Genotype-phenotype investigation of 35 patients from 11 unrelated families with camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome

Thirteen Indians with camptodactyly-arthropathy-coxa vara-pericarditis syndrome

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome (MIM# 208250) is a rare monogenic disorder, characterized by early onset of camptodactyly, progressive coxa vara, bilateral arthropathy and constrictive pericarditis. The syndrome is caused by biallelic loss-of-function variants in PRG4. Deficiency of PRG4 results in progressive worsening of joint deformity with age. Thirteen individuals with CACP syndrome from eight consanguineous Indian families were evaluated. We used exome sequencing to elucidate disease-causing variants in all the probands. These variants were further validated and segregated by Sanger sequencing, confirming the diagnosis of CACP syndrome in them. Seven females and six males aged 2-23 years were studied. Camptodactyly (13/13), coxa vara (11/13), short femoral neck (11/13) and arthritis in large joints (12/13) [wrists (11/13), ankle (11/13), elbow (10/13) and knee (10/13)] were observed commonly. Five novel disease-causing variants (c.3636G>T, c.1935del, c.1134dup, c.1699del and c.962T>A) and two previously reported variants (c.1910_1911del and c.2816_2817del) were identified in homozygous state in PRG4. We describe the phenotype and mutations in one of the large cohorts of patients with CACP syndrome, from India.

A novel mutation in the proteoglycan 4 gene causing CACP syndrome: two sisters report

BACKGROUND

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome, caused by biallelic pathogenic mutations in the proteoglycan 4 (PRG4) gene, is characterized by early-onset camptodactyly, noninflammatory arthropathy, coxa vara deformity, and rarely, pericardial effusion. This syndrome can mimic juvenile idiopathic arthritis. CACP syndrome is caused by mutations in the proteoglycan 4 (PRG4) gene. To date, only 36 pathogenic mutations have been reported in this gene, but none have been reported from Azerbaijan.

CASE PRESENTATION

Herein, we report two siblings presented with chronic polyarthritis, had a prior diagnosis of juvenile idiopathic arthritis, but was subsequently diagnosed as CACP syndrome with novel mutation in the PRG4 gene.

CONCLUSION

Our report expands the knowledge of PRG4 mutations, which will aid in CACP patient counseling.

Dry synovitis, a rare entity distinct from juvenile idiopathic arthritis

BACKGROUND

Dry synovitis (DS) is a rare entity as only a few cases have been reported to date. We describe the clinical features, radiological manifestations and course of DS in comparison with rheumatoid factor negative polyarticular juvenile idiopathic arthritis (RFneg-polyJIA).

METHODS

We performed a multicenter retrospective collection of data of DS patients who presented with progressive joint limitations without palpable synovitis, absence of elevated acute phase reactants, negative ANA and RF, and imaging showing joint and/or osteochondral involvement. For comparative purposes, we included a cohort of RF neg-polyJIA patients.

RESULTS

Twelve DS patients, 8F/4 M, with mean age at onset of 6.1 years, were included. Presenting signs comprised delayed motor development, functional limitations and/or progressive stiffness. Clinical examination showed symmetric polyarticular involvement with variable muscular atrophy. MRI showed mild, diffuse synovial involvement, without effusion. With time, signs of progressive osteochondral damage became evident, despite treatment. All patients were treated with low-dose corticosteroids and methotrexate. Anti-TNF agents were prescribed in five. The response was variable with limited joint mobility in 11/12, and need of joint replacement in 2. In comparison with a cohort of RFneg-polyJIA, DS patients presented higher number of joint involved (p = 0.0001) and contractures (p = 0.0001), less swelling (p = 0.0001) and prolonged diagnostic delay (p = 0.0001).

CONCLUSION

DS represents a unique juvenile-onset arthropathy, distinct from polyarticular JIA. Awareness among pediatricians is essential for early recognition and proper treatment. Further studies, including synovial pathology, immunology and genetics may contribute to a better understanding of this rare disorder of childhood.

Monogenic disorders as mimics of juvenile idiopathic arthritis

BACKGROUND

Juvenile idiopathic arthritis is the most common chronic rheumatic disease of childhood. The term JIA encompasses a heterogenous group of diseases. The variability in phenotype of patients affected by the disease means it is not uncommon for mimics of JIA to be misdiagnosed.

CASE PRESENTATION

We present four cases who were treated in single tertiary rheumatology centre for JIA who were subsequently diagnosed with a rare monogenic disease. All four patients shared the unifying features of presenting in early childhood and subsequently suffered with refractory disease, not amenable to usual standards of treatment. Multicentric Carpotarsal Osteolysis Syndrome and Camptodactyly-arthropathy-coxa vara-pericarditis syndrome are non-inflammatory conditions and patients typically present with arthropathy, normal inflammatory markers and atypical radiological features. Blau syndrome is an autosomal dominant condition and patients will typically have symmetrical joint involvement with a strong family history of arthritis, signifying the genetic aetiology.

CONCLUSIONS

We share our learning from these cases to add to the growing portfolio of JIA mimics and to highlight when to consider an alternative diagnosis. In cases of refractory disease and diagnostic uncertainty further imaging and genetic testing can play a crucial role in establishing the aetiology. In all of these cases the correct diagnosis was made due to careful, longitudinal clinical phenotyping and a close working relationship between rheumatology, radiology and clinical genetics; highlighting the importance of the multidisciplinary team in managing complex patients.

The superficial zone of articular cartilage

The superficial zone of articular cartilage contributes to smooth joint motion through the production of proteoglycan 4 (PRG4), also known as lubricin. Recent studies indicate novel effects of PRG4 as a signaling molecule, other than a simple extracellular matrix protein. Additionally, the accumulating evidence displays that various molecules and signaling pathways are involved in regulating the superficial zone and PRG4 expression. In addition, Prg4-expressing cells include a progenitor population of articular chondrocytes. Several non-clinical and clinical studies have shown that PRG4 and related molecules are promising candidates for disease-modifying drugs for treating osteoarthritis. Since PRG4 is also expressed in the synovium, tendons, and ligaments, further studies of PRG4-related pathways and PRG4-positive cells may elucidate the mechanisms underlying joint homeostasis.

Quadruped Gait and Regulation of Apoptotic Factors in Tibiofemoral Joints following Intra-Articular rhPRG4 Injection in Prg4 Null Mice

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome leads to diarthrodial joint arthropathy and is caused by the absence of lubricin (proteoglycan 4—PRG4), a surface-active mucinous glycoprotein responsible for lubricating articular cartilage. In this study, mice lacking the orthologous gene Prg4 served as a model that recapitulates the destructive arthrosis that involves biofouling of cartilage by serum proteins in lieu of Prg4. This study hypothesized that Prg4-deficient mice would demonstrate a quadruped gait change and decreased markers of mitochondrial dyscrasia, following intra-articular injection of both hindlimbs with recombinant human PRG4 (rhPRG4). Prg4^−/− (N = 44) mice of both sexes were injected with rhPRG4 and gait alterations were studied at post-injection day 3 and 6, before joints were harvested for immunohistochemistry for caspase-3 activation. Increased stance and propulsion was shown at 3 days post-injection in male mice. There were significantly fewer caspase-3-positive chondrocytes in tibiofemoral cartilage from rhPRG4-injected mice. The mitochondrial gene Mt-tn, and myosin heavy (Myh7) and light chains (Myl2 and Myl3), known to play a cytoskeletal stabilizing role, were significantly upregulated in both sexes (RNA-Seq) following IA rhPRG4. Chondrocyte mitochondrial dyscrasias attributable to the arthrosis in CACP may be mitigated by IA rhPRG4. In a supporting in vitro crystal microbalance experiment, molecular fouling by albumin did not block the surface activity of rhPRG4.

Pseudo-rheumatic manifestations of limping: Camptodactyly-arthropathy-coxa vara-pericarditis syndrome: Single case report and review of the literature

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome is a rare genetic disease characterized by tetrad camptodactyly, noninflammatory arthropathy, coxa vara deformity, and pericardial effusion. Arthropathy typically affects large joints and presents with joint swelling in the absence of other signs of inflammation. We described the case of a girl affected by CACP syndrome caused by a novel compound heterozygous variant in proteoglycan 4 gene (c.2831_2832insT; c.3892C > T) and associated with temporomandibular involvement. The patient received treatment with intra-articular hyaluronic acid injections, which presented rapid but transient improvements of pain and range of motion. A literature review of previously reported CACP patients has been performed. Of the patients. 69.2% (101 out of 146) were Middle Eastern, and 65.7% (96) were consanguineous. The median age of onset was 24 months (interquartile range of 12-36 months), and median age of diagnosis was 96 months (interquartile range of 48-156 months). Arthropathy was always present, mainly involving hips (95.2%), knees (92.4%), wrists (87.7%), elbows (79.5%), and ankles (57.5%). Camptodactyly and pericardial effusion were described, respectively, in 97.3% (142) and 15.1% (22) of patients. The main radiological findings were coxa vara (95.2%), femoral changes (64.4%), intraosseus cysts (14.4%), and bone erosion (5%). Of the patients, 32.9% (48) had received a previous juvenile idiopathic arthritis diagnosis. CACP syndrome can be easily misdiagnosed with juvenile idiopathic arthritis. A prolonged lack of response to immunosuppressive therapy associated with typical clinical and radiological features should prompt consideration of this rare syndrome.

"Lessons from Rare Forms of Osteoarthritis"

Osteoarthritis (OA) is one of the most prevalent conditions in the world, particularly in the developed world with a significant increase in cases and their predicted impact as we move through the twenty-first century and this will be exacerbated by the covid pandemic. The degeneration of cartilage and bone as part of this condition is becoming better understood but there are still significant challenges in painting a complete picture to recognise all aspects of the condition and what treatment(s) are most appropriate in individual causes. OA encompasses many different types and this causes some of the challenges in fully understanding the condition. There have been examples through history where much has been learnt about common disease(s) from the study of rare or extreme phenotypes, particularly where Mendelian disorders are involved. The often early onset of symptoms combined with the rapid and aggressive pathogenesis of these diseases and their predictable outcomes give an often-under-explored resource. It is these "rarer forms of disease" that William Harvey referred to that offer novel insights into more common conditions through their more extreme presentations. In the case of OA, GWAS analyses demonstrate the multiple genes that are implicated in OA in the general population. In some of these rarer forms, single defective genes are responsible. The extreme phenotypes seen in conditions such as Camptodactyly Arthropathy-Coxa Vara-pericarditis Syndrome, Chondrodysplasias and Alkaptonuria all present potential opportunities for greater understanding of disease pathogenesis, novel therapeutic interventions and diagnostic imaging. This review examines some of the rarer presenting forms of OA and linked conditions, some of the novel discoveries made whilst studying them, and findings on imaging and treatment strategies.

Camptodactyly-Arthropathy-Coxa Vara-Pericarditis Syndrome Resembling Juvenile Idiopathic Arthritis: A Single-Center Experience from Southern Turkey

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome, caused by biallelic pathogenic mutations in the PRG4 gene, is characterized by early-onset camptodactyly, noninflammatory arthropathy, coxa vara deformity, and rarely, pericardial effusion. Herein, we report 3 patients with CACP syndrome from 2 unrelated families. All patients are female, born to consanguineous parents, and had camptodactyly since the first years of their lives. Two patients had a prior diagnosis of juvenile idiopathic arthritis. Hip changes were present in 2 patients, and 2 of 3 patients had undergone surgery for camptodactyly. Routine echocardiographic evaluations were normal during the 2-year follow-up. This paper represents the third study including CACP patients from Turkey. Clinically, all 3 patients resembled juvenile idiopathic arthritis cases and received unnecessary medication. There is also an ongoing need for improving awareness of CACP and an effective treatment focusing on the lubrication of the joint space in CACP patients.

Coexistence of a novel WISP3 pathogenic variant and an MEFV mutation in an Arabic family with progressive pseudorheumatoid dysplasia mimicking polyarticular juvenile idiopathic arthritis

BACKGROUND

A spectrum of rare noninflammatory disorders may present with arthropathy that arises from bony dysplasia, a thickened synovium, and noninflammatory effusion, leading to a constellation of clinical features that mimics chronic polyarticular juvenile idiopathic arthritis (JIA). We report a unique Arabic family harboring a novel pathogenic variant in the WISP3 gene and presenting with progressive pseudorheumatoid dysplasia (PPRD), a rare noninflammatory arthropathy mimicking polyarticular JIA.

CASE PRESENTATION

An Arabic family with PPRD was diagnosed using whole-exome sequencing (WES), revealing a novel c.707delG pathogenic variant in the WISP3 gene. The proband was referred at 10 years old for possible diagnosis of polyarticular JIA based on progressive arthropathy for three years. He was already on naproxen and methotrexate. We suspected familial noninflammatory arthropathy based on clinical manifestations, imaging findings, and family history. WES confirmed the molecular diagnosis of PPRD in the proband and one sister with a similar phenotype. An unexpected p.A744S MEFV pathogenic variant was detected in the proband, parents, and affected sister.

CONCLUSIONS

Early identification and diagnosis of familial noninflammatory arthropathies such as PPRD can prevent unnecessary use of immunosuppressive medications. Diagnosis requires high suspicion in children with early onset arthritic changes, absence of elevated inflammatory markers, specific imaging findings, and positive family history suggestive of an autosomal recessive disorder. We highlight the advantages of WES over single-gene analysis in such cases.

Syndrome of progressive deforming non-inflammatory arthritis of childhood: two patients of camptodactyly-arthropathy-coxa vara-pericarditis syndrome

Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome is a rare familial arthropathy of childhood, commonly misdiagnosed as juvenile idiopathic arthritis. It is characterized by non-inflammatory arthropathy, coxa vara deformity, and sterile pericarditis. We describe two children with CACP syndrome who were referred to the rheumatology clinic for the suspicion of inflammatory arthritis. A literature search was carried out using PubMed/ Medline and Embase databases. English language reports of mutation-proven cases of CACP syndrome reported until 31 March 2020 were retrieved and analysed. Both the children had a delay in diagnosis (age at diagnosis- 12 and 13 years, respectively) and had received immunomodulatory therapy for suspected inflammatory arthritis. Presence of symmetrical arthropathy of large joints, camptodactyly, and normal inflammatory parameters are clues that indicated CACP syndrome. One child with a novel variant in PRG4 also had associated mitral valve prolapse and regurgitation. Both had severe constrictive pericarditis requiring pericardiectomy. On literature review, a total of 98 mutation-proven cases of CACP syndrome have been reported till date. Arthropathy in CACP syndrome mainly involves knees, wrists, ankles, and hips. Pericarditis is usually mild, however, can present rarely with severe symptoms requiring surgical intervention. CACP syndrome can closely mimic inflammatory arthritis and early clinical recognition is important to avoid misdiagnosis. Molecular confirmation is essential for early diagnosis and future genetic counselling for affected families.

Genotype-phenotype investigation of 35 patients from 11 unrelated families with camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome

Background

The camptodactyly–arthropathy–coxa vara–pericarditis syndrome (CACP) is a rare autosomal recessive condition characterized by camptodactyly, noninflammatory arthropathy, coxa vara, and pericarditis. CACP is caused by mutations in the proteoglycan 4 (PRG4) gene, which encodes a lubricating glycoprotein present in the synovial fluid and at the surface of articular cartilage.

Methods

In the present study, we compared the clinical and molecular findings of CACP syndrome in 35 patients from 11 unrelated families. In 28 patients, whole exome sequencing was used to investigate genomic variations.

Results

We found that camptodactyly of hands was the first symptom presented by most patients. Swelling of wrists, knees, and elbows began before 4 years of age, while the age of joint involvement was variable. Patients reported an increased pain level after the age of 10, and severe hip involvement developed after 20 years old. All patients presented developmental coxa vara and seven patients (~22%) had pleural effusion, pericarditis, and/or ascites. We identified nine novel genomic alterations, including the first case of homozygous complete deletion of exon 1 in the PRG4 gene.

Conclusion

With this study, we contribute to the catalog of CACP causing variants. We confirm that the skeletal component of this disease worsens with age, and presents the potential mechanisms for interfamily variability, by discussing the influence of a modifier gene and escape from nonsense‐mediated mRNA decay. We believe that this report will increase awareness of this familial arthropathic condition and the characteristic clinical and radiological findings will facilitate the differentiation from the common childhood rheumatic diseases such as juvenile idiopathic arthritis.