Common variants near MC4R are associated with fat mass, weight and risk of obesity

Genetics of Obesity

Numerous classical genetic studies have proved that genes are contributory factors for obesity. Genes are directly responsible for obesity associated disorders such as Bardet-Biedl and Prader-Willi syndromes. However, both genes as well as environment are associated with obesity in the general population. Genetic epidemiological approaches, particularly genome-wide association studies, have unraveled many genes which play important roles in human obesity. Elucidation of their biological functions can be very useful for understanding pathobiology of obesity. In the near future, further exploration of obesity genetics may help to develop useful diagnostic and predictive tests for obesity treatment.

FTO genotype and weight loss: systematic review and meta-analysis of 9563 individual participant data from eight randomised controlled trials

OBJECTIVE

 To assess the effect of the FTO genotype on weight loss after dietary, physical activity, or drug based interventions in randomised controlled trials.

DESIGN

 Systematic review and random effects meta-analysis of individual participant data from randomised controlled trials.

DATA SOURCES

 Ovid Medline, Scopus, Embase, and Cochrane from inception to November 2015.

ELIGIBILITY CRITERIA FOR STUDY SELECTION

 Randomised controlled trials in overweight or obese adults reporting reduction in body mass index, body weight, or waist circumference by FTO genotype (rs9939609 or a proxy) after dietary, physical activity, or drug based interventions. Gene by treatment interaction models were fitted to individual participant data from all studies included in this review, using allele dose coding for genetic effects and a common set of covariates. Study level interactions were combined using random effect models. Metaregression and subgroup analysis were used to assess sources of study heterogeneity.

RESULTS

 We identified eight eligible randomised controlled trials for the systematic review and meta-analysis (n=9563). Overall, differential changes in body mass index, body weight, and waist circumference in response to weight loss intervention were not significantly different between FTO genotypes. Sensitivity analyses indicated that differential changes in body mass index, body weight, and waist circumference by FTO genotype did not differ by intervention type, intervention length, ethnicity, sample size, sex, and baseline body mass index and age category.

CONCLUSIONS

 We have observed that carriage of the FTO minor allele was not associated with differential change in adiposity after weight loss interventions. These findings show that individuals carrying the minor allele respond equally well to dietary, physical activity, or drug based weight loss interventions and thus genetic predisposition to obesity associated with the FTO minor allele can be at least partly counteracted through such interventions.

SYSTEMATIC REVIEW REGISTRATION

 PROSPERO CRD42015015969.

Tumour biology of obesity-related cancers: understanding the molecular concept for better diagnosis and treatment

Obesity continues to be a major global problem. Various cancers are related to obesity and proper understanding of their aetiology, especially their molecular tumour biology is important for early diagnosis and better treatment. Genes play an important role in the development of obesity. Few genes such as leptin, leptin receptor encoded by the db (diabetes), pro-opiomelanocortin, AgRP and NPY and melanocortin-4 receptors and insulin-induced gene 2 were linked to obesity. MicroRNAs control gene expression via mRNA degradation and protein translation inhibition and influence cell differentiation, cell growth and cell death. Overexpression of miR-143 inhibits tumour growth by suppressing B cell lymphoma 2, extracellular signal-regulated kinase-5 activities and KRAS oncogene. Cancers of the breast, uterus, renal, thyroid and liver are also related to obesity. Any disturbance in the production of sex hormones and insulin, leads to distortion in the balance between cell proliferation, differentiation and apoptosis. The possible mechanism linking obesity to cancer involves alteration in the level of adipokines and sex hormones. These mediators act as biomarkers for cancer progression and act as targets for cancer therapy and prevention. Interestingly, many anti-cancerous drugs are also beneficial in treating obesity and vice versa. We also reviewed the possible link in the mechanism of few drugs which act both on cancer and obesity. The present review may be important for molecular biologists, oncologists and clinicians treating cancers and also pave the way for better therapeutic options.

An integrative study identifies KCNC2 as a novel predisposing factor for childhood obesity and the risk of diabetes in the Korean population

Obesity is a major risk factor for type 2 diabetes. To unravel the genetic determinants of obesity-associated diabetes, we performed a genome-wide study using the 1,000 Genomes-based imputation in a Korean childhood cohort (KoCAS-1, n = 484) and carried out de novo replication in an independent population (KoCAS-2, n = 1,548). A novel variant (rs10879834) with multiple diverse associations for obesity-related traits was also found to be replicated in an adult cohort (KARE, n = 8,842). Functional annotations using integrative epigenetic analyses identified biological significance and regulatory effects with an inverse methylation-expression correlation (cg27154343 in the 5′-UTR of the KCNC2 gene), tissue-specific enhancer mark (H3K4me1), and pathway enrichment (insulin signaling). Further functional studies in cellular and mouse models demonstrated that KCNC2 is associated with anti-obesogenic effects in the regulation of obesity-induced insulin resistance. KCNC2 shRNA transfection induced endoplasmic reticulum (ER) stress and hepatic gluconeogenesis. Overproduction of KCNC2 decreased ER stress, and treatment with metformin enhanced KCNC2 expression. Taken together, these data suggest that reduction of KCNC2 is associated with modified hepatic gluconeogenesis and increased ER stress on obesity-mediated diabetic risk. An integrative multi-omics analysis might reveal new functional and clinical implications related to the control of energy and metabolic homeostasis in humans.

Test for association of common variants in GRM7 with alcohol consumption

Recent work using a mouse model has identified the glutamate metabotropic receptor 7 (Grm7) gene as a strong candidate gene for alcohol consumption. Although there has been some work examining the effect of human glutamate metabotropic receptor 7 (GRM7) polymorphisms on human substance use disorders, the majority of the work has focused on other psychiatric disorders such as ADHD, major depressive disorder, schizophrenia, bipolar disorder, panic disorder, and autism spectrum disorders. The current study aimed to evaluate evidence for association between GRM7 and alcohol behaviors in humans using a single nucleotide polymorphism (SNP) approach, as well as a gene-based approach. Using 1803 non-Hispanic European Americans (EAs) (source: the Colorado Center on Antisocial Drug Dependence [CADD]) and 1049 EA subjects from an independent replication sample (source: the Genetics of Antisocial Drug Dependence [GADD]), two SNPs in GRM7 were examined for possible association with alcohol consumption using two family-based association tests implemented in FBAT and QTDT. Rs3749380 was suggestively associated with alcohol consumption in the CADD sample (p = 0.010) with the minor T allele conferring risk. There was no evidence for association in the GADD sample. A gene-based test using four Genome-Wide Association Studies (GWAS) revealed no association between variation in GRM7 and alcohol consumption. This study had several limitations: the SNPs chosen likely do not tag expression quantitative trait loci; a human alcohol consumption phenotype was used, complicating the interpretation with respect to rodent studies that found evidence for a cis-regulatory link between alcohol preference and Grm7; and only common SNPs imputed in all four datasets were included in the gene-based test. These limitations highlight the fact that rare variants, some potentially important common signals in the gene, and regions farther upstream were not examined.

Interactions between genetic variants associated with adiposity traits and soft drinks in relation to longitudinal changes in body weight and waist circumference

BACKGROUND

Intake of sugar-sweetened beverages is associated with obesity, and this association may be modified by a genetic predisposition to obesity.

OBJECTIVE

We examined the interactions between a molecular genetic predisposition to various aspects of obesity and the consumption of soft drinks, which are a major part of sugar-sweetened beverages, in relation to changes in adiposity measures.

DESIGN

A total of 4765 individuals were included in the study. On the basis of 50 obesity-associated single nucleotide polymorphisms that are associated with body mass index (BMI), waist circumference (WC), or the waist-to-hip ratio adjusted for BMI (WHRBMI), the following 4 genetic predisposition scores (GRSs) were constructed: a complete genetic predisposition score including all 50 single nucleotide polymorphisms (GRSComplete), a genetic predisposition score including BMI-associated single nucleotide polymorphisms (GRSBMI), a genetic predisposition score including waist circumference-associated single nucleotide polymorphisms (GRSWC), and a genetic predisposition score including the waist-to-hip ratio adjusted for BMI-associated single nucleotide polymorphisms (GRSWHR). Associations between soft drink intake and the annual change (Δ) in body weight (BW), WC, or waist circumference adjusted for BMI (WCBMI) and possible interactions with the GRSs were examined with the use of linear regression analyses and meta-analyses.

RESULTS

For each soft drink serving per day, soft drink consumption was significantly associated with a higher ΔBW of 0.07 kg/y (95% CI: 0.01, 0.13 kg/y; P = 0.020) but not with the ΔWC or ΔWCBMI In analyses of the ΔBW, we showed an interaction only with the GRSWC (per risk allele for each soft drink serving per day: -0.06 kg/y; 95% CI: -0.10, -0.02 kg/y; P = 0.006). In analyses of the ΔWC, we showed interactions only with the GRSBMI and GRSComplete [per risk allele for each soft drink serving per day: 0.05 cm/y (95% CI: 0.02, 0.09 cm/y; P = 0.001) and 0.05 cm/y (95% CI: 0.02, 0.07 cm/y; P = 0.001), respectively]. Nearly identical results were observed in analyses of the ΔWCBMI CONCLUSIONS: A genetic predisposition to a high WC may attenuate the association between soft drink intake and BW gain. A genetic predisposition to high BMI as well as a genetic predisposition to high BMI, WC, and WHRBMI combined may strengthen the association between soft drink intake and WC gain. However, the public health impact may be limited.

Body mass index: Has epidemiology started to break down causal contributions to health and disease?

OBJECTIVES

To review progress in understanding the methods and results concerning the causal contribution of body mass index (BMI) to health and disease.

METHODS

In the context of conventional evidence focused on the relationship between BMI and health, this review considers current literature on the common, population-based, genetic contribution to BMI and how this has fed into the developing field of applied epidemiology.

RESULTS

Technological and analytical developments have driven considerable success in identifying genetic variants relevant to BMI. This has enabled the implementation of Mendelian randomization to address questions of causality. The product of this work has been the implication of BMI as a causal agent in a host of health outcomes. Further breakdown of causal pathways by integration with other "omics" technologies promises to deliver additional benefit.

CONCLUSIONS

Gaps remain in our understanding of BMI as a risk factor for health and disease, and while promising, applied genetic epidemiology should be considered alongside alternative methods for assessing the impact of BMI on health. Potential limitations, relating to inappropriate or nonspecific measures of obesity and the improper use of genetic instruments, will need to be explored and incorporated into future research aiming to dissect BMI as a risk factor.

Selecting instruments for Mendelian randomization in the wake of genome-wide association studies

Mendelian randomization (MR) studies typically assess the pathogenic relevance of environmental exposures or disease biomarkers, using genetic variants that instrument these exposures. The approach is gaining popularity-our systematic review reveals a greater than 10-fold increase in MR studies published between 2004 and 2015. When the MR paradigm was first proposed, few biomarker- or exposure-related genetic variants were known, most having been identified by candidate gene studies. However, genome-wide association studies (GWAS) are now providing a rich source of potential instruments for MR analysis. Many early reviews covering the concept, applications and analytical aspects of the MR technique preceded the surge in GWAS, and thus the question of how best to select instruments for MR studies from the now extensive pool of available variants has received insufficient attention. Here we focus on the most common category of MR studies-those concerning disease biomarkers. We consider how the selection of instruments for MR analysis from GWAS requires consideration of: the assumptions underlying the MR approach; the biology of the biomarker; the genome-wide distribution, frequency and effect size of biomarker-associated variants (the genetic architecture); and the specificity of the genetic associations. Based on this, we develop guidance that may help investigators to plan and readers interpret MR studies.

Melanocortin-4 receptor-regulated energy homeostasis

The melanocortin system provides a conceptual blueprint for the central control of energetic state. Defined by four principal molecular components--two antagonistically acting ligands and two cognate receptors--this phylogenetically conserved system serves as a prototype for hierarchical energy balance regulation. Over the last decade the application of conditional genetic techniques has facilitated the neuroanatomical dissection of the melanocortinergic network and identified the specific neural substrates and circuits that underscore the regulation of feeding behavior, energy expenditure, glucose homeostasis and autonomic outflow. In this regard, the melanocortin-4 receptor is a critical coordinator of mammalian energy homeostasis and body weight. Drawing on recent advances in neuroscience and genetic technologies, we consider the structure and function of the melanocortin-4 receptor circuitry and its role in energy homeostasis.

Robust analysis of secondary phenotypes in case-control genetic association studies

The case-control study is a common design for assessing the association between genetic exposures and a disease phenotype. Though association with a given (case-control) phenotype is always of primary interest, there is often considerable interest in assessing relationships between genetic exposures and other (secondary) phenotypes. However, the case-control sample represents a biased sample from the general population. As a result, if this sampling framework is not correctly taken into account, analyses estimating the effect of exposures on secondary phenotypes can be biased leading to incorrect inference. In this paper, we address this problem and propose a general approach for estimating and testing the population effect of a genetic variant on a secondary phenotype. Our approach is based on inverse probability weighted estimating equations, where the weights depend on genotype and the secondary phenotype. We show that, though slightly less efficient than a full likelihood-based analysis when the likelihood is correctly specified, it is substantially more robust to model misspecification, and can out-perform likelihood-based analysis, both in terms of validity and power, when the model is misspecified. We illustrate our approach with an application to a case-control study extracted from the Framingham Heart Study. Copyright © 2016 John Wiley & Sons, Ltd.

Interactions with the MC4R rs17782313 variant, mental stress and energy intake and the risk of obesity in Genome Epidemiology Study

Background

The melanocortin-4 receptor (MC4R) regulates metabolism by modulating eating behavior and MC4R variants (rs17782313 and rs571312) are associated with obesity in Asians and Caucasians. However, the impact of their interactions with nutritional and lifestyle factors on obesity are poorly described. Therefore, we investigated the interaction of MC4R variants and dietary patterns on the risk of obesity in Korean middle-aged adults.

Methods

Data collected included, genetic variations, anthropometric and biochemical measurements, dietary and lifestyle habits, and food intake. Data were obtained from the 8830 adults aged 40–69 years in the Ansung and Ansan cohort of the Korean Genome Epidemiology Study.

Results

The MC4R rs18882313 minor allele had a higher frequency in the obese group (P < 0.01). MC4R genotypes were not associated with differences in daily energy and macronutrient intakes. However, the intakes of processed foods and fat (as percentages of energy) were significantly higher and intake of fruits were significantly lower in subjects with MC4R minor alleles (P < 0.05). Interestingly, there was a positive interaction between MC4R variants and mental stress levels that were associated with the risk of obesity after adjusting for age, gender, residence area, daily energy intake, smoking status and physical activity (interaction P = 0.0384). Only in subjects with high stress were MC4R minor alleles associated with higher BMIs after adjusting for confounders. The association was present without modulating energy and nutrient intake. In the group with energy intakes higher than estimated energy requirement (EER), subjects with MC4R minor alleles had higher BMIs than those with the major alleles (P < 0.001).

Conclusions

The interactions of mental stress and energy intakes with the MC4R minor allele genotype might be associated with increased risk of obesity in Korean adults. This research might identify subjects with a specific MC4R minor alleles as a human subset of people with a low metabolic tolerance for excessive energy intake, especially when under stress.

Genetics of Common Antipsychotic-Induced Adverse Effects

The effectiveness of antipsychotic drugs is limited due to accompanying adverse effects which can pose considerable health risks and lead to patient noncompliance. Pharmacogenetics (PGx) offers a means to identify genetic biomarkers that can predict individual susceptibility to antipsychotic-induced adverse effects (AAEs), thereby improving clinical outcomes. We reviewed the literature on the PGx of common AAEs from 2010 to 2015, placing emphasis on findings that have been independently replicated and which have additionally been listed to be of interest by PGx expert panels. Gene-drug associations meeting these criteria primarily pertain to metabolic dysregulation, extrapyramidal symptoms (EPS), and tardive dyskinesia (TD). Regarding metabolic dysregulation, results have reaffirmed HTR2C as a strong candidate with potential clinical utility, while MC4R and OGFR1 gene loci have emerged as new and promising biomarkers for the prediction of weight gain. As for EPS and TD, additional evidence has accumulated in support of an association with CYP2D6 metabolizer status. Furthermore, HSPG2 and DPP6 have been identified as candidate genes with the potential to predict differential susceptibility to TD. Overall, considerable progress has been made within the field of psychiatric PGx, with inroads toward the development of clinical tools that can mitigate AAEs. Going forward, studies placing a greater emphasis on multilocus effects will need to be conducted.

From Genome-Wide Association Study to Phenome-Wide Association Study: New Paradigms in Obesity Research

Obesity is a condition in which excess body fat has accumulated over an extent that increases the risk of many chronic diseases. The current clinical classification of obesity is based on measurement of body mass index (BMI), waist-hip ratio, and body fat percentage. However, these measurements do not account for the wide individual variations in fat distribution, degree of fatness or health risks, and genetic variants identified in the genome-wide association studies (GWAS). In this review, we will address this important issue with the introduction of phenome, phenomics, and phenome-wide association study (PheWAS). We will discuss the new paradigm shift from GWAS to PheWAS in obesity research. In the era of precision medicine, phenomics and PheWAS provide the required approaches to better definition and classification of obesity according to the association of obese phenome with their unique molecular makeup, lifestyle, and environmental impact.

Genetic variants influencing effectiveness of exercise training programmes in obesity - an overview of human studies

Frequent and regular physical activity has significant benefits for health, including improvement of body composition and help in weight control. Consequently, promoting training programmes, particularly in those who are genetically predisposed, is a significant step towards controlling the presently increasing epidemic of obesity. Although the physiological responses of the human body to exercise are quite well described, the genetic background of these reactions still remains mostly unknown. This review not only summarizes the current evidence, through a literature review and the results of our studies on the influence of gene variants on the characteristics and range of the body's adaptive response to training, but also explores research organization problems, future trends, and possibilities. We describe the most reliable candidate genetic markers that are involved in energy balance pathways and body composition changes in response to training programmes, such as FTO, MC4R, ACE, PPARG, LEP, LEPR, ADRB2, and ADRB3. This knowledge can have an enormous impact not only on individualization of exercise programmes to make them more efficient and safer, but also on improved recovery, traumatology, medical care, diet, supplementation and many other areas. Nevertheless, the current studies still represent only the first steps towards a better understanding of the genetic factors that influence obesity-related traits, as well as gene variant x physical activity interactions, so further research is necessary.

Analysis of MC4R rs17782313, POMC rs1042571, APOE-Hha1 and AGRP rs3412352 genetic variants with susceptibility to obesity risk in North Indians

BACKGROUND

Obesity is a multi-factorial disorder influenced by genetic and environmental factors. The physiological pathways associated with obesity are complex and involve several genes.

AIM

The aim of this survey is to evaluate the association of genetic variants of melanocortin-4-receptor (MC4R), pro-opiomelanocortin (POMC), apolipoprotein E (APOE) and agouti-related protein (AGRP) with obesity in the North Indian population.

METHODS

MC4R rs17782313, POMC rs1042571, APOE-Hha1 and AGRP rs3412352 polymorphisms were investigated for their association in 396 obese individuals with BMI ≥ 30 kg/m(2) and 300 healthy non-obese individuals with BMI < 30 kg/m(2). Genotyping was performed using Taqman probes and PCR-RFLP methods. Single locus logistic regression analysis was conducted using (SPSS), ver.19 and PLINK software Version 1.01 and high order genetic interactions associated with obesity risk were analysed using MDR software (version 2.3.0.2).

RESULTS

The genotypes of MC4R rs17782313, POMC rs1042571 and APOE-Hha1 were significantly associated with obese individuals (BMI ≥ 30 kg/m(2)) when compared with non-obese individuals (BMI < 30 kg/m(2)). No association of AGRP rs34123523 was seen with obesity.

CONCLUSIONS

The best interaction model for predicting obesity risk by MDR analysis was the three factor model including POMC (C > T), MC4R (T > C) and APOE (Hha1) polymorphisms. Genetic variants in MC4R, POMC and APOE genes might play significant roles in predisposing obesity (BMI ≥ 30 kg/m(2)) in the North Indian population.

60 YEARS OF POMC: Biosynthesis, trafficking, and secretion of pro-opiomelanocortin-derived peptides

Pro-opiomelanocortin (POMC) is a prohormone that encodes multiple smaller peptide hormones within its structure. These peptide hormones can be generated by cleavage of POMC at basic residue cleavage sites by prohormone-converting enzymes in the regulated secretory pathway (RSP) of POMC-synthesizing endocrine cells and neurons. The peptides are stored inside the cells in dense-core secretory granules until released in a stimulus-dependent manner. The complexity of the regulation of the biosynthesis, trafficking, and secretion of POMC and its peptides reflects an impressive level of control over many factors involved in the ultimate role of POMC-expressing cells, that is, to produce a range of different biologically active peptide hormones ready for action when signaled by the body. From the discovery of POMC as the precursor to adrenocorticotropic hormone (ACTH) and β-lipotropin in the late 1970s to our current knowledge, the understanding of POMC physiology remains a monumental body of work that has provided insight into many aspects of molecular endocrinology. In this article, we describe the intracellular trafficking of POMC in endocrine cells, its sorting into dense-core secretory granules and transport of these granules to the RSP. Additionally, we review the enzymes involved in the maturation of POMC to its various peptides and the mechanisms involved in the differential processing of POMC in different cell types. Finally, we highlight studies pertaining to the regulation of ACTH secretion in the anterior and intermediate pituitary and POMC neurons of the hypothalamus.

Neuroendocrinological and Epigenetic Mechanisms Subserving Autonomic Imbalance and HPA Dysfunction in the Metabolic Syndrome

Impact of environmental stress upon pathophysiology of the metabolic syndrome (MetS) has been substantiated by epidemiological, psychophysiological, and endocrinological studies. This review discusses recent advances in the understanding of causative roles of nutritional factors, sympathomedullo-adrenal (SMA) and hypothalamic-pituitary adrenocortical (HPA) axes, and adipose tissue chronic low-grade inflammation processes in MetS. Disturbances in the neuroendocrine systems for leptin, melanocortin, and neuropeptide Y (NPY)/agouti-related protein systems have been found resulting directly in MetS-like conditions. The review identifies candidate risk genes from factors shown critical for the functioning of each of these neuroendocrine signaling cascades. In its meta-analytic part, recent studies in epigenetic modification (histone methylation, acetylation, phosphorylation, ubiquitination) and posttranscriptional gene regulation by microRNAs are evaluated. Several studies suggest modification mechanisms of early life stress (ELS) and diet-induced obesity (DIO) programming in the hypothalamic regions with populations of POMC-expressing neurons. Epigenetic modifications were found in cortisol (here HSD11B1 expression), melanocortin, leptin, NPY, and adiponectin genes. With respect to adiposity genes, epigenetic modifications were documented for fat mass gene cluster APOA1/C3/A4/A5, and the lipolysis gene LIPE. With regard to inflammatory, immune and subcellular metabolism, PPARG, NKBF1, TNFA, TCF7C2, and those genes expressing cytochrome P450 family enzymes involved in steroidogenesis and in hepatic lipoproteins were documented for epigenetic modifications.

Serum 25-Hydroxyvitamin D Status and Longitudinal Changes in Weight and Waist Circumference: Influence of Genetic Predisposition to Adiposity

Studies of the relationship between serum 25-hydroxyvitamin D (25(OH)D) and changes in measures of adiposity have shown inconsistent results, and interaction with genetic predisposition to obesity has rarely been examined. We examined whether 25(OH)D was associated with subsequent annual changes in body weight (ΔBW) or waist circumference (ΔWC), and whether the associations were modified by genetic predisposition to a high BMI, WC or waist-hip ratio adjusted for BMI (WHR_BMI). The study was based on 10,898 individuals from the Danish Inter99, the 1958 British Birth Cohort and the Northern Finland Birth Cohort 1966. We combined 42 adiposity-associated Single Nucleotide Polymorphisms (SNPs) into four scores indicating genetic predisposition to BMI, WC and WHR_BMI, or all three traits combined. Linear regression was used to examine the association between serum 25(OH)D and ΔBW or ΔWC, SNP-score × 25(OH)D interactions were examined, and results from the individual cohorts were meta-analyzed. In the meta-analyses, we found no evidence of an association between 25(OH)D and ΔBW (-9.4 gram/y per 10 nmol/L higher 25(OH)D [95% CI: -23.0, +4.3; P = 0.18]) or ΔWC (-0.06 mm/y per 10 nmol/L higher 25(OH)D [95% CI: -0.17, +0.06; P = 0.33]). Furthermore, we found no statistically significant interactions between the four SNP-scores and 25(OH)D in relation to ΔBW or ΔWC. Thus, in view of the narrow CIs, our results suggest that an association between 25(OH)D and changes in measures of adiposity is absent or marginal. Similarly, the study provided evidence that there is either no or very limited dependence on genetic predisposition to adiposity.

The impact of genetic variants on BMI increase during childhood versus adulthood

BACKGROUND

Genetic variants that predispose individuals to obesity may have differing influences during childhood versus adulthood, and additive effects of such variants are likely to occur. Our ongoing studies to identify genetic determinants of obesity in American Indians have identified 67 single-nucleotide polymorphisms (SNPs) that reproducibly associate with maximum lifetime non-diabetic body mass index (BMI). This study aimed to identify when, during the lifetime, these variants have their greatest impact on BMI increase.

SUBJECTS/METHODS

A total of 5906 Native Americans of predominantly Pima Indian heritage with repeated measures of BMI between the ages of 5 and 45 years were included in this study. The association between each SNP with the rates of BMI increase during childhood (5-19 years) and adulthood (20-45 years) were assessed separately. The significant SNPs were used to calculate a cumulative allelic risk score (ARS) for childhood and adulthood, respectively, to assess the additive effect of these variants within each period of life.

RESULTS

The majority of these SNPs (36 of 67) were associated with rate of BMI increase during childhood (P-value range: 0.00004-0.05), whereas only nine SNPs were associated with rate of BMI change during adulthood (P-value range: 0.002-0.02). These 36 SNPs associated with childhood BMI gain likely had a cumulative effect as a higher childhood-ARS associated with rate of BMI change (β=0.032 kg m(-2) per year per risk allele, 95% confidence interval: 0.027-0.036, P<0.0001), such that at age 19 years, individuals with the highest number of risk alleles had a BMI of 10.2 kg m(-2) greater than subjects with the lowest number of risk alleles.

CONCLUSIONS

Overall, our data indicates that genetic polymorphisms associated with lifetime BMI may influence the rate of BMI increase during different periods in the life course. The majority of these polymorphisms have a larger impact on BMI during childhood, providing further evidence that prevention of obesity will need to begin early in life.

The Impact of Physical Activity and Dietary Measures on the Biochemical and Anthropometric Parameters in Obese Children. Is There Any Genetic Predisposition?

AIM

The aim of the study was to monitor the importance of laboratory, anthropometric and genetic determination of the presence of risk factors for atherosclerosis, obesity, dyslipidemia and components of the metabolic syndrome in obese children and the response to dietary and regimen interventions in obese children.

METHODS

As a part of the study, 353 paediatric patients (46% boys, 54% girls) with obesity and dyslipidemia, aged 8-16 years, participated in a one-month lifestyle intervention programme. The programme involved a reduction of energy intake and supervised exercise programme consisting of 5 exercise units per day, each 50 minutes long. Standard biochemical methods were applied, including Lp-PLA2, as were anthropometric measurements and genetic analyses.

RESULTS

During the reduction programme for the children there was a statistically significant decrease in all anthropometric indicators of bodyweight (p<0.001) as well as in lipid parameters and LpLPA2. Carriers of the FTO GG genotype and/or MC4R CC genotype lost significantly more body weight in comparison to non-carriers.

CONCLUSION

Child obesity is an important social issue. After regimen interventions, there is weight loss as well as an improvement in biochemical parameters. There are individuals with a genetic predisposition for obesity, as well as individuals with a better response to regimen interventions which could, among other things, be determined by the FTO and MC4R genotypes.

New developments in the pathogenesis of obesity-induced hypertension

Obesity is a disorder that develops from the interaction between genotype and environment involving social, behavioral, cultural, and physiological factors. Obesity increases the risk for type 2 diabetes mellitus, hypertension, cardiovascular disease, cancer, musculoskeletal disorders, chronic kidney and pulmonary disease. Although obesity is clearly associated with an increased prevalence of hypertension, many obese individuals may not develop hypertension. Protecting factors may exist and it is important to understand why obesity is not always related to hypertension. The aim of this review is to highlight the knowledge gap for the association between obesity, hypertension, and potential genetic and racial differences or environmental factors that may protect obese patients against the development of hypertension and other co-morbidities. Specific mutations in the leptin and the melaninocortin receptor genes in animal models of obesity without hypertension, the actions of α-melanocyte stimulating hormone, and SNS activity in obesity-related hypertension may promote recognition of protective and promoting factors for hypertension in obesity. Furthermore, gene-environment interactions may have the potential to modify gene expression and epigenetic mechanisms could also contribute to the heritability of obesity-induced hypertension. Finally, differences in nutrition, gut microbiota, exposure to sun light and exercise may play an important role in the presence or absence of hypertension in obesity.

Single Gene and Syndromic Causes of Obesity: Illustrative Examples

Obesity is a significant health problem in westernized societies, particularly in the United States where it has reached epidemic proportions in both adults and children. The prevalence of childhood obesity has doubled in the past 30 years. The causation is complex with multiple sources, including an obesity promoting environment with plentiful highly dense food sources and overall decreased physical activity noted for much of the general population, but genetic factors clearly play a role. Advances in genetic technology using candidate gene approaches, genome-wide association studies, structural and expression microarrays, and next generation sequencing have led to the discovery of hundreds of genes recognized as contributing to obesity. Polygenic and monogenic causes of obesity are now recognized including dozens of examples of syndromic obesity with Prader-Willi syndrome, as a classical example and recognized as the most common known cause of life-threatening obesity. Genetic factors playing a role in the causation of obesity will be discussed along with the growing evidence of single genes and the continuum between monogenic and polygenic obesity. The clinical and genetic aspects of four classical but rare obesity-related syndromes (ie, Prader-Willi, Alström, fragile X, and Albright hereditary osteodystrophy) will be described and illustrated in this review of single gene and syndromic causes of obesity.

Association of FTO and near MC4R variants with obesity measures in urban and rural dwelling Sri Lankans

OBJECTIVES

To investigate the association between the fat mass and obesity related (FTO) gene rs9939609 and near melanocortin-4-receptor (MC4R) gene rs17782313 polymorphisms with obesity measures and metabolic parameters in urban and rural dwelling Sri Lankans.

METHODS

535 subjects (60.9% female) from the general adult population (ages 18-70 years) representative of both urban (28.4%) and rural areas of residence were recruited by multi-stage random sampling. Body mass index (BMI), waist circumference (WC) and waist-to-hip ratio (WHR) was obtained by standard methods. DNA extracted from whole blood was genotyped using real-time PCR.

RESULTS

The FTO risk genotypes (AA+AT) were associated with higher BMI (p=0.03) and WC (p=0.05) measures as well as categorical obesity (BMI ≥27.5kgm^-2 definition) (OR 1.69 95% CI 1.11-2.56, p=0.01). The near MC4R risk genotypes (CC+CT) were associated with greater BMI (p=0.03) as well as categorical obesity (BMI ≥25kgm^-2 definition) (OR 1.57 95% CI 1.11-2.22, p=0.01). In addition the MC4R risk genotype carriers (CC+CT) had significantly higher fasting blood sugar (FBS) levels compared to the 'TT' genotype carriers independent of BMI (p=0.05). Urban living was associated with significantly greater BMI values for FTO risk genotypes compared to rural living (p=0.02).

CONCLUSIONS

FTO and near MC4R variants are associated with obesity measures in Sri Lankan populations whilst urban living accentuates the obesogenic effect of the FTO polymorphism.

Physical activity attenuates genetic effects on BMI: Results from a study of Chinese adult twins

OBJECTIVE

This study aimed to examine the gene-environment interaction of physical activity and body mass index (BMI) using the Chinese National Twin Registry (CNTR).

METHODS

A total of 19,308 same-sex adult twins from CNTR were included in the analysis. Twin zygosity was determined by self-reported questionnaire. Height and weight were measured using self-reported questionnaire. The vigorous physical activity was defined as greater or equal to five times a week of at least 30 min moderate- or high-intensity physical activity. A twin structural equation model was used to analyze the gene-environment interaction of vigorous exercise with BMI among 13,506 monozygotic twins and 5,802 dizygotic twins.

RESULTS

A structural equation model adjusting for age and sex found vigorous exercise significantly moderated the additive genetic effects (P < 0.001) and shared environmental effects (P < 0.001) on BMI. The genetic contributions to BMI were significantly lower for people who adopted a physically active lifestyle [h(2) = 40%, 95% confidence interval (CI): 35%-46%] than those who were relative sedentary (h(2) = 59%, 95% CI: 52%-66%). The observed gene-physical activity interaction was more pronounced in men than women.

CONCLUSIONS

Our results suggested that adopting a physically active lifestyle may help to reduce the genetic influence on BMI among the Chinese population.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

The Geisinger MyCode community health initiative: an electronic health record-linked biobank for precision medicine research

Purpose

Geisinger Health System (GHS) provides an ideal platform for Precision Medicine. Key elements are the integrated health system, stable patient population, and electronic health record (EHR) infrastructure. In 2007 Geisinger launched MyCode^®, a system-wide biobanking program to link samples and EHR data for broad research use.

Methods

Patient-centered input into MyCode^® was obtained using participant focus groups. Participation in MyCode^® is based on opt-in informed consent and allows recontact, which facilitates collection of data not in the EHR, and, since 2013, the return of clinically actionable results to participants. MyCode^® leverages Geisinger’s technology and clinical infrastructure for participant tracking and sample collection.

Results

MyCode^® has a consent rate of >85% with more than 90,000 participants currently, with ongoing enrollment of ~4,000 per month. MyCode^® samples have been used to generate molecular data, including high-density genotype and exome sequence data. Genotype and EHR-derived phenotype data replicate previously reported genetic associations.

Conclusion

The MyCode^® project has created resources that enable a new model for translational research that is faster, more flexible, and more cost effective than traditional clinical research approaches. The new model is scalable, and will increase in value as these resources grow and are adopted across multiple research platforms.

Effects of Obesity Related Genetic Variations on Visceral and Subcutaneous Fat Distribution in a Chinese Population

Genome-wide association studies (GWAS) have uncovered numerous variants associated with body mass index (BMI), waist circumference, and waist-to-hip ratio. Our study aims to investigate how these variants are linked to fat distribution. We genotyped 56 validated variants of BMI, waist circumference, and waist-to-hip ratio in 2958 subjects from Chinese community-based populations and performed linear regression analyses to determine the association with visceral fat area (VFA) and subcutaneous fat area (SFA) imaged by magnetic resonance imaging (MRI). We found rs671 in ALDH2 exhibited the significant associations with VFA and the VFA-SFA ratio in all subjects (P = 9.64 × 10⁻⁵ and 6.54 × 10⁻⁴). rs17782313 near MC4R for VFA and rs4846567 near LYPLAL1 for SFA were found in females only (P = 2.93 × 10⁻⁴ and 0.0015), whereas rs671 in ALDH2 for VFA and the VFA-SFA ratio was restricted to males (P = 1.75 × 10⁻⁸ and 4.43 × 10⁻⁸). Given the robust association of rs671 with alcohol consumption, we next demonstrated the primary effects of rs671 on VFA and the VFA-SFA ratio were restricted to drinkers (P = 1.45 × 10⁻⁴ and 4.65 × 10⁻³). Our data implied that variants of MC4R and LYPLAL1 modulated body fat distribution with sexual dimorphism and that alcohol consumption may mediate the impact of the ALDH2 locus on visceral fat in a Chinese population.

New loci for body fat percentage reveal link between adiposity and cardiometabolic disease risk

To increase our understanding of the genetic basis of adiposity and its links to cardiometabolic disease risk, we conducted a genome-wide association meta-analysis of body fat percentage (BF%) in up to 100,716 individuals. Twelve loci reached genome-wide significance (P<5 × 10(-8)), of which eight were previously associated with increased overall adiposity (BMI, BF%) and four (in or near COBLL1/GRB14, IGF2BP1, PLA2G6, CRTC1) were novel associations with BF%. Seven loci showed a larger effect on BF% than on BMI, suggestive of a primary association with adiposity, while five loci showed larger effects on BMI than on BF%, suggesting association with both fat and lean mass. In particular, the loci more strongly associated with BF% showed distinct cross-phenotype association signatures with a range of cardiometabolic traits revealing new insights in the link between adiposity and disease risk.

Obesity and Cancer: The Oil that Feeds the Flame

Although discussion of the obesity epidemic had become a cocktail party cliché, its impact on public health cannot be dismissed. In the past decade, cancer had joined the list of chronic debilitating diseases whose risk is substantially increased by hypernutrition. Here we discuss recent advances in understanding how obesity increases cancer risk and propose a unifying hypothesis according to which the major tumor-promoting mechanism triggered by hypernutrition is the indolent inflammation that takes place at particular organ sites, including liver, pancreas, and gastrointestinal tract. The mechanisms by which excessive fat deposition feeds this tumor-promoting inflammatory flame are diverse and tissue specific.

The Role of PVH Circuits in Leptin Action and Energy Balance

Although it has been known for more than a century that the brain controls overall energy balance and adiposity by regulating feeding behavior and energy expenditure, the roles for individual brain regions and neuronal subtypes were not fully understood until recently. This area of research is active, and as such our understanding of the central regulation of energy balance is continually being refined as new details emerge. Much of what we now know stems from the discoveries of leptin and the hypothalamic melanocortin system. Hypothalamic circuits play a crucial role in the control of feeding and energy expenditure, and within the hypothalamus, the arcuate nucleus (ARC) functions as a gateway for hormonal signals of energy balance, such as leptin. It is also well established that the ARC is a primary residence for hypothalamic melanocortinergic neurons. The paraventricular hypothalamic nucleus (PVH) receives direct melanocortin input, along with other integrated signals that affect energy balance, and mediates the majority of hypothalamic output to control both feeding and energy expenditure. Herein, we review in detail the structure and function of the ARC-PVH circuit in mediating leptin signaling and in regulating energy balance.

The prevalence of melanocortin-4 receptor gene mutations in Slovak obese children and adolescents

Melanocortin-4 receptor (MC4R) deficiency is the most frequent monogenic form of obesity. The contribution of MC4R mutations to the Slovak population has not been investigated as yet. We screened the coding sequence of the MC4R gene in a cohort of 210 Slovak obese children and adolescents. We identified four different mutations in four patients, giving a mutation detection rate of 0.95%. Of these, three were missense mutations previously identified and characterized by other research groups (p.R7C, p.S127L and p. R305W, respectively). One was a novel nonsense mutation p.W174* detected in a severely obese 7-year-old boy. This mutation was further analyzed in family segregation analysis and exhibited variable penetrance. Two known amino acid polymorphisms (p.V103I and p.I251L) were also identified in seven subjects of our cohort group. We also performed multifactorial statistical analysis to determine the influence of genotypes on standard biochemical blood markers. No significant influence was observed in carriers of DNA variants on tested parameters. We conclude that rare heterozygous MC4R mutations contribute to the onset of obesity only in a few cases in the Slovak population.

Metabolic signals in sleep regulation: recent insights

Sleep and energy balance are essential for health. The two processes act in concert to regulate central and peripheral homeostasis. During sleep, energy is conserved due to suspended activity, movement, and sensory responses, and is redirected to restore and replenish proteins and their assemblies into cellular structures. During wakefulness, various energy-demanding activities lead to hunger. Thus, hunger promotes arousal, and subsequent feeding, followed by satiety that promotes sleep via changes in neuroendocrine or neuropeptide signals. These signals overlap with circuits of sleep-wakefulness, feeding, and energy expenditure. Here, we will briefly review the literature that describes the interplay between the circadian system, sleep-wake, and feeding-fasting cycles that are needed to maintain energy balance and a healthy metabolic profile. In doing so, we describe the neuroendocrine, hormonal/peptide signals that integrate sleep and feeding behavior with energy metabolism.

Evaluation of the Obesity Genes FTO and MC4R for Contribution to the Risk of Large Artery Atherosclerotic Stroke in a Chinese Population

BACKGROUND

Obesity is a well-established risk factor for large artery atherosclerotic (LAA) stroke. The aim of the study was to explore whether obesity genes, such as MC4R and FTO, contribute to LAA stroke risk in the Chinese Han population.

METHODS

322 LAA stroke patients and 473 controls were recruited. Gene polymorphism of MC4R (rs17782313) and FTO (rs8050136 and rs9939609) were genotyped.

RESULTS

No differences were observed in genotype frequencies of variants of FTO (rs8050136 and rs9939609) or MC4R (rs17782313) between LAA stroke patients and control subjects. However, rs17782313 of the MC4R gene was associated with LAA stroke susceptibility in smokers (rs17782313: p = 0.020, OR (95% CI) = 1.55 (1.07-2.23)) in the stratified analysis. Furthermore, multifactor dimensionality reduction analysis revealed that the combination of MC4R variant (rs17782313), hypertension and smoking habit was significantly associated with increased risk of LAA stroke (p < 0.0001, OR (95% CI) = 6.57 (4.79-9.01)).

CONCLUSION

Our study indicated that the synergistic effects of MC4R variants, hypertension, and smoking habit contribute significantly to the risk of LAA stroke in the Chinese Han population. The finding revealed that obesity gene MC4R contribute to the risk of LAA stroke via a synergistic mechanism, which will provide new insight into the genetic architecture of LAA stroke.

Genetic and phenotypic variation in UGT2B17, a testosterone-metabolizing enzyme, is associated with BMI in males

OBJECTIVE

A number of candidate gene and genome-wide association studies have identified significant associations between single nucleotide polymorphisms, particularly in FTO and MC4R, and body weight. However, the association between copy number variation and body weight is less understood. Anabolic androgenic steroids, such as testosterone, can regulate body weight. In humans, UDP-glucuronosyltransferase 2B17 (UGT2B17) metabolizes testosterone to a metabolite, which is readily excreted in urine. We investigate the association between genetic and phenotypic variation in UGT2B17 and body weight.

MATERIALS AND METHODS

UGT2B17 deletion was genotyped and in-vivo UGT2B17 enzymatic activity (as measured by the 3-hydroxycotinine glucuronide to free 3-hydroxycotinine ratio) was measured in 400 Alaska Native individuals and 540 African Americans.

RESULTS

In Alaska Native people, UGT2B17 deletion was strongly associated with lower BMI in male individuals (P<0.001), but not in female individuals, consistent with testosterone being a male dominant steroid. The sex-specific association between UGT2B17 deletion and lower BMI was also observed in African Americans (P=0.01 in male individuals). In both populations, UGT2B17 deletion was significantly associated with lower measured in-vivo UGT2B17 activity. In male individuals, lower in-vivo UGT2B17 activity was associated with lower BMI, as observed in the sex-specific genotypic association.

CONCLUSION

These data suggest that UGT2B17 deletion leads to reduced UGT2B17 activity, and lower BMI in male individuals. This is consistent with the hypothesis that reduced UGT2B17-mediated testosterone excretion results in higher testosterone levels. Future studies could confirm this hypothesis by directly measuring serum testosterone levels.

Genome-wide association studies of human adiposity: Zooming in on synapses

The decade anniversary for genome-wide association studies (GWAS) is approaching, and this experimental approach has commenced a deeper understanding of the genetics underlying complex diseases. In obesity genetics the GIANT (Genetic Investigation of ANthropometric Traits) consortium has played a crucial role, recently with two comprehensive meta-analyses, one focusing on general obesity, analyzing body-mass index (BMI) and the other on fat distribution, focusing on waist-hip ratio adjusted for BMI. With the in silico methods applied in these two studies as the pivot, this review looks into some of the biological knowledge, beginning to emerge from the intricate genomic background behind the genetic determinants of human adiposity. These include synaptic dysfunction, where GWAS pinpoint potential new mechanisms in pathways already known to be linked with obesity.

Hypothalamic carnitine metabolism integrates nutrient and hormonal feedback to regulate energy homeostasis

The maintenance of energy homeostasis requires the hypothalamic integration of nutrient feedback cues, such as glucose, fatty acids, amino acids, and metabolic hormones such as insulin, leptin and ghrelin. Although hypothalamic neurons are critical to maintain energy homeostasis research efforts have focused on feedback mechanisms in isolation, such as glucose alone, fatty acids alone or single hormones. However this seems rather too simplistic considering the range of nutrient and endocrine changes associated with different metabolic states, such as starvation (negative energy balance) or diet-induced obesity (positive energy balance). In order to understand how neurons integrate multiple nutrient or hormonal signals, we need to identify and examine potential intracellular convergence points or common molecular targets that have the ability to sense glucose, fatty acids, amino acids and hormones. In this review, we focus on the role of carnitine metabolism in neurons regulating energy homeostasis. Hypothalamic carnitine metabolism represents a novel means for neurons to facilitate and control both nutrient and hormonal feedback. In terms of nutrient regulation, carnitine metabolism regulates hypothalamic fatty acid sensing through the actions of CPT1 and has an underappreciated role in glucose sensing since carnitine metabolism also buffers mitochondrial matrix levels of acetyl-CoA, an allosteric inhibitor of pyruvate dehydrogenase and hence glucose metabolism. Studies also show that hypothalamic CPT1 activity also controls hormonal feedback. We hypothesis that hypothalamic carnitine metabolism represents a key molecular target that can concurrently integrate nutrient and hormonal information, which is critical to maintain energy homeostasis. We also suggest this is relevant to broader neuroendocrine research as it predicts that hormonal signaling in the brain varies depending on current nutrient status. Indeed, the metabolic action of ghrelin, leptin or insulin at POMC or NPY neurons may depend on appropriate nutrient-sensing in these neurons and we hypothesize carnitine metabolism is critical in the integrative processing. Future research is required to examine the neuron-specific effects of carnitine metabolism on concurrent nutrient- and hormonal-sensing in AgRP and POMC neurons.

Recent Progress in the Understanding of Obesity: Contributions of Genome-Wide Association Studies

Since 2007, discovery of genetic variants associated with general obesity and fat distribution has advanced tremendously through genome-wide association studies (GWAS). Currently, the number of robustly associated loci is 190. Even though these loci explain <3 % of the variance, they have provided us a still emerging picture of genomic localization, frequency and effect size spectra, and hints of functional implications. The translation into biological knowledge has turned out to be an immense task. However, in silico enrichment analyses of genes involved in specific pathways or expressed in specific tissues have the power to suggest biological mechanisms underlying obesity. Inspired by this, we highlight genes in five loci potentially mechanistically linked to leptin-receptor trafficking and signaling in primary cilia. The clinical application of genetic knowledge as prediction, prevention, or treatment strategies is unfortunately still far from reality. Thus, despite major advances, further research is warranted to solve one of the greatest health problems in modern society.

The Genetics of Pediatric Obesity

Obesity among children and adults has notably escalated over recent decades and represents a global major health problem. We now know that both genetic and environmental factors contribute to its complex etiology. Genome-wide association studies (GWAS) have revealed compelling genetic signals influencing obesity risk in adults. Recent reports for childhood obesity revealed that many adult loci also play a role in the pediatric setting. Childhood GWAS have uncovered novel loci below the detection range in adult studies, suggesting that obesity genes may be more easily uncovered in the pediatric setting. Shedding light on the genetic architecture of childhood obesity will facilitate the prevention and treatment of pediatric cases, and will have fundamental implications for diseases that present later in life.

Interaction of smoking and obesity susceptibility loci on adolescent BMI: The National Longitudinal Study of Adolescent to Adult Health

BACKGROUND

Adolescence is a sensitive period for weight gain and risky health behaviors, such as smoking. Genome-wide association studies (GWAS) have identified loci contributing to adult body mass index (BMI). Evidence suggests that many of these loci have a larger influence on adolescent BMI. However, few studies have examined interactions between smoking and obesity susceptibility loci on BMI. This study investigates the interaction of current smoking and established BMI SNPs on adolescent BMI. Using data from the National Longitudinal Study of Adolescent to Adult Health, a nationally-representative, prospective cohort of the US school-based population in grades 7 to 12 (12-20 years of age) in 1994-95 who have been followed into adulthood (Wave II 1996; ages 12-21, Wave III; ages 18-27), we assessed (in 2014) interactions of 40 BMI-related SNPs and smoking status with percent of the CDC/NCHS 2000 median BMI (%MBMI) in European Americans (n = 5075), African Americans (n = 1744) and Hispanic Americans (n = 1294).

RESULTS

Two SNPs showed nominal significance for interaction (p < 0.05) between smoking and genotype with %MBMI in European Americans (EA) (rs2112347 (POC5): β = 1.98 (0.06, 3.90), p = 0.04 and near rs571312 (MC4R): β 2.15 (-0.03, 4.33) p = 0.05); and one SNP showed a significant interaction effect after stringent correction for multiple testing in Hispanic Americans (HA) (rs1514175 (TNNI3K): β 8.46 (4.32, 12.60), p = 5.9E-05). Stratifying by sex, these interactions suggest a stronger effect in female smokers.

CONCLUSIONS

Our study highlights potentially important sex differences in obesity risk by smoking status in adolescents, with those who may be most likely to initiate smoking (i.e., adolescent females), being at greatest risk for exacerbating genetic obesity susceptibility.

Practical Experience of the Application of a Weighted Burden Test to Whole Exome Sequence Data for Obesity and Schizophrenia

For biological and statistical reasons it makes sense to combine information from variants at the level of the gene. One may wish to give more weight to variants which are rare and those that are more likely to affect function. A combined weighting scheme, implemented in the SCOREASSOC program, was applied to whole exome sequence data for 1392 subjects with schizophrenia and 982 with obesity from the UK10K project. Results conformed fairly well with null hypothesis expectations and no individual gene was strongly implicated. However, a number of the higher ranked genes appear plausible candidates as being involved in one or other phenotype and may warrant further investigation. These include MC4R, NLGN2, CRP, DONSON, GTF3A, IL36B, ADCYAP1R1, ARSA, DLG1, SIK2, SLAIN1, UBE2Q2, ZNF507, CRHR1, MUSK, NSF, SNORD115, GDF3 and HIBADH. Some individual variants in these genes have different frequencies between cohorts and could be genotyped in additional subjects. For other genes, there is a general excess of variants at many different sites so attempts at replication would be more difficult. Overall, the weighted burden test provides a convenient method for using sequence data to highlight genes of interest.

Obesity-Related Genetic Variants and their Associations with Physical Activity

BACKGROUND

Meta-analysis of genome-wide association studies identified obesity-related genetic variants. Due to the pleiotropic effects of related phenotypes, we tested six of these obesity-related genetic variants for their association with physical activity: fat mass and obesity-associated (FTO)(rs9939609)T>A, potassium channel tetramerization domain containing (KCTD15) (rs11084753)G>A, melanocortin receptor4 (MC4R)(rs17782313)T>C, neuronal growth regulator 1 (NEGR1)(rs2815752)A>G, SH2B adapter protein 1 (SH2B1)(rs7498665)A>G, and transmembrane protein18 (TMEM18)(rs6548238)C>T.

METHOD

European-American women (n = 263) and men (n = 229) (23.5 ± 0.3 years, 24.6 ± 0.2 kg/m2) were genotyped and completed the Paffenbarger physical activity Questionnaire. Physical activity volume in metabolic energy equivalents [MET]-hour/week was derived from the summed time spent (hour/week) times the given MET value for vigorous, moderate, and light intensity physical activity, and sitting and sleeping, respectively. Multivariable adjusted [(age, sex, and body mass index (BMI)] linear regression tested associations among genotype (dominant/recessive model) and the log of physical activity volume.

RESULT

MC4R (rs17782313)T>C explained 1.1 % (p = 0.02), TMEM18(rs6548238)C>T 1.2 % (p = 0.01), and SH2B1 (rs7498665)A>G 0.6 % (p = 0.08) of the variability in physical activity volume. Subjects with the MC4R C allele spent 3.5 % less MET-hour/week than those with the TT genotype (p = 0.02). Subjects with the TMEM18 T allele spent 4.1 % less MET-hour/week than those with the CC genotype (p = 0.01). Finally, subjects with the SH2B1 GG genotype spent 3.6 % less MET-hour/week than A allele carriers (p = 0.08).

CONCLUSION

Our findings suggest a shared genetic influence among some obesity-related gene loci and physical activity phenotypes that should be explored further. Physical activity volume differences by genotype have public health importance equating to 11-13 lb weight difference annually.

Many obesity-associated SNPs strongly associate with DNA methylation changes at proximal promoters and enhancers

BACKGROUND

The mechanisms by which genetic variants, such as single nucleotide polymorphisms (SNPs), identified in genome-wide association studies act to influence body mass remain unknown for most of these SNPs, which continue to puzzle the scientific community. Recent evidence points to the epigenetic and chromatin states of the genome as having important roles.

METHODS

We genotyped 355 healthy young individuals for 52 known obesity-associated SNPs and obtained DNA methylation levels in their blood using the Illumina 450 K BeadChip. Associations between alleles and methylation at proximal cytosine residues were tested using a linear model adjusted for age, sex, weight category, and a proxy for blood cell type counts. For replication in other tissues, we used two open-access datasets (skin fibroblasts, n = 62; four brain regions, n = 121-133) and an additional dataset in subcutaneous and visceral fat (n = 149).

RESULTS

We found that alleles at 28 of these obesity-associated SNPs associate with methylation levels at 107 proximal CpG sites. Out of 107 CpG sites, 38 are located in gene promoters, including genes strongly implicated in obesity (MIR148A, BDNF, PTPMT1, NR1H3, MGAT1, SCGB3A1, HOXC12, PMAIP1, PSIP1, RPS10-NUDT3, RPS10, SKOR1, MAP2K5, SIX5, AGRN, IMMP1L, ELP4, ITIH4, SEMA3G, POMC, ADCY3, SSPN, LGR4, TUFM, MIR4721, SULT1A1, SULT1A2, APOBR, CLN3, SPNS1, SH2B1, ATXN2L, and IL27). Interestingly, the associated SNPs are in known eQTLs for some of these genes. We also found that the 107 CpGs are enriched in enhancers in peripheral blood mononuclear cells. Finally, our results indicate that some of these associations are not blood-specific as we successfully replicated four associations in skin fibroblasts.

CONCLUSIONS

Our results strongly suggest that many obesity-associated SNPs are associated with proximal gene regulation, which was reflected by association of obesity risk allele genotypes with differential DNA methylation. This study highlights the importance of DNA methylation and other chromatin marks as a way to understand the molecular basis of genetic variants associated with human diseases and traits.

Intelligence: shared genetic basis between Mendelian disorders and a polygenic trait

Multiple inquiries into the genetic etiology of human traits indicated an overlap between genes underlying monogenic disorders (eg, skeletal growth defects) and those affecting continuous variability of related quantitative traits (eg, height). Extending the idea of a shared genetic basis between a Mendelian disorder and a classic polygenic trait, we performed an association study to examine the effect of 43 genes implicated in autosomal recessive cognitive disorders on intelligence in an unselected Dutch population (N=1316). Using both single-nucleotide polymorphism (SNP)- and gene-based association testing, we detected an association between intelligence and the genes of interest, with genes ELP2, TMEM135, PRMT10, and RGS7 showing the strongest associations. This is a demonstration of the relevance of genes implicated in monogenic disorders of intelligence to normal-range intelligence, and a corroboration of the utility of employing knowledge on monogenic disorders in identifying the genetic variability underlying complex traits.

Insights into the Genetic Susceptibility to Type 2 Diabetes from Genome-Wide Association Studies of Obesity-Related Traits

Obesity and type 2 diabetes (T2D) are common and complex metabolic diseases, which are caused by an interchange between environmental and genetic factors. Recently, a number of large-scale genome-wide association studies (GWAS) have improved our knowledge of the genetic architecture and biological mechanisms of these diseases. Currently, more than ~250 genetic loci have been found for monogenic, syndromic, or common forms of T2D and/or obesity-related traits. In this review, we discuss the implications of these GWAS for obesity and T2D, and investigate the overlap of loci for obesity-related traits and T2D, highlighting potential mechanisms that affect T2D susceptibility.

Can metabolically healthy obesity be explained by diet, genetics, and inflammation?

A substantial proportion of obese individuals do not present cardiometabolic complications such as diabetes, hypertension, or dyslipidemia. Some, but not all, prospective studies observe similar risk of cardiovascular events and all-cause mortality among individuals with this so-called "metabolically healthy obese" (MHO) phenotype, compared to the metabolically healthy normal weight or metabolically healthy non-obese phenotypes. Compared to the metabolically unhealthy obese (MUO) phenotype, MHO is often characterized by a more favorable inflammatory profile, less visceral fat, less infiltration of macrophages into adipose tissue, and smaller adipocyte cell size. Tipping the inflammation balance in adipose tissue might be particularly important for metabolic health in the obese. While the potential role of genetic predisposition or lifestyle factors such as diet in the MHO phenotype is yet to be clarified, it is well known that diet affects inflammation profile and contributes to the functionality of adipose tissue. This review will discuss genetic predisposition and the molecular mechanisms underlying the potential effect of food on the development of the metabolic phenotype characteristic of obesity.