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

Genetic Insights into the Enigma of Family Intracranial Aneurysms

Familial intracranial aneurysms (FIAs) are distinguished by significant genetic predisposition, leading to clustering of cases within families and heightening the risk of subarachnoid hemorrhage following aneurysm rupture. This review analyzes recent advancements in understanding the genetic and molecular mechanisms underlying FIAs, focusing on key genetic risk factors and environmental influences. We explore cutting-edge genome-wide association studies and next-generation sequencing technologies, which have identified susceptibility genes such as ANGPTL6, peptidyl proline cis-trans isomerase like protein 4, and NOTCH3 as crucial contributors to FIA pathophysiology. By incorporating findings from multiomics and gene-editing research, we highlight the potential for improved screening, preventive strategies, and therapeutic approaches. These insights are essential to advancing precision medicine in managing FIAs, paving the way for collaborative research and targeted interventions.

Endocrine, genetic, and microbiome nexus of obesity and potential role of postbiotics: a narrative review

Obesity is a public health crisis, presenting a huge burden on health care and the economic system in both developed and developing countries. According to the WHO's latest report on obesity, 39% of adults of age 18 and above are obese, with an increase of 18% compared to the last few decades. Metabolic energy imbalance due to contemporary lifestyle, changes in gut microbiota, hormonal imbalance, inherent genetics, and epigenetics is a major contributory factor to this crisis. Multiple studies have shown that probiotics and their metabolites (postbiotics) supplementation have an effect on obesity-related effects in vitro, in vivo, and in human clinical investigations. Postbiotics such as the SCFAs suppress obesity by regulating metabolic hormones such as GLP-1, and PPY thus reducing feed intake and suppressing appetite. Furthermore, muramyl di-peptides, bacteriocins, and LPS have been tested against obesity and yielded promising results in both human and mice studies. These insights provide an overview of targetable pharmacological sites and explore new opportunities for the safer use of postbiotics against obesity in the future.

Plant-Derived Nutraceuticals Involved in Body Weight Control by Modulating Gene Expression

Obesity is the most prevalent health problem in the Western world, with pathological body weight gain associated with numerous co-morbidities that can be the main cause of death. There are several factors that can contribute to the development of obesity, such as diet, sedentary lifestyle, and genetic make-up. Genetic predispositions play an important role in obesity, but genetic variations alone cannot fully explain the explosion of obesity, which is why studies have turned to epigenetics. The latest scientific evidence suggests that both genetics and environmental factors contribute to the rise in obesity. Certain variables, such as diet and exercise, have the ability to alter gene expression without affecting the DNA sequence, a phenomenon known as epigenetics. Epigenetic changes are reversible, and reversibility makes these changes attractive targets for therapeutic interventions. While anti-obesity drugs have been proposed to this end in recent decades, their numerous side effects make them not very attractive. On the other hand, the use of nutraceuticals for weight loss is increasing, and studies have shown that some of these products, such as resveratrol, curcumin, epigallocatechin-3-gallate, ginger, capsaicin, and caffeine, can alter gene expression, restoring the normal epigenetic profile and aiding weight loss.

Management precautions for risk of obesity are necessary among infants with PKU carrying the rs113883650 variant of the LAT1 gene: A cross-sectional study

Patients with phenylketonuria (PKU), an inborn error of phenylalanine metabolism, require consistent treatment to avoid the brain toxicity caused by hyperphenylalaninemia. The treatment consists of life-long use of a low-phenylalanine diet, which aims at decreasing hyperphenylalaninemia and maintaining blood phenylalanine concentration in a safe range. Problems with balancing diet can result in suboptimal treatment outcomes; however, recent findings suggest that genetic alteration of the transport of phenylalanine might result in an additional health burden. We assessed the effect of a common variant (rs113883650) of the LAT1(SLC7A5) gene, which encodes the main transmembrane phenylalanine transporter, on the development of overweight in 54 infants with PKU who received standard therapy and adhered well to therapeutic prescriptions, and in 55 infants with a milder disease form-the so-called mild hyperphenylalaninemia (MHP), which does not require treatment. We found that infants with PKU-carriers of the rs113883650 variant had significantly higher Body Mass Index (BMI) at 1 year compared to PKU infants without the variant (mean BMI Z-Score of +1.15 SD vs -0.15 SD, respectively; t(52) = 5.25, p = 0.00005). Conversely, no significant BMI differences were detected in the subgroups of infants with MHP (t(53) = 1.15, p = 0.25). Additionally, high BMI in infants with PKU-carriers of the rs113883650 variant positively correlated with high variability of their blood phenylalanine levels (r(52) = 0.42, p = 0.002). It should be noted that this is an observational study, which does not determine causation. Nevertheless, our findings show that the rs113883650 variant of the LAT1 gene may be a risk factor for overweight in properly treated infants with PKU. Management precautions should be taken to prevent the development of overweight and obesity.

Common genetic variants associated with obesity in an African-American and Hispanic/Latino population

INTRODUCTION

Over 35% of all adults in the world are currently obese and risk of obesity in racial or ethnic minority groups exist in the US, but the causes of these differences are not all known. As obesity is a leading cause of cardiovascular disease, an improved understanding of risk factors across racial and ethnic groups may improve outcomes.

OBJECTIVE

The objective of this study was to determine if susceptibility to obesity is associated with genetic variation in candidate single nucleotide polymorphisms (SNPs) in African Americans and Hispanic/Latinos.

MATERIALS AND METHODS

We examined data from 534 African Americans and 557 Hispanic/Latinos participants from the UIC Cohort of Patients, Family and Friends. Participants were genotyped for the top 26 obesity-associated SNPs within FTO, MC4R, TUB, APOA2, APOA5, ADIPOQ, ARL15, CDH13, KNG1, LEPR, leptin, and SCG3 genes.

RESULTS

The mean (SD) age of participants was 49±13 years, 55% were female, and mean body mass index (BMI) was 31±7.5 kg/m2. After adjusting for age and sex, we found that rs8050136 in FTO (odds ratio [OR] 1.40, 95% confidence interval [CI] 1.1-1.8; P = 0.01) among African Americans and rs2272383 in TUB (OR 1.34, 95% CI 1.04-1.71; P = 0.02) among Hispanic/Latinos were associated with obesity. However, none of the SNPs in multivariable analysis of either AA or H/L cohorts were significant when adjusted for multiple correction.

CONCLUSIONS

We show that candidate SNPs in the FTO and TUB genes are associated with obesity in African Americans and Hispanic/Latinos individuals respectively. While the underlying pathophysiological mechanisms by which common genetic variants cause obesity remain unclear, we have identified novel therapeutic targets across racial and ethnic groups.

Genetics of Obesity in East Asians

Obesity has become a public health problem worldwide. Compared with Europe, people in Asia tend to suffer from type 2 diabetes with a lower body mass index (BMI). Genome-wide association studies (GWASs) have identified over 750 loci associated with obesity. Although the majority of GWAS results were conducted in individuals of European ancestry, a recent GWAS in individuals of Asian ancestry has made a significant contribution to the identification of obesity susceptibility loci. Indeed, owing to the multifactorial character of obesity with a strong environmental component, the revealed loci may have distinct contributions in different ancestral genetic backgrounds and in different environments as presented through diet and exercise among other factors. Uncovering novel, yet unrevealed genes in non-European ancestries may further contribute to explaining the missing heritability for BMI. In this review, we aimed to summarize recent advances in obesity genetics in individuals of Asian ancestry. We therefore compared proposed mechanisms underlying susceptibility loci for obesity associated with individuals of European and Asian ancestries and discussed whether known genetic variants might explain ethnic differences in obesity risk. We further acknowledged that GWAS implemented in individuals of Asian ancestries have not only validated the potential role of previously specified obesity susceptibility loci but also exposed novel ones, which have been missed in the initial genetic studies in individuals of European ancestries. Thus, multi-ethnic studies have a great potential not only to contribute to a better understanding of the complex etiology of human obesity but also potentially of ethnic differences in the prevalence of obesity, which may ultimately pave new avenues in more targeted and personalized obesity treatments.

Carriership of the rs113883650/rs2287120 haplotype of the SLC7A5 (LAT1) gene increases the risk of obesity in infants with phenylketonuria

Purpose

Phenylketonuria (PKU) can be effectively treated with the use of a low-phenylalanine diet. However, some patients become overweight despite proper dietary treatment. We hypothesized that this phenomenon could be explained by the presence of specific variants within the genes involved in phenylalanine transport or in the phenylalanine transamination/oxygenation pathway.

Methods

We selected a clinically homogenous group of 100 infants with PKU and assessed their growth patterns in the context of dietary phenylalanine tolerance. Next, within the sample, we performed exome sequencing and assessed a potential relationship between the observed phenotypical variability and the presence of structural variants in a priori selected genes of interest.

Results

We detected a highly significant association between overweight and carriership of the rs113883650/rs2287120 haplotype of the SLC7A5 (LAT1) gene, which encodes the main transmembrane transporter of large neutral amino acids and of thyroid hormones.

Conclusions

Our findings suggest a pharmacogenetic effect of the relatively common rs113883650/rs2287120 haplotype of the SLC7A5 gene. This can have practical implications for patients with PKU, since treatment protocols need to be reassessed to better prevent overweight in the carriers of the above variant.

The Effect Sizes of PPARγ rs1801282, FTO rs9939609, and MC4R rs2229616 Variants on Type 2 Diabetes Mellitus Risk among the Western Saudi Population: A Cross-Sectional Prospective Study

Type 2 diabetes mellitus (T2DM) is a common polygenic disease with associated comorbidities. Obesity is a major risk factor for the development of T2DM. The aim of this study is to determine the allele and genotype frequency of peroxisome proliferator-activated receptor-γ (PPARγ) rs1801282, fat mass and obesity-associated protein (FTO) rs9939609, and melanocortin 4 receptor (MC4R) rs2229616 polymorphisms and their association with risk of T2DM in the western Saudi population as mediators of adiposity phenotypes. In a cross-sectional prospective study, genomic DNA from control and T2DM patients were isolated and genotyped for these single-nucleotide polymorphisms. There was a significant association of the MC4R rs2229616 variant with T2DM, but no association with T2DM was detected with PPARγ rs1801282 or FTO rs9939609. The combination of C/C for PPARγ rs1801282, A/A for FTO rs9939609, and C/C for MC4R rs2229616 increased the risk of T2DM by 1.82. The A/T genotype for FTO rs9939609 was predicted to decrease the risk of T2DM when combined with C/C for PPARγ rs1801282 and C/C for MC4R rs2229616 or C/C for PPARγ rs1801282 and C/T MC4R rs2229616. In conclusion, our study showed the risk of the assessed variants for the development of T2DM in the Saudi population.

Established and emerging strategies to crack the genetic code of obesity

Tremendous progress has been made in the genetic elucidation of obesity over the past two decades, driven largely by technological, methodological and organizational innovations. Current strategies for identifying obesity-predisposing loci/genes, including cytogenetics, linkage analysis, homozygosity mapping, admixture mapping, candidate gene studies, genome-wide association studies, custom genotyping arrays, whole-exome sequencing and targeted exome sequencing, have achieved differing levels of success, and the identified loci in aggregate explain only a modest fraction of the estimated heritability of obesity. This review outlines the successes and limitations of these approaches and proposes novel strategies, including the use of exceptionally large sample sizes, the study of diverse ethnic groups and deep phenotypes and the application of innovative methods and study designs, to identify the remaining obesity-predisposing genes. The use of both established and emerging strategies has the potential to crack the genetic code of obesity in the not-too-distant future. The resulting knowledge is likely to yield improvements in obesity prediction, prevention and care.

Regulation of alternative splicing in obesity-induced hypertension

Obesity is the result of genetics which predisposes an individual to obesity and environmental factors, resulting in excessive weight gain. A well-established linear relationship exists between hypertension and obesity. The combined burden of hypertension and obesity poses significant health and economic challenges. Many environmental factors and genetic traits interact to contribute to obesity-linked hypertension. These include excess sodium re-absorption or secretion by the kidneys, a hypertensive shift of renal-pressure and activation of the sympathetic nervous system. Most individuals suffering from hypertension need drugs in order to treat their raised blood pressure, and while a number of antihypertensive therapeutic agents are currently available, 50% of cases remain uncontrolled. In order to develop new and effective therapeutic agents combating obesity-induced hypertension, a thorough understanding of the molecular events leading to adipogenesis is critical. With the advent of whole genome and exome sequencing techniques, new genes and variants which can be used as markers for obesity and hypertension are being identified. This review examines the role played by alternative splicing (AS) as a contributing factor to the metabolic regulation of obesity-induced hypertension. Splicing mutations constitute at least 14% of the disease-causing mutations, thus implicating polymorphisms that effect splicing as indicators of disease susceptibility. The unique transcripts resulting from the alternate splicing of mRNA encoding proteins that play a key role in contributing to obesity would be vital to gain a proper understanding of the genetic causes of obesity. A greater knowledge of the genetic basis for obesity-linked hypertension will assist in the development of appropriate diagnostic tests as well as the identification of new personalized therapeutic targets against obesity-induced hypertension.

A Study of Short- and Long-term mRNA Levels of the Retn, Iapp, and Drd5 Genes in Obese Mice Induced with High-fat Diet

BACKGROUND/AIM

Adipocyte gene expression is altered in obese individuals through multiple metabolic and biochemical pathways. In this study, we aimed to examine the expression of resistin (Retn), amylin (Iapp), and dopamine receptor domain 5 (Drd5) genes previously suggested to contribute to the pathogenesis of obesity, albeit controversially. We also aimed to determine the effects on short and long-term mRNA levels of these genes in obese mice, induced with high-fat diet (HFD).

MATERIALS AND METHODS

Two obesity models were created in our study: group T1 (20 mice) was fed with HFD (60% fat) for 3 months, and group T2 (20 mice) was fed with HFD (60% fat) for 6 months. The control group T0 (20 mice) was fed with a diet of 10% kcal fat supplement for 6 months. At the end of the experiment, their adipose tissues were dissected surgically. Tissue samples of each group were pooled for RNA isolation, cDNA synthesis was carried out and the mRNA levels were examined by quantitative real-time polymerase chain reaction. Serum resistin levels were measured using multiplex bead (luminex) technology for validation.

RESULTS

In T2 mice, the mRNA expression of Retn showed a moderate up-regulation (fold change=8.32; p=0.0019) in the adipose tissues. Iapp expression was also significantly up-regulated (fold change=9.78; p=0.012). Moreover, a 6.36-fold up-regulation for Drd5 was observed in the adipose tissues of T2 mice (p<0.001). At the same time, serum levels of resistin were found to be high in T1 and T2 mice compared to the control group (p<0.001 and p=0.024, respectively).

CONCLUSION

Our study demonstrated that the mRNA levels of the genetic markers considered to play a role in adipogenesis were different in short- and long-term obesity models formed in C57BL/6J mice using HFD.

SLC35B4, an Inhibitor of Gluconeogenesis, Responds to Glucose Stimulation and Downregulates Hsp60 among Other Proteins in HepG2 Liver Cell Lines

SLC35B4, solute receptor for UDP-N-acetylglucosamine and UDP-xylose, is associated with diabetes and predisposing conditions. This study investigated the localization of SLC35B4 and compared the differential expression between a knockdown of SLC35B4 and controls in HepG2. Responsiveness to glucose, expression, and localization were assayed using Western blot and immunostaining. Localization was confirmed using a proximity ligation assay. Two-dimensional (2D) gel electrophoresis and MALDI-TOF were used to identify differentially expressed proteins and pathway analysis was performed. SLC35B4 was increased by 60% upon glucose stimulation and localized in Golgi apparatus and endoplasmic reticulum. Presence of SLC35B4 in the Golgi apparatus suggests its involvement in the biosynthesis of glycoconjugate proteins. Four proteins were markedly under-expressed (Hsp60, HspA8, TUBA1A, and ENO1) and linked to the pathogenesis of diabetes or post-translationally modified by O-GlcNAc. Glucose levels activate SLC35B4 expression. This triggers a downstream effect via Hsp60 and other proteins. We hypothesize that the downstream effect on the proteins is mediated via altering the glycosylation pattern inside liver cells. The downstream cascade ultimately alters the ability of cultured liver cells to inhibit endogenous glucose production, and this could play a role in the association of the above-listed genes with the pathogenesis of diabetes.

Ethnic and population differences in the genetic predisposition to human obesity

Obesity rates have escalated to the point of a global pandemic with varying prevalence across ethnic groups. These differences are partially explained by lifestyle factors in addition to genetic predisposition to obesity. This review provides a comprehensive examination of the ethnic differences in the genetic architecture of obesity. Using examples from evolution, heritability, admixture, monogenic and polygenic studies of obesity, we provide explanations for ethnic differences in the prevalence of obesity. The debate over definitions of race and ethnicity, the advantages and limitations of multi-ethnic studies and future directions of research are also discussed. Multi-ethnic studies have great potential to provide a better understanding of ethnic differences in the prevalence of obesity that may result in more targeted and personalized obesity treatments.

The emerging role of mRNA methylation in normal and pathological behavior

Covalent RNA modifications were recently rediscovered as abundant RNA chemical tags. Similarly to DNA epigenetic modifications, they have been proposed as essential regulators of gene expression. Here we focus on 3 of the most abundant adenosine methylations: N6-methyladenosine (m⁶ A), N6,2'-O-dimethyladenosine (m⁶ Am) and N1-methyladenosine (m¹ A). We review the potential role of these modifications on mature mRNA in regulating gene expression within the adult brain, nervous system function and normal and pathological behavior. Dynamic mRNA modifications, summarized as the epitranscriptome, regulate transcript maturation, translation and decay, and thus crucially determine gene expression beyond primary transcription regulation. However, the extent of this regulation in the healthy and maladapted adult brain is poorly understood. Analyzing this novel layer of gene expression control in addition to epigenetics and posttranslational regulation of proteins will be highly relevant for understanding the molecular underpinnings of behavior and psychiatric disorders.

A combined linkage and association strategy identifies a variant near the GSTP1 gene associated with BMI in the Mexican population

Obesity is a major public health concern in Mexico and worldwide. Although the estimated heritability is high, common variants identified by genome-wide association studies explain only a small proportion of this heritability. A combination of linkage and association strategies could be a more robust and powerful approach to identify other obesity-susceptibility variants. We thus sought to identify novel genetic variants associated with obesity-related traits in the Mexican population by combining these methods. We performed a genome-wide linkage scan for body mass index (BMI) and other obesity-related phenotypes in 16 Mexican families using the Sequential Oligogenic Linkage Analysis Routines Program. Associated single-nucleotide polymorphisms (SNPs) were tested for associations in an independent cohort. Two suggestive BMI-linkage peaks (logarithm of odds ⩾1.5) were observed at chromosomal regions 11q13 and 13q22. Only rs614080 in the 11q13 region was significantly associated with BMI and related traits in these families. This association was also significant in an independent cohort of Mexican adults. Moreover, this variant was significantly associated with GSTP1 gene expression levels in adipose tissue. In conclusion, the rs614080 SNP near the GSTP1 gene was significantly associated with BMI and GSTP1 expression levels in the Mexican population.

Fto-Deficiency Affects the Gene and MicroRNA Expression Involved in Brown Adipogenesis and Browning of White Adipose Tissue in Mice

Genetic variants in the fat mass- and obesity-associated gene Fto are linked to the onset of obesity in humans. The causal role of the FTO protein in obesity is supported by evidence obtained from transgenic mice; however, the underlying molecular pathways pertaining to the role of FTO in obesity have yet to be established. In this study, we investigate the Fto gene in mouse brown adipose tissue and in the browning process of white adipose tissue. We analyze distinct structural and molecular factors in brown and white fat depots of Fto-deficient mice under normal and obesogenic conditions. We report significant alterations in the morphology of adipose tissue depots and the expression of mRNA and microRNA related to brown adipogenesis and metabolism in Fto-deficient mice. Furthermore, we show that high-fat feeding does not attenuate the browning process of Fto-deficient white adipose tissue as observed in wild-type tissue, suggesting a triggering effect of the FTO pathways by the dietary environment.

Linkage and association analysis of obesity traits reveals novel loci and interactions with dietary n-3 fatty acids in an Alaska Native (Yup'ik) population

OBJECTIVE

To identify novel genetic markers of obesity-related traits and to identify gene-diet interactions with n-3 polyunsaturated fatty acid (n-3 PUFA) intake in Yup'ik people.

MATERIAL AND METHODS

We measured body composition, plasma adipokines and ghrelin in 982 participants enrolled in the Center for Alaska Native Health Research (CANHR) Study. We conducted a genome-wide SNP linkage scan and targeted association analysis, fitting additional models to investigate putative gene-diet interactions. Finally, we performed bioinformatic analysis to uncover likely candidate genes within the identified linkage peaks.

RESULTS

We observed evidence of linkage for all obesity-related traits, replicating previous results and identifying novel regions of interest for adiponectin (10q26.13-2) and thigh circumference (8q21.11-13). Bioinformatic analysis revealed DOCK1, PTPRE (10q26.13-2) and FABP4 (8q21.11-13) as putative candidate genes in the newly identified regions. Targeted SNP analysis under the linkage peaks identified associations between three SNPs and obesity-related traits: rs1007750 on chromosome 8 and thigh circumference (P=0.0005), rs878953 on chromosome 5 and thigh skinfold (P=0.0004), and rs1596854 on chromosome 11 for waist circumference (P=0.0003). Finally, we showed that n-3 PUFA modified the association between obesity related traits and two additional variants (rs2048417 on chromosome 3 for adiponectin, P for interaction=0.0006 and rs730414 on chromosome 11 for percentage body fat, P for interaction=0.0004).

CONCLUSIONS

This study presents evidence of novel genomic regions and gene-diet interactions that may contribute to the pathophysiology of obesity-related traits among Yup'ik people.

Fat mass- and obesity-associated gene Fto affects the dietary response in mouse white adipose tissue

Common variants of human fat mass- and obesity-associated gene Fto have been linked with higher body mass index, but the biological explanation for the link has remained obscure. Recent findings suggest that these variants affect the homeobox protein IRX3. Here we report that FTO has a role in white adipose tissue which modifies its response to high-fat feeding. Wild type and Fto-deficient mice were exposed to standard or high-fat diet for 16 weeks after which metabolism, behavior and white adipose tissue morphology were analyzed together with adipokine levels and relative expression of genes regulating white adipose tissue adipogenesis and Irx3. Our results indicate that Fto deficiency increases the expression of genes related to adipogenesis preventing adipocytes from becoming hypertrophic after high-fat diet. In addition, we report a novel finding of increased Irx3 expression in Fto-deficient mice after high-fat feeding indicating a complex link between FTO, IRX3 and fat metabolism.

Genetic Determinants of Type 2 Diabetes in Asians

Type 2 diabetes (T2D) has become a major health problem throughout the world and the epidemic is particularly severe in Asian countries. Compared with European populations, Asians tend to develop diabetes at a younger age and at much higher incidence rates given the same amount of weight gain. Genome-wide association studies (GWAS) have identified over 70 loci associated with T2D. Although the majority of GWAS results were conducted in populations of European ancestry, recent GWAS in Asians have made important contributions to the identification of T2D susceptibility loci. These studies not only confirmed T2D susceptibility loci initially identified in European populations, but also identified novel susceptibility loci that provide new insights into the pathophysiology of diseases. In this article, we review GWAS results of T2D conducted in East and South Asians and compare them to those of European populations. Currently identified T2D genetic variants do not appear to explain the phenomenon that Asians are more susceptible to T2D than European populations, suggesting further studies in Asian populations are needed.

Obesity and genomics: role of technology in unraveling the complex genetic architecture of obesity

Obesity is a complex and multifactorial disease that occurs as a result of the interaction between "obesogenic" environmental factors and genetic components. Although the genetic component of obesity is clear from the heritability studies, the genetic basis remains largely elusive. Successes have been achieved in identifying the causal genes for monogenic obesity using animal models and linkage studies, but these approaches are not fruitful for polygenic obesity. The developments of genome-wide association approach have brought breakthrough discovery of genetic variants for polygenic obesity where tens of new susceptibility loci were identified. However, the common SNPs only accounted for a proportion of heritability. The arrival of NGS technologies and completion of 1000 Genomes Project have brought other new methods to dissect the genetic architecture of obesity, for example, the use of exome genotyping arrays and deep sequencing of candidate loci identified from GWAS to study rare variants. In this review, we summarize and discuss the developments of these genetic approaches in human obesity.

A genomewide study of body mass index and its genetic correlation with thromboembolic risk. Results from the GAIT project

Thrombosis and obesity are complex epidemiologically associated diseases. The mechanism of this association is not yet understood. It was the objective of this study to identify genetic components of body mass index (BMI) and their possible role in the risk of thromboembolic disease. With the self-reported BMI of 397 individuals from 21 extended families enrolled in the GAIT (Genetic Analysis of Idiopathic Thrombophilia) Project, we estimated the heritability of BMI and the genetic correlation with the risk of thrombosis. Subjects were genotyped for an autosomal genome-wide scan with 363 highly-informative DNA markers. Univariate and bivariate multipoint linkage analyses were performed. The heritability for BMI was 0.31 (p=2.9×10⁻⁵). Thromboembolic disease (including venous and arterial) and BMI had a significant genetic correlation (ρG=0.54, p=0.005). Two linkage signals for BMI were obtained, one at 13q34 (LOD=3.36, p=0.0004) and other at 2q34, highly suggestive of linkage (LOD=1.95). Bivariate linkage analysis with BMI and thrombosis risk also showed a significant signal at 13q34 (LOD=3), indicating that this locus influences at the same time normal variation in the BMI phenotype as well as susceptibility to thrombosis. In conclusion, BMI and thrombosis are genetically correlated. The locus 13q34, which showed pleiotropy with both phenotypes, contains two candidate genes, which may explain our linkage pleiotropic signal and deserve further investigation as possible risk factors for obesity and thrombosis.

Jumping on the Train of Personalized Medicine: A Primer for Non-Geneticist Clinicians: Part 2. Fundamental Concepts in Genetic Epidemiology

With the decrease in sequencing costs, personalized genome sequencing will eventually become common in medical practice. We therefore write this series of three reviews to help non-geneticist clinicians to jump into the fast-moving field of personalized medicine. In the first article of this series, we reviewed the fundamental concepts in molecular genetics. In this second article, we cover the key concepts and methods in genetic epidemiology including the classification of genetic disorders, study designs and their implementation, genetic marker selection, genotyping and sequencing technologies, gene identification strategies, data analyses and data interpretation. This review will help the reader critically appraise a genetic association study. In the next article, we will discuss the clinical applications of genetic epidemiology in the personalized medicine area.

A multilevel model of postmenopausal breast cancer incidence

BACKGROUND

Breast cancer has a complex etiology that includes genetic, biologic, behavioral, environmental, and social factors. Etiologic factors are frequently studied in isolation with adjustment for confounding, mediating, and moderating effects of other factors. A complex systems model approach may present a more comprehensive picture of the multifactorial etiology of breast cancer.

METHODS

We took a transdisciplinary approach with experts from relevant fields to develop a conceptual model of the etiology of postmenopausal breast cancer. The model incorporated evidence of both the strength of association and the quality of the evidence. We operationalized this conceptual model through a mathematical simulation model with a subset of variables, namely, age, race/ethnicity, age at menarche, age at first birth, age at menopause, obesity, alcohol consumption, income, tobacco use, use of hormone therapy (HT), and BRCA1/2 genotype.

RESULTS

In simulating incidence for California in 2000, the separate impact of individual variables was modest, but reduction in HT, increase in the age at menarche, and to a lesser extent reduction in excess BMI >30 kg/m(2) were more substantial.

CONCLUSIONS

Complex systems models can yield new insights on the etiologic factors involved in postmenopausal breast cancer. Modification of factors at a population level may only modestly affect risk estimates, while still having an important impact on the absolute number of women affected.

IMPACT

This novel effort highlighted the complexity of breast cancer etiology, revealed areas of challenge in the methodology of developing complex systems models, and suggested additional areas for further study.

Children's perception on obesity and quality of life: a Mexican survey

BACKGROUND

Child obesity has become a major health problem worldwide. In order to design successful intervention strategies, it is necessary to understand how children perceive obesity and its consequences.

METHODS

With the aim to evaluate scholar children perception of obesity as a significant factor on the quality of life, we developed and validated the "Obesity impact on the quality of life perception-questionnaire" (ObI-Q). We surveyed 1335 healthy children aged 6-12 years, randomly selected from elementary schools in Mexico City. The ObI-Q comprises eight multiple-choice items that explore aspects related to the quality of life during adult life; such as health, life span, emotional status, lifestyle, social recognition and economic status. In order to identify perceptional modifier factors, results were analyzed through multivariable logistic regression. Variables included gender, age, and child nutritional status, as well as the child's perception of parental nutritional status.

RESULTS

ObI-Q results showed that most children (64.71%) considered obesity as a negative condition that influences health and social performance. This perception was inversely related to age (OR = 0.64, p = 0.003), as well as to the perception of their mother nutritional status (OR = 0.47, p = 0.01).

CONCLUSIONS

This study provides an overview of children's perception on obesity and its consequences. Because the high proportion of schoolchildren who do not view obesity as an adverse consequence to the quality of life, then the results of this study could be used as part of strategies for the prevention of overweight and obesity.

FTO genetic variants and risk of obesity and type 2 diabetes: a meta-analysis of 28,394 Indians

OBJECTIVE

To investigate the magnitude of association of FTO variants with obesity, type 2 diabetes (T2DM), and related traits among Asian Indians.

METHODS

Random-effect meta-analysis was performed on pooled data from eight studies (n = 28,394) for obesity and related traits and six studies (n = 24,987) for assessment of T2DM risk in Indians where FTO variants were reported.

RESULTS

The minor A-allele of the FTO variant rs9939609 was associated with increased risk of obesity (OR 1.15, 95% CI 1.08-1.21, p = 2.14 × 10(-) (5) ), BMI (β = 0.30 kg/m2, 95% CI 0.21-0.38, p = 4.78 × 10(-) (11) ) and other regional adiposity measurements [waist (β = 0.74 cm, 95% CI 0.49-0.99), HC (β = 0.52, 95% CI 0.26-0.78), and waist-hip ratio (WHR) (β = 0.002, 95% CI 0.001-0.004)] in Indians (p ≤ 0.001). An increased risk for T2DM (OR 1.11; 95% CI 1.04-1.19, p = 0.002) was observed, which attenuated when adjusted for age, gender, and BMI (OR 1.09; 95%CI 1.02-1.16, p = 0.01).

CONCLUSIONS

Our study provides evidence of association between common FTO variant and obesity risk among Indians with comparable effect sizes as in Caucasians. The attenuation of FTO-T2DM risk on BMI adjustment reinforces that BMI does not fully account for the adiposity effects among Asian Indians who are more centrally obese.

Meta-analysis of genome-wide association data identifies novel susceptibility loci for obesity

Obesity is a major public health problem with strong genetic determination. Multiple genetic variants have been implicated for obesity by conducting genome-wide association (GWA) studies, primarily focused on body mass index (BMI). Fat body mass (FBM) is phenotypically more homogeneous than BMI and is more appropriate for obesity research; however, relatively few studies have been conducted on FBM. Aiming to identify variants associated with obesity, we carried out meta-analyses of seven GWA studies for BMI-related traits including FBM, and followed these analyses by de novo replication. The discovery cohorts consisted of 21 969 individuals from diverse ethnic populations and a total of over 4 million genotyped or imputed SNPs. The de novo replication cohorts consisted of 6663 subjects from two independent samples. To complement individual SNP-based association analyses, we also carried out gene-based GWA analyses in which all variations within a gene were considered jointly. Individual SNP-based association analyses identified a novel locus 1q21 [rs2230061, CTSS (Cathepsin S)] that was associated with FBM after the adjustment of lean body mass (LBM) (P = 3.57 × 10(-8)) at the genome-wide significance level. Gene-based association analyses identified a novel gene NLK (nemo-like kinase) in 17q11 that was significantly associated with FBM adjusted by LBM. In addition, we confirmed three previously reported obesity susceptibility loci: 16q12 [rs62033400, P = 1.97 × 10(-14), FTO (fat mass and obesity associated)], 18q22 [rs6567160, P = 8.09 × 10(-19), MC4R (melanocortin 4 receptor)] and 2p25 [rs939583, P = 1.07 × 10(-7), TMEM18 (transmembrane protein 18)]. We also found that rs6567160 may exert pleiotropic effects to both FBM and LBM. Our results provide additional insights into the molecular genetic basis of obesity and may provide future targets for effective prevention and therapeutic intervention.

Association of the FTO obesity risk variant rs8050136 with percentage of energy intake from fat in multiple racial/ethnic populations: the PAGE study

Common obesity risk variants have been associated with macronutrient intake; however, these associations' generalizability across populations has not been demonstrated. We investigated the associations between 6 obesity risk variants in (or near) the NEGR1, TMEM18, BDNF, FTO, MC4R, and KCTD15 genes and macronutrient intake (carbohydrate, protein, ethanol, and fat) in 3 Population Architecture using Genomics and Epidemiology (PAGE) studies: the Multiethnic Cohort Study (1993-2006) (n = 19,529), the Atherosclerosis Risk in Communities Study (1987-1989) (n = 11,114), and the Epidemiologic Architecture for Genes Linked to Environment (EAGLE) Study, which accesses data from the Third National Health and Nutrition Examination Survey (1991-1994) (n = 6,347). We used linear regression, with adjustment for age, sex, and ethnicity, to estimate the associations between obesity risk genotypes and macronutrient intake. A fixed-effects meta-analysis model showed that the FTO rs8050136 A allele (n = 36,973) was positively associated with percentage of calories derived from fat (βmeta = 0.2244 (standard error, 0.0548); P = 4 × 10(-5)) and inversely associated with percentage of calories derived from carbohydrate (βmeta = -0.2796 (standard error, 0.0709); P = 8 × 10(-5)). In the Multiethnic Cohort Study, percentage of calories from fat assessed at baseline was a partial mediator of the rs8050136 effect on body mass index (weight (kg)/height (m)(2)) obtained at 10 years of follow-up (mediation of effect = 0.0823 kg/m(2), 95% confidence interval: 0.0559, 0.1128). Our data provide additional evidence that the association of FTO with obesity is partially mediated by dietary intake.

From obesity genetics to the future of personalized obesity therapy

Obesity is a disorder characterized by an excess accumulation of body fat resulting from a mismatch between energy intake and expenditure. Incidence of obesity has increased dramatically in the past few years, almost certainly fuelled by a shift in dietary habits owing to the widespread availability of low-cost, hypercaloric foods. However, clear differences exist in obesity susceptibility among individuals exposed to the same obesogenic environment, implicating genetic risk factors. Numerous genes have been shown to be involved in the development of monofactorial forms of obesity. In genome-wide association studies, a large number of common variants have been associated with adiposity levels, each accounting for only a small proportion of the predicted heritability. Although the small effect sizes of obesity variants identified in genome-wide association studies currently preclude their utility in clinical settings, screening for a number of monogenic obesity variants is now possible. Such regular screening will provide more informed prognoses and help in the identification of at-risk individuals who could benefit from early intervention, in evaluation of the outcomes of current obesity treatments, and in personalization of the clinical management of obesity. This Review summarizes current advances in obesity genetics and discusses the future of research in this field and the potential relevance to personalized obesity therapy.

An f2 pig resource population as a model for genetic studies of obesity and obesity-related diseases in humans: design and genetic parameters

Obesity is a rising worldwide public health problem. Difficulties to precisely measure various obesity traits and the genetic heterogeneity in human have been major impediments to completely disentangle genetic factors causing obesity. The pig is a relevant model for studying human obesity and obesity-related (OOR) traits. Using founder breeds divergent with respect to obesity traits we have created an F2 pig resource population (454 pigs), which has been intensively phenotyped for 36 OOR traits. The main rationale for our study is to characterize the genetic architecture of OOR traits in the F2 pig design, by estimating heritabilities, genetic, and phenotypic correlations using mixed- and multi-trait BLUP animal models. Our analyses revealed high coefficients of variation (15–42%) and moderate to high heritabilities (0.22–0.81) in fatness traits, showing large phenotypic and genetic variation in the F2 population, respectively. This fulfills the purpose of creating a resource population divergent for OOR traits. Strong genetic correlations were found between weight and lean mass at dual-energy x-ray absorptiometry scanning (0.56–0.97). Weight and conformation also showed strong genetic correlations with slaughter traits (e.g., r_g between abdominal circumference and leaf fat at slaughtering: 0.66). Genetic correlations between fat-related traits and the glucose level vary between 0.35 and 0.74 and show a strong correlation between adipose tissue and impaired glucose metabolism. Our power calculations showed a minimum of 80% power for QTL detection for all phenotypes. We revealed genetic correlations at population level, for the first time, for several difficult to measure and novel OOR traits and diseases. The results underpin the potential of the established F2 pig resource population for further genomic, systems genetics, and functional investigations to unravel the genetic background of OOR traits.

Moo1 obesity quantitative trait locus in BTBR T+ Itpr3tf/J mice increases food intake

The rising prevalence of obesity is one of the greatest health challenges facing the world today. Discovery of genetic factors affecting obesity risk will provide important insight to its etiology that could suggest new therapeutic approaches. We have previously identified the Modifier of obese 1 (Moo1) quantitative trait locus (QTL) in a cross between leptin-deficient BTBR T(+) Itpr3(tf)/J (BTBR) and C57BL/6J (B6) mice. Understanding the mechanism by which this locus acts will aid in the identification of candidate genes. Here we refined the location of this QTL and sought to determine the mechanism by which Moo1 affects body weight. We found that the effects of Moo1 also alter high fat diet-induced obesity in mice having functional leptin. In detailed metabolic analyses we determined that this locus acts by increasing food intake in BTBR mice, without affecting energy expenditure. The expression levels of the main molecular mediators of food intake in the hypothalamus were not altered, suggesting this locus affects an independent pathway, consistent with its identification in mice lacking functional leptin. Finally, we show that the increased adiposity resulting from Moo1 is sufficient to affect glucose tolerance. These studies show that the Moo1 obesity QTL affects food intake, likely through a novel mechanism, and indicate that modulation of the underlying pathway may not only ameliorate obesity but also its clinical consequences.

The contribution of FTO and UCP-1 SNPs to extreme obesity, diabetes and cardiovascular risk in Brazilian individuals

BACKGROUND

Obesity has become a common human disorder associated with significant morbidity and mortality and adverse effects on quality of life. Sequence variants in two candidate genes, FTO and UCP-1, have been reported to be overrepresented in obese Caucasian population. The association of these genes polymorphisms with the obesity phenotype in a multiethnic group such as the Brazilian population has not been previously reported.

METHODS

To assess the putative contribution of both FTO and UCP-1 to body mass index (BMI) and cardiovascular risk we genotyped SNPs rs9939609 (FTO) and rs6536991, rs22705565 and rs12502572 (UCP-1) from 126 morbidly obese subjects (BMI 42.9 ± 5.6 kg/m2, mean ± SE) and 113 normal-weight ethnically matched controls (BMI 22.6 ± 3.5 kg/m2, mean ± SE). Waist circumference, blood pressure, glucose and serum lipids were also measured. Each sample was also genotyped for 40 biallelic short insertion/deletion polymorphism (indels) for ethnic assignment and to estimate the proportion of European, African and Amerindian biogeographical ancestry in the Brazilian population.

RESULTS

Cases did not differ from controls in the proportions of genomic ancestry. The FTO SNP rs9939609 and UCP-1 SNP rs6536991 were significantly associated with BMI (p= 0.04 and p<0.0001 respectively). An allele dose dependent tendency was observed for BMI for rs6536991 sample of controls. No other significant associations between any SNP and hypertension, hyperlipidemia and diabetes were noted after correction for BMI and no significant synergistic effect between FTO and UCP-1 SNPs with obesity were noted. There was not an association between rs9939609 (FTO) and rs6536991 (UCP-1) in with maximum weight loss after 1 year in 94 obese patients who underwent bariatric surgery.

CONCLUSION

Our data are consistent with FTO rs9939609 and UCP-1 rs6536991 common variants as contributors to obesity in the Brazilian population.

Associations of variants in FTO and near MC4R with obesity traits in South Asian Indians

Recent genome-wide association studies show that loci in FTO and melanocortin 4 receptor (MC4R) associate with obesity-related traits. Outside Western populations the associations between these variants have not always been consistent and in Indians it has been suggested that FTO relates to diabetes without an obvious intermediary obesity phenotype. We investigated the association between genetic variants in FTO (rs9939609) and near MC4R (rs17782313) with obesity- and type 2 diabetes (T2DM)-related traits in a longitudinal birth cohort of 2,151 healthy individuals from the Vellore birth cohort in South India. The FTO locus displayed significant associations with several conventional obesity-related anthropometric traits. The per allele increase is about 1% for BMI, waist circumference (WC), hip circumference (HC), and waist-hip ratio. Consistent associations were observed for adipose tissue-specific measurements such as skinfold thickness reinforcing the association with obesity-related traits. Obesity associations for the MC4R locus were weak or nonsignificant but a signal for height (P < 0.001) was observed. The effect on obesity-related traits for FTO was seen in adulthood, but not at younger ages. The loci also showed nominal associations with increased blood glucose but these associations were lost on BMI adjustment. The effect of FTO on obesity-related traits was driven by an urban environmental influence. We conclude that rs9939609 variant in the FTO locus is associated with measures of adiposity and metabolic consequences in South Indians with an enhanced effect associated with urban living. The detection of these associations in Indians is challenging because conventional anthropometric obesity measures work poorly in the Indian "thin-fat" phenotype.

Overview of paediatric obesity for the paediatric mental health provider

Childhood obesity represents a significant challenge for paediatric healthcare delivery. As obesity rates increase, obese children and adolescents are at significant risk for the development of a myriad of medical and surgical problems as well as mental health problems. Moreover, children with mental health problems are increasingly presenting to their psychiatrists with obesity. Treatment of paediatric obesity requires a multidisciplinary approach with incorporation of the family into the treatment plan although still typically only offering suboptimal results. Paediatric providers from all disciplines should focus efforts primarily on obesity prevention and encouragement of healthy lifestyles, while incorporating treatment for obesity when such efforts fail. The goals of this article are to provide an overview of the epidemiology, pathophysiology, genetics, clinical features and treatment strategies for paediatric obesity.

Effect of Body Composition Methodology on Heritability Estimation of Body Fatness

Heritability estimates of human body fatness vary widely and the contribution of body composition methodology to this variability is unknown. The effect of body composition methodology on estimations of genetic and environmental contributions to body fatness variation was examined in 78 adult male and female monozygotic twin pairs reared apart or together. Body composition was assessed by six methods - body mass index (BMI), dual energy x-ray absorptiometry (DXA), underwater weighing (UWW), total body water (TBW), bioelectric impedance (BIA), and skinfold thickness. Body fatness was expressed as percent body fat, fat mass, and fat mass/height2 to assess the effect of body fatness expression on heritability estimates. Model-fitting multivariate analyses were used to assess the genetic and environmental components of variance. Mean BMI was 24.5 kg/m2 (range of 17.8-43.4 kg/m2). There was a significant effect of body composition methodology (p<0.001) on heritability estimates, with UWW giving the highest estimate (69%) and BIA giving the lowest estimate (47%) for fat mass/height2. Expression of body fatness as percent body fat resulted in significantly higher heritability estimates (on average 10.3% higher) compared to expression as fat mass/height2 (p=0.015). DXA and TBW methods expressing body fatness as fat mass/height2 gave the least biased heritability assessments, based on the small contribution of specific genetic factors to their genetic variance. A model combining DXA and TBW methods resulted in a relatively low FM/ht2 heritability estimate of 60%, and significant contributions of common and unique environmental factors (22% and 18%, respectively). The body fatness heritability estimate of 60% indicates a smaller contribution of genetic variance to total variance than many previous studies using less powerful research designs have indicated. The results also highlight the importance of environmental factors and possibly genotype by environmental interactions in the etiology of weight gain and the obesity epidemic.

High-resolution genome-wide linkage mapping identifies susceptibility loci for BMI in the Chinese population

The genetic loci affecting the commonly used BMI have been intensively investigated using linkage approaches in multiple populations. This study aims at performing the first genome-wide linkage scan on BMI in the Chinese population in mainland China with hypothesis that heterogeneity in genetic linkage could exist in different ethnic populations. BMI was measured from 126 dizygotic twins in Qingdao municipality who were genotyped using high-resolution Affymetrix Genome-Wide Human SNP arrays containing about 1 million single-nucleotide polymorphisms (SNPs). Nonparametric linkage analysis was performed with Merlin software package for linkage analysis using variance components approach for quantitative trait loci mapping. We identified a strong linkage peak at the end of chromosome 7 (7q36 at 186 cM) with a lod score of 4.06 which overlaps with that reported by a large multicenter study in western countries. Multiple loci showing suggestive linkage were found on chromosome 1 (lod score 2.38 at 242 cM), chromosome 8 (2.48 at 95 cM), and chromosome 14 (2.2 at 89.4 cM). The strong linkage identified in the Chinese subjects that is consistent with that found in populations of European origin could suggest the existence of evolutionarily preserved genetic mechanisms for BMI whereas the multiple suggestive loci could represent genetic effect from gene-environment interaction as a result of population-specific environmental adaptation.

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.

Recent advances in obesity: genetics and beyond

The prevalence of obesity, which is a heritable trait that arises from the interactions of multiple genes and lifestyle factors, continues to increase worldwide, causing serious health problems and imposing a substantial economic burden on societies. For the past several years, various genetic epidemiological approaches have been utilized to identify genetic loci for obesity. Recent evidence suggests that development of obesity involves hormones and neurotransmitters (such as leptin, cocaine- and amphetamine-regulated transcript (CART), and ghrelin) that regulate appetite and energy expenditure. These hormones act on specific centers in the brain that regulate the sensations of satiety. Mutations in these hormones or their receptors can lead to obesity. Aberrant circadian rhythms and biochemical pathways in peripheral organs or tissues have also been implicated in the pathology of obesity. More interestingly, increasing evidence indicates a potential relation between obesity and central nervous system disorders (such as cognitive deficits). This paper discusses recent advances in the field of genetics of obesity with an emphasis on several established loci that influence obesity. These recently identified loci may hold the promise to substantially improve our insights into the pathophysiology of obesity and open up new therapeutic strategies to combat growing obesity epidemic facing the human population today.

Genetic polymorphisms in adipokine genes and the risk of obesity: a systematic review and meta-analysis

Polymorphisms in adipokine genes, such as leptin (LEP), leptin receptor (LEPR), resistin (RETN), adiponectin (ADIPOQ), interleukin-1β (IL-1β), IL-6 (IL-6), and tumor necrosis factor-α (TNF-α) may be involved in the development of obesity. We conducted a systematic review of published evidence on the association between different adipokine genes and the risk of obesity. Librarian-designed searches of PubMed and HuGeNet, review of reference lists from published reviews and content expert advice identified potentially eligible studies. The genotyping information and polymorphisms of different adipokine genes, numbers of genotyped cases and controls and frequencies of genotypes were extracted from 48 eligible studies included in this review. Twenty-one polymorphisms each associated with obesity in at least one study were identified. Polymorphisms in the adipokine genes, LEP, LEPR, and RETN were not associated with obesity susceptibility, whereas ADIPOQ G276T (T vs. G: odds ratio (OR), 1.59; 95% confidence interval (CI), 1.39-1.81), IL-1β C3953T (CC vs. CT+TT: OR, 1.61; 95% CI, 1.18-2.20), and TNF-α G308A (GG vs. GA+AA: OR, 1.19; 95% CI, 1.02-1.39) polymorphisms were associated with an increased risk of obesity. The IL-6 G174C polymorphism was also associated obesity when using allelic comparisons, the recessive genetic model and the dominant genetic model with OR (95% CI) of 1.95 (1.37-2.77), 1.44 (1.15-1.80), and 1.36 (1.16-1.59), respectively. No significant evidence of publication bias was present. However, these "null" results were underpowered due to a small pooled sample size, and analysis of additional case-control studies with larger sample sizes should provide further clarifications.

Differential coexpression analysis of obesity-associated networks in human subcutaneous adipose tissue

OBJECTIVE

To use a unique obesity-discordant sib-pair study design to combine differential expression analysis, expression quantitative trait loci (eQTLs) mapping and a coexpression regulatory network approach in subcutaneous human adipose tissue to identify genes relevant to the obese state.

STUDY DESIGN

Genome-wide transcript expression in subcutaneous human adipose tissue was measured using Affymetrix U133 Plus 2.0 microarrays (Affymetrix, Santa Clara, CA, USA), and genome-wide genotyping data was obtained using an Applied Biosystems (Applied Biosystems; Life Technologies, Carlsbad, CA, USA) SNPlex linkage panel.

SUBJECTS

A total of 154 Swedish families ascertained through an obese proband (body mass index (BMI) >30 kg m(-2)) with a discordant sibling (BMI>10 kg m(-2) less than proband).

RESULTS

Approximately one-third of the transcripts were differentially expressed between lean and obese siblings. The cellular adhesion molecules (CAMs) KEGG grouping contained the largest number of differentially expressed genes under cis-acting genetic control. By using a novel approach to contrast CAMs coexpression networks between lean and obese siblings, a subset of differentially regulated genes was identified, with the previously GWAS obesity-associated neuronal growth regulator 1 (NEGR1) as a central hub. Independent analysis using mouse data demonstrated that this finding of NEGR1 is conserved across species.

CONCLUSION

Our data suggest that in addition to its reported role in the brain, NEGR1 is also expressed in subcutaneous adipose tissue and acts as a central 'hub' in an obesity-related transcript network.

Genetic influences in childhood obesity: recent progress and recommendations for experimental designs

The increasing prevalence of pediatric obesity around the world has become an area of scientific interest because of public health concern. Although since early stages of the lifespan body weight might be heavily influenced by an individual's behavior, epidemiological research highlights the involvement of genetic influences contributing to variation in fat accumulation and thus body composition. Results from genome-wide association studies and candidate gene approaches have identified specific regions across the human genome influencing obesity-related phenotypes. Reviewing the scientific literature provides support to the belief that at the conceptual level scientists understand that genes and environments do not act independently, but rather synergistically, and that such interaction might be the responsible factor for differences within and among populations. However, there is still limited understanding of genetic and environmental factors influencing fat accumulation and deposition among different populations, which highlights the need for innovative experimental designs, improved body composition measures and appropriate statistical methodology.

Insulin receptor substrate-2 gene variants in subjects with metabolic syndrome: association with plasma monounsaturated and n-3 polyunsaturated fatty acid levels and insulin resistance

SCOPE

Several insulin receptor substrate-2 (IRS-2) polymorphisms have been studied in relation to insulin resistance and type 2 diabetes. To examine whether the genetic variability at the IRS-2 gene locus was associated with the degree of insulin resistance and plasma fatty acid levels in metabolic syndrome (MetS) subjects.

METHODS AND RESULTS

Insulin sensitivity, insulin secretion, glucose effectiveness, plasma fatty acid composition and three IRS-2 tag-single nucleotide polymorphisms (SNPs) were determined in 452 MetS subjects. Among subjects with the lowest level of monounsaturated (MUFA) (below the median), the rs2289046 A/A genotype was associated with lower glucose effectiveness (p<0.038), higher fasting insulin concentrations (p<0.028) and higher HOMA IR (p<0.038) as compared to subjects carrying the minor G-allele (A/G and G/G). In contrast, among subjects with the highest level of MUFA (above the median), the A/A genotype was associated with lower fasting insulin concentrations and HOMA-IR, whereas individuals carrying the G allele and with the highest level of ω-3 polyunsaturated fatty acids (above the median) showed lower fasting insulin (p<0.01) and HOMA-IR (p<0.02) as compared with A/A subjects.

CONCLUSION

The rs2289046 polymorphism at the IRS2 gene locus may influence insulin sensitivity by interacting with certain plasma fatty acids in MetS subjects.

Molecular basis of obesity: current status and future prospects

Obesity is a global health problem that is gradually affecting each continent of the world. Obesity is a heterogeneous disorder, and the biological causes of obesity are complex. The rapid increase in obesity prevalence during the past few decades is due to major societal changes (sedentary lifestyle, over-nutrition) but who becomes obese at the individual level is determined to a great extent by genetic susceptibility. In this review, we evidence that obesity is a strongly heritable disorder, and provide an update on the molecular basis of obesity. To date, nine loci have been involved in Mendelian forms of obesity and 58 loci contribute to polygenic obesity, and rare and common structural variants have been reliably associated with obesity. Most of the obesity genes remain to be discovered, but promising technologies, methodologies and the use of “deep phenotyping” lead to optimism to chip away at the ‘missing heritability’ of obesity in the near future. In the longer term, the genetic dissection of obesity will help to characterize disease mechanisms, provide new targets for drug design, and lead to an early diagnosis, treatment, and prevention of obesity.

Developments in obesity genetics in the era of genome-wide association studies

Obesity is an important factor contributing to the global burden of morbidity and mortality. By identifying obesity susceptibility genes, scientists aim to elucidate some of its aetiology. Early studies used candidate gene and genome-wide linkage approaches to search for such genes with limited success. However, the advent of genome-wide association studies (GWAS) has dramatically increased the pace of gene discovery. So far, GWAS have identified at least 50 loci robustly associated with body mass index (BMI), waist-to-hip ratio, body fat percentage and extreme obesity. Some of these have been shown to replicate in non-white populations and in children and adolescents. Furthermore, for some loci interaction studies have shown that the BMI-increasing effect is attenuated in physically active individuals. Despite many successful discoveries, the effect sizes of the established loci are small, and combined they explain only a fraction of the inter-individual variation in BMI. The low predictive value means that their value in mainstream health care is limited. However, as most of these newly established loci were not previously linked to obesity, they may provide new insights into body weight regulation. Continued efforts in gene discovery, using a range of approaches, will be needed to increase our understanding of obesity.

Genetic polymorphisms in carnitine palmitoyltransferase 1A gene are associated with variation in body composition and fasting lipid traits in Yup'ik Eskimos

Variants of carnitine palmitoyltransferase 1A (CPT1A), a key hepatic lipid oxidation enzyme, may influence how fatty acid oxidation contributes to obesity and metabolic outcomes. CPT1A is regulated by diet, suggesting interactions between gene variants and diet may influence outcomes. The objective of this study was to test the association of CPT1A variants with body composition and lipids, mediated by consumption of polyunsaturated fatty acids (PUFA). Obesity phenotypes and fasting lipids were measured in a cross-sectional sample of Yup'ik Eskimo individuals (n = 1141) from the Center of Alaska Native Health Research (CANHR) study. Twenty-eight tagging CPT1A SNPs were evaluated with outcomes of interest in regression models accounting for family structure. Several CPT1A polymorphisms were associated with HDL-cholesterol and obesity phenotypes. The P479L (rs80356779) variant was associated with all obesity-related traits and fasting HDL-cholesterol. Interestingly, the association of P479L with HDL-cholesterol was still significant after correcting for body mass index (BMI), percentage body fat (PBF), or waist circumference (WC). Our findings are consistent with the hypothesis that the L479 allele of the CPT1A P479L variant confers a selective advantage that is both cardioprotective (through increased HDL-cholesterol) and associated with reduced adiposity.

Genetic studies on the ghrelin, growth hormone secretagogue receptor (GHSR) and ghrelin O-acyl transferase (GOAT) genes

Ghrelin is a 28 amino acid peptide hormone that is produced both centrally and peripherally. Regulated by the ghrelin O-acyl transferase enzyme, ghrelin exerts its action through the growth hormone secretagogue receptor, and is implicated in a diverse range of physiological processes. These implications have placed the ghrelin signaling pathway at the center of a large number of candidate gene and genome-wide studies which aim to identify the genetic basis of human heterogeneity. In this review we summarize the available data on the genetic variability of ghrelin, its receptor and its regulatory enzyme, and their association with obesity, stature, type 2 diabetes, cardiovascular disease, eating disorders, and reward seeking behavior.