CHI3L1 and osteoarthritis: Comparison of the expression of YKL-39 and YKL-40 in osteoarthritic cartilage revealed, that YKL-39 mRNA is significantly up-regulated in cartilage of patients with osteoarthritis (OA) versus normal subjects, while no significant up-regulation was detected for YKL-40 mRNA in OA cartilage (Steck et al. 2002).