The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) play a particularly important role in glucose metabolism and regulation of food intake and body weight, as evident from their development as therapies for type 2 diabetes and obesity (Campbell et al. 2023). The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.