Studies in type 1 diabetes examining homozygous HLA-DR3 (DRB1*03:01-DQA1*05:01-DQB1*02:01) individuals [57], HLA-DQ8 (HLA-DQA1*03:01-HLA-DQB1*03:02) homozygosity [58], or individual DRB1*03-DQB1*02 and DRB1*04:01-DQB1*03:02 homozygous genotypes [59] also highlight the complexity of the interaction of HLA homozygosity with extended haplotypes and the important effects of genotypic epistasis. Here, HLA-DRB1 is linked to type 1 diabetes mellitus.