Genetic variation in GIPR influences the glucose and insulin responses to an oral glucose challenge.

Glucose levels 2 h after an oral glucose challenge are a clinical measure of glucose tolerance used in the diagnosis of type 2 diabetes. We report a meta-analysis of nine genome-wide association studies (n = 15,234 nondiabetic individuals) and a follow-up of 29 independent loci (n = 6,958-30,620). We identify variants at the GIPR locus associated with 2-h glucose level (rs10423928, beta (s.e.m.) = 0.09 (0.01) mmol/l per A allele, P = 2.0 x 10(-15)). The GIPR A-allele carriers also showed decreased insulin secretion (n = 22,492; insulinogenic index, P = 1.0 x 10(-17); ratio of insulin to glucose area under the curve, P = 1.3 x 10(-16)) and diminished incretin effect (n = 804; P = 4.3 x 10(-4)). We also identified variants at ADCY5 (rs2877716, P = 4.2 x 10(-16)), VPS13C (rs17271305, P = 4.1 x 10(-8)), GCKR (rs1260326, P = 7.1 x 10(-11)) and TCF7L2 (rs7903146, P = 4.2 x 10(-10)) associated with 2-h glucose. Of the three newly implicated loci (GIPR, ADCY5 and VPS13C), only ADCY5 was found to be associated with type 2 diabetes in collaborating studies (n = 35,869 cases, 89,798 controls, OR = 1.12, 95% CI 1.09-1.15, P = 4.8 x 10(-18)).

Gene-environment interactions and obesity--further aspects of genomewide association studies.

Advances in genotyping technologies have facilitated the advent of the genomewide association studies in large study populations and thereby led to the identification of an impressive-and still increasing-number of genetic variants with significant impact on the risk of widespread lifestyle health problems such as obesity, diabetes, and cardiovascular disease. Yet, the scientific community is a long way from reaching a comprehensive picture of the heritable components of these diseases and advancing from plain statistical significance into a biological understanding where the true contribution to a trait is recognized. Increasingly large study populations, denser single-nucleotide polymorphism mapping, deep sequencing, and raised awareness of the importance of structural variants may add to the known genetic variance underlying common complex disorders; however, genetic variance alone probably cannot account for disease susceptibility without the addition of pre- and postnatal environmental and/or behavioral factors. Moreover, an interaction between genetic and environmental factors may hinder the detection of genetic effects if not accounted for, e.g., in genomewide association studies, and prospective cohort studies have hence been proposed to surpass the classic case-control design. With a focus on obesity we describe some of the recently reported gene-environment interactions for polymorphisms identified in the FTO and INSIG2 genes. Ultimately, a thorough understanding of the gene-environment interactions underlying a common complex condition such as obesity may suggest novel treatment or intervention strategies to complement the harmful effect of detrimental genetic variation and thus may assist in improving the quality of life for affected individuals.

Variation in the gene encoding Krüppel-like factor 7 influences body fat: studies of 14 818 Danes.

OBJECTIVE: KLF7 encodes Krüppel-like factor (KLF) 7, a member of the KLF family of transcription factors, initially shown to play important roles in cellular development and differentiation, and reported to be specifically involved in adipogenesis. Several single nucleotide polymorphisms (SNPs) have been identified in KLF7, of which the A-allele of rs2302870 has been associated with type 2 diabetes in a Japanese population; however, a possible association of KLF7 SNPs with obesity has not been investigated. We aimed to identify variation in the putative promoter region, the coding regions, exon/intron boundaries, and 3'-UTR of KLF7, and to examine identified variants in relation to obesity, type 2 diabetes, and related quantitative traits in Danish individuals. METHODS: Identified variants were investigated for association with type 2 diabetes in 8777 individuals and with obesity in 14 818 individuals. RESULTS: We identified four common SNPs in low pairwise linkage disequilibrium; three in the putative promoter region (-1119 G>A, -963 C>A (rs7568369), and -614 G>A) and IVS2+35092 A>C (rs2302870). We failed to confirm an association between rs2302870 and type 2 diabetes. Neither was rs7568369 associated with type 2 diabetes; however, the minor A-allele of rs7568369 protected against obesity (OR=0.90 (0.84-0.96), P=0.001) and in studies of quantitative traits (n=5,535) the variant associated with decreased body mass index (P=0.002) and waist circumference (P=0.003). The -1119 G>A and -614 G>A variants were not associated with obesity or type 2 diabetes. CONCLUSION: We identified a novel association between the minor A-allele of KLF7 rs7568369 and protection against obesity in the Danish population.

Variants near MC4R are associated with obesity and influence obesity-related quantitative traits in a population of middle-aged people: studies of 14,940 Danes.

OBJECTIVE: Variants downstream of the melanocortin-4 receptor gene (MC4R) have been reported to associate with obesity. We examined rs17782313, rs17700633, rs12970134, rs477181, rs502933, and rs4450508 near MC4R for association with obesity-related quantitative traits, obesity, and type 2 diabetes in Danish individuals. RESEARCH DESIGN AND METHODS: The variants were investigated for association with obesity-related quantitative traits in 5,807 population-based sampled individuals, obesity in 14,940 individuals, and type 2 diabetes in 8,821 individuals. RESULTS: The minor risk alleles of rs17782313, rs17700633, and rs12970134 were associated with BMI (effect per allele 0.25 kg/m2, P = 0.01; 0.23, P = 0.01; and 0.31, P = 7 x 10(-4), respectively), waist circumference (0.67 cm, P = 0.006; 0.53, P = 0.02; and 0.85, P = 3 x 10(-4)), and body weight (1.04 kg, P = 6 x 10(-4); 0.71, P = 0.01; and 1.16, P = 8 x 10(-5)). In case-control studies of obesity defined by BMI, the minor C-allele of rs17782313 was associated with overweight/obesity and obesity (odds ratio [OR] 1.09, P = 0.006 and OR 1.12, P = 0.003, respectively). Similarly, the minor A-allele of rs17700633 was associated with overweight/obesity and obesity (1.12, P = 8 x 10(-5) and 1.16, P = 2 x 10(-5)), and the minor A-allele of rs12970134 was also associated with overweight/obesity and obesity (1.13, P = 2 x 10(-5) and 1.15, P = 6 x 10(-5)). rs477181, rs502933, and rs4450508 were not significantly associated with obesity in the Danish population. The frequency of the minor risk alleles of rs17782313 and rs12970134 was higher among patients with type 2 diabetes than among glucose-tolerant individuals (OR 1.08, P = 0.08 and 1.08, P = 0.06, respectively); however, these borderline associations were abolished after adjustment for BMI. CONCLUSIONS: rs17782313, rs17700633, and rs12970134 near MC4R associate with measures of obesity in Danish individuals.

Non-replication of genome-wide based associations between common variants in INSIG2 and PFKP and obesity in studies of 18,014 Danes.

BACKGROUND: The INSIG2 rs7566605 and PFKP rs6602024 polymorphisms have been identified as obesity gene variants in genome-wide association (GWA) studies. However, replication has been contradictory for both variants. The aims of this study were to validate these obesity-associations through case-control studies and analyses of obesity-related quantitative traits. Moreover, since environmental and genetic factors may modulate the impact of a genetic variant, we wanted to perform such interaction analyses. We focused on physical activity as an environmental risk factor, and on the GWA identified obesity variants in FTO (rs9939609) and near MC4R (rs17782313) as genetic risk factors. MATERIALS AND METHODS: The four variants were genotyped in a combined study sample comprising a total of 18,014 subject ascertained from, the population-based Inter99 cohort (n = 6,514), the ADDITION screening cohort (n = 8,662), a population-based study sample (n = 680) and a type 2 diabetic patient group (n = 2,158) from Steno Diabetes Center. RESULTS: No association with overweight, obesity or obesity-related measures was shown for either the INSIG2 rs7566605 or the PFKP rs6602024 variants. However, an interaction between the INSIG2 rs7566605 variant and the level of self-reported physical activity (p(Int) = 0.004) was observed. A BMI difference of 0.53 (SE 0.42) kg/m(2) was found when comparing physically passive homozygous C-allele carriers with physically passive G-allele carriers. No interactions between the two variants and FTO rs9939609 and MC4R rs17782313 were observed. CONCLUSIONS: The INSIG2 rs7566605 and PFKP rs6602024 polymorphisms play no apparent role in the development of common forms of obesity in the Danish population. However, if replicated, the INSIG2 rs7566605 may influence the level of BMI in combination with the level of physical activity.

The -250G>A promoter variant in hepatic lipase associates with elevated fasting serum high-density lipoprotein cholesterol modulated by interaction with physical activity in a study of 16,156 Danish subjects.

CONTEXT: Hepatic lipase plays a pivotal role in the metabolism of high-density lipoprotein (HDL) and low-density lipoprotein by involvement in reverse cholesterol transport and the formation of atherogenic small dense low-density lipoprotein. OBJECTIVES: The objective was to investigate the impact of variants in LIPC on metabolic traits and type 2 diabetes in a large sample of Danes. Because behavioral factors influence hepatic lipase activity, we furthermore examined possible gene-environment interactions in the population-based Inter99 study. DESIGN: The LIPC -250G>A (rs2070895) variant was genotyped in the Inter99 study (n = 6070), the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care Denmark screening cohort of individuals with risk factors for undiagnosed type 2 diabetes (n = 8662), and in additional type 2 diabetic patients (n = 1,064) and glucose-tolerant control subjects (n = 360). RESULTS: In the Inter99 study, the A allele of rs2070895 associated with a 0.057 mmol/liter [95% confidence interval (CI) 0.039-0.075] increase in fasting serum HDL-cholesterol (HDL-c) (P = 8 x 10(-10)) supported by association in the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care study [0.038 mmol/liter per allele (95% CI 0.024-0.053); P = 2 x 10(-7)). The allelic effect on HDL-c was modulated by interaction with self-reported physical activity (P(interaction) = 0.002) because vigorous physically active homozygous A-allele carriers had a 0.30 mmol/liter (95% CI 0.22-0.37) increase in HDL-c compared with homozygous G-allele carriers. CONCLUSIONS: We validate the association of LIPC promoter variation with fasting serum HDL-c and present data supporting an interaction with physical activity implying an increased effect on HDL-c in vigorous physically active subjects carrying the -250 A allele. This interaction may have potential implications for public health and disease prevention.

Low physical activity accentuates the effect of the FTO rs9939609 polymorphism on body fat accumulation.

OBJECTIVE: Three independent studies have shown that variation in the fat mass and obesity-associated (FTO) gene associates with BMI and obesity. In the present study, the effect of FTO variation on metabolic traits including obesity, type 2 diabetes, and related quantitative phenotypes was examined. RESEARCH DESIGN AND METHODS: The FTO rs9939609 polymorphism was genotyped in a total of 17,508 Danes from five different study groups. RESULTS: In studies of 3,856 type 2 diabetic case subjects and 4,861 normal glucose-tolerant control subjects, the minor A-allele of rs9939609 associated with type 2 diabetes (odds ratio 1.13 [95% CI 1.06-1.20], P = 9 x 10(-5)). This association was abolished when adjusting for BMI (1.06 [0.97-1.16], P = 0.2). Among 17,162 middle-aged Danes, the A-allele associated with overweight (1.19 [1.13-1.24], P = 1 x 10(-12)) and obesity (1.27 [1.20-1.34], P = 2 x 10(-16)). Furthermore, obesity-related quantitative traits such as body weight, waist circumference, fat mass, and fasting serum leptin levels were significantly elevated in A-allele carriers. An interaction between the FTO rs9939609 genotype and physical activity (P = 0.007) was found, where physically inactive homozygous risk A-allele carriers had a 1.95 +/- 0.3 kg/m(2) increase in BMI compared with homozygous T-allele carriers. CONCLUSIONS: We validate that variation in FTO is associated with type 2 diabetes when not adjusted for BMI and with an overall increase in body fat mass. Furthermore, low physical activity seems to accentuate the effect of FTO rs9939609 on body fat accumulation.

The functional Pro129Thr variant of the FAAH gene is not associated with various fat accumulation phenotypes in a population-based cohort of 5,801 whites.

Food intake and weight gain are influenced by endocannabinoids whose actions are regulated by the fatty acid amide hydrolase (FAAH) enzyme. The homozygous Thr/Thr genotype of the functional Pro129Thr variant (rs324420) in the gene encoding FAAH was recently reported to associate with overweight and obesity in white and black populations. We investigated the Pro129Thr variant in relation to overweight and obesity in a relatively large population-based study sample of Danish whites (n=5,801). In case-control studies of obesity, a borderline association with the major Pro allele was identified; however, after correction for multiple testing, no association was found. Furthermore, a possible association between the major Pro allele and obesity was not supported by studies of obesity-related quantitative traits. In conclusion, in a large study sample, we were unable to find robust evidence of an association of the Pro129Thr FAAH variant with overweight, obesity, and any related quantitative traits among the examined whites.

Studies of the common DIO2 Thr92Ala polymorphism and metabolic phenotypes in 7342 Danish white subjects.

CONTEXT: The type 2 iodothyronine deiodinase (D2) catalyzes the conversion of T(4) to the active form of thyroid hormone, which is a critical regulator of thermogenesis and glucose metabolism. A Thr92Ala polymorphism in the gene encoding D2 (DIO2) has been reported to associate with insulin resistance. OBJECTIVE: The aim of the present study was to assess the impact of the DIO2 Thr92Ala variant on type 2 diabetes (T2D), obesity, and related quantitative metabolic traits including measures of insulin resistance. Because DIO2 is activated through a beta-adrenergic receptor-dependent pathway, we further hypothesized that variation in the ADRB genes interacts with DIO2 Thr92Ala variant to influence metabolic traits. DESIGN AND PATIENTS: The DIO2 polymorphism was genotyped in a total of 7342 white subjects including 1405 T2D patients. RESULTS: We detected no significant association of the DIO2 Thr92Ala polymorphism with T2D or obesity. We observed nominal significant associations of genotype with increased area under the serum insulin curve during an oral glucose tolerance test (P = 0.03) and elevated fasting plasma glucose (P = 0.02) in homozygous Ala92 allele carriers, the latter strengthened by epistasis with the ADRB2 Gly16Arg variant in a double recessive model (P = 0.004). However, after permutation procedure, performed to correct for multiple hypothesis testing, the associations did not reach study-wide significance. CONCLUSIONS: The DIO2 Thr92Ala variant does not confer an increased risk of T2D, obesity, or insulin resistance.