Any disorder of the joints.

Osteoarthritis (OA) is a degenerative disease of the joints characterized by degradation of the hyaline articular cartilage and remodeling of the subchondral bone with sclerosis (Meulenbelt et al., 2006). Clinical problems include pain and joint stiffness often leading to significant disability and joint replacement. Osteoarthritis exhibits a clear predilection for specific joints; it appears most commonly in the hip and knee joints and lumbar and cervical spine, as well as in the distal interphalangeal and the first carpometacarpal (base of thumb) and proximal interphalangeal joints of the hand; however, patients with osteoarthritis may have 1, a few, or all of these sites affected (Stefansson et al., 2003). According to a conservative estimate, greater than 70% of the population of the United States at age 65 years is affected by the disease, reflecting its age dependence. Genetic Heterogeneity of Susceptibility to Osteoarthritis Susceptibility to osteoarthritis has been associated with variation in other genes: OS2 (140600) with variation in the MATN3 gene (602109) on chromosome 2p24; OS3 (607850) with variation in the ASPN gene (608135) on chromosome 9q22; and OS5 (612400) with variation in the GDF5 gene (601146) on chromosome 20q11. Other susceptibility loci for osteoarthritis have been mapped to chromosomes 2q33 (OS4; 610839) and 3p24 (OS6; 612401).