Identification and functional analysis of GCK gene mutations in 12 Chinese families with hyperglycemia

Abstract

Aims/introduction: To investigate the clinical and genetic characteristics of Chinese patients with a phenotype consistent with maturity-onset diabetes of the young type 2 and explore the pathogenic mechanism of their hyperglycemia.

Materials and methods: We studied 12 probands and their extended families referred to our center for screening mutations in the glucokinase gene (GCK). Clinical data were collected and genetic analysis was carried out. The recombinant wild-type and mutant glucokinase were generated in Escherichia coli. The kinetic parameters and thermal stability of the enzymes were determined in vitro.

Results: In the 12 families, 11 GCK mutations (R43C, T168A, K169N, R191W, Y215X, E221K, M235T, R250H, W257X, G261R and A379E) and one variant of uncertain significance (R275H) were identified. R191W was detected in two unrelated families. Of the 11 GCK mutations, three mutations (c.507G>C, K169N; c.645C>A, Y215X; c.771G>A, W257X; NM_000162.3, NP_000153.1) are novel. Basic kinetics analysis explained the pathogenicity of the five mutants (R43C, K169N, R191W, E221K and A379E), which showed reduced enzyme activity with relative activity indexes between ~0.001 and 0.5 compared with the wild-type (1.0). In addition, the thermal stabilities of these five mutants were also decreased to varying degrees. However, for R250H and R275H, there was no significant difference in the enzyme activity and thermal stability between the mutants and the wild type.

Conclusions: We have identified 11 GCK mutations and one variant of uncertain significance in 12 Chinese families with hyperglycemia. For five GCK mutations (R43C, K169N, R191W, E221K and A379E), the changes in enzyme kinetics and thermostability might be the pathogenic mechanisms by which mutations cause hyperglycemia.

Keywords: Enzyme kinetics; Glucokinase; Maturity-onset diabetes of the young.