Lubricin is defined as a chondroprotective glycoprotein corresponding to proteoglycan 4 (PRG4), superficial zone protein (SZP), megakaryocyte stimulating factor (MSF) precursor, and camptodactyly-arthropathy-coxa vara-pericarditis (CACP) protein [14–17]. Here, PRG4 is linked to arthropathy.