Publisher Correction: Genome-wide association of polycystic ovary syndrome implicates alterations in gonadotropin secretion in European ancestry populations.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Multiethnic genome-wide meta-analysis of ectopic fat depots identifies loci associated with adipocyte development and differentiation.

Variation in body fat distribution contributes to the metabolic sequelae of obesity. The genetic determinants of body fat distribution are poorly understood. The goal of this study was to gain new insights into the underlying genetics of body fat distribution by conducting sample-size-weighted fixed-effects genome-wide association meta-analyses in up to 9,594 women and 8,738 men of European, African, Hispanic and Chinese ancestry, with and without sex stratification, for six traits associated with ectopic fat (hereinafter referred to as ectopic-fat traits). In total, we identified seven new loci associated with ectopic-fat traits (ATXN1, UBE2E2, EBF1, RREB1, GSDMB, GRAMD3 and ENSA; P < 5 × 10-8; false discovery rate < 1%). Functional analysis of these genes showed that loss of function of either Atxn1 or Ube2e2 in primary mouse adipose progenitor cells impaired adipocyte differentiation, suggesting physiological roles for ATXN1 and UBE2E2 in adipogenesis. Future studies are necessary to further explore the mechanisms by which these genes affect adipocyte biology and how their perturbations contribute to systemic metabolic disease.

Genome-wide association of polycystic ovary syndrome implicates alterations in gonadotropin secretion in European ancestry populations.

Polycystic ovary syndrome (PCOS) is a common, highly heritable complex disorder of unknown aetiology characterized by hyperandrogenism, chronic anovulation and defects in glucose homeostasis. Increased luteinizing hormone relative to follicle-stimulating hormone secretion, insulin resistance and developmental exposure to androgens are hypothesized to play a causal role in PCOS. Here we map common genetic susceptibility loci in European ancestry women for the National Institutes of Health PCOS phenotype, which confers the highest risk for metabolic morbidities, as well as reproductive hormone levels. Three loci reach genome-wide significance in the case-control meta-analysis, two novel loci mapping to chr 8p23.1 [Corrected] and chr 11p14.1, and a chr 9q22.32 locus previously found in Chinese PCOS. The same chr 11p14.1 SNP, rs11031006, in the region of the follicle-stimulating hormone B polypeptide (FSHB) gene strongly associates with PCOS diagnosis and luteinizing hormone levels. These findings implicate neuroendocrine changes in disease pathogenesis.

A novel method, the Variant Impact On Linkage Effect Test (VIOLET), leads to improved identification of causal variants in linkage regions.

The Human Genome Project was expected to individualize medicine by rapidly advancing knowledge of common complex disease through discovery of disease-causing genetic variants. However, this has proved challenging. Although linkage analysis has identified replicated chromosomal regions, subsequent detection of causal variants for complex traits has been limited. One explanation for this difficulty is that utilization of association to follow up linkage is problematic given that linkage and association are not required to co-occur. Indeed, co-occurrence is likely to occur only in special circumstances, such as Mendelian inheritance, but cannot be universally expected. To overcome this problem, we propose a novel method, the Variant Impact On Linkage Effect Test (VIOLET), which differs from other quantitative methods in that it is designed to follow up linkage by identifying variants that influence the variance explained by a quantitative trait locus. VIOLET's performance was compared with measured genotype and combined linkage association in two data sets with quantitative traits. Using simulated data, VIOLET had high power to detect the causal variant and reduced false positives compared with standard methods. Using real data, VIOLET identified a single variant, which explained 24% of linkage; this variant exhibited only nominal association (P=0.04) using measured genotype and was not identified by combined linkage association. These results demonstrate that VIOLET is highly specific while retaining low false-negative results. In summary, VIOLET overcomes a barrier to gene discovery and thus may be broadly applicable to identify underlying genetic etiology for traits exhibiting linkage.

A comprehensive analysis of adiponectin QTLs using SNP association, SNP cis-effects on peripheral blood gene expression and gene expression correlation identified novel metabolic syndrome (MetS) genes with potential role in carcinogenesis and systemic inflammation.

BACKGROUND: Metabolic syndrome (MetS) is an aberration associated with increased risk for cancer and inflammation. Adiponectin, an adipocyte-produced abundant protein hormone, has countering effect on the diabetogenic and atherogenic components of MetS. Plasma levels of adiponectin are negatively correlated with onset of cancer and cancer patient mortality. We previously performed microsatellite linkage analyses using adiponectin as a surrogate marker and revealed two QTLs on chr5 (5p14) and chr14 (14q13). METHODS: Using individuals from 85 extended families that contributed to the linkage and who were measured for 42 clinical and biologic MetS phenotypes, we tested QTL-based SNP associations, peripheral white blood cell (PWBC) gene expression, and the effects of cis-acting SNPs on gene expression to discover genomic elements that could affect the pathophysiology and complications of MetS. RESULTS: Adiponectin levels were found to be highly intercorrelated phenotypically with the majority of MetS traits. QTL-specific haplotype-tagging SNPs associated with MetS phenotypes were annotated to 14 genes whose function could influence MetS biology as well as oncogenesis or inflammation. These were mechanistically categorized into four groups: cell-cell adhesion and mobility, signal transduction, transcription and protein sorting. Four genes were highly prioritized: cadherin 18 (CDH18), myosin X (MYO10), anchor protein 6 of AMPK (AKAP6), and neuronal PAS domain protein 3 (NPAS3). PWBC expression was detectable only for the following genes with multi-organ or with multi-function properties: NPAS3, MARCH6, MYO10 and FBXL7. Strong evidence of cis-effects on the expression of MYO10 in PWBC was found with SNPs clustered near the gene's transcription start site. MYO10 expression in PWBC was marginally correlated with body composition (p = 0.065) and adipokine levels in the periphery (p = 0.064). Variants of genes AKAP6, NPAS3, MARCH6 and FBXL7 have been previously reported to be associated with insulin resistance, inflammatory markers or adiposity studies using genome-wide approaches whereas associations of CDH18 and MYO10 with MetS traits have not been reported before. CONCLUSIONS: Adiponectin QTLs-based SNP association and mRNA expression identified genes that could mediate the association between MetS and cancer or inflammation.

Fatty acid binding protein 3 (fabp3) is associated with insulin, lipids and cardiovascular phenotypes of the metabolic syndrome through epigenetic modifications in a Northern European family population.

BACKGROUND: Fatty acid-binding proteins (FABPs) play regulatory roles at the nexus of lipid metabolism and signaling. Dyslipidemia in clinical manifestation frequently co-occurs with obesity, insulin resistance and hypertension in the Metabolic Syndrome (MetS). Animal studies have suggested FABPs play regulatory roles in expressing MetS phenotypes. In our family cohort of Northern European descent, transcript levels in peripheral white blood cells (PWBCs) of a key FABPs, FABP3, is correlated with the MetS leading components. However, evidence supporting the functions of FABPs in humans using genetic approaches has been scarce, suggesting FABPs may be under epigenetic regulation. The objective of this study was to test the hypothesis that CpG methylation status of a key regulator of lipid homeostasis, FABP3, is a quantitative trait associated with status of MetS phenotypes in humans. METHODS: We used a mass-spec based quantitative method, EpiTYPER®, to profile a CpG island that extends from the promoter to the first exon of the FABP3 gene in our family-based cohort of Northern European descent (n=517). We then conducted statistical analysis of the quantitative relationship of CpG methylation and MetS measures following the variance-component association model. Heritability of each methylation and the effect of age and sex on CpG methylation were also assessed in our families. RESULTS: We find that methylation levels of individual CpG units and the regional average are heritable and significantly influenced by age and sex. Regional methylation was strongly associated with plasma total cholesterol (p=0.00028) and suggestively associated with LDL-cholesterol (p=0.00495). Methylation at individual units was significantly associated with insulin sensitivity, lipid particle sizing and diastolic blood pressure (p<0.0028, corrected for multiple testing for each trait). Peripheral white blood cell (PWBC) expression of FABP3 in a separate group of subjects (n=128) negatively correlated with adverse profiles of metabolism (ßWHR=-0.72; ßLDL-c=-0.53) while positively correlated with plasma adiponectin (ß=0.24). Further, we show that differential methylation of FABP3 affects binding activity with nuclear proteins from heart tissue. This region that we found under methylation regulation overlaps with a region actively modified by histone codes in the newly available ENCODE data. CONCLUSIONS: Our findings suggest that DNA methylation of FABP3 strongly influences MetS, and this may have important implications for cardiovascular disease.

Accounting for a quantitative trait locus for plasma triglyceride levels: utilization of variants in multiple genes.

BACKGROUND: For decades, research efforts have tried to uncover the underlying genetic basis of human susceptibility to a variety of diseases. Linkage studies have resulted in highly replicated findings and helped identify quantitative trait loci (QTL) for many complex traits; however identification of specific alleles accounting for linkage remains elusive. The purpose of this study was to determine whether with a sufficient number of variants a linkage signal can be fully explained. METHOD: We used comprehensive fine-mapping using a dense set of single nucleotide polymorphisms (SNPs) across the entire quantitative trait locus (QTL) on human chromosome 7q36 linked to plasma triglyceride levels. Analyses included measured genotype and combined linkage association analyses. RESULTS: Screening this linkage region, we found an over representation of nominally significant associations in five genes (MLL3, DPP6, PAXIP1, HTR5A, INSIG1). However, no single genetic variant was sufficient to account for the linkage. On the other hand, multiple variants capturing the variation in these five genes did account for the linkage at this locus. Permutation analyses suggested that this reduction in LOD score was unlikely to have occurred by chance (p = 0.008). DISCUSSION: With recent findings, it has become clear that most complex traits are influenced by a large number of genetic variants each contributing only a small percentage to the overall phenotype. We found that with a sufficient number of variants, the linkage can be fully explained. The results from this analysis suggest that perhaps the failure to identify causal variants for linkage peaks may be due to multiple variants under the linkage peak with small individual effect, rather than a single variant of large effect.

Hepatic gene networks in morbidly obese patients with nonalcoholic fatty liver disease.

BACKGROUND: Genetic factors alter the risk for nonalcoholic fatty liver disease (NAFLD). We sought to identify NAFLD-associated genes and elucidate gene networks and pathways involved in the pathogenesis of NAFLD. METHODS: Quantitative global hepatic gene expression analysis was performed on 53 morbidly obese Caucasian subjects undergoing bariatric surgery (27 with NAFLD and 26 controls). After standardization of data, gene expression profiles were compared between patients with NAFLD and controls. The set of genes that significantly correlated with NAFLD was further analyzed by hierarchical clustering and ingenuity pathways analyses. RESULTS: There were 25,643 quantitative transcripts, of which 108 were significantly associated with NAFLD (p < 0.001). Canonical pathway analysis in the NAFLD-associated gene clusters showed that the hepatic fibrosis signaling was the most significant pathway in the up-regulated NAFLD gene cluster containing three (COL1A1, IL10, IGFBP3) significantly altered genes, whereas the endoplasmic reticulum stress and protein ubiquitination pathways were the most significant pathways in the down-regulated NAFLD gene cluster, with the first pathway containing one (HSPA5) and the second containing two (HSPA5, USP25) significantly altered genes. The four primary gene networks associated with NAFLD were involved in cell death, immunological disease, cellular movement, and lipid metabolism with several significantly altered "hub" genes in these networks. CONCLUSIONS: This study reveals the canonical pathways and gene networks associated with NAFLD in morbidly obese Caucasians. The application of gene network analysis highlights the transcriptional relationships among NAFLD-associated genes and allows identification of hub genes that may represent high-priority candidates for NAFLD.

Integrated approach for the comprehensive characterization of lipoproteins from human plasma using FPLC and nano-HPLC-tandem mass spectrometry.

The implication of the various lipoprotein classes in the development of atherosclerotic cardiovascular disease has served to focus a great deal of attention on these particles over the past half-century. Using knowledge gained by the sequencing of the human genome, recent research efforts have been directed toward the elucidation of the proteomes of several lipoprotein subclasses. One of the challenges of such proteomic experimentation is the ability to initially isolate plasma lipoproteins subsequent to their analysis by mass spectrometry. Although several methods for the isolation of plasma lipoproteins are available, the most commonly utilized techniques require large sample volumes and may cause destruction and dissociation of lipoprotein particle-associated proteins. Fast protein liquid chromatography (FPLC) is a nondenaturing technique that has been validated for the isolation of plasma lipoproteins from relatively small sample volumes. In this study, we present the use of FPLC in conjunction with nano-HPLC-ESI-tandem mass spectrometry as a new integrated methodology suitable for the proteomic analysis of human lipoprotein fractions. Results from our analysis show that only 200 microl of human plasma suffices for the isolation of whole high density lipoprotein (HDL) and the identification of the majority of all known HDL-associated proteins using mass spectrometry of the resulting fractions.

Genetic variation in PARL influences mitochondrial content.

Given their involvement in processes necessary for life, mitochondrial damage and subsequent dysfunction can lead to a wide range of human diseases. Previous studies of both animal models and humans have suggested that presenilins-associated rhomboid-like protein (PARL) is a key regulator of mitochondrial integrity and function, and plays a role in cellular apoptosis. As a surrogate measure of mitochondrial integrity, we previously measured mitochondrial content in a Caucasian population consisting of large extended pedigrees, with results highlighting a substantial genetic component to this trait. To assess the influence of variation in the PARL gene on mitochondrial content, we re-sequenced 6.5 kb of the gene, identifying 16 SNPs and genotyped these in 1,086 Caucasian individuals, distributed across 170 families. Statistical genetic analysis revealed that one promoter variant, T-191C, exhibited significant effects (after correction for multiple testing) on mitochondrial content levels. Comparison of the transcription factor binding characteristics of the T-191C promoter SNP by EMSA indicates preferential binding of nuclear factors to the T allele, suggesting functional variation in PARL expression. These results suggest that genetic variation within PARL influences mitochondrial abundance and integrity.

Obesity-related dyslipidemia associated with FAAH, independent of insulin response, in multigenerational families of Northern European descent.

UNLABELLED: A more thorough understanding of the genetic architecture underlying obesity-related lipid disorders could someday facilitate cardiometabolic risk reduction through early clinical intervention based upon improved characterization of individual risk. In recent years, there has been tremendous interest in understanding the endocannabinoid system as a novel therapeutic target for the treatment of obesity-related dyslipidemia. AIMS: N-arachidonylethanolamine activates G-protein-coupled receptors within the endocannabinoid system. Fatty acid amide hydrolase (FAAH) is a primary catabolic regulator of N-acylethanolamines, including arachidonylethanolamine. Genetic variants in FAAH have inconsistently been associated with obesity. It is conceivable that genetic variability in FAAH directly influences lipid homeostasis. The current study characterizes the relationship between FAAH and obesity-related dyslipidemia, in one of the most rigorously-phenotyped obesity study cohorts in the USA. MATERIALS & METHODS: Members of 261 extended families (pedigrees ranging from 4 to 14 individuals) were genotyped using haplotype tagging SNPs obtained for the FAAH locus, including 5 kb upstream and 5 kb downstream. Each SNP was tested for basic obesity-related phenotypes (BMI, waist and hip circumference, waist:hip ratio, fasting glucose, fasting insulin and fasting lipid levels) in 1644 individuals within these 261 families. Each SNP was also tested for association with insulin responsiveness using data obtained from a frequently sampled intravenous glucose tolerance test in 399 individuals (32 extended families). RESULTS: A well characterized coding SNP in FAAH (rs324420) was associated with increased BMI, increased triglycerides, and reduced levels of high-density lipoprotein cholesterol. Mean (standard deviation) high-density lipoprotein cholesterol level was 40.5 (14.7) mg/dl for major allele homozygotes, 39.1 (10.4) mg/dl for heterozygotes, and 34.8 (8.1) mg/dl for minor allele homozygotes (p < 0.01, Family-Based Association Test). This SNP was not associated with insulin sensitivity, acute insulin response to intravenous glucose, glucose effectiveness or glucose disposition index. CONCLUSION: Genetic variability in FAAH is associated with dyslipidemia, independent of insulin response.

Genetic variation in cannabinoid receptor 1 (CNR1) is associated with derangements in lipid homeostasis, independent of body mass index.

AIMS: In humans, genetic variation in endocannabinergic signaling has been associated with anthropometric measures of obesity. In randomized trials, pharmacological blockade at the level of the cannabinoid receptor 1 (CNR1) receptor not only facilitates weight reduction, but also improves insulin sensitivity and clinical measures of lipid homeostasis. We therefore tested the hypothesis that genetic variation in CNR1 is associated with common obesity-related metabolic disorders. MATERIALS & METHODS: A total of six haplotype tagging SNPs were selected for CNR1, using data available within the Human HapMap (Centre d'Etude du Polymorphisme Humain population) these included: two promoter SNPs, three exonic SNPs, and a single SNP within the 3'-untranslated region. These tags were then genotyped in a rigorously phenotyped family-based collection of obese study subjects of Northern European origin. RESULTS & CONCLUSIONS: A common CNR1 haplotype (H4; prevalence 0.132) is associated with abnormal lipid homeostasis. Additional statistical tests using single tagging SNPs revealed that these associations are partly independent of body mass index.

Discovery of expression QTLs using large-scale transcriptional profiling in human lymphocytes.

Quantitative differences in gene expression are thought to contribute to phenotypic differences between individuals. We generated genome-wide transcriptional profiles of lymphocyte samples from 1,240 participants in the San Antonio Family Heart Study. The expression levels of 85% of the 19,648 detected autosomal transcripts were significantly heritable. Linkage analysis uncovered >1,000 cis-regulated transcripts at a false discovery rate of 5% and showed that the expression quantitative trait loci with the most significant linkage evidence are often located at the structural locus of a given transcript. To highlight the usefulness of this much-enlarged map of cis-regulated transcripts for the discovery of genes that influence complex traits in humans, as an example we selected high-density lipoprotein cholesterol concentration as a phenotype of clinical importance, and identified the cis-regulated vanin 1 (VNN1) gene as harboring sequence variants that influence high-density lipoprotein cholesterol concentrations.

Meta-analysis of genome-wide linkage studies in BMI and obesity.

OBJECTIVE: The objective was to provide an overall assessment of genetic linkage data of BMI and BMI-defined obesity using a nonparametric genome scan meta-analysis. RESEARCH METHODS AND PROCEDURES: We identified 37 published studies containing data on over 31,000 individuals from more than >10,000 families and obtained genome-wide logarithm of the odds (LOD) scores, non-parametric linkage (NPL) scores, or maximum likelihood scores (MLS). BMI was analyzed in a pooled set of all studies, as a subgroup of 10 studies that used BMI-defined obesity, and for subgroups ascertained through type 2 diabetes, hypertension, or subjects of European ancestry. RESULTS: Bins at chromosome 13q13.2- q33.1, 12q23-q24.3 achieved suggestive evidence of linkage to BMI in the pooled analysis and samples ascertained for hypertension. Nominal evidence of linkage to these regions and suggestive evidence for 11q13.3-22.3 were also observed for BMI-defined obesity. The FTO obesity gene locus at 16q12.2 also showed nominal evidence for linkage. However, overall distribution of summed rank p values <0.05 is not different from that expected by chance. The strongest evidence was obtained in the families ascertained for hypertension at 9q31.1-qter and 12p11.21-q23 (p < 0.01). CONCLUSION: Despite having substantial statistical power, we did not unequivocally implicate specific loci for BMI or obesity. This may be because genes influencing adiposity are of very small effect, with substantial genetic heterogeneity and variable dependence on environmental factors. However, the observation that the FTO gene maps to one of the highest ranking bins for obesity is interesting and, while not a validation of this approach, indicates that other potential loci identified in this study should be investigated further.

Genetic determinants of mitochondrial content.

The mitochondria are the major cellular site of energy production and respiration. Recent research has focused on investigating the role of mitochondria in disease development and it has become increasingly evident that mitochondrial dysfunction contributes to a variety of human diseases. Mitochondrial DNA (mtDNA) quantity is very important for maintaining mitochondrial function and meeting the energy needs of the body. We have measured mitochondrial content in 1259 Mexican American individuals (from 42 extended families) and have shown that mtDNA quantity (a surrogate measure of mitochondrial integrity) has a large genetic component. We performed a genome scan and a genome-wide quantitative transcriptomic scan to identify QTLs influencing mitochondrial content. A variance components linkage-based genome scan utilizing 439 STR markers was used to localize a QTL for mitochondrial content on chromosome 10q (LOD = 3.83). Significant linkage to the mitochondrial genome was also detected for mitochondrial transmission (LOD = 3.39). For replication, we measured mitochondrial content in an independent Caucasian population (1088 individuals) finding evidence for linkage in these same regions. As part of the San Antonio Family Heart Study, we obtained genome-wide quantitative transcriptional profiles from 1240 individuals. Using lymphocyte samples, we quantitated 20 413 transcripts and examined correlations between the expression levels of these transcripts and mitochondrial content using the variance components method. Using regression analysis allowing for residual genetic components, we identified 829 transcripts (including many novel genes) influencing mitochondrial content that vary in their general biological actions, from cell signaling to cell trafficking and ion binding.

SEPS1 protects RAW264.7 cells from pharmacological ER stress agent-induced apoptosis.

Selenoprotein S (SEPS1) is a novel endoplasmic reticulum (ER) resident protein and it is known to play an important role in production of inflammatory cytokines. Here, we show evidence that SEPS1 is stimulated by pharmacological ER stress agents in RAW264.7 macrophages as well as other cell types. Overexpression studies reveal a protective action of SEPS1 in macrophages against ER stress-induced cytotoxicity and apoptosis, resulting in promoting cell survival during ER stress. The protective action of SEPS1 is largely dependent on ER stress-mediated cell death signal with less effect on non-ER stress component cell death signals. Conversely, suppression of SEPS1 in macrophages results in sensitization of cells to ER stress-induced cell death. These findings suggest that SEPS1 could be a new ER stress-dependent survival factor that protects macrophage against ER stress-induced cellular dysfunction.

Insulin resistance causes human gallbladder dysmotility.

Obesity, diabetes, and hyperlipidemia are known risk factors for the development of gallstones. A growing body of animal and human data has correlated insulin resistance with organ dysfunction. The relationship among obesity, diabetes, hyperlipidemia, and abnormal gallbladder motility remains unclear. Therefore, we designed a study to investigate the association among obesity, insulin resistance, hyperlipidemia, and gallbladder dysmotility. One hundred ninety-two healthy adult nondiabetic volunteers were studied. Gallbladder ultrasounds were performed before and after a standardized fatty meal. A gallbladder ejection fraction (EF) was calculated, and an EF of < 25% was considered abnormal. Serum was analyzed for cholesterol, triglycerides, cholecystokinin, leptin, glucose, and insulin. The homeostasis assessment model (HOMA) was used to determine insulin resistance. The volunteers had a mean age of 38 years (range, 18-77), and 55% were female. Thirty subjects (15%) had gallstones and were excluded from the study. Thirty subjects (19%) had abnormal gallbladder motility (EF < 25%). In lean subjects (n = 96) fasting glucose was significantly increased in the 16 subjects with gallbladder EF < 25% versus the 80 subjects with gallbladder EF > 25% (109 +/- 20 mg/dl versus 78 +/- 2 mg/dl, P < 0.05). Similarly, the HOMA index was significantly greater in subjects with gallbladder EF < 25% versus gallbladder EF >25% (3.3 +/- 1.2 versus 2.0 +/- 0.2, P < 0.05). In obese subjects (n = 66), fasting glucose, insulin, and insulin resistance were not associated with a gallbladder EF < 25%. These data suggest that in lean, nondiabetic volunteers without gallstones, gallbladder dysmotility is associated with an elevated fasting glucose as well as a high index of insulin resistance. We conclude that insulin resistance alone may be responsible for gallbladder dysmotility that may result in acalculous cholecystitis or gallstone formation.

Genetic variation in selenoprotein S influences inflammatory response.

Chronic inflammation has a pathological role in many common diseases and is influenced by both genetic and environmental factors. Here we assess the role of genetic variation in selenoprotein S (SEPS1, also called SELS or SELENOS), a gene involved in stress response in the endoplasmic reticulum and inflammation control. After resequencing SEPS1, we genotyped 13 SNPs in 522 individuals from 92 families. As inflammation biomarkers, we measured plasma levels of IL-6, IL-1beta and TNF-alpha. Bayesian quantitative trait nucleotide analysis identified associations between SEPS1 polymorphisms and all three proinflammatory cytokines. One promoter variant, -105G --> A, showed strong evidence for an association with each cytokine (multivariate P = 0.0000002). Functional analysis of this polymorphism showed that the A variant significantly impaired SEPS1 expression after exposure to endoplasmic reticulum stress agents (P = 0.00006). Furthermore, suppression of SEPS1 by short interfering RNA in macrophage cells increased the release of IL-6 and TNF-alpha. To investigate further the significance of the observed associations, we genotyped -105G --> A in 419 Mexican American individuals from 23 families for replication. This analysis confirmed a significant association with both TNF-alpha (P = 0.0049) and IL-1beta (P = 0.0101). These results provide a direct mechanistic link between SEPS1 and the production of inflammatory cytokines and suggest that SEPS1 has a role in mediating inflammation.

Genetic linkage and association of the growth hormone secretagogue receptor (ghrelin receptor) gene in human obesity.

The growth hormone secretagogue receptor (GHSR) (ghrelin receptor) plays an important role in the regulation of food intake and energy homeostasis. The GHSR gene lies on human chromosome 3q26 within a quantitative trait locus strongly linked to multiple phenotypes related to obesity and the metabolic syndrome. Because the biological function and location of the GHSR gene make it an excellent candidate gene, we tested the relation between common single nucleotide polymorphisms (SNPs) in the GHSR gene and human obesity. We performed a comprehensive analysis of SNPs, linkage disequilibrium (LD), and haplotype structure across the entire GHSR gene region (99.3 kb) in 178 pedigrees with multiple obese members (DNA of 1,095 Caucasians) and in an independent sample of the general population (MONICA Augsburg left ventricular hypertrophy substudy; DNA of 1,418 Caucasians). The LD analysis revealed a disequilibrium block consisting of five SNPs, consistent in both study cohorts. We found linkage among all five SNPs, their haplotypes, and BMI. Further, we found suggestive evidence for transmission disequilibrium for the minor SNP alleles (P < 0.05) and the two most common haplotypes with the obesity affection status ("susceptible" P = 0.025, "nonsusceptible" P = 0.045) in the family cohort using the family-based association test program. Replication of these findings in the general population resulted in stronger evidence for an association of the SNPs (best P = 0.00001) and haplotypes with the disease ("susceptible" P = 0.002, "nonsusceptible" P = 0.002). To our knowledge, these data are the first to demonstrate linkage and association of SNPs and haplotypes within the GHSR gene region and human obesity. This linkage, together with significant transmission disequilibrium in families and replication of this association in an independent population, provides evidence that common SNPs and haplotypes within the GHSR region are involved in the pathogenesis of human obesity.