PRG4-Related Camptodactyly–Arthropathy–Coxa Vara–Pericarditis Syndrome Mimicking Juvenile Idiopathic Arthritis: A Case-Based Review

gene, confirming the diagnosis of camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome (OMIM #208250). PRG4 encodes lubricin, a mucin-like glycoprotein essential for boundary lubrication of articular cartilage and maintenance of synovial joint homeostasis. Loss-of-function variants disrupt joint lubrication, leading to mechanical synovial hyperplasia and chronic non-inflammatory joint effusion. This case highlights common diagnostic pitfalls in pediatric rheumatology and underscores the importance of considering genetic causes of chronic arthropathy when clinical and laboratory features are atypical for inflammatory disease. Early molecular diagnosis prevents unnecessary immunosuppressive therapy and enables appropriate multidisciplinary management.