When all participants were pooled, the incretin effect slope was inversely related to the mean total insulin secretion at the three glucose doses during IIGI; the relationship was significantly shifted downwards in patients with T2D (r2 = 0.66, P = 0.03 for total insulin secretion, P<0.02 for the group effect; the significance was maintained after exclusion of the T2D subjects with potentially unreliable incretin effect slope). The gene discussed is GCG; the disease is type 2 diabetes mellitus.