The response to hyperglycemia in mammals is mainly controlled by the interplay between two peptide hormones: insulin, released by pancreatic islet β-cells stimulated by high extracellular glucose levels, and the incretin glucagon-like peptide 1 (GLP-1), released by entero-endocrine cells stimulated by nutrients in the gut. The gene discussed is GCG; the disease is Hyperglycemia.