Showing papers by "Marketa Sjögren published in 2007"

Genome-Wide Association Analysis Identifies Loci for Type 2 Diabetes and Triglyceride Levels

Abstract: New strategies for prevention and treatment of type 2 diabetes (T2D) require improved insight into disease etiology. We analyzed 386,731 common single-nucleotide polymorphisms (SNPs) in 1464 patients with T2D and 1467 matched controls, each characterized for measures of glucose metabolism, lipids, obesity, and blood pressure. With collaborators (FUSION and WTCCC/UKT2D), we identified and confirmed three loci associated with T2D-in a noncoding region near CDKN2A and CDKN2B, in an intron of IGF2BP2, and an intron of CDKAL1-and replicated associations near HHEX and in SLC30A8 found by a recent whole-genome association study. We identified and confirmed association of a SNP in an intron of glucokinase regulatory protein (GCKR) with serum triglycerides. The discovery of associated variants in unsuspected genes and outside coding regions illustrates the ability of genome-wide association studies to provide potentially important clues to the pathogenesis of common diseases.

Mechanisms by which common variants in the TCF7L2 gene increase risk of type 2 diabetes

Abstract: Genetic variants in the gene encoding for transcription factor-7-like 2 (TCF7L2) have been associated with type 2 diabetes (T2D) and impaired beta cell function, but the mechanisms have remained unknown. We therefore studied prospectively the ability of common variants in TCF7L2 to predict future T2D and explored the mechanisms by which they would do this. Scandinavian subjects followed for up to 22 years were genotyped for 3 SNPs (rs7903146, rs12255372, and rs10885406) in TCF7L2, and a subset of them underwent extensive metabolic studies. Expression of TCF7L2 was related to genotype and metabolic parameters in human islets. The CT/TT genotypes of SNP rs7903146 strongly predicted future T2D in 2 independent cohorts (Swedish and Finnish). The risk T allele was associated with impaired insulin secretion, incretin effects, and enhanced rate of hepatic glucose production. TCF7L2 expression in human islets was increased 5-fold in T2D, particularly in carriers of the TT genotype. Overexpression of TCF7L2 in human islets reduced glucose-stimulated insulin secretion. In conclusion, the increased risk of T2D conferred by variants in TCF7L2 involves the enteroinsular axis, enhanced expression of the gene in islets, and impaired insulin secretion.

Variation in GYS1 interacts with exercise and gender to predict cardiovascular mortality.

Abstract: Background. The muscle glycogen synthase gene (GYS1) has been associated with type 2 diabetes (T2D), the metabolic syndrome (MetS), male myocardial infarction and a defective increase in muscle glycogen synthase protein in response to exercise. We addressed the questions whether polymorphism in GYS1 can predict cardiovascular (CV) mortality in a high-risk population, if this risk is influenced by gender or physical activity, and if the association is independent of genetic variation in nearby apolipoprotein E gene (APOE). Methodology/Principal Findings. Polymorphisms in GYS1 (XbaIC>T) and APOE (-219G>T, epsilon 2/epsilon 3/epsilon 4) were genotyped in 4,654 subjects participating in the Botnia T2D-family study and followed for a median of eight years. Mortality analyses were performed using Cox proportional-hazards regression. During the follow-up period, 749 individuals died, 409 due to CV causes. In males the GYS1 XbaI T-allele (hazard ratio (HR) 1.9 [1.2-2.9]), T2D (2.5 [1.7-3.8]), earlier CV events (1.7 [1.2-2.5]), physical inactivity (1.9 [1.2-2.9]) and smoking (1.5 [1.0-2.3]) predicted CV mortality. The GYS1 XbaI T-allele predicted CV mortality particularly in physically active males (HR 1.7 [1.3-2.0]). Association of GYS1 with CV mortality was independent of APOE (219TT/epsilon 4), which by its own exerted an effect on CV mortality risk in females (2.9 [1.9-4.4]). Other independent predictors of CV mortality in females were fasting plasma glucose (1.2 [1.1-1.2]), high body mass index (BMI) (1.0 [1.0-1.1]), hypertension (1.9 [1.2-3.1]), earlier CV events (1.9 [1.3-2.8]) and physical inactivity (1.9 [1.2-2.8]). Conclusions/Significance. Polymorphisms in GYS1 and APOE predict CV mortality in T2D families in a gender-specific fashion and independently of each other. Physical exercise seems to unmask the effect associated with the GYS1 polymorphism, rendering carriers of the variant allele less susceptible to the protective effect of exercise on the risk of CV death, which finding could be compatible with a previous demonstration of defective increase in the glycogen synthase protein in carriers of this polymorphism.

Regulation of skeletal muscle PPAR delta mRNA expression in twins.

Abstract: Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors regulating the expression of genes involved in lipid and glucose metabolism in a complex and to some extent unknown manner. Our aim was to study the impact of different factors on PPARδ mRNA expression in human skeletal muscle on one side, and the impact of PPARδ mRNA expression on these factors, including glucose and lipid metabolism, aerobic capacity, fibre type composition and lipid profile, on the other side. PPARδ mRNA levels were quantified by real-time PCR in muscle biopsies from 176 young and elderly monozygotic and dizygotic twins. Young twins had significantly increased PPARδ mRNA levels compared with elderly twins. A 2 h hyperinsulinaemic euglycaemic clamp had no significant effect on PPARδ mRNA levels. Biometric models were calculated for basal PPARδ mRNA expression to estimate the degree of genetic versus environmental influence. In both young and elderly twins there was a substantial genetic component influencing basal PPARδ mRNA levels. In a regression model, the muscle PPARδ mRNA expression was correlated to birth weight, central adiposity and age. The level of PPARδ mRNA was also positively correlated with markers for oxidative muscle fibres. However, in this apparently healthy study population, we found no correlations between PPARδ mRNA expression and aerobic capacity, lipid profile or glucose and lipid metabolism. In conclusion, we provide evidence that mRNA expression of PPARδ in human skeletal muscle is under genetic control but also influenced by factors such as age, birth weight and central adiposity.

Association testing of common variants in the insulin receptor substrate-1 gene (IRS1) with type 2 diabetes.

Abstract: Aims/hypothesis Activation of the insulin receptor substrate-1 (IRS1) is a key initial step in the insulin signalling pathway. Despite several reports of association of the G972R polymorphism in its gene IRS1 with type 2 diabetes, we and others have not observed this association in well-powered samples. However, other nearby variants might account for the putative association signal. Subjects and methods We characterised the haplotype map of IRS1 and selected 20 markers designed to capture common variations in the region. We genotyped this comprehensive set of markers in several family-based and case-control samples of European descent totalling 12,129 subjects. Results In an initial sample of 2,235 North American and Polish case-control pairs, the minor allele of the rs934167 polymorphism showed nominal evidence of association with type 2 diabetes (odds ratio [OR] 1.25, 95% CI 1.03-1.51, p=0.03). This association showed a trend in the same direction in 7,659 Scandinavian samples (OR 1.16, 95% CI 0.96-1.39, p=0.059). The combined OR was 1.20 (p=0.008), but statistical correction for the number of variants examined yielded a p value of 0.086. We detected no differences across rs934167 genotypes in insulin-related quantitative traits. Conclusion/interpretation Our data do not support an association of common variants in IRS1 with type 2 diabetes in populations of European descent.