Here we consider stratification by HLA diplotype (rather than presence of one haplotype alone), based on the impact of trans-encoded HLA proteins on T1D susceptibility and immune function [8, 68], as observed for the high-risk trans-encoded HLA-DQA1*05:01/DQB1*03:02. The gene discussed is HLA-DQA1; the disease is type 1 diabetes mellitus.