TCF7L2 and diabetes mellitus: In this review, we have introduced the basic concept of the Wnt signaling pathway, summarized the current studies on the role of the Wnt signaling pathway in metabolic homeostasis and the development of metabolic diseases, presented current disputes on the function of Wnt signaling in pancreatic islet β-cells, and discussed the extensive recent work on TCF7L2 as a diabetes susceptibility gene.