Clinical and enzymatic phenotypes in congenital hyperinsulinemic hypoglycemia due to glucokinase‐activating mutations: A report of two cases and a brief overview of the literature

AIMS/INTRODUCTION: The principal aim of this study was to investigate the clinical, genetic and functional characteristics of two cases of congenital hyperinsulinism (CHI) caused by glucokinase (GCK) mutations in young patients. MATERIALS AND METHODS: Novel mutations were detected by CHI next‐generation sequencing, and the kinetic parameters and thermal stability of recombinant wild‐type and mutant glucokinase were determined in vitro. In addition, 18 naturally occurring GCK‐CHI mutations reported previously were also summarized. RESULTS: A de novo mutation (M197V) was found in a 17‐year‐old male with an epilepsy history, whereas an autosomal dominant mutation (K90R) was found in a 20‐year‐old female with inherited asymptomatic hypoglycemia. Kinetic analysis showed increased enzyme activity for both mutants (RAI 4.7 for M197V and 1.6 for K90R) and enhanced thermal stability for the M197V mutant. However, of all the GCK‐CHI mutants, the increase in enzyme activity (RAI between 1.6 and 130) did not correlate strongly with the severity of hypoglycemia. The de novo group (7/19) showed distinctive phenotypes from the autosomal dominant group (12/19), such as a higher proportion of diazoxide unresponsiveness (28.6% vs 0%), a higher incidence of macrosomia (85.7% vs 40%) and a rarer incidence of adulthood onset (0% vs 25%). CONCLUSIONS: The clinical phenotypes of GCK‐CHIs were highly heterogeneous. We have identified two novel GCK‐CHI mutations in young patients and investigated their pathogenicity by enzyme kinetic analysis, which expanded the spectrum of this rare disease.