Furthermore, YKL-40 levels in serum and synovial fluids increased in joint diseases like RA (7, 15, 16) and osteoarthritis (OA) (17, 18), indicating that YKL-40 is a marker of inflammation and tissue remodeling or degradation (6); whereas YKL-40 is not observed in normal joints. Here, CHI3L1 is linked to osteoarthritis.