HLA-DRB1 and autoimmune disease: The dominant genetic risk factor in IIMs, including IBM, is found in the major histocompatibility complex (MHC) within alleles of the evolutionarily highly conserved multigene human 8.1 ancestral haplotype defined by alleles HLA A*0101: Cw*0701: B*0801: DRB1*0301: DQA1*0501: DQB1*0201 [36-38], which has been identified as a risk factor in several autoimmune diseases including the autoimmune GRDs.