GLP1R and obesity due to melanocortin 4 receptor deficiency: Incretin-based therapies represent a novel treatment for both T2DM and obesity, relying on the insulinotropic actions of the gut hormone glucagon-like peptide-1 (GLP-1) and, most recently, on the combined action of GLP-1 and the gastric inhibitory polypeptide (GIP) hormones.