Tirzepatide (Mounjaro) is a novel dual agonist of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors, approved in 2022 for the management of type 2 diabetes mellitus (T2DM) and more recently licensed for obesity due to its notable effects on glycaemic control and weight loss [1]. The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.