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

FTO Obesity Variant Circuitry and Adipocyte Browning in Humans

BACKGROUND

Genomewide association studies can be used to identify disease-relevant genomic regions, but interpretation of the data is challenging. The FTO region harbors the strongest genetic association with obesity, yet the mechanistic basis of this association remains elusive.

METHODS

We examined epigenomic data, allelic activity, motif conservation, regulator expression, and gene coexpression patterns, with the aim of dissecting the regulatory circuitry and mechanistic basis of the association between the FTO region and obesity. We validated our predictions with the use of directed perturbations in samples from patients and from mice and with endogenous CRISPR-Cas9 genome editing in samples from patients.

RESULTS

Our data indicate that the FTO allele associated with obesity represses mitochondrial thermogenesis in adipocyte precursor cells in a tissue-autonomous manner. The rs1421085 T-to-C single-nucleotide variant disrupts a conserved motif for the ARID5B repressor, which leads to derepression of a potent preadipocyte enhancer and a doubling of IRX3 and IRX5 expression during early adipocyte differentiation. This results in a cell-autonomous developmental shift from energy-dissipating beige (brite) adipocytes to energy-storing white adipocytes, with a reduction in mitochondrial thermogenesis by a factor of 5, as well as an increase in lipid storage. Inhibition of Irx3 in adipose tissue in mice reduced body weight and increased energy dissipation without a change in physical activity or appetite. Knockdown of IRX3 or IRX5 in primary adipocytes from participants with the risk allele restored thermogenesis, increasing it by a factor of 7, and overexpression of these genes had the opposite effect in adipocytes from nonrisk-allele carriers. Repair of the ARID5B motif by CRISPR-Cas9 editing of rs1421085 in primary adipocytes from a patient with the risk allele restored IRX3 and IRX5 repression, activated browning expression programs, and restored thermogenesis, increasing it by a factor of 7.

CONCLUSIONS

Our results point to a pathway for adipocyte thermogenesis regulation involving ARID5B, rs1421085, IRX3, and IRX5, which, when manipulated, had pronounced pro-obesity and anti-obesity effects. (Funded by the German Research Center for Environmental Health and others.).

Differences in Weight Loss Between Persons on Standard Balanced vs Nutrigenetic Diets in a Randomized Controlled Trial

BACKGROUND & AIMS

Many companies provide genetic tests for obesity-related polymorphisms (nutrigenetics) and make dietary recommendations for weight loss that are based on the results. We performed a randomized controlled trial to determine whether more participants who followed a nutrigenetic-guided diet lost ≥5% of their body weight than participants on a standard balanced diet for 8 and 24 weeks.

METHODS

We performed a prospective study of 51 obese or overweight U.S. veterans on an established weight management program at the Veterans Administration San Diego Healthcare System (the MOVE! program). Participants were randomly assigned to groups placed on a nutrigenetic-guided diet (balanced, low-carbohydrate, low-fat, or Mediterranean; n = 30) or a standard balanced diet (n = 21). Nutrigenetic diets were selected on the basis of results from the Pathway FIT test.

RESULTS

There was no significant difference in the percentage of participants on the balanced diet vs the nutrigenetic-guided diet who lost 5% of their body weight at 8 weeks (35.0% ± 20.9% vs 26.9% ± 17.1%, respectively; P = .28) or at 24 weeks. Both groups had difficulty adhering to the diets. However, adherence to the nutrigenetic-guided diet correlated with weight loss (r = 0.74; P = 4.0 × 10(-5)), but not adherence to standard therapy (r = 0.34; P = .23). Participants who had low-risk polymorphisms for obesity lost more weight than all other participants at 8 weeks (5.0% vs 2.9%, respectively; P = .02) and had significantly greater reductions in body mass index (6.4% vs 3.6%, respectively; P = .03) and waist circumference (6.5% vs 2.6%, respectively; P = .02) at 24 weeks.

CONCLUSIONS

In a prospective study, a nutrigenetic-based diet did not increase weight loss compared with a standard balanced diet. However, genetic features can identify individuals most likely to benefit from a balanced diet weight loss strategy; these findings require further investigation. ClinicalTrials.gov number: NCT01859403.

Genome-wide association study identifies common variants associated with pharmacokinetics of psychotropic drugs

Individual variation in pharmacokinetics of psychotropic drugs, particularly metabolism, is an important factor to consider in pharmacological treatment in psychiatry. A large proportion of this variance is still not accounted for, but evidence so far suggests the involvement of genetic factors. We performed a genome-wide association study (GWAS) with concentration dose ratio (CDR) as sub-phenotype to assess metabolism rate of psychotropic drugs in a homogenous Norwegian sample of 1334 individuals diagnosed with a severe mental disorder. The GWAS revealed one genome-wide significant marker (rs16935279, p-value=3.95×10(-10), pperm=7.5×10(-4)) located in an intronic region of the lncRNA LOC100505718. Carriers of the minor allele have a lower metabolism rate of antiepileptic drugs compared to major allele carriers. In addition, several nominally significant associations between single nucleotide polymorphisms (SNPs) and CDR for antipsychotic, antidepressant and antiepileptic drugs were disclosed. We consider standardised CDR to be a useful measure of the metabolism rate of a drug. The present findings indicate that common gene variants could affect the metabolism of psychotropic drugs. This warrants further investigations into the functional mechanisms involved as it may lead to identification of predictive markers as well as novel drug targets.

Associations between a common variant near the MC4R gene and serum triglyceride levels in an obese pediatric cohort

Polymorphisms near the MC4R gene may be related to an increased risk for obesity, but studies of variations in this gene and its relation to cardiometabolic profiles and food intake are scarce and controversial. The aim of this study is to evaluate the influence of the variants rs12970134 and rs17782313 near the MC4R gene in food intake, binge eating (BE) behavior, anthropometric parameters, body composition, metabolic profile, and cardiometabolic risk factors in obese children and adolescents. This is a cross-sectional study that included obese children and adolescents. We evaluated anthropometric, metabolic parameters and cardiometabolic risk factors, including hypertension, impaired fasting glucose, hypertriglyceridemia, and low HDL-cholesterol. BE was assessed through the BE scale, and a 24-h recall was used to evaluate total caloric intake and percentage of macronutrients and types of dietary fat. The MC4R variants rs12970134 and rs17782313 were genotyped using TaqMan assay. To assess the magnitude of risk, a logistic regression adjusted for Z-BMI, age, and gender was performed, adopting the significance level of 0.05. The study included 518 subjects (52.1 % girls, 12.7 ± 2.7 years old, Z-BMI = 3.24 ± 0.57). Carriers of the variant rs17782313 exhibit increased triglyceride levels (108 ± 48 vs. 119 ± 54, p = 0.034) and an increased risk of hypertriglyceridemia (OR 1.985, 95 % CI 1.288-3.057, p = 0.002). There was no association of the SNP rs12970134 with clinical, metabolic, or nutritional parameters. The variant rs12970134 and rs17782313 did not influence food intake or the presence of BE. The variant rs17782313 is associated with an increased risk of hypertriglyceridemia in obese children and adolescents.

Lifetime Socioeconomic Status, Historical Context, and Genetic Inheritance in Shaping Body Mass in Middle and Late Adulthood

This study demonstrates body mass in middle and late adulthood as a consequence of the complex interplay among individuals' genes, lifetime socioeconomic experiences, and the historical context in which they live. Drawing on approximately 9,000 genetic samples from the Health and Retirement Study, we first investigate how socioeconomic status (SES) over the life course moderates the impact of 32 established obesity-related genetic variants on body mass index (BMI) in middle and late adulthood. Further, we consider differences across birth cohorts in the genetic influence on BMI and cohort variations in the moderating effects of life-course SES on the genetic influence. Our analyses suggest that persistently low SES over the life course or downward mobility (e.g., high SES in childhood but low SES in adulthood) amplified the genetic influence on BMI, while persistently high SES or upward mobility (e.g., low SES in childhood but high SES in adulthood) compensated for such influence. For more recent birth cohorts, while the genetic influence on BMI became stronger, the moderating effects of lifetime SES on the genetic influence were weaker compared to earlier cohorts. We discuss these findings in light of social changes during the obesity epidemic in the United States.

Variants in the Atherogenic ALOX5AP, THBD, and KNG1 Genes Potentiate the Risk of Ischemic Stroke via a Genetic Main Effect and Epistatic Interactions in a Chinese Population

BACKGROUND

Ischemic stroke (IS) is a multifactorial disease that displays a strong genetic predisposition. However, the genetic architecture of IS has yet to be fully elucidated. It was hypothesized that epistasis between genes in multiple atherothrombotic pathways may play a vital role in determining the susceptibility to IS. The aim of the present study was to investigate the contributions of the hypothesized genetic factors to IS and the interactions between these genetic factors in a Chinese population.

METHODS

In this study, 351 cases with IS and 417 control subjects from a Chinese population were genotyped for single-nucleotide polymorphisms (SNPs) in 12 genes hypothesized to be involved in atherosclerosis, coagulation, and related pathways. We examined SNP main effects and epistatic interactions between these polymorphic loci.

RESULTS

rs710446 of the KNG1 gene was associated with IS susceptibility based on an additive genetic model (rs710446: P = .012; odds ratio [OR], 1.247; 95% confidence interval [CI], 1.050-1.481) after adjusting for covariates. Furthermore, an epistatic interaction between the ALOX5AP, THBD, and KNG1 gene was also identified in association with stroke susceptibility (P < .001 after 1000 permutations). Based on the chi-squared test, the OR of the high-risk combination of the three-locus model increased the risk of IS by 2.53-fold (95% CI, 1.60-4.01; P < .0001).

CONCLUSIONS

Our findings support the association of the epistatic interactions of ALOX5AP, THBD, and KNG1 and present novel evidence for the main effect of KNG1 gene on IS susceptibility, suggesting a modulation of stroke risk by a genetic main effect and gene-gene interactions.

Effects of genetic variants for the swine FABP3, HMGA1, MC4R, IGF2, and FABP4 genes on fatty acid composition

This study aimed to verify genetic relationships between fatty acid composition (FAC) and genotypes of several genes (FABP3, HMGA1, MC4R, IGF2, and FABP4) using pig breeds. The effects of genetic variations on FAC of the longissimus muscle were statistically significant with additive and dominance effects. The polymorphisms of FABP3 and IGF2 had the largest effects on stearic (C18:0, P=0.009) and γ-linoleic (C18:3n6, P=0.039) acids, respectively, whereas HMGA1 and FABP4 did not show significances. The analysis revealed that MC4R was significantly associated with palmitoleic acid (C16:ln7) and MUFA. Allele frequencies of the genes examined in this analysis were significantly skewed or fixed in the Korean native pig (KNP), whereas the allele frequencies of the crossbreds tended to fall between those of the purebreds except that HMGA1 and FABP4 had approximately the same allele frequencies with Duroc and KNP, respectively. The polymorphisms found in this study could be used as genetic markers in breeding programs to simultaneously change proportions of fatty acids in muscle tissues.

Melanocortin receptor accessory proteins in adrenal disease and obesity

Melanocortin receptor accessory proteins (MRAPs) are regulators of the melanocortin receptor family. MRAP is an essential accessory factor for the functional expression of the MC2R/ACTH receptor. The importance of MRAP in adrenal gland physiology is demonstrated by the clinical condition familial glucocorticoid deficiency type 2. The role of its paralog melanocortin-2-receptor accessory protein 2 (MRAP2), which is predominantly expressed in the hypothalamus including the paraventricular nucleus, has recently been linked to mammalian obesity. Whole body deletion and targeted brain specific deletion of the Mrap2 gene result in severe obesity in mice. Interestingly, Mrap2 complete knockout (KO) mice have increased body weight without detectable changes to food intake or energy expenditure. Rare heterozygous variants of MRAP2 have been found in humans with severe, early-onset obesity. In vitro data have shown that Mrap2 interaction with the melanocortin-4-receptor (Mc4r) affects receptor signaling. However, the mechanism by which Mrap2 regulates body weight in vivo is not fully understood and differences between the phenotypes of Mrap2 and Mc4r KO mice may point toward Mc4r independent mechanisms.

Interaction between common variants of FTO and MC4R is associated with risk of PCOS

BACKGROUND

Polycystic ovary syndrome (PCOS) is a common and complex endocrine-metabolic disease. One of the well-documented characteristics of PCOS is obesity or overweightness. It is possible to be genetically predisposed to becoming obese or overweight, and several potentially causative single nucleotide polymorphisms (SNPs), such as rs9939609 (A/T) in the fat mass, and obesity-associated gene (FTO) and rs17782313 (T/C) in the melanocortin-4 receptor gene (MC4R), have been investigated. Further investigation of association between obesity-associated SNPs and PCOS susceptibility will contribute to a better understanding of the disease.

METHODS

In the present study, we enrolled 733 patients with PCOS and 892 control subjects. The common variants FTO rs9939609 and MC4R rs17782313 were genotyped and their relationship with obesity-related traits was evaluated.

RESULTS

Rs9939609 and rs17782313 are associated with PCOS and obesity-related traits and profiles. The association found between PCOS and FTO rs9939609 (p=0.0302) was attenuated after adjustment for BMI (p=0.187). MC4R rs17782313 did not confer an increased risk for PCOS (p=0.368) even after adjustments (p=0.715). Interestingly, the interaction of FTO and MC4R polymorphisms was more significantly associated with PCOS (p=0.031, adjusted for age and BMI). The FTO variant rs9939609 is associated with Chinese women with PCOS; however, this association is affected by BMI.

CONCLUSIONS

The combined pathogenic effect of FTO and MC4R polymorphisms indicates a direct role of the interaction between FTO and MC4R polymorphisms in the development of PCOS.

Metabolic side effects and pharmacogenetics of second-generation antipsychotics in children

Second-generation antipsychotics (SGAs) are increasingly being used to treat children for a range of mental health conditions, for example, anxiety disorder, attention deficit hyperactivity disorder and bipolar disorder. SGA treatment is associated with weight gain and cardiometabolic side effects such as dyslipidemia, insulin resistance and elevated blood pressure, in some, but not all children. This review provides an overview of the potential role of pharmacogenomics in predisposing a child to unhealthy weight gain and cardiometabolic side effects with SGA treatment. Specifically, the review includes a synopsis of the evidence for cardiometabolic side effects in SGA-treated children, illustrating the extent and depth of the problem; summarizes the potential long-term consequences of developing cardiometabolic risk during childhood and highlights genetic variants that may be useful in predicting cardiometabolic side effects in SGA-treated children.

The hunger genes: pathways to obesity

The global rise in the prevalence of obesity and associated co-morbidities such as type 2 diabetes, cardiovascular disease, and cancer represents a major public health concern. The biological response to increased consumption of palatable foods or a reduction in energy expenditure is highly variable between individuals. A more detailed mechanistic understanding of the molecular, physiological, and behavioral pathways involved in the development of obesity in susceptible individuals is critical for identifying effective mechanism-based preventative and therapeutic interventions.

Association between rs12970134 Near MC4R and adiposity indexes in a homogenous population of Caucasian schoolchildren

BACKGROUND

To assess whether previously identified obesity-susceptibility loci were associated with overweight/obesity risk in a homogeneous population of Caucasian schoolchildren and whether these associations varied with age.

METHODS

Seven hundred and forty-five schoolchildren (353 boys, mean age: 8.3 ± 1.4 years) underwent anthropometric assessments. A saliva sample was collected for DNA extraction and assessment of 19 single-nucleotide polymorphisms previously associated with obesity.

RESULTS

Only the rs12970134 in the MC4R gene was significantly associated with overweight/obesity risk, with a higher frequency of the AA risk genotype in children with a BMI >85th (8.3%) than in those with a BMI <85th percentile (3.0%), p = 0.001; odds ratio (95% CI) of 1.544 (1.192-1.998), p = 0.001, after adjusting for age, sex and pubertal stage. BMI standard deviation scores (SDS) and waist-to-height ratio (W/Hr) progressively increased across the rs12970134 genotypes (GG vs. AG vs. AA): BMI SDS, p = 0.004; W/Hr, p = 0.009. When dividing the study population into two groups based on the median age of participants (8.3 years), the differences in BMI SDS and W/Hr across the MC4R genotypes persisted only in children older than 8.3 years.

CONCLUSIONS

In a population of Caucasian schoolchildren, the rs12970134 MC4R variant was significantly associated with excess body weight, particularly in children older than 8 years of age.

New targets to treat obesity and the metabolic syndrome

Metabolic syndrome (MetS) is a cluster ofassociated metabolic traits that collectively confer unsurpassed risk for development of cardiovascular disease (CVD) and type 2 diabetes compared to any single CVD risk factor. Truncal obesity plays an exceptionally critical role among all metabolic traits of the MetS. Consequently, the prevalence of the MetS has steadily increased with the growing epidemic of obesity. Pharmacotherapy has been available for obesity for more than one decade, but with little success in improving the metabolic profiles. The serotonergic drugs and inhibitors of pancreatic lipases were among the few drugs that were initially approved to treat obesity. At the present time, only the pancreatic lipase inhibitor orlistat is approved for long-term treatment of obesity. New classes of anti-diabetic drugs, including glucagon-like peptide 1 receptor (GLP-1R) agonists and Dipeptidyl-peptidase IV (DPP-IV) inhibitors, are currently being evaluated for their effects on obesity and metabolic traits. The genetic studies of obesity and metabolic syndrome have identified novel molecules acting on the hunger and satiety peptidergic signaling of the gut-hypothalamus axis or the melanocortin system of the brain and are promising targets for future drug development. The goal is to develop drugs that not only treat obesity, but also favorably impact its associated traits.

Genetic determinants for gestational diabetes mellitus and related metabolic traits in Mexican women

Epidemiological and physiological similarities among Gestational Diabetes Mellitus (GDM) and Type 2 Diabetes (T2D) suggest that both diseases, share a common genetic background. T2D risk variants have been associated to GDM susceptibility. However, the genetic architecture of GDM is not yet completely understood. We analyzed 176 SNPs for 115 loci previously associated to T2D, GDM and body mass index (BMI), as well as a set of 118 Ancestry Informative Markers (AIMs), in 750 pregnant Mexican women. Association with GDM was found for two of the most frequently replicated T2D loci: a TCF7L2 haplotype (CTTC: rs7901695, rs4506565, rs7903146, rs12243326; P=2.16x10^-06; OR=2.95) and a KCNQ1 haplotype (TTT: rs2237892, rs163184, rs2237897; P=1.98x10^-05; OR=0.55). In addition, we found two loci associated to glycemic traits: CENTD2 (60’ OGTT glycemia: rs1552224, P=0.03727) and MTNR1B (HOMA B: rs1387153, P=0.05358). Remarkably, a major susceptibility SLC16A11 locus for T2D in Mexicans was not shown to play a role in GDM risk. The fact that two of the main T2D associated loci also contribute to the risk of developing GDM in Mexicans, confirm that both diseases share a common genetic background. However, lack of association with a Native American contribution T2D risk haplotype, SLC16A11, suggests that other genetic mechanisms may be in play for GDM.

Association of FTO, LEPR and MTHFR gene polymorphisms with metabolic syndrome in schizophrenia patients receiving antipsychotics

AIM

The occurrence of metabolic syndrome (MS) in schizophrenia patients receiving long-term antipsychotics (APs) contributes to their high mortality rate. We aimed to determine whether genetic polymorphisms of identified candidate genes are associated with MS in our study population.

MATERIALS & METHODS

We recruited 206 schizophrenia patients receiving AP treatment for at least a year. Cross-sectional measurements of weight, height, blood pressure, waist and hip circumference, and other lipid profiles were recorded. Patient DNA was genotyped for 16 candidate gene polymorphisms.

RESULTS

Of these patients, 59.7% were found to have MS while 40.3% did not. All metabolic parameters were significantly different between the two groups. Only three of the 16 polymorphisms studied showed significant association with MS; rs9939609 of the FTO gene confers risk for MS (odds ratio [OR]: 1.73, 95% CI: 1.07-2.78, p = 0.026), while rs1137101 of the LEPR gene (OR: 0.47, 95% CI: 0.28-0.80, p = 0.005) and rs1801133 of the MTHFR gene (OR: 0.59, 95% CI: 0.35-0.99, p = 0.049) are protective against MS.

CONCLUSION

Polymorphisms of the FTO, LEPR and MTHFR genes may play a role in MS in Malaysian schizophrenia patients receiving long-term treatment with APs.

A genome-wide association study of body mass index across early life and childhood

Background: Several studies have investigated the effect of known adult body mass index (BMI) associated single nucleotide polymorphisms (SNPs) on BMI in childhood. There has been no genome-wide association study (GWAS) of BMI trajectories over childhood.

Methods: We conducted a GWAS meta-analysis of BMI trajectories from 1 to 17 years of age in 9377 children (77 967 measurements) from the Avon Longitudinal Study of Parents and Children (ALSPAC) and the Western Australian Pregnancy Cohort (Raine) Study. Genome-wide significant loci were examined in a further 3918 individuals (48 530 measurements) from Northern Finland. Linear mixed effects models with smoothing splines were used in each cohort for longitudinal modelling of BMI.

Results: A novel SNP, downstream from the FAM120AOS gene on chromosome 9, was detected in the meta-analysis of ALSPAC and Raine. This association was driven by a difference in BMI at 8 years (T allele of rs944990 increased BMI; P_SNP = 1.52 × 10⁻⁸), with a modest association with change in BMI over time (P_Wald(Change) = 0.006). Three known adult BMI-associated loci (FTO, MC4R and ADCY3) and one childhood obesity locus (OLFM4) reached genome-wide significance (P_Wald < 1.13 × 10⁻⁸) with BMI at 8 years and/or change over time.

Conclusions: This GWAS of BMI trajectories over childhood identified a novel locus that warrants further investigation. We also observed genome-wide significance with previously established obesity loci, making the novel observation that these loci affected both the level and the rate of change in BMI. We have demonstrated that the use of repeated measures data can increase power to allow detection of genetic loci with smaller sample sizes.

Obesity as a causal risk factor for deep venous thrombosis: a Mendelian randomization study

OBJECTIVE

To test the hypothesis that obesity is causally associated with deep venous thrombosis (DVT).

DESIGN

A Mendelian randomization design.

SETTING

The Copenhagen General Population Study and the Copenhagen City Heart Study combined.

SUBJECTS

Body mass index (BMI) measurements were available for 87, 574 individuals of Danish descent from the adult general population. All subjects completed questionnaires and were genotyped for the FTO rs9939609 variant.

MAIN OUTCOME MEASURE

First events of DVT with or without pulmonary embolism (PE).

ANALYSIS

The results were assessed using Cox regression, instrumental variable analysis and Poisson regression.

RESULTS

Observationally, the risk of DVT increased with increasing BMI (P-trend < 0.0001). The multivariable-adjusted hazard ratio [95% confidence interval (CI)] for DVT was 1.3 (1.1-1.6) in overweight, 1.8 (1.4-2.2) in moderately obese and 3.4 (2.6-4.6) in severely obese compared with normal-weight individuals. For DVT complicated by PE, corresponding hazard ratios (95% CI) were 1.2 (0.8-1.8), 2.1 (1.3-3.5) and 5.1 (2.8-9.2). FTO AA versus TT genotype was associated with a 2.4% increase in BMI with hazard ratios (95% CI) of 1.09 (0.95-1.25) for DVT and 1.54 (1.12-2.10) for DVT complicated by PE. In instrumental variable analysis, the causal odds ratio (95% CI) for an increase in BMI of 1 kg m(-2) was 1.13 (0.92-1.39) for DVT alone and 1.86 (1.14-3.02) for DVT complicated by PE. The absolute 10-year risk of DVT in a high-risk group (i.e. those aged >60 years and homozygous for Factor V Leiden) was 35% in obese individuals and 18% in normal-weight individuals.

CONCLUSION

A strong observational association between obesity and DVT with or without PE, supported by a direct genetic association between the obesity-specific locus FTO and DVT with PE, implies that obesity is likely to be causally associated with DVT.

A stereological analysis of NPY, POMC, Orexin, GFAP astrocyte, and Iba1 microglia cell number and volume in diet-induced obese male mice

The hypothalamic arcuate nucleus (ARC) contains 2 key neural populations, neuropeptide Y (NPY) and proopiomelanocortin (POMC), and, together with orexin neurons in the lateral hypothalamus, plays an integral role in energy homeostasis. However, no studies have examined total neuronal number and volume after high-fat diet (HFD) exposure using sophisticated stereology. We used design-based stereology to estimate NPY and POMC neuronal number and volume, as well as glial fibrillary acidic protein (astrocyte marker) and ionized calcium-binding adapter molecule 1 (microglia marker) cell number in the ARC; as well as orexin neurons in the lateral hypothalamus. Stereological analysis indicated approximately 8000 NPY and approximately 9000 POMC neurons in the ARC, and approximately 7500 orexin neurons in the lateral hypothalamus. HFD exposure did not affect total neuronal number in any population. However, HFD significantly increased average NPY cell volume and affected NPY and POMC cell volume distribution. HFD reduced orexin cell volume but had a bimodal effect on volume distribution with increased cells at relatively small volumes and decreased cells with relatively large volumes. ARC glial fibrillary acidic protein cells increased after 2 months on a HFD, although no significant difference after 6 months on chow diet or HFD was observed. No differences in ARC ionized calcium-binding adapter molecule 1 cell number were observed in any group. Thus, HFD affects ARC NPY or POMC neuronal cell volume number not cell number. Our results demonstrate the importance of stereology to perform robust unbiased analysis of cell number and volume. These data should be an empirical baseline reference to which future studies are compared.

Appetite is a heritable phenotype associated with adiposity

BACKGROUND

The high heritability of adiposity combined with its shifting distribution over time suggests that genetic and environmental influences interact in the etiology of adiposity.

PURPOSE

The purpose of this study is to examine evidence that genetically determined differences in appetite underlie variation in susceptibility to obesogenic environments.

METHODS

Summary of a program of published research.

RESULTS

Recent behavioral and psychometric studies demonstrate that appetitive characteristics such as responsiveness to internal satiety signals and external food cues not only differentiate obese and normal-weight groups, but are quantitatively associated with weight. Twin analyses show that variation in these appetitive traits is highly heritable. Sensitivity to internal satiety cues is linked with the FTO gene and mediates the association between FTO and weight.

CONCLUSIONS

These results indicate that sensitivity to internal and external appetitive signals are heritable phenotypes that increase the risk of overeating in "obesogenic" environments. A behavioral susceptibility model helps to explain how weight is both highly heritable and highly responsive to environmental characteristics.

Obesity susceptibility loci in Qataris, a highly consanguineous Arabian population

OBJECTIVES

In Qataris, a population characterized by a small size and a high rate of consanguinity, between two-thirds to three-quarters of adults are overweight or obese. We investigated the relevance of 23 obesity-related loci in the Qatari population.

METHODS

Eight-hundred-four individuals assessed to be third generation Qataris were included in the study and assigned to 3 groups according to their body mass index (BMI): 190 lean (BMI < 25 kg/m(2)); 131 overweight (25 kg/m(2) ≤ BMI < 30 kg/m(2)) and 483 obese (BMI ≥ 30 kg/m(2)). Genomic DNA was isolated from peripheral blood and genotyped by TaqMan.

RESULTS

Two loci significantly associated with obesity in Qataris: the TFAP2B variation (rs987237) (A allele versus G allele: chi-square = 10.3; P = 0.0013) and GNPDA2 variation (rs10938397) (A allele versus G allele: chi-square = 6.15; P = 0.013). The TFAP2B GG genotype negatively associated with obesity (OR = 0.21; P = 0.0031). Conversely, the GNDPA2 GG homozygous genotype associated with higher risk of obesity in subjects of age < 32 years (P = 0.0358).

CONCLUSION

We showed a different genetic profile associated with obesity in the Qatari population compared to Western populations. Studying the genetic background of Qataris is of primary importance as the etiology of a given disease might be population-specific.

[Novel achievements in development and application of GPCR-peptides]

One of the approaches to creating the regulators of G-protein-coupled receptors (GPCR) is the development of peptides that structurally correspond to the functionally important regions of the intracellular extracellular loops of the receptors. GPCR-peptides can selectively regulate the functional activity of homologous receptor and affect the hormonal signal transduction via the receptor. Among the peptides corresponding to the intracellular regions of GPCR, their derivatives modified with hydrophobic radicals exhibit the highest activity and selectivity of action in vitro and in vivo. Ample evidence demonstrates that lipophilic GPCR-peptides may be used to treat diseases and various abnormalities that depend on the functional activity of receptors homologous to them. In turn, the peptides corresponding to the extracellular regions of GPCR can be used as functional probes for studying the specific interaction between the receptors and their ligands, as well as for studying the etiology and pathogenesis of autoimmune diseases caused by the production of antibodies to GPCR antigenic determinants that are localized in the receptor extracellular loops. The present review focuses on the recent achievements in development and application of GPCR-peptides and on the prospects for their further use in medicine and fundamental biology.

Is the adiposity-associated FTO gene variant related to all-cause mortality independent of adiposity? Meta-analysis of data from 169,551 Caucasian adults

Previously, a single nucleotide polymorphism (SNP), rs9939609, in the FTO gene showed a much stronger association with all-cause mortality than expected from its association with body mass index (BMI), body fat mass index (FMI) and waist circumference (WC). This finding implies that the SNP has strong pleiotropic effects on adiposity and adiposity-independent pathological pathways that leads to increased mortality. To investigate this further, we conducted a meta-analysis of similar data from 34 longitudinal studies including 169,551 adult Caucasians among whom 27,100 died during follow-up. Linear regression showed that the minor allele of the FTO SNP was associated with greater BMI (n = 169,551; 0.32 kg m(-2) ; 95% CI 0.28-0.32, P < 1 × 10(-32) ), WC (n = 152,631; 0.76 cm; 0.68-0.84, P < 1 × 10(-32) ) and FMI (n = 48,192; 0.17 kg m(-2) ; 0.13-0.22, P = 1.0 × 10(-13) ). Cox proportional hazard regression analyses for mortality showed that the hazards ratio (HR) for the minor allele of the FTO SNPs was 1.02 (1.00-1.04, P = 0.097), but the apparent excess risk was eliminated after adjustment for BMI and WC (HR: 1.00; 0.98-1.03, P = 0.662) and for FMI (HR: 1.00; 0.96-1.04, P = 0.932). In conclusion, this study does not support that the FTO SNP is associated with all-cause mortality independently of the adiposity phenotypes.

Obesity: interactions of genome and nutrients intake

Obesity has become one of the major public health problems all over the world. Recent novel eras of research are opening for the effective management of obesity though gene and nutrient intake interactions because the causes of obesity are complex and multifactorial. Through GWASs (genome-wide association studies) and genetic variations (SNPs, single nucleotide polymorphisms), as the genetic factors are likely to determine individuals’ obesity predisposition. The understanding of genetic approaches in nutritional sciences is referred as “nutrigenomics”. Nutrigenomics explores the interaction between genetic factors and dietary nutrient intake on various disease phenotypes such as obesity. Therefore, this novel approach might suggest a solution for the effective prevention and treatment of obesity through individual genetic profiles and help improve health conditions.

Indications for potential parent-of-origin effects within the FTO gene

Genome-Wide Association Studies (GWAS) were successfully applied to discover associations with obesity. However, the GWAS design is usually based on unrelated individuals and inheritance information on the parental origin of the alleles is missing. Taking into account parent-of-origin may provide further insights into the genetic mechanisms contributing to obesity. We hypothesized that there may be variants within the robustly replicated fat mass and obesity associated (FTO) gene that may confer different risk for obesity depending on transmission from mother or father. Genome-wide genotypes and pedigree information from the Sorbs population were used. Phased genotypes among 525 individuals were generated by AlphaImpute. Subsequently, 22 SNPs within FTO introns 1 to 3 were selected and parent-of-origin specific association analyses were performed using PLINK. Interestingly, we identified several SNPs conferring different genetic effects (P≤0.05) depending on parental origin—among them, rs1861868, rs1121980 and rs9939973 (all in intron 1). To confirm our findings, we investigated the selected variants in 705 German trios comprising an (extremely) obese child or adolescent and both parents. Again, we observed evidence for POE effects in intron 2 and 3 (P≤0.05) as indicated by the parental asymmetry test. Our results suggest that the obesity risk transmitted by several FTO variants may depend on the parental origin of the allele. Larger family-based studies are warranted to replicate our findings.

Contribution of common non-synonymous variants in PCSK1 to body mass index variation and risk of obesity: a systematic review and meta-analysis with evidence from up to 331 175 individuals

Polymorphisms rs6232 and rs6234/rs6235 in PCSK1 have been associated with extreme obesity [e.g. body mass index (BMI) ≥ 40 kg/m(2)], but their contribution to common obesity (BMI ≥ 30 kg/m(2)) and BMI variation in a multi-ethnic context is unclear. To fill this gap, we collected phenotypic and genetic data in up to 331 175 individuals from diverse ethnic groups. This process involved a systematic review of the literature in PubMed, Web of Science, Embase and the NIH GWAS catalog complemented by data extraction from pre-existing GWAS or custom-arrays in consortia and single studies. We employed recently developed global meta-analytic random-effects methods to calculate summary odds ratios (OR) and 95% confidence intervals (CIs) or beta estimates and standard errors (SE) for the obesity status and BMI analyses, respectively. Significant associations were found with binary obesity status for rs6232 (OR = 1.15, 95% CI 1.06-1.24, P = 6.08 × 10(-6)) and rs6234/rs6235 (OR = 1.07, 95% CI 1.04-1.10, P = 3.00 × 10(-7)). Similarly, significant associations were found with continuous BMI for rs6232 (β = 0.03, 95% CI 0.00-0.07; P = 0.047) and rs6234/rs6235 (β = 0.02, 95% CI 0.00-0.03; P = 5.57 × 10(-4)). Ethnicity, age and study ascertainment significantly modulated the association of PCSK1 polymorphisms with obesity. In summary, we demonstrate evidence that common gene variation in PCSK1 contributes to BMI variation and susceptibility to common obesity in the largest known meta-analysis published to date in genetic epidemiology.

First genome-wide association study in an Australian aboriginal population provides insights into genetic risk factors for body mass index and type 2 diabetes

A body mass index (BMI) >22kg/m2 is a risk factor for type 2 diabetes (T2D) in Aboriginal Australians. To identify loci associated with BMI and T2D we undertook a genome-wide association study using 1,075,436 quality-controlled single nucleotide polymorphisms (SNPs) genotyped (Illumina 2.5M Duo Beadchip) in 402 individuals in extended pedigrees from a Western Australian Aboriginal community. Imputation using the thousand genomes (1000G) reference panel extended the analysis to 6,724,284 post quality-control autosomal SNPs. No associations achieved genome-wide significance, commonly accepted as P<5x10-8. Nevertheless, genes/pathways in common with other ethnicities were identified despite the arrival of Aboriginal people in Australia >45,000 years ago. The top hit (rs10868204 Pgenotyped = 1.50x10-6; rs11140653 Pimputed_1000G = 2.90x10-7) for BMI lies 5' of NTRK2, the type 2 neurotrophic tyrosine kinase receptor for brain-derived neurotrophic factor (BDNF) that regulates energy balance downstream of melanocortin-4 receptor (MC4R). PIK3C2G (rs12816270 Pgenotyped = 8.06x10-6; rs10841048 Pimputed_1000G = 6.28x10-7) was associated with BMI, but not with T2D as reported elsewhere. BMI also associated with CNTNAP2 (rs6960319 Pgenotyped = 4.65x10-5; rs13225016 Pimputed_1000G = 6.57x10-5), previously identified as the strongest gene-by-environment interaction for BMI in African-Americans. The top hit (rs11240074 Pgenotyped = 5.59x10-6, Pimputed_1000G = 5.73x10-6) for T2D lies 5' of BCL9 that, along with TCF7L2, promotes beta-catenin's transcriptional activity in the WNT signaling pathway. Additional hits occurred in genes affecting pancreatic (KCNJ6, KCNA1) and/or GABA (GABRR1, KCNA1) functions. Notable associations observed for genes previously identified at genome-wide significance in other populations included MC4R (Pgenotyped = 4.49x10-4) for BMI and IGF2BP2 Pimputed_1000G = 2.55x10-6) for T2D. Our results may provide novel functional leads in understanding disease pathogenesis in this Australian Aboriginal population.

Genetics and Epigenetics of Eating Disorders

Eating disorders (EDs) are serious psychiatric conditions influenced by biological, psychological, and sociocultural factors. A better understanding of the genetics of these complex traits and the development of more sophisticated molecular biology tools have advanced our understanding of the etiology of EDs. The aim of this review is to critically evaluate the literature on the genetic research conducted on three major EDs: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). We will first review the diagnostic criteria, clinical features, prevalence, and prognosis of AN, BN, and BED, followed by a review of family, twin, and adoption studies. We then review the history of genetic studies of EDs covering linkage analysis, candidate gene association studies, genome-wide association studies, and the study of rare variants in EDs. Our review also incorporates a translational perspective by covering animal models of ED-related phenotypes. Finally, we review the nascent field of epigenetics of EDs and a look forward to future directions for ED genetic research.

Genetic association studies of obesity in Africa: a systematic review

Obesity is increasing in Africa, but the underlying genetic background largely remains unknown. We assessed existing evidence on genetic determinants of obesity among populations within Africa. MEDLINE and EMBASE were searched and the bibliographies of retrieved articles were examined. Included studies had to report on the association of a genetic marker with obesity indices and the presence/occurrence of obesity/obesity trait. Data were extracted on study design and characteristics, genetic determinants and effect estimates of associations with obesity indices. According to this data, over 300 polymorphisms in 42 genes have been studied in various population groups within Africa mostly through the candidate gene approach. Polymorphisms in genes such as ACE, ADIPOQ, ADRB2, AGRP, AR, CAPN10, CD36, C7orf31, DRD4, FTO, MC3R, MC4R, SGIP1 and LEP were found to be associated with various measures of obesity. Of the 36 polymorphisms previously validated by genome-wide association studies (GWAS) elsewhere, only FTO and MC4R polymorphisms showed significant associations with obesity in black South Africans, Nigerians and Ghanaians. However, these data are insufficient to establish the true nature of genetic susceptibility to obesity in populations within Africa. There has been recent progress in describing the genetic architecture of obesity among populations within Africa. This effort needs to be sustained via GWAS studies.

ACTH: The forgotten therapy

Although anti-inflammatory drugs are among the most common class of marketed drugs, chronic inflammatory conditions such as rheumatoid arthritis, multiple sclerosis or inflammatory bowel disease still represent unmet needs. New first-in-class drugs might be discovered in the future but the repurpose and further development of old drugs also offers promise for these conditions. This is the case of the melanocortin adrenocorticotropin hormone, ACTH, used in patients since 1952 but regarded as the last therapeutic option when other medications, such as glucocorticoids, cannot be used. Better understanding on its physiological and pharmacological mechanisms of actions and new insights on melanocortin receptors biology have revived the interest on rescuing this old and effective drug. ACTH does not only induce cortisol production, as previously assumed, but it also exerts anti-inflammatory actions by targeting melanocortin receptors present on immune cells. The endogenous agonists for these receptors (ACTH, α-, β-, and γ-melanocyte stimulating hormones), are also produced locally by immune cells, indicating the existence of an endogenous anti-inflammatory tissue-protective circuit involving the melanocortin system. These findings suggested that new ACTH-like melanocortin drugs devoid of steroidogenic actions, and hence side effects, could be developed. This review summarizes the actions of ACTH and melanocortin drugs, their role as endogenous pro-resolving mediators, their current clinical use and provides an overview on how recent advances on GPCR functioning may lead to a novel class of drugs.

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.

Clinically relevant known and candidate genes for obesity and their overlap with human infertility and reproduction

PURPOSE

Obesity is a growing public health concern now reaching epidemic status worldwide for children and adults due to multiple problems impacting on energy intake and expenditure with influences on human reproduction and infertility. A positive family history and genetic factors are known to play a role in obesity by influencing eating behavior, weight and level of physical activity and also contributing to human reproduction and infertility. Recent advances in genetic technology have led to discoveries of new susceptibility genes for obesity and causation of infertility. The goal of our study was to provide an update of clinically relevant candidate and known genes for obesity and infertility using high resolution chromosome ideograms with gene symbols and tabular form.

METHODS

We used computer-based internet websites including PubMed to search for combinations of key words such as obesity, body mass index, infertility, reproduction, azoospermia, endometriosis, diminished ovarian reserve, estrogen along with genetics, gene mutations or variants to identify evidence for development of a master list of recognized obesity genes in humans and those involved with infertility and reproduction. Gene symbols for known and candidate genes for obesity were plotted on high resolution chromosome ideograms at the 850 band level. Both infertility and obesity genes were listed separately in alphabetical order in tabular form and those highlighted when involved with both conditions.

RESULTS

By searching the medical literature and computer generated websites for key words, we found documented evidence for 370 genes playing a role in obesity and 153 genes for human reproduction or infertility. The obesity genes primarily affected common pathways in lipid metabolism, deposition or transport, eating behavior and food selection, physical activity or energy expenditure. Twenty-one of the obesity genes were also associated with human infertility and reproduction. Gene symbols were plotted on high resolution ideograms and their name, precise chromosome band location and description were summarized in tabular form.

CONCLUSIONS

Meaningful correlations in the obesity phenotype and associated human infertility and reproduction are represented with the location of genes on chromosome ideograms along with description of the gene and position in tabular form. These high resolution chromosome ideograms and tables will be useful in genetic awareness and counseling, diagnosis and treatment to improve clinical outcomes.

Pharmacogenetics of second-generation antipsychotics

This review considers pharmacogenetics of the so called 'second-generation' antipsychotics. Findings for polymorphisms replicating in more than one study are emphasized and compared and contrasted with larger-scale candidate gene studies and genome-wide association study analyses. Variants in three types of genes are discussed: pharmacokinetic genes associated with drug metabolism and disposition, pharmacodynamic genes encoding drug targets, and pharmacotypic genes impacting disease presentation and subtype. Among pharmacokinetic markers, CYP2D6 metabolizer phenotype has clear clinical significance, as it impacts dosing considerations for aripiprazole, iloperidone and risperidone, and variants of the ABCB1 gene hold promise as biomarkers for dosing for olanzapine and clozapine. Among pharmacodynamic variants, the TaqIA1 allele of the DRD2 gene, the DRD3 (Ser9Gly) polymorphism, and the HTR2C -759C/T polymorphism have emerged as potential biomarkers for response and/or side effects. However, large-scale candidate gene studies and genome-wide association studies indicate that pharmacotypic genes may ultimately prove to be the richest source of biomarkers for response and side effect profiles for second-generation antipsychotics.

Metabolic regulation and energy homeostasis through the primary Cilium

Obesity and diabetes represent a significant healthcare concern. In contrast to genome-wide association studies that, some exceptions notwithstanding, have offered modest clues about pathomechanism, the dissection of rare disorders in which obesity represents a core feature have highlighted key molecules and structures critical to energy regulation. Here we focus on the primary cilium, an organelle whose roles in energy homeostasis have been underscored by the high incidence of obesity and type II diabetes in patients and mouse mutants with compromised ciliary function. We discuss recent evidence linking ciliary dysfunction to metabolic defects and we explore the contribution of neuronal and nonneuronal cilia to these phenotypes.

A genetic risk tool for obesity predisposition assessment and personalized nutrition implementation based on macronutrient intake

There is little evidence about genetic risk score (GRS)-diet interactions in order to provide personalized nutrition based on the genotype. The aim of the study was to assess the value of a GRS on obesity prediction and to further evaluate the interactions between the GRS and dietary intake on obesity. A total of 711 seekers of a Nutrigenetic Service were examined for anthropometric and body composition measurements and also for dietary habits and physical activity. Oral epithelial cells were collected for the identification of 16 SNPs (related with obesity or lipid metabolism) using DNA zip-coded beads. Genotypes were coded as 0, 1 or 2 according to the number of risk alleles, and the GRS was calculated by adding risk alleles with such a criterion. After being adjusted for gender, age, physical activity and energy intake, the GRS demonstrated that individuals carrying >7 risk alleles had in average 0.93 kg/m(2) of BMI, 1.69 % of body fat mass, 1.94 cm of waist circumference and 0.01 waist-to-height ratio more than the individuals with ≤7 risk alleles. Significant interactions for GRS and the consumption of energy, total protein, animal protein, vegetable protein, total fat, saturated fatty acids, polyunsaturated fatty acids, total carbohydrates, complex carbohydrates and fiber intake on adiposity traits were found after adjusted for confounders variables. The GRS confirmed that the high genetic risk group showed greater values of adiposity than the low risk group and demonstrated that macronutrient intake modifies the GRS association with adiposity traits.

Metabolic syndrome: a closer look at the growing epidemic and its associated pathologies

Obesity is reaching epidemic proportions with recent worldwide figures estimated at 1.4 billion and rising year-on-year. Obesity affects all socioeconomic backgrounds and ethnicities and is a pre-requisite for metabolic syndrome. Metabolic syndrome is a clustering of risk factors, such as central obesity, insulin resistance, dyslipidaemia and hypertension that together culminate in the increased risk of type 2 diabetes mellitus and cardiovascular disease. As these conditions are among the leading causes of deaths worldwide and metabolic syndrome increases the risk of type 2 diabetes mellitus fivefold and cardiovascular disease threefold, it is of critical importance that a precise definition is agreed upon by all interested parties. Also of particular interest is the relationship between metabolic syndrome and cancer. Metabolic syndrome has been associated with a plethora of cancers including breast, pancreatic, colon and liver cancer. Furthermore, each individual risk factor for metabolic syndrome has also an association with cancer. Our review collates internationally generated information on metabolic syndrome, its many definitions and its associations with life-threatening conditions including type 2 diabetes mellitus, cardiovascular disease and cancer, providing a foundation for future advancements on this topic.

Association between MC4R rs17782313 polymorphism and overeating behaviors

BACKGROUND/OBJECTIVES

Melanocortins have a crucial role in appetite and weight regulation. Although the melanocortin 4 receptor (MC4R) gene has been repeatedly linked to obesity and antipsychotic-induced weight gain, the mechanism behind how it leads to this effect in still undetermined. The goal of this study was to conduct an in-depth and sophisticated analysis of MC4R polymorphisms, body mass index (BMI), eating behavior and depressed mood.

SUBJECTS/METHODS

We genotyped 328 individuals of European ancestry on the following MC4R markers based on the relevant literature on obesity and antipsychotic-induced weight gain: rs571312, rs17782313, rs489693, rs11872992, and rs8087522. Height and weight were measured, and information on depressed mood and overeating behaviors was obtained during the in-person assessment.

RESULTS

BMI was associated with rs17782313 C allele; however, this finding did not survive correction for multiple testing (P = 0.018). Although rs17782313 was significantly associated with depressed mood and overeating behaviors, tests of indirect effects indicated that emotional eating and food cravings, rather than depressed mood, uniquely accounted for the effect of this marker and BMI (n = 152).

CONCLUSIONS

To our knowledge, this is the first study to investigate the link between MC4R rs17782313, mood and overeating behavior, as well as to demonstrate possible mechanisms behind MC4R's influence on body weight. If replicated in a larger sample, these results may have important clinical implications, including potential for the use of MC4R agonists in the treatment of obesity and disordered eating.

Advancement in genetic variants conferring obesity susceptibility from genome-wide association studies

Obesity prevalence has increased in recent years. Lifestyle change fuels obesity, but genetic factors cause more than 50% of average variations in obesity. The advent of genome-wide association studies (GWAS) has hastened the progress of polygenic obesity research. As of this writing, more than 73 obesity susceptibility loci have been identified in ethnic groups through GWAS. The identified loci explain only 2% to 4% of obesity heritability, thereby indicating that a large proportion of loci remain undiscovered. Thus, the next step is to identify and confirm novel loci, which may exhibit smaller effects and lower allele frequencies than established loci. However, achieving these tasks has been difficult for researchers. GWAS help researchers discover the causal loci. Moreover, numerous biological studies have been performed on the polygenic effects on obesity, such as studies on fat mass- and obesity-associated gene (FTO), but the role of these polygenic effects in the mechanism of obesity remains unclear. Thus, obesity-causing variations should be identified, and insights into the biology of polygenic effects on obesity are needed.

An obesity genetic risk score predicts risk of insulin resistance among Chinese children

A great number of body mass index (BMI)/obesity-related loci have been identified by recent genome-wide association studies. The objective of the study is to investigate the associations of 11 obesity-related loci with insulin resistance (IR) in a Chinese children population. Participants included 3,468 Chinese children, aged 6-18 years. The 75 percentile (equal to 2.93) of homeostasis model assessment of IR (HOMA-IR) index was considered as the cut-off of IR. A total of 868 IR cases and 2,600 control children were identified. In age- and sex-adjusted model, only two SNPs in/near GNPDA2 and KCTD15 genes were significantly associated with risk of IR [GNPDA2 rs10938397: allelic odds ratio (OR) = 1.19, 95 % confidence interval (CI) 1.06-1.34, P = 0.003; KCTD15 rs29941: allelic OR = 1.15, 95 % CI = 1.01-1.31, P = 0.034]; genetic risk score was also significantly associated risk of IR (OR = 1.08, 95 % 1.04-1.12, P = 1.18 × 10(-4)). After additional adjustment for BMI, none remained significant. The associations of GNPDA2 rs10938397 and the SNPs in combination with risk of IR remained statistically significant after correction for multiple testing. The present study demonstrated that the associations of GNPDA2 rs10938397 and the SNPs in combination with risk of IR were statistically significant, which were dependent on BMI.

Combined effect of established BMI loci on obesity-related traits in an Algerian population sample

Background

Genome-wide association studies have identified variants associated with BMI in populations of European descent. We sought to establish whether genetic variants that are robustly associated with BMI could modulate anthropometric traits and the obesity risk in an Algerian population sample, the ISOR study.

The ISOR study of 787 adult subjects (aged between 30 and 64) provided a representative sample of the population living in the city of Oran (north-west of Algeria). We investigated the combined effect of 29 BMI established genetic variants using a genetic predisposition score (GPS) on anthropometric traits and obesity risk in 740 subjects.

Results

We found that each additional risk allele in the GPS was associated with an increment in the mean [95% CI] for BMI of 0.15 [0.06 - 0.24] kg/m² (p = 0.001). Although the GPS was also associated with higher waist (p = 0.02) and hip (p = 0.02) circumferences, these associations were in fact driven by BMI. The GPS was also associated with an 11% higher risk of obesity (OR [95%CI] = 1.11 [1.05 - 1.18], p = 0.0004).

Conclusions

Our data showed that a GPS comprising 29 BMI established loci developed from Europeans seems to be a valid score in a North African population. Our findings contribute to a better understanding of the genetic susceptibility to obesity in Algeria.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-014-0128-1) contains supplementary material, which is available to authorized users.

Comparing partial least square approaches in a gene- or region-based association study for multiple quantitative phenotypes

On thinking quantitatively of complex diseases, there are at least three statistical strategies for association studies: one single-nucleotide polymorphism (SNP) on a single trait, gene or region (with multiple SNPs) on a single trait, and gene or region on multiple traits. The third approach is the most general in dissecting genetic mechanisms underlying complex diseases underpinning multiple quantitative traits. Gene or region association methods based on partial least square (PLS) approaches have been shown to have apparent power advantage. However, few approaches have been developed for multiple quantitative phenotypes or traits underlying a condition or disease, and the performance of various PLS approaches used in association studies for multiple quantitative traits have not been assessed. Here we exploit association between multiple SNPs and multiple phenotypes or traits, from a regression perspective, through exhaustive scan statistics (sliding window) using PLS and sparse PLS regressions. Simulations were conducted to assess the performance of the proposed scan statistics and compare them with existing methods. The proposed methods were applied to 12 regions of genome-wide association study data from the European Prospective Investigation of Cancer-Norfolk study.

Identification of allelic heterogeneity at type-2 diabetes loci and impact on prediction

Although over 60 single nucleotide polymorphisms (SNPs) have been identified by meta-analysis of genome-wide association studies for type-2 diabetes (T2D) among individuals of European descent, much of the genetic variation remains unexplained. There are likely many more SNPs that contribute to variation in T2D risk, some of which may lie in the regions surrounding established SNPs - a phenomenon often referred to as allelic heterogeneity. Here, we use the summary statistics from the DIAGRAM consortium meta-analysis of T2D genome-wide association studies along with linkage disequilibrium patterns inferred from a large reference sample to identify novel SNPs associated with T2D surrounding each of the previously established risk loci. We then examine the extent to which the use of these additional SNPs improves prediction of T2D risk in an independent validation dataset. Our results suggest that multiple SNPs at each of 3 loci contribute to T2D susceptibility (TCF7L2, CDKN2A/B, and KCNQ1; p<5×10⁻⁸). Using a less stringent threshold (p<5×10⁻⁴), we identify 34 additional loci with multiple associated SNPs. The addition of these SNPs slightly improves T2D prediction compared to the use of only the respective lead SNPs, when assessed using an independent validation cohort. Our findings suggest that some currently established T2D risk loci likely harbor multiple polymorphisms which contribute independently and collectively to T2D risk. This opens a promising avenue for improving prediction of T2D, and for a better understanding of the genetic architecture of T2D.

Genetic & epigenetic approach to human obesity

Obesity is an important clinical and public health challenge, epitomized by excess adipose tissue accumulation resulting from an imbalance in energy intake and energy expenditure. It is a forerunner for a variety of other diseases such as type-2-diabetes (T2D), cardiovascular diseases, some types of cancer, stroke, hyperlipidaemia and can be fatal leading to premature death. Obesity is highly heritable and arises from the interplay of multiple genes and environmental factors. Recent advancements in Genome-wide association studies (GWAS) have shown important steps towards identifying genetic risks and identification of genetic markers for lifestyle diseases, especially for a metabolic disorder like obesity. According to the 12th Update of Human Obesity Gene Map there are 253 quantity trait loci (QTL) for obesity related phenotypes from 61 genome wide scan studies. Contribution of genetic propensity of individual ethnic and racial variations in obesity is an active area of research. Further, understanding its complexity as to how these variations could influence ones susceptibility to become or remain obese will lead us to a greater understanding of how obesity occurs and hopefully, how to prevent and treat this condition. In this review, various strategies adapted for such an analysis based on the recent advances in genome wide and functional variations in human obesity are discussed.

The role of the FTO (Fat Mass and Obesity Related) locus in regulating body size and composition

Genomewide association studies (GWAS) have indicated that SNPs on a chromosome 16 locus encompassing FTO, as well as IRX3, 5, 6, FTM and FTL are robustly associated with human obesity. GWAS, however, are by nature gene agnostic, and SNPs reaching the appropriate statistical threshold for a given phenotype can appear anywhere in the genome, within, near or far away from any coding sequence. Thus a major challenge in the field has been to translate these statistical hits into real biological insight. The key question is which of these genes are responsible for the association with obesity, and what is the underlying mechanism? With loss of function FTO mutations in both mice and humans resulting in severe growth retardation and mice globally over-expressing FTO being obese, the initial attention was focussed on this gene. We and others have shown that in vitro, recombinant FTO is able to catalyse the Fe(II)- and 2OG-dependent demethylation of single stranded nucleic-acids, with a preference for RNA. We have shown that FTO expression is regulated by essential amino acids (AAs) and that it couples amino acid levels to mammalian Target of Rapamycin Complex 1 (mTORC1) signalling, through a mechanism dependent on its ability to demethylate. Thus FTO is an AA sensor and plays a key role regulating appropriate growth and translation. However, recent data focussing on obesity associated variants within FTO have implicated two neighbouring genes, RPGRIP1L and IRX3, as having a functional link between the SNP and the observed human phenotypes. As with Fto, perturbing the expression of these genes in mice results in a bodyweight phenotype, with homozygous deletion of Irx3 resulting in a smaller mouse and heterozygous deletion of Rpgrip1l leading to a mild obesity phenotype. Thus it may be that a number of genes in this region play an important role in determining body composition.

Interaction between genetic predisposition to adiposity and dietary protein in relation to subsequent change in body weight and waist circumference

Background

Genetic predisposition to adiposity may interact with dietary protein in relation to changes of anthropometry.

Objective

To investigate the interaction between genetic predisposition to higher body mass index (BMI), waist circumference (WC) or waist-hip ratio adjusted for BMI (WHR_BMI) and dietary protein in relation to subsequent change in body weight (ΔBW) or change in WC (ΔWC).

Design

Three different Danish cohorts were used. In total 7,054 individuals constituted the study population with information on diet, 50 single-nucleotide polymorphisms (SNPs) associated with BMI, WC or WHR_BMI, as well as potential confounders. Mean follow-up time was ∼5 years. Four genetic predisposition-scores were based on the SNPs; a complete-score including all selected adiposity- associated SNPs, and three scores including BMI, WC or WHR_BMI associated polymorphisms, respectively. The association between protein intake and ΔBW or ΔWC were examined and interactions between SNP-score and protein were investigated. Analyses were based on linear regressions using macronutrient substitution models and meta-analyses.

Results

When protein replaced carbohydrate, meta-analyses showed no associations with ΔBW (41.0 gram/y/5 energy% protein, [95% CI: −32.3; 114.3]) or ΔWC (<−0.1 mm/y/5 energy % protein, [−1.1; 1.1]). Similarly, there were no interactions for any SNP-scores and protein for either ΔBW (complete SNP-score: 1.8 gram/y/5 energy% protein/risk allele, [−7.0; 10.6]) or ΔWC (complete SNP-score: <0.1 mm/y/5 energy% protein/risk allele, [−0.1; 0.1]). Similar results were seen when protein replaced fat.

Conclusion

This study indicates that the genetic predisposition to general and abdominal adiposity, assessed by gene-scores, does not seem to modulate the influence of dietary protein on ΔBW or ΔWC.