A drop in blood glucose levels below the euglycemic range (≤3.9 mmol/L, classified as level 1 hypoglycemia) (International Hypoglycaemia Study Group, 2017) activates the release of chief counterregulatory hormone, glucagon, from islet α-cells at a glucose threshold of 3.6–3.9 mmol/L (Mitrakou et al., 1991) Along with epinephrine, glucagon stimulates hepatic glycogenolysis and gluconeogenesis to prevent and correct hypoglycemia (Cryer et al., 1984). The gene discussed is GCG; the disease is Hypoglycemia.