(1991) found consanguineous parentage in 5 of 28 families. Consanguinity was evident in the Bedouin and Arab families. (1990) reported a total of 21 cases in 7 pedigrees, which included a large Bedouin family, an Arab family, and 5 Jewish families of Eastern European origin (Ashkenazi). In addition, a brother and sister who died in the neonatal period were probably affected. (1989) described the disorder in a brother and sister whose parents were consanguineous. Four of the group I patients had the Beckwith EMG syndrome ( 130650). Group II patients ranged in age from 3 to 15 years. Group I patients were 8 months old or younger. (1980) recognized 2 histologic groups of nesidioblastosis among cases of hyperinsulinemic hypoglycemia: group I had diffuse hyperplasia of the islets of Langerhans as well as nesidioblastosis group II had more subtle nesidioblastosis alone. The disorder presented as severe neonatal hypoglycemia. (1979) observed the disorder in 5 children of both sexes from 2 families with unaffected parents. (1971) was first to report nesidioblastosis in a series of infants with intractable hypoglycemia. 'Nesidio' comes from a Greek word for islet. The term nesidioblastosis (meaning neoformation of islets of Langerhans from pancreatic duct epithelium) was coined by Laidlaw (1938) to describe the diffuse abnormality of the pancreas in which there is extensive, often disorganized formation of new islets. There is evidence of further genetic heterogeneity of HHF. HHF7 ( 610021) is caused by mutation in the SLC16A1 ( 600682) on chromosome 1p13. HHF6 ( 606762) is caused by mutation in the GLUD1 gene ( 138130) on chromosome 10q23. HHF5 ( 609968) is caused by mutation in the insulin receptor gene (INSR 147670) on chromosome 19p13. HHF4 ( 609975) is caused by mutation in the HADH gene ( 601609) on chromosome 4q25. HHF3 ( 602485) is caused by mutation in the glucokinase gene (GCK 138079) on chromosome 7p13. HHF2 ( 601820) is caused by mutation in the KCNJ11 gene ( 600937) on chromosome 11p15. Genetic Heterogeneity of Hyperinsulinemic Hypoglycemia Unless early and aggressive intervention is undertaken, brain damage from recurrent episodes of hypoglycemia may occur ( Thornton et al., 1998). Familial hyperinsulinism, also referred to as congenital hyperinsulinism, nesidioblastosis, or persistent hyperinsulinemic hypoglycemia of infancy (PPHI), is the most common cause of persistent hypoglycemia in infancy and is due to defective negative feedback regulation of insulin secretion by low glucose levels.

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