HLA-DRB1 and type 1 diabetes mellitus: T1D is primarily determined by genetic predisposition, with HLA class II genes, particularly HLA-DRB*103-DQA*105-DQB*102 (DR*3-DQ*2) and HLA-DRB*104-DQA*103-DQB*103:02 (DR*4-DQ*8), as well as HLA class I genes (HLA- A*24, HLA- B*18, and HLA- B*39 alleles), playing a key role.