Congenital hyperinsulinism (excessive insulin production) is the most common cause of persistent or recurring hypoglycemia (low blood sugar) in infancy. Many infants and children affected with any of the various forms of hyperinsulinism have recurring, severe episodes of hypoglycemia both before and after diagnosis that can cause seizures, brain damage and developmental delay. Since undiagnosed hyperinsulinism or failure of treatment for hyperinsulinism significantly increases the risk of mental retardation