For the initial genome-wide screen, we recruited 15 T1D–discordant MZ twin pairs (Table S1), selected according to the following criteria: (i) European origin; (ii) both co-twins available for study; (iii) diabetic twin had T1D diagnosed at <20 years of age; (iv) neither twin was receiving drugs other than human insulin for the diabetic twin; (v) diabetic twin had no current major diabetes complications; (vi) non-diabetic twin had low disease risk, that is <2% based on the lack of diabetes-associated autoantibodies (GADA, I-A2A and ZnT8A), and normal glucose tolerance [5], [16]. This evidence concerns the gene INS and type 1 diabetes mellitus.