Hyperinsulinemic Hypoglycemia, Familial, 2

Alternative Names

  • HHF2
  • Persistent Hyperinsulinemic Hypoglycemia of Infancy
  • PHHI
  • Hyperinsulinemic Hypoglycemia, Persistent
  • Hyperinsulinemic Hypoglycemia due to Focal Adenomatous Hyperplasia
  • Hyperinsulinism, Neonatal
  • Hyperinsulinism, Congenital
  • Hyperinsulinism, Familial
  • Nesidioblastosis
  • Autosomal Recessive Hyperinsulinism due to Kir6.2 Deficiency
  • Autosomal Recessive Hyperinsulinemic Hypoglycemia due to Kir6.2 Deficiency
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WHO-ICD-10 version:2010

Endocrine, nutritional and metabolic diseases

Diabetes mellitus

OMIM Number

601820

Mode of Inheritance

Autosomal recessive and autosomal dominant

Gene Map Locus

11p15.1

Description

Nesidioblastosis is the most common cause of persistent hypoglycaemia in neonates. It is characterized by inappropriately high levels of serum insulin, C-peptide, and proinsulin. In HHF2, this defective regulation of insulin secretion is caused by the abnormal function or regulation of the ATP-dependent potassium (KATP) channel of the pancreatic beta cells. The disorder can be of 2 types: a diffuse form, caused by beta cell abnormality spread throughout the pancreas, and the focal form of HHF2 with clusters of nodular hyperplasia.

While the global incidence of Nesidioblastosis is 1 in 50,000 individuals, in Saudi Arabia it has been found to affect 1 in 2675 live births. It is a congenital disorder and depending on severity, may present in the early days of infancy or early childhood. Infants with HHF2 are large for their gestational age and exhibit islet cell hyperplasia. Symptoms may also include jitteriness, lethargy, cyanosis, seizures, hypotonia, poor feeding and apnea. Recurrent episodes of prolonged sublethal hypoglycemia can result in permanent neurological damage, including developmental delay and mental retardation.

Diagnosis can be made based on elevated serum insulin levels with low serum ketone bodies and an increased glucose response to glucagon administration. Treatment involves dietary interventions and the administration of beta cell potassium channel agonists such as diazoxide. Patients unresponsive to medication may require a partial pancreatectomy to resolve their persistent hypoglycaemia.

Molecular Genetics

HHF2 is caused by mutations in the KCNJ11 gene that encodes the Kir6.2 subunit of the ATP sensitive, inward rectifier potassium ion channel. Mutations can result in deficiency of the protein, failure of the protein to be incorporated into the plasma membrane or failure to respond appropriately to ATP signals.

While HHF2 has generally been shown to follow an autosomal recessive pattern of inheritance, rare autosomal dominant forms have also been reported. Focal forms of the disorder have been found to occur due to a paternally inherited mutation and loss of the normal maternal allele in hyperplastic regions of the pancreas.

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Qubbaj et al. (2011) reported the case of a 36 year old Saudi woman undergoing preimplantation genetic diagnosis (PGD). The woman was married to her first cousin and had four children with congenital hyperinsulinism. As they did not respond well to diazoxide, all four children required partial pancreatectomy in infancy to control their hypoglycaemia. Three of the affected children later developed diabetes mellitus and were dependent on insulin. All children showed normal development and growth. Genetic testing revealed a novel homozygous 902G>C transversion in the KCNJ11 gene resulting in an Arg301Pro substitution. Oocytes were retrieved from the woman and intracytoplasmic sperm injection was carried out. The resulting embryos were subjected to PGD by whole genome amplification and mutation detection along with short tandem repeat identifier analysis and this resulted in the birth of two healthy twin girls; one a carrier for the mutation and one homozygous for the normal allele. A second cycle of PGD using haplotyping resulted in the birth of a healthy boy with a carrier haplotype.

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