While the precocious cartilage failure observed in patients with CACP and in Prg4−/− mice indicates that lubricin is essential for chondroprotection, it is not known whether lubricin dosage that is below wild-type (Prg4+/+) levels, but not completely absent, can also impair chondroprotection. Here, PRG4 is linked to camptodactyly-arthropathy-coxa vara-pericarditis syndrome.