HLA-DRB1 and type 1 diabetes mellitus: More recently, it has been established that two positions in DRB1 (13 and 71) together with position 57 of DQB1 capture more than 90% of the phenotypic variance attributed to the HLA locus (9), implicating the P4 and P9 pockets in the antigen-binding groove of DRB1 and DQB1, respectively, in T1D risk.