Non-metabolizable analogues of gut peptides, particularly the incretins GLP-1 and GIP, are approved for use in the treatment of type 2 diabetes mellitus and obesity in the form of non-metabolizable GLP-1 receptor agonists and inhibitors of the principal peptide hydrolytic enzyme dipeptidyl peptidase (DPP)-IV31, reflecting the emerging interest in the therapeutic potential of gut hormones9. The gene discussed is GLP1R; the disease is obesity due to melanocortin 4 receptor deficiency.