T1D patients were grouped into those who carry the very high-risk HLA class II genotype known as ‘DR3/4' (DRB1*03:01-DQA1*05:01-DQB1*02:01 and DRB1*04:01/02/04/05/08-DQA1*03:01-DQB1*03:02/04 or *02:01) and those who do not (‘non-3/4'). This evidence concerns the gene HLA-DRB1 and type 1 diabetes mellitus.