler et al., 2004). Two
hundred thirty four proteins are identified either in high stringent conditions of Y2H (104
proteins) or affinity pull down followed by mass spectrometry (130 proteins) using cell
extracts from different types of cells. Only 4 proteins are common in these two methods.
Among the interacting proteins thus obtained, 8 randomly chosen proteins are confirmed by
IP out of 11 proteins tested. Thus, only ~63% of the proteins obtained by high throughput
assay are true interactors. In an attempt to establish the functional role of the interacting
proteins, randomly chosen proteins obtained using these two methods were tested in fly
model of the disease. Either specific gene was over expressed together with mutant HTT or
the mutant HTT was expressed in the flies with mutations in the homologous genes. About
80% of the proteins (48/60) modulate the toxicity in the fly model (Kaltenbach et al., 2007).
We collated all these data from literatures and various databases and obtained 311 proteins
that were identified to interact with wild type or mutated HTT. Given that ~40% of the
proteins obtained in Y2H assay are false positive, we searched for the proteins that have been
confirmed by another independent study, using a second method or shown to modulate the
toxicity or aggregates in cell or animal models of the disease. Out 311 HTT interacting
proteins only 141 proteins are validated by these criteria. Cytoscape, a bioinformatics tool for
visualizing molecular interaction networks (http://www.cytoscape.org/) representation of
these HTT interacting proteins is shown in the Figure 2. In further analysis, we concentrate
only on 141 validated HTT interacting proteins.
43
.ucsf.edu/Research/genentech/genehub-gepis/genehub-gepis-search.html),
although
the
tissues represent in this database were not the same as that of TiGER. In few cases, we also
gather expression information provided in the Genecard (http://www.genecards.org/). In
TiGER, ESTs for HTT gene was available for 25 tissues, except in heart, peripheral nervous
system, soft tissue, spleen and thymus. In Gene card, expressions of HTT gene were shown in
heart and thymus. EST for HTT gene was also present in spleen in GeneHub database. Taking
together out of 30 tissues in TiGER, HTT gene expresses in 28 tissues, except in peripheral
nervous system and soft tissue. Similarly, we cataloged the expressions of 141 validated HTT
interacting proteins.
Figure 2. Cytoscape representation of the validated 141 HTT interacting proteins. Red colored 26 proteins
(including EIF2AK2 that interacts with mutant HTT RNA) preferentially interacts with mutated HTT, green
colored 19 proteins interact preferentially with the wild type HTT, and light yellow colored 33 proteins
interact equally with wild and mutated HTT. Information for 61 proteins shown in white color is not known.
Two proteins (NFYA and NFYC) interact with mutant HTT aggregates only are not shown in the picture.
44
It was evident that all 141 proteins are expressed in brain. Percent of interacting protein
express in lung, eye, kidney, pancreas, muscle, liver, heart, spleen and thymus were 99%,
97%, 91%, 91%, 90%, 84%, 79%, 48% and 38% respectively. Striatal region is the major
affected site in HD, however other organs are also affected resulting in risk of other diseases
(reviewed in Sassone et al, 2009. van der Burg and Brundin, 2009). Absence of expression of
the interacting partners may be cause of the lack of the effects of the HTT mutation in
different tissues. Further studies are required to test the hypothesis.
Alterations of Expressions
of the HTT Interacting Proteins
in Caudate of HD Patients
Deregulation of transcription in HD is thought to be one of the important mechanisms for
contribution to pathological effects in HD (Sugar and Rubeinztein, 2003 Cha, 2007).
Recruitment of transcription factors to mutant HTT aggregates and loss of their functions
could be the simplest explanation for such deregulation
Figure 3. Cytoscape representations of the validated 141 HTT interacting proteins. Proteins (53) with red
color are down regulated; green (36) colored proteins are increased, white colored proteins (46) are unaltered
and expressions of proteins (6) with blue color are not known.
45
. Mutant HTT directly interacts with DNA sequences, changes conformation of DNA that
allows transcription factors to bind to DNA easily and increase the activities of several
transcription factors (Benn et al., 2008). In addition, several micro RNA that in general
regulates the expressions of genes negatively in HD have been identified (reviewed in
Johnson and Buckley, 2009). Thus, in HD several mechanisms for deregulation of genes
might operate. However, it remains unknown whether the HTT interacting proteins are also
deregulated in HD. Depending on the level of expression, protein-protein interaction may
alter; causing cellular dysfunctions in HD.
To address whether HTT interacting proteins are altered in HD, we searched the
published microarray data in caudate of HD patients. For identification of altered expressions,
we followed the same criteria as described (Hodges et al., 2006). Out of 141 validated HTT
interactors, expressions of 36 proteins were increased, 53 proteins were decreased
significantly (p <0.002), while the expressions of 46 genes are unaltered. Information of six
genes is not available. Cytoscape representation of these proteins is shown in the Figure 3. It
is to be noted that even these genes are observed in microarray assay, only few has been
validated by another method, which is essential for the confirmation. SNAP25, which is
decreased in caudate of HD patients, has shown to be depleted in sensory motor cortex of HD
models indicating a role of this protein in HD pathogenesis (Freeman and Morton, 2004,
Smith et al., 2007). Increased or decreased expressions of the HTT interacting protein is
likely to alter the over all HTT interaction network and may result in the observed cellular
dysfunctions in HD.
46
triggers apoptosis and/or gene expression (Gervais et al., 2002; Majumder et al., 2006,
Bhattacharyya et al., 2008). Similar differential interaction of REST with wild type and
mutant HTT may result in alterations of gene expressions (Zuccato et al., 2007). It is shown
that wild-type HTT sequesters REST/NRSF in the cytoplasm thereby permitting activated
transcription of the target gene such as BDNF. In the presence of mutant HTT, which interacts
weekly with REST, REST accumulates in the nucleus resulting in decrease of BDNF
transcription (Zuccato et al., 2003).
Interacting Partners of
HTT Interacting Proteins
There are several databases that catalogue the interacting partners of proteins from
various experimental data and literature searches. One of such databases is BioGRID (Stark et
al., 2006), which includes data from Y2H, reconstituted complex (in vitro interactions with
purified proteins), affinity capture-western blot or mass spectrometry and genetic interactions.
In our search for interacting partners of HTT interacting proteins, we use only those proteins
that are identified from first three methods. There are 21 proteins (SETD2, ASPH CPT1B,
ZNF91, GPRASP2, ADD3, DLG4, GLOD4, F8A1, HYPK, CACNA2D1, NEGR1,
NDUFB10, DNAJC21, CDH13, GPM6A, BMP2K, SRGAP1, HIP14, API5 and SRGAP2),
which do not have any known partners presently. The other HTT partners have 1 (for example
APBB2) to 214 interacting partners (p53). All together for 120 proteins, there are 2989
interactions of 1780 unique proteins including 67 HTT interacting proteins. As mentioned
above, 25 proteins prefer the mutant HTT protein while EIF2AK2 prefers to interact with the
mutant HTT RNA. From protein interaction network point of view, these are the new
interactions in diseased condition. Twenty-six HTT interacting proteins (including one mutant
RNA interacting protein), which preferentially interact with mutant HTT ineract with 748
proteins among which 36 proteins are HTT interacting proteins, altogether make 970
interactions. Such interactions are specific for the mutants HTT and thus are disease specific.
It is important to know the expression of the partners of HTT interacting proteins in different
tissues including brain to access role of the partners of HTT interacting proteins in HD and
requires further studies.
47
Besides, in various cell models HTT interacting proteins are co-expressed with exon1 of the
mutant HTT and the aggregates and toxicity/apoptosis are measured. Among 141 validated
HTT interacting proteins, we collected information for 60 proteins. Over expression of 25
proteins (CDC3, CLTC, CTNNB1, GAPDH, KIF5C, MEF2D, MLLT4, NDUFB10, PPARG,
SUMO1, VDAC2, ADD3, DNAJC21, GIT1, TRIO, YWHAB, YWHAZ, CACNA2D1,
GNAZ, GPM6A, ITPR1, NAPA, PSMC2, STX1A, YWHAE) enhance mutant HTT
aggregates or the toxicity, while expressions of 35 proteins (CEP63, DNAJC11, DNCI2,
DYNC1H1, FEZ1, GFAP, GPI, NEGR1, ODF2L, PPL, SORBS1, TLN1, BAG1, BMP2K,
CREB1, CRSP3, CTIP2, DNAJB1, EEF1A1, HAP1, HIP1, HIP2, HMGB1, HMGB2,
HSPA4, HSPA8, HYPK, MLF1, MLF2, PRKCBP1, TCERG1, VAMP2, PTK6, USP9X,
ZNF91) are suppressed mutant HTT aggregates/toxicity. Depending on the function of HTT
interacting protein, it may modulate the disease in different way. For example over expression
of chaperones may involve in the early stage of aggregate formation by reversing the misfolded mutant HTT to normal state, while proteins in proteosomal degradation pathway
would enhance the clearing stage of the damaged/misfolded proteins. On the basis several
experimental result (Muchowski and Wacker 2005, McCampbell et al. 2000, KazemiEsfarjani and Benzer 2002) sequestered poly Q hypothesis, that states over expression of
any one of the HTT interacting proteins would reverse the effects of the mutant HTT, was put
forwarded.
48
Figure 4. Pictorial presentation for sequestered poly Q hypothesis using MLF1 as a model. Over expression
of MLF1 releases p53, CREB and CBP from the mutant aggregates. Released p53 increases the expression of
GADD45A (Banerjee M and Bhattacharyya NP, unpublished observation).
This further implies that the recruited proteins to the HTT aggregate compromise their
normal functions and contribute to the cellular abnormalities observed in HD. We recently
obtained results with HTT interacting protein MLF1 that support the hypothesis (M. Banerjee
and NP Bhattacharyya, unpublished observations). The pictorial presentation of this
hypothesis is shown in the Figure 4. Other proteins, which alter the different functions, may
increase the toxicity/mutant HTT aggregates. Thus, several HTT interacting proteins that are
altered in HD as described above are capable modulating the pathogenesis.
Direct evidence that HTT interacting proteins alter the age at onset are also available.
Imperfect CAGGCC repeat encoding Gln-Ala repeats in transcriptional coactivator CA150
gene explains the small but statistically significant variability in the age at onset in HD
patients (Holbert et al., 2001) and subsequently confirmed in various populations with diverse
genetic background (Chattopadhyay et al., 2003, Andresen et al., 2007). Analyzing 980
European HD patients, it is observed that that patients homozygous for the M441 genotype at
HAP1, a HTT interacting protein delays the age at onset of the disease. Functional assays
further show that homozygous M441-HAP1 interacts preferentially with mutant HTT that of
T441-HAP1 reduces soluble HTT degraded products and protects against HTT-mediated
toxicity (Metzger et al., 2008). Thus it is likely that variations HTT interacting proteins may
alter the HD pathogenesis.
49
analysis shows that even these proteins are not validated for their interactions with HTT, their
functions are altered in HD.
Among various interactors of HTT, chaperones play an important role in reduction of
poly Q aggregates and toxicity (Raychaudhuri et al., 2008, Opal and Zoghbi, 2002). The
effects of chaperones on the mutated HTT aggregates and toxicity have been extensively
investigated in a diverse range of HD models including yeast, worms, flies and mice as well
as in vitro. Chaperones may act on the aggregate formation by reversing the misfolded or
conformation changed mutant HTT. HTT interacting protein GIT1 is a multi-domain protein
and involves in diverse cellular processes. It is known that GIT1 and other member of the
family of protein GIT2 traffic between three distinct cellular compartments namely
cytoplasmic complexes, focal adhesions and the cell periphery (Hoefen and Berk 2006). In a
recent review, it has been concluded that HTT regulates vesicular trafficking for the organelle
transport along cellular cytoskeleton (Caviston and Holzbaur, 2009). Thus, 20 cytoskeleton
proteins that interact with HTT are involved in the normal function of HTT; alterations of
such interactions may contribute towards the pathogenesis of the disease.
Moleculer Function
(panther ID)
Gene ontology ID
Gene Name
Chaperone (MF00077)
Unfolded protein
binding
(GO:0051082
Structural protein of
cytoskeleton
(GO:0005200)
Cytoskeletal protein
(MF00091)
Membrane traffic
protein (MF00267)
No match
Proteins in
Human Genome
(Normalized %)
176 (1.21%)
HTT Interacting
protein
(Normalized %)
9 (7.83%)
Level of
Significance
(p value)
0.000
FDR (Q
Value)
878 (6.06%)
20 (17.39%)
0.000
359 (2.48%)
8 (6.96%)
0.003
0.0215
51
52
Biological Process
(panther ID)
Gene ontology ID
Gene Name
Proteins in Human
Genome (Normalized %)
Apoptosis (BP00179)
Apoptosis
(GO:0006915)
531 (3.76%)
Neuronal activities
(BP00166)
Transmission of
nerve impulse
(GO:0019226)
Protein targeting;
GO:0008104 protein
localization
(GO:0006605)
Cytoskeleton
organization and
biogenesis
(GO:0007010)
Cell cycle
(GO:0007049)
FDR
(Q Value)
15 (12.71%)
Level of
Significance
(p Value)
0.000
569 (4.03%)
14 (11.86%)
0.000
253 (1.79%)
8 (6.78%)
0.000
1148 (8.14%)
22 (18.64%)
0.000
1009 (7.15%)
19 (16.10)
0.000
Biological Pathway
(PANTHER ID)
Gene Name
Huntington disease
(P00029)
Proteins in Human
Genome
(Normalized %)
172 (5.74%)
HTT interacting
protein
(Normalized %)
19 (20.69%)
Level of Significance
(p value)
0.000
FDR
(Q
Value)
0
136 (4.54%)
11 (17.19%)
0.000
36 (1.20%)
5 (7.81%)
0.000
131 (4.37%)
9 (14.06%)
0.000
59 (1.97%)
5 (7.81%)
0.001
0.0255
150 (5.01%)
9 (14.06%)
0.002
0.0383
106 (3.54%)
7 (10.94%)
0.002
0.0383
55
Conclusion
Biological functions are carried out by macromolecular complexes composed of many
proteins and regulated through concerted actions of many proteins interacting with each other.
There are increasing evidences that onset and progression of genetic diseases arise from the
interplay of these interconnected proteins. Here, we show that HTT interacts with at least 141
proteins, which again interacts with ~ 1000 other proteins. HTT interacting proteins are
involved in HD pathogenesis. Effects of such interaction may depend on the level of
expression of these proteins and affinity of these proteins towards wild type or mutated HTT.
Protein-protein interaction network operating in normal condition may alter in diseased state.
In some cases, the interaction is lost in HD, in other cases, new interactions take place with
the mutated HTT. This may explain, at least partially, the loss of function as well as gain of
functions of the network. Such alterations in turn may result in cellular dysfunctions observed
in HD. It has been shown recently that among HD patients as well as in animal models of HD,
various tissues other than striatum are affected by HTT mutation. Tissue specific expressions
of the HTT interacting proteins and protein-protein interactions may contribute to such tissue
specific affects of the HTT mutation. Further, in depth analysis of HTT interacting network,
tissue specific expressions, and affinity towards wild type or mutated HTT are necessary to
understand molecular alterations leading to pathological condition in brain and other tissues.
HTT interacting proteins are enriched significantly in various pathways indicating that these
pathways are altered in HD. This observation confirms the general notion that even though
HD is a monogenic disease, at the molecular level it is quite complex. Understanding this
molecular complexity is necessary to combat the devastating disease.
Acknowledgment
Mr. Srijit Das acknowledges the financial support for Junior Research Fellowship to C. S.
I. R, Govt. of India.
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Caviston, J. P., Holzbaur, E. L. (2009). Huntingtin as an essential integrator of intracellular
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Abraham, C., Bauer, B., Hasenbank, R., Fritzsche, A., Ludewig, A. H., Bssow, K.,
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neuronal genes. Nat. Genet. 35, 7683
Chapter III
Abstract
Huntington's disease (HD) is a progressive neurodegenerative disorder resulting in
cognitive impairment, choreiform movements and death which usually occurs 15-20
years after the onset of the symptoms. A CAG repeat expansion within exon 1 of the gene
encoding for huntingtin (IT15) causes the disease. In the normal population the number of
CAG repeats is maintained below 35, while in individuals affected by HD it ranges from
35 to more than 100, resulting in an expanded polyglutamine segment in the protein. HD
age at onset is inversely correlated with the CAG repeat length; moreover the CAG repeat
length seems to be related to the rate of progression of neurological symptoms and motor
impairment. Somatic CAG repeat expansion in the huntingtin gene has been observed in
several tissues of HD patients, but particularly in the striatum, the region most affected by
the disease. An age-dependent somatic CAG repeat expansions was also observed in
tissues of HD transgenic mice. Recently, it was found that somatic CAG repeat expansion
is induced by oxidative stress in cultured HD fibroblasts and occurs during the repair of
oxidized base lesions, dependent on a single base excision repair (BER) enzyme, the
DNA glycosylase OGG1 which specifically removes oxidized guanine (8-oxo-G) from
the DNA. It was therefore hypothesized that an age-dependent increase in 8-oxo-G
formation in post-mitotic neurons could induce a DNA damage response mediated by
OGG1 and give rise to a CAG repeat expansion that likely contributes to the onset and
the progression of the disease. Further studies confirmed that somatic expansion of the
CAG repeat tract in the brain is associated with an earlier HD age at onset. Preliminary
results from our group suggest that a common OGG1 Ser326Cys polymorphism could
contribute to CAG repeat number and disease age at onset. Several subsequent studies
support a role for oxidative DNA damage and BER to somatic instability of CAG repeats.
There is also evidence that another DNA repair pathway, the mismatch repair (MMR), is
*
Corresponding author: Department of Neuroscience, University of Pisa, Via Roma 67, 56126 Pisa, ITALY.,
Current Address: Department of Human and Environmental Sciences, University of Pisa, Via S. Giuseppe 22,
56126 Pisa, ITALY. Phone: +39 050 2211028, E-mail: f.coppede@geog.unipi.it
62
Fabio Copped
required for the active mutagenesis of expanded CAG repeats. Since MMR is required for
the repair of mismatched adenine opposite to 8-oxo-G, it remains to be seen if both BER
and MMR co-operate physically in the process of CAG repeat expansion.
Introduction
Huntingtons disease (HD) is a progressive neurodegenerative disorder resulting in
cognitive impairment, choreiform movements and death which usually occurs 15-20 years
after the onset of the symptoms. The disease is also characterized by psychiatric and
behavioural disturbances. HD is an autosomal dominant disorder caused by a CAG repeat
expansion within exon 1 of the gene encoding for huntingtin (IT15) on chromosome 4. In the
normal population the number of CAG repeats is maintained below 35, while in individuals
affected by HD it ranges from 35 to more than 100, resulting in an expanded polyglutamine
segment in the protein. Huntingtin plays a role in protein trafficking, vesicle transport,
postsynaptic signalling, transcriptional regulation, and apoptosis. Thus, a loss of function of
the normal protein and a toxic gain of function of the mutant huntingtin contribute to the
disruption of multiple intracellular pathways, ultimately leading to neurodegeneration [Gil
and Rego, 2008]. Age at onset (AAO) of the disease is inversely correlated with the CAG
repeat length; moreover the length of the expanded polyglutamine segment seems to be
related to the rate of clinical progression of neurological symptoms and to the progression of
motor impairment, but not to psychiatric symptoms [Furtado et al., 1996; Penney et al., 1997;
Rosenblatt et al., 2006; Vassos et al., 2008].
The CAG repeat length accounts for 70% of the variability in HD AAO. However, 90%
of individuals worldwide with expanded alleles possess between 40 and 50 CAG repeats. For
these people, the size of their repeat only determines almost 50% of the variability in disease
AAO [Gayn et al., 2008]. Significant variance remains in residual age at onset even after
CAG repeat length is factored out, and studies in both HD patients and transgenic HD mice
models suggest that other genetic and environmental factors can modify the onset and
progression of motor symptoms, as well as physical, cognitive and social functions [Van
Dellen et al., 2005; Nithianantharajah et al., 2008].
Errors in DNA replication are thought to underlie the lengthening of tracts of repeated
DNA that occurs in HD and other neurodegenerative diseases [Mirkin, 2006]. However,
recent findings indicate that mechanisms for repairing damaged DNA may also be
responsible. Particularly, several studies support the notion that DNA repair contributes to
somatic instability of CAG repeats, though other DNA associated processes, such as DNA
replication, may also play a role [Pearson et al., 2005 . At least two repair processes appear to
regulate in vivo somatic instability in the brain of HD mouse models. The mismatch repair
process (MMR), whose role in somatic CAG repeat instability is well documented, and the
DNA base excision repair (BER) pathway, which is specialized in the removal of damaged
bases, such as oxidized bases Manley et al., 1999; Kovtun et al., 2007]. This chapter
describes in details the most recent findings linking the base excision repair of oxidatively
modified bases to somatic CAG repeat expansion. A brief description of the contribution of
the MMR pathway is given in the last section of the chapter.
63
64
Fabio Copped
mice appear to have different propensities for mutation length gains; in particular, smaller
mutation length gains occur in nitric oxide synthase-positive striatal interneurons (a relatively
spared cell type in HD) compared with the pan-striatal neuronal population [Shelbourne et al.,
2007]. These data demonstrated that neuronal changes in HD repeat length can be at least as
great, if not greater, than those observed in the germline, and the fact that significant CAG
repeat length gains occur in non-replicating cells also argues that processes such as
inappropriate DNA repair rather than DNA replication are involved in generating mutation
instability in HD brain tissues [Shelbourne et al., 2007].
The link between somatic CAG repeat expansion and HD age at onset was supported in a
recent study [Swami et al., 2009]. Researchers from the Center for Human Genetic Research
of the Massachusetts General Hospital, Boston, quantified somatic instability in the cortex
region of the brain from a cohort of HD individuals exhibiting phenotypic extremes of young
and old disease onset as predicted by the length of their constitutive HD CAG repeat lengths.
After accounting for constitutive repeat length, somatic instability was found to be a
significant predictor of onset age, with larger repeat length gains associated with earlier
disease onset. These data were consistent with the hypothesis that somatic CAG repeat length
expansions in target tissues contribute to the HD pathogenic process, and supported pursuing
factors that modify somatic instability as viable therapeutic targets [Swami et al., 2009].
65
FUNCTION
Removal of 8-oxo-G
and other oxidized
bases from nucleotide
pools
Removal of 8-oxo-G
from the DNA
APE1
Endonuclease
Creation of abasic
sites
POL
DNA polymerase
Gap filling
DNA ligase I
DNA ligation
INVOLVMENT IN HD
Protects against oxidative stress
induced HD-like symptoms
REFERENCES
De Luca et al., 2008
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Fabio Copped
67
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Fabio Copped
I with reduced ligation activity did not alter instability. Authors distinguished the DNA
processes through which ligase I contributes to trinucleotide instability. The highest levels of
repeat instability were observed under the ligase I over-expression and were linked to reduced
slipped-DNAs repair efficiencies Lpez Castel et al., 2009 . Therefore, this paper suggests
that the replication-mediated instability can partly be attributed to errors during replication
but also to the poor repair of slipped-DNAs formed during this process. The addition of
purified proteins suggests that disruption of ligase I and PCNA interactions influences
trinucleotide repeat instability Lpez Castel et al., 2009 . Overall, the paper by Lpez Castel
and co-workers, which is based on the use of mammalian cell lines impaired for ligase I,
extends the number of steps of the BER process which are relevant for somatic CAG repeat
instability by suggesting that the coordination with the downstream ligation step is also
crucial.
69
instability in somatic tissues and to HD age at onset, our results should however be taken
with caution since we only had DNA from blood cells of 91 HD subjects to search for a
correlation between the mean number of CAG repeats and the OGG1 genotype. Even if we
identified a significant correlation between the OGG1 genotype and the mean number of
CAG repeats in blood cells, the results should be confirmed in other tissues, such as the
striatum in the brain, where the CAG expanded tract is much more instable than in the blood.
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Fabio Copped
There is evidence that MMR proteins are required for the active mutagenesis of expanded
CAG repeats, but the biological mechanism is still unclear. Studies in transgenic mice
containing (CAG)n tracts have shown that certain MMR proteins are required for the somatic
increase in repeat length. Particularly, in mice deficient for MSH2, MSH3 or PMS2, repeats
are somatically stabilized, whereas deficiencies in MSH6 either lead to no change in somatic
instability or else an increase in expansions. Moreover, deficiency of MSH2 or MSH3
resulted in CAG repeats instability in all tissues tested (for recent reviews see [McMurray,
2008; Slean et al., 2008]). Slean et al. [2008] suggested that there may be at least two distinct
pathways for CAG repeat instability: one that is OGG1-dependent and independent of
MSH2MSH3, and another that is MSH2MSH3-dependent, but independent of OGG1.
However, since the failure to repair 8-oxo-G prior to DNA replication can lead to the
formation of base mismatches, it remains to be seen if both OGG1 and MMR co-operate
physically in the process of CAG repeat expansion [Slean et al., 2008].
Conclusion
Increasing evidence suggests a role for oxidative DNA damage and impaired DNA repair
in the onset of several age-related neurodegenerative diseases, including Alzheimers disease,
Parkinsons disease, Amyotrophic Lateral Sclerosis, Huntingtons disease, and many others
Copped and Migliore, 2010 . In the present chapter I have reviewed recent evidence
suggesting that oxidative DNA damage and impairments in the DNA base excision repair
pathway might be involved in somatic CAG repeat expansion in HD subjects, thus affecting
disease symptoms and age at onset. Table 1 describes all the steps of the BER pathway which
have been involved in somatic CAG instability. All these studies have been performed in the
last two-three years, therefore we are at the beginning of the understanding of this process.
Moreover, since most of the studies have been performed in vitro or in animal models of the
disease, further investigation is required to confirm that something similar occurs in the
striatum of HD subjects. Overall, the BER pathway is an emerging and exciting candidate to
explain the origin of somatic CAG instability, but another DNA repair system, the mismatch
repair, seems also to be involved Slean et al., 2008 . Further studies are required to address
the mechanism of action of the MMR pathway leading to somatic CAG instability and its
possible interaction with the BER pathway, if any.
References
Bravard, A., Vacher, M., Moritz, E., Vaslin, L., Hall, J., Epe, B. & Radicella J. P. (2009).
Oxidation status of human OGG1-S326C Polymorphic variant determines cellular DNA
repair capacity. Cancer Res., 69, 3642-9.
Cannella, M., Maglione, V., Martino, T., Ragona, G., Frati, L., Li, G. M. & Squitieri, F.
(2009). DNA instability in replicating Huntington's disease lymphoblasts. BMC Med
Genet, 10, 11.
Cannella, M., Maglione, V., Martino, T., Simonelli, M., Ragona, G. & Squitieri F. (2005).
New Huntington disease mutation arising from a paternal CAG34 allele showing somatic
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Kovtun, I. V., Liu, Y., Bjoras, M., Klungland, A., Wilson, S. H. & McMurray, C. T. (2007).
OGG1 initiates age-dependent CAG trinucleotide expansion in somatic cells. Nature,
447, 447-52.
Kunkel, T. A. & Erie, D. A. (2005). DNA mismatch repair. Annu Rev Biochem., 74, 681-710.
Lenzmeier, B. A. & Freudenreich, C.H. (2003). Trinucleotide repeat instability: a hairpin
curve at the crossroads of replication, recombination, and repair. Cytogenet Genome Res.,
100, 7-24.
Liu, Y., Prasad, R., Beard, W. A., Hou, E. W., Horton, J. K., McMurray, C. T. & Wilson, S.
H. (2009). Coordination between Polymerase beta and FEN1 can modulate CAG repeat
expansion. J Biol Chem, 284, 28352-66.
Lpez Castel, A., Tomkinson, A. E. & Pearson, C. E. (2009). CTG/CAG repeat instability is
modulated by the levels of human DNA ligase I and its interaction with proliferating cell
nuclear antigen: a distinction between replication and slipped-DNA repair. J Biol Chem.,
284, 26631-45.
Manley, K., Shirley, T. L., Flaherty, L. & Messer, A. (1999). Msh2 deficiency prevents in
vivo somatic instability of the CAG repeat in Huntington disease transgenic mice. Nat
Genet., 23, 471-3.
McMurray, C. T. (2008). Hijacking of the mismatch repair system to cause CAG expansion
and cell death in neurodegenerative disease. DNA Repair (Amst). 7, 1121-34.
Mirkin, S. M. (2006). DNA structures, repeat expansions and human hereditary disorders.
Curr Opin Struct Biol., 16, 351-8.
Nithianantharajah, J., Barkus, C., Murphy, M. & Hannan, A. J. (2008). Gene-environment
interactions modulating cognitive function and molecular correlates of synaptic plasticity
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Pearson, C. E., Nichol Edamura, K. & Cleary, J.D. (2005). Repeat instability: mechanisms of
dynamic mutations. Nat Rev Genet., 6, 729-42.
Penney, J. B., Vonsattel, J. P., MacDonald, M. E., Gusella, J. F. & Myers R. H. (1997). CAG
repeat number governs the development rate of pathology in Huntington's disease. Ann
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Rosenblatt, A., Liang, K. Y., Zhou, H., Abbott, M. H., Gourley, L. M., Margolis, R. L.,
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Saft, C., Zange, J., Andrich, J., Mller, K., Lindenberg, K., Landwehrmeyer, B., Vorgerd, M.,
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73
Chapter IV
Abstract
Huntingtons Disease (HD) is a late onset autosomal dominant neurodegenerative
disease leading to movement disorders, dementia and psychiatric manifestations. The
management of these patients, for whom there is still no cure, has been for long time
neglected by clinicians.
The identification of HD mutation in 1993 has raised a new interest in research as
well as in clinical field and experimental data on patients care have begun to heap up.
Among pharmacological therapies, data have become available on management of motor
disorders with different types of neuroleptics or other classes of drugs while for the
treatment of psychiatric and parkinsonian symptoms the available evidence is not specific
for HD.
Among non pharmacological therapies, rehabilitation has recently provided good
results supported by measurable outcomes.
Although these advances in management are encouraging, HD poses so many
problems on so many different levels, that the way to attain an evidence based best care is
still long.
76
Introduction
Care for Huntingtons Disease (HD) patients has been for long time neglected. The rarity
of the disorder (with a prevalence of 5-10/100.000) and the difficulty to have large and
homogeneous cohorts of patients for clinical trials were certainly some of the causes, but
other factors have to be considered. The progressive cognitive deterioration of these patients,
their psychiatric symptoms (including aggressiveness, depression, schizophrenia) and
different motor disabilities (be it bradychinesia and rigidity or choreic movements) have for a
long time determined their confinement in asylums or nursing homes and justified their
exclusion from the interest of clinicians and researchers.
Further aspects of the disease making it difficult for patients to reach research-oriented
health centres are: the age at onset (around 40), in the mid of productive life, causing the loss
of the job and economic difficulties; the possible presence of more than one patient in the
same nuclear family at the same time due to the autosomal dominant transmission and to the
symptoms onset anticipation over the generations; the length of disease duration (around 20
years) and the consequent economic burden quite often determining the progressive descent
of familys social level and dramatic changes in caregivers and family members standards of
life.
In 1993, the identification of the genetic cause of the disease, the expansion of a CAG
repeat in gene IT15, has given impulse to the investigation on the functional role of normal
and mutated huntingtin, the protein coded by the gene. These investigations have shown the
analogies with the neurodegenerative processes of other disorders, polyglutamine disorders
and, in general, disorders due to misfolded proteins, and determined a new scientific interest
in the disease and in the care of patients.
In the review of Bonelli et al. [1] of 218 papers published between 1965 and 2005, about
the pharmacological management of HD, only three drugs were considered "possibly useful"
for the treatment of chorea: haloperidol, fluphenazine, and olanzapine. In the last years a
growing body of studies, according to the rules of evidence-based medicine, has emerged and
the number of medications commonly used in the management of HD have dramatically
increased [2].
However, when translating data into clinical practice some problems may arise either
because the impact of treatments on patients quality of life or daily activities is not
monitored, or because sample size are small and patients are not always randomized
according to the length of CAG expansion or because the modifying effect of self
medications, often practiced by patients, has not been considered.
On the ground of non pharmacologic therapies, physiotherapy has quit only in the last
years an anecdotal way of reporting its effects to enter the realm of measurable outcomes,
while nutrition lacks trials on the best way to overcome the weight reduction often
accompanying the disease.
77
This chapter will provide, whenever possible, evidence for HD best care and, when
experimental data are lacking, the authors experience will be used, acquired outside an
experimental setting, in about twenty years clinical practice with HD patients. Surgical
treatments will not be discussed, as the evidence on their effectiveness and safety is
insufficient at present, and they are still to be considered experimental procedures.
Considerations about psychological and ethical problems posed by the disease will also be
expressed.
The Diagnosis
Caring for HD patients begins during the diagnostic process. Once non-genetic choreas
have been excluded [3] and the hypothesis of HD has become possible or probable, clinicians
usually ask for a confirmatory genetic test. The time and ways of communicating the genetic
test result and the clinical diagnosis should be accurately planned according to the patients
psychiatric status and the familial and social context, in order to lead the affected individual
and the family members, whenever possible, towards a gradual awareness and knowledge of
the disease. In fact, the early phases of the disease are characterized by patients and family s
fragile equilibrium that can be easily broken with possible catastrophic effects (suicidal
ideations or attempts) [4].
The diagnosis of HD has implications for the whole family and particular attention
should be devoted to the conflicts that could arise between the desire of the patient to
maintain the confidentiality of the diagnosis and the right of relatives to know their risk. The
decision to communicate it or not to all family members should be agreed with the patient in
the context of a counseling session, where the pros and cons of maintaining the
confidentiality could be analyzed. Genetic counselling should be available also for family
members, to provide either information on genetic risk and natural history of the disease or
support in the process of coping with the many burdensome effects of the disease, such as
social isolation and discrimination, loss of work and social role, disclosing children the truth.
Contacts with lay organizations are invaluable for all these aspects.
In case at risk relatives would apply for the presymptomatic test, it should be performed
following the ad hoc international guidelines published in 1994 [5]. Whenever an individual
at risk results to be a presymptomatic gene-carrier, psychological support and clinical follow
up should be offered with the aim of reassuring the testee about the possible presence of
anxiety, depression and sleep disorders, which can often characterize the post test period,
independently from the disease.
Based on data and clinical experience with HD, as well as with other movement disorders
(Parkinsons Disease, dystonia, epilepsy, akathisia and so on), we will adopt a symptomoriented approach to the pharmacological management of the classical features of HD:
movement disturbances, cognitive decline and behavioural problems. The medications
commonly used as best treatments in different stages of the disease are summarized in Table
1 while Table 2 provides some advices on how to take therapeutic decisions.
78
Disease Burden
Pharmacologic Intervention
Presymptomatic
Early (I-II)
No treatment or:
Tetrabenazine
Atypical Neuroleptics
Amantadine
Benzodiazepines
Serotonin Reuptake Inhibitors
Valproate, Gabapentin
Insomnia
Melatonine, Mirtazapine
Forgetfulness, difficulty in
planning strategies
Middle (II)
Advanced
(IV-V)
Psychological support,
Psychotherapy
Day-to-day strategies
(memory notes, planning
charts) Cognitive
rehabilitation
Weight loss
Chorea
Dietary supplementation
Tetrabenazine,Neuroleptics
Parkinsonism
Levodopa, Dopamine-agonists,
Amantadine
Atypical Neuroleptics, mood
stabilizers; (injectable potent
neuroleptics only for
emergencies)
Psychiatric Symptoms
Non pharmachologycal
intervention
Psychological counseling
Genetic counseling
Psychological support,
Psychotherapy
Physical therapy,
Encourage active life.
Focal dystonia/contracture
Weight loss
Cognitive decline
Chorea
Hypokinesia
Rigidity
Anxiety or Depression
Obsessions, Psychosis
Dysphagia
Dietary supplementation
(proteins, vitamins)
Dysartria
Psychological support
Wheel-chaired or bedridden
Pressure sore prevention
The ShoulsonFahn Scale measures independence in activities of daily living. Functional capacity ranges from Stage 1 to
Stage 5, with Stage 1 representing the most independent level of function. (Shoulson I, Fahn S. Huntington disease:
79
2.
3.
4.
5.
6.
7.
Start the decisional process on therapeutic approach, after a detailed anamnestic interview
to patient and caregivers, widely oriented to all disease aspects (mentation, behaviour,
mood, affectivity, sleep, weight loss, appetite, impulse control, verbal and physical
aggressivity, suicidal ideation).
Discuss with patient and caregivers the therapeutic options, elucidate which advantages is
reasonable to expect, alert them on the expected side effects. This is a respectful approach
and improves the compliance.
Treat only the symptoms affecting patients quality of life, tailoring drugs and doses on
the patient.
Even when hyperkinesias are the sole manifestation of HD, it is advisable to avoid potent
D2-blockers, as these drugs precipitate /worsen/induce parkinsonism and other side
effects such as anaffectivity, anedonia, lack of motivation, catatonia, and should be taken
into consideration only to treat severe psychotic symptoms or in the emergency.
In the course of the disease the clinical picture changes: test the need for antipsychotic
and antidyskinetic drugs along the time, and stop what is unnecessary.
The decision to treat the patient should be taken according to the status of HD. Some
times the best thing is not to use any drug, particularly in the latest stages of the disease
Not all that can be done, must be done: the choice on how far should the assistance be
pushed during the latest stage of the disease should belong to the patient. Therefore, all
these medical-ethical aspects regarding which kind of end-of life support should be
used, have to be discussed with the patient and caregivers in advance, never in the
emergency room, so as to give patient and family the opportunity to express their will and
to choose.
Dyskinesias
Typical neuroleptics such as haloperidol, fluphenazine and sulpiride have been
extensively used in the past. However, their adverse effects such as parkinsonism, tardive
dyskinesias, apathy, excessive sedation, together with the availability of less harmful drugs
have drastically limited their use. More recently, depletors of dopamine presynaptic vesicles
proved to be highly effective and safe in controlling choreic movements. In particular
Tetrabenazine, a reversible and selective blocker of central monoamine transporter, has been
extensively studied [6, 7, 8, 9, 10].
When chorea is prominent, tetrabenazine at low doses (12.5 mg/day) can be started and
slowly titrated until hyperkinesias are reasonably reduced. The most serious potential adverse
effect of tetrabenazine is depression, that should not be neglected as it might be very severe.
When tetrabenazine is insufficient or contraindicated (e.g. previous or present diagnosis
of depression), atypical neuroleptics such as olanzapine and risperidone should be considered.
Amantadine, an antiglutammatergic drug, also resulted to improve motor performance
[11, 12] without deleterious effects on parkinsonism and cognition.
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Parkinsonism
Early, in the course of the rigid-akinetic form (Westphal variant) or late, in the last stages
of the most common hyperkinetic form of HD, akinesia, bradykinesia, and tremor may be,
sometimes, more invalidating then the chorea itself.
As a first step, particular care should be devoted in assessing whether the appearance of
parkinsonism is due to the use of antidopaminergics, in which case the dosages should be
reduced, or typical neuroleptics should be abandoned in favour of the atypical ones.
One should be aware that rigidity and akinesia are part of the phenotypic expression of
HD, and this awareness should guide the choice of drugs since the disease onset, by avoiding
potent D2-blockers for the management of dyskinesias and minor psychiatric symptoms.
Amantadine can be positively used to alleviate parkinsonism while anticholinergics
should not be used, as they might exacerbate chorea.
Epilepsy
Associated with mental decline and rigidity, epilepsy is more common among juvenile
HD patients. Myoclonic epilepsy often responds to valproate, lamotrigine, clonazepam. Also
levetiracetam should be considered, as it might also reduce dyskinesias [14]. The status
epilepticus should be treated according to the currently shared guidelines.
Spasticity is an uncommon feature of HD, mostly complicating the latest stages of the
disease. Diazepam and other benzodiazepines may be used to reduce it.
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Psychiatric Symptoms
Although mood disorders, anxiety and depression are particularly frequent in HD
patients, rigorous trials on best pharmacologic treatment of this population are lacking.
Tryciclic antidepressants (amitriptiline, nortriptiline) may lead to anticholinergic effects
and no data are available supporting the use, in HD patients, of newer antidepressant drugs,
such as paroxetine, fluoxetine, sertraline, or mirtazapine and venlafaxine. In a very recent
study on 26 HD patients with diagnosis of major depression Venlafaxine XR (extended
release) was demonstrated to produce significant ameliorations of symptoms of depression
with evident clinical improvement. However, relevant side effects were reported in five
patients and further exploration is needed in the future [15]. Among psychiatrists there is
some debate on the potential increase of suicidal ideation in patients with mood disorders,
especially the young patients [16], after the introduction of antidepressants. In our experience,
such an increase has not been observed, but higher degree of irritability and aggressiveness
have been reported sometimes by patients and caregivers. In any case, when an antidepressant
is prescribed, patients observation should be warranted, and the drug should be introduced
and slowly titrated without concomitant adjunct of benzodiazepines, as they may mask side
effects such as agitation, irritability, excitation. According to our experience, mood stabilizers
such as valproate, carbamazepine or atypical antipsychotic (quetiapine), may be useful to treat
depression with concomitant anxiety and sleep disorders. When psychosis is prominent,
clozapine and quetiapine (unfrequently causing extrapyramidal side effects) should be
considered, while haloperidol should be left as a second choice. There is a general agreement
that Lithium is the best choice to treat suicide risks in bipolar disorders and so is clozapine in
schizophrenic patients [17] while there is no specific evidence for HD [18].
Acute psychosis with agitation and aggressive behaviours can be treated with risperidone
or olanzapine, [19] or, when really severe, with i.m. haloperidol and concomitant use of
valproate or benzodiazepine [19].
Cognition
Rivastigmine has been recently reported to have a positive effect on MMSE score in HD
patients, [20] but more data are needed to confirm this result. Memantine was found
beneficial in 27 HD subjects with reported no decline for 2 years in both cognitive and motor
parameters [21] A pilot open label carried out in 12 patients was not confirming effects on
cognitive domain [22] . A larger placebo controlled trial of this drug for use in Huntington's
disease primarily testing for cognitive signs is presently underway.
82
Rehabilitation Therapy
Bilney et al [27] and Busse et al [28] in reviewing literature data on rehabilitation
therapies in HD found that physiotherapy is generally reported as beneficial, but the studies
have a poor methodology, small sample sizes, and insufficient information about the
protocols and selection criteria.
Recently, however, the effects of an intensive multidisciplinary rehabilitation program
were assessed through motor and functional scales in a sample of 40 HD patients [29]. The
results showed that the treatment has a positive, short-medium term effect on motor and
functional performance in patients with early- and middle-stage HD and no severe psychiatric
symptoms. In addition no decline in motor, functional, emotional and cognitive scores was
evident in a subsample of 11 patients who underwent rehabilitation treatment for two years
[29]. New valid, reliable and responsive tools to measure walking activity, mobility, risk of
fall and balance in HD patients, have been recently proposed [30, 31, 32] which will be used
to provide further and accurate evidence on the effects of rehabilitation.
In the early stages of the disease, when minimal impairments (chorea, impaired balance,
reduced flexibility) and functional limitations (difficulties in performing activities necessary
to fully participate in daily life at work or at home) are present, balance and core stability
training may be useful to prevent falls and to delay the onset of mobility restrictions. Speech
and respiratory therapy can jointly help to maintain lung capacity and induce relaxation.[29].
Exercise aimed at maintaining cardiovascular fitness are important to prevent additional
limitations or impairments. Patients should be encouraged to maintain their usual activity for
as long as possible. Occupational therapy may play a relevant role in this, helping patients to
adapt to new conditions, promoting safety and delaying the loss of social role at work and at
home.
At these early stages, subtle cognitive deficits such as attention and memory deficits,
reduced speed of processing, decreased cognitive flexibility and decision making ability are
also usually present. Retraining or stimulation exercise focused on attention and memory can
be useful and compensation and adaptation strategies should be suggested to overcome
deficits in more complex cognitive abilities [33, 27].
With the progression of HD functional limitations increase. Difficulty in postural
changes, impaired balance, weakness of stabilizing muscles, dystonia, chorea, contribute to
lower mobility, increase the risk of falls and impair everyday activities (personal hygiene,
dressing oneself, eating, house cleaning, cooking, etc). At this stage of the disease
interventions should be aimed at increasing the strength of stabilizing muscle and at
suggesting strategies to perform at best the personal and household activities.
Environmental modifications at home are frequently needed and aids can be used to
reduce the risks of falls (walking aids) and to protect vulnerable parts (e.g hip protectors, knee
and elbow pads, etc). Speech and respiratory therapy is essential for maintaining
communication, safe eating and expectorating.
In the later stages functional limitations are severe. The rehabilitative approach should be
mainly devoted to avoid secondary complications such as muscle contractures, pressure sores
and chest infections and at maximizing comfort, maintaining contact with external
environment and easing caregivers burden as a full time caring is needed. The
physiotherapist should be working closely with the speech and language therapist in order to
83
develop program and strategies to minimize the risk of choking and aspiration of the fluid
into the lungs and, ultimately, chest infections.
Nutrition
Although weight loss and increased energy expenditure have been repeatedly
documented in HD patients [34, 35, 36, 37], very little or no evidence is available on best diet
to overcome this problem. A hypercaloric diet, particularly in early and middle stages of the
disease, is an obvious empirical treatment. The amount of calories to be added should be
assessed on the base of the weight loss and the actual food intake. An addition of 473kc/day
to the usual diet was found to be a sufficient supplement [38]. Oral hygiene should be
particularly cared for and dentist visits planned 2-3 times/year in order to prevent the
worsening of chewing problems.
A randomized, placebo-controlled, double-blind study has shown that highly unsaturated
fatty acids seem to be beneficial to patients with Huntington's disease [39]. Creatine, a
guanidine compound produced endogenously and acquired exogenously through diet, seems
to be a relevant component in maintaining much cellular energy.
Strong evidence exists for early oxidative stress in HD, coupled with mitochondrial
dysfunction, exacerbating each other and leading to an energy deficit. [40]. The addition of
antioxidants to the diet could be beneficial, although no data are available at present.
As dysphagia progresses and nutrition becomes more problematic dry food should be
avoided in favour of wet food, cut in small pieces or grinded, and liquids with jellying agents
should be offered. It may be necessary to offer individual assistance to help the patient to
complete the meal. In many institutional settings, feeding tubes are used routinely. In our
opinion this choice should be taken into consideration only when patients swallowing
deteriorates more rapidly that other functions of the body. In fact, the meal represents an
opportunity for the patient to receive time and attention, it is a social interaction with an
affective value and until the patient can manage the meal with pureed food we think the effort
to avoid feeding tubes can be worthwhile.
Although artificial nutrition may improve life span, some patients refuse to be fed
artificially and are upset when such solution is proposed. The use of life supports should be
discussed with patients in advance, at the early stages of the disease, when they are able to
understand medical explanations, when speech and cognition are still strong and it is possible
to make meaningful choices, so as to be prepared if and when the progression of disease
poses the question. [41,42].
Conclusion
HD is a long-duration, neurologic, dementing, and psychiatric disorder with an autosomal
dominant inheritance. All these aspects have far-reaching effects, meaning that patients and
families will need care and assistance for years, generation after generation. The ideal model
of caring for HD patients is to set up a team with a physician receiving input from many
health care professionals (neurologists, psychiatrists, rehabilitation therapists, psychologists,
84
genetic counsellors, nurses, social workers and other specialists) and from family members in
order to develop a care-plan. The best approach to patient care is being flexible: although the
symptoms and functional difficulties follow some common patterns, their combination widely
vary between individuals. In addition, the course of the disease and the patients quality of
life throughout the disease is highly dependent on their personality characteristics (e.g. goodhumour, ability to cope, previous interests, friendliness) as well as on the social context
(family background, type of work, meaningful social relationships, community resources, and
external sources of help) which have influence on behaviour through the disease. Because of
the genetic implications of HD, the team should also be concerned for the care and support of
the whole family, as the social and emotional needs of family members are very closely
linked to those of the patient.
Referrals to lay organizations is a further resource to be considered either for support
groups and sharing experience or for bringing the needs of people with HD to the attention of
institutional bodies and society at large.
Acknowledgments
We thank Dr. Michele Raja for sharing his experience on the management of the
psychiatric burden of the disease, and Dr. Paolo Zappata for his expertise in HD patient
multidisciplinary rehabilitation. We are indebted to the three lay associations AICH-RomaNapoli-Milano for their joint effort in publishing an Italian Consensus Handbook on
Huntington Disease which has been a guide in preparing this paper**. Finally we thank all
HD patients and their relatives from whom we drew our caring experience.
**Abruzzese G., Albanese A., Bandettini M., Bentivoglio A.R., De Michele G., Di Maio L., Frontali M., Jacopini G., Raja
M., Soleti F., Soliveri P., Zinzi P. La Malattia di Huntington. Parma: Chiesi. 2008
References
[1] Bonelli, RM, Wenning, GK. Pharmacological Management Of Huntington's Disease: An
Evidence-Based Review. Curr Pharm Des, 2006, 12, 2701-2720.
[2] Phillips, W; Shannon, KM; Barker, RA. The Current Clinical Management Of
Huntington's Disease. Mov Disord., 2008, 23(11), 1491-504.
[3] Cardoso, F. Chorea: Non Genetic Causes Curr Opin Neurol, 2004, 17, 433-436.
[4] Paulsen, JS; Hoth, KF; Nehl, C; Stierman, L. Critical Period Of Suicide Risk In
Huntingtons Disease. Am J Psychiatry, 2005, 162, 725-731.
[5] International Huntington Association (IHA) And The World Federation Of Neurology
(WFN) Research Group On Huntington's Chorea. Guidelines For The Molecular
Genetics Predictive Test In Huntington's Disease. Neurology, 1994, 44, 1533-1536.
[6] Huntington Study Group. Tetrabenazine As Antichorea Therapy In Huntington Disease:
A Randomized Controlled Trial. Neurology, 2006, 66, 366-372.
[7] Frank, S; Ondo, W; Fahn, S; Et Al. A Study Of Chorea After Tetrabenazine Withdrawal
In Patients With Huntingtons Disease. Clin Neuropharmacol, 2008, 31, 127-133.
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[8] Mclellan, DL; Chalmers, RJ; Johnson, RH. A Double-Blind Trial Of Tetrabenazine,
Thiopropazate, And Placebo In Patients With Chorea. Lancet, 1974, 1, 104-107.
[9] Jankovic, J. Treatment of Hyperkinetic Movement Disorders With Tetrabenazine: A
Doubleblind Cross-Over Study. Ann Neurol, 1982, 11, 41-47.
[10] Hayden, MR; Leavitt, BR; Yasothan, U; Kirkpatrick, P. Tetrabenazine. Nat Rev Drug
Discov., 2009, 8, 17-18.
[11] Lucetti, C; Del Dotto, P; Gambaccini, G; Et, Al. IV Amantadine Improves Chorea In
Huntingtons Disease: An Acute Randomized, Controlled Study. Neurology, 2003, 60,
1995-1997.
[12] Verhagen Metman, L; Morris, MJ; Farmer, C; Et Al. Huntingtons Disease: A
Randomized, Controlled Trial Using The NMDA-Antagonist Amantadine. Neurology,
2002, 59, 694-699.
[13] Saft, C; Lauter, T; Kraus, PH; Przuntek, H; Andrich, J. Dose-Dependent Improvement Of
Myoclonic Hyperkinesia Due To Valproic Acid In Eight Huntingtons Disease Patients:
A Case Series. BMC Neurol, 2006, 6, 11.
[14] Woods, SW; Saksa, JR; Baker, CB; Cohen, SJ; Tek, C. Effects Of Levetiracetam On
Tardive Dyskinesia: A Randomized, Double-Blind, Placebo-Controlled Study. J Clin
Psychiatry., 2008, 69, 546-554.
[15] Holl, AK; Wilkinson, L; Painold, A; Holl, EM; Bonelli, RM. Combating Depression In
Huntington's Disease: Effective Antidepressive Treatment With Venlafaxine XR. Int
Clin Psychopharmacol., 2010, 25(1), 46-50.
[16] Hetrick, S; Merry, S; Mckenzie, J; Sindahl, P; Proctor, M. Selective Serotonin Reuptake
Inhibitors (Ssris) For Depressive Disorders In Children And Adolescents. Cochrane
Database Syst Rev., 2007, 3, CD004851.
[17] Pompili, M; Lester, D; Innamorati, M; Tatarelli, R; Girardi, P. Assessment And
Treatment Of Suicide Risk In Schizophrenia. Expert Rev Neurother., 2008, 8, 51-74.
[18] Pompili, M; Rihmer, Z; Innamorati, M; Lester, D; Girardi, P; Tatarelli, R. Assessment
And Treatment Of Suicide Risk In Bipolar Disorders Expert Rev Neurother., 2009, 9,
109-136.
[19] Wilhelm, S; Schacht, A; Wagner, T. Use Of Antipsychotics And Benzodiazepines In
Patients With Psychiatric Emergencies: Results Of An Observational Trial. BMC
Psychiatry., 2008, 22, 61
[20] De Tommaso, M; Difruscolo, O; Sciruicchio, V; Specchio, N; Livrea, P. Two Years'
Follow-Up Of Rivastigmine Treatment In Huntington Disease. Clin Neuropharmacol.,
2007, 30, 43-46.
[21] Beister, A; Kraus, P; Kuhn, W; Dose, M; Weindl, A; Gerlach, M. The N-Methyl-DAspartate Antagonist Memantine Retards Progression Of Huntington's Disease. J
Neural Transm Suppl., 2004, (68), 117-22.
[22] Ondo, WG; Mejia, NI; Hunter, CB. A Pilot Study Of The Clinical Efficacy And Safety
Of Memantine For Huntington's Disease. Parkinsonism Relat Disord., 2006, 13, 453-4
[23] Van Dellen, A; Blakemore, C; Deacon, R; York, D; Hannan, AJ. Delaying The Onset Of
Huntington's In Mice. Nature, 2000, 404, 721-722.
[24] Carter, RJ; Hunt, MJ; Morton, AJ. Environmental Stimulation Increases Survival In Mice
Transgenic For Exon 1 Of The Huntington's Disease Gene. Mov Disord, 2000, 15, 925937.
[25] Hockly, E; Cordery, PM; Woodman, B; Et Al. Environmental Enrichment Slows Disease
Progression In R6/2 Huntington's Disease Mice. Ann Neurol, 2002, 51, 235-242.
[26] Spires, TL; Grote, HE; Varshney, NK; Et, Al. Environmental Enrichment Rescues
Protein Deficits In A Mouse Model Of Huntington's Disease, Indicating A Possible
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86
Chapter V
With the many advances in medical care, the dentist will be quite likely to be asked to
treat patients with special health care needs. The dentist may be asked to recommend
preventive regimens to maintain good oral health or provide comprehensive treatment of
advanced dental disease. The patient with Huntingtons disease is but one example of the
debilitating effects systemic disease can have upon the oral cavity. There are no direct
adverse affects on the oral cavity due to Huntingtons disease; however complications
associated with the disease increase the risk for dental caries and periodontal disease. As
Huntingtons disease progress, the persons ability to cooperate will diminish as functional
and cognitive abilities decline. This will require the development of realistic treatment plans
and easily maintainable dental restorations. Caregivers will need to be involved throughout
the process as oral complications are likely throughout this long and difficult disease.
Huntington characterized the disease by a triad of symptoms to include gradual
personality changes, dementia and choreiform movements. Other symptoms include
dysarthria, disturbances of gait and oculomotor dysfunction. The dementia is characterized by
forgetfulness, slowness of thought and altered personality with apathy or depression. The
patient can also become moody, irritable and incapable of dealing with the routine details of
life. Subtle personality changes often become apparent before any motor symptoms arise. [14] These conditions can all play a role in maintaining a healthy mouth. The dentist is likely to
be among the first to notice a deterioration in oral health status.
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Robert Rada
89
negative anaerobes from inflamed gingival tissues. Microorganisms can travel into the lungs
through aspiration of bacteria rich saliva due to poor oral health. The risk for aspiration
pneumonia increases when high levels of bacteria are present in the mouth. There is a
demonstrated relationship between aspiration pneumonia and periodontal disease, dental
caries and poor oral hygiene.[14, 15]
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Robert Rada
Many well-advertised mouthwashes contain alcohol, which can desiccate and dehydrate the
oral mucosa. Individuals with xerostomia should purchase mouthwashes which are alcohol
free. Petroleum jelly should be avoided because it dries out the lips.[16,17,19]
91
Protective stabilization may be necessary to provide safe and effective care while treating
patients with Huntingtons disease.[6] The sudden, uncontrolled movements may result in
injury to the patient or dental health care worker when using sharp instruments or the dental
drill in the mouth. Frequently this can be managed with simple hand holding and head
support offered by family members or caregivers. If full body, uncontrolled movements are
present, then a papoose board or full body wrap can be useful.
Informed consent must be obtained prior to using any type of restraint. This would
involve a description of the method of restraint to be used as well as the amount of time and
reasons that protective stabilization is necessary. It is also a good idea to discuss these issues
with both the patient a family member.[23] Without consensus misunderstandings can easily
arise. Alternatives of sedation and general anesthesia may need to be discussed.[24] Part of
the dialogue will include the consequences of no treatment.
When a patient undergoes extensive oral rehabilitation a one week follow-up is
appropriate. Frequently these patients are best placed on a three month recall program, at
which a prophylaxis polish and topical fluoride treatment is performed. Even the patient who
exhibits significant choreiform movements can have regular preventive maintenance
appointments. With frequent breaks and light restraint, such as hand holding and head
stabilization by a dental assistant and family member, a thorough job is possible. The dental
office staff should continually attempt to reinforce oral hygiene techniques. However
effecting any change, if the patient has been lax in maintaining good oral hygiene in the past
can be difficult. This will require much positive reinforcement. For example having the
patient understand the benefits of an electric toothbrush, and encouraging assistance from
caregivers can help. In addition, educating the role a healthy mouth plays on overall health
cannot be understated.
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Disease Prevention
Prevention of dental disease is of utmost importance in maintaining the overall health of a
patient with Huntingtons disease. The modalities will differ between individuals and may
vary as the disease progresses. For some, 3 month recall appointments will be necessary,
others may require a specialized or mechanical toothbrush, many will benefit from topically
applied chemotherapeutic agents to reduce bacterial plaque. The cornerstone of preventive
therapy will be oral hygiene evaluation, instruction and reinforcement as a significant part of
each dental appointment.[6]
Caregivers may be incapable, unwilling, or too overwhelmed with multiple
responsibilities to provide effective daily care. It is important to ensure that caregivers have
the knowledge, skill and willingness to help with oral healthcare. For example, in studies of
nurses providing care to patients who have had a stroke, the nurses were relatively unaware of
the impact a patients oral health has on overall health.[32] An oral health teaching program
should be part of training for all types of caregivers. Quality of life can be enhanced if the
discomfort and potential hazard of poor oral health are reduced.[33]
93
Battery operated mechanical toothbrushes are available in either a rotating brush head or
a sonic oscillating style. Both have been shown to be effective and the choice is generally
up to individual preference and personal cleaning effectiveness. The dentist or dental
hygienist can help with recommending a particular type and offering personalized instructions
for use. Mechanical toothbrushes have been shown to be an effective choice for patients with
disabilities.[35] In addition the NIDCR has produced a brochure on the causes of xerostomia
and ways to manage the associated discomfort.[36] The Importance of Dental Care[37] and
Eating and Swallowing Difficulties[38] are two of many publications distributed by the
Huntingtons Disease Association. These provide valuable information for patients,
caregivers and health care workers regarding oral health challenges and ways to overcome the
challenges associated with Huntingtons disease.
The fundamentals of maintaining good oral health involve plaque removal through
brushing and flossing, the use of fluoridated toothpaste, drinking and cooking with
fluoridated water, reducing the intake of fermentable carbohydrates and regularly scheduling
professional oral care. Frequently, brushing and flossing will not be enough to prevent the
development of dental caries or advancement of periodontal disease. In these situations
adjunctive therapies become necessary. In these cases fluoride application and chlorhexidine
rinses become the next step. Protocols for use of these agents for the prevention of dental
disease in community settings for people with special needs have been researched and
developed. [39]
Topical Fluorides
Topically applied fluorides have become universally accepted for the anti-caries activity.
Topical fluorides are easy to use, effective, inexpensive and safe. Fluorides function to inhibit
tooth demineralization, enhance remineralization and inhibit bacterial plaque.[40] The
fluoride products available in the United States are sodium fluoride, acidulated phosphate
fluoride, stannous fluoride and sodium monofluorophosphate. Clinician will chose the
particular product based on caries risk, anticaries objectives and the patients ability to
comply with treatment recommendations.[41]
Fluoride mouth rinses, purchased over the counter, are 230 ppm sodium fluoride. They
are intended for an individual who can safely rinse and expectorate without ingestion. If the
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individual cannot rinse or spit out the solution, it can be applied with a cotton swab or sponge
applicator twice daily. [41]
High concentration fluoride toothpastes or gels are beneficial for individuals suffering
from medication induced xerostomia. High concentration fluoride products need to be
prescribed by a dentist. Their use may need to be overseen by a caregiver depending on the
ability of the patient. These products contain 5000 ppm sodium fluoride gel and can be toxic
if excessive amounts are swallowed. The toothpastes are brushed on to the teeth at bedtime
and the excess spit out, leaving the residual paste on the teeth while sleeping. Water should
not be used for rinsing. Custom trays can also be fabricated by the dentist into which the
fluoride gel can placed. The patient can then give themselves a daily fluoride treatment. [41]
Fluoride varnishes are much faster to apply and for some individuals may be better
tolerated. These agents contain 5 percent sodium fluoride which is painted on each tooth as a
thin adherent film with a small brush. Application of fluoride varnish is regulated by state
law, so it must be applied by a healthcare professional. Those allowed to apply the varnish
varies from state to state. Fluoride varnish requires removal of food or debris from the teeth
prior to application. One protocol recommends application of fluoride varnish three times per
week, once per year, or applying a single coat of fluoride varnish once every six months.[41]
Fluoride varnishes offer a benefit of low total fluoride exposure and high tooth surface
concentration.
Chlorhexidine Rinses
Chlorhexidine has been safely and effectively used as a dental plaque reducing rinse in
two intraoral concentrations; 0.12% in the United States and 0.2% in Europe. Chlorhexidine
is an effective agent in breaking down oral biofilms. The chemical acts to disrupt the cell
membrane so that exposed bacteria are unable to maintain their osmotic balance in the oral
environment. [43] Chlorhexidine is an approved and effective treatment of gingivitis. It is also
used in varying prescriptions for caries management strategies. Chlorhexidine is formulated
as an alcohol based and alcohol free product. The patient suffering with xerostomia and
mucosal sensitivity may be better prescribed the alcohol free product. One suggested regimen
is to rinse with a half-ounce of chlorhexidine solution for 1 minute twice daily for two weeks.
The regimen should be repeated 4 times per year. A dental professional should be involved in
determining whether chlorhexidine rinses would be useful and in monitoring the efficacy of
treatment. [42]
95
The chief complaints of palliative care patients are xerostomia and symptoms from
poorly fitting dentures. Candidiasis is often present, but it is not usually the most frequently
verbalized complaint.[43] The dentist is an expert in diagnosis and treatment of these areas.
The dentist may even be able to excavate tooth decay bedside and place a sedative filling to
eliminate a toothache. Water-soluble lubricants should be used to lubricate the oral tissues.
Biotene Oral Balance gel (GlaxoSmithKline Consumer Healthcare) is an excellent watersoluble agent and an alternative to the typical lubricants as it contains lactoperoxidase,
lysozyme, glucose oxidase, lactoferrin and no glycerin. Nursing staff should be instructed to
apply the product thinly all around the mouth using a foam brush.[44]
End of life mouth care may be unfamiliar to medical practitioners. One literature review
has highlighted a number of inconsistencies in both the knowledge of mouth care and its
implementation by nursing staff.[45] The goals of oral health palliative care are simple;
eliminate pain and infection, keep the mouth moist and clear from dental plaque or food
debris.[46] Increased awareness by all health care professionals of palliative oral care would
go a long way in providing relief, comfort, and consolation to terminally ill patients and their
families.
Summary
Huntingtons disease exemplifies the importance of cooperation between physician and
dentist to positively impact the overall health of an individual through improved oral health.
Frequently oral health problems in severely medically compromised individuals are dismissed
as trivial. This should not be the case. Oral health professionals should be involved at every
stage of this disease. It is essential that dentists understand medical terminology and the
pathophysiology of disease to be able to manage these medically compromised patients.
Medical technology will continue to advance and there will be no shortage of these types of
patients arriving at dental offices in the future. It is essential that individuals with
Huntingtons disease be able to enjoy optimum oral health throughout the course of this
illness. Good oral health will undoubtedly impact their quality of life.
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96
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Naarding, P; Kremer, HP; Zitman, FG. Huntingtons disease: a review of the literature
on prevalence and treatment of neuropsychiatric phenomena. Eur Psychiatry, 2001, 16,
439-45.
Tran, P; Mannen, J. Improving oral heathcare: improving the quality of life for patients
after a stroke. Spec Care Dentist, 2009, 29, 218-221.
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dentistry services: seamless care for people in their middle years- part 1. Br Dent J,
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Cardoso, F. Huntington disease and other choreas. Neurol Clin, 2009, 27, 719-736.
Ferozali, F; Johnson, G; Cavagnaro, A. Health benefits and reductions in bacteria from
enhanced oral care. Spec Care Dent, 2007, 27, 168-176.
Moline, DO; Iglehart, DR. Huntingtons chorea: review and case report. Gen Dent,
1985, 33, 131-133.
Hamakawa, S; Koda, C; Umeno, H; Yoshida, Y; Nakishima, T; Asaoka, K; Shoji, H.
Oropharyngeal dysphagia in a case of Huntingtons disease. Auris Nasus Larynx, 2004,
31, 171-176.
Nash, MC; Ferrell, RB; Lombardo, MA; Williams, RB. Treatment of bruxism in
Huntingtons disease with botulinum toxin. J Neuropsychiatry Clin Neurosci, 2004,
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Dysphagia, 1992, 7, 106-114.
Bilney, B; Morris, ME; Perry, A. Effectiveness of physiotherapy, occupational therapy,
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for nosocomial bacterial pneumonia and chronic obstructive pulmonary disease. A
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Terpenning, MS; Taylor, GW; Lopatin, DE; Kerr, CK; Dominguez, BL; Loesche, WJ.
Aspiration pneumonia: dental and oral risk factors in an older veteran population. J Am
Geriatr Soc, 2001, 49, 557-563.
Moore, PA; Guggenheimer, J. Medication induced hyposlivation: etiology, diagnosis
and treatment. Compend Contin Educ Dent., 2008, 29(1), 50-5.
Turner, MD; Ship, JA. Dry mouth and its effects on the oral health of elderly people.
JADA, 2007, 138(9 supplement):15S-20S.
Bonelli, RM; Wenning, GK. Pharmacological management of Huntingtons disease: an
evidence based review. Current Pharaceutical Design, 2006, 12(21), 2701-2720.
Guggenheimer, J; Moore, PA. Xerostomia: etiology, recognition and treatment. JADA,
2003, 61-69.
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2004, 58, 673-7.
Yuen, HK; Pope, C. Oral home telecare for adults with tetraplegia: a feasibility study.
Spec Care Dent, 2009, 29, 204-209.
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and orofacial manifestations, medical and dental management. JADA, 2009, 140, 658669.
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[41] Jacobsen, P; Young, D. The use of topical fluoride to prevent or reverse dental caries.
Spec Care Dentist, 2003, 23, 177-179.
[42] Anderson, M. Chlorhexidine and xylitol gum in caries prevention. Spec Care Dentist,
2003, 23, 173-176.
[43] Wiseman, MA. Palliative care dentistry. Gerodontology, 2000, 17(1), 49-51.
[44] Wiseman, MA. The treatment of oral problems in the palliative patient. J Can Dent
Assoc, 2006, 72, 453-8.
[45] Gillam, JL; Gillam, DG. The assessment and implementation of mouth care in palliative
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[46] Saini, R; Marawar, PP; Shete, S; Saini, S; Mani, A. Dental expression and role in
palliative treatment. Indian J Palliat Care [serial online] 2009, 15, 26-9. http://www.
jpalliativecare.com/text.asp?2009/15/1/26/53508 (accessed December 12, 2009).
Chapter VI
Abstract
Huntingtons Disease (HD) is an autosomal-dominant neuropsychiatric disorder
characterized by irreversible physical and mental deterioration, personality change,
mental disorder, and increased susceptibility to suicidal ideation and suicide. Typically
the disease has a very long course to run before death. There is little that the affected or
HD persons who find out their carrier status can do, although if they come early for
genetic testing, they can make reproductive choices. If the diagnosis or the predictive
information has little therapeutic value to the patient, especially if there is no family, one
possible available action is planning of a suicide. Higher suicide rates are reported for
HD patients compared to the general population. It is also well known that persons with
HD have an increased propensity to psychiatric dysfunction and elevated rates of
catastrophic social events. Furthermore, surveys of attitudes about likelihood of
attempted suicide have indicated that 5-29% of at risk individuals would contemplate
suicide if they received a result indicating a carrier status. The prevalence of suicide and
suicide attempts is difficult to estimate because of methodological problems. Suicide
rates of HD populations vary among countries, and they are affected by factors such as
socio-economic status, age, sex, and prevalence of HD. It appears that cases of suicide
vary from 1.6% to 13.8% in HD populations. In this chapter, suicidal behaviour,
psychological affect of predictive testing, suicidal ideation and behaviour before and after
* Address for communication:Tarja-Brita Robins Wahlin, Department of Neurobiology, Care Sciences and Society,
Karolinska Institutet, Novum plan 5, 141 86 Stockholm, Sweden, Tel. +46 8 5858 9397, Fax: +46 8 5858
5470, E-mail: Tarja-Brita.Robins.wahlin@ki.se
100
Introduction
Most investigators of Huntingtons disease (HD) would agree that George Huntingtons
(1872) description of the disease was correct when he drew attention to the three peculiarities
in this disease; (1) its hereditary nature; (2) tendency to insanity and suicide; (3) its
manifesting itself as a grave disease only in adult life. In this original description George
Huntington refers to HD as sometimes that form of insanity which leads to suicide,
suggesting that mental illness and possible suicide is secondary to the disease. Indeed, the
potential for suicide in HD has been recognised for more than a century as a serious
consequence of HD (Di Maio, et al., 1993; Farrer, 1986; Hayden, Ehrlich, Parker, & Ferera,
1980; Huntington, 1872; Paulsen, Nehl, et al., 2005; Reed & Chandler, 1958; Robins Wahlin,
2007; Schoenfeld, Myers, Cupples, et al., 1984; Srensen & Fenger, 1992).
HD is an autosomal-dominant neuropsychiatric disorder characterized by irreversible
physical and mental deterioration, personality change, and increased susceptibility to mental
disorder (Paulsen, Ready, Hamilton, Mega, & Cummings, 2001). Predictive testing for HD
has been available from the middle of the 1980s, initially as linkage analyses, carried out
first in USA (Gusella, et al., 1983; Meissen, et al., 1988) and Canada (Fox, Bloch, Fahy, &
Hayden, 1989) and soon afterwards in many centres around the world (World Federation of
Neurology Research Group on Huntington's Disease, 1993). Ten years after the discovery of
markers for the HD gene (Gusella, et al., 1983), a CAG trinucleotide repeat showing
expansion on the HD chromosome was identified (Huntingtons Disease Collaborative
Research Group, 1993), and this permitted direct testing of the mutation associated with HD.
Following the first descriptions of a pilot project in British Columbia on genetic testing
(Bloch, Fahy, Fox, Hayden, & James, 1989; Fox, et al., 1989), several testing centres from
over the world have developed predictive testing programs for HD. Guidelines for predictive
testing (Huntington's Disease Society of America, 1989) have provided an additional
supplement to psychosocial, ethical, and legal considerations.
The preliminary guidelines for predictive testing protocols were developed to exclude
adverse reactions and catastrophic events which may arise during the testing process. These
protocols were designed to determine the psychiatric, psychosocial, and social consequences
of predictive testing, whether pre-test characteristics of individuals can predict negative
consequences of testing, and whether pre-test education and counselling, and post-test clinical
follow-up, can prevent negative outcomes such as catastrophic reaction and suicides (Quaid,
1991). These guidelines have often been modified due to different health care systems and
have thus presented a framework for testing programs around the world. However, although
some countries have several testing centres, no unified test program has been established.
HD is a late-onset disorder characterized by increasing and irreversible physical and
mental deterioration. It typically involves a very long course of disease before death. There is
little that HD persons who find out their carrier status can do, although if they come early for
101
genetic testing, they can make reproductive choices. If the diagnosis or the predictive
information have little therapeutic value to the patient, especially if there is no family, one
possible evasive action is available: planning suicide (Davis, 1999).
Suicidal Behaviour
Suicidal behaviour in HD is well recognized (Farrer, 1986; Hayden, et al., 1980;
Huntington, 1872; Kessler, 1987a, 1987b; Ranen, 2002; Robins Wahlin, 2007; Schoenfeld,
Myers, Cupples, et al., 1984). Higher suicide rates are reported for HD patients compared to
the general population (Di Maio, et al., 1993; Hayden, et al., 1980; Robins Wahlin, et al.,
2000; Schoenfeld, Myers, Cupples, et al., 1984; Srensen & Fenger, 1992). It is also well
known that persons with HD have an increased frequency of psychiatric dysfunction
(Dewhurst, Oliver, & McKnight, 1970; Kessler, 1987b; Oliver, 1970; Robins Wahlin, et al.,
2000; Wallace & Parker, 1973) and elevated rates of catastrophic social events (Kessler,
Field, Worth, & Mosbarger, 1987). Furthermore, surveys of attitudes about likelihood of
attempted suicide have indicated that 5-21% of at risk individuals would contemplate suicide
if they received a result indicating increased risk (Kessler, 1987b; Mastromauro, Myers, &
Berkman, 1987), and a later study by Robins Wahlin and co-workers (2000) indicated much
higher figures. They reported that 29% of at risk persons would attempt suicide when
developing symptoms of HD.
The prevalence of suicide and suicide attempts is difficult to estimate because in the
majority of HD studies subjects are identified mainly from questionnaires and psychiatric
hospital medical records. Another reason is that death certificates may give erroneous
diagnoses of causes of death and therefore are subject to uncertainty. Srensen and Fenger
(1992) found the diagnosis of HD given in only 76% of the cases where they had evidence
that the patient suffered from HD. Thirdly, data collected by questionnaire and genealogical
reports from relatives may have been underreported. Under-identification of suicide attempts
and suicides may result from reluctance of patients and families to admit the presence of a
mental disorder and the need to seek medical attention. However, some estimates of the
frequency of suicide indicate that this occurs between seven and 200 times more often in HD
than in the general population (Farrer, 1986; Hayden, 1981; Hayden, et al., 1980; Wexler,
1979). Unfortunately, a variety of methodological problems in studies of patients makes
calculation of suicidal behaviour virtually impossible (Stenager & Stenager, 1992).
Bates, Harper and Jones (2002) report that cases of suicide vary from 4% to 12.7% in HD
population. A review from France reports a four times higher suicidal occurrence in manifest
HD than in general population (Bindler, Travers, & Millet, 2009). This is probably a fair
estimation as the observed frequencies of suicide in HD population were 5.6% in Denmark
(Srensen & Fenger, 1992), 3.4% in South Africa (Hayden, et al., 1980), 5.7% (Farrer, 1986),
and 7.3% (Di Maio, et al., 1993) in the USA. Schoenfeld, Myers, Cupples, et al. (1984) found
a rate of 4% in a sample of 506 Huntington cases also in the USA. However, suicides
accounted for 12.7% of those cases (157) where a specific cause of death was reported (see
Table 1). A somewhat lower frequency of 2% has been reported by Haines and Coneally
(1986) also in the USA. Lanska, Lavine, Lanska, & Schoenberg, (1988) noted suicide as 6%
cause of death. However, if death was attributed to suicide in all cases in which accidents,
102
poisonings, and violence was reported as cause of death, this would account for 7.9% of the
deaths. Chiu and Alexander (1982) observed a low frequency of 1.6% in Australia and a
lower suicide rate has also been observed in Mexico (Alonso, et al., 2009). On the other hand
an epidemiological study from Yugoslavia reported a normal prevalence of HD (4.46/100,000
population) but very high occurrence of suicide (Sepcic, Antonelli, Sepic-Grahovac, &
Materljan, 1989). The authors traced ten families from Rijeka district and recorded nine
deaths in the families, of which six were suicides. These variations in the suicide rates in
different countries may be real, or accounted for by the variations in the methods used for
identifying suicides, or both (Srensen & Fenger, 1992). An overview of frequency of
suicides and accidental deaths in HD patients and family members is provided in Table 1.
Country
No. of n (%)
persons suicides (deaths) affected
persons
203
n (%)
n (%)
suicides accidents
family affected
members persons
n/a
n/a
n (%)
Reported Comments
accidents suicide family normal
members population
n/a
n/a
n/a
10 (6.4%n/a
of known
deaths)
1%
n/a
n/a
n/a
Norway
506
20 (4%)
(157
known
deaths)
199
1
USA
452
25 (5.7%) n/a
14 (3.2%) n/a
1.5%
3238
20 (0.6%) n/a
257
(7.9%)
n/a
n/a
87
n/a
n/a
n/a
n/a
15
(5.3%)
23 (5.8%) 20
(7.1%)
2.7%
91
(3.5%)
2
n/a
n/a
n/a
n/a
n/a
n/a
n/a
396
40 (10%) 27 (7%) n/a
deaths
n/a
Saugstad and
degrd, 1986
(1916-1975)
Farrer, 1986
(n/a-1984)
Yugoslavia
677;
22 (5.6%)
395 HD
+ 282
sibs
2793 114
(4.4%)
300
9 (3.0%)
Hungary
The National Huntingtons Disease Research Roster at Indiana University, USA (Farrer,
1986), reported that 5.7% of deaths among affected persons resulted from suicide and 27.6%
of patients attempted suicide at least once. Of these attempted suicides, 7.2% had two to three
attempts. Suicide was the third most common primary cause of death in HD (Farrer, 1986).
103
However, the frequency of suicide might be higher, because the cause of death was listed as
Huntingtons Disease in 92 cases. Interestingly, they found that the female attemptedsuicide rate was higher (22.0%) than the male rate (18.5%). This could be due to a higher
success rate in males (who succeed after the first attempt rather than a long train of attempts).
Farrer (1986) also noted that suicide in HD was four times greater than the reported rate 1.0%
- 1.3 % for the general population in USA (Roy, 1995).
A later evaluation by Di Maio et al. (1993) studied 2793 people registered with the
National Huntingtons Disease Research Roster. Suicide was the reported cause of death in
205 cases, comprising 9.3% affected, 21.5% possibly-affected, 4.5% at 50% risk, 2.6%
at 25% risk, 7.1% children of possibly affected subjects, and 3.2% spouses and family
members with no risk. The authors recorded three times more male suicides than females.
Although the exact suicide ratio between patients and family members and the US population
were not calculated, their data show an increased frequency in all risk categories of HD
family members including patients spouses.
Schoenfeld, Myers, Cupples, et al. (1984) examined the proportions of deaths attributed
to suicide among 506 deceased individuals with suspected or diagnosed HD from New
England, USA. There were 20 documented suicides, nine in diagnosed HD and 11 in
suspected HD individuals. These suicides accounted for 4% of all HD deaths, which was four
times higher than the suicide rate in the Massachusetts general population. These suicides
occurred during a period of 26 years. Sixteen of the 20 persons committing suicide were
male. Methods of suicide included drowning, gunshot, hanging, drug overdose, fire, jumping
from a high place, and asphyxiation by poisonous gas. The mean age of the persons was 47.7
years. This suggests that most of the suicides occurred early in the disease. Suicide was the
third most common cause of death in HD patients after pneumonia and heart disease.
A Danish study examined causes of death for 395 HD subjects and 282 unaffected
siblings and compared the causes of deaths with the general Danish population (Srensen &
Fenger, 1992). The proportion of deaths from suicide was 5.6% among the HD subjects, 5.3%
among the sibs, both of which are higher than in the general Danish population (2.7%). Once
again suicide was the third most common cause of death in HD subjects. Accidents as a
primary cause of death occurred with a frequency of 3.8% in the affected and 7.1% among the
siblings. The authors did not report the methods of suicides, but reported causes of accidents
in HD and at risk subjects. In 13 cases of 23, patients aspiration was the cause of the
accidental death and five accidental falls were reported.
Methods used to commit suicide by HD subjects are often drowning, jumping from a
high place, hanging and poisonous gas (Baliko, Csala, & Czopf, 2004; Schoenfeld, Myers,
Cupples, et al., 1984). Ready availability of firearms is associated with an increased risk of
suicide in the home (Baliko, et al., 2004; Kellermann, Rivara, Somes, & Reay, 1992) and
handguns are responsible for some of the suicides in HD families, mainly in USA. Lipe,
Schultz, & Bird (1993) reported 11 suicides: four by drowning, three by handguns and one
using a single vehicle auto crash. All of these 8 suicides were males. The three female cases
were overdose, carbon monoxide poisoning and cutting of wrists. Srensen & Fenger (1992)
listed accidents among 23 HD patients and 20 at risk subjects. Thirteen patients were
classified as dying from aspiration, as mentioned before, and 11 at risk subjects had traffic
accidents. Six of these accidents were a crash with a vehicle in the opposite lane and all were
male single drivers. The attempted suicide methods reported by Robins Wahlin et al. (2000)
were drug overdoses and cutting of wrists, all in females. This seems to indicate that females
104
prefer less dramatic methods than men, who seem to choose methods which succeed better.
Lipe et al. (1993) also noted geographic influences in suicide methods, reporting three
persons who jumped from bridges, reflecting the availability of water.
If the HD diagnosis is made when subtle signs are apparent, it gives an opportunity for
patients to discuss feelings about the disease and problems that have brought them to the
physician. However, in many cases patients suspect that the disease has taken its first steps,
but they are not willing to seek help. Many of them are familiar with the disease and its
symptoms and want to cope alone. Schoenfeld, Myers, Cupples, et al. (1984) reported that
among 157 HD patients with an established cause of death, 18.4% of observed suicides
occurred in the age group 10-49 years and more than half of the suicides occurred in
individuals who showed early signs of the illness but who had not been diagnosed. Lipe et al.
(1993) found that 5 of the 9 HD subjects committed suicide within the first year of symptom
onset. This implies that people in early stages of HD are particularly prone to suicide. Indeed,
there appears to be a consensus that those who are early in the disease course, and those who
have not yet been diagnosed with the disease, are at greatest risk of suicide (Cina, Smith,
Collins, & Conradi, 1996; Di Maio, et al., 1993; Farrer, 1986; Hayden, et al., 1980;
Huntington, 1872; Lanska, et al., 1988; Lipe, et al., 1993; Paulsen, Hoth, Nehl, & Stierman,
2005; Reed & Chandler, 1958). Hence, suicide among HD patients is seen in the third
through fifth decades.
An increased risk of suicide is not limited to the person with HD. Several studies suggest
that family members, including spouses and children of the afflicted, also appear to be at
higher risk (Cina, et al., 1996; Di Maio, et al., 1993; Kessler, 1987b; Lipe, et al., 1993;
Robins Wahlin, et al., 2000). Huntington (1872) presents two married men, whose wives
are living, and who are constantly making love to some young lady not seeming to be aware
that there is any impropriety in it. These frontal symptoms of HD can lead to unhappy
circumstances in the family, and personality changes are not rare in the early course of the
disease. The tragedies of the HD families are difficult for an outsider to understand. Lipe et
al. (1993) report suicides of an unaffected spouse with HD husband and two affected children
and one unaffected at risk daughter of an affected mother. Kessler et al. (1987) found that
37.3% at risk subjects reported at least one attempted or completed suicide among relatives,
and about 34.3% reported that a close relative had been hospitalised for psychiatric reasons.
Two of 67 subjects (3%) had attempted suicide themselves (Kessler, 1987b). Similarly,
Robins Wahlin et al. (2000) revealed that 69.2% of carriers and 85.7% of noncarriers had a
close relative with psychiatric disorder related to HD. Furthermore, 30.8% of the carriers
reported suicide or suicide attempts in the family, whereas the corresponding figure for
noncarriers was 14.3%.
Srensen & Fenger (1992) found that accidents as a primary cause of death occurred
among the sibs with a frequency of 7.1% which is even higher than their suicide frequency
(5.3%). These accidents were striking in their character, three were poisoned with carbon
monoxide and six of the 23 accidents of at risk persons were car crashes with a truck in the
opposite lane. All were male single drivers. This indicates clearly that some accidents leading
to death may have been hidden suicides. Farrer (1986) questions also the possibility that
several at risk sibs reported to have died accidentally may actually have been suicide victims.
He remarks that only 1.8% of HD sibs were reported to have died by suicide and 5.5% known
death cases were reported as accidents.
105
The increased occurrence of suicide among persons with HD may not represent a
disproportionate increase over patients with other serious disorders (Schoenfeld, Myers,
Cupples, et al., 1984). Because of the late onset of HD, asymptomatic at risk persons who die
at an early age may have been carriers. An association between suicidal potential and organic
disease has been suggested among other diseases (Chapdelaine, 1993) such as Acquired
Immunodeficiency Syndrome (AIDS, Komiti, et al., 2001), cancer (Louhivuori & Hakama,
1979), diabetes (Macgregor, 1977), renal failure (Washer, Schroter, Starzl, & Weil III, 1983)
and psychiatric disorders (Tsuang, 1978). A better basis for computing the relative risk of
suicide in persons with HD could be by comparing them with similar serious disease groups
rather than the general population. Any disease leading to physical and mental disorder
followed by death may predispose to higher risk of suicide. Declining cognitive function and
eventual dementia involve barriers to social life, isolation and depression and may engender
suicide attempts (Haw, Harwood, & Hawton, 2009). Some suffering, especially with physical
pain, can be addressed by medication, but it is difficult to compensate for other forms of
suffering such as that brought about by loneliness and indignity in HD. Davis (1999) argues
that persons at risk of genetic disease resulting in long periods of mental incompetence have
unique reasons for serious consideration of suicide.
A quarter of all HD patients attempt suicide at least once (Farrer, 1986). There is a well
established association between suicide and psychiatric disorders (Tsuang, 1978). The
propensity of suicidal behaviour could therefore be a direct consequence of familial
neuropathology. However, Farrer (1986) did not find any hereditary patterns for suicide
among the affected members of the families, although the recorded suicide attempts were
27.6% (148 known suicide attempts and 54 unsure suicide attempts in 727 individuals with
HD). Di Maio et al. (1993) noted the occurrence of further cases of suicide in the same family
after a first suicide, suggesting a possible genetic effect, but this phenomenon also occurs in
families without HD (Roy, 1983). Furthermore, it should not be overlooked that psychosocial
elements, such as witnessing gradual cognitive decline and dementia of the parent or
relatives, learning behaviour patterns of the family, turbulent social background and years of
constant symptom-seeking might aid the onset of the suicidal tendencies.
For several reasons, the studies of suicide among HD patients may underestimate its
frequency. Suicide may be suspected in accidents leading to death but may not be recorded
officially. As mentioned before, Srensen & Fenger (1992) observed accidents among
patients which were due to aspiration and to falls. Schoenfeld, Myers, Cupples, et al. (1984)
excluded ten accidents (6.4%) from the suicide category because of lack of verification.
Further, these authors classified only those patients for whom suicide was definitely reported
as the cause of death by relatives, medical records and death certificates. This would exclude
cases of which relatives may not wish to record the death as a suicide if there was some
doubt. Farrer (1986) found 14 accidental deaths that accounted for 3.2% in their sample of
452 HD individuals. Religious reasons, the desire to protect the rest of the family, and other
factors such as insurance benefits, may also play a role in underreporting of suicidal attempts
and suicides (Kessler, 1987a). Similarly, inaccurate suicide reporting is also known in the
general population (Brown, 1975).
106
107
of HD, finding an incidence of 6.9 per million per year (Almqvist, Elterman, MacLeod, &
Hayden, 2001). The UK Huntingtons Prediction Consortium observed that only around 15%
of those at high risk undergo predictive testing in England (Harper, Lim, & Craufurd, 2000).
In summary, around 3 to 21% of at risk persons enter predictive testing programs now
that DNA testing is available worldwide. Bird (1999) estimated that overall 25% of at risk
persons are enrolled in genetic testing programs. However, in most countries the initiative for
genetic testing stems from the individual and the uptake of predictive testing in most
countries seems to be much lower than 20% (Evers-Kiebooms, Decruyenaere, Fryns, &
Demyttenaere, 1997). So if the uptake is low, what characteristics compel the majority of HD
population not to seek genetic testing?
Tibben, Niermeijer et al. (1992) sought information on the motives of persons who were
not enrolled in the program although aware of its existence. They concluded that nonparticipants tended to overemphasize the negative consequences of the genetic test, such as
depression, fear of HD, inability to cope with the results, if positive outcome, and depression,
being banned from the family, and guilt feelings if the test is negative. Feeling of not having
courage to get carrier status, was stated as a reason for not taking the predictive testing for
HD in 45% of at risk persons in a small sample at Stockholm. Another frequent answer in an
open-ended questionnaire by Robins Wahlin et al. (2000) was that it is easier to bear
uncertainty than certainty (Robins Wahlin, unpublished data).
Individuals who enter a predictive testing program are faced with a variety of complex
personal and ethical questions. It may be the most important decision in their entire life and is
complicated by the fact that there are no absolutely right or wrong choices. What may be right
for one person may not be right for another. It is widely agreed that the decision to proceed
with testing should be entirely up to the individual (Robins Wahlin, et al., 1997).
At present, there is no cure or adequate treatment for HD. Therefore, are there any
benefits of predictive testing for healthy individuals? At the beginning of the genetic testing
era Wexler (1985) reviewed this complex issue and asked the poignant question: Would this
new genetic knowledge be life enriching or destructive? In an invited editorial about the risk
of suicide in genetic testing for Huntingtons disease Bird (1999) asks about the emotional
toll of such testing. The answer to these questions is always very complex and personal, but it
has to be answered by the candidate who is considering entering a predictive testing program.
Potential candidates from HD families face a twenty-first century dilemma in the deepest
possible way. To paraphrase Hamlet (Shakespeare, 1992): To know or not to know, That is
the question (Robins Wahlin, 2007).
Codori and Brandt (1994) pointed out that predictive testing may lead to both negative
and positive psychological consequences, regardless of the outcome of the test. The major
benefit they reported was relief from the uncertainty of not knowing. In addition, noncarriers
were relieved by the fact that their children were spared. Negative effects of predictive testing
for noncarriers included psychological distress and feelings of guilt. In addition, carriers may
feel guilty for having transferred risk status to their children, whereas noncarriers may feel
guilty because they were spared from HD (Kessler, 1994). The latter, paradoxical, reaction
has been referred to as survivor's guilt (Lifton, 1979; Tibben, et al., 1990; Tibben, Vegter-van
der Vlis, et al., 1992).
Although prior research has been informative regarding the psychosocial consequences of
genetic testing, Wiggins et al. (1992) emphasized the need of continued longitudinal
assessment of predictive testing groups to examine psychological and social effects of genetic
108
testing. Several authors have argued that programs for predictive testing can potentially be
harmful (Kessler, 1987b; Kessler, et al., 1987). However, at the same time these programs
may enhance the quality of life (Wiggins, et al., 1992). The Canadian Collaborative Study of
Predictive Testing for Huntington disease reported a slight improvement compared with
baseline in well-being and lower depression scores, even for carriers, at the 12-month followup (Wiggins, et al., 1992). Predictive testing has also been noted to be beneficial in reducing
overall ill-health symptoms and increasing well-being for those expressing concerns about
HD (Larsson, Luszcz, Bui, & Robins Wahlin, 2006). However, Codori and Brandt (1994)
noted that there was attrition in the high-risk group, leaving open the possibility that the most
distressed persons dropped out during the one-year follow-up period. They also made the
point that persons who were tested were self-selected, and questioned whether the favourable
reactions to HD testing would continue in the future. Further, some at risk persons surveyed
have predicted that they would experience anxiety and contemplate suicide if the test results
indicated carrier status (Kessler, 1987b; Robins Wahlin, et al., 2000).
Baum, Friedman, and Zakowski (1997) suggested that, by reducing uncertainty and
providing outcome information, some of the anxiety and stress associated with being at risk
of HD may be reduced. Mutation analysis provides the individual with news of either being a
carrier, which is bad news, or a noncarrier which ought to be perceived as good news.
However, research suggests that this is not always the case (Bloch, Adam, Wiggins, Huggins,
& Hayden, 1992; Codori & Brandt, 1994; Robins Wahlin, et al., 1997; Tibben, et al., 1993).
Some carriers have the capacity to anticipate and arrange their future and manage to cope
with a carrier status, whereas others experience the new status as a threat and feel distress
facing the future disease (Bloch, et al., 1992; Codori & Brandt, 1994; Huggins, et al., 1992;
Robins Wahlin, et al., 1997; Tibben, et al., 1993). Also a noncarrier status may be associated
with unexpected costs or coping problems (Codori & Brandt, 1994; Huggins, et al., 1992;
Tibben, et al., 1993). How people manage to cope with the new status varies with the coping
strategy, how well they are prepared, what capacity they have in terms of active coping
resources, and personal factors such as optimism, beliefs, and social support (Baum et al.,
1997). Thus the coping outcome from participating in predictive testing is dependent on
individual differences in various characteristics before entering the program (Larsson, et al.,
2006).
When planning predictive testing programs, there are three obstacles which complicate
the establishment of such programs. First, clinicians, psychologists, geneticists, and
researchers do not commonly share their knowledge of benefits of programs that can be used
in clinical work. Second, a relatively large proportion of the population in many countries
lives in rural areas, and community-based programs may meet with economic obstacles.
Third, cautious attitudes among people who want to participate and people who can offer
genetic testing counteract potential benefits of the genetic services (Robins Wahlin, et al.,
2000).
Baum et al. (1997) noted that HD societys technological capacities may have outpaced
its understanding of psychological consequences. In a study by Kessler and colleagues
(1987), all of the 69 persons taking part in the survey stated that the predictive testing should
be available even though no cure for HD exists. Kessler (1987b) and Copley, et al. (1995)
reported that persons taking part in predictive testing programs value the counselling highly.
Further, Copley et al. (1995) found that 96% of their participants were satisfied with the
testing program and less than 3% of those persons whose risk status was changed felt that the
109
results had diminished their quality of life. Hence, the wheel of genetic testing progress rolls
further in most developed countries.
Carriers****
n = 13
n%
I have never thought or attempted to kill myself.
5 38.5
I have thought about suicide before I discovered that I
were at risk for HD.
3 23.1
I have thought about suicide since I have known that I
am at risk for HD.
5 38.5
I have thought about suicide within the past year.
6 46.1**
Suicide has sometimes been a passing thought and/or I
have briefly considered it.
5 38.5
I have had a plan for killing myself and seriously
considered carrying it out.
2 15.4
I attempted to kill myself.
1 7.7
It is likely that I will attempt suicide when I begin
developing symptoms of HD.
1 7.7**
It is likely that I will attempt suicide when I get
middle/advanced stages of HD.
3 23.1***
Noncarriers
n = 21
n%
7 33.3
Total
n =34
n%
12 35.3
8 38.1
11 32.3
8 38.1
3 14.3
13 38.2
9 26.5
7 33.3
12 35.3
2 9.5
5 23.8
4 11.8
6 17.6
9 42.8
10 29.4
11 52.4
14 41.2
* Reproduced with permission from Acta Neurologica Scandinavica, Blackwell Publishing, Robins
Wahlin et al, 2000.
** p .05, ***p .10
**** One carrier committed homicide-suicide, father and son, after the data collection.
This study did not reveal any significant differences in social and demographic
characteristics of the carriers and noncarriers and the groups did not differ in any of the
assessed pre-test attitudes, expectations, general well-being, life satisfaction or style, need for
110
support, estimated sense of well-being, or degree of health. Although the study indicated few
differences between the two groups in suicidal ideation and behaviour, carriers exhibited a
significantly higher rate of suicidal thoughts within the past year than noncarriers, despite the
fact that the carriers reported being fairly satisfied with their own health and indicated even
marginally better health satisfaction than did the noncarriers in the Life Satisfaction Index
(LSI). Importantly, six of the 34 participants (17.6%) had attempted suicide before entering
the predictive testing program and five of them were given noncarrier status and only one of
them was a carrier. One noncarrier had been hospitalised in a psychiatric ward for over a year
in connection with three serious suicide attempts and another noncarrier had taken drug
overdose on nine occasions. The remaining noncarriers and one carrier had tried to kill
themselves either by overdose or by cutting their wrists. Of interest, method of suicide
reflects country and social background. None of the suicide attempts were made by guns
(which is the most common method of suicide in USA, Kellermann, et al., 1992). Four
participants (two carriers and two noncarriers) were judged to be at an immediate suicidal
risk, but these participants had not attempted suicide before entering the program. Robins
Wahlin et als. (2000) results suggest that psychosocial determinants rather than genetic
factors may influence at risk persons' patterns of suicidal behaviour. An overview of the
participants' suicidal thoughts or tendencies is provided in Table 2.
Further, both at risk groups in this study, showed considerably higher tendencies for
suicidal behaviour and psychiatric dysfunction than the normal Swedish population (Center
for Suicide Research and Prevention, 1994). A survey of a normal population aged 20-67
years (n = 8800) in the county of Stockholm, revealed that 19.7% had thought about suicide,
and that 7% had thought about suicide within the last 12 months (Center for Suicide Research
and Prevention, 1994). In the Robins Wahlin et al. (2000) sample which ranged in age
between 23-57 years and came from the same area, 35% had considered suicide and 26% had
done so within the last year (see Table 2). The attempted suicide rate of 17.6% was five times
higher than the 3.5% documented for the general population between 20-67 years in
Stockholm during the same period. This is in line with the estimated and completed frequency
of suicide in HD population as compared to that of the general population in USA (Kessler,
1987a, 1987b; Schoenfeld, Myers, Cupples, et al., 1984; Wexler, 1979) confirming markedly
elevated suicide rates for the HD population. In a survey by Kessler et al. (1987) 5% indicated
that they would commit suicide if the predictive test results were positive and 11% of the
subjects would consider suicide as a potential response. Mastromauro et al. (1987) found that
about 21% at risk persons said that they might commit suicide if they did get positive results.
The finding that 41% considered suicide if-or-when they reached middle/advances stages in
the disease is in line also with a survey by Wexler (1979), in which around half of the 35
persons at risk for HD indicated that they would commit suicide if they became ill. Bloch et
al. (1989) reported that 33% considered suicide a possibility in the future if the results
indicated an increased risk. Counsellors and other professionals should take suicidal thoughts
very seriously, if and when reported. The author has encountered one case where a carrier
who had expressed suicidal thoughts subsequently killed not only himself but also his carrier
son.
Farrer (1987) pointed out that HD is a slowly progressing disease and years of searching
for signs of HD may aid in forming suicidal tendencies. A general population study in
Sweden (Dahlgren, 1977) observed that about 11% of attempted suicides later resulted in
completed suicides, suggesting that at risk persons in the Robins Wahlin sample would have a
111
high possibility of repeating their self-injurious behaviour. The estimated casualty rate would
be about 5%, a figure in line with a study of Beck et al. (Beck, Steer, Beck, & Newman,
1993), which followed 207 patients hospitalised because of suicidal ideation. Of all the data
collected at the time of the hospitalisation, by Beck et al. only the pessimism item of the Beck
Depression Inventory (BDI) predicted suicide rate. In Robins Wahlins study (2000), 76.9%
of the carriers and 52.4% of the noncarriers received a value of 1 or 2 on the BDI pessimism
item. Thus, the observation that 61.8% of the total group felt discouraged about the future
provides further support of high suicidal ideation in this sample. However, it is noteworthy
that life satisfaction of at risk persons was average despite the high frequency of selfdestructive behaviour. Robins Wahlin et al. (2000) noted that the Life Satisfaction Index
(Campbell, Converse, & Rodgers, 1976) for eight domains of life experiences indicated for
both at risk groups average or higher-than-average life satisfaction. Interestingly, only in the
domain of economy were carriers less satisfied than the average hypothesised mean. In all
eight domains of life experience the participants rated economy and work as least satisfying
and marriage as most satisfying.
Previous documentation (Folstein, Folstein, & McHugh, 1979; Kessler, 1987b; Kessler,
et al., 1987) indicates that a turbulent history predisposes the individuals at risk for
psychiatric dysfunction and/or suicide attempts. Hence, should a person with a history of
suicide attempts be excluded automatically from genetic testing? Lam et al. (1988)
recommends that, along with personal and family history of suicidal behaviour, other factors
need to be assessed. These would include suicidal ideation, personal resources, and social
support system. The authors recommend that a history of serious suicidal behaviour should
necessitate follow-up psychiatric evaluation and professional support after presentation of
results of the genetic test (Lam, et al., 1988). In an early study by Kessler et al. (1987) 39% at
risk subjects believed that even if a person was suicidal or psychologically unstable, that
person had the right to be tested.
As at risk persons approach predictive testing an adequate support system is very
important to assist them in dealing with potentially adverse outcomes (Kessler, 1987b). The
Swedish sample (Robins Wahlin, et al., 2000) reported that their social support net involved
an average of 4 persons and that they were fairly satisfied with their social network. They had
better external sources of support than at risk groups surveyed in northern California, USA,
where 5 to 11% reported that they had no external source of support (Kessler, 1987b; Kessler,
et al., 1987). Moreover, an open attitude toward utilizing professional help is necessary to
prevent catastrophic events. Robins Wahlin et al. (2000) reported that about 85% considered
seeing a psychologist or social worker, and a support group was desired by 62%. The fears
and stresses imposed by bad outcomes may erode even the best social support systems. Also,
some at risk persons may not accept therapy or counselling when in crisis. In the study by
Kessler et al. (1987) 19% of participants said that, if they were found to be carriers, they
would not seek counselling to help them cope. A lack of social skills, personality factors such
as avoidant or schizoid tendencies, or habitual pattern of social interaction, may affect the
individuals personal responses. Some at risk individuals may be unprepared to deal
adequately with the destructive feelings that a positive test results evoke (Kessler, 1987b).
These marked persons may develop suicidal tendencies and kill themselves prematurely.
112
113
114
blind the at risk person. The at risk individuals should face the thought of how they might
react to bad news, and how this change would affect their lives (Bird, 1999). Many predictive
programs offer detailed printed information of predictive testing (Robins Wahlin, et al., 2000)
but the people seeking genetic information are not always psychologically mature enough to
change their genetic status. The genetic counsellors should not promote nor advocate
presymptomatic DNA-testing as many at risk persons do not feel strong enough to go through
the emotional changes that may follow a positive result. Given everything known about
responses to medical diagnosis of HD, the likelihood of catastrophic reactions to positive test
outcomes among at risk individuals is high (Kessler, 1987a).
On the contrary, a two year follow-up study of depression and suicidal ideation after
predictive testing, reported much lower suicidal ideation than expected in Sweden (Larsson,
et al., 2006). The authors reported a follow-up of depression, self injurious behavior, life
satisfaction, general health, well-being, and lifestyle of 35 carriers and 58 noncarriers before
the predictive test and 24 months afterwards. Both carriers and noncarriers showed high
suicidal ideation before the genetic testing. However, depression scores and frequency of
suicidal thoughts increased more for carriers, compared to noncarriers, over the restrictive
time period. Interestingly, no differences were found regarding life satisfaction or life style
between carriers and noncarriers (Larsson, et al., 2006).
Sometimes a person may enter the predictive testing program thinking that the outcome
concerns if-and-when the disease will develop in the future. However, the early signs of the
disease may already have started and the news changes the character of the counselling.
These persons receive a double dose of bad news and are extremely vulnerable. Patients with
unsuspected early disease, who would not otherwise have learned of HD presence if
predictive testing were not offered, are not prepared to deal with the unexpected news and are
most likely to suffer severe catastrophic reaction (Lam, et al., 1988). Although the importance
of a sensitive approach to conveying bad news to the patient, the possibility of depressive
reactions and suicidal behaviour is not always seen as a likely outcome (Draper, Peisah,
Snowdon, & Brodaty, 2010). Post-test casualties due to suicidal ideation and suicide, need an
optimal management of these adverse reactions and may be an important determinant of the
number of catastrophic events.
115
suggests that depression, apathy, and aggression are common and suicide rate are well over
those of the general population (Di Maio, et al., 1993; Paulsen, et al., 2001). Although
patients early in the clinical course of the disease are at the greatest risk of suicide, the
depression may occur in any phase of HD (Paulsen, Nehl, et al., 2005). If a major depression
with dementia occurs in the late course of the disease, it may impair the patients ability to
commit suicide.
In the general population suicidal behaviour has many contributing factors: it may be
based on the belief of being trapped in an impossible situation; it may be a symptom of
mental disorder or specific disease; it may be the result of hostility turned against the self; or
it may be a cry for help (for an overview, see Beck, Kovacs, & Weissman, 1975). In short,
depression is often characterized by feelings of hopelessness (Folstein, 1989).
Depression is commonly discussed in terms of feelings of hopelessness (Farrer, 1986;
Kessler, 1987a). Beck et al. (1975) argued that, irrespective of the diagnosis, the negative
expectations or hopelessness appear to be a primary feature in suicidal intent. Beck and
Kovacs (1979) found that 51% of females and 67% of males, in a group of 90 hospitalised for
suicide had received a diagnosis of depressive disorder. Furthermore, Beck et al. (1993) found
that higher levels of suicidal ideation were associated with increasing severity of self-reported
depression, and negative expectancies about the future.
Affective disorders are the most commonly described psychiatric syndrome (excluding
dementia) associated with HD (Hayden, 1981). Stern and Eldridge (1975) found that patients
with early HD and their families were often concerned about mental changes. Folstein, et al.
(1979) noted that HD patients who were not referred for psychiatric reasons nevertheless had
a high frequency of psychotic disorders. Specifically, 45% of the patients met the criteria for
manic-depressive disorder and 18 % were diagnosed with an auditory hallucinatory state.
Moreover the HD patients were reactively depressed in stressful situations brought on by the
disease, such as learning of the diagnosis, losing their jobs, being isolated at home, and losing
manual skills. These kinds of complications are familiar to HD families and may also be
brought on by a change in genetic status.
Roy (1983) found that there was a marked association between suicidal history,
attempted suicide and the presence of depression and/ or recurrent affective disorder within
family. These patients may be more vulnerable than usual to major depression (Hayden,
1981). The author (1981) implied that patients in early stages of HD who are minimally
demented but severely depressed run the highest risk of suicide. Later studies report evidence
that brain changes precede the traditional clinical diagnosis and psychiatric manifestations
may predate neurological signs (Gutekunst, et al., 1999; Paulsen, et al., 2001). The
comparison of onset age of HD and suicide age shows that at risk subjects suicide may occur
at the first appearance of symptoms (Di Maio, et al., 1993). The fact that depressive episodes
can appear before the neurological symptoms of HD, suggests a direct neurobiological link
between depression and the disease (Lam, et al., 1988). The degenerative disease process
could directly result in depression, rather than being a simple psychological reaction to
illness.
Paulsen et al. (2001) described 69.2% in their sample of 52 patients as having dysphoria
and that it was the most common symptom (along with agitation) in HD. The authors note
that most of their patients were prescribed antidepressant medication and that it is likely that
rates of depression are even higher than that reported in literature. Depression has been
associated with the orbito-frontal circuit that projects from the anterior and lateral orbito-
116
frontal cortex via the ventro-medial caudate nucleus to the ventral anterior and medial dorsal
nuclei of the thalamus (Paulsen, et al., 2001). This is consistent with the view that HD is
characterized as a frontostriatal dementia, in which cognitive deficits may result from
pathological changes at multiple sites in the frontostriatal circuitry (Bckman, Robins Wahlin,
Lundin, Ginovart, & Farde, 1997; Robins Wahlin, Larsson, & Luszcz, 2010; Robins Wahlin,
Lundin, & Dear, 2007). Furthermore, most research and clinical reports have found that, in
virtually all cases, the manifestation of depression is either simultaneous with or subsequent
to the motor onset of HD (Di Maio, et al., 1993; Hayden, 1981).
Lipe et al. (1993) found in a retrospective study of nine instances of suicides in HD
families that 50% of suicides and 39% of controls with HD but without suicide attempts, had
a history of depression. Although many of HD subjects had a history of alcoholism and
violence, it did not distinguish the suicide subjects from other HD patients. These behaviours
may reflect the use of alternate coping methods (Lipe, et al., 1993).
Nevertheless, the stress of learning the diagnosis of HD, which results eventually in
losing one's job, being isolated at home, and losing cognitive and manual skills could also
contribute to a reactive depression. The need to carefully explore these issues with at risk
persons prior to predictive testing may be an important factor in clarifying thinking and
helping them to plan appropriately for the post-test period (Kessler, 1987a). Taking into
account that many at risk subjects seek predictive testing when they are near the critical age,
it is of importance to consider carefully the possibility of an increased suicide risk of these
persons.
Folstein et al. (1979) stressed that the demoralizing feelings usually subsided following
counselling, and when patients accepted their situation. They also observed that the clinical
state of persons at risk varies widely. Hence, they recommended quantification and
documentation of psychiatric symptoms. This would permit classification of clinical
symptoms and assist with treatment and research. Further, Lester, Beck and Mitchell (1979)
concluded that specific scores on depression inventories of persons who attempt suicide might
be important in predicting suicidal deaths. The authors extrapolated two monotonic trends
from attempted and completed suicides; the more serious attempters had higher scores both
on depression (Beck, Ward, Mendelson, Mock, & Erbaugh, 1961) and on a hopelessness scale
(Beck, Weissman, Lester, & Trexler, 1974). Beck, Herman, & Schuyler (1974) devised a test
to measure the cognitive component of depression, which they labelled hopelessness. They
found that hopelessness correlates more highly than does depression with suicidal intent in
attempted suicides and with suicidal ideation. Therefore, depression, hopelessness, anxiety,
emotional distress, suicidal tendencies, and social dysfunction grading should be important in
predictive testing of HD. The psychological well being of predictive testing program
participants should be documented by questionnaires and/ or in depth interviews, which
should index different aspect of psychological and social dysfunction in the case of
catastrophic events, such as suicide attempts. Farrer (1987, in a letter to editor) urged that
professional involvement should become mandatory in the setting up of predictive testing.
Low mood or depressive thoughts are often reported in counselling for HD predictive
testing. To evaluate the degree of depression of participants and General Health Symptoms
before predictive testing for Huntington's disease, Robins Wahlin et al. (2000) employed BDI
(Beck, et al., 1961) and the General Health Questionnaire (GHQ; Goldberg & Williams,
1988). These results are depicted in the Table 3. Robins Wahlin et al. (2000) observed that
26% of the at risk participants reported mild to severe depression as measured by BDI, and
117
47% reported mild to severe degrees of general health symptoms as indicated by GHQ. 46%
of the carriers and 48% of noncarriers scored above the normal range in the GHQ-30. This is
a pure state measure of general mental health. Hence, a high score should be taken as an
indication for the counsellor to focus the interview, to follow up the person carefully, and to
prepare him or her for possible adverse effects of the genetic result. Depressive and selfdestructive attitudes, thoughts, tendencies, and wishes, are often manifest and identifiable in
persons at risk of HD.
Normal range a
11 (84.6%)
14 (66.7%)
25 (73.5%)
Normal range c
Mild - Severe b
2 (15.4%)
7 (33.3%)
9 (26.5%)
Mild - Severe d
Carriers (n = 13)
Noncarriers (n = 21)
Total (n = 34)
7 (53.8%)
11 (52.4%)
18 (52.9%)
6 (46.1%)
10 (47.6%)
16 (47.0%)
Huggins et al. (1992) observed that concerns about predictive testing centred around the
counsellors ability to identify persons who would be unable to cope with the consequences of
a carrier status. They concluded that approximately 10% of noncarriers might also be
vulnerable to adverse effects of the test results, and require professional intervention and
ongoing counselling. As pointed out by Codori and Brandt (1994) and Robins Wahlin et al.
(2000; 1997), at risk persons should be cautioned that testing could create, rather than
alleviate, problems. A high frequency of depression and psychiatric affection, even for
noncarriers (Larsson, et al., 2006; Robins Wahlin, et al., 2000), suggests that a careful followup is justified not only for carriers but also for noncarriers (Tibben, et al., 1993; Tibben, et al.,
1990).
For those people for whom autonomy, mental competence and independence are prime
values, predictive testing for HD presents an opportunity for acting according to those values
before it is too late. These life tragedies take radically different forms, with different levels of
burden and adaptation, and some of the newly diagnosed HD persons might choose to end
their life. Hence, a planned suicide can also be a response to diagnosis of future dementia and
thus be a rational and defensible strategy (Davis, 1999). Suicide may not always be an
adverse reaction to bad news. The candidate may view suicide as an option, i.e. rational
suicide. It can be viewed in the light that a diagnosis of impending dementia is a warning
that one is about to be invaded by an enemy army that will always win. It is entirely sensible
to burn down the fort and refuse it a home (Davis, 1999).
Kessler and Bloch (1989) ascribe system factors that may account for suicidal ideation
and behaviour. They observe that professional pessimism about the lack of cure and treatment
118
of HD often affects the perceptions of patients and their relatives, and may contribute to the
avoidance of further professional contact. Suicidal ideation can be fostered by social attitudes
towards the chronically ill, their long-term care and social costs. Further, Kessler and Bloch
(1989) claim that the prospect of financial drain unsupported by societal willingness to
provide for such catastrophic situations provides the backdrop for the shame, neglect,
depression, and suicidal behaviours among affected individuals and their relatives. They
describe, by using case examples, that events leading to the suicidal act reflect a system
pressure promoting behaviour that leaves little choice but suicide. The belief to be a burden to
the rest of the family, and specifically when depression narrows the scope of social
interactions and support, may cause the affected to try the suicidal outcome.
It is understandable that some members of the HD population may see suicide as an
appropriate response to impending dementia. However, biological, psychological, social, and
even situational factors may interact and end up in catastrophic reactions and eventual
suicide. Counsellors and other professionals face a painful ethical dilemma in dealing with
issues of suicidal ideation and suicide in HD. Kessler (1987a) makes an important point that if
suicide is viewed as a rational and dignified act to an increasingly deteriorating life, the
professional course of action may differ towards the affected and family from if the
professional believes that suicide is a demented act. Kessler (1987a) asks, should
professionals act in good faith that the affected has impaired judgment, and protect the patient
against the suicidal act? Furthermore, should the professionals act against the family members
who out of anguish, despair, lack of will or resources may encourage suicide, even in a
passive manner or covertly? Potential for suicidal ideation and suicidal behaviour exists
particularly for those testing positive for HD and the affected.
New technologies, such as positron emission tomography (PET), have increased the
possibility of early diagnosis of HD (Paulsen, 2009). Research using PET suggests that
underlying brain abnormalities such as dopamine neurotransmission parameters for caudate
and putamen as well as the volumetric measurements of these structures may show changes
and precede overt symptoms (Aylward, et al., 2004; Bckman, et al., 1997). Early diagnosis
without adequate treatment and cure of HD, may have traumatic effects on the affected
individual and their family. Taken together, degenerative, rapid course of HD, cognitive
decline, and absence of cure, suicidal behaviour may provide an outlet for feelings of
hopelessness, shame, depression, and endless suffocation by negative affect.
Looking at the milestones of the progress in HD research huge steps have been taken.
Gusella et al. made predictive testing possible by linkage analyses in 1983 and direct testing
became available in 1993 after the discovery of the mutation associated with HD
(Huntingtons Disease Collaborative Research Group, 1993). However, central to these issues
are effective treatment and eventually cure for HD. In the 1980s and afterwards many
persons believed that a cure for HD would probably be found in their own or their childs
lifetime (Kessler, et al., 1987). Now in the twenty-first century, clinical trials are underway to
slow the progression of HD in clinically affected patients and there are also plans to treat preclinical patients. This may give new hope to the at risk population and might even decrease
the incidence of suicide in HD and their relatives. At the present, the problems associated
with suicidal ideation and suicide in HD populations, worldwide, are much the same as two
decades ago. Literature published about suicide and suicide attempts in HD populations is
sparse. More research with larger samples is needed in order to be able to focus on
119
catastrophic events and suicidal behaviour in at risk persons, carriers, noncarriers and HD
families alike.
Acknowledgments
The research was supported by grants from Stockholm County Council, PickUp, grant No
20070033 and No 20050940; Alzheimers Australia Research; and the Swedish Association
of Neurologically disabled (NHR) to Tarja-Brita Robins Wahlin. I am indebted to A. Frick,
M. Cook, and A. Holmes for valuable comments on the manuscript.
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Chapter VII
Abstract
This chapter makes two contributions to the psychology of decision making. It draws
on empirical work to document how family members make and live with reproductive
decisions as they become aware of their risk for a serious late-onset genetic disorder,
Huntingtons disease (HD). Decision-making involves negotiating two dimensions of
reproductive risk that for any child which might be born and the uncertainty that arises
about the at-risk parents ability to sustain a parenting role should he or she become
symptomatic. A detailed account is given of how the model of responsibility was
generated from their narratives. This model encapsulates what families find important
when making reproductive decisions. It demonstrates that how people make decisions can
become as important as what they decide. Examples are given to show how the model
provides a framework for comparing how people deal with each dimension of risk, to
compare different peoples decision-making and to illuminate decision-making in the
face of change. This includes how they address new options generated by recent
A version of this chapter was also published in Psychology of Decision Making in Medicine and Health Care,
edited by Thomas E. Lynch published by Nova Science Publishers, Inc. It was submitted for appropriate
modifications in an effort to encourage wider dissemination of research.
1
Correspondence to: Centre for Family Research, University of Cambridge, Free School Lane, Cambridge, England
CB2 3RF cd10008@cam.ac.uk
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developments in molecular genetics which can resolve uncertainty about, or avoid these
risks. A detailed account is also given of the process of their decision-making. These
findings are used to evaluate claims being made by naturalistic decision-making (NDM)
initiatives to account for decision-making in the real world. An outline of this initiative
prefaces the research findings. Beachs (1990) image theory, used to illustrate the NDM
approach, emphasises the role that values play in forming, negotiating, implementing and
living with decisions that arise in everyday lives. Participants accounts support this
claim - revealing how values such as responsibility become established and contribute to
decision-making. This and other findings lend support to the NDM claims. The chapter
concludes with suggestions about how the model might be used more generally to further
our understanding of the psychology of decision-making in the face of risk.
Introduction
This chapter is about decision-making in the face of genetic risk. It presents a model of
responsibility that encapsulates what families find important when making reproductive
decisions in the growing awareness of their risk for a late-onset genetic disorder,
Huntingtons disease (HD). It will be argued that this model facilitates our understanding of
how those living with genetic risk plan their lives in the age of the new genetics. These
comprise advances in molecular genetics making it possible to offer genetic testing both
prenatal and predictive to those identified as at-risk from their family history for an
increasing number of disorders. Testing establishes whether mutations, which are likely to
result in these disorders, are present in genes. It differs from other forms of medical testing in
that any body tissue can be used and it can be performed at any stage of life from conception.
Results may be sought to inform personal decision making rather than medical care.
Concerns about one value, responsibility, have been consistently cited as motivating the
new decisions that people faced about predictive testing (Cox, 2002, 2003; Kenen, 1994,
1996; Kay, E. & Kingston H.,2002; Hallowell, 1999; Robertson, 2000; Smith, Stephenson
and Quarrel, 1999; Taylor, 2004). Decision-making is instigated and constrained by social
and biological connections to others such as biological family members who share similar
risks, future generations, and partners (Hallowell, 1999; Burgess and dAgincourt-Canning,
2001; Downing, 2002, 2005). Responsibility is not enacted from a single script: those at-risk
for HD report aiding their adult childrens reproductive decision-making as an important
consideration both when choosing to have or not have predictive testing (Smith, Stephenson
and Quarrel, 1999). This finding suggests how new decisions become part of ones people
have always faced in their everyday lives - such as those around reproduction. It also shows
that these decisions can continue to be made without recourse to clinical settings and the
additional information that genetic testing provides.
Reproductive decision-making in the face of genetic risk has been an under-researched
area. A review of 547 studies published between 1986 and 1996 categorised as being about
informed decision-making yielded only seven that dealt with genetic factors, and none which
addressed late onset disorders or examined how reproductive decision-making is experienced
as new options to clarify risk status have become available (Bekker et al, 1999:32). The indepth qualitative study of reproductive decision-making in the face of late-onset genetic risk
whose findings are reported in this chapter was undertaken to address this lacunae.
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The chapter also addresses suggestions that adopting a decision theoretic approach could
enhance our understanding of how people make reproductive decisions under these conditions
(Huys, Evers-Kiebooms and d'Yedwalle, 1992; Shiloh, 1996; Broadstock and Michie, 2000).
The introduction notes problems inherent in traditional approaches used to study decisionmaking in the face of risk and suggests why the naturalistic decision-making (NDM) initiative
offers to become a more informative resource. The study findings will be used to test their
claim to account for personal decision-making. In preparation for this evaluation the
introduction presents key tenets of NDM, reasons for focusing on one NDM model, Beachs
(1990) image theory, what this comprises, what was previously known about perception of
genetic risk, reproductive decision-making in the face of genetic risk and what is different
about late-onset risks.
Another limitation has been these approaches tendency to focus on the individual.
Individual factors do shape decision-making: holding internal or external attributions of
causality (Wallston, 1992) being risk averse or seeking (Lopes, 1987) and decision averse or
confronting (Beattie et al, 1994) contributes much to how people assess problems confronting
them, constrains their ability to deal with them, and to negotiate with others. But, as
Kahneman (1991: 145), in a personal reflection on the field of the psychological study of
judgement and decision-making points out, it is essential to acknowledge that significant
decisions are made in a social and emotional context. The value of a multiplicity of studies
over the years has been to document social constraints in which risk is actually experienced
and acted on. Health psychology has identified other factors, such as perceived social support
and efficacy, which can mitigate these constraints. Efforts have been made to incorporate
these factors in subsequent health psychology models such as the protective motivation theory
(Rogers, 1994) and self regulation theory (Leventhal, Nerenz and Steele, 1994).
Considerable overlaps occur between evolving health psychology models and decision
theories. Theoretical overlaps occur in concepts, such as risk perception, perceived benefits of
actions, beliefs about self-efficacy and response-efficacy and perceived control, used to
explain behaviour in the face of risk. Correspondences exist in findings about how people
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perceive and react to the presentation of risk information. For example, laboratory based
normative decision theory studies have yielded a taxonomy of heuristics and biases that shape
the way people process risk information when making decisions (Kahneman and Tversky,
1984) which have been replicated in health settings and used to inform clinical practice. Both
approaches have come to depict decision-making as a process, with a preliminary period of
cognitive restructuring preceding choice. The health belief model now postulates that taking
preventative measures is a function of considering perceived susceptibility to the risk,
benefits of taking actions such as genetic testing and barriers to taking this action whilst the
protection motivation theory emphasises the role played by beliefs about magnitude and
likelihood of threat, and the efficacy of envisaged responses.
Three characteristics distinguish NDM initiatives from previous decision-theoretic
approaches: their focus on decision-making in real life contexts; their recognition of the
competence that people achieve when making decisions under difficult conditions; and, being
open to a range of disciplines and perspectives thought to contribute to a richer understanding
of decision-making. These characteristics are considered in more detail below.
For detailed accounts of NDM approaches see Montgomery and Svenson (1989); Klein (1999); Klein, Orasanu,
Calderwood and Zsambok, (1993); Svenson and Maule (1993); Svenson, (1996), Klein (1997); Zsambok and Klein
(1997).
For further details of these models see Klein et al (1993) and in particular Klein's diagrammatic representation of their
communalities in figure 22.1, page 391.
131
employed at various stages of decision-making. The second group, process models, suggests
what these stages might be. How these approaches coalesce is outlined below.
Process models distinguish three broad stages. These are: (i) the preliminary work needed
to come to a decision, (ii) implementation of choices, and (iii) living with decisions.
Preliminary work involves perception of the situation, which may include evaluation of risks,
formulation of goals, and assessment of options open and strategies available to realise these
goals. Models differ in how they conceptualise this work: as screening out unacceptable
options according to values held (Beach, 1990); as the search for a dominant option
(Montgomery, 1993); or, as differentiation and consolidation of chosen options (Svenson,
1991). It is probable that people act in all of these ways, but by limiting their focus, models
remain manageable. Implementation is characterized by mental simulation of chosen
strategies, realising them, and modifying them in the light of progress decisions about their
ability to achieve goals. Progression through these stages may be both linear and recursive.
For example, living with decisions involves post decision evaluation, which can then
contribute to preliminary work for subsequent decisions. It may also include drawing on
decisions made by others.
If decisions are perceived as clear, acceptable, feasible and familiar, passage through
these stages becomes unproblematic. Little overt consideration is required, and the processing
style employed is described as intuitive. It will be suggested that this frequently characterises
reproductive decision-making in general populations.
A different picture of decision-making emerges when decision-makers perceive
themselves as confronting unfamiliar decisions or uncertain, ambiguous, redundant or
incomplete information - such as genetic risk. Under these circumstances decision-making
may necessitate a more analytical processing style. Action feedback loops (which may
include previous decisions) and mental simulations may be employed in order to structure and
implement decisions and reflect on them. Feedback loops and mental simulations blur
distinctions between the stages. As Orasanu and Connolly (1993:19) explain:
Instead of analyzing all facets of a situation, making a decision, and then acting, it
appears that in complex realistic situations people think a little, act a little, and then evaluate
the outcomes and think and act some more. ... Development of this knowledge [is] ... an
integral part of decision making.
Competing and shifting goals may emerge which have to be resolved within a temporal
emotional framework of anticipation, hindsight and regret (Kahneman, 1991). Conflict, which
may lead to procrastination, is seen as the price one pays for the freedom to choose
(Tversky and Shafir, 1992: 358).
Recognition of Competence
NDM models emphasize the competence people achieve whilst operating within the
constraints inherent in naturalistic settings. As Klein (1999: 1-2) explains:
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Instead of trying to show how people do not measure up to ideal strategies for performing
tasks, we have been motivated by curiosity about how people do well under difficult
conditions.
Competence is conceptualized as feedback loops showing the ability to benefit from past
experience. This can take several forms: shaping values (Beach, 1990); recognition of ability
to adapt to changing situations and priorities (Payne, Bettman and Johnson, 1993), which may
involve the creation of new pathways and perspectives (Willen and Montgomery, 2000); and,
developing the expertise to utilise appropriate and disparate sources of power, such as
intuition, mental simulation, metaphor and storytelling. Klein (1999: 3) elaborates on how
these strategies coalesce:
The power of intuition enables us to size up a situation quickly. The power of mental
simulation lets us imagine how a course of action might be carried out. The power of
metaphor lets us draw on our experience by suggesting parallels between the current situation
and something else we have come across. The power of story telling helps us consolidate our
experiences to make them available in the future, either to ourselves or to others.
Competence is also associated with exercising control, in that decisions represent a desire
to:
... act upon the world, to make sure that the future does not look like the past. Decision
makers go to great lengths to insure that they have the ability to control future events, (Beach
and Lipshitz, 1993: 26).
Where decisions involve risks, which can be defined as uncertainty about negative or
adverse outcomes (Teigen and Brun, 1997), it may not be possible to realise this objective.
Under these circumstances competence may become making decisions that it is possible to
live with.
Transtheoretical Aspects
The third distinguishing aspect of NDM is that it is open to a variety of theoretical
perspectives thought to provide additional insights into decision-making. These include
phenomenology (Karlsson, 1987), identity formation (Sloan, 1986; Nelson and Nelson,
1995), social approaches to risk (Wartofsky, 1982; Krimsky and Golding, 1992; Palmlund,
1992) and narrative accounts (Beach, 1997; Cox, 2002, 2003; Klein; 1999). What these
perspectives comprise and can contribute is outlined below.
Phenomenology captures how people experience exercising their will, develop a sense of
competence, reflect on what they should do and structure decisions as realisable projects with
others (Karlsson, 1987). Decision-making shapes identity in that it contributes to the way we
are perceived, by others and ourselves. As Nelson and Nelson (1995: 136) explain:
Choices made ... in a very important way determine who we are, who we have been, and
who we will be as moral people; this gives the choices their proper weight, and defends us
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from the kind of self-deception that is sometimes a part of having to decide in morally
difficult circumstances.
Social approaches to risk elaborate how identity is shaped. Conceptualising decisionmaking as social drama, consisting of competing stories involving justifications of actions
and attributions of blame, identifies a range of roles that are played out when making
decisions in relation to risk (Palmlund, 1992). These include risk bearers, risk generators, risk
informers and risk arbiters. Questions that can be explored in empirical work include how
these roles come to be allocated and assumed in families, the expectations they arouse, and
how these expectations can constrain or facilitate decision-making (Downing, 2005).
Answering these questions involves formulating looser definitions which draw on
narrative approaches. For example, Beach (personal communication, August 1997) describes
decision-making as allowing people to tell stories to construct alternative futures and find
ways of making the stories they like happen. This definition connects us to studies such as
those of Cox (2002, 2003) which enhance our understanding of the different ways in which
people 'progress' from intentions to implementation of predictive genetic testing through
examination of this as a narrative moment. Her participants' stories of evolving towards it,
having to know and taking the decision bear little similarity to conventional notions of
decision-making as a rational planned process of decision and implementation. In this way,
stories become natural experiments, linking a network of causes to effects (Klein, 1999:
196). Exploration of narratives reveals and challenges prevailing cultural stories, as shown in
Sandelowski and Jones' (1996) qualitative study of women's constructions of choice after the
detection of fetal abnormalities.
Image Theory as an Example of NDM Approaches
Underlying similarities in how NDM models conceptualize decision-making enable their
principles to be illustrated in more detail by one particular model, image theory (Beach,
1990). An additional reason for focusing on this model was that it evolved from a normative
study of reproductive decision-making in a general population and thus can demonstrate how
NDM approaches offer a far richer understanding of decision-makers perspectives and
processes.
The original research involved construction and employment of a decision analysis tool,
the Optional Parenthood Questionnaire, to help couples think more rationally about the costs
and benefits of having a/another child (Beach, Townes, Campbell and Keating, 1976).
Partners were asked to rate a list of pre-determined values - gleaned from birth planning
literature - which children could fulfil for parents. Values were narrowly defined as utilitarian
benefits and costs. They indicated considerations such as caring for children with health
problems which people might take into account when making reproductive decisions.
Questions were weighted equally making it impossible to assess, even under hypothetical
circumstances, the relative importance people placed on each aspect. These constraints,
inherent in a traditional decision-analysis approach, were subsequently removed when values
were re-conceptualised more loosely as 'images' in image theory.
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135
Further insights into the relationship between emotional engagement and decisionmaking are provided by Willen and Montgomery (2000). They show that people in troubled
marital relationships can only move towards a decision situation after they have changed their
form of involvement, termed 'perspective'. Reconfiguring partners previously positively
regarded qualities as negative produces psychologically more 'distant' (or less emotionally
involved) perspectives on these relationships. This shift enables them to contemplate divorce.
As they distance themselves from their relationship, decision-makers become increasingly
emotionally involved with future perspectives. These incorporate possible outcomes of
divorce, such as how it will affect them, their life and those they care about and how these
concerns can be reconciled with values important to them.
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In this way, narratives come to provide an ethical basis for decision-making:
The narrative ... asserts that the quality of the decision matters as well as who is making
it. (Nelson and Nelson, 1995: 107).
Support is therefore shown for claims that additional insights into the decision-making
process will be provided by links made to other domains, such as narrative approaches
(Beach, 1997). Testing these claims involves deploying qualitative methods that provide
access to decision-makers narratives.
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time for different cohorts, but cannot access the decision-making that culminates in these
outcomes. As Wexler (1980: 322) - herself at-risk for HD - states, decision-making, being
essentially a private matter, requires different approaches. :
We know so pitifully little about the myriad of complex motivations that propel people to
propagate their kind, particularly now that birth control methods are giving people such
freedom of choice. Counting facts retained and babies born is not enough. What goes into that
crucial decision?
Answering this question involves qualitative approaches that seek out and prioritize
perspectives of those making decisions. Exploratory interview studies reveal decision-making
to be a process, characterised by a multiplicity of decision points rather than a single 'choice'
(Busfield and Paddon, 1977; Payne, 1978; Richards, 1978; Dowrick and Grundberg, 1980;
Fox, 1982; Currie, 1988; Willen, 1994). As well as deciding whether to have a child, these
include with whom, whether to have further children, when to do this, under what conditions,
and what action should be taken to achieve these goals. These considerations face everyone
including those contending with difficulties, such as infertility or genetic risk even if as will
be shown, they come to conceptualize them differently.
These studies also show how people construct and resolve these decision points.
Establishing shared social realities forms a significant preliminary step. For example, many of
Willen's (1994) respondents framed reproductive decision-making primarily as a relationship
question, focusing not so much on whether to have children as with whom. Reproduction
becomes part of the 'natural' pattern of acceptable relationships and, as such, not requiring
overt reflection or negotiation, except about what might be the 'right time' to implement
previously unexpressed and unquestioned intentions. This is revealed to be a subjective
judgment of circumstances rather than a chronological point (Currie, 1988). These
observations are consistent with other findings, such as those from an earlier study (Mansfield
and Collard, 1988) which found that newly-wed couples did not discuss reproduction, and
were evocative of the commonly used expression, 'falling for a baby' which suggest little in
the way of conscious planning.
Adopting a NDM perspective enables us to construct a coherent account of these
findings. This confirms that decision-making does occur but in a more intuitive form,
consistent with the values reproduction represents for those concerned. As Beck and BeckGernsheim (1995:196) postulate:
A child represents ... the 'natural' side of life ... Motherhood seems to offer the woman an
alternative refuge from the working world, where it is imperative to behave responsibly, and
soberly, and emotions are generally considered a nuisance. Committing yourself to a child
means contradicting the cognitive side of life, and finding a living counterweight to all that
soul-destroying routine.
Taking a 'natural' stance can thus be interpreted as conforming to existing norms that
children will 'happen' within relationships and do not need to be consciously 'decided' or
planned. The existence of these norms is corroborated by the experiences of the involuntarily
childless who cannot fulfil them (Pfeffer and Woollett, 1983; Mason, 1993; Read, 1995), and
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Claudia Downing
the voluntary childless who must resist them (Campbell, 1985; Kiernan, 1989; Bartlett, 1994;
Morell, 1994; McAllister and Clarke, 1996).
Reproductive Decision-Making in the Face of Genetic Risk
Questions arise about whether the seemingly unquestioning acceptance of norms to have
children and associated intuitive processing can be sustained (and how) once decision-makers
become aware of genetic risk. In contrast with the 'normal' experience outlined above,
reproduction in the face of genetic risk is depicted as involving the recognition of uncertainty
about potentially severe and possibly irreversible consequences, and that decision-making has
significant implications for the decision-makers, other family members and future
generations. Factors thought to influence reproductive decision-making under these
circumstances are: the value placed on having children; the perception of genetic risk; and
personal experience of the condition (Shiloh, 1996). How these factors are thought to operate
is considered below.
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McAllister and Clarke (1996) found that only a third of women self-categorised as voluntarily
childless had initially made a firm decision never to have children and ten percent were still
ambivalent. Many of their respondents had regular, and valued, contact with other people's
children. These observations suggested that factors other than values held about children were
crucial in implementing womens decisions. It emerged that a key aspect was holding
negative images of parenthood: they viewed parenthood as sacrificing hard won social lives,
financial independence and jobs. Not wanting to experience these losses made them reluctant
to become mothers.
Perception and Experience of Genetic Risk
The psychometric work conducted by Slovic, Lichstenstein, and Fischhoff, (1984) and
Slovic (1987) provides a useful starting point for learning how people perceive risk. Analysis
of peoples ratings of a variety of risks on a number of given dimensions generated three
underlying factors. These are:
(i) dread risk, which relates to perceptions of the uncontrollability of exposure to risk,
dread associated with its impact and whether distribution is judged as inequitable;
(ii) unknown risk which reflects the extent of personal experience and expert knowledge
that exists of a risk, how observable it is, and whether effects are considered to be
immediate or delayed. The impact of experience of risk on decision-making is likely
to be complex. It has been suggested that risks which are known are more likely to be
perceived as less threatening (Slovic, 1987; 1992);
(iii) the number of people likely to be exposed to or affected by a risk.
Their findings (despite not drawing specifically on genetic risk) are consistent with
prevailing discourses about genetics. For example, Rothman (1998: 233) explains how
genetic determinism views an individual's genetic makeup as an uncontrollable accident of
fate which has a great impact in that it holds the key to identity, and because it is readily
observable to those with expert knowledge:
A story is written into our bones and skin and hair, there to be read by anyone who
knows the code.
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Thus what risk means and what people are prepared to do about it is likely to vary
according to their underlying value systems. If, as has been claimed earlier in this chapter,
values are formed in social contexts, decision-making about genetic risk will also be shaped
by the wider social and cultural framework in which decision-makers live (Douglas, 1985).
As Rothman (1998: 39-40) remarks, risks become enmeshed with:
our own personal troubles, our daily lives, our intimate concerns, and the world in which
we live, the issues that face us collectively. We live a biography, a personal tale, but we live it
in a moment of history, in a collective time.
Rothmans comment reminds us of the need to acknowledge that reproductive decisionmaking differs from other decisions about genetic risk in that it is embedded in a particular
history. In addition to their biological inheritance, families have had to contend with a 'social'
legacy of opposition to their existence and reproduction. Social legacies, as well as current
attitudes, vary between cultures. Within living memory, members of HD families were
murdered in Nazi Germany. In other western countries sterilization was advocated, and
sometimes enforced in some American states (Davenport and Muncey, 1916; Wexler, 1980;
Harper, 1996a; Thom and Jennings, 1996). Reducing the incidence of at-risk births remained
as an objective of genetic counselling in Britain for many years (Carter and Evans, 1979;
Harper et al, 1979; Thom and Jennings, 1996). These eugenic measures were justified as
being the responsible way to promote the wellbeing of future generations. Perception of this
legacy is thought to have caused many of those at-risk who wished to have children to remain
"doctor shy" (Wexler, 1979: 200) long after more liberal attitudes came to prevail.
In many countries it has subsequently become unacceptable to suggest that those at-risk
should refrain from reproduction. It is now generally assumed that people want to feel in
charge of their own destinies, are able to exercise freedom of choice in ways that benefit their
wellbeing and wish to take an active role in managing their own affairs, including negotiating
genetic risk (Conrad and Gabe, 1999). What has not changed is an underlying assumption on
the part of health care professionals and the general public that, given a choice, people would
prefer not to pass on known risks.
This assumption is borne out by prenatal studies in general populations which identify a
moral and a 'technological imperative' to make use of risk avoiding possibilities (Tymstra,
1989). It explains why some women terminating an abnormal pregnancy identified through
routinely offered prenatal testing report having had "no choice" - when clearly they did because the alternatives were rejected as unacceptable, or too difficult to justify (Green,
Statham and Snowdon, 1992). Pregnancy is changed even for those who decide not to make
use of fetal diagnosis. As Green (1990: 38) explains:
mothers who decline to take part will always know that they could have had that
knowledge and could have acted on it .
Nelson and Nelson (1995: 69-76) argue that expectations arise that both parents will act
in their childs interests:
"Parents' duties to children, arise from their direct responsibility for bringing the
children into existence, whether they meant to or not - and for putting them into the world in a
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condition of extreme vulnerability ... Nor can one parent release the other from this
responsibility, as it is the child, and not the other parent, to whom the debt is owed.
Parents are likely to be viewed as irresponsible if they act in a way that is judged by
others not to be in their fetus' best interests (Lippman, 1992).
Potential quality of life, becomes a paramount consideration when making decisions
about testing and termination for fetuses at-risk for, or affected by, disorders that manifest at
birth or in infancy (Kitcher, 1996). The more a disorder is perceived to negatively affect
quality of life the more willing people are to consider termination (Evers-Kiebooms et al,
1993; Drake, Reid and Marteau, 1996).
Little is known about how people view these considerations in relation to a life that might
be 'normal' until adulthood, but then be affected by a genetic disorder. HD offers a
particularly rich context to explore them, in that the clinical picture presents families with two
decision-making dilemmas. The first is whether to have children who, in later life, may
develop the disease. The second is whether it is justifiable to have children - given that
uncertainty arises about the at-risk parents ability to sustain a parenting role. HDs late-onset
makes it likely that people will have had had to make decisions about childbearing, and know
of their risk, before developing any overt symptoms. Affecting both men and women these
comprises cognitive changes, loss of control over voluntary movements, psychiatric
symptoms and marked physical decline over a period of ten to fifteen years leading to
inevitable death both men and cognitive changes, loss of control over voluntary movements,
psychiatric symptoms and marked physical decline over a period of ten to fifteen years
leading to inevitable death (Harper, 1996b). The mutation is highly penetrant, meaning that,
providing they live long enough, most people who inherit it will develop HD. If they were to
develop the disorder, the current lack of any effective treatment or cure would then threaten
their ability to mother or father their children.
Few have utilized genetic testing since its introduction in the late 1980s to resolve these
dilemmas (Harper, Lim and Craufurd, 2000; Hayden, 2000; Simpson and Harding, 1993).
Low uptake of predictive testing has been attributed to reluctance to make contact with
clinical genetics services, reluctance to lose hope, uncertainty about ability to cope given the
continuing lack of treatments, and threats to identity. Van der Steenstraten et al (1994) found
that non-requesters of predictive testing were more likely to have learnt of their risk before
adulthood than requesters. This led them to hypothesise that non-requesters were more likely
to have incorporated HD into their identity and have less need to resolve their uncertainty
than requesters who perceived their risk as threatening their previously established identity.
Making decisions about prenatal testing concerns both general populations who undergo
routine antenatal screening as well as those aware of genetic risk. Decisions about whether or
not to employ prenatal and subsequent decisions about terminations may need to be made
under severe time constraints. Factors found to be associated with use of prenatal testing for
early onset disorders include perceived accuracy of the test, willingness to consider
termination, and other family members' attitudes towards termination (Shiloh, 1996).
Values held about abortion can be either absolute or relative, in that people might accept
abortion for disorders that affect children's quality of life but not see it as appropriate for HD.
If, as has been suggested above, those growing up in affected families see HD as part of their
identity, they can be reluctant to consider termination, seeing it as rejection of themselves
(Hayes, 1992; Wexler, 1992; Richards, 1993; van de Steenstraten et al, 1994). Those unable
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Claudia Downing
to agree (for whatever reason) to termination of high risk fetuses are unlikely even to be
offered prenatal testing. However, documented cases of women discharging themselves from
hospital at the penultimate moment rather than undergoing a termination (Tolmie et al, 1995)
and of continued high risk pregnancies (Bloch and Hayden, 1990) reveal that people cannot
always predict how they will react as the decision-making process unfolds.
Learning more about clinical encounters can shed some light on what they can contribute
to the decision-making process. For those uncertain about their reproductive decisions - one
third of the participants in one study (Wertz, Sorenson and Heeren, 1984) - counselling can be
helpful at an early stage of decision-making, as part of (Kessler 1989: 350):
an ongoing process, over time, of evaluation, weighing of options, and of responses to
personal and interpersonal factors all of which contribute to reproductive decision making
Jungermann's (1997) advice giving and taking (AGT) model offers an explanation of
what happens when counselling occurs at this pre-choice stage of decision-making. He
focuses on interactions, such as those which arise between consultants prepared to give advice
and clients prepared to consider advice. Advice is defined as the preferences of another
person. Four components thought to comprise this process are: description of the problem
followed by identification of appropriate options; justification of particular options; particular
options being offered as advice by consultants; and clients' evaluation and consideration of
this advice culminating in either acceptance or rejection. Willingness to accept advice is
linked with factors such as perceived credibility and confidence felt about the person giving
advice. Jungermann (1997) suggests that uptake of advice is limited because decision-making
is frequently guided by values, about which clients are the experts, rather than facts, such as
the probability of a negative genetic outcome, which are the provenance of the consultant.
Other research reveals Jungermann's dichotomy as too simplistic, in that it is not possible
for facts to be provided in a neutral way. Comparisons made between professional groups
have shown them to evaluate risks differently (Marteau, Drake and Bobrow, 1994) which can
then influence how they convey information. It is also necessary to acknowledge the
taxonomy of cognitive heuristics and biases that shape the way people process information
presented to them (Kahneman and Tversky, 1979; 1984). These findings have implications
for clinical practice. As Wexler (1992: 219) comments:
It is so important to explain genetic information both in terms of gain and loss. Telling
clients they have one chance in four of having an affected child conveys one psychological
message, saying that they have three chances in four to have a normal baby conveys a
different one - even though the statistics are the same.
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partially explain why uptake of prenatal testing is very low for HD (Hayden, 2000) and
practically non-existent for other late-onset disorders such as inherited breast, ovarian and
bowel cancers (McAllister, 1999). Very little interest has been expressed in prenatal testing
for HD (Mastromauro, Myers and Berkman, 1987) and even fewer have actually used it after
it became available (Hayden, 2000).
Genetic counselling has a different impact when it coincides with a later stage of
decision-making. A review of prospective studies of genetic counselling concluded that
counselling then confirms or reinforces decisions already taken (Kessler, 1989). Counselling
can also reduce anxiety about implementing decisions already taken. This supposition would
account for an observed post counselling increase in births for those who perceived
themselves to be at high risk.
Clinical studies, some of which are cited above, report only the views of a small and
unrepresentative proportion of the total estimated HD at-risk population willing to make their
family history known. Clinical studies focus on the 'patient' also means they fail to address
the social aspects of decision-making. Aggregation of existing data makes it impossible to
learn how couples come to see HD as an issue for their reproductive decision-making and
decide to contact clinicians.
Studies adopting a family systems approach produce useful insights into how risk about
HD is experienced, perceived and communicated. Focusing on interactions within families,
they reveal that crucial cognitions and behaviour are shaped long before reproduction is
contemplated. Members may collude to 'preselect' one of their members, sometimes on the
basis of lay beliefs about gender vulnerability or physical resemblance, as the future sufferer
(Kessler, 1988). It produces an illusion of control and alleviates uncertainty about other
family members' risk. This provides welcome reassurance if, as Korer and Fitzsimmons
(1985) found, the statement that HD 'does not skip generations' is sometimes interpreted as
meaning that someone from each generation will definitely be affected. Interpreting the same
nominal risk quite differently for, and by, each family member, generates contrasting
expectations about what comprises responsible decision-making (Downing, 2005).
Knowledge of HD also influences how family members relate with outsiders. Families
can become either "HD orientated" (defined as becoming excessively preoccupied with HD)
resulting in them leading socially isolated lives, or "independently orientated", with HD being
given a less prominent role and families remaining open to contact with others (Korer and
Fitzsimmons, 1985). These different perspectives affect how partners are informed about HD.
Existing family members may collude to keep information from them. The nature and extent
of information divulged, when this occurs, and the impact that information has on decisionmaking can vary considerably (Barette and Marsden, 1979; Shakespeare, 1992). Wives of HD
patients felt vital information had been kept from them until after they had had children, and
that they would have made different reproductive decisions if they had been fully informed
(Hans and Koeppen, 1980). This could explain why Barette and Marsden (1979) found that
over sixty percent of their respondents were prepared to tell their children not to procreate.
In order to comprehend the minutiae of how HD is experienced it is necessary to access
personal accounts. Their evidence, though compelling, is often criticised as being of an
anecdotal nature. The onus is placed on the researcher to impose rigor on how they are
gathered and analyzed in order to decipher underlying commonalities yet preserve their
diversity. The following aspects of the grounded theory approach adopted in the study help
meet these requirements. These include grounding the analysis in the data, making analytic
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Claudia Downing
Ethical Approval
The Local Clinical Research Ethics Committee, the Huntington's Disease Consortium and
the Cambridge University Psychology Research Ethics Committee granted ethical approval
for the study. All names and some details have been changed to protect confidentiality.
Methods
Recruitment and Characteristics of Participants
Theoretical sampling (to find those encompassing a range of relevant experiences and
address the gaps noted earlier in this chapter) involved seeking out people at various stages of
the reproductive process; of different ages and gender; with varied experiences of HD,
Huntingtons Disease Association (HDA) support groups and clinical genetics services;
making a range of choices such as accepting or avoiding passing on the risk; and, of doing
this in several ways, including having predictive, prenatal testing and undergoing termination
of high-risk pregnancies. Seventy-six participants, comprising two generations, lateral kin and
their partners within 17 kinships, were recruited to the study through the HDA, a Regional
Clinical Genetics Centre and 'snowballing', or seeking chain referrals from initial respondents.
Recruiting through family members offered a broader range of people the opportunity to
opt in to the study than a purely direct approach by the researcher would have done. This
technique provided access to people not in contact with either the clinical genetics centres or
the HDA, and who would not have otherwise known about the study.
Characteristics of participants are shown in Table 1 below. The older generation had
completed their reproductive decision-making before genetic testing was introduced. They
could still play an active part in the younger generations decision-making in the following
ways: ascertaining their status through predictive or diagnostic testing; providing samples for
linkage or prenatal testing; or by being supportive or critical of their childrens decisionmaking. The younger generation, who formed the main focus for the study, were those
making reproductive decisions prior to and at the time of interview. Some of them had made
decisions before as well as after the introduction of genetic testing. Including siblings and
cousins who face similar risks enabled the study to explore whether lateral kin provide
guidelines for each other and how different responses are tolerated
145
Reproduction
Category
Risk
Genetic testing
Contact
Details
Male
Female
range
Married
Single
Separated/ Divorced
Widowed
No children
One child
More than one child
Intending to have child/ more children
Details
At risk
Partner at risk
Affected
Partner affected
Tested positive
Partner tested positive
Tested negative
Partner tested negative
Used prenatal testing
No contact with Clinical Genetics
No contact with HDA
Gen 1
9
17
46-70 yrs
23
0
1
2
0
4
22
0
Gen 1
4
1
2
12
0
0
1
1
0
15
11
Gen 2
21
29
20-49 yrs
38
8
3
1
25
13
12
23
Gen 2
20
14
0
0
2
2
6
5
4 couples
18
10
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Claudia Downing
Accordingly, in addition to reading about HD, contact was made with people at the
following locations: a regional clinical genetics centre, HDA support groups and
organisations such as Sue Ryder homes and the Crossroads service providing care for those
affected. Another reason for contacting the regional clinical genetics department was to
establish how many HD families they knew to exist in the vicinity. Concerns had been
expressed that it might be difficult to recruit enough families. It was reassuring (from a
research point of view) to establish that, despite HD being thought of as a rare disorder,
approximately 250 families had been seen there over the last twenty years. Contact with
families had varied and information about family structure was sometimes incomplete. Being
given permission by clinicians to examine these records gave me an invaluable understanding
of the work of clinical genetics departments in pre- and post-testing eras. I learnt that it was
not unusual for clinicians to present an optimistic picture to those at the beginning of their
reproductive life, setting up expectations that genetic testing would become available one day.
This had lead them to encourage the use of temporary rather than permanent methods of birth
control. It also became apparent that people had faced considerable practical difficulties in
realising certain options, such as prenatal testing, which were first introduced in only one or
two centres. Being in the department and sitting in on consultations informed me of current
work, including preparation for the predictive testing programme. Contact with a second
regional clinical genetics department refined these ideas.
Visits to Sue Ryder care homes and spending time with the local Crossroads family
support service enabled me to learn what happens when families can no longer cope unaided.
Regular attendance at one HDA support group's meeting, and joining in social activities with
families over a period of a year and a half - which overlapped with the commencement of
data collection - enabled me to 'hear the talk' outside medical settings. These meetings varied
from informal chat to structured discussion of particular issues, such as reproduction. With
the group's permission, I tape recorded some of these more focused sessions in order to reflect
on them.
Key points emerging from preparatory work
The preparatory work enabled me to show the families that I had made some effort to
understand their perspectives before we met for the interviews. It facilitated drawing up a list
of core questions and phrasing them in terms reflecting participants' language. Hearing of the
difficulties people experienced when talking about HD within families indicated that it would
be advisable to interview each person separately. Stories told of affected parenting led me to
realise that what are normally regarded as non-threatening questions such as early childhood
memories (Yow, 1994), and which are therefore often asked first in interviews, might need to
be approached later in the interview.
During the group discussions I first heard people prefacing their stories with comments
about knowing or not knowing about HD, or of knowing but not really understanding what it
could mean. I was to return to these observations when I subsequently identified 'awareness'
as the causal condition for my model.
Subsequent data collection and analysis
Taking part in the study involved completing a short questionnaire to gather background
information and enable participants to state what they felt the study should address. They
were subsequently individually interviewed at a place of their choice, normally their home.
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Results
This section provides an overview of the model, discusses the analysis that generated it,
and then outlines how it provides a framework to account for variations in what people do. A
subsequent section discusses what emerged about the process of decision-making.
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Claudia Downing
parenthesis and the form these take in the study model are italicised. The 'causal condition' is
one that provides the context in which the phenomena of interest occur. Comparisons of
aware and unaware decisions identify this to be awareness of the risks for HD. A key aspect
of the model is that it encapsulates the two dimensions of reproductive risk identified above:
that which may be passed on to any children born, and that of not being able to sustain a
parenting role. These are the child-centred and the parenting risks. The 'consequence' of
becoming aware of these risks is that reproductive decision-making becomes defined as
problematic. This prompts people to redefine certain elements of their situation - such as the
nature of the risks, themselves, fertility, and relationships. The form this 'strategy' takes
reflects modifying factors such as the values that people hold, their concept of the future and
their perception of social support. The 'consequence' of redefining is to enable people to tell a
different story when subsequently accepting, modifying or avoiding one or both of these risks.
Concerns about one value, responsibility, dominate these stories - identifying responsibility as
the 'core concept' for the model. A key aspect of the model is that it demonstrates that how
people are perceived to make decisions can become as important as what they decide.
F ACTUAL
FACTUAL
AWARENESS
AWARENE SS
CHILD
C H IL D
CENETERED
CENT ERE D RIRISK
SK
AWARENESS
AWARENESS
OF RISK
P ARENT
ING RI SK
PARENTING
RISK
L IVE DLIVED
AW ARE NESS
AWARENESS
R ISK
RISK
VALUE S
VALUES
C ONCEPT OF F UTURE
CONCEPT OF FUTURE
REDEFINE
REDEFI
NE
ELELEMENTS
EMENTS
SEL F
SELF
REL ATI ONS H IP S
RELATIONSHIPS
ESTABLISH SELF
ESTABLISH
SELFAS AS
RESPONSIBLE
RESPON
SIB LE
DECISION
MAKER
DECIS ION MA KER
ACCEPT RISK
ACCEPT RISK
MO DIF Y
MODIFY
AVOID
AVOID RISK
RISK
149
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Claudia Downing
Further analysis revealed that barriers to communication took different forms in each
generation. The older generation spoke of those affected being hidden away by their families.
Their reluctance to make the condition known was not altogether surprising in view of the
'social' legacy of opposition to their existence and reproduction noted above. Another
explanation to emerge was there was less incentive for the previous generation to consider the
outcome of their decisions because they held different expectations about life.
Then, if you got to fifty you were lucky ... You might have died of pneumonia, or TB, or
half of the children that had Huntington's could have been stillborn anyway. ... It's only NOW
that you expect to have longer quality of life that it's become such a problem. That you feel
you're entitled, you know, you sort of say, "Oh, I'm not even going to get fifty years."
Older generation participants who had known about HD reported information being
linked in uncompromising terms to reproduction. They were told either not to have children
or to go away and get on with things. In the latter case this could be interpreted as not
questioning widely held expectations that marriage would lead to having children.
The younger generation reported that their parents had waited divulge relevant but
limited information until their teenage years or when they had formed serious relationships.
Now that HD is cited on the school science curriculum families report feeling obliged to
discuss it earlier and in more depth than they might otherwise have done.
Finally, individual variations in information accessing and processing skills affected the
speed with which awareness occurred. This included the prior establishment of schemas - for
example, from professional experience, or from contact with sufferers of other illnesses - with
which to make sense of information as it emerged. Such schemas could both help those at-risk
to explain what HD involves and partners to make sense of the information.
Cognitive Processing
Distinctions participants made between decision-making before and after becoming
aware of HD revealed how it changed with growing awareness. People commented that
before becoming aware "there had been no decision to make" that was any different to other
peoples reproductive decisions, i.e. taking into account desires, financial and travel plans and
waiting for the right time (Currie, 1988; Willen, 1994). Accounts of aware decision-making
drew on physical metaphors of burden, such as weight and size. These metaphors conveyed
the effort required to weigh, balance, or set aside the child-centred and parenting risks
associated with HD. As had been surmised, like those facing infertility cited in the
introduction, references were made to a sense of loss - the loss of normal expectations for
reproduction. It was having to consciously address these considerations that turned
reproductive decisions into difficult ones. Difficulty was compounded by complex and
multiple analytical concerns, such as those around termination and determining risk status.
Decision-making also felt onerous because as awareness increased people felt obliged to
account - to themselves and others - for their intentions and actions. This observation
provided an early indication that responsibility would become the core concept for the model.
151
As in the previous stage concerns arose in connection with reproduction. How health care
professionals reacted to the mention of HD then became the crucial factor in determining how
seriously these concerns were taken. Naomi held her doctor accountable for having had a
child at-risk in that she felt he had not ensured she and her at-risk husband had understood the
magnitude of the risks:
He SHOULD'VE warned us, properly, and MADE us understand, how serious, it all is.
And if he had the SLIGHTEST doubt that we didn't understand, he should've SAID it again,
and again and again, until that, he was fully satisfied that we, understood FULLY what we
were about to enter into.
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Claudia Downing
strategies such as prenatal testing that could ensure that these children would not be at-risk.
Modifying strategies comprised timing of reproduction and determining family size. People
could even have more children than they might otherwise have done, in the hope that at least
one had not inherited the mutation and could care for any affected siblings. Avoidance
strategies included not having children to seeking gamete donation, clarifying risk by testing
and termination and seeking (unsuccessfully) to adopt or foster.
Some participants experienced a fifth stage, refined awareness, when risks became
certainties as a result of genetic testing or diagnosis. A few chose a non-disclosing form of
prenatal testing, prenatal exclusion testing (PNET) which did not clarify the parents status
but enabled them to have children known to be at low risk. This form of testing is
complicated to understand. It requires parents to terminate any high risk fetus known to be
at the same fifty percent risk of having inherited the HD mutation as the parent. This means
that there is a fifty percent chance that it does not have the mutation. It works by comparing
markers on the gene from three generations, to see if the fetus has inherited the at-risk
parents copy from the affected or non-affected grandparent. The idea becomes to only
proceed with pregnancies shown to be at minimal risk in that they have almost certainly not
inherited a copy from the affected person. For a detailed account of how couples live with
their decisions under these circumstances see Downing (2005). Donating samples to inform
testing enabled the older generation to retrospectively define themselves as responsible
decision-makers.
Growing awareness also involves acknowledging how reproduction becomes embedded
in a 'HD life cycle'. This consists of the following events and stages: being born at-risk, being
parented by an affected parent, discovering the risk, developing ways of living with risk,
deciding whether to tell prospective partners about HD as a preliminary to reproductive
decision-making, undergoing changes in risk status arising from diagnosis and predictive
testing, becoming a suffer or carer for parents, one's children or other relatives, and coping
with death and loss. People do not necessarily experience all of these events, the order in
which they occur can vary, and events may coincide. For example, some people only learn
that they were born at-risk when an affected relative died. Learning how HD events are
experienced, resolved and map onto the 'normal' life cycle (Erikson, 1963) can elucidate the
varied responses that people show to the reproductive risks for HD. As intimated above, how
and when people discover their risk seems to affect how HD is taken into account when
subsequently making reproductive decisions. Being brought up with the knowledge that HD
is in their family, enabled some people to assimilate having at-risk children with a 'normal'
life trajectory. Others, appraised of their risk at a later age, found it more difficult to
accommodate reproductive risk with normal expectations for reproduction.
Redefining as a Response to Awareness
Redefining denotes a strategy of restructuring elements of peoples situation, either
cognitively or through actions, in order to have a different story to tell. New narratives
incorporate changes in their perceptions of risk, fertility, themselves or their partners, and
reproduction thereby enabling them to account for having accepted, modified or avoided
either or both of the risks in a responsible way.
Deconstructing participants references to denial - a powerful form of redefining revealed three ways this could manifest. The first corresponded to the accepted clinical
psychological definition as unconscious repression of painful information, such as learning of
153
the risk. The second, 'affected' denial, was associated with the medical onset of HD. The third
and most common way was a conscious strategy of distancing oneself from threatening
information. In contrast with clinical denial people could acknowledge this was happening
and unwanted information remained accessible. Distancing was evidenced by HD only being
spoken of in connection with more distant kin, such as cousins, or in relation to physical
distancing, or severing contact between affected and non-affected kin.
Resorting to distancing was a function of the degree of fear engendered by the risk,
control felt over it, and individual differences in the amount of information that could be
tolerated about HD. If distancing was widespread in families, a closed awareness context
resulted - similar to that identified by Glaser and Strauss (1966) when studying dying
patients. As Angela explained, family members knew about HD but colluded in not openly
acknowledging or discussing it.
We used to live a life of pretending it isn't happening. .... When we were at home, we
used to react as if nothing had happened, and it became like a family trait. If dad choked on
some food, you'd sort it out, organize it, and then carry on with the meal as if nothing had
happened.
It also became difficult to implement choices, such as prenatal or linkage testing, which
depended on other family members acknowledging the need for their assistance. As Tara said:
We had to plead with him to give his blood, for the comparisons, for mine and my
brother's test, because he didn't want to know, and he didn't want us to know.
As well as denying risks, narratives could redefine them in ways that appeared to lessen
them or clarify them through genetic testing. Those at-risk, or their partners, whose values
allowed them to accept a semi-biological child could redefine themselves as temporarily
infertile in order to gain access to new reproductive technologies and bypass their genetic
risk. Reproduction could be redefined as a challenge to the disease, or as replacing an affected
person who had died. Others redefined partners as potential single parents so as to counteract
the uncertainties surrounding their own ability to sustain a parenting role. Parenting could
also be redefined, for example, through becoming an uncle or by caring for children in a
professional capacity which would enable a person to relinquish responsibility on becoming
symptomatic.
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Claudia Downing
Choosing not to proceed with an at-risk pregnancy enabled one to be redefined by others
as acting responsibly. Sabina explained what else she had gained from her unplanned, and
terminated, pregnancy. Making decisions about another life allowed her to redefine herself as
a responsible caring mother, through having:
the experience of GENUINELY meddling in another person's life and shaping it
irrevocably so that it can never be as it would have been without my interventions knowing
that you have taken upon yourself that kind of assumption of responsibility which you have,
as a parent, I haven't missed. The, the knowledge of being wholly responsible for life and
death of another individual umn, I had with deciding to have an abortion. .... I talked to Sam Sam's the guy, I named him / her, and sort of explained what I was doing, and all the rest of it,
and explained why it was, this was the best life for that person to have. So, I did all of that.
Redefining thus illustrates how people make creative and adaptive responses to difficult
dilemmas, consistent with naturalistic decision making (NDM) accounts of personal decisionmaking (Payne, Bettman and Johnson, 1993).
155
the introduction of each person involved in decision making. Those who saw reproduction as
central to their existence found it difficult to think of a life without children and easier to
downplay other considerations. Flora explained:
I wanted children MORE than I thought the risk would be to her.
Conversely, men and women who placed less value on having a child found it convenient
to draw on HD as a responsible reason for remaining childless. Matthews comment was
typical of this standpoint:
Plenty of other people are busily producing babies. And if you are unsuitable to provide
them, why worry?
Decision-making values
related to the importance
placed on:
Making decisions
More frequently decision-making entailed resolving central but conflicting values, such
as wanting to have biological children, not wanting to pass on the risk, valuing an at-risk life,
and being opposed to abortion. Thus certain strategies such as prenatal testing or utilizing
donated gametes, could be screened out by the values that people held. For a detailed analysis
of uptake of various risk limiting and avoiding strategies according to the values that they
involved see Downing (2002).
Vision of the Future
How people viewed the future affected whether or not they were prepared to accept the
risks. It also illuminated how some people (who would have been prepared to accept
termination of pregnancy) justified rejecting genetic testing. They construed availability of
testing as an indication that treatments for HD would follow in the near future. Envisaging the
future in terms of promise made it easier to redefine the risk as acceptable and reject testing
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Claudia Downing
or other risk avoiding strategies. Hearing about on going research into possible treatments fed
into this optimism.
Others, more cautious about the future, were more likely to take steps to avoid passing on
the risk. Whilst they were able to accept their own existence as a result of the previous
generation's limited awareness they doubted that the next generation would necessarily be so
tolerant. They saw the future as a time of reckoning, when they would become accountable
for the decisions that they had made. Their priority was to be seen as responsible decisionmakers by their future as well as existing families. As Rupert explained:
I would really HATE to have the discussion with a child of mine which went: "Why did
you let me live when you knew I had this disease?"
How the future was conceptualised reflected concepts of agency. Many participants
holding a 'chance' perspective of the parenting risk saw their future as predetermined and their
role as reactive. Others holding a 'choice' perspective saw themselves as shaping the future.
They deployed options such as genetic testing to clarify and control their risk of becoming an
affected parent, or had children earlier than they might otherwise have done in the hope that
they would be grown up before the parent became symptomatic.4 This dichotomy accorded
with well established psychological concepts relating to internal and external locus of control
(Rotter, 1966; Wallston, Wallston and DeVellis, 1978; Wallston, 1997). It clarified
contrasting constructions of responsibility in connection with the parenting risk. Those
holding chance perspectives took a reactive perspective of responsibility, seeing it as coping
with whatever fate presented. Conversely those holding choice perspectives became proactive
about responsibility, employing interventions such as predictive testing or gamete donation in
order to inform and control outcomes. It became possible to explain why people might not act
consistently in regard to the two risks, seeing the parents risk as predetermined and that for
any child as a matter of choice.
Perceived Social Support
This factor similarly started to shape decision-making long before any thoughts of
reproduction. One interesting finding was that those growing up in families affected by HD
were more willing to accept the uncertainty associated with their ability to sustain a parenting
role if they had experienced a supportive sibling relationship. Conversely, only children, and
participants whose siblings had not been perceived as supportive, reported feeling more
vulnerable and less willing to take on this risk.
Support concurrent with decision-making ranged from endorsement of, or practical
assistance with choices made to tolerance of differences. This was more likely to be
forthcoming if people could demonstrate that they had acted as responsible decision-makers,
or in a manner consistent with their central values. Those whose partners, families and friends
were able to show non critical support for whatever path had been chosen acknowledged how
helpful this had been. Case studies drawing on the model as a framework illuminated how
support changed with repeated decision-making and could come to involve clinicians as well
as families (Downing, 2005).
These terms were coined by Marshall (1995) to account for contrasting attitudes to new reproductive technology.
157
Although the word mitigated suggests that constraint has a negative effect on decision-making, this may not
necessarily be the case. Constraint may help people arrive at a decision by reducing the alternatives.
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Claudia Downing
cooperate in providing samples and could result in the breakdown of relationships within
families.
The impact of genetic testing needs to be seen as a function of which form of testing is
being employed or considered. Linkage predictive testing, for example, had a limited impact
because it was not available for all who considered it. Another constraint encountered in
connection with predictive testing, both linkage and mutation, was that this was seen as a
decision that could only be made by those at-risk. In contrast, pursuing prenatal testing was
seen as a decision involving both partners. This observation was an important one as it
challenged the appropriateness of the widespread tendency in the literature to refer solely to
women when speaking of decision-makers.
Partners of those who did not want to know their status faced making uninformed
decisions or having non-disclosing exclusion prenatal testing (PNET). Uptake of PNET has
been very low worldwide (Adam et al, 1993; Maat-Kievet et al, 1999; Hayden, 2000,
Simpson and Harper, 2001). Fewer than ten prenatal tests were done in Canada between
1990-1995, and the rate in the USA was similarly low. It was therefore a significant
achievement for this study to have accessed ten couples who seriously considered employing
it, and four who actually used it. Their experiences were very informative about the decisionmaking of those considering but not using prenatal testing, the problems associated with
negotiation of its use, considerations arising with its repeated employment, and the impact of
different outcomes.
Some of the ways that using prenatal testing made a difference - such as creating
tentative pregnancies (Rothman, 1986) whilst waiting for results, setting up assumptions that
people will act on the information received and terminate wanted but high risk pregnancies,
or having to involve others in decision-making - were not unique to HD. Neither was the
experience of two of the couples who had to cope with the subsequent miscarriage of
pregnancies shown to be at low risk (Robinson et al, 1991). The predicament associated with
PNET of terminating 'high risk' fetuses which may not be affected, was also not a new one.
This dilemma has been previously documented in connection with Duchenne muscular
dystrophy and other sex linked conditions. Prior to the introduction of genetic testing some
people chose to terminate any male fetus (a proportion of which would not have been
affected) in order to ensure that they only had a child that they knew would not be affected
(Parsons and Clarke, 1993).
The low uptake of prenatal testing observed in this study appeared to be influenced by
weighing these issues in relation to a risk that would almost certainly not manifest until adult
life. What the study revealed was that participants were faced with considerations of the
quality of a 'tentative life', that is, the life to be lived at-risk. This meant that those who would
have been prepared to consider termination for early onset disorders could have difficulty in
seeing it as appropriate for HD because they saw their, or their partner's, life as worthwhile.
Interesting findings emerged about repeated reproductive decision-making. Those who
did not initially use prenatal testing, but then employed it for subsequent pregnancies, were
able to accept that their decision-making would result in them having different information
about the status of each child. However, couples who started to use a certain type of prenatal
testing felt compelled to use it for subsequent pregnancies. This effect was apparent for
individuals who had both high and low risk results. What this meant was that couples
continued to employ PNET even after a more informative and predictive test, direct mutation
prenatal testing, became available. Those who had previously terminated on the basis of a
159
high risk result stated that the distress experienced was preferable to being confronted with
the realization that, in the event of the parent having a negative predictive test, termination
had not been necessary. This finding illustrated the limitations of classic decision theory
models which fail to take account of the input from past decisions. It was consistent however,
with studies that have showed what has been called the "sunk cost" phenomenon (Arkes and
Blumer, 1985). This refers to a situation that arises favouring continuing with a pattern of
behaviour because the investment made - which can be emotional, financial or practical makes it difficult to assess subsequent decisions independently.
Participants saw genetic testing primarily as an extension of existing methods - such as
sterilization and using donated gametes - offering control over risks. This was compatible
with Strathern's (1995) observations of the different ways in which people make sense of new
reproductive technology, seeing it as either innovative or linked to established ways of having
children. It suggests that there may be underlying consistencies in how people make sense of
a range of technological changes.
Conceptualizing testing as an extension of existing methods of control generates
additional questions. First, to what extent do the various technological developments offering
control over reproduction and risk - which includes improved contraception, early
identification of pregnancy and prenatal testing techniques - enable people to actually feel
more in control of reproductive risks? Perception and tolerance of residual uncertainty
associated with testing varied. One of the most interesting findings to emerge from the study
was that perceived lack of confidence in low risk PNET results formed a significant barrier to
its use. Doubts about the reliability of low risk results could also arise later, after repeated
high risk results, through actual experience of laboratory error, or from learning that testing
for other conditions, such as HIV, was fallible. These findings are illustrative of cognitive
biases, such as the availability bias (Tversky and Kahneman, 1973), which have been
previously well documented in relation to a range of risks (Kahneman, Slovic, and Tversky,
1982). The key point to be made in relation to HD was that although experiences such as
these could engender uncertainty about the reliability of testing, they did not necessarily
dissuade people from employing it.
A related question arises about how much people want to feel in control of reproduction.
It was interesting to note that unplanned pregnancies did occur to both those accepting and
wanting to avoid passing on the risk. Defining a pregnancy as a chance unplanned event - for
which one cannot therefore be held accountable - was shown to facilitate acceptance of the
risks. Another indication of ambivalence relating to control was that those who felt strongly
about not passing on the risk did not necessarily employ contraception, or, if they did, did not
use the most reliable methods.
The few who had learnt their status felt that the increased information clarified their
subsequent decision-making. Previous research had suggested that learning there is no longer
any risk appears to facilitate implementing previously expressed reproductive intentions.
Decruyenaere, Evers-Kiebooms, Boogaerts, Cassiman, et al (1996) et al (1996) showed that
within a year of the partner testing negative all 13 couples had had a child, were pregnant or
were intending to have a child. In contrast, 13 other couples who learnt that the partner had
tested positive had decided not to have a child or more children, were contemplating
reproduction only in conjunction with prenatal testing, or were still undecided. However,
what people then did with this information varied considerably, adding further support to the
claim that people do not necessarily prioritize exercising control over the risk in their
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Claudia Downing
decision-making. This finding supports that from another study which interviewed couples
after a longer time period to show that reproductive behaviour of those who test positive is
complex and does not always correspond to pre or post test intentions (Tibben, Frets, van de
Kamp, Niermeijer et al,1993).
Applying the Model
The model provides a framework in which to re-examine the observed complexity of
decision-making. This involves systematically comparing and accounting for:
variations in responses shown between people, including partners and other family
members
variations in responses to each dimension of risk
choices of risk avoiding or modifying strategies
responses to change such as increasing awareness of HD, pre and post testing
reproductive decision-making, decision-making with different partners
making decisions before and after becoming parents
decision-making at different stages of the reproductive decision-making process
including how decision-making becomes shared.
A comprehensive account of these applications is given in Downing (2002). A few
examples are presented here to indicate the versatility of the model. The first deconstructs
why first and subsequent pregnancies presented different issues, making them feel like
different decisions. First pregnancies involved framing decision-making as about whether to
reproduce and the extent to which identity is shaped by becoming a father or a mother.
Families were more supportive of those at-risk having one child for this reason. Making
decisions about subsequent children became more complicated - involved reconciling
expectations voiced by others outside the family about 'having another one' with diminishing
support from other family members, the projected needs of existing children and the at-risk
parent, from the perspective of being a parent. Having additional children therefore included
acknowledging these needs and presenting oneself as addressing them in a responsible way.
Becoming a responsible decision-maker involved deciding which of these needs would be
prioritized.
The second example, set out in Table 3, uses the model as a framework to compare
different responses to the parenting risk.
The third example illuminates what is different about risk splitting and linking and
provides insights into how couples decision-making became shared. As Beach (1993; 1996)
had suggested, individuals engaged in preliminary restructuring of their situation and options
to reflect their own values before negotiating with partners. Negotiation involved checking
whether their values were compatible. Difficulties could arise if partners were not in accord as Ingrid's comments revealed:
You know, I'm not prepared to let those children have what he's had.. .... He never agreed
with me on that - he said, I should have children at-risk. He didn't see that it was that bad. He
said, "I've had a good life. You know, I'm thirty seven. A lot of people don't get to that age, if
you're over in Rwanda or something." But maybe, I wonder whether, if, he's in a different
position to me, isn't he? Because he's < > if he agrees that you shouldn't have kids, maybe he
161
feels that his life isn't, wouldn't have been worth anything. I mean he'd have been, you know, I
don't know if he'd have wiped out, because I don't know the, what how his result would have
been.
In the event of disagreement about prenatal testing and terminations the woman's views
prevailed. As she explained:
One of you's got to do it, you see, and I, I decided it was MY choice as far as whether to
have the tests for the baby, and my choice whether to have a termination and you can't
compromise on that. You either do it or you don't do it. So my husband didn't really feature in
it, which was TERRIBLE.
For most couples decision-making about predictive testing was seen as the prerogative of
the at-risk partner. Focusing on non-disclosing prenatal testing and termination enabled Ingrid
to split the risks and redefine both risks: that for the child as negligible and that for her
partner as less stressful:
I'm cutting down on my anxiety so it's quite selfish, in a way. ... I want to reduce my
anxieties, see? And, at the moment, I'm only worrying about my husband. I don't want to
worry about them as well.
VALUES
FUTURE
SOCIAL
SUPPORT
REDEFINING
STRATEGIES
ACCEPT
Identity as a parent,
parenting as
natural
optimistic, focus on
present ability
compensating,
forthcoming from
partner and previous
generation
risk splitting:
between child and
parenting risk seeing
parenting risk as
predetermined
MODIFY
compensating,
forthcoming from
partner and previous
generation
timing: redefine oneself
as a responsible
informed decisionmaker by having
children earlier to
lessen possible impact
of affected parenting.
AVOID
Value childs needs
over need to reproduce
cautious, focus on
future limitations
diminished, children
and partners seen as
having competing needs
risk linking: redefining
self as responsible by
drawing comparisons
with others as selfish
In contrast, Martin and his at-risk partner agreed in their views that the risks were firmly
linked. He explained, that for them:
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Claudia Downing
The logical approach is Mum wants kids. Mum is at-risk. Mum has the test. If mum's got
it, mum cuts the tubes. But only when you've cleared mum, then the whole thing -then, and
then you're back to normality. ... UNTIL - until somebody comes up with some - is it cystic
fibrosis where they've now got something you can pop up people's noses to do wonderful
things against the gene? Fine. If somebody can come up with, with some wonderful thing
which takes all your, all your cells out, scrubs the genes over, shakes them into order and
bungs them back in again.
The model has also been used to clarify clinical encounters with multiple decisionmakers. It is being used as an on-line teaching tool in conjunction with case studies exploring
decision-making about prenatal testing (Downing, 2005).
The Process of Reproductive Decision-Making
The study generated the first detailed account of the process of reproductive decisionmaking in the growing awareness of HD. This was shown to involve a multiplicity of
decision points, requiring people to draw on a variety of resources to engage in private and
shared considerations of a number of areas. These included how genetic risks are perceived,
the responsibilities that genetic risks entail, how technological developments are assimilated
and, as Richards (1993) and van der Steenstraten et al (1994) had suggested, how identity is
constructed. This section provides an overview of what emerged about the four stages
comprising the decision-making process: pre-contemplative; pre-implementation;
implementation; post-decision evaluation.
Pre-contemplative stage
The qualitative approach adopted in the study showed the importance of acknowledging
an additional, pre-contemplative, stage where no knowledge might be held of HD, nor any
considerations entertained about procreation, but that shaped later reactions by forming
individual attitudes and values. Support is therefore shown for NDM claims claim that
additional insights into the decision-making process will be provided by links made to other
domains, such as narrative approaches (Nelson and Nelson (1995) which provide access to
how values are formed in families.
This stage could encompass being parented by a parent who was affected but not yet
diagnosed. Connections were shown to exist between how affected parenting was
experienced, intervening factors such as social support, and the subsequent value placed on
avoiding this risk for future generations. Narratives from different family members confirmed
the concept of preselection in connection with risk status (Kessler, 1988) and extended it to
incorporate particular children being singled out for abusive treatment. Younger children in
families were more likely to be exposed to affected parenting, but this could be mitigated by
163
sibling support. Only children were the most vulnerable. This meant that affected parenting as
well as risk could be interpreted quite differently by each family member leading to them
placing different values on avoiding this risk for the next generation.
Pre-Implementation stage
The second, or pre-implementation, stage of decision-making was initiated by becoming
aware of the risk and culminated in forming potential responses to it. Intermediary steps
involved at this stage were:
becoming aware of the risks that HD presented;
assessing the impact of these risks on reproduction;
defining reproductive decision-making as a difficult decision;
redefining reproductive goals and evaluating them for compatibility with values held;
evaluating strategies for their ability to realise these goals and their
compatibility
with values;
mental simulation of implementation and outcomes;
re-assessment.
Decision-making became shared at this stage. Comparison of different family members'
accounts revealed how this happened. As the example presented in the previous section shows
the findings supported Beachs (1993) claim that individual processing preceded negotiated,
or social, decision-making. People considered the issues in relation to the values they held
and these values shaped the way they subsequently presented them to others. I had speculated
that partners, because they had not shared the same family experiences, might hold different
values about passing on the risk, or ability to parent. This was shown not to be the case.
Members of a couple did not necessarily hold the same values but acceptance, modification or
avoidance responses were made to the risk by both those at-risk and their partners. Partners
were able to draw on other experiences, such as having a parent die from cancer, to
understand the dilemmas that HD presented.
Analysis of how the younger generations accounts revealed three distinct forms that
negotiation could take. These were 'partnership', characterised by collaboration, 'facilitating',
where one person made a decision and the other facilitated it, and 'deadlock', where it was
difficult to find common ground. These patterns were similar to those identified by Beach
(1996) in a corporate context. Successful negotiation created shared values that became a
resource to be drawn on in times of stress, for example when facing terminations. This
suggested that once shared values were established they became more powerful and took
precedence over individual ones.
These patterns of negotiation extended to others who were involved in the decisionmaking process. This included lateral kin such as siblings and cousins, the previous
generation from both the affected and non-affected families, work colleagues, friends and
health care professionals and sometimes even laboratory staff. Conflicting ideas about
appropriate responses could cause temporary breakdowns in relationships between family
members. Case studies presented elsewhere documented how the health care professionals
and laboratory staff can come to be seen as a substitute family when this happened (Downing,
2005).
Certain areas emerged as not negotiable. One was the decision whether to have a
predictive test - which was seen as the prerogative of the at-risk partner. Another was whether
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to have a termination - which was seen as the woman's decision. However, couples might still
discuss these decisions and partners decide whether to facilitate the choices made.
Information seeking formed another aspect of social decision-making. Constraints could
arise according to how HD was managed within a family. If the family coped by not talking
this could result in frustration and bitterness if it was not compatible with partners' needs to
know. Tensions could also arise if partners had more factual knowledge than the family,
especially if it contradicted the myths, incompleteness and misinformation that could exist
about HD.6 For some, this stage included making contact with clinical genetics services.
Implementation
Passage through these stages could be rapid or slow. The retrospective design of the
study made it possible to encompass this variation. For example, one couple waited twelve
years for a new strategy - genetic testing - to become available to achieve their goal of a child
free from risk. The limitations of studying personal decision-making through hypothetical
situations were shown: what people actually did when in a situation could be quite different
from what they thought they would do. Further difficulty could arise at this stage from having
to confront additional choices, for example, around termination. Previous experience aided
implementation of subsequent decisions by providing procedural expertise and feelings of
increased confidence. However, it could prove to be disconcerting if new scenarios arose,
such as the contrast between reproductive decision-making for first and subsequent children
described above.
Post-decision evaluation
The final stage of decision-making was post-decision evaluation which could be positive,
negative or mixed. Individuals could be reticent about divulging post decision distress in
order to protect partners. They could also be reluctant to share their feelings if they sensed
that their partner was at a different stage to them in working through post-decision reactions.
This was especially noticeable in the accounts given of post termination distress. These
observations suggest that decision-making is most likely to be shared in the preimplementation and implementation stages.
People subsequently justified having children at-risk in diverse ways. Many felt they
have been deprived enough - citing lack of nurturing in childhood and repeated bereavements
- and questioned why they should have to give up having children as well. Reproduction
enabled them to do something normal, reassuring affected relatives that at-risk lives were not
constrained, compensating those they love and bringing them a measure of hope. Children
continued the generations, replacing other family members who had died. They became
symbols of their parent's continuing health, providing a notion of immortality to counteract
fears of premature death. One of the commonest fears expressed by those at-risk is that of
being abandoned if they develop HD. Having children, provided potential carers - what better
carer than someone who has seen it all and seen others coping with it? Having more than one
child provided potential carers for the carers should they in turn become affected.
This was especially the case for those who had come across HD in a professional capacity.
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This can be illustrated by the following example, concerning a considerable disparity that
occurred in accounts given by a sister and a brother about when they learnt of their parent's
diagnosis. The sister placed it at a time before either of them had had children, the brother
after they both had. Had this time gap actually occurred? Was the initial information not in
fact passed on by the woman to her brother - which then tells us something about the time that
such information may take to filter through families? Or, was it because her attempt to
challenge the existing diagnosis of Parkinson's disease was met with extreme hostility from
other family members, and, a firm refusal to accept that it might be HD until much later when their remaining sibling was diagnosed with HD? Or, did it mean that she recalled the
information because it was more salient to her than to her brother, as she was considering
having children at that time, and he was not? It was likely that in this case the distress that she
could envisage from not having children also helped to structure the vivid memory that she
had of having to confront this diagnosis. Bruner (1986;1990), amongst others, has stressed
how important emotion and affect are in structuring memories and how events become
coloured by the emotional state people are in when they experience and recall them. This
example reinforces the point made earlier in this chapter that 'knowing about' HD is not the
event of a single moment, but is rather an unfolding awareness which was evidently
happening at a different time or pace for these siblings.
Another interpretation of the contradictions in their accounts was that she could accept
that she had knowingly had children at-risk whilst he could not. This last point suggests that
people may have very good reasons for choosing to remember experiences in ways which
may not reflect the actual sequence of events. Evidence existed within their narratives for all
of these explanations and it was difficult to prioritize any one of them. However, by looking
at a number of these instances it became possible to create a detailed picture of the
complexity in which events occurred, were recalled and came to have significance for people.
Similar conclusions are deduced by Song (1998: 115) in a study of siblings' experiences of
working in family businesses. She too had found that "the result of combining and analysing
two siblings' interviews was greater than the mere sum of the two interviews." This was not
necessarily because of any additional information provided but because "multiple interviews
helped reveal the complexities, contradictions, and tensions in people's accounts and in their
daily lives."
Conclusion
The specific findings presented above are of particular importance as reproductive
decision-making in the face of genetic risk remains an under-researched area. Bekker et als
review cited in the introduction of 547 studies published between 1986 and 1996 categorised
as being about informed decision-making yielded only seven that dealt with genetic factors,
and none which addressed late onset disorders. Their description of reproductive decisionmaking as facing relatively simple clearly-defined options with known risks does not
accord with actual accounts of how decision-making is experienced in the face of genetic risk.
The grounded theory analysis revealed that considerable complexities exist in the way genetic
risks are perceived which need to be identified and acknowledged in order to understand the
multiplicity of responses that people show to them.
167
From an early stage in the analytic process concepts emerging from the data were able to
be integrated with and extend existing NDM theoretical frameworks. Overall similarities in
the ways in which NDM models convey the process of personal decision-making enabled
their principles to be illustrated by one particular model, image theory (Beach, 1990).
Comparisons made between the model of responsibility generated from data and image theory
revealed shared features. For example, both models stress that the values that people hold
play a crucial part in shaping their decision-making. An important contribution made by the
grounded theory analysis conducted as part of the study was to identify which values
participants saw as salient in the context of reproductive decision-making and HD risks. It
then became possible to account for varied responses shown to the child-centred and
parenting risks by identifying which of these values decision-makers chose to prioritize, in
combination with other contributing factors.
Another point of correspondence between image theory and the study model was the
recognition of the importance of pre-choice processing, including coming to an understanding
of the decision situation. Awareness was shown to be the prime causal condition in this
process. Empirical support also was found for the claim forwarded in the introduction that
decision-theoretic and health psychology form complementary rather than competing
approaches. For example, a related finding that awareness included emotional and cognitive
aspects is consistent with theoretical frameworks advanced in health psychology models such
as the parallel response model (Leventhal et al, 1980, Leventhal et al, 1997). However, as
McAllister (1999) also noted in relation to her model of engagement, the grounded theory
analysis revealed that emotional and cognitive aspects interact dynamically rather than as
parallel responses. Decision-making became shared in the way that Beach (1996) had
suggested, in that individual decision-making preceded shared decision-making. Patterns of
negotiation emerging from the data mapped onto those identified by Beach in other contexts.
What the study additionally contributed was to reveal how negotiation can engender shared
values that become a valuable resource facilitating implementing difficult decisions, such as
proceeding with the termination of a wanted pregnancy. These correspondences suggest that
NDM models have much to offer as frameworks in which to study decision-making in the
face of genetic risk.
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people would employ interventions such as predictive testing in order to inform and control
outcomes. These constructions map onto the choice or chance perspectives referred to earlier
in this chapter.
Other features of Callahan's analysis accord with the present study's findings. Callahan
(1979: 235) distinguished between "exercising responsibility as a parent and responsibility in
becoming a parent", which corresponds to the two aspects of reproductive risk associated with
HD. He suggested that individuals could become either more or less accepting of risk when
they came into contact with others in their social context, in accordance with a wide range of
findings concerning the "risky shift" phenomenon which states that individuals modify their
acceptance of risk in social contexts (Lamm and Myers, 1978). This is consistent with the
finding from this study that responsibility involved both individual assessment and social
evaluation.
Responsibility was shown to be both a private and a public concern. People had to
convince themselves that their decision-making involved acting responsibly to the issues that
HD raised for reproduction, and this provided the incentive for cognitive restructuring, or
redefining, which could operate in various ways and lead to different outcomes. For example,
a few participants redefined themselves as infertile, enabling them to utilize gamete donation
in order to have a child and assure themselves that they had acted responsibly because they
had bypassed the genetic risk. Redefining was consistent with NDM accounts depicting
personal decision-making as making creative and adaptive responses to difficult dilemmas
(Payne, Bettman and Johnson, 1993). Creativity involved reconciling discourses of genetic
determinism and control within a framework of genetic connection in such a way as to
present themselves as acting responsibly
This chapter has presented an account of how decision-making is experienced at a time
when it has become possible to clarify uncertainty about risk for HD and utilize strategies to
avoid passing this on to the next generation but when no effective treatments or cure yet
exists for HD.
The model can be used to study uptake options such as preimplantation genetic diagnosis
(PDG) that have subsequently become available. PGD enables people to have children who
are known to be gene-negative and avoids ethical issues associated with terminating a
pregnancy. Eggs are harvested, fertilized in vitro and tests performed on single cells biopsied
at the eight-cell embryo (day 3 of development. Only those testing gene-negative are
implanted. The main impediments to PGD are its expense, the low efficiency of in vitro
fertilization (IVF), with only 20% to 30% of couples achieving pregnancy per IVF cycle
(Pickering et al.) in the first 100 PDG cycles performed at the Guys and St. Thomas Centre
in London. Some programs offer non disclosing PDG for couples who do not wish to undergo
HD presymptomatic testing. The parental gene status is not revealed during the protocol and
only gene negative embryos are implanted.
It is suggested that when effective treatments for HD become a reality concepts of
responsibility will change again. Discourses of control could, as Rothman (1998) speculates,
generate a more proactive form of decision-making:
'It's genetic' might very quickly not be a throwing-up-of-your-sleeves kind of problem.
'It's genetic' might be coming to mean, so let's fix it, let's engineer it, let's construct it to order.
Let us make the determination, and let us predetermine (Rothman, 1998: 210-211).
169
The factors identified by Slovic (1987) can be used to predict, as shown in Table 4 below,
how perceptions of genetic risk might change.
Questions arise about the extent to which it is possible to generalize from the findings
from the study. Previous research shows the need for caution when attempting to generalise
about responses to risks categorised as belonging to a particular domain. Variations that risks
demonstrate on attributes other than risk category contribute to how they are perceived.
Hypothetical scenarios constructed within the general category of rail accidents enabled
researchers to conclude that responses varied according to specific attributes of trains,
cargoes, accidents, locations, and causes of accidents (Kraus and Slovic, 1988). Similar
findings were shown in connection with risk perception within other risk domains such as car
faults (Slovic, MacGregor and Kraus, 1987), medicines (Slovic, Kraus et al, 1989), and
unwanted environmental features (Slovic, 1992).
Attributes of genetic risk which seem likely to affect how they are perceived in relation to
reproduction include mode of inheritance, perceived severity, possibilities for surveillance,
treatment, cure and genetic testing, and age of onset. For example, varied modes of
inheritance produce quite different scenarios of reproductive risk decision-making - some of
which are briefly sketched out below.
Carriers of recessive disorders, such as cystic fibrosis, often remain unaware of the risk
until after becoming parents. Frequently it is not until after the birth of an affected baby, or
the development of symptoms in a previously healthy child, that they perceive their carrier
status.7 Parental anxiety arises from having to cope with the different and extra demands that
an affected child creates. Both parents of children with recessive disorders are, and will
remain, symptomless carriers. Carriers may also experience increased anxiety on learning of
their status (Mennie et al, 1993; Marteau and Anionwu, 1996), which could influence
subsequent reproductive decision-making. Reproductive dilemmas arise around whether or
not to have further children who have a one in four chance of inheriting the disorder
(Snowdon and Green, 1994, 1997). As was suggested at the beginning of this chapter, these
scenarios differ from those associated with late onset dominant disorders, such as HD. A
crucial difference is that those who inherit one mutated copy of a dominant gene are likely to
develop the associated disorder. Thus, unlike carriers of recessive disorders, they face risks in
connection with their own health or premature mortality. This can impact on their ability to
sustain a mothering or fathering role.
Gender considerations arise in relation to another group of disorders - X-linked ones which are passed on by females but mostly affect males.8 The risk scenario that emerges for
these conditions is that having males is perceived as more risky than having females (Parsons
and Clarke, 1993; Kay, E. & Kingston H. (2002).
How people frame reproductive decision-making in relation to one late-onset disorder
such as HD will not necessarily correspond to other late onset disorders.
This may or may not be their first child. It is only when a child inherits an affected copy of the gene from each
parent that this occurs. Otherwise they are either unaffected or symptomless carriers.
Fragile X primarily affects males but one third of carrier females show some degree of intellectual impairment
(Davies, 1989).
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Claudia Downing
Table 4. Drawing on Slovics (1987) factors to predict the impact of genetic testing &
treatments for HD on perceptions of genetic risk
Factor
Dread risk
Unknown risk
Number of people
The likelihood of the parent becoming affected depends on the degree of penetrance
shown by the particular mutation.9 Some, such as that associated with HD show almost 100%
penetrance whilst others, such as the BRAC1 gene mutation, associated with some inherited
breast and ovarian cancers, and that associated with early onset Alzheimer's disease, show a
much lower rate. Clarifying risks for these diseases is further complicated in that they also
arise sporadically, creating a general population risk for those with no family history. This
means that those shown not to carry genes for familial breast, ovarian and bowel cancers can
still develop these disorders but those found to carry the genes may not. Other differences
exist between these cancers and HD. As mentioned above, those who will develop HD cannot
yet benefit from the surveillance measures or treatments which exist for cancer sufferers, and
they are likely to develop psychiatric as well as physical symptoms. The first comparative
study of the psychological effects of predictive testing of neurodegenerative and cancer
syndrome late-onset autosomal dominantly inherited genetic disorders lend support to this in
that the groups at-risk for neurodegenerative disorders showed more distress than those at-risk
for the cancer syndromes (Dudok de Wit, 1997).10 Families with neurodegenerative disorders
were also more focused upon support for the individual at-risk and partner whilst in families
with cancer the focus was upon the post-test treatment options and their outcome (Dudok de
Wit et al, 2000).
It may well be that findings in relation to decision-making and HD could have as much, if
not more, to contribute to debates about reproductive decision-making in non-genetic
situations that have aroused public concern about ability to sustain a parenting role. These
include mothers and fathers with learning difficulties (Booth and Booth, 1994), parents who
are HIV positive (Bor and Elford, 1998), teenage single mothers (Rains, Davies and
McKinnon, 1998) parents who are lesbian and gay (Dunne, 2000), who face deafness
(Gregory, 1991), and the experiences of women wishing to become impregnated under
unconventional circumstances such as being post-menopausal or wanting to utilize sperm
from deceased partners.
10
171
Acknowledgments
Thanks are due to the participating families for entrusting me with their thoughts and
experiences some of which are touched on here; to the Medical Research Council for funding
the study under their GAHH initiative and to my supervisors, Jo Green and Martin Richards,
for their encouragement and guidance. The Huntingtons Disease Association and
Addenbrookes Regional Clinical Genetics Centre shared their expertise with me and helped
recruit participants to the study. I am also grateful to Martin Richards, Nina Hallowell, Helen
Statham, Robert Osborne and Helena Willen for their helpful comments on subsequent drafts
of this chapter. I am currently funded by The Wellcome Trust (Award Reference: 065207,
2002-2005) under their biomedical ethics programme.
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Chapter VIII
Cambridge Centre for Brain Repair, E.D. Adrian Building, Forvie Site,
Cambridge, England, CB2 2PY
2
Department of Neurology, Addenbrookes Hospital, Hills Road, Cambridge, England,
CB2 2QQ
Abstract
Neurogenesis is the processes whereby newborn neurons are formed and occurs in
mammals in adulthood in specialised areas, known as neurogenic niches. The
subventricular zone, and subgranular zone of the dentate gyrus of the hippocampus are
such specialised neurogenic niches and newborn neurons formed here contribute to
learning and memory, but neurogenesis may occur elsewhere in the brain to a more
limited extent. The neurogenic niche is composed of specialised glial cells, basal lamina,
ependymal cells, neurotransmitter complement and vasculature. Neurogenesis is a
complex process, involving many different cell types, and several stages of neuronal
maturation; and each component may be affected by many different microenvironmental
perturbations. External perturbations, like seizures and lesions alter the
microenvironment and in turn, alter neurogenesis. Chronic disease can also affect
neurogenesis and the inherited neurodegenerative condition Huntingtons disease may do
so through an alteration of the microenvironment. We will use the example of
Huntingtons disease to explore how changes in the microenvironment might impact on
neurogenesis and, thus identify potential therapeutic targets.
Corresponding author: Dr. Wendy Phillips, Cambridge Centre for Brain Repair, E.D. Adrian Building, Forvie Site,
Cambridge, CB2 2PY. E-mail: wp212@cam.ac.uk; Tel: +44 1223 331160; Fax: +44 1223 331174.
182
1. Neurogenesis
1.1. Introduction
Neurogenesis is the formation of new neurons, from stem cells (which are self-renewing,
multipotent and have longevity) or progenitor cells (which have a more limited potential)
(Weiss et al. 1996). Neurogenesis in the adult mammalian brain (Altman and Das
1965;Kaplan 1981) occurs in specialised neurogenic niches: the subventricular zone (SVZ)
and subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus (Gage 2000).
These areas are said to undergo constitutive neurogenesis, i.e. neurogenesis occurs at all
times under basal conditions, whereas other brain areas may undergo non-constitutive
neurogenesis when the microenvironment is altered by lesions and seizures, for example
(Parent 2003). This is contentious, with some authors claiming the existence of constitutive
neurogenesis in the non-classical areas. Furthermore, neuronal precursor cells (NPCs) (a
mixed or unknown population containing stem and progenitor cells) can be isolated from
areas throughout the brain in vitro (Palmer et al. 1999;Weiss et al. 1996;Tropepe et al.
2000;Lie et al. 2002).
The distinction between constitutive and non-constitutive neurogenesis is an important
one. An area of constitutive neurogenesis implies that it is functionally important for the
animal under normal circumstances, and the existence of a specialised microenvironment,
which allows neurogenesis to continue into adulthood. The function of neuronal precursors
that exist in areas of non-constitutive neurogenesis is unknown. The precursors may be
quiescent, produce neurons constitutively at a difficult-to-detect level, or produce glia
constitutively.
Neurogenesis clearly occurs developmentally but it seems more difficult to envisage this
process occurring in adulthood, and it took some time for this idea to become accepted.
Neurogenesis declines with age in adult mammals, with the microenvironment of the aged
brain becoming more hostile (Kuhn et al. 1996;Shetty et al. 2004;Limke and Rao
2002;Tropepe et al. 1997). The neurogenic niches retain many aspects of the embryonic brain
within a small, defined area. The niche contains specialised glial cells, basal lamina,
ependymal cells, a specific neurotransmitter milieu and vasculature, which are permissive for
continued neurogenesis in a hostile environment.
The Control of Adult Neurogenesis by the Microenvironment and How This 183
al. 2006). Basal neurogenesis in the DG may be involved in emotion and the cognitiveaffective interface (Sapolsky 2004;Kempermann 2002).
Neurogenesis occurs in humans in vivo (Eriksson et al. 1998;Sanai et al. 2004) and in
vitro (Arsenijevic et al. 2001;Roy et al. 2000;Kukekov et al. 1999). Neurons from human
SVZ in vitro display maturing electrophysiological properties over 4 weeks in culture (Moe et
al. 2005). Bromodeoxyuridine (BrdU) is a thymidine analogue that labels dividing cells
during the S-phase of mitosis and can be used as a marker for cell proliferation (Miller and
Nowakowski 1988). Cell proliferation has been demonstrated in vivo in the DG after patients
were given BrdU during treatment for head and neck cancer (Eriksson et al. 1998).
Proliferating cells and, possibly, immature neurons have been found in human Huntingtons
disease (HD) SVZ (Curtis et al. 2003;Curtis et al. 2005b;Curtis et al. 2005a;Pearson et al.
2005) and in the human OB (Bedard and Parent 2004), although there is no well-defined
RMS in the human brain (Sanai et al. 2004).
The function of non-constitutive neurogenesis is more elusive. Neurogenesis may occur
constitutively in the primate neocortex (Gould et al. 1999), rodent visual cortex (Kaplan
1981), substantia nigra (SN) (Zhao et al. 2003), dorsal vagal complex (Bauer et al. 2005) and
piriform cortex and amygdala (Bernier et al. 2002), although this is controversial
(Frielingsdorf et al. 2004;Ehninger and Kempermann 2003;Koketsu et al. 2003;Lie et al.
2002;Kornack and Rakic 1999). Neurogenesis increases in the striatum in response to
ischaemia and excitotoxic lesions (Arvidsson et al. 2002;Parent et al. 2002b;Phillips et al.
2005;Tattersfield et al. 2004), in the cortex in response to apoptosis (Magavi et al. 2000), in
the hypothalamus in response to growth factors (Kokoeva et al. 2005) and in the caudal SVZ
and hippocampus in response to ischaemia and seizures (Nakatomi et al. 2002;Parent et al.
1997;Phillips et al. 2005). Neurogenesis occurring after lesions may contribute to self-repair
after injury (Nakatomi et al. 2002;Arvidsson et al. 2002).
184
weeks. SGZ astrocytes secrete neurogenesin-1, which acts as a BMP inhibitor, paralleling the
function of Noggin in the SVZ (Ueki et al. 2003).
Endothelial cells release soluble factors, which are crucial for neurogenesis (Shen et al.
2004). NPCs in the SGZ are closely associated with capillaries and a proportion of NPCs
express endothelial cell markers (Palmer et al. 2000). Consistent with a vascular niche for
neurogenesis, angiogenic factors such as vascular endothelial derived growth factor (VEGF),
insulin-like growth factor (IGF), fibroblast growth factor (FGF) and erythropoetin promote
neurogenesis; and neurogenic factors such as brain derived neurotrophic factor (BDNF), glial
cell line derived neurotrophic factor (GDNF) and nerve growth factor (NGF) promote
angiogenesis (reviewed by Park et al. 2003; Greenberg and Jin 2006).
Astrocytes are also important to neurogenesis, as co-culture of NPCs with astrocytes
from a neurogenic area (hippocampus) promotes a neuronal fate, but not when astrocytes
from a non-neurogenic area are used (Song et al. 2002). Astrocytes in neurogenic areas
secrete growth factors that can enhance neurogenesis (Hagg 2005), as well as neurogenic
factors (such as neurogenesin-1) (Ueki et al. 2003). Certain cytokines promote neurogenesis
and migration of NPCs (Belmadani et al. 2006;Battista et al. 2006). Furthermore, astrocytes
instruct newborn neurons to form functional synapses (Ullian et al. 2001), and support the
migration of neuroblasts (Mason et al. 2001).
Neurotransmitters affect neurogenesis and the SVZ has a distinct complement of
neurotransmitter input, such as an overlap of dopaminergic and serotonergic input (Hoglinger
et al. 2004;Hagg 2005) (table 1.1). Type 2 cells in the DG receive gamma amino butyric acid
(GABA)-ergic excitatory input, which leads to upregulation of NeuroD, a transcription factor
important to neurogenesis (Miyata et al. 1999;Tozuka et al. 2005).
The basal lamina is rich in laminin and collagen-1, which may concentrate cytokines or
growth factors from surrounding cells in the neurogenic niche (Mercier et al. 2002;AlvarezBuylla and Lim 2004;Hagg 2005).
Neurogenic niches contain molecules normally associated with embryonic development:
Notch and cognate receptor Jagged, sonic hedgehog (SHH), BMPs, Wnt, ephrins (AlvarezBuylla and Lim 2004). Notch and BMP signalling may keep neural stem cells (NSCs)
quiescent (Alvarez-Buylla and Lim 2004). SHH overexpression increases SGZ proliferation
and neurogenesis (Lai et al. 2003), and in animals lacking the SHH co-receptor, Smoothened,
SGZ and SVZ neurogenesis is reduced (Machold et al. 2003). In the SGZ, NPCs express
receptors and signalling components for Wnt proteins, overexpression of Wnt3 increases
neurogenesis, and blockade of Wnt signalling dramatically reduces neurogenesis in vivo (Lie
et al. 2005). From the SGZ to the GCL, neuroblasts are guided by persistent radial glial
elements (Seri et al. 2001) and possibly by stromal cell derived factor-1 (Lu et al. 2002).
Type A neuroblasts from the SVZ have an elongated morphology and a leading process
containing a growth cone (Wichterle et al. 1997), and they may contain locomotory
mechanisms used by growing axons such as collapsing-response mediated protein 4 (Nacher
et al. 2000).
The Control of Adult Neurogenesis by the Microenvironment and How This 185
Table 1.1. Some molecular factors affecting neurogenesis
Factor
GABA
Effect on neurogenesis in DG
(Tozuka et al. 2005)
Effect in SVZ/ OB
(Nguyen et al. 2003)
Glutamate
Dopamine
Serotonin
via 5HT1A/ 2C
(Banasr et al. 2004)
Acetlycholine
Noradrenaline
Nitric oxide
Neuropeptide Y
(NPY)
Adenosine
Estrogen
Prolactin
Gluco-corticoids
Thyroid
hormone
Erythropoetin
BDNF
IGF
VEGF
FGF
CNTF
PDGF
186
The Control of Adult Neurogenesis by the Microenvironment and How This 187
Dietary restriction increases neurogenesis, possibly via increases in BDNF (Lee et al.
2000). Interestingly, dietary restriction can improve the phenotype of HD mice (Mattson et al.
2004), raising the possibility that increased neurogenesis might be responsible.
Olfactory learning increases neurogenesis in the OB (Rochefort et al. 2002) and wheel
running and environmental enrichment increases neurogenesis only in the DG (Brown et al.
2003). In normal animals, environmental enrichment increases neurogenesis and enhances
existing neurones, mediated in part by growth factors such as VEGF, BDNF, IGF, and
angiogenesis (van Praag et al. 2000).
Neurogenesis declines with age (Kuhn et al. 1996;Kempermann et al. 1998b). When
SVZ NPCs from aged animals are grown in culture, they proliferate at the same rate and
differentiate into the same proportion of neurons as NPCs from young animals (Tropepe et al.
1997). This suggests that the in vivo microenvironment may be responsible for the reduction
in neurogenesis with age. Glucocorticoids increase with age and the decline in neurogenesis
with age can be restored to that of younger animals by adrenalectomy (Nichols et al.
2001;Montaron et al. 1999;Cameron and Gould 1994). Similarly, levels of FGF, EGF and
IGF decline with age and restoration of these growth factors restores neurogenesis in the aged
brain (Lichtenwalner et al. 2001;Jin et al. 2003). Dopamine and noradrenaline levels in the
hippocampus decline with age, in parallel with decline in performance in the Morris water
maze (Stemmelin et al. 2000).
Depression is associated with low levels of neurogenesis, although it does not necessarily
follow that there is a causal relationship (Sapolsky 2004;Vollmayr et al. 2003). Depressed
patients have smaller hippocampi than controls (Sheline et al. 2003;MacQueen et al. 2003),
but this could be due to cell death and neurite retraction and, again does not imply that
decreased neurogenesis and depression are causally related. It is interesting, however, that
depressed women who have suffered abuse have smaller hippocampi than depressed women
without abuse (Vythilingam et al. 2002), raising the possibility that the early abuse triggered
the small hippocampus that predisposed to depression, making it potentially amenable to
early treatment (MacQueen et al. 2003;Sheline et al. 2003). Depression is associated with
perturbed serotonergic transmission and selective serotonin reuptake inhibitors such as
fluoxetine increase neurogenesis via the 5HT1A receptor, although hippocampal neurogenesis
in 5HT1A receptor knock-out mice is unimpaired implying the receptor is not an absolute
requirement for neurogenesis (Malberg and Duman 2003;Malberg et al. 2000;Santarelli et al.
2003). Stress and depression are associated with high cortisol levels, which in turn reduce
neurogenesis (Sapolsky 2000;Sonino and Fava 2001;Gould et al. 1997;Cameron and Gould
1994), and the effect of cortisol on neurogenesis may be via reductions in BDNF (Cosi et al.
1993).
Alzheimers disease (AD) is the most common cause of dementia in both younger
patients and the elderly (Lobo et al. 2000;Harvey et al. 2003). Interestingly, the hippocampus
degenerates, particularly the CA1 and subiculum but the DG is relatively spared (Bobinski et
al. 1997). Neurogenesis is impaired in the DG of some AD mouse models (Haughey et al.
2002;Wen et al. 2004;Wang et al. 2004), possibly due to lower expression of BDNF in AD
(Phillips et al. 1991), loss of cholinergic neurons and a loss of function effect of normal
soluble amyloid precursor protein (APP) and presenilin-1 (PS1) (Caille et al. 2004;Hitoshi et
al. 2002). Neurogenesis is however, increased in one mouse model of AD that has lower
glutamate transmission (Jin et al. 2004a), and in AD patients (Jin et al. 2004b).
188
2. Huntingtons Disease
2.1. Huntingtons Disease: History
HD is an inherited neurodegenerative disorder characterised by movement disorder,
dementia and psychiatric disturbance. It occurs usually in middle age and is relentlessly
progressive with no treatments proven to halt or reverse the disease (Bates et al. 2002).
The discovery of the gene and intense research in recent years has provided some hope
for curative therapies, including cellular repair, to overcome this distressing condition. The
disease is crucially important also because it has served as a paradigmatic disorder, for many
themes including molecular genetics; mechanisms of neurodegeneration; protein
abnormalities and aggregates in neurodegenerative disorders; selective vulnerability and lateonset; and, perhaps, neurogenesis in chronic disease.
The eponymous George Huntington, a general practitioner in Long Island, New York,
described HD in 1872, from his own observations and those of his father and grandfather
(reviewed by Harper in Bates et al. 2002), although the disease had been definitively
described earlier by Waters (1841). He recognised the autosomal dominant pattern of
heredity; once the thread is broken the grandchildren of the original shakers may rest
assured that they are free from the disease and it never skips a generation to manifest in
another; once having yielded its claims, it never regains them. The cognitive impairments
were described; in many amounting to insanity, including the fronto-striatal-based loss of
judgement They are men of about 50 years of age, but never let an opportunity to flirt with a
girl go past unimproved. The effect is ridiculous in the extreme. Psychiatric disturbances, a
nervous temperament and particularly suicide were also recognised by Huntington. The
adult onset is described as its coming on only in adult life while those who pass the
fortieth year without symptoms of the disease are seldom attacked. The progressive and
destructive nature of the disorder was chillingly recounted, It is spoken of by those in whose
veins the seeds of the disease are known to exist, with a kind of horror, and not at all alluded
to except through dire necessity (The disease develops) gradually but surely, increasing by
degrees, and often occupying years in its development, until the hapless sufferer is but a
quivering wreck of his former self.
Meynert (1877) originally proposed the striatum as the principal pathological site in HD,
confirmed later in 1908 by Jelgersma, who also described global brain atrophy.
The autosomal dominant nature of HD, as well as many other aspects of HD genetics was
recognised definitively in 1908 by Punnett, and by Jelliffe.
The field of HD research has benefited from collaborative research groups such as, the
Hereditary Disease Foundation (founded by Dr Milton Wexler), The Huntingtons Study
The Control of Adult Neurogenesis by the Microenvironment and How This 189
Group, EuroHD (a collaboration of European HD research groups) and the Network of
European CNS Transplantation and Restoration (NECTAR; founded in 1990, focusing on
two main programs, one pertaining to transplantation in PD and the other in HD, named
NEST-HD). The HD Collaborative Research Group conducted linkage analysis of large HD
kindreds in Venezuela over 10 years, leading to the cloning of the gene, as well as detailed
clinical studies. The cloning of the gene that leads to HD paved the way for development of
animal models of the disease based on the genetic abnormality (Mangiarini et al.
1996;Rubinsztein 2002).
190
1993). Overall, 50-69% of the variance of age at onset can be accounted for by CAG repeat
length, with other genetic factors and environmental influences also being important
(Rubinsztein et al. 1997;Andrew et al. 1993;Wexler et al. 2004;van Dellen et al. 2005).
The Control of Adult Neurogenesis by the Microenvironment and How This 191
2.4. Huntingtin (Htt)
Htt is a large 348kDa protein, with 3144 amino acids. It is ubiquitously expressed,
particularly in neurons (Sharp et al. 1995; Sapp et al. 1997; Wilkinson et al. 1999). In the
brain, high levels of endogenous htt are found in cortical pyramidal cells, cerebellar Purkinje
cells and calbindin-positive cells of the striatum (Gutekunst et al. 1995; Ferrante et al. 1997).
Subcellularly, htt is found predominantly in the cytoplasm in somatodendritic regions and less
so in axons, and associates with microtubules and vesicles (Gutekunst et al. 1995; Gutekunst
et al. 1998).
Htt is essential for development because lack of the gene is embryonically lethal (Duyao
et al. 1995). HD-/- embryonic stem (ES) cells, however, develop normally into neurons
(Metzler et al. 1999), and because normal extra-embryonic tissue can rescue homozygote
HD-/- mutants from lethality, htt may deliver nutrition to developing cells, particularly given
the function of htt in cellular transport (Harjes and Wanker 2003; Dragatsis et al. 1998). Htt
also has a role in later brain development because gene targeted mice that express <50%
normal htt display severe mid- and hind-brain abnormalities and die perinatally (White et al.
1997).
192
The Control of Adult Neurogenesis by the Microenvironment and How This 193
expression of an N-terminal fragment with 120Q (under the human htt promoter) has many
neuronal nuclear inclusions (NII) but no neurodegenerative phenotype (Slow et al. 2005).
This may negate the aggregate theory, or it may be the precise structure of fragment/
aggregate that confers toxicity.
194
2.9. Excitotoxicity
Animals treated with excitotoxins and mitochondrial toxins recapitulate many
phenotypical and pathological features of HD, and were indeed used to produce the first
animal models of HD (Ferrante et al. 1993;Beal et al. 1993). There is some evidence for
impaired energy metabolism in HD, and degeneration of mitochondria, although this may be
a secondary phenomenon (Brennan, Jr. et al. 1985;Goebel et al. 1978;Jenkins et al.
1993;Tabrizi et al. 2000;Guidetti et al. 2001).
Glutamate is an essential mediator of excitotoxicity (Beal 1992). Glial glutamate uptake
is reduced in HD, which may increase synaptic glutamate levels (Behrens et al. 2002;Lievens
et al. 2001). Wild type (WT) htt may modulate the post-synaptic density protein 95 (PSD-95)
that is involved in the post-synaptic clustering of N-methyl-D-aspartate (NMDA) receptors
and mutant htt alters this binding to PSD-95, resulting in sensitisation of these receptors to
glutamate, and thus possible toxicity (Sun et al. 2001).
2.10. Pathology
Pathological grade in patients is assigned according to the Vonsattel scale (Vonsattel et
al. 1985). Focal degeneration occurs particularly in the caudate nucleus, which may atrophy
years before the onset of symptoms (Aylward et al. 2000), but is widespread especially in the
late stages of the disease (Vonsattel et al. 1985). Moderate astrogliosis occurs and tends also
to predominate in the striatum (Myers et al. 1991). There is a dorsal-to-ventral, anterior-toposterior and medial-to-lateral progression of neuronal death in the caudate nucleus
(Vonsattel et al. 1985).
Other brain areas also dysfunction and degenerate early in the disease, such as the insula,
hippocampus, cortex and amygdala (Rosas et al. 2003;Thieben et al. 2002), and the
significance of this is becoming increasingly recognised, and may underlie some of the
cognitive and psychiatric problems of HD (section 2.14). Hypothalamic atrophy (Kremer
1992) may underlie some of the metabolic symptoms and signs seen in HD (Pratley et al.
2000).
Caspases are upregulated and activated in HD (Friedlander 2003), and terminal
deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) staining has been
reported in HD brains (Dragunow et al. 1995;Portera-Cailliau et al. 1995). Necrosis occurs at
least in late stage HD (Vonsattel et al. 1985).
The Control of Adult Neurogenesis by the Microenvironment and How This 195
excitotoxic stress of the susceptible neurons (Mitchell et al. 1999) may all contribute to make
the striatum more vulnerable to degeneration. In addition, striatal glial cells may fail to take
up glutamate (Lievens et al. 2001;Behrens et al. 2002), thus increasing the concentration of
glutamate in the striatum.
N-terminal htt fragments preferentially accumulate in the striatum (Li et al. 2000) and
this, along with tissue specific proteolysis and ubiquinisation (Mende-Mueller et al. 2001)
may provide a basis for selective neurodegeneration.
CAG repeats are unstable and tend to expand particularly in the striatum (Kennedy and
Shelbourne 2000;Telenius et al. 1994). The mechanism for this somatic instability may be
due to excessive repair mechanisms because in R6/1 mice lacking the mismatch repair gene
(msh2) there is no such somatic instability (Manley et al. 1999). It is not clear, however, that
somatic instability and longer CAG repeats in the striatum produce deleterious effects.
It is possible that cellular dysfunction occurs initially in the cortex rather than the
striatum, as has been the traditional view. NII are found initially in the cortex (Kuemmerle et
al. 1999) and there may be dysfunction of striatal glutamate afferents (Cepeda et al. 2003) or
failure of cortical release of neurotrophic factors, such as BDNF (Zuccato et al. 2001).
As well as selective vulnerability of the striatum, compared to the rest of the brain,
distinct subpopulations within the striatum degenerate. In the striatum, D2-expressing
medium, spiny, GABA-ergic projection (MSP) neurons selectively degenerate. Large
cholinergic and medium aspiny inter-neurons containing somatostatin (SS), neuropeptide Y
(NPY), and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase are
relatively resistant to the disease process (Ferrante et al. 1985;Ferrante et al. 1987a;Ferrante
et al. 1987b). It may be the case that stimulation of NADPH diaphorase neurons by glutamate
from corticostriatal afferents generate harmful free radicals and kill surrounding MSP neurons
(Bates et al. 2002). MSP neurons contain relatively high levels of the NR1A/2B receptor
subunits that show enhanced sensitivity to glutamate receptor activation (Zeron et al. 2004).
It must be remembered that other brain areas also dysfunction and degenerate early in the
disease, which may have been somewhat overlooked due to the striatum-centric view of HD
(section 2.14).
List 2.1. Putative Reasons for Selective Vulnerability of the Striatum
Vulnerability to glutamate-mediated excitotoxicity:
Heavy glutamatergic cortical afferent projections
Striatal glia fail to remove synaptic glutamate
Sensitivity of NR2B to glutamate
High [glutamate] activates adjacent resistant neurons, which release free radicals and kill
MSP neurons
Paucity of calcium binding proteins in vulnerable subpopulation of MSP neurons
High-energy requirements of vulnerable neurons
Accumulation of particularly toxic species of mutant htt
htt cleaved differently in the striatum
More N-terminal fragments in the striatum
Differential ubiquinisation
Somatic mosaicism
Murder by the cortex (failure to release neurotrophic factors or release of excessive
glutamate)
196
The Control of Adult Neurogenesis by the Microenvironment and How This 197
control. Psychiatric and cognitive dysfunction may also be due to the dysfunction and atrophy
in the limbic system (Rosas et al. 2003;Thieben et al. 2002) (section 2.14). The emotional and
cognitive dysfunction, as opposed to the motor dysfunction, is arguably the most important
symptoms of HD, and is therefore vitally important that we understand how it arises.
198
Neurogenesis has been described in the piriform cortex (Pekcec et al. 2006) and
amygdala (Bernier et al. 2002;Bernier and Parent 1998) but the existence of newborn neurons
in some of these regions may be transient (Takemura 2005;Pekcec et al. 2006). It has been
shown that the numbers of DCX-positive cells are reduced in the piriform cortex and absent
in the insular cortex in R6/2 mice, which may represent a reduction in neurogenesis or
plasticity ion these regions (Phillips et al. 2006).
Table 2.1. Neurotransmitter changes in R6/2 mice and HD patients. A summary of
neurotransmitter changes in the R6 transgenic mouse model and in humans. The
neurotransmitters refer to those in the striatum unless otherwise indicated
Neurotransmitter
GABA
Serotonin
in striatum and
hippocampus (Reynolds et
al. 1999)
Glutamate
Dopamine
Acetylcholine
Choline acetyltransferase
Noradrenaline
Human
in striatum, cortex and
hippocampus (Reynolds and
Pearson 1987)
in cortex/ striatum not
hippocampus (Reynolds and
Pearson 1987;Kish et al. 1987)
(Waeber and Palacios 1989)
(Reynolds and Pearson
1987)
(Reynolds and Garrett
1986), (Kish et al. 1987)
striatum and hippocampus
(Spokes 1980)
(Spokes 1980)
2.15. Neurochemistry of HD
The level of many neurotransmitters is perturbed in HD and in mouse models, and this is
detailed in table 2.1.
The Control of Adult Neurogenesis by the Microenvironment and How This 199
2.16. Summary of Pathophysiological Mechanisms That May Cause
Disease: The Common Final Pathways?
The following list illustrates a selection of pathophysiological mechanisms, which may
contribute in different degrees to pathology; as primary or secondary phenomena. They may
arise via loss of function of normal htt (by insufficient protein product, or sequestration
within aggregates), dysfunction of other proteins by mutant htt, sequestration of other proteins
into aggregates, or compensatory mechanisms.
1. Disruption of synaptic function. Pre- and postsynaptic receptor distribution is altered
in R6/2 mice (Cha et al. 1998), and receptors show altered function in HD, often
before overt disease (Zeron et al. 2004). Low frequency synaptic transmission at
hippocampal synapses in R6/2 mice is normal, but high frequency synaptic
transmission is abnormal (Murphy et al. 2000). Protein and mRNA trafficking to
synapses is impaired possibly due to the presence of neuropil aggregates and
disruption of cytoskeletal structures (Li et al. 2001).
2. Disruption of vesicle transport. Huntingtin activating protein-1 (HAP1) interacts
with both htt and with proteins involved in vesicle transport (Rubinsztein 2002). For
example, both HAP-1 and htt enhance transport of BDNF along microtubules. BDNF
transport is impaired by reducing the levels of normal htt (a loss of function), or by
the mechanical effects of aggregates (a gain of function) (Gauthier et al. 2004;Ross
2004).
3. Disruption of transcription. Mutant htt is found in the nucleus as well as cytoplasm
(Wheeler et al. 2000;Hodgson et al. 1999). mRNA associated with inflammatory or
cell cycle functions are increased; and mRNA associated with signal transduction,
ion channels, transcription, G-protein coupled receptors, metabolism, calcium
signalling, retinoid signalling and cell structure are decreased in HD mice (LuthiCarter et al. 2000). Many of the genes downregulated in HD are CRE-responsive, a
feature common to other poly-Q diseases (Rubinsztein 2002). An important change
of transcription in HD is reduction of transcription of BDNF, and this may produce
disease through a loss-of-function effect (Zuccato et al. 2005;Zuccato et al. 2001).
Expression of receptors, particularly the G-protein coupled metabotrobic glutamate
receptors, D1 (Cha et al. 1998) and cannabinoid (CB)1 (Denovan-Wright and
Robertson 2000) is decreased in HD mice, which may also impact on synaptic
function. Htt also binds to histone deacetylase and histone deacetylase inhibitors
improve the HD phenotype (Rubinsztein 2002;Ferrante et al. 2003).
4. Altered plasticity. Long-term potentiation (LTP) is reduced early in mouse models of
HD, which could contribute to learning impairments in these mice (see Bates et al.
2002;Murphy et al. 2000;Mangiarinini et al. 1996).
5. Disruption of protein-removing machinery e.g. proteasomes (Jana et al. 2001).
Disruption of proteasomal activity is reversible however, because abnormal protein
200
The Control of Adult Neurogenesis by the Microenvironment and How This 201
Promoter
Not
applicable
Phenotype
Phenotype
resembles HD
Transgenic:
exon-1 R6
lines
Transgenic:
longer exon-1
e.g. N171-82Q
Human
HD
promoter
Human
prion
promoter
Severe
Early,
widespread
Transgenic:
full length
mutant protein
e.g. YAC
Q72, cDNA
(48,89 CAG
repeats)
Knock-in
Human
HD
promoter
(YAC),
CMV
(cDNA)
Variable, less
severe than
R6, onset ~3
months
Hyperactive at
6 months
Mild, Detloff
mice have
more severe
phenotype
(Lin et al.
2001)
Mouse
HD
promoter
NII
Pathology
Striatal
degeneration,
sparing of
NAPDH
diaphorase
neurons (for QA
model)
Little cell loss
References
(Coyle and
Schwarcz
1976;Sanberg et
al.
1989;Borlongan et
al. 1995;Beal et
al. 1991)
(Mangiarini et al.
1996)
Yes
(Schilling et al.
2004)
Late
Striatal atrophy at
12 months
(Hodgson et al.
1999;Reddy et al.
1998)
Some have
NII (Lin et
al. 2001;
Rubinsztein
2002)
(Rubinsztein
2002)
No
Lazic et al 2004
(R6/1)
Gil et al 2005
(R6/2)
Phillips et al
2005(R6/2)*
Grote et al 2005
(R6/1)
Jin et al 2005
(R6/2)
Lazic et al 2006
(R6/1)
Proliferation
Morphology
Neural
differentiation
Neurogenesis
(DCX)
ns
nd
Newborn
neuron
survival
nd
Effect of
intervention
ns
ns
ns
ns
ns
ns
ns
ns
no upregulation
after seizures
differentiation
and survival
(fluoxetine)
(subcut FGF)
, #
202
Also, because of the long repeats, the transgenic models may recapitulate juvenile onset
HD, as opposed to the adult onset disease and the short life span of the mouse reduces their
value in exploring specifically the gradual disease process.
Yeast artificial chromosome (YAC) mice express the full-length htt protein, display a
progressive phenotype over a longer time course and do show similar pathological changes to
the human disease (table 2.2). Knock-in mice, such that CAG repeats are inserted directly into
the endogenous gene, display limited motor abnormalities, and the pathological changes do
not parallel human pathology (table 2.3).
The Control of Adult Neurogenesis by the Microenvironment and How This 203
Morton colony (Lione et al. 1999;Carter et al. 2000) versus Jackson lab colony. The former
have longer CAG repeat lengths, greater longevity, and fewer seizures; and the method of
maintaining the strain is different for the two colonies. Additionally, the Morton colony mice
are housed with plastic toys and running equipment, which may be deemed environmental
enrichment; and even minimal environmental enrichment ameliorates disease progression in
R6/2 mice (Hockly et al. 2002). Additionally, Lazic et al. (2006) found similar basal rates of
cell proliferation between R6/1 and WT mice at 25 weeks of age, although reduced
proliferation in R6/1 mice at 10 weeks of age. Indeed, we have preliminary data using Jackson
lab mice, which shows a larger difference in neurogenesis between genotypes.
The differentiation fate and survival of NPCs were intact in R6/2 mice in one study
(Phillips et al. 2005) but not in another (Gil et al. 2005). Lazic et al. (2004) could not
demonstrate BrdU/NeuN co-localisation in R6/1 mice at 2 weeks but Gil et al. (2005) found
that the 2-week survival of BrdU-positive cells was lower in R6/2 compared to WT mice.
Similarly, Lazic et al (2006) found reduced newborn neuron survival in the DG in R6/1 mice
after 4 weeks. All these studies showed that percentage co-localisation of BrdU with NeuN
was no different between genotypes.
The reasons for the difference in survival rates between studies are unclear but may
involve subtle differences in mouse colonies such as the frequency of handling-induced
seizures and CAG repeat length, different methods of quantification, and differences in BrdU
dosing regimens and time of sacrifice (Prickaerts et al. 2004) (see above).
204
dependent cognitive decline in HD mice (Grote et al. 2005), although the two observations
are not necessarily causally linked.
FGF affects neuronal morphology and migration in the DG (Lowenstein and Arsenault
1996) and is one of the most potent proliferative agents for neuronal progenitors (Gensburger
et al. 1987). It is possible, then, that reduced levels of FGF in R6/2 mice may be responsible
for reduced proliferation of NPCs and abnormal morphology of newborn neurons in R6/2
mice. FGF levels have not been studied in R6/2 mice; FGF is upregulated in the striatum and
midbrain in HD patients (Tooyama et al. 1993), but the level of FGF in the hippocampus in
humans is unknown.
The altered morphology of newborn granule neurons in the R6/2 mouse may also be due
to abnormal cytoskeletal reorganisation and dendritic growth (reviewed by Harjes and
Wanker, 2003; Jarabek et al. 2004). This is consistent with the observation that DCX-positive
cells are reduced in the piriform cortex of R6/2 mice, which may reflect a general reduction in
structural plasticity (Phillips et al. 2006).
Following 3 weeks of repeated emotional stress, there are fewer long thin spines and
more short stubby spines in the prefrontal cortex of normal mice (Radley and Morrsion 2005).
Spines sequester calcium and it may be that these morphological changes provide a
neuroprotective mechanism from excitotoxic insults (discussed in section 3.8). This may
however, be at the expense of a functionally impaired neuron. It is possible that the observed
morphological changes are in reaction to a hostile microenvironment in R6/2 mice (Phillips
et al. 2005) with consequent functional impairment.
These morphological changes of newborn neurons in R6 mice may contribute to the
cognitive impairment of R6/2 mice. Newborn neurons are more amenable to LTP (Wang et
al. 2000;Schmidt-Hieber et al. 2004) but LTP is reduced in R6/2 mice (Murphy et al. 2000),
and it is tempting to speculate that fewer or abnormal newborn neurones may contribute to
this deficit in LTP.
Ageing mice also have morphological abnormalities in newborn neurons. Rao et al.
(2005) showed that rats from 12 months of age had a higher ratio of more immature DCXpositive cells in the DG, less branching and shorter dendritic lengths. Migration of immature
granule neurons from the SGZ to the GCL was also reduced in older mice but the neurons
reached a similar position in the GCL as in their younger counterparts after several months.
van Praag et al (2005), however, did not find morphological differences in newborn neurons
between young and aged rats. As may be the case for R6/2 mice, such morphological changes
with age may be postulated to cause functional abnormalities in newborn neurons.
The Control of Adult Neurogenesis by the Microenvironment and How This 205
1. A decrease of factors permissive for neurogenesis
Growth factors: BDNF, FGF, IGF, VEGF
Neurotransmitters: serotonin, dopamine, acetylcholine, noradrenaline
2. Abnormal components of the neurogenic niche
Glia
Vasculature
Basement membrane
Neurones (autocrine and paracrine factors)
NPCs (abnormalities undetectable by neurosphere assay)
3. An increase in factors non-permissive for neurogenesis
Glucocorticoids
Inflammatory cytokines
BDNF is important for basal neurogenesis in the DG (Lee et al. 2000;Lowenstein and
Arsenault 1996), and levels are reduced in the hippocampus of R6 mice (Spires et al. 2004b).
FGF is also important for neurogenesis (Lowenstein and Arsenault 1996), and although FGF
levels are increased in the striatum, midbrain and SVZ of HD patients (Tooyama et al. 1993),
the levels of FGF in the DG in HD patients or R6/2 mice are unknown. Other growth factors
that are required for neurogenesis may be deficient in HD, contributing to the observed
impairment of neurogenesis in R6/2 mice.
Serotonin plays an important role in neurogenesis (see Hagg 2005), and serotonin levels
are reduced in the hippocampus from 8 weeks of age (in the striatum from 12 weeks) in the
R6/2 mouse (Reynolds et al. 1999). The SVZ and SGZ receive dopaminergic fibres,
dopamine increases neurogenesis and the overlap of dopaminergic and serotonergic signalling
in neurogenic areas may contribute to a neurogenic niche (Hoglinger et al. 2004;Hagg 2005).
Levels of dopamine in the R6/2 hippocampus (and striatum) are, however low, although not
to the same extent as other transmitters such as serotonin or noradrenaline (Reynolds et al.
1999). Depletion of noradrenaline reduces DG NPC proliferation but does not affect
differentiation and survival (Kulkarni et al. 2002). R6/2 mice have a particularly marked
decline of noradrenaline in the hippocampus, but noradrenaline levels are intact in the
striatum (Reynolds et al. 1999). Thus, a paucity of noradrenaline could explain all the
observed abnormalities seen in one study: reduced proliferation in the DG, intact
differentiation and survival, intact neurogenesis in the striatum and a perturbed
microenvironment (Phillips et al. 2005).
Soluble and membrane bound factors released from glia are critically important for
neurogenesis (Song et al. 2002), and microglial activity may also influence neurogenesis
(Ekdahl et al. 2003;Monje et al. 2002). Microglial activation inhibits neurogenesis (Ekdahl et
al. 2003;Monje et al. 2002) and the numbers and morphology of microglia are altered in HD
(Sapp et al. 2001;Ma et al. 2003). Interleukin-6 may be involved in this inflammationinduced downregulation of neurogenesis (Monje et al. 2003). Blockade of inflammation
induced by seizures and cell death or LPS infusion (Ekdahl et al. 2003;Monje et al. 2003)
restores neurogenesis. However, microglia do release trophic factors and may have a
beneficial role during inflammation (Liu and Hong 2003). It may therefore be the degree,
timing or nature of any inflammatory response that is important for neurogenesis and
neuronal survival following brain insults. In the Phillips et al. (2005) study, microglia did not
negatively correlate with neurogenesis and there was no difference in the amount of microglia
206
The Control of Adult Neurogenesis by the Microenvironment and How This 207
whether this may be different in R6/2 mice. The mRNA and protein levels of many growth
factors and cytokines are increased after seizures (Jankowsky and Patterson 2001).
Transcription is abnormal in HD (van Dellen et al. 2005) and it is possible that up-regulation
of growth factors is impaired post-seizure, accounting for the failure of up-regulation of
neurogenesis.
Transmitter release is impaired during periods of intense synaptic activity in R6/2 mice
(Murphy et al. 2000), thus during seizures, pre-synaptic terminals from R6/2 mice might
release less neurotransmitters, possibly curtailing the neurogenic response.
Activity-dependent neuronal excitation is coupled to NPC proliferation (Deisseroth et al.
2004), and there may be less neuronal excitation in the R6/2 hippocampus because there is
less LTP (Murphy et al. 2000), less newborn neurons, morphologically abnormal newborn
neurons and disruption of synaptic activity. If there is indeed less neuronal activity in the
R6/2 DG, this excitation coupling may provide an explanation for why neurogenesis does not
increase in response to activity-dependent stimuli.
208
2006); chemokines (Belmadani et al. 2006); stem cell factor (Sun et al. 2004;Jin et al. 2002);
growth factors (Jankowsky and Patterson 2001); and astrocyte-derived factors (Mason et al.
2001).
The Control of Adult Neurogenesis by the Microenvironment and How This 209
12 weeks of age (Bogdanov et al. 1998). This pattern was seen to a certain extent by Phillips
et al. (2005), with resistance to seizures tending to occur in 9 week old but not 13-week-old
R6/2 mice.
Resistance to cell death from excitotoxins in certain mouse models of HD is likely to be
related to the expression of fragments of mutant htt, as opposed to full-length mutant htt.
Resistance to excitotoxins develops coincident with the appearance of NII (Hansson et al.
2001b), and which are few in number in YAC mice (Hodgson et al. 1999). Furthermore, in
shortstop mice (which have many NII but have no behavioral abnormalities), there is also
resistance to excitotoxins (Slow et al. 2005). NII may therefore be protective (Saudou et al.
1998;Hickey and Morton 2000), may induce compensatory changes in the cell, or may be an
epiphenomenon.
Table 3.1. Resistance to lesions in mouse models of HD
Toxin
QA
Resistance
Reference
Resistant
Sensitive
cell swelling in
older mice
Systemic KA
R6/2 (12)
R6/2 (6 to 15 weeks),
71 CAG, 94 CAG
knock-in (7 to 15
weeks)
R6/2 (3, 9)
Resistant
3NP
Resistant
Malonate
Partial resistance
(not in 6 week R6/1)
Resistant to QA and
NMDA agonist
3NP
NMDA agonist
QA, NMDA
agonist, AMPA
agonist
DA, 6OHDA
QA, NMDA,
AMPA
Ischaemia
QA
YAC72 (6, 10
months)
R6/1 (18)
cDNA (18, 46, 100
CAG repeats)
Partial resistance at
16 weeks
Sensitive to QA,
NMDA
Resistant
No change
210
which may reduce NMDA-evoked currents; neuronal nitric oxide synthase (NOS) and PSD95 (which are required for NMDA R function), and citron (a protein involved in dendritic
spine function), are all reduced in the transgenic mouse, providing more mechanisms for
resistance (Jarabek et al. 2004). Hansson et al. (1999) postulated that low-grade sustained
excitotoxicity produced during the disease process causes resistance to excitotoxins by a
mechanism akin to ischaemic tolerance. This is an attractive suggestion because it may
explain the time window of resistance, the putative threshold by which R6/2 mice succumb
more quickly to insults (Morton and Leavens 2000) and the late onset of the disease. Such a
mechanism may even underlie the observed reduction of neurogenesis in the DG and failure
to upregulate DG, SVZ and striatal neurogenesis (Lazic et al. 2004;Gil et al. 2005;Phillips et
al. 2005). Repeated stress causes calcium-sequestering dendritic spines to become short and
stubby, as a neuroprotective mechanism (Radley and Morrsion 2005); this may occur in R6
mice in response to high basal calcium levels and might cause neuronal dysfunction and
morphological abnormalities. Interestingly, Levine et al. (1999) showed that striatal neurons
from R6/2 mice have increased sensitivity of NMDA receptors, with resulting cell swelling.
An excess of cell death was not, however, seen. It is possible that striatal neurons from R6/2
mice have increased sensitivity to neuronal dysfunction after excitotoxins, but these cells are
resistant to cell death. Increased cell swelling, however, occurred in mice of an older age
(greater than 9 weeks, up to 15 weeks of age) and this may be when the neuroprotection
breaks down (Bogdanov et al. 1998).
Levels of FGF are high in striatal astrocytes in HD brains, providing another mechanism
for neuroprotection in the striatum in response to insults (Tooyama et al. 1993). NMDA
receptor mediated excitotoxicity is dependent on dopamine and adenosine 2A receptors
(Reynolds et al. 1998;Popoli et al. 2002). Dopamine and purine metabolism is disturbed in
R6 mice, which may also account for neuroprotection to excitotoxic insult (table 2.1).
Increased sensitivity to cell death from excitotoxins in YAC mice might be explained by
NR2B subunit-mediated increased evoked current amplitude and caspase-3 activation (Zeron
et al. 2004a).
The Control of Adult Neurogenesis by the Microenvironment and How This 211
particularly as the proportion of III-tubulin cells was not increased in the HD SVZ (Curtis et
al. 2005a).
It would be interesting to study the DG in HD patients given the data from animal studies
and because abnormal DG neurogenesis may contribute to some of the cognitive and
psychiatric disorders seen in HD. It would be interesting to study the striatum in humans,
because this is the main site of pathology in HD; and the OB, as it depends on SVZ
neurogenesis and neuroblast migration, and olfaction is reduced in HD patients (Hamilton et
al. 1999;Moberg et al. 1987).
The reason for the discrepancy between humans and mouse models is unknown. One
possibility is that the stimulus for SVZ proliferation in humans may be neurodegeneration in
the adjacent caudate nucleus, which is minimal in the R6/2 mouse (Mangiarini et al. 1996).
However, SVZ proliferation did not increase in R6/2 mice after striatal injury (Phillips et al.
2005) (although the mechanism and time-course of cell death is different). It may also be that
intrinsic species differences, such as anatomy (Sanai et al. 2004) and neurotransmitter and
growth factor milieu (Ferrer et al. 2000;Spires et al. 2004b;Reynolds and Pearson 1987;Kish
et al. 1987), account for differences in neurogenesis. A recent study, however, has shown that
while NPCs in the SVZ may be unchanged in HD mice, neural stem cells may be increased
compared to WT mice (Batista et al. 2006).
The human SVZ stem cell niche is composed of an astrocyte ribbon, and there is no
RMS with chains of migrating neuroblasts to the OB although scattered neuroblasts can be
found between the SVZ and olfactory cortex in humans (Sanai et al. 2004). The SVZ, RMS
and OB are more developed in rodents, which is not surprising given the important role of
olfaction in the rodent. The lack of an RMS does not preclude a role for SVZ neurogenesis in
humans: new neurons destined for the OB may still play a role in humans, the SVZ may
deliver neurons to the amygdala and piriform cortex (Bernier et al. 2002) and hippocampus
(Bull and Bartlett 2005;Nakatomi et al. 2002), and may contribute to self-repair and upkeep
in adjacent structures. Furthermore, neurogenesis is ongoing in the human olfactory system
(Bedard and Parent 2004). However, the anatomical differences between humans and rodents
may provide an as yet unidentified explanation for the differences in SVZ neurogenesis
between humans and rodents with HD.
Neurotransmitters affect neurogenesis (table 1.1) and there are species differences in
neurotransmitters (table 2.1). Serotonin increases neurogenesis (Hagg 2005), but serotonin
levels are reduced in the R6/2 striatum from 12 weeks of age (Reynolds et al. 1999) and
increased in human HD cortex and striatum (Reynolds and Pearson 1987). Increased striatal
serotonin might account for increased SVZ proliferation in HD patients. Noradrenaline
contributes to NPC proliferation (Kulkarni et al. 2002); R6/2 mice have very low levels of
noradrenaline in the hippocampus, but normal levels in the striatum (Reynolds et al. 1999);
and noradrenaline is increased in the HD striatum (Spokes 1980). These alterations of
noradrenaline levels could therefore explain reduced NPC proliferation in the R6/2 DG,
normal R6/2 SVZ proliferation, and high SVZ proliferation in human HD patients.
212
Mouse
No cell loss in caudate nucleus (until late stages)
Well defined SVZ and RMS
Serotonin normal or reduced
Noradrenaline normal in striatum
Level of FGF in SVZ unknown
Mice might die before SVZ proliferation is detected
Human
Atrophy of caudate nucleus
Astrocyte ribbon
Serotonin increased
Noradrenaline increased in striatum
FGF increased in the SVZ
Longer lifespan in human
The level of striatal FGF is unknown in mice, but is very high in the SVZ adjacent to the
caudate nucleus in HD patients, which may provide a mechanism for increased SVZ
proliferation in HD patients (Tooyama et al. 1993).
Finally, it is possible that SVZ proliferation may actually increase in mouse models, but
their lifespan is so short that they die before this proliferation can be detected. Indeed, Jin et
al. (2006) reported a modest increase in SVZ proliferation in 14-and-a-half and 15-and-a-half
week old R6/2 mice. Again, neural stem, as opposed to precursor, cells may increase with age
in R6/2 mice in the SVZ (Batista et al. 2006).
The Control of Adult Neurogenesis by the Microenvironment and How This 213
Table 3.3. Possible reasons for discrepancy between
mouse SVZ and mouse DG proliferation
Mouse SVZ
Possibly less sensitive to deprivation of
certain growth factors e.g. BDNF, IGF, FGF
Apposition to CSF
Noradrenaline levels intact
True stem cells in situ
Mouse DG
Possibly more sensitive to the deprivation of
certain growth factors e.g. BDNF, IGF, FGF
Not apposed to CSF
Noradrenaline levels reduced
NPCs may have to migrate to the DG from
the SVZ
There may be intrinsic differences in the potency of stem-like cells (Bull and Bartlett
2005;Seaberg and van der Kooy 2002). It is even possible that NPCs in the DG have migrated
from the caudal SVZ (Bull and Bartlett 2005). The lack of proliferation, neurogenesis and upregulation of neurogenesis seen in the R6/2 DG may be a consequence of retarded migration
of precursors from the caudal SVZ, particularly given that retarded migration was seen in the
DG itself (Phillips et al. 2005).
R6/2 mice have a particularly marked decline of noradrenaline in the hippocampus, but
noradrenaline levels are intact in the striatum (Reynolds et al. 1999). Furthermore, there is a
noradrenergic input into the DG but not the SVZ, making it unlikely that noradrenaline
mediates SVZ neurogenesis (Hagg 2005). Thus a paucity of noradrenaline (a promoter of
neurogenesis, particularly NPC proliferation) may account for reduced neurogenesis in the
DG. Indeed, enhancing levels of noradrenaline improves the phenotype of R6/2 mice (Morton
et al. 2005a).
There are many components that contribute to a neurogenic niche, which may be
different in the two areas that may, in turn, account for the different sensitivity of
neurogenesis in the SVZ and DG.
214
is complex, given that R6/2 mice are resistant to excitotoxic injury. Finally, proliferation of
SVZ stem, as opposed to precursor, cells may increase with age in R6/2 mice (Batista et al.
2006).
The Control of Adult Neurogenesis by the Microenvironment and How This 215
One, the functional consequences of impaired neurogenesis in HD mice and humans is
unknown. Two, increasing the numbers of newborn neurons (by infusion of growth factors,
for example) might result in functionally abnormal neurons (in a continued non-permissive
microenvironment), excessive numbers, and cells that proliferate but do not survive, for
example. Infusion of growth factors may have to be tailored, delivered as a cocktail (one to
mediate proliferation, one maturation, one survival, and so on), delivered with other
substances such as Noggin, and the microenvironmental milieu may have to be altered to
support the newly formed neurons. Finally, increasing neurogenesis may be detrimental,
promoting tumours, kindling, impaired clearance of memories, and so on. More research is
warranted into this area, certainly before trials on humans are considered.
3.15. Conclusion
The discovery that neurogenesis persists in the adult mammalian brain has lead to much
excitement in the scientific community: both in terms of potential therapies and in the
implication that this has for brain plasticity. That disturbed neurogenesis and plasticity is
involved in psychiatric disorders is of immense importance and implies that by manipulating
neurogenesis, these distressing disorders may be alleviated.
Regarding HD, most studies have shown that neurogenesis is impaired in the R6 mouse
DG but intact in the SVZ; but precursor cell proliferation in the human SVZ is increased.
Furthermore, neurogenesis or plasticity may be impaired in the piriform and insular cortex
(Phillips et al. 2006), and speculatively of course, this may be responsible in part for atrophy
of the insular cortex seen in HD patients (Thieben et al. 2002). Thus, it seems that impaired
neurogenesis may be implicated in the cognitive and psychiatric disorder of HD and not the
striatal degeneration. Indeed, striatal repopulation post-injury with newborn neurons is very
limited (Arvidsson et al. 2002). SVZ/ striatal neurogenesis cannot be upregulated after injury
in R6/2 mice (albeit with the reservations previously discussed) (Phillips et al. 2005), and this
might have some implications for slow neurodegeneration. Thus, impairments in
neurogenesis could contribute to the neurodegenerative process, and cognitive and psychiatric
problems seen in HD, as well as an inability to cope with and adapt to stressors and novel
stimuli.
Much of the work published on neurogenesis in HD is observational and it will be
important in time, to assess the functional consequences of altered neurogenesis and plasticity
in HD mice and humans, and whether enhancement of neurogenesis would arrest the disease.
Thus, studies of neurogenesis in neurodegenerative disease could allow us to discover
important pathological mechanisms and open up avenues for therapeutic intervention by
either altering the microenvironmental milieu, enhancing conditions for cellular
transplantation or enhancing endogenous neurogenesis, and with this the potential for curative
therapies.
216
Abbreviations
3NP
5HT
AD
APP
BDNF
BG
BMP
BrdU
CA
CAG
CBP
CMV
CNTF
CREB
CSF
DCX
DG
ECT
EGF
ES
FGF
GABA
GCL
GDNF
GFAP
GP
GPe
GPi
HAP1
HD
htt
IGF
IL
INF
IT15
KA
LPS
LTP
LV
mRNA
MSP
mTOR
NADPH
3-nitropropionic acid
5-hydroxytryptamine (serotonin)
Alzheimers disease
amyloid precursor protein
brain derived neurotrophic factor
basal ganglia
bone morphogenic protein
bromodeoxyuridine
cornu ammonis
cysteine adenine guanine
CREB binding protein
cytomegalovirus
ciliary neurotrophic factor
cyclic adenosine monophosphate response element binding protein
cerebrospinal fluid
doublecortin
dentate gyrus
electroconvulsive therapy
epidermal growth factor
embryonic stem cell
fibroblast growth factor
gamma amino butyric acid
granule cell layer
glial cell derived neurotrophic factor
glial fibrillary acidic protein
globus pallidus
globus pallidus externa
globus pallidus interna
huntingtin associated protein1
Huntingtons disease
huntingtin
insulin-like growth factor
interleukin
interferon
interesting transcript 15
kainic acid
lipopolysaccharide
long-term potentiation
lateral ventricle
messenger RNA
medium spiny projection
mammalian target of rapamycin
nicotinamide adenine dinucleotide phosphate (reduced)
The Control of Adult Neurogenesis by the Microenvironment and How This 217
NCAM
NECTAR
NeuN
NGF
NII
NMDA
NOS
NPC
NPY
NSC
OB
PCNA
PD
PDGF
PET
PFC
PS1
PSA-NCAM
PSD-95
Q
QA
RMS
RNA
SBMA
SCA
SGZ
SHH
SN
SNc
SNr
SS
STN
SVZ
TUNEL
VEGF
WT
YAC
218
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238
Index
A
abnormalities, 133, 173, 178
abortion, 141, 154, 155
abuse, 112, 187
access, 46, 136, 137, 143, 144, 153, 162, 165
accounting, 64, 160, 207
accuracy, 134, 141
acetylcholine, 51, 53, 205
acetylcholinesterase, 222
acid, 19, 28, 31, 32, 59, 69, 184, 200, 216, 217, 219,
221, 224, 228, 229, 230, 231, 232, 233, 235
acidic, 183, 216
activation, 186, 193, 195, 196, 205, 210, 223, 225,
227, 229, 230
AD, 187, 216, 221, 226, 227, 232, 233
adaptation, 82, 92, 117
adenine, ix, 62, 64, 65, 189, 195, 216
adenosine, 210, 216, 223, 232, 235
adhesion, 217, 230
administration, 186, 200, 227, 238
ADP, 28
adulthood, x, 3, 135, 141, 181, 182, 191, 193
affective disorder, 115
Africa, vii, 101, 113
aggregates, 4, 18, 21, 22, 23, 24, 25, 31, 32, 35, 36,
40, 42, 43, 44, 45, 46, 47, 48, 51, 57, 121, 188,
192, 193, 199, 200, 220, 224, 226, 229, 233
aggregation, vii, 2, 4, 18, 34, 51, 55, 192, 193
aggression, 40, 115
aging, 225, 227, 230
aging process, 69
agonist, 200, 209
aiding, 128, 171
AIDS, 105, 122
akathisia, 77
akinesia, 80
alanine, 3
alcohol, 90, 94
alcoholism, 116
alkylation, 64
allele, 4, 14, 15, 40, 45, 63, 68, 70, 73, 112, 189
alternative, 133, 135, 137, 138, 202
alternatives, 140, 147, 157
alters, 40, 194
Alzheimer's, 221, 224, 225, 229, 231, 237
Alzheimer's disease, 170, 221, 224, 225, 229, 231,
237
amino, 184, 191, 200, 216, 230, 233
amino acid, 191, 200, 230, 233
amino acids, 19, 20, 22, 191, 200
AMPA, 185, 209, 218
amplitude, 80, 210
Amsterdam, 176
amygdala, 20, 183, 194, 196, 197, 198, 211, 219
Amyloid, 220
amyloid beta, 224
anatomy, 211, 218, 226
androgen, 24
angiogenesis, 184, 186, 187, 206
animal models, 189, 194, 232, 233
animals, 184, 187
anthropological, 145
anthropology, 145
anti-apoptotic, 209
anticholinergic, 81
anticholinergic effect, 81
antidepressant, 81, 115, 228
antidepressant medication, 115
antidepressants, 233
antigen, 65, 67, 72, 206, 210, 217
antipsychotic, 79, 81
anxiety, 40, 77, 78, 81, 91, 106, 108, 112, 114, 116,
138, 143, 161, 169, 190
anxiety disorder, 91
apathy, 79, 87, 114
240
Index
apoptosis, 27, 32, 35, 36, 37, 40, 45, 46, 50, 51, 55,
57, 62, 183, 186, 208, 225, 233
apoptotic, 200, 209, 232, 238
apoptotic pathway, 238
applications, 160, 174
appointments, 91, 92
Argentina, 1
aspartate, 12, 36, 37, 194, 227, 235
aspiration, 83, 88, 91, 103, 105
aspiration pneumonia, 88
assessment, 9, 58, 98, 107, 112, 119, 131, 163, 168,
171, 218
Astrocyte, 212
astrocytes, 184, 208, 210, 221
astrogliosis, 21, 194, 201
asymptomatic, 13, 71, 72, 105, 197
ataxia, 6, 19, 37, 55, 189, 200, 217, 226
ATP, 12, 27, 51, 57
atrophy, 6, 12, 16, 19, 20, 24, 33, 34, 119, 188, 189,
194, 197, 201, 215, 217, 218
attention, 190
attitudes, x, 99, 101, 106, 108, 109, 117, 118, 120,
134, 140, 141, 147, 156, 157, 162, 171, 173, 175,
178, 179
attribution, 135
attribution theory, 135
Australia, 99, 102, 119, 120, 177
authors, 11, 15, 68, 77, 102, 103, 105, 108, 111, 112,
114, 115, 116, 129, 182
autonomy, 117, 123
autophagy, 192, 232
autosomal dominant, ix, 4, 40, 45, 62, 75, 76, 83,
170, 173, 188
availability, 79, 103, 155, 159
avoidance, 118, 163
awareness, 77, 80, 95, 128, 139, 146, 148, 149, 150,
151, 152, 153, 154, 156, 160, 162, 166, 167
axon terminals, 192
axonal degeneration, 22, 32, 227
axons, 20, 21, 26, 184, 191, 192
B
B cell, 183, 210
B cells, 183, 210
babies, 137, 155
background, 47, 84, 105, 110, 146, 208
background information, 146
bacteria, 88, 89, 94, 96
barriers, 105, 130, 150
basal ganglia, 6, 16, 51, 196, 197, 216, 218, 223, 237
Basal ganglia, 218
basal lamina, x, 181, 182, 184
base pair, 13
C
Ca2+, 36
calcium, vii, 2, 27, 34, 36, 195, 199, 204, 206, 209,
224, 231, 234
calorie, 78
Canada, 100, 102, 106, 120, 121, 122, 158, 172
cancer, 71, 105, 123, 163, 170, 177, 183
candidates, 107, 120
capsule, 21
carbohydrates, 93
carbon, 103, 104
Index
carbon monoxide, 103, 104
cardiomyopathy, 6
caregivers, 79, 81, 82, 91, 92, 93
caries, ix, 87, 89, 92, 93, 94, 97, 98
carrier, ix, 77, 99, 100, 106, 107, 108, 109, 110, 112,
113, 117, 122, 124, 169, 175, 176, 177
case examples, 118
case study, 173
Caspase-8, 34, 58
caspases, 193, 222
catatonia, 79
category b, 105
Caucasian population, 9, 40
causal relationship, 187
cDNA, 34, 201, 203, 209, 232
cell adhesion, 217, 230
cell cycle, 50, 199
cell death, 4, 28, 32, 34, 51, 58, 72, 186, 187, 192,
205, 208, 209, 210, 211, 224, 232, 233
cell division, 183
cell line, 27, 31, 68, 184, 223
cell lines, 28, 31, 68, 223
cell signaling, 26
central nervous system, 89, 229, 230
cerebellum, 17, 20, 67, 71, 229
cerebral cortex, 16, 17
cerebral ischemia, 225, 234
cerebrospinal fluid, 216
CGC, 6
challenges, 93, 133, 172, 177
channels, 34, 199
chaperones, 23, 47, 48, 57
chemokine receptor, 228
chemokines, 208
chemotherapeutic agent, 92
chemotherapy, 30, 222
childbearing, 130, 141, 173, 180
childhood, 3, 146, 147, 164, 172
childless, 137, 138, 155, 172, 175
children, 3, 4, 77, 103, 104, 107, 128, 133, 137, 138,
140, 141, 143, 144, 145, 148, 150, 151, 152, 153,
155, 156, 157, 159, 160, 161, 162, 164, 165, 166,
168, 169, 172, 173, 174, 177
China, 40
cholinergic neurons, 187
chorea, vii, 1, 4, 6, 9, 76, 79, 80, 82, 88, 96, 97, 119,
122, 123, 124, 125, 171, 172, 174, 175, 190, 196,
221, 223, 229, 234, 237
choreoathetosis, 7
chromosome, 8, 13, 34, 40, 62, 100, 189, 202, 217
chronic obstructive pulmonary disease, 96
cilia, 183, 212
cilium, 212
241
classical, 171
classification, 36, 48, 116, 237
cleaning, 82, 93
cleavage, vii, 2, 22, 23, 24, 36, 64, 66, 193, 223, 237
clinical diagnosis, 77, 115, 120, 122
clinical presentation, 9, 12
clinical symptoms, 116
clinical trials, 76, 118
clinics, 142, 151
clozapine, 81
CNS, vii, 1, 12, 189, 217, 222, 230, 235, 237
codes, 40, 149, 180, 189
coding, vii, 1, 3, 5, 18
cognition, 12, 79, 83, 197, 202, 213, 227, 230
cognitive abilities, ix, 82, 87
cognitive biases, 159
cognitive deficit, 7, 11, 17, 82, 116, 124, 226
cognitive deficits, 7, 11, 17, 82, 116, 124, 226
cognitive dissonance, 134, 173
cognitive dysfunction, 12, 197
cognitive flexibility, 11, 82
cognitive function, vii, 12, 72, 105
cognitive impairment, viii, 6, 7, 40, 61, 62, 188, 204
cognitive models, 175, 179
cognitive process, 130, 134
cognitive processing, 130, 134
cohesins, 34
collaboration, 163, 189
collagen, 184
Colombia, 106
colonization, 88
common symptoms, 40
communication, 16, 82, 90, 99, 133, 149, 150
community, 2, 84, 93, 97, 108, 215
compatibility, 163
compensation, 82, 197
competence, 117, 130, 131, 132, 165
complement, x, 67, 90, 181, 184, 209
complexity, 54, 160, 166
compliance, 79
complications, ix, 82, 87, 88, 89, 91, 115
components, 134, 142, 147, 184, 186, 205, 213
compounds, 29
compulsive behavior, 40
computers, 177
computing, 105
concentration, 51, 90, 94, 195
conception, 128
concordance, 17, 20
condensation, 200
confidence, 11, 142, 159, 164
confidence interval, 11
confidentiality, 77, 144
242
Index
connective tissue, 6
consensus, 91, 104, 136
consolidation, 131, 134, 179
constraints, 129, 131, 133, 141
control, 12, 16, 22, 27, 79, 91, 129, 132, 137, 138,
141, 143, 146, 153, 156, 159, 167, 168, 178, 180,
196, 200, 202, 210
coordination, vii, 67, 68
coping strategies, 149
coping strategy, 108, 175
corpus callosum, 207
correlation, 4, 10, 12, 14, 34, 69
correlations, 9, 12, 69
cortex, vii, 1, 16, 17, 18, 20, 34, 45, 58, 63, 64, 116,
183, 194, 195, 196, 197, 198, 200, 204, 206, 207,
208, 211, 214, 215, 217, 218, 219, 221, 225, 231
cortical neurons, 203
cortisol, 187
costs, 108, 118, 120, 133, 171
counseling, 77, 78, 172, 175, 178, 180
counseling psychology, 178
couples, 133, 137, 138, 143, 145, 152, 158, 159, 160,
161, 164, 165, 168, 172
cross-sectional study, 71
CSF, 212, 213, 216
culture, 63, 171, 183, 184, 187
curiosity, 132
curriculum, 150
Cushing's syndrome, 235
cycling, 219, 227
cystic fibrosis, 162, 169, 176
cytochrome, 27, 225
cytokines, 184, 205, 207, 225
cytomegalovirus, 216
cytoplasm, vii, viii, 2, 18, 21, 22, 23, 25, 45, 50, 191,
192, 193, 199
cytoskeleton, 26, 48, 49, 50
D
daily living, 78, 90
dance, 9, 190
data collection, 109, 146
database, 29, 42
death, viii, ix, 4, 6, 22, 28, 29, 32, 34, 35, 40, 41, 51,
57, 58, 61, 62, 72, 88, 99, 100, 101, 102, 103,
104, 105, 106, 120, 121, 123, 124, 125, 141, 152,
154, 164, 175, 186, 187, 192, 194, 200, 206, 208,
209, 210, 211, 218, 224, 226, 232, 233, 235
deaths, 102, 103, 105, 116, 120
decay, 92, 95
decision makers, 134, 147
decision making, x, 82, 127, 128, 131, 142, 154, 155,
171, 172, 174, 175, 176, 177, 179, 180
Index
disease gene, 4, 30, 31, 34, 35, 37, 71, 218, 220, 221,
225, 231, 234, 236
disease progression, 3, 11, 12, 13, 21, 23, 34, 203,
224, 230, 232
diseases, vii, 1, 4, 9, 16, 19, 21, 27, 29, 35, 43, 54,
55, 62, 70, 92, 95, 105, 124, 170, 189, 199, 214,
219, 222, 226, 228, 229, 231, 232
disequilibrium, 8, 13
disinhibition, 190
disorder, vii, viii, ix, x, 1, 6, 9, 11, 13, 40, 51, 61, 62,
76, 83, 99, 100, 101, 104, 105, 106, 115, 121,
127, 128, 136, 141, 146, 147, 169, 170, 188, 213,
215
dissonance, 134, 173
distress, 107, 108, 112, 116, 159, 164, 166, 170
distribution, vii, 1, 21, 33, 139, 199, 221, 222, 236
diversity, 72, 143
divorce, 112, 130, 135
DNA, v, vii, viii, 1, 8, 13, 14, 18, 21, 25, 30, 44, 55,
61, 62, 63, 64, 65, 66, 67, 69, 70, 71, 72, 73, 107,
112, 114, 121, 123, 124, 125, 173, 178, 179, 189,
221, 223
DNA damage, viii, 61, 63, 64, 65, 66, 67, 70, 71
DNA lesions, 66, 67
DNA ligase, 65, 67, 69, 72
DNA polymerase, 65
DNA repair, ix, 61, 62, 64, 66, 69, 70, 72, 73, 189
DNA testing, 107, 112, 124, 173, 179
dominance, 13, 176
dopamine, 40, 79, 118, 197, 203, 205, 210, 223, 226,
231, 232, 236
dopaminergic, 58, 119, 184, 188, 196, 205, 222, 236
dopaminergic neurons, 222
dosage, 89
dosing, 203
drawing, 131, 139, 146, 156, 161
Drosophila, 24, 26, 30, 35, 55, 56, 57
drug delivery, 202
drug therapy, 79, 230
drugs, ix, 75, 76, 79, 80, 81, 178
duration, 12, 76, 83, 190, 219
dynamics, 157, 179
dysarthria, 87, 190
dysphagia, 78, 83, 88, 96, 190
dysphoria, 114, 115
dystonia, 7, 9, 40, 77, 78, 80, 82, 190
E
eating, 82, 88, 89, 190
economic status, x, 99, 113
Education, 124, 171, 180
elderly, 14, 96, 97, 187, 233
electrophysiological properties, 183
243
244
Index
F
factual knowledge, 164
failure, 7, 70, 105, 195, 196, 202, 206, 210
family history, 106, 111, 128, 143, 170
family life, 175, 177
family members, x, 76, 77, 84, 91, 102, 103, 104,
106, 109, 114, 118, 127, 128, 135, 138, 139, 141,
143, 144, 147, 151, 153, 157, 160, 162, 163, 164,
165, 166, 189
family planning, 78
family structure, 146
family support, 146
family system, 143, 179
family therapy, 135, 145
familyError! Bookmark not defined. structure, 146
FAS, 50, 53
fatty acids, 83
FDA, 24
fear, 106, 107, 153, 176
fears, 111, 164
feedback, 90, 131, 132, 147
feelings, 104, 107, 111, 115, 116, 118, 138, 155, 164
females, 103, 112, 113, 115, 169
fermentable carbohydrates, 93
fertility, 7, 148, 152, 157, 172, 173, 177, 200
fertilization, 168
fetal, 133, 140, 173, 176, 177, 178
fetal abnormalities, 133, 173, 178
fetal tissue, 214
fetus, 141, 152, 158
fetuses, 141, 142, 158
fibroblast growth factor, 184, 216, 223, 226, 236
fibroblasts, viii, 61, 63, 64, 69
fibrosis, 162, 169, 176
financial support, 54
firearms, 103
first degree relative, 124, 235
fluid, 83, 216
fluoxetine, 81, 187, 201, 223, 228
focusing, x, 100, 129, 133, 137, 189
food, 83, 88, 94, 95, 153
food intake, 83
forebrain, 219, 222, 228, 231, 234, 236
foundations, 174
Fox, 137, 173
fragmentation, 221
fragments, 18, 22, 23, 24, 31, 32, 35, 191, 193, 195,
208, 209, 223, 227, 229, 234
free radicals, 195
freedom, 131, 137, 140, 153
freedom of choice, 137, 140
frontal cortex, 17, 116, 197
frustration, 90, 164
fusion, 31, 223
G
GABA, 184, 185, 195, 196, 198, 216, 223, 230
GABAergic, 236
gait, 9, 78, 87
gamete, 152, 156, 168
gametes, 139, 155, 159
Ganglia, 196
gender, 10, 11, 143, 144, 157
gene expression, 12, 17, 18, 24, 28, 32, 33, 45, 55,
56, 193, 225, 230
gene promoter, 22, 55, 200
gene targeting, 233
general anesthesia, 91
General Health Questionnaire, 116, 117, 121
general practitioner, 188
generation, 14, 20, 24, 83, 143, 144, 145, 150, 151,
152, 156, 161, 163, 165, 168, 188, 224
generators, 133
genes, 2, 4, 13, 19, 24, 25, 32, 42, 44, 45, 46, 48, 50,
51, 58, 59, 65, 128, 162, 170, 199, 209, 228
genetic counselling, 16, 140, 142, 143
genetic defect, vii, 1, 18
genetic disease, 54, 105, 177
genetic disorders, 138, 170, 173
genetic factors, 11, 110, 128, 166, 190
genetic information, 114, 142, 167
genetic linkage, 8, 13
genetic marker, 13
genetic screening, 122
genetic testing, ix, 99, 100, 101, 107, 108, 109, 111,
113, 114, 119, 120, 121, 128, 130, 133, 141, 144,
145, 146, 147, 152, 153, 155, 156, 157, 158, 159,
164, 165, 169, 170, 173, 176, 179
genetics, x, 2, 4, 56, 123, 128, 139, 141, 144, 145,
146, 147, 164, 176, 177, 178, 179, 180, 188
genome, viii, 39, 48, 50, 66, 191, 200
genotype, 9, 14, 47, 69, 203, 233
Germany, 140
GHQ, 116, 117
gingival, 89
gingivitis, 89, 94
glia, viii, 2, 21, 51, 63, 182, 183, 195, 205, 236, 237
glial, x, 181, 182, 183, 184, 186, 195, 196, 216, 231
Glial, 194
Index
glial cells, x, 181, 182, 195
glioma, 59, 207
gliosis, 210
globus, 17, 20, 51, 196, 216
glucocorticoids, 230
glucose, 51, 57, 95
glucose oxidase, 95
glutamate, 20, 34, 51, 57, 187, 194, 195, 196, 199,
200, 209, 219, 227, 238
glutamic acid, 232
glutamine, 189, 217, 219, 237
glycerin, 95
glycolysis, 51, 57
goals, 95, 131, 134, 137, 155, 157, 163, 165
G-protein, 199
grades, 16, 21
grading, 17, 116
granule cells, 229, 234
gray matter, 12
groups, 9, 84, 88, 105, 107, 109, 110, 111, 112, 130,
142, 144, 146, 170, 188
growth, 25, 32, 35, 89, 183, 184, 186, 187, 202, 204,
205, 207, 208, 211, 212, 213, 215, 216, 217, 219,
223, 225, 226, 227, 228, 229, 230, 236
growth factor, 25, 32, 35, 183, 184, 186, 187, 202,
205, 207, 208, 211, 212, 213, 215, 216, 217, 219,
223, 225, 226, 227, 228, 229, 230, 236
growth factors, 183, 184, 186, 187, 202, 205, 207,
208, 212, 213, 215, 225, 228
guanine, viii, 61, 64, 66, 69, 189, 216
guidance, 51, 171
guidelines, 77, 80, 100, 144, 147, 176, 177
guilt, 106, 107, 151, 157
gynecomastia, 7
H
hairpins, 66, 67, 192
haploinsufficiency, 191
haplotypes, 13, 33
Harvard, 172, 180
head and neck cancer, 183
health, ix, 76, 83, 87, 88, 89, 90, 91, 92, 93, 95, 96,
97, 100, 108, 109, 110, 114, 117, 129, 133, 135,
140, 151, 163, 164, 167, 169, 173, 174, 175, 176,
177, 178, 180
health care, ix, 83, 87, 88, 91, 93, 95, 100, 140, 151,
163
health care professionals, 83, 95, 140, 151, 163
health care system, 100
health education, 90
health problems, 95, 133
health psychology, 129, 167, 178
health services, 177
245
246
Index
hypothesis, 20, 22, 24, 25, 28, 44, 47, 64, 68, 77,
109, 111, 196
hypoxia, 51, 59
I
ideal, 13, 83, 92, 132
identification, ix, 20, 45, 57, 75, 76, 101, 142, 159,
165
identity, 132, 133, 138, 139, 141, 155, 160, 162, 232
idiopathic, 222
IFN, 220
image, x, 128, 129, 133, 134, 167
images, 133, 134, 135, 139
immunocytochemistry, 222
immunohistochemistry, 229
immunoprecipitation, 42
immunoreactivity, 51, 210, 214, 236
impaired energy metabolism, 194
impairments, 7, 70, 82, 188, 199, 215, 228, 229
implementation, 95, 98, 106, 131, 133, 162, 163,
164, 165
in situ, 186, 213
in situ hybridization, 17
in vitro, 27, 42, 46, 48, 66, 67, 69, 70, 92, 168, 182,
183, 192, 223, 225, 226, 233, 234, 237
in vitro fertilization, 168
in vitro fertilization (IVF), 168
in vivo, 12, 22, 25, 33, 35, 55, 57, 62, 68, 72, 92,
183, 184, 187, 192, 214, 225, 226, 227, 228, 232,
233, 234
incentive, 150, 168
incidence, 89, 107, 118, 119, 140
inclusion, 4, 29, 192, 219
independence, 78, 117, 139
indexing, 109
India, 39, 54, 55, 57
indication, 64, 65, 68, 117, 150, 155, 157, 159
individual differences, 108, 153, 154, 170
infection, 88, 95
infertile, 138, 153, 168
infertility, 136, 137, 138, 150, 176, 177
inflammation, 88, 205, 228
inflammatory, 199, 205
inflammatory response, 205
information processing, 157, 227
information seeking, 155, 157, 176
inheritance, 4, 13, 83, 140, 167, 169
inherited, 143, 152, 170
inherited disorder, 29
inhibition, 24, 28, 30, 92, 196, 222, 232
inhibitor, 31, 51, 183, 184, 186, 219
injections, 200, 206, 207, 231
injury, 21, 91, 183, 206, 207, 208, 211, 214, 215,
230, 234, 235
inositol, 25, 36
input, 159
insanity, 100, 188
insemination, 138
insertion, 3, 191, 200
insight, viii, 39
instability, ix, 3, 14, 15, 31, 34, 61, 62, 63, 64, 65,
67, 68, 70, 71, 72, 189, 195, 223, 226, 228
insulin, 6, 184, 216, 227
insulin resistance, 6
insurance, 105, 106, 112
intentions, 133, 135, 137, 150, 159
interaction, vii, 2, 26, 27, 31, 41, 42, 44, 45, 46, 50,
54, 55, 58, 67, 70, 72, 83, 111, 134, 157, 224
interactions, vii, viii, 1, 2, 4, 24, 25, 26, 28, 30, 32,
39, 41, 42, 45, 46, 48, 54, 58, 68, 72, 73, 118,
142, 143, 193, 236
interdisciplinary, 173
interface, 92, 183, 214
interferon, 186, 216
interleukin, 186, 216
internet, 90
interneurons, 16, 21, 64, 182, 196
interpersonal factors, 142
interpersonal relations, 174
interpretation, 166, 208, 213
interval, 11, 165
intervention, 78, 117, 124, 167, 201, 215, 228
interview, 79, 106, 117, 123, 137, 144, 146
interviews, 146, 147, 165, 166
investment, 159
ion channels, 34, 199
Ireland, 113
irritability, 81, 114
ischaemia, 183, 186
ischemia, 225, 234
isolation, 23, 77, 105, 136, 197, 230
Italy, 61, 75
IVF, 168
J
Japan, 40
jobs, 115, 139
judgment, 118, 137
justification, 142
K
kainic acid, 216, 221, 230
kidney, 42, 43, 125
kinetics, 220
Index
L
lactoferrin, 95
language, 11, 78, 82, 146
late-onset, x, 127, 128, 129, 141, 142, 147, 169
later life, 141
law, 149, 173, 180
lead, 191, 192, 196, 215
learned helplessness, 237
learning, x, 105, 115, 116, 139, 152, 159, 169, 170,
172, 180, 181, 182, 187, 199, 214, 224, 228, 234,
235, 236, 237
learning difficulties, 170, 172
Lesion, 208, 221
lesions, viii, x, 35, 61, 63, 66, 67, 73, 89, 181, 182,
183, 186, 207, 208, 209, 213, 219, 222, 223, 229,
233
life cycle, 152
life expectancy, 15
life experiences, 111
life satisfaction, 109, 111, 114
life span, 22, 83, 200
lifespan, 200, 212
likelihood, x, 29, 99, 101, 114, 130, 170
limbic system, 197, 198, 214
limitation, 129
limitations, 129, 159, 161, 164
Lincoln, 177
line, 27, 110, 111, 162, 183, 184, 189, 223, 232
linear, 131, 165
linkage, 8, 13, 66, 71, 100, 112, 113, 118, 144, 153,
157, 158, 189
links, 55, 136, 149, 162
lipopolysaccharide, 186, 216, 220
liquids, 83, 88, 89
liver, 42, 43
localization, viii, 2, 8, 16, 22, 23, 31, 32, 34, 36, 50,
52, 223, 224, 229, 233, 237
locomotor, 233
locus, 30, 35, 156, 167, 180
Locus of Control, 180
London, 168, 171, 172, 173, 174, 175, 176, 177, 178,
179
longevity, 182, 203
longitudinal study, 224, 235
long-term potentiation, 216, 221
Long-term potentiation, 199
Long-term potentiation (LTP), 199
love, 104, 164, 171
low risk, 152, 158, 159
LPS, 186, 205, 216
LTP, 199, 204, 207, 216
Luo, 220
247
lymph, 42
lymph node, 42
lymphoblast, 28
lymphocytes, 68
lysozyme, 95
M
machinery, 16, 65, 199
magnetic resonance, 17
magnetic resonance imaging, 17
maintenance, 91, 224, 228
Maintenance, 231
major depression, 81, 114, 115, 120, 225, 228, 237
majority, 14, 23, 50, 101, 107, 112, 113, 136
males, 103, 112, 115, 169
mammalian brain, 182, 215, 221, 231
mammalian cells, 238
management, ix, 28, 75, 76, 77, 80, 84, 91, 94, 96,
97, 114, 123
mapping, 8, 13
marriage, 111, 135, 150, 172, 176, 177, 180
mass spectrometry, 42, 46
matrix, 207, 238
maturation, x, 181, 183, 215
meanings, 147, 174
measures, 12, 78, 130, 140, 170
medical care, ix, 87, 128
medication, 89, 94, 105, 115
medicine, 145, 175, 177, 180
memory, x, 11, 78, 82, 140, 166, 181, 182, 190, 224,
232, 237
men, 104, 112, 113, 138, 141, 155, 157, 176, 188
menopause, 151
mental disorder, ix, 99, 100, 101, 105, 115
mental health, 117
mental illness, 100
mental model, 147, 172
mental retardation, 3, 6, 35
mental simulation, 131, 132, 163, 165
mental state, 16
messenger RNA, 216, 221
meta-analysis, 134, 174
metabolism, 20, 25, 32, 33, 35, 57, 194, 199, 210,
225
methodology, 82, 145, 172
Mexico, 102
MHC, 220
microdialysis, 230
microenvironment, x, 181, 182, 186, 187, 202, 204,
205, 212, 214, 215, 232
Microenvironment, 181, 186, 214
microglia, 186, 205, 219, 220, 222, 228, 233
microscopy, 18
248
Index
N
narratives, x, 127, 133, 135, 136, 147, 152, 153, 166,
172
National Health Service, 172
natural, 133, 137, 161, 167, 174
necrosis, 186
negative consequences, 100, 107
Index
NMR, 225
noise, 90
noradrenaline, 187, 205, 211, 213
Noradrenaline, 185, 198, 211, 212, 213
norepinephrine, 226
normal, 138, 141, 142, 150, 151, 152, 164, 171
norms, 137, 138, 172
Norway, 102, 124
novel stimuli, 202, 213, 215
nuclear family, 76
nuclei, 20, 23, 65, 116, 196, 238
nucleic acid, 64
nucleotides, 65, 69
nucleus, vii, viii, 2, 16, 18, 20, 21, 22, 23, 24, 25, 31,
32, 34, 35, 45, 50, 51, 65, 116, 192, 193, 194,
196, 197, 199, 210, 211, 212, 217, 223, 226, 230,
233
nurses, 84, 92, 97, 176
nutrition, 76, 83, 191
O
observations, 12, 14, 20, 24, 47, 67, 137, 139, 146,
159, 164, 188, 204
occupational therapy, 96
oculomotor, 87, 218
odor memory, 232
olanzapine, 76, 79, 81
olfactory, 182, 197, 211, 217, 219, 220, 223, 229,
231, 232
oligomerization, 233
opportunities, 95, 155
opposition, 140, 150
oral cavity, ix, 87, 90, 91
oral health, ix, 87, 88, 89, 90, 92, 93, 95, 96
oral health problems, 95
order, 16, 68, 77, 82, 83, 84, 113, 118, 131, 134, 143,
145, 146, 152, 153, 156, 157, 158, 162, 164, 166,
168, 189, 197
organelles, 20
organic disease, 105
organization, 174
organizational culture, 171
ovarian cancer, 170
ovarian cancers, 170
overlap, 184, 205
overload, 27, 134
oxidation, 63, 64, 68, 69
oxidative damage, 64, 66, 71
oxidative stress, viii, 40, 61, 63, 64, 65, 68, 83
P
p53, 46, 47, 50, 51, 53, 55, 58, 235
249
250
personality, ix, 7, 84, 87, 99, 100, 104, 111
personality characteristics, 84
personality disorder, 7
personality factors, 111
persuasion, 174
pessimism, 111, 117, 120
PET, 118, 119, 197, 217, 231
phenomenology, 15, 132
phenotype, vii, 1, 9, 14, 20, 23, 30, 31, 36, 187, 189,
190, 191, 192, 193, 199, 200, 201, 202, 213, 222,
228
pheochromocytoma, 35
Phoenix, 174
phosphate, 195, 216
phosphorylation, 12, 27, 29
physical activity, 220
physical exercise, 212
physical interaction, 42
physical resemblance, 143
physiology, 218
pilot studies, 145
placebo, 81, 83
planning, ix, 12, 78, 99, 101, 108, 133, 137, 171, 190
planning decisions, 171
plaque, 90, 92, 93, 94, 95
plasma, 71, 200
plasma membrane, 200
plasticity, 28, 72, 73, 193, 198, 199, 204, 213, 214,
215, 230, 231, 234, 235, 236
pneumonia, 88, 89, 96, 103, 150
polarization, 175
polymerase, 65
polymorphism, ix, 34, 61, 65, 68
polymorphisms, 13
poor, 67, 82, 88, 89, 92, 190
population, viii, ix, 9, 13, 61, 62, 63, 66, 81, 96, 97,
99, 101, 102, 103, 105, 106, 107, 108, 109, 110,
113, 115, 118, 125, 133, 143, 170, 182, 189, 202,
206, 223, 228
positive reinforcement, 90, 91
positron, 118, 197, 217
positron emission tomography, 118, 197, 217
power, 132, 175
precursor cells, 182, 223, 225, 230
prediction, 120
preference, 45, 93
prefrontal cortex, 34, 204, 217
pregnancy, 140, 149, 154, 155, 159, 167, 168, 178
pregnant, 154, 159, 173
pregnant women, 173
premature death, 106, 164
prenatal care, 142
prescription drugs, 178
Index
pressure, 82, 118, 172, 177, 179
pressure sore, 82
prevention, 23, 78, 93, 97, 98, 174
private, 130, 136, 137, 139, 149, 162, 168
proactive, 156, 167, 168
probability, 142, 179
problem solving, 11, 12, 136
production, vii, 2, 28, 223, 230, 234
profession, 151
progenitor cells, 182, 219, 220, 221, 226, 227, 229,
230, 233, 236
prognosis, 149
program, 82, 83, 91, 92, 100, 106, 107, 108, 110,
114, 116, 122, 179, 230
progressive neurodegenerative disorder, vii, viii, 1,
6, 40, 61, 62
project, 16, 100, 121
prolactin, 234
proliferation, 183, 184, 202, 204, 205, 207, 208, 210,
211, 212, 213, 214, 215, 218, 219, 220, 221, 222,
223, 224, 225, 226, 227, 228, 229, 230, 232, 236,
237, 238
promoter, 22, 51, 193, 200, 201, 213
properties, 25, 58, 183, 226, 236, 237
prophylaxis, 91
prosthesis, 92
protective role, vii, 2
protein, 183, 184, 187, 188, 189, 191, 192, 193, 194,
199, 200, 201, 202, 207, 210, 216, 217, 219, 220,
222, 223, 224, 230, 233, 234, 235
protein family, 50
protein misfolding, 21
protein-protein interactions, 26, 28, 54, 193
proteins, vii, viii, 1, 2, 4, 18, 19, 20, 21, 23, 24, 25,
26, 30, 31, 33, 39, 40, 41, 42, 43, 44, 45, 46, 47,
48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 65, 67, 68,
69, 70, 71, 72, 76, 78, 89, 184, 192, 193, 195,
196, 199, 209, 225
proteolysis, 22, 23, 24, 32, 195, 222, 229
protocol, x, 94, 100, 120, 168
PSD, 194, 210, 217
psychiatric disorders, 7, 73, 105, 112, 211, 214, 215
psychiatric illness, 113
psychiatry, 124
psychological distress, 107, 112, 170
psychological problems, 112
psychologist, 111, 122
psychology, x, 127, 129, 145, 167, 171, 174, 175,
176, 177, 178, 180
psychosocial stress, 223
Psychosomatic, 178
psychotic symptoms, 79
purines, 71
Index
Purkinje, 191
Purkinje cells, 191
pyramidal cells, 191
Q
qualitative differences, 206
qualitative research, 172, 174, 176, 177, 179
quality control, 16
quality of life, 76, 79, 84, 88, 95, 96, 97, 108, 109,
141, 150, 154
questionnaire, 146, 165, 176
quetiapine, 81
quinolinic acid, 217, 219, 224, 228, 231, 232, 233,
235
Quinones, 233
R
rain, 182, 202, 226
range, vii, 1, 3, 10, 11, 12, 14, 15, 48, 117, 130, 133,
144, 145, 154, 159, 168, 190, 200
rapamycin, 192, 216
reactions, 100, 108, 112, 113, 114, 118, 124, 149,
162, 164, 178, 189
reason, 101, 107, 133, 142, 146, 155, 160, 162, 211
recall, 11, 91, 92, 165, 166
receptor agonist, 200
receptors, 25, 36, 56, 57, 184, 194, 199, 210, 220,
235
recognition, 2, 11, 69, 96, 106, 130, 132, 138, 167,
229
recombination, 8, 13, 72
recommendations, 93
reconstruction, 17
recovery, 91, 227
reduction, 187, 192, 193, 198, 199, 202, 204, 206,
210
reflection, 129, 137
regenerative capacity, 213
region, viii, 8, 13, 23, 24, 33, 34, 40, 43, 61, 63, 64,
191, 193, 207, 212
regional, 146, 219
regulation, 28, 34, 54, 55, 62, 129, 206, 213
rehabilitation, ix, 75, 78, 82, 83, 84, 91
rehabilitation program, 82
reinforcement, 90, 91, 92, 178
rejection, 141, 142
relationship, 10, 11, 12, 27, 29, 31, 89, 112, 121,
135, 137, 145, 156, 165, 187, 192, 218, 224
relationships, 135, 137, 148, 150, 158, 163, 165, 177
relatives, 14, 77, 84, 101, 104, 105, 106, 118, 124,
152, 164, 235
relevance, 14, 25, 232
251
S
saccadic eye movement, 190
sacrifice, 203, 206
safety, 77, 82, 178
salivary glands, 89
sample, 145, 212
satisfaction, 109, 110, 111, 114
schizophrenia, 34, 76
schizophrenic patients, 81
scientific community, 215
scores, 82, 108, 114, 116
search, 8, 25, 43, 46, 69, 131, 134, 147, 176, 179
252
secrete, 183, 184
seizures, x, 181, 182, 183, 186, 190, 201, 202, 203,
205, 206, 207, 209, 219, 225, 231
selective serotonin reuptake inhibitor, 186, 187
selectivity, 12, 194
self injurious behavior, 114
self-efficacy, 129
self-esteem, 138
self-identity, 138
self-renewal, 234
self-repair, 183, 202, 211
sensitivity, 37, 94, 194, 195, 208, 210, 213, 227, 230,
231
sensitization, 36, 235
serotonin, 186, 187, 205, 211, 216, 226
Serotonin, 185, 198, 205, 211, 212, 218, 237
sertraline, 81
services, 141, 144, 164, 177
severity, 9, 12, 16, 34, 41, 115, 169, 194, 210, 219
sex, x, 99, 113, 158, 236
shape, 129, 130, 134, 142, 156
shaping, 132, 154, 156, 167
sharing, 3, 84, 135
shock, 57, 114, 200
short-term memory, 11
sibling, 156, 163, 166, 179
sibling support, 163
siblings, 9, 13, 103, 144, 152, 156, 163, 165, 166
side effects, 79, 81, 88
signal transduction, 199
signaling, 227, 228, 234, 235
signaling pathway, 25, 50, 51, 53
signalling, 62, 184, 193, 199, 205, 227
signs, 51, 78, 81, 104, 110, 114, 115, 194, 200
similarity, 133
simulation, 131, 132, 163, 165
simulations, 131
sites, 207, 214, 219, 237
skeletal muscle, 12, 33, 35, 232
skills, 111, 115, 116, 150
sleep-wake cycle, 190, 230
small intestine, 42
social activities, 146
social attitudes, 118
social consequences, 100
social context, 77, 84, 140, 165, 168
social costs, 118
social evaluation, 168
social events, ix, 99, 101
social influence, 130
social influences, 130
social learning, 180
social learning theory, 180
Index
social life, 105
social network, 111, 130
social psychology, 175
social relations, 84
social relationships, 84
social sciences, 173
social skills, 111
social support, 108, 111, 129, 148, 149, 154, 162,
165
social workers, 84
sociology, 145, 172
sodium, 30, 93, 94, 222
software, 147
somatic cell, 72
somatostatin, 195, 217
Sonic hedgehog, 226, 228
South Africa, 101, 113, 122
species, 19, 186, 192, 195, 206, 211
spectroscopy, 225
spectrum, 3, 64, 80
speech, 7, 9, 82, 83, 88, 96
speed, 82, 150
sperm, 170, 236
spermatogenesis, 189, 193
spinal cord, 237
spine, 203, 210, 235
sprouting, 203, 219
stability, 66, 82
stabilization, 91, 97
stabilizers, 78, 81
stages, x, 131, 134, 144, 151, 152, 160, 162, 164,
165, 181, 190, 194, 196, 206, 212, 218
stakeholders, 135
statistics, 120, 142
status epilepticus, 80
stem cells, 182, 184, 202, 211, 213, 214, 218, 221,
222, 223, 224, 227, 229, 230, 233, 234, 235, 236,
237, 238
sterilization, 140, 159
stigma, 106
stigmatized, 175
stimulus, 12, 211
storytelling, 132
strain, 186, 203, 206, 208
strategies, viii, 11, 13, 28, 29, 40, 78, 82, 83, 94, 97,
106, 131, 132, 138, 149, 152, 155, 156, 160, 163,
165, 168, 228
strategy, 18, 27, 108, 117, 148, 152, 153, 157, 164,
175
stress, viii, 40, 61, 63, 64, 65, 68, 71, 83, 89, 106,
108, 109, 116, 138, 163, 167, 179, 195, 204, 210,
223, 228, 229
Index
striatum, vii, viii, 1, 12, 13, 16, 17, 18, 20, 21, 24,
51, 54, 57, 58, 61, 63, 67, 69, 70, 71, 183, 186,
188, 191, 194, 195, 196, 197, 198, 200, 204, 205,
207, 208, 210, 211, 212, 213, 221, 226, 229, 230,
231, 232, 235, 236
stroke, 92, 93, 96, 218, 220, 231, 236
subgranular zone, x, 181, 182, 217, 225
subjective, 137, 149
substance abuse, 112
substantia nigra pars compacta, 217
substrates, 67, 218
subventricular zone, x, 181, 182, 217, 218, 220, 223,
225, 228, 231, 236
suicidal behavior, 119, 122
suicidal ideation, ix, 77, 79, 81, 99, 106, 109, 110,
111, 112, 114, 115, 116, 117, 118, 120, 122, 124
suicide, ix, 81, 99, 100, 101, 102, 103, 104, 105, 106,
107, 108, 109, 110, 111, 112, 113, 114, 115, 116,
117, 118, 119, 120, 121, 122, 123, 124, 125, 188,
190
suicide attempts, x, 99, 101, 104, 105, 110, 111, 112,
116, 118, 119
suicide rate, ix, 99, 101, 102, 103, 110, 111, 113, 115
Sun, 24, 36, 55, 56, 194, 208, 225, 235
surveillance, 169, 170
survival, 30, 56, 186, 192, 201, 203, 205, 215, 220,
223, 225, 226, 228, 232, 237
survival rate, 203
susceptibility, ix, 28, 88, 99, 100, 130, 208, 231, 232,
233
swallowing, 190
Sweden, 99, 106, 110, 113, 114, 123, 178
swelling, 209, 210
Switzerland, 179
symbols, 164
symptom, 12, 77, 80, 88, 104, 105, 114, 115
symptoms, viii, ix, 9, 12, 13, 15, 16, 20, 22, 28, 40,
51, 61, 62, 65, 68, 69, 70, 75, 76, 78, 79, 80, 81,
82, 84, 87, 89, 95, 101, 104, 106, 108, 109, 113,
114, 115, 116, 117, 118, 141, 169, 170, 188, 190,
194, 196, 197, 200, 202, 213, 233
synaptic plasticity, 28, 72, 193, 230, 234
synaptic transmission, 32, 199
synaptic vesicles, 25, 51
synaptogenesis, 207
syndrome, 2, 3, 36, 115, 170, 189, 190, 234, 235
synthesis, 12, 66
T
tardive dyskinesia, 79
targets, viii, xi, 2, 28, 64, 181
taxonomy, 130, 136, 142
TBP, 7, 24
253
254
Index
transcription, 20, 24, 25, 26, 31, 34, 35, 36, 40, 44,
45, 55, 58, 59, 65, 184, 192, 193, 199, 231, 235,
238
transcription factors, 24, 25, 36, 44
transforming growth factor, 219
transgene, 28, 69
transgenic, 186, 191, 192, 193, 198, 200, 202, 203,
204, 208, 210, 214, 220, 221, 223, 224, 225, 226,
227, 228, 230, 231, 232, 234, 235, 236, 238
transmission, 2, 4, 11, 32, 76, 89, 187, 188, 199
transplantation, 125, 189, 202, 215
transport, 18, 20, 25, 26, 27, 29, 30, 36, 48, 50, 51,
55, 62, 191, 193, 199, 219, 223
trauma, 186, 237
tremor, 6, 7, 80, 188, 190, 200
trial, 81, 89
trophic support, 214
tropism, 218, 238
tumor, 55, 238
typology, 130
tyrosine, 32
U
UK, 107, 121, 172, 174, 178
uncertainty, x, 101, 107, 108, 127, 132, 138, 141,
143, 156, 157, 159, 168, 174, 180
uniform, 9
United States, 93, 94, 122, 123
unplanned pregnancies, 154, 159
V
values, x, 128, 130, 131, 132, 133, 134, 135, 137,
139, 140, 142, 148, 149, 153, 154, 155, 156, 160,
162, 163, 165, 167, 172, 174
variability, 3, 47, 62, 73
variance, 10, 62, 190
variation, 164, 235
variations, 16, 47, 63, 102, 147, 150, 160, 165
vasculature, x, 181, 182, 206
VEGF, 184, 185, 187, 205, 212, 217, 222
W
weakness, 6, 7, 82
wealth, 40
weight changes, 190
weight loss, 11, 79, 83, 200
weight reduction, 76
wellbeing, 140
well-being, 108, 109, 114
western blot, 46
western countries, 140
Western Europe, vii
white matter, 207, 230, 235
wholesale, 136
wild type, viii, 39, 40, 41, 42, 43, 45, 46, 54, 68, 217
wives, 104
women, 112, 113, 133, 138, 139, 140, 141, 142, 145,
155, 157, 158, 165, 170, 173, 174, 175, 177, 187,
190, 237
workers, 67, 84, 93, 101
working memory, 190
X
xerostomia, 88, 89, 90, 92, 93, 94, 95
X-linked, 138, 169, 175
Y
YAC, 22, 31, 201, 202, 209, 210, 217, 224, 238
yeast, 25, 41, 46, 48, 217
Yugoslavia, 102, 124