Common variants in CDKAL1, CDKN2A/B, IGF2BP2, SLC30A8, and HHEX/IDE genes are associated with type 2 diabetes and impaired fasting glucose in a Chinese Han population

OBJECTIVE— Genome-wide association studies have identified common variants in CDKAL1, CDKN2A/B, IGF2BP2, SLC30A8, HHEX/IDE, EXT2, and LOC387761 loci that significantly increase the risk of type 2 diabetes. We aimed to replicate these observations in a population-based cohort of Chinese Hans and examine the associations of these variants with type 2 diabetes and diabetes-related phenotypes.RESEARCH DESIGN AND METHODS— We genotyped 17 single nucleotide polymorhisms (SNPs) in 3,210 unrelated Chinese Hans, including 424 participants with type 2 diabetes, 878 with impaired fasting glucose (IFG), and 1,908 with normal fasting glucose.RESULTS— We confirmed the associations between type 2 diabetes and variants near CDKAL1 (odds ratio 1.49 [95% CI 1.27–1.75]; P = 8.91 × 10⁻⁷) and CDKN2A/B (1.31 [1.12–1.54]; P = 1.0 × 10⁻³). We observed significant association of SNPs in IGF2BP2 (1.17 [1.03–1.32]; P = 0.014) and SLC30A8 (1.12 [1.01–1.25]; P = 0.033) with combined IFG/type 2 diabetes. The SNPs in CDKAL1, IGF2BP2, and SLC30A8 were also associated with impaired β-cell function estimated by homeostasis model assessment of β-cell function. When combined, each additional risk allele from CDKAL1-rs9465871, CDKN2A/B-rs10811661, IGF2BP2-rs4402960, and SLC30A8-rs13266634 increased the risk for type 2 diabetes by 1.24-fold (P = 2.85 × 10⁻⁷) or for combined IFG/type 2 diabetes by 1.21-fold (P = 6.31 × 10⁻¹¹). None of the SNPs in EXT2 or LOC387761 exhibited significant association with type 2 diabetes or IFG. Significant association was observed between the HHEX/IDE SNPs and type 2 diabetes in individuals from Shanghai only (P < 0.013) but not in those from Beijing (P > 0.33).CONCLUSIONS— Our results indicate that in Chinese Hans, common variants in CDKAL1, CDKN2A/B, IGF2BP2, and SLC30A8 loci independently or additively contribute to type 2 diabetes risk, likely mediated through β-cell dysfunction.The rapid increase in prevalence of type 2 diabetes has been a major public health challenge worldwide, including China. The total number of people with diabetes in China is estimated to increase from 20.8 million in 2000 to 42.3 million in 2030 (1). Besides the important contribution of environmental factors, including changes in dietary patterns and lifestyle, genetic determinants also play a major role in type 2 diabetes susceptibility. Over the past decade, serious efforts have been put into the search for type 2 diabetes susceptibility genes, but progress has been slower than anticipated (2,3). Although common variants in a few genes including PPARG, KCNJ11, and TCF7L2 have been convincingly replicated in individuals with European ancestry, relatively few studies have been conducted in Chinese, and, so far, no variants have been unambiguously confirmed as diabetes susceptibility loci in Chinese. However, recent advances in genome-wide association studies (GWASs) have revived the initial optimism and accelerated the discovery of diabetes susceptibility genes (4–6).The first GWAS, conducted in a French case-control cohort, confirmed TCF7L2 as a major type 2 diabetes susceptibility gene and identified four novel loci consistently associated with type 2 diabetes (7). These loci are located in chromosomal regions that harbor several genes involved in β-cell function or development, including a variant in the SLC30A8 (zinc transporter solute carrier family 30 member 8) gene, variants located in a linkage disequilibrium (LD) block that contains the IDE (insulin-degrading enzyme), KIF11 (kinesin family member 11), and the HHEX (hematopoietically expressed homeobox) genes, as well as variants in another LD block that contains genes encoding EXT2 (exostosin 2). A fourth locus mapped to a hypothetical gene LOC387761 on chromosome 11. Four subsequent GWASs (8–12), performed in European case-control studies, confirmed the SLC30A8 and HHEX/IDE genes as type 2 diabetes susceptibility loci. Furthermore, additional variants in several new gene regions were also identified, including single nucleotide polymorhisms (SNPs) in the CDKAL1 gene, which encodes the CDK5 regulatory subunit associated protein 1-like 1; in the CDKN2A/B genes, which encode the cyclin-dependent kinase inhibitor p15^INK4a and p16^INK4b; in the IGF2BP2 gene, which encodes the IGF-2 mRNA binding protein 2; and a variant in a region of chromosome 11, not known to contain any genes. Most of these newly identified loci are suggested to play a role in the regulation of insulin production and β-cell function (5,7,9,12–15). It is unclear whether these variants have the same effect in Chinese populations, which have a different genetic background and lower diabetes prevalence compared with European populations (16–18).Although case-control studies provide a useful design for the discovery of susceptibility loci, they are limited in providing insight into the mechanisms through which genetic variants exert their effect on the risk of type 2 diabetes. Population-based cohort studies with detailed measures of diabetes-related traits, however, might unravel the physiopathology that underlies the association between the newly discovered genetic variants and diabetes. The purpose of this study is to examine whether these novel variants are individually or collectively associated with type 2 diabetes and related traits in a population-based Chinese Han cohort including 3,210 unrelated individuals from Beijing and Shanghai.     

Association analysis in african americans of European-derived type 2 diabetes single nucleotide polymorphisms from whole-genome association studies

OBJECTIVE— Several whole-genome association studies have reported identification of type 2 diabetes susceptibility genes in various European-derived study populations. Little investigation of these loci has been reported in other ethnic groups, specifically African Americans. Striking differences exist between these populations, suggesting they may not share identical genetic risk factors. Our objective was to examine the influence of type 2 diabetes genes identified in whole-genome association studies in a large African American case-control population.RESEARCH DESIGN AND METHODS— Single nucleotide polymorphisms (SNPs) in 12 loci (e.g., TCF7L2, IDE/KIF11/HHEX, SLC30A8, CDKAL1, PKN2, IGF2BP2, FLJ39370, and EXT2/ALX4) associated with type 2 diabetes in European-derived populations were genotyped in 993 African American type 2 diabetic and 1,054 African American control subjects. Additionally, 68 ancestry-informative markers were genotyped to account for the impact of admixture on association results.RESULTS— Little evidence of association was observed between SNPs, with the exception of those in TCF7L2, and type 2 diabetes in African Americans. One TCF7L2 SNP (rs7903146) showed compelling evidence of association with type 2 diabetes (admixture-adjusted additive P [P_a] = 1.59 × 10⁻⁶). Only the intragenic SNP on 11p12 (rs9300039, dominant P [P_d] = 0.029) was also associated with type 2 diabetes after admixture adjustments. Interestingly, four of the SNPs are monomorphic in the Yoruba population of the HAPMAP project, with only the risk allele from the populations of European descent present.CONCLUSIONS— Results suggest that these variants do not significantly contribute to interindividual susceptibility to type 2 diabetes in African Americans. Consequently, genes contributing to type 2 diabetes in African Americans may, in part, be different from those in European-derived study populations. High frequency of risk alleles in several of these genes may, however, contribute to the increased prevalence of type 2 diabetes in African Americans.Recently, several whole-genome association (WGA) studies have reported evidence for the existence of multiple type 2 diabetes susceptibility genes. These results were primarily observed in different European-derived study populations. Included in these loci are polymorphisms in TCF7L2 (1–5), HHEX (1–6), SLC30A8 (1–4,6), CDKAL1 (2–6), IGF2BP2 (3–6), FTO (4–7), PKN2 (3,4), FLJ39370 (3), EXT2/ALX4 (1), and LOC387761 (1). Despite the compelling evidence of association of many of these genes in European-derived study populations, little or no investigation of association has been reported for African Americans.Differences between European-derived and African American populations (e.g., haplotype block structure and allele frequency discrepancies) suggest that the genetic risk factors of each may not be identical. Previously, we have reported that common genetic variants in TCF7L2 and HNF4A contribute to type 2 diabetes in African Americans, whereas polymorphisms in CAPN10, TCF1, and PPARG have little or no evidence of association (8). Lack of association with other type 2 diabetes susceptibility loci in African Americans has also been observed (9). In addition, differences in allele frequencies of risk polymorphisms between ethnicities have been shown (e.g., Chandalia et al. [10]). These substantial discrepancies could contribute to the differences in overall prevalence of type 2 diabetes within these ethnic groups. Consequently, we examined the influence of single nucleotide polymorphisms (SNPs) recently identified in WGA studies on type 2 diabetes susceptibility in a large African American case-control population.     

Comprehensive association study of type 2 diabetes and related quantitative traits with 222 candidate genes

OBJECTIVE—Type 2 diabetes is a common complex disorder with environmental and genetic components. We used a candidate gene–based approach to identify single nucleotide polymorphism (SNP) variants in 222 candidate genes that influence susceptibility to type 2 diabetes.RESEARCH DESIGN AND METHODS—In a case-control study of 1,161 type 2 diabetic subjects and 1,174 control Finns who are normal glucose tolerant, we genotyped 3,531 tagSNPs and annotation-based SNPs and imputed an additional 7,498 SNPs, providing 99.9% coverage of common HapMap variants in the 222 candidate genes. Selected SNPs were genotyped in an additional 1,211 type 2 diabetic case subjects and 1,259 control subjects who are normal glucose tolerant, also from Finland.RESULTS—Using SNP- and gene-based analysis methods, we replicated previously reported SNP-type 2 diabetes associations in PPARG, KCNJ11, and SLC2A2; identified significant SNPs in genes with previously reported associations (ENPP1 [rs2021966, P = 0.00026] and NRF1 [rs1882095, P = 0.00096]); and implicated novel genes, including RAPGEF1 (rs4740283, P = 0.00013) and TP53 (rs1042522, Arg72Pro, P = 0.00086), in type 2 diabetes susceptibility.CONCLUSIONS—Our study provides an effective gene-based approach to association study design and analysis. One or more of the newly implicated genes may contribute to type 2 diabetes pathogenesis. Analysis of additional samples will be necessary to determine their effect on susceptibility.Type 2 diabetes is a metabolic disorder characterized by insulin resistance and pancreatic β-cell dysfunction and is a leading cause of morbidity and mortality in the U.S. and worldwide. The incidence of type 2 diabetes is rapidly increasing, with 1.6 million new cases of diabetes diagnosed in individuals aged ≥20 years in the U.S. in 2007 (available at http://www.diabetes.niddk.nih.gov/dm/pubs/statistics/). While environmental factors play a major role in predisposition to type 2 diabetes, substantial evidence supports the influence of genetic factors on disease susceptibility. For example, the twin concordance rate is an estimated 34% for monozygotic twins and 16% for dizygotic twins (1). However, the underlying genetic variants are just beginning to be identified (2).Numerous published reports (3–5) have identified association between type 2 diabetes and common genetic variants in human populations; however, until very recently, variants in only a few genes have been consistently replicated across populations and with large sample sizes. Among these are the Pro12Ala (rs1801282) variant in peroxisome proliferator–activated receptor γ (PPARG) (6), the Glu23Lys (rs5210) variant in the potassium channel gene KCNJ11 (7), and several variants in the Wnt-receptor signaling pathway member TCF7L2 (8).Recent genome-wide studies have implicated many previously unreported genes in type 2 diabetes susceptibility. The first reported genome-wide association (GWA) scan implicated variants at five susceptibility loci that include TCF7L2 and novel loci near the genes SLC30A8, IDE-KIF11-HHEX, LOC387761, and EXT-ALX4 (9). Three companion GWA studies (10–12), including one by our group, replicated evidence for PPARG, KCNJ11, TCF7L2, SLC30A8, and IDE-KIF11-HHEX and provided new evidence for CDKAL1, CDKN2A-CDKN2B, IGF2BP2, FTO, and a region of chromosome 11 with no annotated genes. Additional GWA studies (13–18) provided additional evidence for TCF7L2, CDKAL1, and SLC30A8. The candidate genes WFS1 (19) and TCF2 (20,21) have also been confirmed in large samples, bringing the current list of type 2 diabetes susceptibility loci to at least 10. The recent discovery of these loci still explains only a small fraction (∼2.3%) of the overall risk of type 2 diabetes (12). Therefore, novel susceptibility genes remain to be identified through increasingly comprehensive analyses of both individual genes and the entire genome.The Finland-U.S. Investigation of Type 2 Diabetes Genetics (FUSION) study aims to identify variants influencing susceptibility to type 2 diabetes and related quantitative traits in the Finnish population (22). FUSION has previously identified modest type 2 diabetes association in Finns with variants in HNF4A (23); four genes known to cause maturity-onset diabetes of the young (5,23,24); PPARG, KCNJ11, ENPP1, SLC2A2, PCK1, TNF, IL6 (5), and TCF7L2 (25); and the loci identified in the GWA studies.As a complementary approach to GWA studies, which are conducted without a priori biological hypotheses, we sought to perform an in-depth analysis of >200 genes likely to influence susceptibility to type 2 diabetes and quantitative trait variation that we selected by applying CandidAtE Search And Rank (CAESAR), a text- and data-mining algorithm (26). We aimed to analyze the full spectrum of HapMap-based common variation in each of these candidate genes. The combination of high throughput genotyping, linkage disequilibrium (LD) information from HapMap (27), the ability to impute ungenotyped variants (28), and the improved functional annotation of the genome makes in-depth candidate gene–based association analysis possible.     

Implication of genetic variants near TCF7L2, SLC30A8, HHEX, CDKAL1, CDKN2A/B, IGF2BP2, and FTO in type 2 diabetes and obesity in 6,719 Asians

OBJECTIVE— Recent genome-wide association studies have identified six novel genes for type 2 diabetes and obesity and confirmed TCF7L2 as the major type 2 diabetes gene to date in Europeans. However, the implications of these genes in Asians are unclear.RESEARCH DESIGN AND METHODS— We studied 13 associated single nucleotide polymorphisms from these genes in 3,041 patients with type 2 diabetes and 3,678 control subjects of Asian ancestry from Hong Kong and Korea.RESULTS— We confirmed the associations of TCF7L2, SLC30A8, HHEX, CDKAL1, CDKN2A/CDKN2B, IGF2BP2, and FTO with risk for type 2 diabetes, with odds ratios ranging from 1.13 to 1.35 (1.3 × 10⁻¹² < P_unadjusted < 0.016). In addition, the A allele of rs8050136 at FTO was associated with increased BMI in the control subjects (P_unadjusted = 0.008). However, we did not observe significant association of any genetic variants with surrogate measures of insulin secretion or insulin sensitivity indexes in a subset of 2,662 control subjects. Compared with subjects carrying zero, one, or two risk alleles, each additional risk allele was associated with 17% increased risk, and there was an up to 3.3-fold increased risk for type 2 diabetes in those carrying eight or more risk alleles. Despite most of the effect sizes being similar between Asians and Europeans in the meta-analyses, the ethnic differences in risk allele frequencies in most of these genes lead to variable attributable risks in these two populations.CONCLUSIONS— Our findings support the important but differential contribution of these genetic variants to type 2 diabetes and obesity in Asians compared with Europeans.Type 2 diabetes is a major health problem affecting more than 170 million people worldwide. In the next 20 years, Asia will be hit hardest, with the diabetic populations in India and China more than doubling (1). Type 2 diabetes is characterized by the presence of insulin resistance and pancreatic β-cell dysfunction, resulting from the interaction of genetic and environmental factors. Until recently, few genes identified through linkage scans or the candidate gene approach have been confirmed to be associated with type 2 diabetes (e.g., PPARG, KCNJ11, CAPN10, and TCF7L2). Under the common variant–common disease hypothesis, several genome-wide association (GWA) studies on type 2 diabetes have been conducted in large-scale case-control samples. Six novel genes (SLC30A8, HHEX, CDKAL1, CDKN2A and CDKN2B, IGF2BP2, and FTO) with modest effect for type 2 diabetes (odds ratio [OR] 1.14–1.20) had been reproducibly demonstrated in multiple populations of European ancestry. Moreover, TCF7L2 was shown to have the largest effect for type 2 diabetes (1.37) in the European populations to date (2–8). Although many of these genes may be implicated in the insulin production/secretion pathway (TCF7L2, SLC30A8, HHEX, CDKAL1, CDKN2A/B, and IGF2BP2) (6,9–11), FTO is associated with type 2 diabetes through its regulation of adiposity (8,12,13). Moreover, two adjacent regions near CDKN2A/B are associated with type 2 diabetes and cardiovascular diseases risks, respectively (7,14–16). Despite the consistent associations among Europeans, the contributions of these genetic variants in other ethnic groups are less clear. Given the differences in environmental factors (e.g., lifestyle), risk factor profiles (body composition and insulin secretion/resistance patterns), and genetic background (linkage disequilibrium pattern and risk allele frequencies) between Europeans and Asians, it is important to understand the role of these genes in Asians. A recent case-control study in 1,728 Japanese subjects revealed nominal association to type 2 diabetes for variants at the SLC30A8, HHEX, CDKAL1, CDKN2B, and FTO genes but not IGF2BP2 (17). In the present large-scale case-control replication study of 6,719 Asians, we aimed to test for the association of six novel genes from GWA studies and TCF7L2, which had the largest effect in Europeans, and their joint effects on type 2 diabetes risk and metabolic traits.     

Association testing of novel type 2 diabetes risk alleles in the JAZF1, CDC123/CAMK1D, TSPAN8, THADA, ADAMTS9, and NOTCH2 loci with insulin release, insulin sensitivity, and obesity in a population-based sample of 4,516 glucose-tolerant middle-aged Danes

OBJECTIVE— We evaluated the impact on diabetes-related intermediary traits of common novel type 2 diabetes–associated variants in the JAZF1 (rs864745), CDC123/CAMK1D (rs12779790), TSPAN8 (rs7961581), THADA (rs7578597), ADAMTS9 (rs4607103), and NOTCH2 (rs10923931) loci, which were recently identified by meta-analysis of genome-wide association data.RESEARCH DESIGN AND METHODS— We genotyped the six variants in 4,516 middle-aged glucose-tolerant individuals of the population-based Inter99 cohort who were all characterized by an oral glucose tolerance test (OGTT).RESULTS— Homozygous carriers of the minor diabetes risk G-allele of the CDC123/CAMK1D rs12779790 showed an 18% decrease in insulinogenic index (95% CI 10–27%; P = 4 × 10⁻⁵), an 18% decrease in corrected insulin response (CIR) (8.1–29%; P = 4 × 10⁻⁴), and a 13% decrease in the ratio of area under the serum-insulin and plasma-glucose curves during an OGTT (AUC-insulin/AUC-glucose) (5.8–20%; P = 4 × 10⁻⁴). Carriers of the diabetes-associated T-allele of JAZF1 rs864745 had an allele-dependent 3% decrease in BIGTT-AIR (0.9–4.3%; P = 0.003). Furthermore, the diabetes-associated C-allele of TSPAN8 rs7961581 associated with decreased levels of CIR (4.5% [0.5–8.4]; P = 0.03), of AUC-insulin/AUC-glucose ratio (3.9% [1.2–6.7]; P = 0.005), and of the insulinogenic index (5.2% [1.9–8.6]; P = 0.002). No association with traits of insulin release or insulin action was observed for the THADA, ADAMTS9, or NOTCH2 variants.CONCLUSIONS— If replicated, our data suggest that type 2 diabetes at-risk alleles in the JAZF1, CDC123/CAMK1D, and TSPAN8 loci associate with various OGTT-based surrogate measures of insulin release, emphasizing the contribution of abnormal pancreatic β-cell function in the pathogenesis of type 2 diabetes.Recent discoveries using genome-wide association (GWA) studies have led to progression in the understanding of the molecular genetic background of type 2 diabetes, dramatically increasing the number of common validated type 2 diabetes loci with modest impact on relative diabetes risk (1–5). The Diabetes Genetics Replication and Meta-analysis (DIAGRAM) consortium recently reported the outcome of a meta-analysis of data from three GWA studies. Six additional type 2 diabetes loci reaching genome-wide significance levels were identified in the JAZF1, CDC123/CAMK1D, TSPAN8, THADA, ADAMTS9, and NOTCH2 loci; all were modestly affecting disease risk with odds ratios between 1.09 and 1.15 (6).As for most other findings obtained from GWA studies, little is known about the function of the putative regional candidate genes thought to be affected by the at-risk variants. Recent studies have, however, shown that many validated type 2 diabetes risk variants confer an impaired pancreatic β-cell function, which seems to be the case for risk alleles in the CDKAL1, SLC30A8, HHEX/IDE, CDKN2A/2B, IGF2BP2, TCF7L2, and KCNJ11 loci (2,7–9). Indeed, only the PPARG Pro12Ala variant has so far displayed a diabetogenic potential through affecting peripheral insulin sensitivity (10) and variants in FTO by increasing fat accumulation (11). Of the six novel type 2 diabetes loci (6), the biological function of NOTCH2 points to an impact on pancreatic β-cell function because of its critical role in fetal pancreatic development (12), yet little or no prior implication in the pathogenesis of type 2 diabetes or diabetes-related phenotypes can be claimed for genes in the JAZF1, CDC123/CAMK1D, TSPAN8, THADA, or ADAMTS9 regions.Given the sparse knowledge of the biological functions of the six novel type 2 diabetes–associated variants, we have characterized the influence of these variants on quantitative surrogate measures of oral glucose-stimulated insulin release, insulin sensitivity, and body fat accumulation in a population-based study of glucose-tolerant middle-aged Danes who all had undertaken an oral glucose tolerance test (OGTT).     

Population-specific risk of type 2 diabetes conferred by HNF4A P2 promoter variants: a lesson for replication studies

OBJECTIVE—Single nucleotide polymorphisms (SNPs) in the P2 promoter region of HNF4A were originally shown to be associated with predisposition for type 2 diabetes in Finnish, Ashkenazi, and, more recently, Scandinavian populations, but they generated conflicting results in additional populations. We aimed to investigate whether data from a large-scale mapping approach would replicate this association in novel Ashkenazi samples and in U.K. populations and whether these data would allow us to refine the association signal.RESEARCH DESIGN AND METHODS—Using a dense linkage disequilibrium map of 20q, we selected SNPs from a 10-Mb interval centered on HNF4A. In a staged approach, we first typed 4,608 SNPs in case-control populations from four U.K. populations and an Ashkenazi population (n = 2,516). In phase 2, a subset of 763 SNPs was genotyped in 2,513 additional samples from the same populations.RESULTS—Combined analysis of both phases demonstrated association between HNF4A P2 SNPs (rs1884613 and rs2144908) and type 2 diabetes in the Ashkenazim (n = 991; P < 1.6 × 10⁻⁶). Importantly, these associations are significant in a subset of Ashkenazi samples (n = 531) not previously tested for association with P2 SNPs (odds ratio [OR] ∼1.7; P < 0.002), thus providing replication within the Ashkenazim. In the U.K. populations, this association was not significant (n = 4,022; P > 0.5), and the estimate for the OR was much smaller (OR 1.04; [95%CI 0.91–1.19]).CONCLUSIONS—These data indicate that the risk conferred by HNF4A P2 is significantly different between U.K. and Ashkenazi populations (P < 0.00007), suggesting that the underlying causal variant remains unidentified. Interactions with other genetic or environmental factors may also contribute to this difference in risk between populations.The presence of type 2 diabetes susceptibility genes on chromosome 20 has been suggested by linkage scans in several populations. The 20q12–q13 region (Online Mendelian Inheritance in Man [OMIM] 603694) is the best replicated and harbors the gene HNF4A, mutations that lead to type 1 maturity-onset diabetes of the young (OMIM 125850). Evidence for association between SNPs in the β-cell P2 promoter region of HNF4A has been recognized in Finnish (1) and Ashkenazi (2) populations, with data suggesting that the HNF4A P2 SNPs (or variants in strong linkage disequilibrium with them) contribute to the linkage signal on chromosome 20q (1,2). Association with HNF4A promoter SNPs has been replicated in some (3–7) but not all (8–12) populations tested. In other populations, there was evidence for association with SNPs or haplotypes in the HNF4A region other than the P2 SNPs (10,13–15). More recently, the association between HNF4A promoter SNPs and type 2 diabetes has been confirmed in Scandinavians but not in a broader meta-analysis with additional populations (16), suggesting that P2 SNPs confer varying risk effects in different populations, possibly due to the underlying causal variant not having been identified. We investigated a 10-Mb interval (38.1–48.2 Mb National Center for Biotechnology Information build 35) centered around HNF4A, including genotypes from 4,608 nonredundant (r² < 1) SNPs (one SNP per 2 Kb, on average) in five type 2 diabetic case-control populations, to evaluate whether we could confirm and refine the association signal in Ashkenazim and whether this association was also present in U.K. populations. We were also interested in assessing whether there was evidence for additional association signals within this broader interval. We tested an Ashkenazi type 2 diabetes case-control study (n = 998), including novel samples (n = 531) not previously tested for linkage or association with HNF4A P2 SNPs (2); two U.K. population-based case-control studies where linkage and association studies with HNF4A P2 had not be carried out (n = 2,189); and two additional U.K. case-control collections (n = 1,842), with one enriched for earlier-onset type 2 diabetes where linkage studies had not been done but that showed suggestive association with HNF4A P2 SNPs (4) and one that included samples where, despite no evidence of linkage to chromosome 20q, association of HNF4A P2 SNPs with type 2 diabetes risk had previously been suggested (4,17).     

Association of Adiponectin Gene Polymorphisms With Type 2 Diabetes in an African American Population Enriched for Nephropathy

OBJECTIVE—Polymorphisms in the adiponectin gene (ADIPOQ) have been associated with type 2 diabetes and diabetic nephropathy in type 1 diabetes, in mostly European-derived populations.RESEARCH DESIGN AND METHODS—A comprehensive association analysis of 24 single-nucleotide polymorphisms (SNPs) in the adiponectin gene was performed for type 2 diabetes and diabetic nephropathy in African Americans.RESULTS—The minor allele (A) in a single SNP in intron 1 (rs182052) was associated with diabetic nephropathy (P = 0.0015, odds ratio [OR] 1.37, CI 1.13–1.67, dominant model) in an African American sample of 851 case subjects with diabetic nephropathy and 871 nondiabetic control subjects in analyses incorporating adjustment for varying levels of racial admixture. This association remained significant after adjustment of the data for BMI, age, and sex (P = 0.0013–0.0004). We further tested this SNP for association with longstanding type 2 diabetes without nephropathy (n = 317), and evidence of association was also significant (P = 0.0054, OR 1.46, CI 1.12–1.91, dominant model) when compared with the same set of 871 nondiabetic control subjects. Combining the type 2 diabetes and diabetic nephropathy samples into a single group of case subjects (n = 1,168) resulted in the most significant evidence of association (P = 0.0003, OR 1.40, CI 1.17–1.67, dominant model). Association tests between age at onset of type 2 diabetes and the rs182052 genotypes also revealed significant association between the presence of the minor allele (A/A or A/G) and earlier onset of type 2 diabetes.CONCLUSIONS—The SNP rs182052 in intron 1 of the adiponectin gene is associated with type 2 diabetes in African Americans.Type 2 diabetes and diabetic nephropathy are more prevalent among African Americans than European Americans, even when taking into consideration ethnic differences in socioeconomic status, prevalence and severity of hypertension, and access to adequate health care (1–3). Studies of African American families with type 2 diabetes (4) or diabetic nephropathy (5) have revealed clustering of both diseases, indicating a genetic component to susceptibility. Genome scans in families have supported a genetic contribution to susceptibility to type 2 diabetes and diabetic nephropathy in African Americans (4,6).Plasma adiponectin levels are inversely correlated with diabetes and insulin resistance (7,8). In contrast, plasma adiponectin has been shown to be increased in patients with kidney disease (9), and studies suggest that increased adiponectin concentration is a predictor of subsequent kidney disease (10).Adiponectin gene (ADIPOQ) polymorphisms have been implicated in type 2 diabetes (11) and type 1 diabetic nephropathy (12,13). Few studies have addressed genetic variants in adiponectin and association with diabetes in Africans (14) or African Americans (15). This second report in African Americans noted several differences between European-derived samples and African Americans regarding associations between ADIPOQ polymorphisms and body composition and lipid phenotypes highlighting potential ethnic differences in the adiponectin gene and the importance of investigating variants in this gene in African Americans.Given the paucity of studies on adiponectin gene polymorphisms and type 2 diabetes or diabetic nephropathy in African Americans and the high risk of these diseases in this population, a thorough interrogation of this gene in African Americans was warranted. We tested 24 single-nucleotide polymorphisms (SNPs) in the adiponectin gene for association with type 2 diabetes and diabetic nephropathy in a large collection of African Americans residing in the southeastern U.S.     

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 × 10⁻⁴, respectively), waist circumference (0.67 cm, P = 0.006; 0.53, P = 0.02; and 0.85, P = 3 × 10⁻⁴), and body weight (1.04 kg, P = 6 × 10⁻⁴; 0.71, P = 0.01; and 1.16, P = 8 × 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 × 10⁻⁵ and 1.16, P = 2 × 10⁻⁵), and the minor A-allele of rs12970134 was also associated with overweight/obesity and obesity (1.13, P = 2 × 10⁻⁵ and 1.15, P = 6 × 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.Obesity and the accompanying risk of common diseases such as type 2 diabetes and premature cardiovascular morbidity and mortality are increasing global health burdens. Multiple variations in genes are likely to contribute to the pathogenesis of obesity. Monogenic forms of obesity have been identified, with mutations in the gene encoding the melanocortin-4 receptor (MC4R) being the most prevalent (1–3). MC4R is located on chromosome 18q22 (4) and expressed in the central nervous system (5) where the encoded protein is involved in appetite regulation (6). Variation in MC4R has been reported to associate with common forms of obesity (7–9). Variation in the fat mass and obesity-associated gene (FTO) was the first example of common genetic variation for which there is widely replicated evidence of association with obesity in the general population (10–12). Recently, in a study analyzing genome-wide association data from white Europeans informative for BMI, variation in FTO was also found with the strongest BMI-association signal, followed by signals mapping to chromosome 18q21, 188 kb (rs17782313), and 109 kb (rs17700633) downstream of MC4R (13). Case-control studies confirmed associations of rs17782313 and rs17700633 with obesity, and a separate analysis identified a relationship between rs17782313 and morbid obesity (13). Low pairwise linkage disequilibrium was found between the two variants (r² = 0.10 in CEU HapMap). An independent genome-wide association study performed in Indian people identified four variants (rs12970134, rs477181, rs502933, and rs4450508) in high linkage disequilibrium (0.57–1.0 in CEU HapMap) ∼150 kb downstream of MC4R associated with increased waist circumference, body weight, waist-to-hip ratio, and insulin resistance, of which the most strongly associated variant (rs12970134) (14) was in high linkage disequilibrium with rs17782313 (0.81 in CEU HapMap).The aim of the present study was to examine the influence of rs17782313, rs17700633, rs12970134, rs477181, rs502933, and rs4450508 near MC4R on obesity-related quantitative traits in the general population of middle-aged people and to validate previously published associations of the variants with obesity (13,14) in the Danish population. Finally, a potential association of these obesity-associated variants with type 2 diabetes was explored.     

Extension of type 2 diabetes genome-wide association scan results in the diabetes prevention program

OBJECTIVE— Genome-wide association scans (GWASs) have identified novel diabetes-associated genes. We evaluated how these variants impact diabetes incidence, quantitative glycemic traits, and response to preventive interventions in 3,548 subjects at high risk of type 2 diabetes enrolled in the Diabetes Prevention Program (DPP), which examined the effects of lifestyle intervention, metformin, and troglitazone versus placebo.RESEARCH DESIGN AND METHODS— We genotyped selected single nucleotide polymorphisms (SNPs) in or near diabetes-associated loci, including EXT2, CDKAL1, CDKN2A/B, IGF2BP2, HHEX, LOC387761, and SLC30A8 in DPP participants and performed Cox regression analyses using genotype, intervention, and their interactions as predictors of diabetes incidence. We evaluated their effect on insulin resistance and secretion at 1 year.RESULTS— None of the selected SNPs were associated with increased diabetes incidence in this population. After adjustments for ethnicity, baseline insulin secretion was lower in subjects with the risk genotype at HHEX rs1111875 (P = 0.01); there were no significant differences in baseline insulin sensitivity. Both at baseline and at 1 year, subjects with the risk genotype at LOC387761 had paradoxically increased insulin secretion; adjustment for self-reported ethnicity abolished these differences. In ethnicity-adjusted analyses, we noted a nominal differential improvement in β-cell function for carriers of the protective genotype at CDKN2A/B after 1 year of troglitazone treatment (P = 0.01) and possibly lifestyle modification (P = 0.05).CONCLUSIONS— We were unable to replicate the GWAS findings regarding diabetes risk in the DPP. We did observe genotype associations with differences in baseline insulin secretion at the HHEX locus and a possible pharmacogenetic interaction at CDKNA2/B.The increasing incidence of diabetes continues to have a tremendous impact on diabetes-related morbidity and mortality around the world. Although much emphasis has been placed on the contribution of a Western lifestyle characterized by increasing caloric intake and physical inactivity to the diabetes epidemic, the role genetics plays in the development of diabetes is generally poorly understood. Additional insight into the contribution of genetic variants to diabetes incidence, gene-lifestyle interactions, and pharmacological response to antidiabetes medications is required to slow this tragic epidemic.The recent implementation of genome-wide association scans (GWASs) as an investigative tool has resulted in a qualitative leap in identifying diabetes-related genes (1,2). These surveys, which are agnostic to candidate genes, can cover ∼80% of common human genome variants with current technology, thus providing unprecedented insight into the genetic architecture of type 2 diabetes. In 2007, the first published type 2 diabetes GWAS confirmed the important impact of TCF7L2 on diabetes incidence (odds ratio [OR] 1.65, P < 1.0 × 10⁻⁷) and identified several new type 2 diabetes loci, SLC30A8 (1.26, P = 5.0 × 10⁻⁷), HHEX (1.21, P = 9.1 × 10⁻⁶), LOC38771 (1.14, P = 2.9 × 10⁻⁴), and EXT (1.26, P = 1.2 × 10⁻⁴) (3). SLC30A8 encodes a zinc transporter protein that carries zinc from the cytoplasm into insulin secretory vesicles within the pancreatic β-cell, an important step in insulin synthesis and secretion (4). HHEX is essential for the development of the pancreas and liver and is a target of the Wnt signaling pathway (5).After the initial GWAS publication, four other high-density scans were published simultaneously by different groups, confirming many of the initial findings. In addition to replicating the prior associations of TCF7L2, HHEX, and SCL30A8, investigators from Iceland identified CDK5 regulatory subunit associated protein 1-like 1 (CDKAL1) as another potential diabetes-related gene (OR 1.2, P = 1.8 × 10⁻⁴) (6). This gene is hypothesized to lead to β-cell degeneration by modulating CDK5/CDK5R1 activity. The Diabetes Genetics Initiative, the Wellcome Trust Case Control Consortium, and the Finland–U.S. Investigation of Type 2 Diabetes Genetics concomitantly published GWASs that were combined in a preliminary meta-analysis of >30,000 samples (7–9). Again, the above findings were confirmed, and novel diabetes loci in or near IGF2BP2 (1.14, P = 8.9 × 10⁻¹⁶) and CDKN2A/B (1.2, P = 7.8 × 10⁻¹⁵) were identified. The EXT2 and LOC387761 gene regions have not been replicated in these or additional studies (10,11). Taken together, these studies support the potential power of GWASs in unraveling the genetic basis of type 2 diabetes.Several studies have attempted to characterize the physiological mechanisms affected by these genetic variants. Pascoe et al. (12) performed 75-g oral glucose tolerance tests (OGTTs) and hyperinsulinemic-euglycemic clamps on 1,276 healthy European subjects and demonstrated that common variants in CDKAL1 and HHEX are associated with decreased pancreatic β-cell function. Grarup et al. (13) reported that variants of HHEX, CDKN2A/B, and IFG2BP2 are associated with type 2 diabetes, and single nucleotide polymorphisms (SNPs) within the HHEX and CDKN2A/B loci impaired glucose-induced insulin release in healthy subjects, emphasizing the central role of pancreatic β-cell dysfunction in disease pathogenesis. Staiger et al. (14) found that the major alleles of the SLC30A8 and the HHEX SNPs associate with reduced insulin secretion stimulated by orally administered glucose but not with insulin resistance; the other reported type 2 diabetes SNPs within the EXT2 and LOC387761 loci did not associate with insulin resistance or β-cell dysfunction. Finally, a quantitative trait analysis of GWAS-identified type 2 diabetes susceptibility loci was recently completed by Palmer et al. (15) in their analysis of the Insulin Resistance Atherosclerosis Family Study (IRAS-FS). This study of 1,268 Hispanic and 581 African American subjects revealed that the increase in diabetes risk associated with variants in GWAS-identified gene regions, including CDKAL1, IGF2BP2, SLC30A8, and LOC387761, is mediated in part via defects primarily in insulin secretion. In Hispanic Americans, the acute insulinogenic response to glucose challenge decreased in high-risk genotype subjects at CDKAL1 (P = 0.005), and the disposition index was reduced in subjects with the high-risk genotype at IGF2BP2 (P = 0.01). Paradoxically, in Hispanic Americans, the previously identified risk allele of LOC387761 was significantly associated with an increased acute insulin response (P = 0.005) and disposition index (P = 0.036). IGF2BP2 rs4402960 was the only GWAS-identified SNP that associated with type 2 diabetes as a categorical trait (P = 0.02). Even fewer studies have attempted to analyze the influence of these genetic variants on response to pharmacological or behavioral interventions (16,17).The current study attempts to replicate and extend recent GWAS findings in the Diabetes Prevention Program (DPP) cohort. As a multiethnic, interventional study of >3,000 people at high risk for diabetes who have been carefully characterized, the DPP provides the opportunity to study insulin dynamics according to genotype and potential drug-genotype interactions. Studying pre-diabetic subjects as opposed to patients with overt diabetes provides insight into the role of genetic variation in the early stages of disease progression. As a longitudinal interventional study, the DPP provides the opportunity to carefully study the impact of genetic variation on insulin secretion and resistance over time. Finally, having multiple treatment arms allows for the identification of potential interactions of genotype with the results of the interventions. Studying gene-treatment interactions helps elucidate mechanisms of disease, identify specific treatments that may ameliorate the genetic predisposition to disease, and focus on subgroups that respond particularly well (or poorly) to specific therapies.     

Common variation in the fat mass and obesity-associated (FTO) gene confers risk of obesity and modulates BMI in the Chinese population

OBJECTIVE— Genetic variants in the fat mass and obesity-associated (FTO) gene have been linked with obesity and type 2 diabetes in European populations. We aimed to test the role of FTO genetic variants in obesity and type 2 diabetes in the Chinese population.RESEARCH DESIGN AND METHODS— We genotyped 19 single-nucleotide polymorphisms (SNPs) spanning from the 3′ end of the neighboring RPGRIP1L gene to the 5′ flanking region of the FTO gene. We analyzed their associations with obesity (638 case and 1,610 control subjects), type 2 diabetes (759 case and 784 control subjects), and obesity-related traits in nondiabetic subjects.RESULTS— Among the 19 SNPs, the rs9939609 A allele was strongly associated with obesity (P = 7.0 × 10⁻⁴) and BMI (P = 0.0024) in the Chinese population. The odds ratio for obesity was 2.60 (95% CI 1.24–5.46) (P = 0.011) for the AA genotype and 1.32 (1.05–1.66) (P = 0.018) for the AT genotype compared with the TT genotype. Each additional copy of the rs9936609 A allele was associated with a BMI increase of ∼0.37 kg/m². The rs9939609 A allele was substantially less common in the Chinese population than in the European population (12.6 vs. 45%). We did not find significant associations of the 19 SNPs with type 2 diabetes or other obesity-related traits.CONCLUSIONS— Genetic variation in the FTO gene is strongly associated with obesity and BMI in the Chinese population. The risk variant is less common in the Chinese population, but its effect size on BMI is comparable with that in the European population.Obesity is strongly influenced by genetic factors, with an estimated heritability of >60% BMI (1,2). Genetic susceptibility to the common form of obesity appears to be polygenic. Although theoretical analyses emphasized the power of genetic association study in common polygenic diseases, the search for genes conferring the risk of obesity has thus far not been very successful. A few reported associations with genes such as GAD2, ENPP1, and INSIG2 also yielded inconsistent results in replication efforts (3–5).Recently, several independent studies using different approaches reported strong associations of genetic variants in the fat mass and obesity-associated (FTO) gene with obesity in populations of European origin (6,7). Zeggini et al. (8) initially found the association of FTO genetic variants with type 2 diabetes in a genome-wide association study for type 2 diabetes. However, the association was abolished by adjustment for BMI, indicating that the association with type 2 diabetes was mediated through an effect of obesity (8). They replicated the associations (rs9939609) with obesity in a total of 38,759 individuals (6). Dina et al. (7) concurrently reported strong associations of single-nucleotide polymorphisms (SNPs) (rs1421085 and rs17817449) of the FTO gene with childhood and severe adult obesity. Two other genome-wide association studies (9,10) also independently reported the associations of nearby FTO genetic variants (rs9930506, rs8050136, rs7193144, rs1121980, and rs9939973) with obesity and obesity-related traits in European and Hispanic populations. All these SNPs fall in a region of strong linkage disequilibrium (LD) in intron 1 of the FTO gene (11). The effect of FTO genetic variants on common obesity is also substantial in the European population. Adults who are homozygous for the risk-conferring rs9939609 A allele weighed ∼3 kg more and had a 1.67-fold increased odds ratio of obesity when compared with those without a risk allele (6). The calculated population-attributable risk is ∼22% for common obesity in populations of European origin (6).Reproducibility is essential for reported genetic associations, especially among populations of different ethnic backgrounds. However, studies in an Oceanic population (12), African Americans (10), Han Chinese (13), and Japanese (14) failed to detect associations between previously reported SNPs and obesity or obesity-related traits. Although the limited sample size and power of these studies is the most likely reason for the lack of association, there is emerging evidence showing that other FTO SNPs not in LD with rs9939609 may be the causative variant in non-European populations (15). In this study, we aimed to investigate the association of FTO genetic variants with obesity and type 2 diabetes in the Chinese population. Instead of testing only a few variants, we used a gene-based approach (16) by selecting potentially functional and common SNPs from the 3′ end of the neighboring RPGRIP1L gene to the 5′ flanking region of the FTO gene. Their associations with obesity-related quantitative metabolic traits were also analyzed.     

Predicting type 2 diabetes based on polymorphisms from genome-wide association studies: a population-based study

OBJECTIVE—Prediction of type 2 diabetes based on genetic testing might improve identification of high-risk subjects. Genome-wide association (GWA) studies identified multiple new genetic variants that associate with type 2 diabetes. The predictive value of genetic testing for prediction of type 2 diabetes in the general population is unclear.RESEARCH DESIGN AND METHODS—We investigated 18 polymorphisms from recent GWA studies on type 2 diabetes in the Rotterdam Study, a prospective, population-based study among homogeneous Caucasian individuals of 55 years and older (genotyped subjects, n = 6,544; prevalent cases, n = 686; incident cases during follow-up, n = 601; mean follow-up 10.6 years). The predictive value of these polymorphisms was examined alone and in addition to clinical characteristics using logistic and Cox regression analyses. The discriminative accuracy of the prediction models was assessed by the area under the receiver operating characteristic curves (AUCs).RESULTS—Of the 18 polymorphisms, the ADAMTS9, CDKAL1, CDKN2A/B-rs1412829, FTO, IGF2BP2, JAZF1, SLC30A8, TCF7L2, and WFS1 variants were associated with type 2 diabetes risk in our population. The AUC was 0.60 (95% CI 0.57–0.63) for prediction based on the genetic polymorphisms; 0.66 (0.63–0.68) for age, sex, and BMI; and 0.68 (0.66–0.71) for the genetic polymorphisms and clinical characteristics combined.CONCLUSIONS—We showed that 9 of 18 well-established genetic risk variants were associated with type 2 diabetes in a population-based study. Combining genetic variants has low predictive value for future type 2 diabetes at a population-based level. The genetic polymorphisms only marginally improved the prediction of type 2 diabetes beyond clinical characteristics.Type 2 diabetes is a multifactorial disease caused by a complex interplay of multiple genetic variants and many environmental factors. With the recent genome-wide association (GWA) studies, the number of replicated common genetic variants associated with type 2 diabetes has rapidly increased (1–7). A total of 18 polymorphisms have been firmly replicated (1–7). It is unclear whether and how the currently known genetic variants can be used in practice, because the combined effect of these variants has not been investigated in a population-based study. Particularly, because most GWA studies were enriched for patients with a positive family history and early onset of the disease, association of these variants to type 2 diabetes risk in the general population, including elderly individuals, remains to be determined.Because complex diseases are caused by multiple genetic variants, predictive testing based on a single genetic marker will be of limited value (8,9). Simulation studies suggest that the predictive value could be improved by combining multiple common low-risk variants (10–13). Several empirical studies on the predictive value of genetic polymorphisms have been conducted before the recent GWA data were available (14–16). In a case-control study, Weedon et al. (16) showed that combining the information of three polymorphisms improved disease prediction, albeit to a limited extent. Vaxillaire et al. (15) investigated 19 polymorphisms and found that the predictive value was low compared with clinical characteristics.Genetic variants associated with risk of type 2 diabetes could potentially be useful for the prediction, prevention, and early treatment of the disease. We investigated whether combining the currently known and well-replicated genetic variants predicts type 2 diabetes in the Rotterdam Study, a prospective population-based follow-up study. We investigated whether these genetic variants improve prediction beyond clinical characteristics.     

Genetic Variant in the IGF2BP2 Gene May Interact With Fetal Malnutrition to Affect Glucose Metabolism

OBJECTIVE

Fetal malnutrition may predispose to type 2 diabetes through gene programming and developmental changes. Previous studies showed that these effects may be modulated by genetic variation. Genome-wide association studies discovered and replicated a number of type 2 diabetes–associated genes. We investigated the effects of such well-studied polymorphisms and their interactions with fetal malnutrition on type 2 diabetes risk and related phenotypes in the Dutch Famine Birth Cohort.

RESEARCH DESIGN AND METHODS

The rs7754840 (CDKAL1), rs10811661 (CDKN2AB), rs1111875 (HHEX), rs4402960 (IGF2BP2), rs5219 (KCNJ11), rs13266634 (SLC30A8), and rs7903146 (TCF7L2) polymorphisms were genotyped in 772 participants of the Dutch Famine Birth Cohort Study (n = 328 exposed, n = 444 unexposed). Logistic and linear regression models served to analyze their interactions with prenatal exposure to famine on type 2 diabetes, impaired glucose tolerance (IGT), and area under the curves (AUCs) for glucose and insulin during oral glucose tolerance testing (OGTT).

RESULTS

In the total population, the TCF7L2 and IGF2BP2 variants most strongly associated with increased risk for type 2 diabetes/IGT and increased AUC for glucose, while the CDKAL1 polymorphism associated with decreased AUC for insulin. The IGF2BP2 polymorphism showed an interaction with prenatal exposure to famine on AUC for glucose (β = −9.2 [95% CI −16.2 to −2.1], P = 0.009).

CONCLUSIONS

The IGF2BP2 variant showed a nominal interaction with exposure to famine in utero, decreasing OGTT AUCs for glucose. This may provide a clue that modulation of the consequences of fetal environment depends on an individual''s genetic background.The fetal origins hypothesis (1,2) states that malnutrition during fetal development predisposes to adverse health outcomes, such as type 2 diabetes. According to the hypothesis, fetal adaptation to a low-caloric intrauterine environment may involve programming to optimize the use of restricted nutrient supply. Programming may lead to altered gene expression profiles and eventually to disease later in life. In addition, adverse intrauterine circumstances may divert nutrients to critical organs such as the brain at the expense of organs such as the pancreas, liver, or muscles (3).Type 2 diabetes and defective insulin secretion show high heritabilities (4). Genetic variation is likely to interact with the fetal response to an extreme nutritional situation. We found that the effects of the Pro12Ala polymorphism of the peroxisome proliferator–activated receptor (PPAR)γ2 gene depend on prenatal exposure to famine (5), and several studies (6–8) have shown interactions of genes with size at birth, a marker of fetal environment. Such interactions may have consequences for development and function. Previously, the PPARγ, TCF7L2, and KCNJ11 genes were identified by linkage and candidate gene studies as type 2 diabetes risk loci (9–11). Recently, genome-wide association studies have identified and replicated new genetic variants associated with type 2 diabetes (12–15). Notably, a number of these variants are thought to be involved in the development and function of critical organs for glucose metabolism, such as the pancreatic β-cell (16–18).Based on the findings described above, we hypothesized that these genes interact with fetal exposure to famine. In the Dutch Famine Birth Cohort, we investigated the effects of genetic variation in these loci on type 2 diabetes, impaired glucose tolerance (IGT), oral glucose tolerance testing (OGTT), and their interaction with fetal malnutrition.     

Vessel shrinkage as a sign of atherosclerosis progression in type 2 diabetes: a serial intravascular ultrasound analysis

OBJECTIVE—The aim of this study was to determine the natural history of vascular remodeling of atherosclerotic plaques in patients with type 2 diabetes and the predictors of vessel shrinkage.RESEARCH DESIGN AND METHODS—In this serial intracoronary ultrasound (IVUS) study, 237 coronary segments from 45 patients enrolled in the DIABETES I, II, and III trials were included. Quantitative volumetric IVUS analyses (motorized pullbacks at 0.5 mm/s) were performed in the same coronary segment after the index procedure and at the 9-month follow-up. Nontreated mild lesions (angiographic stenosis <25%) with ≥0.5 mm plaque thickening and length of ≥5 mm assessed by IVUS were included. Vessel shrinkage was defined as a Δexternal elastic membrane area/Δplaque area < 0. Statistical adjustment by multiple segments and multiple lesions per patient was performed.RESULTS—Vessel shrinkage was identified in 37.1% of segments and was associated with a significant decrease in lumen area at 9 months (vessel shrinkage, 10 ± 4 mm² vs. non–vessel shrinkage, 11 ± 4 mm²; P = 0.04). Independent predictors of vessel shrinkage were insulin requirements (odds ratio 4.6 [95% CI 1.40–15.10]; P = 0.01), glycated hemoglobin (1.5 [1.05–2.10]; P = 0.02), apolipoprotein B (0.96 [0.94–0.98]; P < 0.001), hypertension (3.7 [1.40–10.30]; P = 0.009), number of diseased vessels (5.6 [2.50–12.50]; P < 0.001), and prior revascularization (17.5 [6.50–46.90]; P < 0.001).CONCLUSIONS—This serial IVUS study suggests that progression of coronary artery disease in patients with type 2 diabetes may be mainly attributed to vessel shrinkage. Besides, vessel shrinkage is influenced by insulin requirements and metabolic control and is associated with more advanced coronary atherosclerosis.Coronary artery remodeling is a phenomenon by which vessel dimension changes in response to atherosclerotic plaque accumulation. This concept was initially described by Glagov et al. (1) in a postmortem, histopathological study and confirmed by in vivo studies using intracoronary ultrasound (IVUS) analysis (2–7). Two different patterns of coronary remodeling have been described: a compensatory enlargement of the vessel in response to an increase of atherosclerotic plaque (positive remodeling) and a failure to enlarge or even vessel shrinkage (negative remodeling). The latter is a common finding in coronary stenosis of diabetic patients (8,9). In cross-sectional studies, negative remodeling has been associated with coronary risk factors, such as hypertension (5) and smoking (4), with the type of plaque (2,7) (calcified, hard plaques), and with metabolic control in diabetic patients (10–12). In most studies, remodeling has been evaluated only at a single time point. Therefore, the natural history of this process has not been properly addressed. In addition, remodeling index has been assessed by comparing vessel dimension at target site and that at the most normal-looking cross-section within 10 mm from the lesion taken as reference segment (2–7). However, reference segments are rarely disease free (9) and therefore may be also subject to the remodeling process. This may be especially true in diabetic patients (9). Nevertheless, no previous serial IVUS study has shown the factors associated with coronary remodeling in diabetic patients. Therefore, the aim of this study was to determine the natural history of vascular remodeling of atherosclerotic plaques in diabetic patients and the predictors of vessel shrinkage during time.     

The common P446L polymorphism in GCKR inversely modulates fasting glucose and triglyceride levels and reduces type 2 diabetes risk in the DESIR prospective general French population

OBJECTIVE— Hepatic glucokinase (GCK) is a key regulator of glucose storage and disposal in the liver, where its activity is competitively modulated, with respect to glucose, by binding to glucokinase regulatory protein (GCKR) in the presence of fructose 6-phosphate. Genome-wide association studies for type 2 diabetes identified GCKR as a potential locus for modulating triglyceride levels. We evaluated, in a general French population, the contribution of the GCKR rs1260326-P446L polymorphism to quantitative metabolic parameters and to dyslipidemia and hyperglycemia risk.RESEARCH DESIGN AND METHODS— Genotype effects of rs1260326 were studied in 4,833 participants from the prospective DESIR (Data from an Epidemiological Study on the Insulin Resistance syndrome) cohort both at inclusion and using the measurements at follow-up.RESULTS— The minor T-allele of rs1260326 was strongly associated with lower fasting glucose (−1.43% per T-allele; P = 8 × 10⁻¹³) and fasting insulin levels (−4.23%; P = 3 × 10⁻⁷), lower homeostasis model assessment of insulin resistance index (−5.69%; P = 1 × 10⁻⁸), and, conversely, higher triglyceride levels (3.41%; P = 1 × 10⁻⁴) during the 9-year study. These effects relate to a lower risk of hyperglycemia (odds ratio [OR] 0.79 [95% CI 0.70–0.88]; P = 4 × 10⁻⁵) and of incident cases during the study (hazard ratio [HR] 0.83 [0.74–0.95]; P = 0.005). Moreover, an additive effect of GCKR rs1260326(T) and GCK (−30G) alleles conferred lower fasting glycemia (P = 1 × 10⁻¹³), insulinemia (P = 5 × 10⁻⁶), and hyperglycemia risk (P = 1 × 10⁻⁶).CONCLUSIONS— GCKR-L446 carriers are protected against type 2 diabetes despite higher triglyceride levels and risk of dyslipidemia, which suggests a potential molecular mechanism by which these two components of the metabolic syndrome can be dissociated.The enzyme glucokinase (GCK) is the major glucose sensor of the pancreatic β-cells, where it adapts insulin secretion to blood glucose levels. GCK also participates in regulating glycogen synthesis and gluconeogenesis in the liver (1). GCK activity is allosterically controlled in hepatocytes by the glucokinase regulatory protein (GCKR), which reversibly binds to GCK and inhibits its activity in the presence of fructose 6-phosphate. GCKR acts as a competitive inhibitor of GCK with respect to glucose and is suppressed by the specific metabolite fructose 1-phosphate (2).In GCKR-deficient mice, the disruption of this regulation and the subsequent decrease in GCK activity leads to altered glucose metabolism and impaired postprandial glycemic control (3,4), although no change in fasting blood glucose concentration is observed. Adenoviral-mediated hepatic overexpression of GCKR in mice with high-fat diet–induced diabetes improves fasting and glucose-induced glycemia and leads to a concomitant increase in insulin sensitivity and triglyceride levels and a decrease in leptin levels (5). Heterozygous mutations in GCK resulting in a reduction of enzymatic activity are responsible for a subtype of monogenic diabetes (maturity-onset diabetes of the young-2) (1,6). Previous genetic studies at the GCKR locus have not reported intragenic mutations associated with type 2 diabetes in humans (7,8).The Diabetes Genetics Initiative (DGI) genome-wide association study for type 2 diabetes and quantitative metabolic traits reported an intronic polymorphism of GCKR (rs780094) explaining interindividual variability in plasma triglyceride (TG) levels and a trend toward association with lower fasting glycemia, less insulin resistance, and lower risk for type 2 diabetes (9). The HapMap II CEU data (www.hapmap.org) showed that rs780094 is in strong linkage disequilibrium (r² = 0.932) with a non-synonymous GCKR variant (Pro446Leu, rs1260326) that we previously identified by the DNA sequencing of French individuals (7). Marju Orho-Melander and colleagues recently communicated their fine-mapping data showing the strongest signal for TG levels at the coding single nucleotide polymorphism (SNP) (rs1260326; P = 1.5 × 10⁻⁹), with lesser associations to fasting glycemia and insulin sensitivity (M. Orho-Melander, O. Melander, V. Lyssenko, for the DGI, unpublished data). Similar findings for the intronic variant rs780094 were reported in a Danish population (10).We evaluated the association between GCKR rs1260326-P446L and TG levels in a middle-aged general French population with a follow-up of 9 years (11). Given the key role of GCKR in hepatic glucose metabolism, we also assessed the effect of rs1260326 on glucose homeostasis parameters and on the risk of impaired fasting glycemia and type 2 diabetes. Furthermore, as we previously showed a strong association of the GCK (−30A) promoter variant (rs1799884) to increased fasting glycemia and type 2 diabetes risk in the same study cohort (11), we also assessed possible additive effects of GCKR rs1260326-P446L and GCK −30G/A SNPs on fasting glucose, insulin, TG levels, and hyperglycemia risk.     

Impact of Common Variants of PPARG, KCNJ11, TCF7L2, SLC30A8, HHEX, CDKN2A, IGF2BP2, and CDKAL1 on the Risk of Type 2 Diabetes in 5,164 Indians

OBJECTIVE

Common variants in PPARG, KCNJ11, TCF7L2, SLC30A8, HHEX, CDKN2A, IGF2BP2, and CDKAL1 genes have been shown to be associated with type 2 diabetes in European populations by genome-wide association studies. We have studied the association of common variants in these eight genes with type 2 diabetes and related traits in Indians by combining the data from two independent case–control studies.

RESEARCH DESIGN AND METHODS

We genotyped eight single nucleotide polymorphisms (PPARG-rs1801282, KCNJ11-rs5219, TCF7L2-rs7903146, SLC30A8-rs13266634, HHEX-rs1111875, CDKN2A-rs10811661, IGF2BP2-rs4402960, and CDKAL1-rs10946398) in 5,164 unrelated Indians of Indo-European ethnicity, including 2,486 type 2 diabetic patients and 2,678 ethnically matched control subjects.

RESULTS

We confirmed the association of all eight loci with type 2 diabetes with odds ratio (OR) ranging from 1.18 to 1.89 (P = 1.6 × 10⁻³ to 4.6 × 10⁻³⁴). The strongest association with the highest effect size was observed for TCF7L2 (OR 1.89 [95% CI 1.71–2.09], P = 4.6 × 10⁻³⁴). We also found significant association of PPARG and TCF7L2 with homeostasis model assessment of β-cell function (P = 6.9 × 10⁻⁸ and 3 × 10⁻⁴, respectively), which looked consistent with recessive and under-dominant models, respectively.

CONCLUSIONS

Our study replicates the association of well-established common variants with type 2 diabetes in Indians and shows larger effect size for most of them than those reported in Europeans.Type 2 diabetes is a complex metabolic disorder with both genetic and environmental factors such as food habits and lifestyle contributing to its pathogenesis (1). Due to its complex etiology, the progress of discovery of genetic components for type 2 diabetes had been very slow until the advent of high throughput genome-wide association (GWA) studies (2). Until recently, only a few common variants in PPARG (3), KCNJ11 (4), and TCF7L2 (5) were shown to be associated with type 2 diabetes. With the advent of GWA studies, there are at least 20 loci identified today that are associated with the risk of type 2 diabetes (6). The first GWA study in the French population revealed SLC30A8 and HHEX as new loci for type 2 diabetes in addition to replicating the strong association with TCF7L2 (7). Further, GWA studies added several new genes including CDKAL1, CDKN2A, IGF2BP2, and FTO to the list of type 2 diabetes–associated loci and confirmed the associations for PPARG, KCNJ11, and TCF7L2 (8–12).India harbors the maximum number of diabetic patients, which is projected to double by the year 2030 (13). Indians are diagnosed with diabetes a decade earlier and at a lower BMI than Europeans, which may be partly explained by their excess central obesity (14,15). Hence, determination of genetic risk factors predicting the risk of type 2 diabetes in the Indian population is highly desirable. Recent evidence suggests that the genetic basis of several diseases in Indians might be different from that of Europeans (16,17), which could be due to differences in the risk allele frequency and pattern of linkage disequilibrium. A report from the Indian Genome Variation Consortium also suggested that most of the populations in the Indian subcontinent are distinct from HapMap populations (18). Hence, genes associated with a disease in other populations need to be assessed for their role in the Indian population. The present study evaluated the association of eight most replicated and well-established genetic variants of PPARG, KCNJ11, TCF7L2, SLC30A8, HHEX, CDKN2A, IGF2BP2, and CDKAL1 with type 2 diabetes and related quantitative traits in Indians. We also performed allele dosage analysis of these variants and investigated their influence on quantitative metabolic traits related to type 2 diabetes.     

Baseline serum 25-hydroxy vitamin d is predictive of future glycemic status and insulin resistance: the Medical Research Council Ely Prospective Study 1990-2000

OBJECTIVE—Accumulating epidemiological evidence suggests that hypovitaminosis D may be associated with type 2 diabetes and related metabolic risks. However, prospective data using the biomarker serum 25-hydroxyvitamin D [25(OH)D] are limited and therefore examined in the present study.RESEARCH DESIGN AND METHODS—A total of 524 randomly selected nondiabetic men and women, aged 40–69 years at baseline, with measurements for serum 25(OH)D and IGF-1 in the population-based Ely Study, had glycemic status (oral glucose tolerance), lipids, insulin, anthropometry, and blood pressure measured and metabolic syndrome risk (metabolic syndrome z score) derived at baseline and at 10 years of follow-up.RESULTS—Age-adjusted baseline mean serum 25(OH)D was greater in men (64.5 nmol/l [95% CI 61.2–67.9]) than women (57.2 nmol/l [54.4,60.0]) and varied with season (highest late summer). Baseline 25(OH)D was associated inversely with 10-year risk of hyperglycemia (fasting glucose: β = −0.0023, P = 0.019; 2-h glucose: β = −0.0097, P = 0.006), insulin resistance (fasting insulin β = −0.1467, P = 0.010; homeostasis model assessment of insulin resistance [HOMA-IR]: β = −0.0059, P = 0.005), and metabolic syndrome z score (β = −0.0016, P = 0.048) after adjustment for age, sex, smoking, BMI, season, and baseline value of each metabolic outcome variable. Associations with 2-h glucose, insulin, and HOMA-IR remained significant after further adjustment for IGF-1, parathyroid hormone, calcium, physical activity, and social class.CONCLUSIONS—This prospective study reports inverse associations between baseline serum 25(OH)D and future glycemia and insulin resistance. These associations are potentially important in understanding the etiology of abnormal glucose metabolism and warrant investigation in larger, specifically designed prospective studies and randomized controlled trials of supplementation.Though the most well-known role of vitamin D is the regulation of calcium absorption and bone metabolism, it is becoming clear that this hormone has pleiotropic effects with possible roles in the pathogenesis of cancer (1), cardiovascular disease (2), multiple sclerosis (3), and type 1 diabetes (4). Recent epidemiological evidence (5–9) also points to a potential association of vitamin D insufficiency with adverse metabolic risk, including that for type 2 diabetes (10,11). While the exact mechanisms that underlie the multiple effects of vitamin D on different tissues are not currently understood, one unifying factor is the expression of vitamin D receptors (VDRs) in >30 tissues, including pancreatic islet cells (12). There is some evidence that polymorphisms in the VDR gene may be associated with insulin resistance, insulin secretion, and fasting glucose concentrations (13–16), suggesting that vitamin D is likely to contribute to glucose metabolism (8). It is also becoming clear that there are physiological interactions between vitamin D, IGF-1, and its binding proteins IGFBP-1 and IGFBP-3 (17,18). Variations in circulating IGF-1 and its binding proteins are associated with variations in glycemia (19) and may interact with vitamin D status to influence metabolic syndrome risk (7).Epidemiological studies examining vitamin D status and the risk of hyperglycemia or insulin resistance have thus far been suggestive of inverse associations but are inconclusive. Most studies that have used the biomarker serum 25-hydroxy vitamin D3 [25(OH)D] concentration, generally recognized as a marker of human vitamin D status, have been cross-sectional in nature; hence, the temporal sequence of associations is unclear. Need et al. previously reported that lower serum 25(OH)D was associated with higher fasting glucose throughout the range of serum 25(OH)D measured and most marked when 25(OH)D levels were <40 nmol/l (20). Ford et al. (6), in the Third National Health and Nutrition Examination Survey of 8,421 men and women, reported an inverse association between 25(OH)D and metabolic syndrome risk, particularly for hyperglycemia, hypertriglyceridemia, and abdominal obesity. Hypponen et al. (7) most recently reported in the 1958 birth cohort study of 6,810 men and women that higher serum 25(OH)D was associated with lower risk of metabolic syndrome (odds ratio 0.33 [95% CI 0.26–0.42]) and each of its individual components cross-sectionally, including an inverse association with A1C level as a marker of glucose status. They found an interaction between 25(OH)D and IGF-1 on metabolic risk, such that metabolic syndrome risk was lowest when both 25(OH)D and IGF-1 were highest. To our knowledge, there has only been one previous prospective study (21) of the association between serum 25(OH)D and the risk of type 2 diabetes, but the inverse association was attenuated and made nonsignificant after adjustment for confounders. There are no prospective studies, to the best of our knowledge, of the association between serum 25(OH)D and future continuous distribution of glycemic status or insulin resistance. Several studies (11,22,23) have examined the association of diabetes or metabolic syndrome risk with dietary and/or supplemental vitamin D intake, but this represents only a small proportion of vitamin D available in humans, especially in the U.K., where few foods are vitamin D fortified (e.g., margarine) or naturally rich in vitamin D (e.g., egg yolk and oily fish). The main source of vitamin D is from sunlight exposure of the skin, in which a narrow band of ultraviolet-B radiation converts its prehormone, endogenously, into vitamin D3 in the skin, while liver, kidneys, and other activating tissues then hydroxylate it to form 25(OH)D and 1,25-dihydroxyvitamin D3 (calcitriol), respectively. There is general agreement that serum 25(OH)D concentrations best reflect vitamin D repletion or “status,” current definitions being suggested to be “sufficiency” (concentrations >75 nmol/l or 30 μg/l), “hypovitaminosis D” (<75 nmol/l or <30 μg/l), “insufficiency” (<50 nmol/l or <20 μg/l) (12), and classical “deficiency” (<25 nmol/l).The aim of our study was to investigate the prospective association between serum 25(OH)D concentration and markers of metabolic risk, including glucose, insulin, insulin resistance, and a continuous metabolic syndrome risk z score. We further wanted to test whether any associations observed were independent of a comprehensive range of potential confounding or effect-modifying factors, including circulating IGF-1 or its binding proteins.     

Fat mass-and obesity-associated (FTO) gene variant is associated with obesity: longitudinal analyses in two cohort studies and functional test

OBJECTIVE—To examine the longitudinal association of fat mass–and obesity-associated (FTO) variant with obesity, circulating adipokine levels, and FTO expression in various materials from human and mouse.RESEARCH DESIGN AND METHODS—We genotyped rs9939609 in 2,287 men and 3,520 women from two prospective cohorts. Plasma adiponectin and leptin were measured in a subset of diabetic men (n = 854) and women (n = 987). Expression of FTO was tested in adipocytes from db/db mice and mouse macrophages.RESULTS—We observed a trend toward decreasing associations between rs9939609 and BMI at older age (≥65 years) in men, whereas the associations were constant across different age groups in women. In addition, the single nucleotide polymorphism (SNP) rs9939609 was associated with lower plasma adiponectin (log[e]− means, 1.82 ± 0.04, 1.73 ± 0.03, and 1.68 ± 0.05 for TT, TA, and AA genotypes, respectively; P for trend = 0.02) and leptin (log[e]− means, 3.56 ± 0.04, 3.63 ± 0.04, and 3.70 ± 0.06; P for trend = 0.06) in diabetic women. Adjustment for BMI attenuated the associations. FTO gene was universally expressed in human and mice tissues, including adipocytes. In an ancillary study of adipocytes from db/db mice, FTO expression was ∼50% lower than in those from wild-type mice.CONCLUSIONS—The association between FTO SNP rs9939609 and obesity risk may decline at older age. The variant affects circulating adiponectin and leptin levels through the changes in BMI. In addition, the expression of FTO gene was reduced in adipocytes from db/db mice.In a recent genome-wide association study, Frayling et al. (1) identified a common variant in fat mass–and obesity-associated (FTO) gene (rs9939609) that was related to higher BMI in both children and adults. In addition, adiposity appeared to mediate the association between FTO variant and the risk of type 2 diabetes (2,3). Several other studies have also observed associations between FTO variants and obesity-related traits in various populations (4–13).Because most available data are cross-sectional, the longitudinal pattern of the associations between FTO variants and adiposity and age-specific genetic effects are not clearly defined. The primary aim of the present study is to address these issues by assessing the genetic effects in two prospective cohorts. Obesity status affects the endocrine function of adipose tissue by altering the secretion of adipokines, such as adiponectin and leptin, which have been related to ectopic fat accumulation, insulin sensitivity, and diabetes risk in epidemiological studies (14–16). We therefore examined the associations of FTO variant with circulating levels of adiponectin and leptin. In addition to the association analyses, to shed light on its potential functions, we also examined the expression of FTO gene in various tissues from humans and mice and investigated the expression in adipocytes from db/db mice and mice macrophages in response to inflammatory stimulants.