CamptodactylyArthropathyCoxa

Camptodactyly-arthropathy-coxa vara syndrome (CACP) is a rare autosomal recessive genetic disorder characterized by camptodactyly (finger flexion deformities), noninflammatory arthropathy with persistent joint effusions, and coxa vara deformity of the hip. The condition is caused by biallelic mutations in the PRG4 gene, which encodes lubricin, a boundary lubricant essential for normal synovial joint function. Loss of lubricin leads to noninflammatory joint swelling and contractures.

Clinical features typically appear in infancy or early childhood and include camptodactyly of the fingers along with swelling of multiple large joints without signs of inflammatory arthritis. Hip involvement with coxa vara can cause gait abnormalities; other joints such as the knees, wrists, and ankles may be affected. Some patients may develop mild pericardial or other serous effusions. Inflammatory markers (ESR, CRP) are usually normal. Imaging often shows joint effusions without erosions, and radiographs reveal coxa vara.

Diagnosis rests on clinical presentation, imaging findings of a noninflammatory arthropathy, and confirmed genetic testing identifying PRG4 mutations. It is important to distinguish CACP from inflammatory arthropathies such as juvenile idiopathic arthritis, which may have similar joint swelling but inflammatory signs and erosions.

Management is supportive and multidisciplinary. There is no cure; treatment focuses on maintaining range of motion through physical therapy, orthopedic interventions for deformities when needed, and symptomatic pain management. Monitoring for serous effusions and associated complications, along with genetic counseling for families, is recommended. Prognosis varies with severity of contractures; overall lifespan is not typically affected. See also: PRG4, lubricin; camptodactyly.