The impact on diabetes of the rs7903146 variant of the TCF7L2 or other variants of the gene associated with T2DM appears to be mediated by decreased insulin secretion associated or not with defects in insulin processing [4, 5, 10–12], reduced effects of glucagon-like peptide-1 (GLP-1) [13, 14], increased hepatic glucose production [10, 11, 13], and insulin resistance [8, 15]. The gene discussed is GCG; the disease is diabetes mellitus.