Even if GLP-1 levels remain unaffected by diabetes status, evidence suggests that its insulinotropic effect and suppression of glucagon secretion are impaired in individuals with T2DM compared to both healthy controls and those with IGT [34, 84] However, some studies have reported no significant difference in GLP-1-mediated glucagon suppression between T2DM patients and healthy individuals [85]. This evidence concerns the gene GCG and diabetes mellitus.