As an oral hypoglycemic agent approved by FDA, sitagliptin increases the activity of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide by highly selective inactivation of DPP4, thereby promoting insulin secretion from β-cells and inhibiting glucagon secretion from α-cells, so sitagliptin is widely used in the treatment of type 2 diabetes [14–17]. The gene discussed is GCG; the disease is type 2 diabetes mellitus.