The replicated T2DM risk loci fall into three categories (Table S1): (i) those that impact the T2DM risk through impaired β-cell function (ALX4, BCL11A, CDKAL1, CDKN2A/B, GCK, HNF1A, HNF1B, HNF4A, IGF2BP2, JAZF1, KCNJ11, KCNQ1, SLC30A8, TCF7L2, WFS1); (ii) those that act through modulating insulin action (ADAMTS9, DUSP9, PPARγ); and (iii) those that were primarily associated with BMI, obesity and adiposity but subsequently identified also as affecting T2DM risk through insulin action (FTO, GNPDA2, MC4R, TFAP2B). This evidence concerns the gene TCF7L2 and type 2 diabetes mellitus.