We suggest that the hyperinsulinaemia that is observed in TPP may be linked to the ATP-sensitive K(+)/SUR1 alanine variant and, therefore, contribute to the major feedforward precipitating factors in the pathophysiology of TPP.
We describe the interesting case of an infant with PNDM, in whom a compound heterozygous activating/ inactivating mutation was found with clinically unaffected parents, each carrying a heterozygous mutation in ABCC8, one predicting gain of function (neonatal diabetes) and the other a loss of function (hyperinsulinemia).
Mutations of the same conserved glutamate residue in NBD2 of the sulfonylurea receptor 1 subunit of the KATP channel can result in either hyperinsulinism or neonatal diabetes.
It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinism of infancy, while activating mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes.
Multiple mutations in Kir6.x and SUR genes have implicated K(ATP) channels in various diseases ranging from diabetes and hyperinsulinism to cardiac arrhythmias and cardiovascular disease.
Here we report that two hyperinsulinism-associated SUR1 missense mutations, R74W and E128K, surprisingly reduce channel inhibition by intracellular ATP, a gating defect expected to yield the opposite disease phenotype neonatal diabetes.
Loss- and gain-of-function mutations in the genes encoding the Kir6.2 and SUR1 subunits of this channel cause hyperinsulinism of infancy and neonatal diabetes, respectively.
A combined immunohistochemistry and fluorescent in situ hybridization study on beta-cell interphase nuclei with probes covering two genes located in this region (ABCC8 and CDKN1C genes) was performed in four cases of focal forms of hyperinsulinism.
Loss of function mutations in the KCNJ11 and ABCC8 genes that encode for Kir6.2 and SUR1 can cause over-secretion of insulin and result in hyperinsulinism of infancy, while gain of function mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes.Genetic testing is important for patients with hyperinsulinism or neonatal diabetes, as identification of a K(ATP) channel mutation confirms a diagnosis of their disorder.
Consistent with this paradigm, loss-of-function mutations in the genes (KCNJ11 and ABCC8) that encode the two subunits (Kir6.2 and SUR1, respectively) of the ATP-sensitive K(+) (K(ATP)) channel underlie hyperinsulinism in humans, a genetic disorder characterized by dysregulated insulin secretion.
Although the absence of enlarged islet cell nuclei is a useful discriminant of focal hyperinsulinism associated with a paternal ABCC8 mutation, further research is needed to understand the pathophysiology of other histological abnormalities in patients with HI, which may have implications for mechanisms of ductal and islet cell proliferation.
It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinemia (HI) of infancy; however, heterozygous activating mutations in KCNJ11 that result in the opposite phenotype of diabetes have recently been described.
An amniocentesis was performed at 16 weeks gestation at which time two mutations in the SUR1 gene were identified consistent with the diagnosis of diffuse hyperinsulinism.
Genotype-phenotype correlations in children with congenital hyperinsulinism due to recessive mutations of the adenosine triphosphate-sensitive potassium channel genes.
In contrast to focal islet-cell hyperplasia, always sporadic to our knowledge, diffuse hyperinsulinism is a heterogeneous disorder involving several genes, various mechanisms of pathogenic mutations and different transmissions: (i) channelopathy involving the genes encoding the sulphonylurea receptor (SUR1) or the inward-rectifying potassium channel (Kir6.2) in recessively inherited HI or more rarely dominantly inherited HI; (ii) metabolic disorders implicating the short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) enzyme inrecessively inherited HI, the glucokinase gene (GK), the glutamate dehydrogenase gene (GLUD1) when hyperammonemia is associated, dominant exercise-induced HI with still-unknown mechanism, and more recently the human insulin receptor gene in dominantly inherited hyperinsulinism.
We selected 15 hyperinsulinism of infancy patients and systematically sequenced the promoter and all coding exons and intron/exon boundaries of ABCC8 and KCNJ11.