Genome-wide association studies (GWASs) have identified about 30 susceptibility genes for T2DM in different populations [2], [3], [4], [5], [6], [7], [8], of which the most important (based on estimated size effect) are PPARG, SLC30A8, HHEX, TCF7L2, KCNJ11, IGFBP-2, CDKAL1, CDKN2A/B and FTO. Nevertheless, these polymorphisms have, individually, only small effects on T2DM risk, with odds ratios around 1.3. This evidence concerns the gene TCF7L2 and type 2 diabetes mellitus.