HLA-DRB1 and type 1 diabetes mellitus: Further work on DRB1 and DQB1 showed that there was LD between these molecules and, along with DQA1, they were found to form part of extended haplotypes DRB1*03-DQB1*02-DQA1*0501 (DR3) and DRB1*04-DQB1*0302-DQA1*0301 (DR4) associated with T1D [2, 31].