TCF7L2 and type 2 diabetes mellitus: TCF7L2 has been revealed as an susceptibility gene for type 2 diabetes.11 Selective disruption of TCF7L2 in the pancreatic β cell impairs secretory function and lowers β cell mass.12 Clinical studies suggested that TCF7L2 gene impaired glucose tolerance through effects on glucagon as well as insulin secretion.13 Several meta-analysis14–18 also concluded that TCF7L2 gene polymorphisms were associated with DM.