Bovine cartilage explants, lubricated with lubricin-deficient synovial fluid from humans with camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP), an arthritis-like autosomal recessive disorder, reveal increased friction coefficients and increased chondrocyte apoptosis as compared to normal synovial fluid or CACP synovial fluid to which lubricin has been added [21]. This evidence concerns the gene PRG4 and arthritic joint disease.