Linkage analysis of glucokinase gene with NIDDM in Caucasian pedigrees

Clinical characteristics of subjects with a missense mutation in glucokinase

The clinical characteristics of subjects with a missense glucokinase mutation, gly299-->arg, were studied in a large pedigree, BX, initially characterized by some members having Maturity Onset Diabetes of the Young (MODY). Glucose tolerance, beta cell function and insulin sensitivity were measured with Homeostasis Model Assessment (HOMA) and with a 'Continuous Infusion of Glucose with Model Assessment' (CIGMA) test. Diabetic complications were clinically assessed. Subjects with glucokinase gly299-->arg were the same age, height, and obesity as the subjects without the mutation. Diabetes was usually asymptomatic at diagnosis and was treated with diet alone in 15 of the 18 subjects. Five of the 11 adult females had been diagnosed when they developed gestational diabetes. The fasting plasma glucose concentrations at the time of study were 4.3-12.6 mmol l-1, with the higher levels being in the more obese (p < 0.05) and in the older subjects (p < 0.05). In subjects with the mutation, beta cell function was impaired, being geometric mean 63% (normal-100%) compared with 126% in the subjects without the mutation (p < 0.001) measured by HOMA and in a subset assessed by CIGMA 59% and 127% (p < 0.01), respectively. There was no difference in fasting insulin concentrations, insulin sensitivity, lipid concentrations or blood pressure between the groups. The haemoglobin A1c was raised (mean 6.5% compared with 5.5% in the subjects without the mutation), but microvascular and macrovascular complications were uncommon. The subjects with the mutation did not have microalbuminuria but had an impaired vibration perception threshold compared with subjects without the mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of Japanese families with early-onset type 2 (non-insulin dependent) diabetes mellitus and screening for mutations in the glucokinase and mitochondrial tRNA(Leu(UUR)) genes

Genetic linkage studies of families with early-onset type 2 diabetes have facilitated the identification of diabetes-susceptibility genes. In order to assess the feasibility of using linkage approaches to identify genes responsible for the development of type 2 diabetes in Japanese subjects, we examined our clinical records for multigenerational families suitable for genetic studies. We identified 16 families in which at least one subject was diagnosed with type 2 diabetes before 25 years of age. Seven of these families had a pattern of inheritance consistent with a diagnosis of maturity-onset diabetes of the young (MODY) and nine families showed a complex pattern of inheritance of type 2 diabetes with transmission of diabetes-susceptibility genes from both parents. The glucokinase and mitochondrial tRNA(Leu(UUR)) genes were screened for mutations in at least one affected subject from each family in order to assess the contribution of mutations in these genes to the development of the diabetes. No mutations were found, which suggests that the diabetes in these families resulted from mutations in other genes.

Segregation analysis of NIDDM in Caucasian families

Non-insulin-dependent diabetes mellitus (NIDDM) has a substantial genetic component, but the mode of inheritance and the molecular basis are unknown. We have undertaken segregation analysis of NIDDM after studying 247 subjects in 59 Caucasian nuclear pedigrees ascertained without regard to family history of the disorder. The analyses were performed using POINTER and COMDS, which are computer programs which apply statistical models to the data. POINTER analysis was performed defining the phenotype as a presence or absence of hyperglycaemia. Among single locus hypothesis, the analyses rejected a recessive model and favoured a dominant model, but could not statistically show that this fitted better than a mixed model (a single locus against a polygenic background) or a polygenic model. COMDS analysis assumed a continuum of hyperglycaemia from normality to NIDDM, classified family members into a series of diathesis classes with increasing plasma glucose levels and compared the distribution with that found by screening the normal population. This analysis improved the likelihood of a dominant single locus model and suggested a gene frequency of 7.4%. It raised the possibility of a second locus, but cannot identify or exclude a polygenic model. In conclusion, two types of segregation analyses rejected a recessive model and favoured a dominant model of inheritance, although they could not statistically show that this fitted better than the polygenic model. The results raised the possibility of a common dominant gene with incomplete penetrance, but genetic analysis of NIDDM needs to take into account the likelihood of polygenic inheritance with genetic heterogeneity.

Linkage analysis does not support a role for glucokinase gene in the aetiology of type 2 diabetes mellitus among north western Italians

The contribution of a 3' glucokinase gene polymorphism to the aetiology of type 2 diabetes mellitus was studied in 17 diabetic pedigrees from North-Western Italy; linkage methodology was used. A CA repeat sequence was employed as a marker and amplified by PCR. Three alleles were found: Z (195 bp), Z + 4 (199 bp) and Z + 10 (205 bp). Since in diabetic families linkage analysis gave values of LOD score between -0.000438 and 0.026, the association between GK polymorphism and type 2 diabetes could not be either excluded or accepted. Based on these data, we conclude that glucokinase polymorphism is not a major determinant of type 2 diabetes mellitus, at least in our population, but, consistent with LOD score obtained, in some pedigrees it could assume a minor role in the aetiology of this disease.

Glucokinase gene polymorphisms: a genetic marker for glucose intolerance in a cohort of elderly Finnish men

Although mutations in the glucokinase gene are implicated in the pathogenesis of glucose intolerance in pedigrees with maturity-onset diabetes of the young, the role of such mutations in typical Type 2 diabetes is poorly characterized. We studied a cohort of elderly men born (between 1900 and 1919) in two Finnish communities and exhibiting a continuous spectrum of glucose tolerance at assessments made in 1984 and 1989. Individuals were typed at two polymorphic microsatellites straddling the glucokinase gene, GCK(3') (n = 169) and GCK(5') (n = 166): these two markers were in linkage equilibrium in this cohort. Significant associations between alleles at the GCK(3') marker and glucose tolerance were evident (p = 0.002), the frequency of the (z + 2) allele rising from zero in control subjects (n = 88 chromosomes) to 6.5% (n = 62) in subjects with impaired tolerance and 12.2% (n = 188) in subjects with diabetes. Mean 2-h glucose levels were 10.5 (9.6-11.4, 95% confidence interval) mmol l-1 in individuals with the (z + 2) allele and 8.1 (7.6-8.7) mmol l-1 in those without (p = 0.01, corrected for multiple comparisons). No association was evident between GCK(5') alleles and glucose tolerance. The GCK(3') microsatellite is a marker for abnormal glucose tolerance in this cohort of elderly Finnish men.

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

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.(ABSTRACT TRUNCATED AT 250 WORDS)

Microsatellite polymorphisms at the glucokinase locus: a population association study in Caucasian type 2 diabetic subjects

Glucokinase has a central role in glucose metabolism in pancreatic beta cells and hepatocytes and is an important candidate gene for Type 2 diabetes. Mutations of the glucokinase gene have been reported in Caucasian pedigrees with maturity-onset diabetes of the young and late-onset Type 2 diabetes. In population studies of American Blacks and Mauritian Creoles an association between alleles of a glucokinase polymorphism and Type 2 diabetes has been described. Two microsatellite polymorphisms (GCK 1 and GCK 2) flanking the glucokinase gene were investigated in Caucasian subjects. There was no significant linkage disequilibrium between the alleles of the two polymorphisms. The overall allelic frequencies for GCK 1 and the combined haplotyes did not significantly differ between 95 Type 2 diabetic and 76 normoglycaemic subjects. In an expanded cohort of 151 diabetic subjects the allelic frequencies at GCK 2 were also similar to controls. These results suggest that a single mutation of the glucokinase gene is not a common cause of Type 2 diabetes in English Caucasians.

Positive association in the absence of linkage suggests a minor role for the glucokinase gene in the pathogenesis of type 2 (non-insulin-dependent) diabetes mellitus amongst south Indians

Mutations of the glucokinase gene have been implicated in the development of glucose intolerance in pedigrees with maturity-onset diabetes of the young. However, the contribution of the glucokinase gene to the aetiology of common Type 2 (non-insulin-dependent) diabetes mellitus is uncertain. We have studied the role of the glucokinase gene in the pathogenesis of Type 2 diabetes in South Indians, using both population-association and linkage methodology. A pair of CA-repeat sequences (GCK(3') and GCK(5')) straddling the glucokinase gene were employed as markers, each subject being typed using the polymerase chain reaction and polyacrylamide gel electrophoresis. Comparisons of allele frequencies at these markers were made between 168 Type 2 diabetic subjects and 70 racially-matched control subjects. No differences in allele frequencies were apparent at the GCK(5') marker; however, there were significant differences in allele frequencies at the GCK(3') marker between the Type 2 diabetic subjects and control subjects (chi 2 = 11.6, df = 3, p = 0.009) with an increase of the z allele (78.0% vs 66.4%) and a decrease of the z + 2 allele (13.7% vs 25.0%) amongst the diabetic subjects. Linkage between glucose intolerance and the glucokinase gene was studied in 53 nuclear pedigrees under a variety of genetic models. Linkage was excluded (lod score < -2) at a recombination fraction of zero under five of the ten models used and highly unlikely (-2 < lod score < -1) under the others. The combination of positive association and negative linkage suggests that glucokinase acts as a minor gene influencing the development of Type 2 diabetes within this population.

Mammalian glucokinase and its gene

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Two microsatellite repeat polymorphisms flanking opposite ends of the human glucokinase gene: use in haplotype analysis of Welsh Caucasians with type 2 (non-insulin-dependent) diabetes mellitus

The purpose of this study was to evaluate the role of potential glucokinase defects contributing to susceptibility to Type 2 (non-insulin-dependent) diabetes mellitus in Welsh Caucasians. For this analysis, two microsatellite repeat polymorphisms flanking opposite ends of the gene were employed. For a recently described microsatellite (GCK2), located 6 kilobases upstream of islet exon 1, six different sized alleles were observed, with heterozygosity of 0.50 and polymorphism information content 0.44. Combined heterozygosity with another microsatellite repeat (GCK1) was 0.72. Significant linkage disequilibrium was noted between GCK2 and GCK1, suggesting that haplotypes may be a better predictor of Type 2 diabetes than analysis with either microsatellite alone. Using these two markers, the association with Type 2 diabetes was examined. The frequencies of alleles and genotypes at GCK1 did not differ between the patients with Type 2 diabetes (n = 157) and control subjects (n = 73). Similarly no differences were observed in GCK2 alleles or genotypes. The frequencies of haplotypes, derived from the two markers, also did not differ between the two groups. To investigate the possibility of minor metabolic effects of glucokinase defects, we also studied the association between the GCK alleles or haplotypes and the response profiles to meal tolerance tests. No association was observed between plasma glucose or insulin responses to meal tolerance tests with GCK haplotypes or alleles. These results suggest that glucokinase mutations in Welsh Caucasians are not major determinants of susceptibility to the common type of Type 2 diabetes.