GLP-1 and GIP play important roles in the control of glucose levels after a meal via the physiological response known as the “incretin effect.” This occurs when higher levels of glucose-stimulated insulin secretion are observed when glucose is administered orally rather than intravenously, an effect that is lost in type 2 diabetes but preserved in T1D [57]. The gene discussed is GLP1R; the disease is type 1 diabetes mellitus.