In recent years, technological advances in drug discovery has led to the development of a series of peptide hormone receptor co-agonists, including several GLP-1/glucagon and GLP-1/gastrointestinal insulinotropic polypeptide (GIP) receptor co-agonists, that have potent anti-obesity effects and are in various phases of clinical trials [180]. The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.