Engagement of GIP in a biochemical liaison with GLP-1 seems at first glance counterintuitive, given that the insulinotropic effects and the incretin effect of GIP are severely reduced in people with type 2 diabetes [2, 22] (see earlier), and that GIP receptor-deficient mice are lean and protected from diet-induced obesity [85]. The gene discussed is GIP; the disease is obesity due to melanocortin 4 receptor deficiency.