Group 3 included patients with mild mental retardation since childhood and disorders of behavior or personality with no definite psychiatric syndrome, and concerned: homocystinurias, cerebrotendinous xanthomatosis, nonketotic hyperglycinaemia, monoamine oxidase A deficiency, succinic semialdehyde dehydrogenase defects, creatine transporter deficiency, and α- and β-mannosidosis. The gene discussed is MAOA; the disease is hyperinsulinemic hypoglycemia, familial, 4.