PRG4 and camptodactyly-arthropathy-coxa vara-pericarditis syndrome: Since most identified CACP disease-causing mutations in PRG4 abolish lubricin production, the sensitivity of the competition ELISA as a diagnostic test for CACP should be high; however, other diagnostic strategies including sequencing of PRG4, will be required for the minority of patients with CACP who have mutations that affect lubricin function rather than production.