Abstract
Heterozygous glucokinase (GCK) mutations cause a subtype of maturity-onset diabetes of the young (GCK-MODY). Over 600 GCK mutations have been reported of which ∼65% are missense. In many cases co-segregation has not been established and despite the importance of functional studies in ascribing pathogenicity for missense variants these have only been performed for <10% of mutations. The aim of this study was to determine the minimum prevalence of GCK-MODY amongst diabetic subjects in Slovakia by sequencing GCK in 100 Slovakian probands with a phenotype consistent with GCK-MODY and to explore the pathogenicity of identified variants through family and functional studies.Twenty-two mutations were identified in 36 families (17 missense) of which 7 (I110N, V200A, N204D, G258R, F419S, c.580-2A>C, c.1113–1114delGC) were novel. Parental DNA was available for 22 probands (covering 14/22 mutations) and co-segregation established in all cases. Bioinformatic analysis predicted all missense mutations to be damaging. Nine (I110N, V200A, N204D, G223S, G258R, F419S, V244G, L315H, I436N) mutations were functionally evaluated. Basic kinetic analysis explained pathogenicity for 7 mutants which showed reduced glucokinase activity with relative activity indices (RAI) between 0.6 to <0.001 compared to wild-type GCK (1.0). For the remaining 2 mutants additional molecular mechanisms were investigated. Differences in glucokinase regulatory protein (GKRP) –mediated-inhibition of GCK were observed for both L315H & I436N when compared to wild type (IC50 14.6±0.1 mM & 20.3±1.6 mM vs.13.3±0.1 mM respectively [p<0.03]). Protein instability as assessed by thermal lability studies demonstrated that both L315H and I436N show marked thermal instability compared to wild-type GCK (RAI at 55°C 8.8±0.8% & 3.1±0.4% vs. 42.5±3.9% respectively [p<0.001]). The minimum prevalence of GCK-MODY amongst Slovakian patients with diabetes was 0.03%.In conclusion, we have identified 22 GCK mutations in 36 Slovakian probands and demonstrate that combining family, bioinformatic and functional studies can aid the interpretation of variants identified by molecular diagnostic screening.
Highlights
Heterozygous inactivating mutations in the glucokinase gene (GCK) are one cause of maturity-onset diabetes of the young (MODY) characterized by stable elevated fasting plasma glucose levels [1,2]
We report an investigation of the minimum prevalence of GCK-MODY in Slovakia followed by an exploration of the pathogenicity of identified variants through family, bioinformatic and functional studies
GCK mutational screening and clinical characterisation Mutational screening identified 22 GCK mutations in 36 of the probands (Table 1); 17 missense, 1 frame-shift, 2 in frame deletions, 1 promoter and 1 splice-site. Seven of these mutations were novel (I110N, V200A, N204D, G258R, F419S, c.5802A.C, c.1113-1114delGC), they were absent from 200 control chromosomes from normoglycaemic individuals
Summary
Heterozygous inactivating mutations in the glucokinase gene (GCK) are one cause of maturity-onset diabetes of the young (MODY) characterized by stable elevated fasting plasma glucose levels [1,2]. The prevalence of GCK-MODY is difficult to assess as the mild hyperglycaemia and absence of symptoms mean that many patients are not diagnosed. Large scale population based studies have not been performed but a number of studies have ascertained the prevalence of GCK-. MODY in subjects with impaired glucose tolerance and diabetes [4,5,6,7,8,9,10,11]. There are differences in prevalence across these studies which likely reflect both the age of the population tested and the ascertainment criteria [12,13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
