Diabetes mellitus type 1 is one of the most complex diseases with the highest incidence in Mexico; the DQB1*05:01 and DQB1*02:01 alleles that occur in linkage disequilibrium with the DRB1*03:01 [46] allele, are presented with a frequency >1%. The gene discussed is HLA-DRB1; the disease is type 1 diabetes mellitus.