Heterogeneity in disease severity in a family with a novel G68V GCK activating mutation causing persistent hyperinsulinaemic hypoglycaemia of infancy
Article first published online: 1 NOV 2007
Volume 24, Issue 12, pages 1393–1399, December 2007
How to Cite
Wabitsch, M., Lahr, G., Van de Bunt, M., Marchant, C., Lindner, M., Von Puttkamer, J., Fenneberg, A., Debatin, K. M., Klein, R., Ellard, S., Clark, A. and Gloyn, A. L. (2007), Heterogeneity in disease severity in a family with a novel G68V GCK activating mutation causing persistent hyperinsulinaemic hypoglycaemia of infancy. Diabetic Medicine, 24: 1393–1399. doi: 10.1111/j.1464-5491.2007.02285.x
- Issue published online: 26 NOV 2007
- Article first published online: 1 NOV 2007
- Accepted 19 June 2007
- persistent hyperinsulinaemic hypoglycaemia of infancy
Background/aim Glucokinase (GCK)-activating mutations cause persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI). GCK-PHHI patients have regulated insulin secretion and can usually be treated with diazoxide. The six reported cases suggest that the severity of the mutation predicts the clinical phenotype. The aim of this study was to relate genotype to phenotype [clinical phenotype, glucose-stimulated insulin release (GSIR) and GCK functional analysis] in a large pedigree with eight affected individuals.
Methods The genes encoding B-cell GCK and the KATP channel subunits (ABCC8 and KCNJ11) were sequenced to identify mutations for functional analysis. Genetic variants influencing B-cell function were genotyped in affected individuals. Islet secretory capacity was determined by oral glucose tolerance test
Results A novel GCK mutation (G68V) co-segregating with hypoglycaemia was identified in eight family members. Kinetic analysis revealed that G68V-GCK activity is ~16 times more than wild-type-GCK with an increased affinity for glucose [concentration at half maximal activation (S0.5) 1.94 ± 0.16 vs. 7.43 ± 0.12, mutant vs. wild type, mean ± sem]. Mathematical modelling predicted a threshold for GSIR of 1.9 mmol/l in the mutant. Oral glucose tolerance tests showed regulated insulin secretion. The severity of hypoglycaemia and related symptoms in affected subjects were heterogeneous. Clinical presentations were asymptomatic (n = 1), extreme hunger (n = 3), seizures (n = 2) and loss of consciousness (n = 2); 7/8 were managed with diet but the proband was treated with diazoxide and octreotide. Phenotypic modification by a second mutation in the KATP channel genes (ABCC8, KCNJ11) or by common genetic variants in KCNJ11, GCK and TCF7L2 was excluded.
Conclusion The novel activating GCK mutation G68V is associated with variable phenotypic severity, supporting modification of GSIR by genetic and/or environmental factors.