Camptodactyly-Arthropathy-Coxa Vara-Pericarditis Syndrome Caused by Truncating Mutations in the Prg4 Gene: Case Series and Literature Review.

Introduction: Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome is an autosomal recessive condition characterized by early-onset camptodactyly, noninflammatory arthropathy, coxa vara deformity, and, rarely, pericardial effusion. The disease gene has been assigned to human chromosome regions 1q25-q31, and truncating mutations have been identified in the proteoglycan-4 (PRG4) gene formerly known as megakaryocyte stimulating factor gene.

Methods: A literature review was performed with the findings in patients in terms of CACP syndrome. Also, whole-exome sequencing was performed for all cases. Segregation analyses of the detected variants were performed according to the possibilities.

Results: We present 3 Turkish patients with CACP syndrome mimicking juvenile idiopathic arthritis (JIA). All patients were exposed to biologic therapy due to recalcitrant JIA. We have detected two pathogenic PRG4 variants. Case 3 had a novel pathogenic PRG4 variant not reported for the CACP syndrome so far. These two variants cause premature truncation of the protein. A deletion was detected in case 1 in the homozygous state in the PRG4 gene (NM_005807.6: c.3848del, p.Gly1283GlufsTer6, chr1-186281360-G-). A previously described deletion was detected in case 2 and case 3 in the homozygous state in the PRG4 gene (NM_005807.6: c.1910_1911delCT, p.Pro637ArgfsTer9, chr1-186276761-CT).

Conclusion: In the current study, we report three pathogenic PRG4 variants including a novel mutation. We consider that a detailed anamnesis, including kinship and meticulous physical examination of camptodactyly in the absence of inflammatory response, may reveal CACP syndrome masquerading as JIA. The PRG4 gene analysis presents the early diagnosis for patients and prenatal counseling and preimplantation genetic diagnosis for carrier families.