Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the known incretin hormones that are responsible for the incretin effect (a two- to three-fold higher insulin secretory response to oral as compared to intravenous glucose administration), which becomes blunted or even absent in patients with T2D [8]. The gene discussed is GCG; the disease is type 2 diabetes mellitus.