While originally developed as incretin-based therapies for type 2 diabetes mellitus (T2DM) and, more recently, obesity, GLP-1 RAs exert a range of physiological effects by mimicking the action of endogenous GLP-1—a gut-derived hormone that enhances glucose-dependent insulin secretion, suppresses glucagon release, slows gastric emptying, and promotes satiety. The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.