An inherited autosomal recessive syndrome characterized by the disorganized formation of new islets in the pancreas and congenital hyperinsulinism. It is due to focal hyperplasia of pancreatic islet cells budding off from the ductal structures and forming new islets of langerhans. Mutations in the islet cells involve the potassium channel gene kcnj11 or the atp-binding cassette transporter gene abcc8, both on chromosome 11. The disease is MONDO_0005803 (hyperinsulinemic hypoglycemia). Also known as: hyperinsulinemia hypoglycemia, hyperinsulinemic hypoglycemia (disease), islet cell hyperplasia, persistent hyperinsulinemia hypoglycemia of infancy.