A dramatic increase of Cxcl12 is found in the synovial fluid in the knee joints of rheumatoid arthritis and OA patients.29 Secondly, in vitro experiments have demonstrated that Cxcl12 regulates chondrocyte catabolic activity by stimulating the release of matrix metalloproteinase-3 (MMP-3) and MMP-13.29,30 These findings strongly suggest that Cxcl12 induces articular cartilage matrix degeneration during OA development. The gene discussed is CXCL12; the disease is rheumatoid arthritis.