COL9A1 (collagen type IX alpha 1 chain), also known as MED. It is expected to be located in extracellular space, and the protein is enriched in the brain, choroid plexus and prostate. This gene encodes one of the three alpha chains of type IX collagen, which is a minor (5-20%) collagen component of hyaline cartilage. Type IX collagen is usually found in tissues containing type II collagen, a fibrillar collagen. Mutations in this gene are associated with osteoarthritis in humans, with multiple epiphyseal dysplasia, 6, a form of chondrodysplasia, and with Stickler syndrome, a disease characterized by ophthalmic, orofacial, articular, and auditory defects. The molecular weight of COL9A1 is 64 kDa.