The diagnosis of HI is defined by detectable plasma insulin level (>2–3 μU/ml) at the time of hypoglycemia or by signs of inappropriate excess of insulin, such as suppressed NEFA (<1.7 mM), hypoketonemia (<1.8 mM), a hyperglycemic response to i.m. glucagon (delta glucose>30 mg/dl in 30 min) and a high glucose demand (>10 mg/kg/min in neonates) (4–6). This evidence concerns the gene GCG and Hypoglycemia.