Several studies in European-descent populations have addressed the frequency of high-risk alleles, including the highest-risk heterozygous genotype HLA-DRB1*03:01-DQA1*05:01-DQB1*02:01/DRB1*04-DQA1*03:01-DQB1*03:02 (HLA-DRB1*04 summarizing the HLA-DRB1*04:01/02/04/05 alleles), in children younger than six years at the time of T1D diagnosis [9,13,14,15,16]. This evidence concerns the gene HLA-DRB1 and type 1 diabetes mellitus.