A frameshift mutation in the <i>PRG4</i> gene causing camptodactyly-arthropathy-coxa vara-pericarditis syndrome: a case report

Camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP) is an example of a rare non-inflammatory familial arthropathy inherited in an autosomal recessive manner. The proteoglycan 4 (PRG4) gene, located on chromosome 1q25-q31, is responsible for encoding a lubricating glycoprotein found in the synovial fluid and on the surface of articular cartilage. Pathogenic mutations in the PRG4 gene have been associated with CACP disease. The present study investigated the clinical and molecular findings of the patient with CACP. Whole-genome sequencing was performed in this patient to investigate the genomic variations. The case presented in this study is a 20-year-old male who was admitted to the clinic. He had swelling in his wrists and limited mobility in his elbows as well as a family history of anaemia. The patient was initially diagnosed with juvenile idiopathic arthritis (JIA). Further genetic testing revealed a homozygous frameshift variant in the PRG4 gene (C.1290del; p.T431Lfs*481), which was classified as likely pathogenic and consistent with a diagnosis of CACP. Although this specific variant has been previously reported in the literature, this study contributes to the existing body of knowledge by emphasising the importance of comprehensive genetic analysis in differentiating CACP from other childhood rheumatic diseases such as JIA. Additionally, we discuss its location in exon 7 and potential effects on gene expression, including the possibility of nonsense-mediated decay or a truncated protein product.