Among the genetic factors, there is overwhelming evidence linking RA to genes of the classical major histocompatibility complex (MHC) [7], known in humans as Human Leukocyte Antigen (HLA), a 3.6 megabase-pair (Mb) region of the genome located on the short arm of chromosome 6 (6p21). The gene discussed is HLA-C; the disease is rheumatoid arthritis.