Understanding better the role of the entero-pancreatic hormones in the regulation of feeding, appetite and glycaemia (Fig. 1) has led to the development of the glucagon-like peptide-1 (GLP-1) receptor agonists (RA) as safe and effective treatments for T2D and obesity. The gene discussed is GLP1R; the disease is obesity due to melanocortin 4 receptor deficiency.