Background: Congenital Hyperinsulinism (CHI) is a common cause of persistent hypoglycaemia in the neonatal and infant period. It is most commonly caused by mutations in one of the KATP channel subunits, either SUR1 encoded by the gene ABCC8 or Kir6.2 encoded by the gene KCNJ11. Patients carrying mutations in the ABCC8 and KCNJ11 genes simultaneously have not been reported yet.
Objective and hypotheses: Our aim was to describe the clinical phenotype and to perform in-vitro functional analysis of a combination of novel heterozygous ABCC8 (Y1293D) and KCNJ11 (R50W) mutations found in one Czech patient with CHI in order to clarify the pathogenic effect on the pancreatic β-cell function.
Method: Novel heterozygous ABCC8 (Y1293D) and KCNJ11 (R50W) mutations were created in vitro using site-directed mutagenesis. The functional analysis using radioactive Rubidium (86+Rb) was performed in HEK293 cell cultures transfected with a combination of these novel heterozygous ABCC8 and KCNJ11 genes mutations. Mutant and wild type (WT) channels were exposed to different drug conditions: control (DMSO), 100 μM diazoxide, 100 μM diazoxide and 10 μM glibenclamide, 2.5 mM NaCN and 20 mM 2-deoxy-D-glucose and 2.5 mM NaCN, 20 mM 2-deoxy-D-glucose and 10 μM glibenclamide. 86+Rb efflux was measured in a liquid scintillation counter using Cherenkov radiation.
Results: The functional study of this heterozygous combination of ABCC8 (Y1293D) and KCNJ11 (R50W) mutations revealed that the activation by diazoxide in mutated KATP channels was decreased by 60.1% when compared to WT channels.
Conclusion: We report for the first time a patient with CHI caused by a combination of novel heterozygous mutations in both of the genes (ABCC8 and KCNJ11) encoding the KATP channel subunits. We have proved a pathogenic effect on the pancreatic β-cell function of this combination of mutations by an in vitro functional study.
Funding: This work was supported by the ESPE Short-term Research Fellowship for Dr Klára Roženková and the Grant Agency of Charles University, Prague, Czech Republic (GAUK 248 213).
01 Oct 2015 - 03 Oct 2015