Molecular screening of the glucokinase gene in familial Type 2 (non-insulin-dependent) diabetes mellitus

Summary

The glucokinase locus has been implicated by linkage studies in several Caucasian pedigrees with early onset, autosomal dominant diabetes, and mutations have been identified in a large number of these pedigrees. Although mutations have been reported in some pedigrees with late onset Type 2 (non-insulin-dependent) diabetes mellitus, linkage studies of typical familial Type 2 diabetes did not suggest a major role for this locus. Nonetheless, linkage studies were consistent with the hypothesis that mutations of the glucokinase gene were responsible for the pathogenesis of Type 2 diabetes in a minority of pedigrees or one gene in a polygenic disorder. To systematically address this hypothesis, we examined 60 diabetic members of 18 pedigrees ascertained for two or more Type 2 diabetic siblings and eight unrelated diabetic spouses. Initially, the coding regions from each of the 11 glucokinase exons were examined by the sensitive technique of single strand conformation polymorphism analysis to screen for single nucleotide substitutions. Subsequently, we also sequenced each exon from an affected member of the single pedigree in which a glucokinase allele was most likely to segregate with diabetes. Single strand conformation polymorphism analysis detected only three variants, none of which altered the amino acid sequence. No coding or splice site mutations were detected. Likewise, no additional mutations were detected upon direct sequence analysis. However, additional screening of promoter and 3′ untranslated regions detected a variant pattern in the untranslated region of exon 10 which appeared to segregate with diabetes and impaired glucose tolerance in one pedigree. Sequence analysis demonstrated the deletion of a cytosine in exon 10 at position 906, but this deletion was not associated with Type 2 diabetes among unrelated spouses, was not linked to diabetes, and was not associated with significant elevations of fasting glucose or insulin among non-diabetic pedigree members. Similarly, two common variants in the islet promoter did not segregate with diabetes. We conclude that among typical familial Type 2 diabetes in a population representative of Northern European Caucasians, glucokinase mutations are an unlikely cause of diabetes.