Genome-wide association studies revealed that approximately half of the genetic risk for T1D is conferred by the genomic region harbouring the major histocompatibility complex (MHC) class II genes, primarily Human Leukocyte Antigen (HLA) DRB1, DQA1, and DQB1 [7,8,9]. The gene discussed is HLA-DRB1; the disease is type 1 diabetes mellitus.