Glucose-dependent insulinotropic polypeptide (GIP) dose-dependently increases glucagon secretion under euglycemic and hypoglycemic conditions in healthy individuals (11, 12) and in people with type 1 diabetes (T1D) and T2D (12–14), with no direct effect on insulin secretion in healthy individuals (11, 12). This evidence concerns the gene GCG and type 1 diabetes mellitus.