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

Chromosome 7p linkage and association study for diabetes related traits and type 2 diabetes in an African-American population enriched for nephropathy

BACKGROUND

Previously we performed a linkage scan of 638 African American affected sibling pairs (ASP) with type 2 diabetes (T2D) enriched for end-stage renal disease (ESRD). Ordered subset linkage analysis (OSA) revealed a linkage peak on chromosome 7p in the subset of families with earlier age of T2D diagnosis.

METHODS

We fine mapped this region by genotyping 11 additional polymorphic markers in the same ASP and investigated a total of 68 single nucleotide polymorphisms (SNPs) in functional candidate genes (GCK1, IL6, IGFBP1 and IGFBP3) for association with age of T2D diagnosis, age of ESRD diagnosis, duration of T2D to onset of ESRD, body mass index (BMI) in African American cases and T2D-ESRD in an African American case-control cohort. OSA of fine mapping markers supported linkage at 28 cM on 7p (near D7S3051) in early-onset T2D families (max. LOD = 3.61, P = 0.002). SNPs in candidate genes and 70 ancestry-informative markers (AIMs) were evaluated in 577 African American T2D-ESRD cases and 596 African American controls.

RESULTS

The most significant association was observed between ESRD age of diagnosis and SNP rs730497, located in intron 1 of the GCK1 gene (recessive T2D age-adjusted P = 0.0006). Nominal associations were observed with GCK1 SNPs and T2D age of diagnosis (BMI-adjusted P = 0.014 to 0.032). Also, one IGFBP1 and four IGFBP3 SNPs showed nominal genotypic association with T2D-ESRD (P = 0.002-0.049). After correcting for multiple tests, only rs730497 remanined significant.

CONCLUSION

Variant rs730947 in the GCK1 gene appears to play a role in early ESRD onset in African Americans.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (ε4) and decrease (ε2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

Transgenic knockouts reveal a critical requirement for pancreatic beta cell glucokinase in maintaining glucose homeostasis

The secretion of insulin is controlled by the rate of glucose metabolism in the pancreatic beta cells. As phosphorylation by glucokinase (GLK) appears to be the rate-limiting step for glucose catabolism in beta cells, this enzyme may be the glucose sensor. To test this possibility and to resolve the relative roles of liver and beta cell GLK in maintaining glucose levels, we have generated mice completely deficient in GLK and transgenic mice in which GLK is expressed only in beta cells. In mice with only one GLK allele, blood glucose levels are elevated and insulin secretion is reduced. GLK-deficient mice die perinatally with severe hyperglycemia. Expression of GLK in beta cells in the absence of expression in the liver is sufficient for survival. These mice demonstrate the critical need for beta cell GLK in maintaining normal glucose levels and provide a novel model for one form of noninsulin-dependent diabetes.

CA-repeated microsatellite polymorphism of the glucokinase gene and its association with non-insulin-dependent diabetes mellitus in Taiwanese

Mutation of the glucokinase gene has recently been identified as a cause of maturity-onset diabetes of the young (MODY), a subset of non-insulin-dependent diabetes mellitus (NIDDM). However, its role in the wide variety of NIDDM remains controversial due to conflicting reports of association studies, negative results of linkage studies and low prevalence of glucokinase mutations in the common variety of NIDDM. In this study, two (CA)n-microsatellite polymorphisms flanking both ends of the glucokinase gene, termed GCK1 and GCK2, were used to evaluate the role of glucokinase on NIDDM susceptibility of Taiwanese. For GCK1, three alleles (Z,Z+2 and Z+4 with a polymorphic information content index (PIC) of 0.53) and six genotypes were evident in 119 Taiwanese. When compared with control subjects, the NIDDM group had a much less frequency of the Z+2 allele (14.0% vs. 23.9%). In addition, the Z+2 allele was noted to have a marginal protective effect for NIDDM in Taiwanese with the odds ratio of 0.52 (95% confidence interval (C.I.) 0.26-1.03, P = 0.058). For GCK2, four alleles (0, 2, 4 and 6 with a PIC of 0.48) and seven genotypes were identified. There was no significant difference in allele frequency between NIDDM and control groups in the locus of GCK2. Our data were in agreement with reports from American Blacks, Mauritian Creoles, Asian Indians, Japanese and Finnish--that there is a positive association of GCK1 and a negative association of GCK2 with NIDDM. Furthermore, the Z+2 allele was a protective factor for NIDDM in Taiwanese.

The beta cell in NIDDM: giving light to the blind

Impairment of glucose-induced insulin secretion in non-insulin-dependent diabetes mellitus (NIDDM) may be caused by GLUT 2 underexpression in the pancreatic beta cell, a mutation of the glucokinase gene, glucose 6-phosphatase overactivity, FAD-linked glycerophosphate dehydrogenase deficiency, a mitochondrial DNA defect and/or a secondary phenomenon of so-called glucotoxicity possibly involving glycogen accumulation in the beta-cell. It is proposed tht the methyl esters of succinic acid and related molecules may represent new tools with which to bypass these defects in glucose transport, phosphorylation and further catabolism and, hence, to stimulate both proinsulin biosynthesis and insulin release in NIDDM.

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.