TCF7L2 and type 2 diabetes mellitus: TCF7L2 is a transcription factor involved in the activation of Wnt target genes that specifically repress proglucagon synthesis in enteroendocrine cells. TCF7L2 polymorphisms can increase susceptibility to type 2 diabetes by decreasing the production of glucagon-like peptide-1 (GLP-1) [43] and decreased insulin production.