G × D interactions (Figure 2, Table S6) of TCF7L2 variants have been the most widely studied so far.14, 19, 20, 21, 22, 23, 24 In particular, the TCF7L2 variant rs7903146 is of interest as it is considered to be strongly associated with T2D risk and known to modify the effect of incretins on insulin secretion. The gene discussed is GCG; the disease is type 2 diabetes mellitus.