HLA-DRB1 and type 1 diabetes mellitus: The DRB1*03:01:01~DQA1*05:01:01~DQB1*02:01:01 haplotype exhibited a higher frequency of homozygosity in the group of early age at onset, indicating that this haplotype in homozygous form confers a higher risk of developing T1D at an early age.