Lubricin, also designated proteoglycan-4 or megakaryocyte stimulating factor, is important for boundary lubrication within articulating joints. It is a disulfide-linked homodimer (between Cysteine 1146 and Cysteine 1403) that is essential for protein cleavage. Lubricin inhibits synovial cell adhesion to the cartilage surface, but also prevents the deposition of proteins from synovial fluid onto cartilage. Lubricin is highly expressed in cartilage, liver and synovial tissue. Defects in the gene encoding for lubricin can cause Jakobs syndrome, also designated camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP). CACP is an autosomal recessive disorder characterized by joint failure associated with noninflammatory synoviocyte hyperplasia and subinitimal fibrosis of the synovial capsule. Lubricin undergoes different levels of glycosylation and may be detected at varying molecular weights.