Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome.

Camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP) is a rare autosomal recessive disease caused by mutation in proteoglycan 4 (PRG4) gene on chromosome 1q25-q31. We faced a dilemma and delay in diagnosis in two sisters. The elder sister had pericardial effusion with constrictive pericarditis, underwent pericardiectomy and received empirical treatment for suspected tuberculosis. After 2 years, she developed bilateral knee swelling with restriction of movement. At the same time, her younger sister also presented with bilateral knee swelling which aroused the suspicion of genetic disease. The whole-genome sequencing revealed homozygous PRG4 mutation suggestive of CACP syndrome.