The largest genetic contribution is provided by the major histocompatibility complex (MHC) Class II genes, in particular HLA-DRB1 alleles, several of which (HLA-DRB1*0401, *0404, *0405, *0408, *0101, *0102,*1001 and *1402) are associated with susceptibility to RA. The gene discussed is HLA-DRB1; the disease is rheumatoid arthritis.