Its essential role in normal intrauterine growth is suggested by findings of severe intrauterine growth retardation (IUGR) in babies with pancreatic agenesis [23] or mutations in the insulin receptor gene [24,25] and in studies of leprechaunism, a congenital disorder caused by a mutation in the insulin receptor gene, which is characterized by insulin resistance, fasting hypoglycemia and severe pre- and post-natal growth restriction [26]. The gene discussed is INSR; the disease is Leprechaunism.