Type 2 diabetes (T2D) is a common, polygenic chronic disease with high heritability. The purpose of this whole-genome association study was to discover novel T2D-associated genes. We genotyped 500 familial cases and 497 controls with >300,000 HapMap-derived tagging single-nucleotide-polymorphism (SNP) markers. When a stringent statistical correction for multiple testing was used, the only significant SNP was at TCF7L2, which has already been discovered and confirmed as a T2D-susceptibility gene. For a replication study, we selected 10 SNPs in six chromosomal regions with the strongest association (singly or as part of a haplotype) for retesting in an independent case-control set including 2,573 T2D cases and 2,776 controls. The most significant replicated result was found at the AHI1-LOC441171 gene region.

In population-based studies, dyslipidemia related to insulin resistance (high triglyceride level and low high-density lipoprotein cholesterol level) is a risk factor for type 2 diabetes. Therefore, variants in genes regulating lipid and lipoprotein metabolism are potential candidate genes for diabetes. We investigated whether the G-250A polymorphism of the hepatic lipase gene (LIPC) predicts the conversion from impaired glucose tolerance (IGT) to type 2 diabetes in the Finnish Diabetes Prevention Study. This study randomized subjects to either the intervention group (lifestyle modification aimed at weight loss, such as changes in diet and increased physical exercise) or the control group. Genotyping at position -250 of the LIPC gene was performed with PCR amplification, DraI enzyme digestion, and gel electrophoresis in 490 subjects with IGT whose DNA was available. In the entire study population, the conversion rate to type 2 diabetes was 17.8% among subjects with the G-250G genotype and 10.7% among subjects with the -250A allele (P = 0.032). In univariate analysis, the odds ratio for the G-250G genotype to predict the conversion from IGT to type 2 diabetes was 1.80 (95% confidence interval, 1.05-3.10; P = 0.034). In multivariate logistic regression analysis, the G-250G genotype predicted the conversion to diabetes independently of the study group (control or intervention), gender, weight, waist circumference at baseline, and change in weight and waist circumference. In the intervention group, 13.0% of subjects with the G-250G genotype and 1.0% of the subjects with the -250A allele converted to diabetes (P = 0.001). We conclude that the G-250G genotype of the LIPC gene is a risk factor for type 2 diabetes. Therefore, genes regulating lipid and lipoprotein metabolism may be potential candidate genes for type 2 diabetes.

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Abstract. Zacharova J, Todorova BR, Chiasson J.-L., Laakso M for the STOP-NIDDM Study Group

Objectives: Altered glucocorticoid activity is one possible mechanism linking fetal growth restriction with later insulin resistance (IR) and type 2 diabetes. We aimed to investigate whether serum glucocorticoid parameters are related to IR in children born small for gestational age (SGA). Design: A total of 110 children (55 age-and gender-matched pairs born SGA or appropriate for gestational age (AGA) in a case-control setting) were studied at the mean age of 12.2 (S.D. 0.2) years. Methods: Serum cortisol, corticosteroid-binding globulin (CBG), free cortisol index (FCIZcortisol/CBG), and glucocorticoid bioactivity (GBA, transactivation assay) were analyzed and related to serum adiponectin and insulin-like growth factor-binding protein 1 (IGFBP1) concentrations and homeostasis model assessment for IR (HOMA-IR) and QUICKI indices. Results: In the pooled study population, GBA correlated well with cortisol and FCI (rZ0.681 and 0.586 respectively; P!0.001 for both). Serum cortisol, CBG, FCI, GBA, HOMA-IR, or QUICKI did not differ between the SGA and AGA subjects, but the SGA children had lower body mass index (PZ0.005) and waist circumference (WC) (PZ0.001). The mean GBA in the highest GBA quartile was higher among the SGA subjects than among the AGA subjects (138.6 vs 96.4 nmol/l cortisol equivalents, P!0.001). In the SGA children, GBA correlated positively with HOMA-IR (rZ0.522, P!0.001) and inversely with adiponectin (rZK0.278, PZ0.042) (WC/height ratio adjustments), and in logistic regression analysis, higher GBA (odds ratio (OR) 1.3; PZ0.013), lower adiponectin (OR 1.4; PZ0.038), and lower IGFBP1 (OR 1.9; PZ0.010) associated independently with higher HOMA-IR. Conclusions: These findings suggest that increased glucocorticoid activity and low serum adiponectin concentrations associate with IR in SGA children.