TCF7L2 and type 2 diabetes mellitus: Research about the association between genetic polymorphisms of TCF7L2 gene and T2DM was first reported by Grant et al. [6], they demonstrated that a strong association of variants in TCF7L2 with increased risk of T2DM in Icelandic individuals, and this association was replicated in Danish and US cohorts (combined OR = 1.56, p = 4.7×10−18).