Genome-wide scan for metabolic syndrome and related quantitative traits in Hong Kong Chinese and confirmation of a susceptibility locus on chromosome 1q21-q25

Association Study of CACNA1D, KCNJ11, KCNQ1, and CACNA1E Single-Nucleotide Polymorphisms with Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a complex chronic disease characterized by decreased insulin secretion and the development of insulin resistance. Previous genome-wide association studies demonstrated that single-nucleotide polymorphisms (SNPs) present in genes coding for ion channels involved in insulin secretion increase the risk of developing this disease. We determined the association of 16 SNPs found in CACNA1D, KCNQ1, KCNJ11, and CACNA1E genes and the increased probability of developing T2DM. In this work, we performed a case-control study in 301 Mexican adults, including 201 cases with diabetes and 100 controls without diabetes. Our findings indicate a moderate association between T2DM and the C allele, and the C/C genotype of rs312480 within CACNA1D. The CAG haplotype surprisingly showed a protective effect, whereas the CAC and CGG haplotypes have a strong association with T2DM. The C allele and C/C genotype of rs5219 were significantly associated with diabetes. Also, an association was observed between diabetes and the A allele and the A/A genotype of rs3753737 and rs175338 in CACNA1E. The TGG and CGA haplotypes were also found to be significantly associated. The findings of this study indicate that the SNPs examined could serve as a potential diagnostic tool and contribute to the susceptibility of the Mexican population to this disease.

Association of MTHFR C677T gene polymorphism with metabolic syndrome in a Chinese population: a case-control study

Objective

To investigate the association of the MTHFR C677T gene polymorphism with metabolic syndrome (MetS) in people in Hubei Province, China.

Methods

A case–control study was conducted with 651 subjects with MetS (MetS group) and 727 healthy controls (control group) at Renmin Hospital of Wuhan University between January and December 2016. The MTHFR C677T genotype was detected by the gene chip technique and clinical data were collected.

Results

Body mass index, waist circumference, the waist-hip-ratio, systolic and diastolic blood pressure, fasting blood glucose, fasting insulin, triglyceride, total cholesterol, low-density lipoprotein-cholesterol, and homocysteine levels, and the homeostasis model assessment of insulin resistance were higher in the MetS group than in controls. The risk of MetS was higher for the TT genotype and T allele carriers than for the CC genotype and C allele carriers. With MetS, the TT genotype increased the risk of elevated blood pressure, fasting glucose levels, and triglyceride levels. Patients with MetS and the TT genotype showed more severe abdominal obesity, dyslipidaemia, insulin resistance, elevated blood pressure, elevated fasting glucose levels, and hyperhomocysteinaemia compared with those with the CC genotype.

Conclusions

In this population, MTHFR C677T gene polymorphism may be a risk factor for MetS.

Association between changes in systolic blood pressure and incident diabetes in a community-based cohort study in Korea

An association between hypertension and diabetes has been reported; however, the temporal relationship of blood pressure changes and incident diabetes has not been fully investigated in the general population. We examined whether increasing blood pressure is associated with the risk of developing diabetes among community-dwelling Korean adults. This study included 2225 participants (859 men and 1366 women) aged 27-87 years from the Korean Genome Epidemiology Study. The participants were free of diabetes and cardiovascular disease at baseline. Incident diabetes was defined as fasting blood glucose⩾126 mg dl^-1 or hemoglobin a1c ⩾6.5% (48 mmol mol^-1) at follow-up examination and/or a physician's diagnosis of diabetes during the follow-up period. The effects of the baseline level and change in blood pressure on the risk of incident diabetes were assessed by multivariate logistic regression analysis. During the mean follow-up of 2.6 years, new-onset diabetes was observed in 5.0% (43/859) of the men and 3.4% (47/1366) of the women. In the multivariate model, the baseline systolic blood pressure was not significantly associated with incident diabetes (adjusted odds ratio 0.93 per 10 mmHg, P=0.747). However, an increase in systolic blood pressure during the follow-up period was independently associated with incident diabetes (adjusted odds ratio 5.53 per 5 mmHg per year, P=0.002) after adjusting for the baseline blood pressure and other potential confounders. Increasing blood pressure, but not a high baseline blood pressure, was independently associated with the risk of diabetes in Korean adults.

Psoriasis and comorbid diseases: Epidemiology

Psoriasis is a common chronic inflammatory disease of the skin that is increasingly being recognized as a systemic inflammatory disorder. Psoriatic arthritis is a well-known comorbidity of psoriasis. A rapidly expanding body of literature in various populations and settings supports additional associations between psoriasis and cardiometabolic diseases, gastrointestinal diseases, kidney disease, malignancy, infection, and mood disorders. The pathogenesis of comorbid disease in patients with psoriasis remains unknown; however, shared inflammatory pathways, cellular mediators, genetic susceptibility, and common risk factors are hypothesized to be contributing elements. As additional psoriasis comorbidities continue to emerge, education of health care providers is essential to ensuring comprehensive medical care for patients with psoriasis.

Diabetes induced by gain-of-function mutations in the Kir6.1 subunit of the KATP channel

Kir6.2-containing K_ATP channels are prominent in pancreatic β cells, and gain-of-function mutations in these channels are the most common cause of human neonatal diabetes mellitus. Remedi et al. find that Kir6.1 subunits are also present in pancreatic K_ATP channels and that gain-of-function mutations can also cause impaired glucose tolerance and insulin secretion.

Gain-of-function (GOF) mutations in the pore-forming (Kir6.2) and regulatory (SUR1) subunits of K_ATP channels have been identified as the most common cause of human neonatal diabetes mellitus. The critical effect of these mutations is confirmed in mice expressing Kir6.2-GOF mutations in pancreatic β cells. A second K_ATP channel pore-forming subunit, Kir6.1, was originally cloned from the pancreas. Although the prominence of this subunit in the vascular system is well documented, a potential role in pancreatic β cells has not been considered. Here, we show that mice expressing Kir6.1-GOF mutations (Kir6.1[G343D] or Kir6.1[G343D,Q53R]) in pancreatic β cells (under rat-insulin-promoter [Rip] control) develop glucose intolerance and diabetes caused by reduced insulin secretion. We also generated transgenic mice in which a bacterial artificial chromosome (BAC) containing Kir6.1[G343D] is incorporated such that the transgene is only expressed in tissues where Kir6.1 is normally present. Strikingly, BAC-Kir6.1[G343D] mice also show impaired glucose tolerance, as well as reduced glucose- and sulfonylurea-dependent insulin secretion. However, the response to K⁺ depolarization is intact in Kir6.1-GOF mice compared with control islets. The presence of native Kir6.1 transcripts was demonstrated in both human and wild-type mouse islets using quantitative real-time PCR. Together, these results implicate the incorporation of native Kir6.1 subunits into pancreatic K_ATP channels and a contributory role for these subunits in the control of insulin secretion.

Genome-wide association study identifies African-ancestry specific variants for metabolic syndrome

The metabolic syndrome (MetS) is a constellation of metabolic disorders that increase the risk of developing several diseases including type 2 diabetes and cardiovascular diseases. Although genome-wide association studies (GWAS) have successfully identified variants associated with individual traits comprising MetS, the genetic basis and pathophysiological mechanisms underlying the clustering of these traits remain unclear. We conducted GWAS of MetS in 1427 Africans from Ghana and Nigeria followed by replication testing and meta-analysis in another continental African sample from Kenya. Further replication testing was performed in an African American sample from the Atherosclerosis Risk in Communities (ARIC) study. We found two African-ancestry specific variants that were significantly associated with MetS: SNP rs73989312[A] near CA10 that conferred increased risk (P=3.86 × 10(-8), OR=6.80) and SNP rs77244975[C] in CTNNA3 that conferred protection against MetS (P=1.63 × 10(-8), OR=0.15). Given the exclusive expression of CA10 in the brain, our CA10 finding strengthens previously reported link between brain function and MetS. We also identified two variants that are not African specific: rs76822696[A] near RALYL associated with increased MetS risk (P=7.37 × 10(-9), OR=1.59) and rs7964157[T] near KSR2 associated with reduced MetS risk (P=4.52 × 10(-8), Pmeta=7.82 × 10(-9), OR=0.53). The KSR2 locus displayed pleiotropic associations with triglyceride and measures of blood pressure. Rare KSR2 mutations have been reported to be associated with early onset obesity and insulin resistance. Finally, we replicated the LPL and CETP loci previously found to be associated with MetS in Europeans. These findings provide novel insights into the genetics of MetS in Africans and demonstrate the utility of conducting trans-ethnic disease gene mapping studies for testing the cosmopolitan significance of GWAS signals of cardio-metabolic traits.

Genetic polymorphisms of PCSK2 are associated with glucose homeostasis and progression to type 2 diabetes in a Chinese population

Proprotein convertase subtilisin/kexin type 2 (PCSK2) is a prohormone processing enzyme involved in insulin and glucagon biosynthesis. We previously found the genetic polymorphism of PCSK2 on chromosome 20 was responsible for the linkage peak of several glucose homeostasis parameters. The aim of this study is to investigate the association between genetic variants of PCSK2 and glucose homeostasis parameters and incident diabetes. Total 1142 Chinese participants were recruited from the Stanford Asia-Pacific Program for Hypertension and Insulin Resistance (SAPPHIRe) family study, and 759 participants were followed up for 5 years. Ten SNPs of the PCSK2 gene were genotyped. Variants of rs6044695 and rs2284912 were associated with fasting plasma glucose, and variants of rs2269023 were associated with fasting plasma glucose and 1-hour plasma glucose during OGTT. Haplotypes of rs4814605/rs1078199 were associated with fasting plasma insulin levels and HOMA-IR. Haplotypes of rs890609/rs2269023 were also associated with fasting plasma glucose, fasting insulin and HOMA-IR. In the longitudinal study, we found individuals carrying TA/AA genotypes of rs6044695 or TC/CC genotypes of rs2284912 had lower incidence of diabetes during the 5-year follow-up. Our results indicated that PCSK2 gene polymorphisms are associated with pleiotropic effects on various traits of glucose homeostasis and incident diabetes.

Exploring the associations between genetic variants in genes encoding for subunits of calcium channel and subtypes of bipolar disorder

BACKGROUND

Associations of two voltage-gated calcium channel (Cav) genes, CACNA1C and CACNB2, were identified for bipolar disorder (BP) in different ethnic groups in recent genome-wide association studies. The current study aimed to evaluate the associations of several Cav genes and subtypes of BP in genetically more homogeneous Taiwanese samples. Additionally, we tested interaction effects among genes that encode for α1, β and γ-subunits of calcium channel.

METHODS

8 Cav genes were selected based on evidence in prior association studies and significant linkage regions for BP. 280 BP patients and 200 controls were recruited. Multifactor dimensionality reduction was performed for interaction testing in these discovery samples. Replication was conducted for two markers using additional 495 Taiwanese cases and 1341 controls.

RESULTS

Weak associations for CACNA1C (rs10848635), CACNA1E (rs10848635), CACNB2 (rs11013860), and CACNG2 (rs2284018) genes were observed. Joint analysis of four markers revealed higher accumulative risk with increasing numbers of risk genotypes an individual endorsed for BP-I (Ptrend=0.006) and BP-II (Ptrend=0.017) disorders. Combined analysis with independent replication samples further supported the association of rs11013860 in CACNB2 with BP subtype I (P=1×10(-6)). Suggestive interactions were found between genes encoded for different subunits of calcium channel (α1, β, and γ).

LIMITATIONS

Moderate sample size and incomplete markers coverage for the chosen Cav genes.

CONCLUSIONS

Our results support the involvement of different calcium channel genes in bipolar illness, in particular the beta-subunit in the Asian population. Further investigation of functional property of these genes can contribute on understanding the etiological mechanisms of bipolar illness.

Diabetes in the Western Pacific Region--past, present and future

In the 2013 issue of the International Diabetes Federation (IDF) Diabetes Atlas, the prevalence of diabetes in the Western Pacific (WP) Region was reported to be 8.6% in 2013, or 138 million adults, and estimated to rise to 11.1%, or 201 million adults, in 2035. The prevalence estimates of impaired glucose tolerance in 2013 and 2035 were 6.8% and 9.0%, respectively. Over 50% of people with diabetes were undiagnosed. In 2013, 187 million deaths were attributable to diabetes, 44% of which occurred in the under the age of 60. The WP Region is home to one quarter of the world's population, and includes China with the largest number of people with diabetes as well as Pacific Islands countries with the highest prevalence rates. There is a rapid increase in diabetes prevalence in the young-to-middle aged adults, possibly driven by high rates of childhood obesity and gestational diabetes as well as rapid demographic and sociocultural transitions. Differences in genetics, ethnicity, cultures and socioeconomic development have led to complex host-environment-lifestyle interactions with marked disease heterogeneity, further influenced by access to care and treatment. Despite these challenges, the WP Region has provided notable examples to prevent and control diabetes.

Familial young-onset diabetes, pre-diabetes and cardiovascular disease are associated with genetic variants of DACH1 in Chinese

In Asia, young-onset type 2 diabetes (YOD) is characterized by obesity and increased risk for cardiovascular disease (CVD). In a genome-wide association study (GWAS) of 99 Chinese obese subjects with familial YOD diagnosed before 40-year-old and 101 controls, the T allele of rs1408888 in intron 1 of DACH1(Dachshund homolog 1) was associated with an odds ratio (OR) of 2.49(95% confidence intervals:1.57-3.96, P = 8.4 × 10(-5)). Amongst these subjects, we found reduced expression of DACH1 in peripheral blood mononuclear cells (PBMC) from 63 cases compared to 65 controls (P = 0.02). In a random cohort of 1468 cases and 1485 controls, amongst top 19 SNPs from GWAS, rs1408888 was associated with type 2 diabetes with a global P value of 0.0176 and confirmation in a multiethnic Asian case-control cohort (7370/7802) with an OR of 1.07(1.02-1.12, P(meta)  = 0.012). In 599 Chinese non-diabetic subjects, rs1408888 was linearly associated with systolic blood pressure and insulin resistance. In a case-control cohort (n = 953/953), rs1408888 was associated with an OR of 1.54(1.07-2.22, P = 0.019) for CVD in type 2 diabetes. In an autopsy series of 173 non-diabetic cases, TT genotype of rs1408888 was associated with an OR of 3.31(1.19-9.19, P = 0.0214) and 3.27(1.25-11.07, P = 0.0184) for coronary heart disease (CHD) and coronary arteriosclerosis. Bioinformatics analysis revealed that rs1408888 lies within regulatory elements of DACH1 implicated in islet development and insulin secretion. The T allele of rs1408888 of DACH1 was associated with YOD, prediabetes and CVD in Chinese.

Association of genetic variants in the adiponectin gene with metabolic syndrome: a case-control study and a systematic meta-analysis in the Chinese population

Background

The prevalence of metabolic syndrome has been rising worldwide, including in China, but knowledge on specific genetic determinants of metabolic syndrome is very limited. A number of studies have reported that polymorphisms in the ADIPOQ gene are associated with metabolic syndrome in Chinese Han populations. However, data is still conflicting. The objective of this study was to examine the associations of the adiponectin genetic variants with metabolic syndrome by a case-control study and meta-analyses in Chinese.

Methods

We first investigated the association of ADIPOQ rs2241766 (+45T>G in exon 2), rs266729 (−11377C>G in promoter) and rs1501299 (+276G>T in intron 2) polymorphisms with metabolic syndrome in a Hubei Han Chinese population with 322 metabolic syndrome patients and 161 normal controls recruited from the Yichang, Hubei. Then we comprehensively reviewed the association between ADIPOQ rs2241766/rs266729/rs1501299 and metabolic syndrome in the Chinese populations via a meta-analysis. The strength of association was assessed by odds ratios (ORs) with 95% confidence intervals (CI).

Results

The G allele frequency of rs2241766 in metabolic syndrome patients was significantly higher than those of controls group (29.8% vs 23.3%, OR = 1.40, P = 0.033). The logistic regression analysis adjusted by gender and age showed a nominally significant association for rs2241766 GG+GT genotype (P = 0.065, OR = 1.55) and rs1501299 GG genotype in recessive model (OR = 1.54, P = 0.066). However, no association was observed for rs266729 in our sample. We identified thirteen studies for rs2241766 (2,684 metabolic syndrome patients and 2,864 controls), three studies for rs266729, and eleven studies for rs1501299 (2,889 metabolic syndrome patients and 3,304 controls) in Chinese. Meta-analysis indicated significant associations for the rs2241766 G allele (OR = 1.14, 95%CI = 1.05–1.24, P = 0.003), rs266729 GG+GT genotypes (OR = 0.80, 95%CI = 0.68–0.92, P = 0.003) and rs1501299 GG+TG genotypes (OR = 1.42, 95%CI 1.16–1.75, P = 0.001).

Conclusions

Our results demonstrated ADIPOQ as a pleiotropic locus for metabolic syndrome and its components in the Han Chinese population.

Metabolic syndrome is linked to chromosome 7q21 and associated with genetic variants in CD36 and GNAT3 in Mexican Americans

The prevalence of metabolic syndrome (MS) has been rising alarmingly worldwide, including in the United States, but knowledge on specific genetic determinants of MS is very limited. Therefore, we planned to identify the genetic determinants of MS as defined by National Cholesterol Education Program/Adult Treatment Panel III (NCEP/ATPIII) criteria. We performed linkage screen for MS using data from 692 Mexican Americans, who participated in the San Antonio Family Diabetes/Gallbladder Study (SAFDGS). We found strong evidence for linkage of MS on chromosome 7q (LOD = 3.6, empirical P = 6.0 × 10(-5)), between markers D7S2212 and D7S821. In addition, six chromosomal regions exhibited potential evidence for linkage (LOD ≥1.2) with MS. Furthermore, we examined 29 single-nucleotide polymorphisms (SNPs) from the fatty acid translocase (FAT or CD36, 18 SNPs) gene and guanine nucleotide binding protein, α transducing 3 (GNAT3, 11 SNPs) gene, located within the 1-LOD support interval region for their association with MS and its related traits. Several SNPs were associated with MS and its related traits. Remarkably, rs11760281 in GNAT3 and rs1194197 near CD36 exhibited the strongest associations with MS (P = 0.0003, relative risk (RR) = 1.6 and P = 0.004, RR = 1.7, respectively) and several other related traits. These two variants explained ~18% of the MS linkage evidence on chromosome 7q21, and together conferred approximately threefold increase in MS risk (RR = 2.7). In conclusion, our linkage and subsequent association studies implicate a region on chromosome 7q21 to influence MS in Mexican Americans.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Linkage Analysis of Factors Underlying Insulin Resistance: Strong Heart Family Study

In previous work in non-diabetic participants of the Strong Heart Family Study, we identified three heritable principal components of nine insulin resistance (IR) phenotypes: 1) a glucose/insulin/obesity factor, 2) a blood pressure factor, and 3) a dyslipidemia factor. To localize quantitative trait loci (QTL) potentially influencing these factors, we conducted a genome scan of factor scores in Strong Heart Family Study participants. Approximately 599 men and women, >or=18 years of age, in 32 extended families at three centers (in Arizona, Oklahoma, and North and South Dakota), were examined between 1997 and 1999. We used variance components linkage analysis to identify QTLs for the IR factors. With age, sex, and study center as covariates, we detected linkage of the glucose/insulin/obesity factor to chromosome 4 (robust logarithm of the odds (LOD) = 2.2), the dyslipidemia factor to chromosome 12 (robust LOD = 2.7), and the blood pressure factor to chromosome 1 (robust LOD = 1.6). The peak linkage signals identified for these IR factors support several positive findings from other studies and occur in regions harboring interesting candidate genes. The corroboration of existing QTLs will bring us closer to the identification of the functional genes that predispose to IR.

Loss of function of Ifi202b by a microdeletion on chromosome 1 of C57BL/6J mice suppresses 11β-hydroxysteroid dehydrogenase type 1 expression and development of obesity

Nob3 is a major obesity quantitative trait locus (QTL) identified in an intercross of New Zealand Obese (NZO) mice with C57BL/6J (B6), and by introgression of its 38 Mbp peak region into B6 (B6.NZO-Nob3.38). B6.NZO-Nob3.38 mice carrying the NZO allele exhibited markedly increased body weight, fat mass, lean mass and a lower energy expenditure, than the corresponding B6 allele carriers. For positional cloning of the responsible obesity gene, five additional congenic lines (RCS) were generated and characterized, allowing to define a critical genomic interval comprising 43 genes. mRNA profiling and western blotting indicated that Ifi202b, a member of the Ifi200 family of interferon inducible transcriptional modulators, was expressed in NZO-allele carriers but was undetectable in tissues of homozygous B6-allele carriers due to a microdeletion, including the first exon and the 5'-flanking region of Ifi202b in B6. Transcriptome analysis of adipose tissue of RCS revealed a marked induction of 11β-hydroxysteroid dehydrogenase type 1 (11β-Hsd1) expression in mice expressing Ifi202b. Furthermore, siRNA-mediated Ifi202b suppression in 3T3-L1 adipocytes resulted in a significant inhibition of 11β-Hsd1 expression, whereas an adenoviral-mediated overexpression of Ifi202b increased 11β-Hsd1 mRNA levels. Expression of human IFI orthologues was significantly increased in visceral adipose tissue of obese subjects. We suggest that the disruption of Ifi202b in B6 is responsible for the effects of the obesity QTL Nob3, and that Ifi202b modulates fat accumulation through expression of adipogenic genes such as 11β-Hsd1.

Genetic and environmental factors associated with type 2 diabetes and diabetic vascular complications

Faced with a global epidemic of type 2 diabetes (T2D), it is critical that researchers improve our understanding of the pathogenesis of T2D and related vascular complications. These findings may ultimately lead to novel treatment options for disease prevention or delaying progression. Two major paradigms jointly underlie the development of T2D and related coronary artery disease, diabetic nephropathy, and diabetic retinopathy. These paradigms include the genetic risk variants and behavioral/environmental factors. This article systematically reviews the literature supporting genetic determinants in the pathogenesis of T2D and diabetic vasculopathy, and the functional implications of these gene variants on the regulation of beta-cell function and glucose homeostasis. We update the discovery of diabetes and diabetic vasculopathy risk variants, and describe the genetic technologies that have uncovered them. Also, genomic linkage between obesity and T2D is discussed. There is a complementary role for behavioral and environmental factors modulating the genetic susceptibility and diabetes risk. Epidemiological and clinical data demonstrating the effects of behavioral and novel environmental exposures on disease expression are reviewed. Finally, a succinct overview of recent landmark clinical trials addressing glycemic control and its impact on rates of vascular complications is presented. It is expected that novel strategies to exploit the gene- and exposure-related underpinnings of T2D will soon result.

Diabetes and hypertension: is there a common metabolic pathway?

Diabetes and hypertension frequently occur together. There is substantial overlap between diabetes and hypertension in etiology and disease mechanisms. Obesity, inflammation, oxidative stress, and insulin resistance are thought to be the common pathways. Recent advances in the understanding of these pathways have provided new insights and perspectives. Physical activity plays an important protective role in the two diseases. Knowing the common causes and disease mechanisms allows a more effective and proactive approach in their prevention and treatment.

APOE genotype-function relationship: evidence of -491 A/T promoter polymorphism modifying transcription control but not type 2 diabetes risk

Background

The apolipoprotein E gene (APOE) coding polymorphism modifies the risks of Alzheimer's disease, type 2 diabetes, and coronary heart disease. Aside from the coding variants, single nucleotide polymorphism (SNP) of the APOE promoter has also been shown to modify the risk of Alzheimer's disease.

Methodology/Principal Findings

In this study we investigate the genotype-function relationship of APOE promoter polymorphism at molecular level and at physiological level: i.e., in transcription control of the gene and in the risk of type 2 diabetes. In molecular studies, the effect of the APOE −491A/T (rs449647) polymorphism on gene transcription was accessed by dual-luciferase reporter gene assays. The −491 A to T substitution decreased the activity (p<0.05) of the cloned APOE promoter (−1017 to +406). Using the −501 to −481 nucleotide sequence of the APOE promoter as a ‘bait’ to screen the human brain cDNA library by yeast one-hybrid system yielded ATF4, an endoplasmic reticulum stress response gene, as one of the interacting factors. Electrophoretic-mobility-shift assays (EMSA) and chromatin immuno-precipitation (ChIP) analyses further substantiated the physical interaction between ATF4 and the APOE promoter. Over-expression of ATF4 stimulated APOE expression whereas siRNA against ATF4 suppressed the expression of the gene. However, interaction between APOE promoter and ATF4 was not −491A/T-specific. At physiological level, the genotype-function relationship of APOE promoter polymorphism was studied in type 2 diabetes. In 630 cases and 595 controls, three APOE promoter SNPs −491A/T, −219G/T (rs405509), and +113G/C (rs440446) were genotyped and tested for association with type 2 diabetes in Hong Kong Chinese. No SNP or haplotype association with type 2 diabetes was detected.

Conclusions/Significance

At molecular level, polymorphism −491A/T and ATF4 elicit independent control of APOE gene expression. At physiological level, no genotype-risk association was detected between the studied APOE promoter SNPs and type 2 diabetes in Hong Kong Chinese.

Multivariate linkage scan for metabolic syndrome traits in families with type 2 diabetes

The purpose of this study was to evaluate evidence for linkage to interrelated quantitative features of the metabolic syndrome (MetS). Data on eight quantitative MetS traits (body weight, waist circumference, systolic and diastolic blood pressure, high-density lipoprotein (HDL) cholesterol, triglycerides (TGs), and fasting glucose and insulin measurements) and a 10 cM genome scan were available for 78 white families (n = 532 subjects). These data were used to conduct multipoint, multivariate linkage analyses, including tests for coincident linkage and complete pleiotropy. The strongest evidence for linkage from the bivariate analyses was observed on chromosome 1 (1p22.2) (HDL-TG; univariate lod score equivalent (lod(eq) = 3.99)) with stronger results from the trivariate analysis at the same location (HDL-TG-Insulin; lod(eq) = 4.32). Seven additional susceptibility regions (lod(eq) scores >1.9) were observed (1p36, 1q23, 2q21.2, 8q23.3, 14q23.2, 14q32.11, and 20p11.21). The results from this study indicate that several correlated traits of the MetS are influenced by the same gene(s) that account for some of the clustering of the MetS features.

Adiponectin gene polymorphism is selectively associated with the concomitant presence of metabolic syndrome and essential hypertension

Objective

Cardiovascular risk increases with the presence of both metabolic syndrome (MetS) and hypertension (HTN). Although the adiponectin (ADIPOQ) gene has been reported to be involved in MetS, its association with HTN remained undetermined. This study aimed to investigate the association of ADIPOQ gene with the phenotypes of HTN and MetS.

Methods

A total of 962 participants from 302 families from the Taiwan young-onset hypertension genetic study were enrolled. Plasma adiponectin were measured, and association analysis was conducted by using GEE regression-based method. Another study, of 1448 unrelated participants, was conducted to replicate the association between ADIPOQ gene and variable phenotypes of MetS with or without HTN.

Results

Among 962 subjects from family samples, the lowest plasma adiponectin value was observed in MetS with HTN component (9.3±0.47 µg/ml) compared with hypertensives (13.4±0.74 µg /ml) or MetS without HTN (11.9±0.60 µg/ml, P<0.05). The SNP rs1501299 (G276T) in ADIPOQ gene was found associated with the presence of HTN in MetS (odds ratio for GG+GT vs. TT = 2.46; 95% CI: 1.14-5.3, p = 0.02), but not rs2241766 (T45G). No association of ADIPOQ gene with HTN alone or MetS without HTN was observed. The significant association of the SNP rs1501299 (G276T) with the phenotype of presence of HTN in MetS was confirmed (odds ratio for GG+GT vs. TT = 2.15; 95% CI: 1.1–4.3) in the replication study.

Conclusions

ADIPOQ genetic variants were selectively and specifically associated with the concomitant presence of MetS and HTN, suggesting potential genetic linkage between MetS and HTN.

Association of a genetic variant in the apolipoprotein A5 gene with the metabolic syndrome in Chinese

OBJECTIVE

Single nucleotide polymorphisms (SNPs) in the apolipoprotein A5 gene (APOA5) are associated with hypertriglyceridaemia in our population. We studied the associations of SNPs in APOA5 with the metabolic syndrome (MetS) in the Hong Kong and Guangzhou Chinese.

METHODS

We genotyped five tagging SNPs in 1330 unrelated subjects from the Hong Kong Cardiovascular Risk Factor Prevalence Study cohort with follow-up after a median interval of 6·4 years; 1952 subjects from the Guangzhou Biobank Cohort Study-Cardiovascular Disease Subcohort were used to replicate the findings. The MetS was defined according to the consensus criteria proposed jointly by several organizations in 2009.

RESULTS

The SNP rs662799 (-1131T>C) was associated with the MetS (odds ratio = 1·47, P = 0·00082) and the number of its components present (regression coefficient = 0·204, P = 4·6 × 10(-5) ) after adjusting for age, sex, smoking, drinking and education in Hong Kong subjects at baseline. Similar association of this SNP was found in Hong Kong subjects at follow-up (P = 0·010 and 0·00021, respectively) and in Guangzhou subjects (P = 0·0041 and 0·017, respectively). The association of rs662799 with the number of the MetS components was significant regardless of age, sex, obesity and alcohol drinking, but almost disappeared after further adjusting for plasma triglycerides.

CONCLUSION

Our results showed that the -1131T>C polymorphism in APOA5 was associated with the MetS because of its strong effect on plasma triglycerides. This may partly explain the higher cardiovascular risk in people with this polymorphism.

Association of the POU class 2 homeobox 1 gene (POU2F1) with susceptibility to Type 2 diabetes in Chinese populations

AIMS

POU class 2 homeobox 1 (POU2F1), also known as octamer-binding transcription factor-1 (OCT-1), is a ubiquitous transcription factor that plays a key role in the regulation of genes related to inflammation and cell cycles. POU2F1 is located on chromosome 1q24, a region with linkage for Type 2 diabetes in Chinese and other populations. We examined the association of POU2F1 genetic variants with Type 2 diabetes in Hong Kong Chinese using two independent cohorts.

METHODS

We genotyped five haplotype-tagging single nucleotide polymorphisms at POU2F1 in 1378 clinic-based patients with Type 2 diabetes and 601 control subjects, as well as 707 members from 179 families with diabetes.

RESULTS

We found significant associations of rs4657652, rs7532692, rs10918682 and rs3767434 (OR = 1.26-1.59, 0.0003 < P(unadjusted) < 0.035) with Type 2 diabetes in the clinic-based case-control cohorts. Rs3767434 was also associated with Type 2 diabetes (OR = 1.55, P(unadjusted) = 0.013) in the family-based cohort. Meta-analysis revealed similar associations. In addition, the risk G allele of rs10918682 showed increased usage of insulin treatment during a mean follow-up period of 7 years [hazard ratio = 1.50 (1.05-2.14), P = 0.025].

CONCLUSIONS

Using separate cohorts, we observed consistent results showing the contribution of multiple variants at POU2F1 to the risk of Type 2 diabetes.

The hypertension-diabetes continuum

Hypertension and type 2 diabetes are both common chronic conditions that affect a major proportion of the general population. They tend to occur in the same individual, suggesting common predisposing factors, which can be genetic or environmental. Although the genes causing hypertension or diabetes await elucidation, the environmental causes of these diseases are well known. Obesity and physical activity are the 2 leading factors that predispose to both diseases. Individuals with abdominal obesity are likely to develop lipid abnormalities and elevation of blood pressure and glucose. In time, hypertension and diabetes ensue. Because of the shared etiology, there is substantial overlap between hypertension and diabetes. In the Hong Kong Cardiovascular Risk Factor Prevalence Study, 40% of the subjects in the community had either raised blood pressure or raised blood glucose. Only 42% of people with diabetes had normal blood pressure and only 56% of people with hypertension had normal glucose tolerance. The presence of hypertension or diabetes should alert the clinician to the possibility of the other condition. Obesity, lipid abnormalities, raised blood pressure, and glucose are all components of the metabolic syndrome. The syndrome therefore implies a pathologic process, which is potentially reversible in the early stages. Previous efforts targeting smoking, hypertension, and hypercholesterolemia have started to bear fruit. However, obesity is on the increase in developed and developing countries. It is now time to focus on obesity and the metabolic syndrome, which require more a public health than a pharmacologic approach.

Untangling HDL quantitative trait loci on mouse chromosome 5 and identifying Scarb1 and Acads as the underlying genes

Two high-density lipoprotein cholesterol quantitative trait loci (QTL), Hdlq1 at 125 Mb and Hdlq8 at 113 Mb, were previously identified on mouse distal chromosome 5. Our objective was to identify the underlying genes. We first used bioinformatics to narrow the Hdlq1 locus to 56 genes. The most likely candidate, Scarb1 (scavenger receptor B1), was supported by gene expression data consistent with knockout and transgenic mouse models. Then we confirmed Hdlq8 as an independent QTL by detecting it in an intercross between NZB and NZW (LOD = 12.7), two mouse strains that have identical genotypes for Scarb1. Haplotyping narrowed this QTL to 9 genes; the most likely candidate was Acads (acyl-coenzymeA dehydrogenase, short chain). Sequencing showed that Acads had an amino acid polymorphism, Gly94Asp, in a conserved region; Western blotting showed that protein levels were significantly different between parental strains. A previously known spontaneous deletion causes loss of ACADS activity in BALB/cBy mice. We showed that HDL levels were significantly elevated in BALB/cBy compared with BALB/c mice and that this HDL difference cosegregated with the Acads mutation. We confirmed that Hdlq1 and Hdlq8 are independent QTL on mouse chromosome 5 and demonstrated that Scarb1 and Acads are the underlying genes.

NOS1AP variant associated with incidence of type 2 diabetes in calcium channel blocker users in the Atherosclerosis Risk in Communities (ARIC) study

AIMS/HYPOTHESIS

To validate the reported association between rs10494366 in NOS1AP (the gene encoding nitric oxide synthase-1 adaptor protein) and the incidence of type 2 diabetes in calcium channel blocker (CCB) users and to identify additional NOS1AP variants associated with type 2 diabetes risk.

METHODS

Data from 9 years of follow-up in 9,221 middle-aged white and 2,724 African-American adults free of diabetes at baseline from the Atherosclerosis Risk in Communities study were analysed. Nineteen NOS1AP variants were examined for associations with incident diabetes and fasting glucose levels stratified by baseline CCB use.

RESULTS

Prevalence of CCB use at baseline was 2.7% (n = 247) in whites and 2.3% (n = 72) in African-Americans. Among white CCB users, the G allele of rs10494366 was associated with lower diabetes incidence (HR 0.57, 95% CI 0.35-0.92, p = 0.016). The association was marginally significant after adjusting for age, sex, obesity, smoking, alcohol use, physical activity, hypertension, heart rate and electrocardiographic QT interval (HR 0.63, 95% CI 0.38-1.04, p = 0.052). rs10494366 was associated with lower average fasting glucose during follow-up (p = 0.037). No other variants were associated with diabetes risk in CCB users after multiple-testing correction. No associations were observed between any NOS1AP variant and diabetes development in non-CCB users. NOS1AP variants were not associated with diabetes risk in either African-American CCB users or non-CCB users.

CONCLUSIONS/INTERPRETATION

We have independently replicated the association between rs10494366 in NOS1AP and incident diabetes among white CCB users. Further exploration of NOS1AP variants and type 2 diabetes and functional studies of NOS1AP in type 2 diabetes pathology is warranted.

Genome-wide linkage scan for factors of metabolic syndrome in a Chinese population

BACKGROUND

Shared genetic factors may contribute to the phenotypic clustering of different components of the metabolic syndrome (MES). This study aims to identify genetic loci that contribute to individual or multiple factors related to MES.

RESULTS

We studied 478 normoglycemic subjects ascertained through 163 families participating in the Hong Kong Family Diabetes Study. Factor analysis on 15 MES-related traits yielded 6 factors including adiposity factor (body mass index, waist and hip circumferences), insulin factor (fasting insulin and insulin AUC during OGTT), glucose factor (fasting glucose and glucose AUC during OGTT), TC-LDLC factor (total cholesterol and LDL-cholesterol), blood pressure factor (systolic and diastolic blood pressure) and TG-HDLC factor (triglycerides and HDL-cholesterol). Genome-wide linkage analyses were performed on these factors using variance component approach. Suggestive evidence for linkage (LOD = 1.24 - 2.46) were observed for adiposity factor (chromosome 1 at 187 cM, chromosome 9 at 34 cM and chromosome 17 at 10 cM), insulin factor (chromosome 2 at 128 cM, chromosome 5 at 21 cM and chromosome 12 at 7 cM), glucose factor (chromosome 7 at 155 cM), TC-LDLC factor (chromosome 7 at 151 cM and chromosome 13 at 15 cM) and TG-HDLC factor (chromosome 7 at 155 cM).

CONCLUSIONS

In summary, our findings suggest the presence of susceptibility loci that influence either single (chromosomes 1, 2, 5, 9, 12, 13 and 17) or multiple factors (chromosome 7) for MES in Hong Kong Chinese without diabetes.

Genome-wide linkage of obstructive sleep apnoea and high-density lipoprotein cholesterol in a Filipino family: bivariate linkage analysis of obstructive sleep apnoea

Increasing evidence supports an association between obstructive sleep apnoea (OSA) and metabolic syndrome (MeS) in both children and adults, suggesting a genetic component. However, the genetic relationship between the diseases remains unclear. We performed a bivariate linkage scan on a single Filipino family with a high prevalence of OSA and MeS to explore the genetic pathways underlying these diseases. A large rural family (n = 50, 50% adults) underwent a 10-cM genome-wide scan. Fasting blood was used to measure insulin, triglycerides, total cholesterol and high density lipoprotein (HDL) cholesterol. Attended overnight polysomnography was used to quantify the respiratory disturbance index (RDI), a measure of sleep apnoea. Body mass index z-scores and insulin resistance scores were calculated. Bivariate multipoint linkage analyses were performed on RDI and MeS components. OSA prevalence was 46% (n = 23; nine adults, 14 children) in our participants. MeS phenotype was present in 40% of adults (n = 10) and 48% of children (n = 12). Linkage peaks with a logarithm of odds (LOD) score >3 were demonstrated on chromosome 19q13.4 (LOD = 3.04) for the trait pair RDI and HDL cholesterol. Candidate genes identified in this region include the killer cell immunoglobulin-like receptor genes. These genes are associated with modulating inflammatory responses in reaction to cellular stress and initiation of atherosclerotic plaque formation. We have identified a novel locus for genetic links between RDI and lipid factors associated with MeS in a chromosomal region containing genes associated with inflammatory responses.

Upstream transcription factor 1 influences plasma lipid and metabolic traits in mice

Upstream transcription factor 1 (USF1) has been associated with familial combined hyperlipidemia, the metabolic syndrome, and related conditions, but the mechanisms involved are unknown. In this study, we report validation of Usf1 as a causal gene of cholesterol homeostasis, insulin sensitivity and body composition in mouse models using several complementary approaches and identify associated pathways and gene expression network modules. Over-expression of human USF1 in both transgenic mice and mice with transient liver-specific over-expression influenced metabolic trait phenotypes, including obesity, total cholesterol level, LDL/VLDL cholesterol and glucose/insulin ratio. Additional analyses of trait and hepatic gene expression data from an F2 population derived from C57BL/6J and C3H/HeJ strains in which there is a naturally occurring variation in Usf1 expression supported a causal role for Usf1 for relevant metabolic traits. Gene network and pathway analyses of the liver gene expression signatures in the F2 population and the hepatic over-expression model suggested the involvement of Usf1 in immune responses and metabolism, including an Igfbp2-centered module. In all three mouse model settings, notable sex specificity was observed, consistent with human studies showing differences in association with USF1 gene polymorphisms between sexes.

Microsatellites and SNPs linkage analysis in a Sardinian genetic isolate confirms several essential hypertension loci previously identified in different populations

Background

A multiplicity of study designs such as gene candidate analysis, genome wide search (GWS) and, recently, whole genome association studies have been employed for the identification of the genetic components of essential hypertension (EH). Several genome-wide linkage studies of EH and blood pressure-related phenotypes demonstrate that there is no single locus with a major effect while several genomic regions likely to contain EH-susceptibility loci were validated by multiple studies.

Methods

We carried out the clinical assessment of the entire adult population in a Sardinian village (Talana) and we analyzed 16 selected families with 62 hypertensive subjects out of 267 individuals. We carried out a double GWS using a set of 902 uniformly spaced microsatellites and a high-density SNPs map on the same group of families.

Results

Three loci were identified by both microsatellites and SNP scans and the obtained linkage results showed a remarkable degree of similarity. These loci were identified on chromosome 2q24, 11q23.1–25 and 13q14.11–21.33. Further support to these findings is their broad description present in literature associated to EH or related phenotypes. Bioinformatic investigation of these loci shows several potential EH candidate genes, several of whom already associated to blood pressure regulation pathways.

Conclusion

Our search for major susceptibility EH genetic factors evidences that EH in the genetic isolate of Talana is due to the contribution of several genes contained in loci identified and replicated by earlier findings in different human populations.

Phosphoinositide cycle gene polymorphisms affect the plasma lipid profile in the Quebec Family Study

BACKGROUND

The small, dense LDL phenotype is associated with an increased cardiovascular disease risk. A genome-wide scan performed on 236 nuclear families of the Quebec Family Study (QFS) revealed a QTL for LDL-peak particle size (LDL-PPD) on the 17q21 region. Three positional candidates were identified in this region according to their implication in the phosphoinositide (PI) cycle: the myotubularin-related protein 4 (MTMR4), the phospholipase C, delta 3 (PLCD3), and the diacylglycerol kinase E (DGKE) genes.

OBJECTIVES

To test the association between MTMR4, PLCD3, and DGKE gene polymorphisms, LDL-PPD and plasma lipid parameters.

METHODS

Analyses were performed on 680 subjects of QFS. LDL-PPD was measured by gradient gel electrophoresis on non-denaturating 2-16% polyacrylamide gradient gels. Direct sequencing was performed to identify genetic variations within these genes.

RESULTS

The c.-754G>C, c.183G>A, and c.579C>A DGKE SNPs were significantly associated with higher plasma triglyceride levels (p=0.029, p=0.008, p=0.001, respectively). The c.508C>G and c.890T>G MTMR4 polymorphisms were associated with plasma total-cholesterol concentrations (p=0.02, p=0.02, respectively), while no association was observed with PLCD3 gene polymorphisms.

CONCLUSION

The c.579C>A DGKE gene polymorphism is associated with plasma triglyceride levels, while MTMR4 SNPs seem to predict variations in plasma cholesterol levels.

Agreement among type 2 diabetes linkage studies but a poor correlation with results from genome-wide association studies

AIMS/HYPOTHESIS

Little of the genetic basis for type 2 diabetes has been explained, despite numerous genetic linkage studies and the discovery of multiple genes in genome-wide association (GWA) studies. To begin to resolve the genetic component of this disease, we searched for sites at which genetic results had been corroborated in different studies, in the expectation that replication among studies should direct us to the genomic locations of causative genes with more confidence than the results of individual studies.

METHODS

We have mapped the physical location of results from 83 linkage reports (for type 2 diabetes and diabetes precursor quantitative traits [QTs, e.g. plasma insulin levels]) and recent large GWA reports (for type 2 diabetes) onto the same human genome sequence to identify replicated results in diabetes genetic 'hot spots'.

RESULTS

Genetic linkage has been found at least ten times at 18 different locations, and at least five times in 56 locations. All replication clusters contained study populations from more than one ethnic background and most contained results for both diabetes and QTs. There is no close relationship between the GWA results and linkage clusters, and the nine best replication clusters have no nearby GWA result.

CONCLUSIONS/INTERPRETATION

Many of the genes for type 2 diabetes remain unidentified. This analysis identifies the broad location of yet to be identified genes on 6q, 1q, 18p, 2q, 20q, 17pq, 8p, 19q and 9q. The discrepancy between the linkage and GWA studies may be explained by the presence of multiple, uncommon, mildly deleterious polymorphisms scattered throughout the regulatory and coding regions of genes for type 2 diabetes.

Genetic variants at the PDZ-interacting domain of the scavenger receptor class B type I interact with diet to influence the risk of metabolic syndrome in obese men and women

The scaffolding protein PDZ domain containing 1 (PDZK1) regulates the HDL receptor scavenger receptor class B type I. However, the effect of PDZK1 genetic variants on lipids and metabolic syndrome (MetS) traits remains unknown. This study evaluated the association of 3 PDZK1 single nucleotide polymorphisms (SNP) (i33968C > T, i15371G > A, and i19738C > T) with lipids and risk of MetS and their potential interactions with diet. PDZK1 SNP were genotyped in 1000 participants (481 men, 519 women) included in the Genetics of Lipid Lowering Drugs and Diet Network study. Lipoprotein subfractions were measured by proton NMR spectroscopy and dietary intake was estimated using a validated questionnaire. The PDZK1_i33968C > T polymorphism was associated with MetS (P = 0.034), mainly driven by the association of the minor T allele with higher plasma triglycerides (P = 0.004) and VLDL (P = 0.021), and lower adiponectin concentrations (P = 0.022) than in participants homozygous for the major allele (C). We found a significant gene x BMI x diet interaction, in which the deleterious association of the i33968T allele with MetS was observed in obese participants with high PUFA and carbohydrate (P-values ranging from 0.004 to 0.020) intakes. Conversely, a there was a protective effect in nonobese participants with high PUFA intake (P < 0.05). These findings suggest that PDZK1_i33968C > T genetic variants may be associated with a higher risk of exhibiting MetS. This gene x BMI x diet interaction offers the potential to identify dietary and other lifestyle changes that may obviate the onset of MetS in individuals with a specific genetic background.

Genome-wide linkage scan for genes influencing plasma triglyceride levels in the Veterans Administration Genetic Epidemiology Study

OBJECTIVE

Elevated plasma triglyceride concentration is a component of the insulin resistance syndrome and is commonly associated with type 2 diabetes, obesity, and coronary heart disease. The goal of our study was to perform a genome-wide linkage scan to identify genetic regions that influence variation in plasma triglyceride levels in families that are enriched with individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We used phenotypic and genotypic data from 1,026 individuals distributed across 294 Mexican-American families, who were ascertained for type 2 diabetes, from the Veterans Administration Genetic Epidemiology Study (VAGES). Plasma triglyceride values were transformed, and a variance-components technique was used to conduct multipoint linkage analysis.

RESULTS

After adjusting for the significant effects of sex and BMI, heritability for plasma triglycerides was estimated as 46 +/- 7% (P < 0.0001). Multipoint linkage analysis yielded the strongest evidence for linkage of plasma triglycerides near marker D12S391 on chromosome 12p (logarithm of odds [LOD] = 2.4). Our linkage signal on chromosome 12p provides independent replication of a similar finding in another Mexican-American sample from the San Antonio Family Diabetes Study (SAFDS). Combined multipoint linkage analysis of the VAGES and SAFDS data yielded significant evidence for linkage of plasma triglycerides to a genetic location between markers GATA49D12 and D12S391 on 12p (LOD = 3.8, empirical P value = 2.0 x 10(-5)). This region on 12p harbors the gene-encoding adiponectin receptor 2 (AdipoR2), where we previously have shown that multiple single nucleotide polymorphisms are associated with plasma triglyceride concentrations in the SAFDS. In the present study, we provided suggestive evidence in favor of association for rs929434 with triglyceride concentrations in the VAGES.

CONCLUSIONS

Collectively, these results provide strong evidence for a major locus on chromosome 12p that influences plasma triglyceride levels in Mexican Americans.

Lack of association between PKLR rs3020781 and NOS1AP rs7538490 and type 2 diabetes, overweight, obesity and related metabolic phenotypes in a Danish large-scale study: case-control studies and analyses of quantitative traits

Background

Several studies in multiple ethnicities have reported linkage to type 2 diabetes on chromosome 1q21-25. Both PKLR encoding the liver pyruvate kinase and NOS1AP encoding the nitric oxide synthase 1 (neuronal) adaptor protein (CAPON) are positioned within this chromosomal region and are thus positional candidates for the observed linkage peak. The C-allele of PKLR rs3020781 and the T-allele of NOS1AP rs7538490 are reported to strongly associate with type 2 diabetes in various European-descent populations comprising a total of 2,198 individuals with a combined odds ratio (OR) of 1.33 [1.16–1.54] and 1.53 [1.28–1.81], respectively. Our aim was to validate these findings by investigating the impact of the two variants on type 2 diabetes and related quantitative metabolic phenotypes in a large study sample of Danes. Further, we intended to expand the analyses by examining the effect of the variants in relation to overweight and obesity.

Methods

PKLR rs3020781 and NOS1AP rs7538490 were genotyped, using TaqMan allelic discrimination, in a combined study sample comprising a total of 16,801 and 16,913 individuals, respectively. The participants were ascertained from four different study groups; the population-based Inter99 cohort (n_PKLR = 5,962, n_NOS1AP = 6,008), a type 2 diabetic patient group (n_PKLR = 1,873, n_NOS1AP = 1,874) from Steno Diabetes Center, a population-based study sample (n_PKLR = 599, n_NOS1AP = 596) from Steno Diabetes Center and the ADDITION Denmark screening study cohort (n_PKLR = 8,367, n_NOS1AP = 8,435).

Results

In case-control studies we evaluated the potential association between rs3020781 and rs7538490 and type 2 diabetes and obesity. No significant associations were observed for type 2 diabetes (rs3020781: p_AF = 0.49, OR = 1.02 [0.96–1.10]; rs7538490: p_AF = 0.84, OR = 0.99 [0.93–1.06]). Neither did we show association with overweight or obesity. Additionally, the PKLR and the NOS1AP genotypes were demonstrated not to have a major influence on diabetes-related quantitative metabolic phenotypes.

Conclusion

We failed to provide evidence of an association between PKLR rs3020781 and NOS1AP rs7538490 and type 2 diabetes, overweight, obesity or related quantitative metabolic phenotypes in large-scale studies of Danes.

Genetics of metabolic syndrome

Metabolic syndrome (MetS) is a common phenotype, affecting about 24% of the US population. It is associated with an increased risk for type 2 diabetes and cardiovascular disease. Although there is no universally accepted definition for MetS, affected individuals commonly have a cluster of features, including abdominal obesity, hypertension, dyslipidemia, and dysglycemia. Recently, there has been extensive interest in potential genetic contributions to MetS. At present, no single gene or cluster of genes has been consistently replicated for MetS among different populations, likely due to the complex interplay between gene and environment necessary for expression of this phenotype. We review recent studies regarding the genetic contributions to MetS.

Cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) gene V115F (G-->T) polymorphism is associated with phenotypes of metabolic syndrome in Japanese men

Cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) regulates energy expenditure in the adipose tissue and is implicated in the development of obesity. A single nucleotide polymorphism in the CIDEA gene that causes an amino acid substitution of valine 115 to c(V115F) has recently been shown to be associated with obesity in the Swedish population. Here, we determined the effects of this polymorphism on phenotypes of metabolic syndrome within the Japanese population. Two hundred seventy unrelated Japanese male workers (mean age, 44.5 years) were analyzed in a cross-sectional study. The clinical features regarding metabolic syndrome, as well as CIDEA V115F polymorphism, were determined for each individual. The V115F polymorphism associated with waist circumference and fasting plasma glucose. These parameters were at higher levels in the VF + FF group than in the VV group (P < .05). The VF + FF group compared with the VV group had a higher prevalence for abdominal obesity (odds ratio [OR] = 1.89; 95% confidence interval [CI], 1.03-3.44), high fasting plasma glucose (OR = 2.81; 95% CI, 1.03-7.67), and metabolic syndrome (OR = 3.15; 95% CI, 1.05-9.48). These results suggest that the F allele of the CIDEA gene may serve as a risk factor for phenotypes related to metabolic syndrome in Japanese men.

Association of F11 receptor gene polymorphisms with central obesity and blood pressure

OBJECTIVES

F11 receptor, also known as junctional adhesion molecule-1, in the autonomic nervous system is implicated in the development of hypertension in spontaneous hypertensive rats. We investigated the association of single nucleotide polymorphisms (SNPs) in the F11 receptor gene (F11R) with hypertension and central obesity in Hong Kong Chinese.

METHODS

Seven tagging SNPs were identified in the HapMap database. Genotyping was performed using Sequenom MassArray in 263 hypertensive subjects and 393 normotensive controls, of whom 263 matched the cases in age and sex.

RESULTS

When subjects on anti-hypertensive medication were excluded, rs790056 and rs2774276 were associated with lower systolic blood pressure (TT:124.8 +/- 18.3 mmHg vs. TC + CC: 120.2 +/- 15.5 mmHg, P = 0.004 and CC: 124.7 +/- 18.5 mmHg vs. CG+GG: 120.5 +/- 15.1 mmHg, P = 0.007 respectively). Comparing 213 subjects with central obesity with 213 controls matched for sex and age, rs2481084 and rs3737787 were associated with lower odds of central obesity (odds ratio = 0.516, P = 0.002 and odds ratio = 0.540, P = 0.005 respectively). All these associations remained significant after correction for multiple testing. Analysis of statistically similar SNPs suggested that the causative variants for systolic blood pressure were located in F11R, whilst those for central obesity could be due to causative variants in the transcription factor 1 gene immediately upstream.

CONCLUSIONS

F11 receptor plays a role in blood pressure regulation, not only in rats but also in man. The link between F11 receptor and central obesity merits further investigation.

Variants in the Ca V 2.3 (alpha 1E) subunit of voltage-activated Ca2+ channels are associated with insulin resistance and type 2 diabetes in Pima Indians

OBJECTIVE

Linkage to type 2 diabetes has been reported on chromosome 1q21-25 in Pima Indians. Fine mapping identified single nucleotide polymorphisms (SNPs) near the CACNA1E gene associated with this disease. CACNA1E encodes the voltage-dependent calcium channel Ca(v)2.3 Ca(2+), and mice lacking this channel exhibit impaired glucose tolerance and insulin secretion. Therefore, CACNA1E was investigated as a positional candidate gene.

RESEARCH DESIGN AND METHODS

CACNA1E was sequenced, and 28 SNPs were genotyped in the same group of Pima subjects who had been analyzed in the linkage study. Allele-specific expression was used to functionally evaluate a variant in the 3' untranslated region (UTR).

RESULTS

A novel G/A variant in the 3'-UTR was associated with young-onset type 2 diabetes (odds ratio 2.09 per copy of the G-allele [95% CI 1.31-3.33], adjusted P = 0.001) and had an effect on the evidence for linkage at chromosome 1q21-25 (P = 0.004). Among 372 nondiabetic Pima subjects who had undergone metabolic testing, the risk allele was associated with reduced insulin action including increased fasting, 30, 60, and 120 min plasma glucose concentrations and increased fasting plasma insulin during an oral glucose tolerance test (all P < 0.01), as well as a decreased rate of insulin-stimulated glucose disposal at both physiologically and maximally stimulated insulin concentrations (both P < 0.002). Functional analysis of this variant showed that the nonrisk allele had a 2.3-fold higher expression compared with the risk allele.

CONCLUSIONS

A functional variant in CACNA1E contributes to type 2 diabetes susceptibility by affecting insulin action. This variant partially explains the linkage to type 2 diabetes on chromosome 1q21-25 in Pima Indians.

A chromosome 11q quantitative-trait locus influences change of blood-pressure measurements over time in Mexican Americans of the San Antonio Family Heart Study

Although previous genome scans have searched for quantitative-trait loci (QTLs) influencing variation in blood pressure (BP), few have investigated the rate of change in BP over time as a phenotype. Here, we compare results from genomewide scans to localize QTLs for systolic, diastolic, and mean arterial BPs (SBP, DBP, and MBP, respectively) and for rates of change in systolic, diastolic, and mean arterial BPs (rSBP, rDBP, and rMBP, respectively), with use of the longitudinal data collected about Mexican Americans of the San Antonio Family Heart Study (SAFHS). Significant evidence of linkage was found for rSBP (LOD 4.15) and for rMBP (LOD 3.94) near marker D11S4464 located on chromosome 11q24.1. This same chromosome 11q region also shows suggestive linkage to SBP (LOD 2.23) and MBP (LOD 2.37) measurements collected during the second clinic visit. Suggestive evidence of linkage to chromosome 5 was also found for rMBP, to chromosome 16 for rSBP, and to chromosomes 1, 5, 6, 7, and 21 for the single-time-point BP traits collected at the first two SAFHS clinic visits. We also present results from fine mapping the chromosome 11 QTL with use of SNP-association analysis within candidate genes identified from a bioinformatic search of the region and from whole-genome transcriptional expression data collected from 1,240 SAFHS participants. Our results show that the use of longitudinal BP data to calculate the rate of change in BP over time provides more information than do the single-time measurements, since they reveal physiological trends in the subjects that a single-time measurement could never capture. Further investigation of this region is necessary for the identification of the genetic variation responsible for QTLs influencing the rate of change in BP.

Replication and identification of novel variants at TCF7L2 associated with type 2 diabetes in Hong Kong Chinese

OBJECTIVE

Variations at a large linkage disequilibrium (LD) block of transcription factor 7-like 2 gene (TCF7L2) were reported to be associated with type 2 diabetes (T2D) in Icelandic, Danish and European-American populations and further replicated in other populations of European, African, and Asian ancestries. However, data for Chinese and comprehensive survey of the whole gene are lacking.

DESIGN

We attempted to examine 22 tagging single-nucleotide polymorphisms (SNPs) spanning across the TCF7L2 gene for association with T2D in Hong Kong Chinese. We first studied a case-control sample involving 433 hospital cases with familial early-onset T2D and 419 normal controls and further studied the associated SNPs in 450 members of 142 diabetic families.

RESULTS

Two of the previously reported risk alleles at rs11196205 (C) and rs7903146 (T) were rare in Chinese (0.013 and 0.024, respectively, in controls). Rs11196205 was associated with T2D [odds ratio (OR) [95% confidence interval (CI)] = 2.11 (1.04-4.26)], whereas the association for rs7903146 [OR (95% CI) = 1.27 (0.71-2.29)] was not significant in the case-control sample. Interestingly, another SNP (rs11196218 G allele) located in adjacent LD block conferred independent risk for T2D [OR (95%CI) =1.43 (1.14-1.79)] and contributed high-population attributable risk of 42%. The association finding of rs11196218 and its haplotype for T2D was also replicated in the family sample (P < 0.05).

CONCLUSIONS

Our results are consistent with others' findings that variations at TCF7L2 contribute to T2D, including Chinese. The presence of association signals spanning several LD blocks warrants further examination of extended regions to reveal the causal variant(s) for this important T2D gene.