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Published in final edited form as:
Arthritis Rheum. 2012 March ; 64(3): 895–907. doi:10.1002/art.33368.
Mutations in PSMB8 Cause CANDLE Syndrome with Evidence of
Genetic and Phenotypic Heterogeneity
Yin Liu, MD1,*, Yuval Ramot, MD, MSc2,3,*, Antonio Torrelo, MD4, Amy S. Paller, MD, MS5,
Nuo Si, BM6, Sofia Babay, BSc3, Peter W. Kim, MD7, Afzal Sheikh7, Chyi-Chia Richard Lee,
MD, PhD8, Yongqing Chen, MD, PhD1, Angel Vera, MD9, Xue Zhang, MD, PhD6, Raphaela
Goldbach-Mansky, MD, MHS1,*, and Abraham Zlotogorski, MD2,3,*
1National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of
Health Bethesda, MD, USA
2Department
of Dermatology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
3Center
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for Genetic Diseases of the Skin and Hair, Hadassah-Hebrew University Medical Center,
Jerusalem, Israel
4Departments
of Pediatric Dermatology, Hospital Niño Jesús, Madrid
5Departments
of Dermatology and Pediatrics, Feinberg School of Medicine, Northwestern
University, Chicago, IL, USA
6McKusick-Zhang
Center for Genetic Medicine and State Key Laboratory of Medical Molecular
Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & Peking
Union Medical College, Beijing, China
7National
Human Genome Research Institute, National Institutes of Health Bethesda, MD, USA
8National
Cancer Institute, National Institutes of Health Bethesda, MD, USA
9Hospital
Carlos Haya, Málaga, Spain
Abstract
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Objective—Chronic atypical neutrophilic dermatosis with lipodystrophy and elevated
temperature (CANDLE) syndrome is an autoinflammatory syndrome recently described in
children. We investigated the clinical phenotype, genetic cause and the immune dysregulation in
nine CANDLE patients.
Methods—Genomic DNA from all patients was screened for PSMB8 (Proteasome subunit beta
type-8) mutations. Serum cytokine levels were measured from four patients. Skin biopsies were
evaluated immunohistochemically and blood microarray profile (n=4) and stat-1 phosphorylation
(n=3) were assessed.
Results—One patient was homozygous for a novel nonsense mutation in PSMB8 (c.405C>A)
suggesting a protein truncation, four patients were homozygous and two were heterozygous for a
previously reported missense mutation (c.224C>T), and one patient showed no mutation. None of
these sequence changes was observed in chromosomes from 750 healthy controls. Of the four
patients with the same mutation, only two share the same haplotype indicating a mutational hot
Address correspondence to: Abraham Zlotogorski, MD, Department of Dermatology, Hadassah-Hebrew University Medical Center,
Jerusalem 91120, Israel, zloto@cc.huji.ac.il, Phone: +972-507874158 or Raphaela Goldbach-Mansky, MD, MHS, NIAMS, NIH,
Bethesda, MD 20892, USA, goldbacr@mail.nih.gov, Phone: +301-435-6243.
*These authors contributed equally to this work
Conflict of interest: None.
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spot. PSMB8 mutation-positive and -negative patients expressed high IP-10 (Interferon gammainduced protein 10) levels. Levels of MCP-1, IL-6, and IL-1Ra were moderately elevated.
Microarray profiles and monocyte stat-1 activation suggested a unique interferon (IFN) signaling
signature, unlike in other autoinflammatory disorders.
Conclusion—CANDLE is caused by mutations in PSMB8, a gene recently reported to cause
JMP syndrome (joint contractures, muscle atrophy and panniculitis induced lipodystrophy) in
adults. We extend the clinical and pathogenic description of this novel autoinflammatory
syndrome, thereby expanding the clinical and genetic disease spectrum of PSMB8-associated
disorders. IFN may be a key mediator of the inflammatory response and may present a therapeutic
target.
Auto-inflammatory diseases were first characterized more than 10 years ago by episodic,
systemic and organ-specific inflammation (1, 2). These disorders differ from autoimmune
diseases in that they primarily result from perturbations in the innate immune system, rather
than in adaptive immunity, although overlapping features may occur (2, 3). During the past
decade, the genetic basis for many autoinflammatory diseases has been revealed (1).
Elucidating the underlying molecular basis for these monogenic disorders has increased the
understanding of inflammation and has led to improved therapy, particularly interleukin-1
(IL-1) inhibition for patients with cryopyrin-associated periodic syndromes (CAPS) (4).
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Chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature
(CANDLE syndrome) is a newly described autoinflammatory condition, now reported in
five patients (5, 6). It is characterized by onset during the first year of life, recurrent fevers,
purpuric skin lesions, violaceous swollen eyelids, arthralgias, progressive lipodystrophy,
hypochromic or normocytic anemia, delayed physical development and increased acute
phase reactants. Variable clinical features include hypertrichosis, acanthosis nigricans and
alopecia areata (5, 6). The skin biopsy findings of a characteristic atypical, mixed
mononuclear and neutrophilic infiltrate further confirm the diagnosis (5). A genetic etiology
was suggested, possibly inherited in an autosomal recessive pattern. In order to elucidate the
molecular basis of CANDLE syndrome, we performed genome-wide analysis and
sequencing in eight families with nine affected patients.
MATERIALS AND METHODS
Patients
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The present study includes nine patients (3 Spanish, 3 Hispanic, 1 Ashkenazi Jew and 2
American/Caucasian) from eight families who were seen at five international centers (two in
Spain, Israel and two in the US). The study was approved by the institutional review board
at the respective sites and written informed consent was obtained from the subjects or their
parents. Blood samples were collected from eight patients and their unaffected family
members where available. All of the patients included in this study were discussed among
the lead investigators of the five centers to ensure the diagnosis of CANDLE before they
were included. All patients had to have episodic fevers, typical erythematous eruptions,
arthralgia/arthritis and evidence of systemic inflammation (elevation of acute phase
reactants). In addition, a skin biopsy showing an atypical mixed myeloid, neutrophilic, and
histiocytic infiltrate positive for myeloperoxidase and CD68 had to be present. Patients 1–4
were previously described by Torrelo et al. (5), and patient 5 was reported by Ramot et al.
(6); patient 3 died at 14 years of age, and blood samples were not available for analysis (5).
Patients 6–9 have not been described before.
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Genetic Analysis
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A genome-wide analysis of single-nucleotide polymorphisms was performed using the
GeneChip Human Mapping 250K SNP Array of Affymetrix. For this analysis we used the
blood samples of patients 1, 2, 4, 5 and 9. Genome-wide homozygosity analysis was
performed by Homozygosity Mapper (7).
In parallel with the conventional Sanger sequencing, we also performed whole exome
sequencing in patient 5. DNA captured with the Agilent SureSelect Human All Exon 50Mb
kit was sequenced on an Illumina HiSeq 2000 platform. Sequence data were analyzed with a
custom bioinformatics pipeline.
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To identify additional mutations in PSMB8 (Proteasome subunit beta type-8) in the two
patients who are heterozygous for the PSMB8 mutation T75M, and in the patient who did
not have any mutation in PSMB8 on exonic sequencing, we sequenced the other five exons
and all of the introns of the longest isoform of PSMB8 (Ensemble nomenclature,
PSMB8.001). Alternative and cryptic splicing events were ruled out by sequencing the
cDNA. We searched for genomic deletions by long range PCR with primers spanning the
entire gene and ruled out the possibility of a heterozygous deletion at the primer binding site
by sequencing the c.224C>T mutation using the long range PCR amplicon as template. In
patients 6 and 7 both the maternal and paternal copies are present at PSMB8 locus, and the
PSMB8 cDNA is of full-length (8). Assuming digenic inheritance in patient 7, we sequenced
all the other beta subunits from PSMB1 to PSMB10 and two alpha subunits (PSMA6 and
PSMA7). PSMB8 mRNA levels are similar to healthy controls by RT-qPCR from cDNA
made from peripheral blood.
In silico modeling
A structural model of both mutations identified was assembled. Structures are based on a
previously published model (9). Figures were made with Pymol.
Cytokine Analysis
Serum was collected from patients 6, 7 and 8 and stored at −80°C. Cytokine concentrations
were measured using the Bio-Plex system (Bio-Rad) in batches including patient control and
healthy serum.
Microarray analysis
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Total RNA was extracted from blood samples collected in Paxgene tubes (from patients 4, 6,
7, and 8) and processed as recommended by the manufacturer (Qiagen). RNA integrity was
analyzed with an Agilent 2100 Bioanalyzer. cDNA synthesis and target amplification was
done with the NuGene Ovation® Whole Blood Solution kit. Affimetrix HU-133 plus 2.0
gene chips were used for hybridization. Data analysis was done with Genespring 11.5
software and Partek software, after removal of non-annotated genes. Genes differentially
expressed in comparison to the mean expression in healthy controls were at least 2 fold
higher (FCH>2) with a p-value less than 0.05 adjusted for multiple hypotheses testing and
controlling the false-discovery rate (FDR) (FDR<0.05). Groups were compared using the
two-tailed Welch t-test. DEGs were then analyzed in Ingenuity pathway analysis (IPA)
(Ingenuity Systems, Inc., http://www.ingenuity.com) to investigate dysregulated canonical
pathways and gene ontology. Results for interferon induced genes were plotted as a heat
map with upregulated genes in shades of red and downregulated genes in shades of blue.
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Cell stimulation and Stat-1 phosphorylation assay
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Peripheral blood mononuclear cells (PBMC) were isolated by standard Ficoll density
gradient centrifugation and frozen in liquid nitrogen. Cells were thawed, washed and
resuspended in 0.1% BSA PBS at 2×106/ml and then aliquoted at 0.5ml per tube. For studies
with the small molecule JAK kinase inhibitor tofacitinib[3-[(3R,4R)-4-methyl-3[methyl(7H-pyrrolo[2,3-d]pyrimidin-4-yl)amino]piperidin-1-yl]-3-oxopropanenitrile,
synthesized by Dr. Craig Thomas, NCGC/NIH], cells were treated with the inhibitor for 15
min before stimulation. Cells were stimulated with various concentrations of IFN-γ or
control PBS buffer at 37°C for 15 min, fixed with 4% paraformaldehyde and then stained
with CD14.PE and pSTAT1 Alexa 647 (BD Pharmingen) and analyzed with BD
FACSCanto according to standard procedures. Data were analyzed with Flowjo software.
Immunohistochemistry and Special Stains
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Punch biopsies of lesional skin were fixed in 10% neutral buffered formalin and routinely
processed. Serial tissue sections of 5-μm thickness were made and spread on poly-L-lysine
coated glass slides. Immunohistochemical staining was carried out using the Ventana
Benchmark XT fully automatated slide preparation system (Ventana Medical Systems, Inc)
using the following antibodies: MPO (DAKO; 1:1000 dilution), CD163 (Novacastra
Laboratories: 1:100 dilution), and KP1/CD68 (DAKO: 1:400 dilution). Staining is
developed with 3, 3′-diaminobenzidine tetrahydrochloride and counterstained with Meyer’s
hematoxylin and mounted. Leder staining (Naphthol AS-D chloracetate esterase or specific
esterase), which identifies cells of the granulocyte lineage, from the early promyelocyte
stage to mature neutrophils, was carried out using the Sigma-Aldrich 91C-1KT following
manufacturer’s protocol.
RESULTS
Clinical characteristics in patients with CANDLE
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Table 1 summarizes the demographic characteristics and clinical presentation of the affected
children. Most patients presented within the first 2–4 weeks of life (all by 6 months of age)
with fever and repeated attacks of erythematous and violaceous, annular cutaneous plaques,
lasting for a few days or weeks and leaving residual purpura. Later during infancy, patients
developed persistent periorbital erythema and edema, finger or toe swelling and
hepatomegaly with variable elevation of acute phase reactants. Other common clinical
features that developed in the first years of life included progressive loss of peripheral fat
(lipodystrophy), failure to thrive, lymphadenopathy and hypochromic or normocytic anemia.
More variable findings included perioral swelling, parotitis, conjunctivitis/episcleritis,
acanthosis nigricans and hypertrichosis, chondritis, aseptic meningitis, interstitial lung
disease, nephritis, epididymitis, hypertriglyceridemia and intermittent positivity of ANA or
ANCA autoantibodies (Table 1 and Figure 1). Our series includes 4 previously unreported
patients from non-consanguineous families: two Caucasian males and a Hispanic female
from the USA (patients 6–8), and one Caucasian male from Spain (patient 9) (Figures 1A–
G). An MRI from the thigh showed irregular enhancement of fat, suggesting panniculitis,
but no myositis (Figures 1H, I). Synovial enhancement, consistent with joint discomfort and
arthralgia and/or arthritis was also seen (Figure 1J).
Responses to treatment have been variable (Table 1). Most clinical symptoms, including
cutaneous eruption, joint pain and fever respond to high doses of steroids 1–2mg/kg/day, but
rebound with tapering (around 0.5mg/kg/day). Responses to steroid sparing agents have
been inconsistent. Methotrexate in combination with calcineurin inhibitors have permitted
administration of lower doses of steroids, however skin and joint flares with fever in
between led to the further addition of biologics. TNF-alpha inhibitors have provided
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temporary improvement in some cases, but flares in others. Anti-IL-1 therapy has not
allowed a decrease in steroids, and IL-6 blocking agents have normalized acute phase
reactants and anemia, but have had limited success in reducing the cutaneous eruption and
improving fatigue (dose ranges of biologics see Table 1). The lipodystrophy has invariably
progressed despite immunosuppressive therapy.
Histological evaluation identifies a dense dermal infiltrate of immature neutrophils and
activated macrophages
Skin biopsies stained with hematoxyilin and eosin (H&E) were reviewed from all patients.
Characteristic features included a dense interstitial infiltrate of mononuclear cells with
nuclear atypia and both mature and immature neutrophils, with areas of karyorrhexis (Figure
2A,B). Interstitial dermal collagen degeneration is seen. Immunohistochemical staining
disclosed a mononuclear infiltrate composed of immature neutrophils/myeloid precursors
(myeloperoxidase and Leder stains, Figure 2C), as well as atypical mononuclear cells that
are most likely activated macrophages (positive for CD68-KP1 and CD163, negative for
Leder stain) (Figure 2D–F).
Genetic analyses reveal that mutations in PSMB8 cause CANDLE
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A region of homozygosity shared by four patients (patients 1, 2, 4 and 5) was identified in
chromosome 6p21 (haplotype cluster rs6924453- rs3763341) (Figure 3A), but not in patient
9. This region spans ~2.7Mb, and includes 164 genes, including 120 protein-coding genes,
encompassing the major histocompatibility complex. Given that CANDLE is an immunemediated disease, with prominent involvement of the skin and adipose tissues, we performed
direct sequencing of the following candidate genes: AGPAT1 (gene ID 10554), TRIM27
(gene ID 5987), ITGB1 (gene ID 3688), SLC39A7 (gene ID 7922), NOTCH4 (gene ID
4855), SLC44A4 (gene ID 80736) and PSMB8 (gene ID 5969).
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Sequencing of the six exons of the PSMB8 gene in patient 5 revealed a homozygous c.
405C>A mutation in exon 3, changing cysteine at amino acid 135 to a stop codon (p.C135X;
in accordance with ENST00000374882 transcript) (Figure 3B, supplementary Table 1). The
cysteine at position 135 is highly conserved across species. A homozygous missense
mutation, c.224C>T, which leads to the substitution of threonine with methionine at position
75 (p.T75M), was found in the patients 1, 2, 4 and 8. Interestingly, two patients were
heterozygous for the mutation (patients 7 and 9) and, despite extensive analysis, no second
mutation has been found; one patient (patient 6) shows no mutation in PSMB8. The
genotype of the deceased pt 3 was deduced from her sister (pt 4) as both had the same
disease. Mutations for the neighboring subunit PSMB2, and the other immunoproteasome (iproteasome) specific subunits PSMB9 and PSMB10 were negative, but further analyses are
ongoing (Figure 3C, supplementary Table 1). None of these sequence changes was observed
in 750 healthy controls, including 100 Ashkenazi Jews.
Whole exome sequencing done in parallel generated 2.4 Gb of mappable sequence data and
achieved 20-fold coverage of the targeted exome. On average, 57.74% of the bases
originated from the targeted exome, with 81% of the targeted bases covered at least four
times. Initial variant sites calling (>4x) resulted in the identification of 20,012 genetic
variants, including 153 within the shared homozygous region on chromosome 6p21. Eight
individual reads were mapped back to the genomic position of the c.405C>A PSMB8
mutation, confirming the homozygous nonsense mutation (Figure 3D).
In silico analysis suggests improper formation of the immunoproteasome
We modeled mutations identified in PSMB8 in a ribbon diagram (Figure 4A). The β units of
the i- proteasome are organized in 2 overlying rings containing 7 subunits each. Two of the
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mutations, one previously published in adults with severe lipodystrophy (p.T75M) (10) and
the novel nonsense mutation, p.C135X, identified in the Jewish patient are shown (left
image). The p.C135X mutation leads to a large deletion of the terminal 141 amino acids of
the inducible β5i subunit. Intact residues are shown as red and deleted residues are shown as
gray. The deleted residues would normally interact with the neighboring β4 subunit in the
same ring, but also bind to the β4 unit of the adjacent ring (right image). The nonsense
mutation therefore provided us with structural evidence that the i-proteasome, which
requires the incorporation of the β5i subunit, cannot form. The T75 amino acid that is
mutated in the other patients is represented by a purple ball.
Functional analyses suggest an inflammatory response involving the interferon pathway
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To assess the dysregulated inflammatory response in CANDLE patients, we performed
cytokine profiling in serum from peripheral blood of 3 patients: one patient with PSMB8
mutations on both alleles; one with only one identified PSMB8 mutation to date; and one
without a detectable mutation in PSMB8. All showed very high, but variable levels of IP-10.
Mean IP-10 levels in CANDLE patients were 77 fold higher than those observed in healthy
controls and more than 30 fold higher than in untreated patients with an IL-1 mediated
autoinflammatory syndrome neonatal-onset multisystem inflammatory disease (NOMID).
Other cytokines that were significantly elevated in CANDLE patients compared to healthy
controls and NOMID patients were MCP-1 and RANTES (Figure 4B). Notably, IL-6 and
IL-1Ra were modestly elevated not only in CANDLE syndrome patients, but also in patients
with NOMID.
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The very high levels of IP-10 suggested excessive interferon responses in CANDLE patients
(Supplementary figure 1). To probe for evidence of excessive IFN signaling in CANDLE
patients in vivo, we assessed the transcriptome in whole blood microarray analysis in four
CANDLE patients and four age and gender matched healthy controls. CANDLE patients
had 507 genes (650 transcripts) that were more than two-fold differentially expressed
compared to healthy controls (p<0.05) (Supplementary table 2). Differentially expressed
genes (DEGs) were analyzed by the Ingenuity pathway analysis (IPA) program to identify
dyregulated canonical pathways and the IFN pathway was the most differentially regulated
in CANDLE patients (p=4.73E-06). Of the IFN induced gene list in IPA, most were IFN-γ
induced (n=42) and 6 were also regulated by IFNα/β. The genes were plotted on a colorcoded heat map and the pattern of increased (shades of red) and decreased DEGs (shades of
blue) were strikingly similar among CANDLE patients, regardless of the presence or
absence of detectable PSMB8 mutations (Figure 4C). IP-10 (CXCL10) which is highly
expressed in the patients’ serum was among the IFN induced upregulated genes. We also
compared our DEG list to interferon regulated genes published in www.interferome.org and
119 of the 507 DEGs were found to be interferon regulated.
Since Stat-1 is a downstream mediator of interferon-α/β and -γ signaling, we studied Stat-1
phosphorylation in the monocytes in response to IFN-γ stimulation. Compared with
monocytes from healthy controls and a patient with NOMID, monocytes from CANDLE
patients showed stronger Stat-1 phosphorylation in response to all IFN-γ concentrations used
for stimulation (Figure 5A).
To assess the effect of various treatments the patients received on the IFN induced genes,
blood samples from multiple visits were obtained in two patients, including one patient
treated at different times with anti-TNF-alpha and anti-IL-6 therapy (supplementary figure
2). Although temporary clinical improvement was seen with anti-TNF-alpha and anti-IL-6
treatment (unpublished observation), the “IFN signature” did not improve. IL-6 blocking
therapy normalized IL-6 inducible genes (data not shown) and CRP levels, however, skin
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lesions, fatigue or joint pain did not significantly improve and peripheral fat loss progressed,
suggesting a possible association between the IFN signature and disease activity.
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JAK kinases are critical signaling molecules mediating IFN signaling on the IFN receptors.
To determine the effect of a JAK kinase inhibitor, tofacitinib, on the excessive interferon
response in CANDLE patients, we assessed its inhibiting effect on stat-1 phosphorylation in
patients’ monocytes stimulated with IFN-γ. Tofacitinib decreased stat-1 phosphorylation in a
dose dependent manner in both CANDLE patients and healthy control monocytes (Figure
5B). Tofacitinib also inhibited IFN-γ induced IP-10 production in PBMC in a dose
dependent manner and its inhibitory effect was more efficient than with the IL-1 receptor
agonist anakinra or anti-IL-6 blockade with tocilizumab (data not shown). As tofacitinib and
other agents blocking the IFN pathways are not available to use as a treatment in our
patients, we could not assess the effect of blocking the IFN signaling pathway on the clinical
and laboratory symptoms of CANDLE patients.
DISCUSSION
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In the current study we identified mutations in the PSMB8 gene as the cause of CANDLE
syndrome, extending the phenotypic spectrum of a novel recently described
autoinflammatory syndrome caused by PSMB8 mutations (10). We also identified
dysregulation of the IFN signaling pathway and suggest that the interferon pathway may be
a target for treatment in these patients.
After the original report of CANDLE syndrome in four children, a syndrome diagnosed in
three adult patients with joint contractures, muscle atrophy, microcytic anemia, and
panniculitis-induced childhood-onset lipodystrophy was reported under the acronym “JMP”
(10). Patients with JMP were recently demonstrated to carry a mutation in the PSMB8 gene
(8). The patients described were homozygous for the same mutation, p.T75M, that we found
in five of our patients (8, 10).
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Although CANDLE patients have some overlapping features with JMP patients, including a
cutaneous eruption and lipodystrophy (10), none of our patients has developed joint
contractures and muscle atrophy was not a prominent disease feature, although two patients
(1 and 7) developed an acute, self-healing attack of myositis. CANDLE patients, on the
other hand, showed several key features that have not been described in the JMP patients,
particularly recurrent febrile episodes, elevated acute phase reactants and a characteristic
neutrophilic dermatosis with a mononuclear interstitial infiltrate including “immature”
neutrophils in the dermis that seems pathognomonic for CANDLE syndrome. In fact two
patients have been misdiagnosed as acute cutaneous myelogenous leukemia. Nevertheless,
the detection of the same and additional mutations in PSMB8 unifies these disorders as a
novel i-proteasome associated autoinflammatory syndrome. Clinical reports of children with
disease manifestations that closely resemble CANDLE syndrome from families in Japan and
Lebanon (11–13) might allow for the discovery of further molecular causes of this disease.
While our data in young children illustrate manifestations of early severe, and potentially
lethal disease and alert to the fact that muscle involvement and joint contractures may not
present until later in life, the findings in the adult patients likely illustrate the natural course
of the disease in untreated or partially treated patients (10, 11).
In one of our patients, no mutation in PSMB8 was discovered, and two patients showed a
mutation in only 1 allele, despite sequencing the entire exonic and intronic sequence of the
gene. In the boy without a mutation on either allele (patient 6), we similarly found no
mutation in sequencing the two other i-proteasome specific subunits. These data indicate
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genetic heterogeneity underlying CANDLE syndrome and raises the prospect of other genes
as the genetic cause for CANDLE syndrome.
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The gene mutated in CANDLE, PSMB8, encodes the inducible β5i subunit of the
proteasome, a protein complexe that consists of two α rings and two β rings, each ring is
formed of 7 different globular α or β-subunits. Proteasomes are evolutionary conserved
cylindrical structures that are critical for protein degradation (14). Upon IFN stimulation
critical subunits of a constitutive proteasome, the β1, 2 and 5 subunits, are replaced with
inducible i-subunits, β1i, β2i and β5i, to form i-proteasomes which are highly expressed in
hemopoietic cells (15).
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The functions of the i-proteasomes have been studied in vitro and in animal models. The iproteasome can generate antigenic peptides for MHC class I presentation (16), but recent
data in psmb8/lmp7 knockout mice (17) suggest an important additional role in maintaining
cell homeostasis by removing accumulating proteins marked for degradation from the cells
(18). Cellular stress such as infections or radiation lead to type I IFN induced production of
reactive oxygen species and newly synthesized proteins that are particularly sensitive to
oxidation (19–21). Failure to process/degrade protein will result in formation of ubiquitinrich cytoplasmic aggregates or inclusions and consequently increase cellular sensitivity to
apoptosis (18). It is thought that the excessive demand for protein processing/degradation is
mainly met by cytokine-mediated upregulation of the ubiquitination machinery and
increased assembly of the highly efficient i-proteasome (22, 23).
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The persistent IFN signature in CANDLE patients on microarray and the increased Stat-1
phosphorylation in monocytes from CANDLE patients in response to IFN-γ stimulation
could reflect ongoing “cellular stress” in CANDLE patients. In concordance with the current
understanding of the i-proteasome function, we have suggested a disease model
(supplementary figure 1) which proposes that defects in i-proteasome function may lead to
accumulation of damaged proteins resulting in more cellular stress and a vicious cycle of
increased IFN signaling. Interestingly, CANDLE flares are observed with infections and
other stressful events. Some cells such as fat or muscle cells may be subject to cellular
apoptosis due to accumulation of damaged proteins. In fact a Japanese patient with severe
fat loss, muscle atrophy and suspected CANDLE syndrome died of cardiac failure at the age
of 47. Histological examination of skeletal muscle on autopsy revealed intramitochondrial
paracrystalline inclusions and cytoplasmic and myeloid bodies in muscle cells (24). Whether
the inclusions seen constitute accumulation of oxidant damaged/aggregated proteins that
cause cell death is an attractive hypothesis to account for muscle loss later in life, but studies
on the cell specific effect of the i-proteasome deficiency are needed to explain the observed
visceral effects of the mutations.
IP-10 is a type I or type II IFN induced protein, that functions as a C-X-C motif chemokine,
also known as CXCL10 (supplementary figure 1). It is produced in a variety of cell types,
including endothelial cells, keratinocytes, fibroblasts, mesangial cells, monocytes, dendritic
cells, neutrophils and activated T cells (25). IP-10/CXCL10 is an important chemoattractant
for effector T cells, its serum level has been shown to correlate with the extent of T cell
infiltration in the tissue. IP-10 may contribute to the pathology in CANDLE patients by
acting as a chemoattractant for T cells into tissues such as the skin with the described
inflammatory infiltrate. Whether the inflammatory skin infiltrate of immature neutrophils
and activated myeloperoxidase positive histiocytic cells is a consequence of IFN signaling
needs further evaluation. However, the important role of IFN-γ in the recruitment of
neutrophils through the induction of CCL3 (26) and the stimulation of myeloperoxidase
production in monocyte/macrophages (27) are consistent with a possible pathogenic role of
IFN in skin.
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Given our own data and the clinical reports of devastating disease manifestations in adults,
the outcome of untreated disease is expected to be poor. The partial responses and the
continued need for steroids despite being on treatment with targeted therapies including IL-1
receptor antagonist, TNF-alpha blockage and IL-6 receptor inhibitors (see Table 1) urge the
need for a better understanding of the disease pathogenesis and for identifying more
effective targets for therapeutic intervention. Whether the persistence of the IFN signature
on the treatment with targeted agents offers a clue to a more effective intervention is a
testable hypothesis as agents blocking IFN signaling (including JAK inhibitors) are in
clinical trials.
CANDLE and the other PSMB8-associated syndromes illustrate the profound effect of iproteasome dysfunction on inflammation and organ function. In the current study we have
established PSMB8 as the causative gene for CANDLE syndrome and describe clinical and
histological features that can establish early diagnosis. The mutations in PSMB8, also found
in JMP, illustrate the clinical and genetic spectrum of this novel i-proteasome associated
autoinflammatory syndrome. Further studies to fully explore the role of the i-proteasome in
autoinflammatory diseases and to identify other mutations in PSMB8 mutation negative
CANDLE patients are needed and are ongoing.
Supplementary Material
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Refer to Web version on PubMed Central for supplementary material.
Acknowledgments
This research was supported by the Intramural Research Program of the National Institute of Arthritis and
Musculoskeletal and Skin Diseases at the NIH, and by the Authority for Research and Development, Hebrew
University of Jerusalem (AZ), the Hadassah Medical Center Young Clinician Award (YR).
The authors would like to thank Nikki Plass, RN., Deborah Stone M.D., Dawn Chapelle RN, Sapna Patel Vaghani,
MD, and Rhina Castillo MD, for their help organizing patient visits and patient examinations. Adam Reinhardt MD,
Elizabeth Brown MD, Paulina Navon-Elkan MD and Kristina Rother MD for their collaboration on patient
treatment, Ivona Aksentijevich MD for her help with the interpretation of the genetic data, Hang Pham, MT for her
help with the cytokine analysis, Max Gadina, PhD for his help with the initial cytokine analysis and the sharing of
the synthetic CP-690550 (tofacitinib), and Isabel Colmenero MD, Luis Requena MD and Heinz Kutzner MD for
their help in immunohistochemistry studies.
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Figure 1.
Clinical features of CANDLE syndrome. A–D: Facial features and eruption in patients with
CANDLE. Note the violaceous periorbital discoloration and edema, perinasal erythema, and
significant fat loss most prominent in B. E, F: Finger swelling and violaceous lesions on the
heel and toes. G: Discrete erythematous nodules and post-inflammatory hyperpigmentation.
H, I: T2-weighted MRI of thighs (H) in one patient suggested loss of subcutaneous fat,
particularly on the posterior aspect of both thighs; STIR image (I) showed increased signal
intensity in the subcutaneous fat, suggesting panniculitis (asterisks). J: Synovial
enhancement with rice body formation extending to the suprapatellar pouch.
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Figure 2.
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Histopathology of lesional skin. A: H&E staining showed a dense perivascular and
interstitial mononuclear dermal infiltrate. The overlying epidermis appears unremarkable.
(H&E, 100× original magnification). B: Areas of karyorrhexis are shown. (H&E, 400×
original magnification); C: Leder stain (Naphthol AS-D chloracetate esterase stain or
specific esterase) specifically identifies cells of the granulocyte lineage, from the early
promyelocyte stage to mature neutrophils. At high magnification (C-1: right upper panel),
some of the mononuclear cells are Leder stain-positive, suggestive of immature neutrophils,
and rare mature neutrophils. Another high magnification view (C-2: right lower panel) also
shows karyorrhectic nuclear debris surrounded by a rim of Leder stain positive cytoplasm.
(Leder stain, 400× original magnification). D–F: Staining for the macrophage markers KP-1
(CD68) (D) and CD163 (E), and myeloperoxidase positive cells (F). (Immunohistochemical
stains, 200× original magnification).
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Figure 3.
Genetic analyses. A: Genome-wide homozygosity peaks discovered by
HomozygosityMapper analysis. Black arrow indicates the chromosomal region of
homozygosity shared by four patients (patients 1, 2, 4 and 5). B: Sequence analysis of
PSMB8. a) wild type; b) heterozygous c.405C>A mutation; and c) homozygous c.405C>A
mutation in patient 5. C: Sequence analysis of PSMB8. a) wild type; b) heterozygous c.
224C>T mutation; and c) homozygous c.224C>T mutation in patients 1, 2, 4, 7, 8 and 9. D:
Overview of PSMB8 coverage by exome sequencing demonstrating the identification of a
homozygous mutation in PSMB8.
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Figure 4.
Functional assessment of PSMB8 mutations. A: Structural model of 20S proteasome. The
model on the left shows a ring of β subunits in a proteasome, the inset on the upper right
corner shows the position of the ring in 20S proteasome. The intact residues of the β5i
subunit in the patient with the C135X mutation are shown in red and the deleted residues in
gray. The T75 amino acid is represented by a purple ball. The model on the right shows two
β4 subunits interacting with two β5i subunits on two adjacent rings, the inset on the upper
right corner shows their position in a 20S proteasome. B: Cytokine expression in CANDLE
patients 6, 7, 8, healthy controls, and NOMID patients. Data are shown on a log10 scale with
error bars indicating standard errors of the mean (SEM). C: Whole blood microarray
analysis was done on 4 CANDLE patients and 4 healthy age/gender matched controls. A
color-coded heat map was generated on 42 IFN regulated genes from a transcript list that
were two fold differentially expressed (p<0.05). Red indicates increased expression levels
and blue indicates decreased expression levels compared to the mean of healthy controls.
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Figure 5.
Stat-1 -phosphorylation in CANDLE patients’ monocytes in response to IFN-γ stimulation,
and inhibition by a JAK kinase inhibitor (tofacitinib). A: Stat-1 phosphorylation in response
to 15 min IFN-γ stimulation in monocytes from CANDLE patients, healthy controls and a
NOMID patient. The dashed line indicates an isotype control, the solid gray graph indicates
the response of a healthy control and the solid line of the CANDLE patient. In the lower
panels the bolded dashed line indicates the response of a NOMID patient. B: PBMCs from a
healthy control and from pt7 were stimulated with 10IU/ml IFN-γ for 15 min in the absence
(solid line) and presence of in 0.1 and 0.5μmol of tofacitinib (dashed and dotted lines
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Page 17
respectively). A dose depended inhibition in stat-1 phosphorylation is seen in patient and
control.
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13
1 month
+
+
+
+
+
+
+
Finger swelling
Hepatosplenomegaly
Lymphadenopathy
Low weight and height
Muscle atrophy
Arthritis/arthralgia
Prominent abdomen
Violaceous eyelids
Arthritis Rheum. Author manuscript; available in PMC 2013 March 1.
+
−
+
Basal ganglia calcifications
−
−
+
−
+
Aseptic meningitis
−
−
+
+
Wide-spaced nipples
Slight nose chondritis
+
Ear and nose chondritis
−
+
Hypertrichosis
+
+
+
−
+
−
−
Acanthosis nigricans
+
+
+
Hypochromic anemia and
increased platelet counts
+
+
+
−
+
Hypochromic anemia
+
+
+
+
−
+
+
+
−
+
+ (only hepatomegaly)
+
Yes
+
+
Violaceous annular plaques
1 week
Alive and Failure to thrive
Hispanic
Female
2
Patient 4*
+ (only hepatomegaly)
+
Yes/peripheral and face
+
+
Fever, violaceous plaques and
nodules and hepatomegaly
During 1st 6 months
Deceased age 14 years
Hispanic
Female
Died at 14yrs
Patient 3*
−
+
−
+
−
Conjunctivitis/episcleritis
+
−
+
−
+
Parotitis
+
Hypochromic anemia
+
+/−
+
+
+
+
+ (only hepatomegaly)
+
Yes/upper limbs and cheeks
+
+
Fever and skin lesions
6 months
Alive and Failure to thrive
Spanish
Female
10
Patient 2*
Perioral swelling
MORE VARIABLE FINDINGS
Elevated LFTs
Hypochromic
anemia and
increased platelet
counts
+
Lipodystrophy
Anemia and other hematologic
manifestations
+
Yes/peripheral,
especially face and
upper limbs
Annular plaques
+
Fever and skin
lesions
Recurrent fevers and elevated acute
phase reactants (ESR, CRP)
Symptoms of initial presentation
Age of clinical presentation
Clinical Characteristics
Spanish
Alive and Failure to
thrive
Clinical Outcome
Male
Ethnicity/Origin
Sex
Age yr
Patient 1*
NIH-PA Author Manuscript
Demographic
Characteristics
−
−
+
−
+
−
−
−
+
+
Hypochromic anemia
+
+
+
−
+
−
+ (only hepatomegaly)
+
Yes
+
+
Fever and skin lesions
1 month
Alive and Failure to thrive
Jewish-Ashkenazi
Male
12.5
Patient 5*
ND§
−
−
−
−
−
−
−
−
intermittent
Hypochromic anemia
+
+
+
−
+
+
+
+
Yes/upper and lower body
+
+
Rash and foot swelling, periorbital
erythema
2weeks
Alive and Failure to thrive
Americ/Caucasian
Male
5.5
Patient 6
NIH-PA Author Manuscript
Demographics and Clinical Disease Manifestations
−
ND
−
−
−
+
+
−
−
−
+
Neutropenia and thrombocytopenia
ND
−
−
possible
+
−
−
−
−
−
+
+
−
−
+
−
+
+
−
−
Hypochromic anemia
+
+
+
+
+
−
+
+
+
+
Fever and skin lesions
1 month
Alive
Spanish
Male
2.5
Patient 9
Hypochromic anemia in the past
+
−
−
+
+
−
+
−
+
−
+
−
Upper limit of normal
−
+
yes/upper body
+
+
Fever, violaceous plaques periorbital and
erythema
2 weeks
Alive
Hispanic
Female
6
Patient 8
Yes/upper body mainly proximal
+
+
Periorbital erythema and swelling
2 months
Alive
Amerc/Caucasian
Male
3.5
Patient 7
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Table 1
Liu et al.
Page 18
−
−
−
−
Metabolic manifestations
Autoantibodies (intermittent)
ND demotes not done
NSAIDs Methotrexate
Azathioprine Infliximab
Cyclosporine Rituximab
Pulsed steroids
Coombs-positive hemolytic
anemia Positive lupus
anticoagulant
Hyper- triglyceridemia
NA
Otitis
+
Interstitial lung disease
IVIG Anakinra Dapsone
Ibuprofen Pulsed steroids
−
Hyper- triglyceridemia
NA
Otitis
−
−
Patient 4*
Hydroxychloroquine Pulsed steroids
Alopecia areata and positive C-ANCA
Anakinra** Tocilizumab**
Tocilizumab**
Anakinra** Adalimumab**
Methylprednisolone Adalimumab**
Prednisone†† Methylprednisolone
Tacrolimus** Methotrexate**
Prednisolone†† Tocilizumab**
Methylprednisolone
ANA antibody positive in past
Elevated TSH, high LDL and triglycerides
NA
Recurrent upper respiratory infections
−
−
Patient 8
Prednisolone†† Infliximab**
ANCA 1:20 now negative
+
Otitis and recurrent sinusitis
−
−
Patient 7
Tacrolimus** Methotrexate**
−
Mild hyper- triglyceridemia
−
−
Elevated TSH Triglycerides ND
Otitis and recurrent sinusitis
−
BOOP like
Patient 6
−
−
−
Patient 5*
No
Hypergammaglobuli nemia
Low HDL
−
+
−
−
Patient 9
Prednisone is tapered to control symptoms of fever, rash and joint pain with doses between 0.3–3mg/kg/dose and pulses have been administered in between to control symptoms
††
Drug doses and treatment duration in these patients were known and dose ranges and maximal exposure times were as follows (methotrexate (for greater than 4 years), tacrolimus (4mg/day for greater than 12 months), infliximab (5– 12.5mg/kg/dose q 4 weeks up to 12
months), adalimumab (20–40mg q10 days for 4 months then discontinued), anakinra (1–5mg/kg/day for 3 months), tocilizumab (5–12mg/kg/dose q14 days, 2 patients are still on treatment >6 months, one developed a drug reaction warranting discontinuation), pts 5 and 6 were
on prednisolone and tacrolimus in addition to one biologic, pt 7 is on prednisone in combination with tocilizumab.
**
§
NA denotes: not applicable
†
Patients were previously reported
*
NA†
+
Epididymitis
NSAIDs PUVA Methotrexate
−
−
Recurrent infections
NSAIDs Colchicine
Dapsone
Methotrexate
Etanercept Anakinra
−
−
Nephritis
Treatments
−
−
Lung manifestations
Patient 3*
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Patient 2*
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Patient 1*
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Demographic
Characteristics
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