There are hints of an altered mitochondrial function in obesity. Nuclear-encoded genes are relevant for mitochondrial function (3 gene sets of known relevant pathways: (1) 16 nuclear regulators of mitochondrial genes, (2) 91 genes for oxidative phosphorylation and (3) 966 nuclear-encoded mitochondrial genes). Gene set enrichment analysis (GSEA) showed no association with type 2 diabetes mellitus in these gene sets. Here we performed a GSEA for the same gene sets for obesity. Genome wide association study (GWAS) data from a case-control approach on 453 extremely obese children and adolescents and 435 lean adult controls were used for GSEA. For independent confirmation, we analyzed 705 obesity GWAS trios (extremely obese child and both biological parents) and a population-based GWAS sample (KORA F4, n = 1,743). A meta-analysis was performed on all three samples. In each sample, the distribution of significance levels between the respective gene set and those of all genes was compared using the leading-edge-fraction-comparison test (cut-offs between the 50th and 95th percentile of the set of all gene-wise corrected p-values) as implemented in the MAGENTA software. In the case-control sample, significant enrichment of associations with obesity was observed above the 50th percentile for the set of the 16 nuclear regulators of mitochondrial genes (pGSEA,50 = 0.0103). This finding was not confirmed in the trios (pGSEA,50 = 0.5991), but in KORA (pGSEA,50 = 0.0398). The meta-analysis again indicated a trend for enrichment (pMAGENTA,50 = 0.1052, pMAGENTA,75 = 0.0251). The GSEA revealed that weak association signals for obesity might be enriched in the gene set of 16 nuclear regulators of mitochondrial genes.
The SH2B1 gene (Src-homology 2B adaptor protein 1 gene) is a solid candidate gene for obesity. Large scale GWAS studies depicted markers in the vicinity of the gene; animal models suggest a potential relevance for human body weight regulation.
We performed a mutation screen for variants in the SH2B1 coding sequence in 95 extremely obese children and adolescents. Detected variants were genotyped in independent childhood and adult study groups (up to 11,406 obese or overweight individuals and 4,568 controls). Functional implications on STAT3 mediated leptin signalling of the detected variants were analyzed in vitro.
We identified two new rare mutations and five known SNPs (rs147094247, rs7498665, rs60604881, rs62037368 and rs62037369) in SH2B1. Mutation g.9483C/T leads to a non-synonymous, non-conservative exchange in the beta (βThr656Ile) and gamma (γPro674Ser) splice variants of SH2B1. It was additionally detected in two of 11,206 (extremely) obese or overweight children, adolescents and adults, but not in 4,506 population-based normal-weight or lean controls. The non-coding mutation g.10182C/A at the 3’ end of SH2B1 was only detected in three obese individuals. For the non-synonymous SNP rs7498665 (Thr484Ala) we observed nominal over-transmission of the previously described risk allele in 705 obesity trios (nominal p = 0.009, OR = 1.23) and an increased frequency of the same allele in 359 cases compared to 429 controls (nominal p = 0.042, OR = 1.23). The obesity risk-alleles at Thr484Ala and βThr656Ile/γPro674Ser had no effect on STAT3 mediated leptin receptor signalling in splice variants β and γ.
The rare coding mutation βThr656Ile/γPro674Ser (g.9483C/T) in SH2B1 was exclusively detected in overweight or obese individuals. Functional analyzes did not reveal impairments in leptin signalling for the mutated SH2B1.
SH2B1; Obesity; BMI; rs7498665; Mutation screen
Doublecortin and calmodulin like kinase 1 (DCLK1) is implicated in synaptic plasticity and neurodevelopment. Genetic variants in DCLK1 are associated with cognitive traits, specifically verbal memory and general cognition. We investigated the role of DCLK1 variants in three psychiatric disorders that have neuro-cognitive dysfunctions: schizophrenia (SCZ), bipolar affective disorder (BP) and attention deficit/hyperactivity disorder (ADHD). We mined six genome wide association studies (GWASs) that were available publically or through collaboration; three for BP, two for SCZ and one for ADHD. We also genotyped the DCLK1 region in additional samples of cases with SCZ, BP or ADHD and controls that had not been whole-genome typed. In total, 9895 subjects were analysed, including 5308 normal controls and 4,587 patients (1,125 with SCZ, 2,496 with BP and 966 with ADHD). Several DCLK1 variants were associated with disease phenotypes in the different samples. The main effect was observed for rs7989807 in intron 3, which was strongly associated with SCZ alone and even more so when cases with SCZ and ADHD were combined (P-value = 4×10−5 and 4×10−6, respectively). Associations were also observed with additional markers in intron 3 (combination of SCZ, ADHD and BP), intron 19 (SCZ+BP) and the 3′UTR (SCZ+BP). Our results suggest that genetic variants in DCLK1 are associated with SCZ and, to a lesser extent, with ADHD and BP. Interestingly the association is strongest when SCZ and ADHD are considered together, suggesting common genetic susceptibility. Given that DCLK1 variants were previously found to be associated with cognitive traits, these results are consistent with the role of DCLK1 in neurodevelopment and synaptic plasticity.
Data from meta-analyses of genome-wide association studies provided evidence for an association of polymorphisms with body mass index (BMI), and gene expression results indicated a role of these variants in the hypothalamus. It was consecutively hypothesized that these associations might be evoked by a modulation of nutritional intake or energy expenditure.
It was our aim to investigate the association of these genetic factors with BMI in a large homogenous population-based sample to explore the association of these polymorphisms with lifestyle factors related to nutritional intake or energy expenditure, and whether such lifestyle factors could be mediators of the detected single-nucleotide polymorphism (SNP)-association with BMI. It was a further aim to compare the proportion of BMI explained by genetic factors with the one explained by lifestyle factors.
The association of seven polymorphisms in or near the genes NEGR1, TMEM18, MTCH2, FTO, MC4R, SH2B1and KCTD15 was analyzed in 12 462 subjects from the population-based MONICA/KORA Augsburg study. Information on lifestyle factors was based on standardized questionnaires. For statistical analysis, regression-based models were used.
The minor allele of polymorphism rs6548238 C>T (TMEM18) was associated with lower BMI (−0.418 kg/m2, p=1.22×10−8), and of polymorphisms rs9935401 G>A (FTO) and rs7498665 A>G (SH2B1) with increased BMI (0.290 kg/m2, p=2.85×10−7 and 0.145 kg/m2, p=9.83×10−3). The other polymorphisms were not significantly associated. Lifestyle factors were correlated with BMI and explained 0.037 % of the BMI variance as compared to 0.006 % of explained variance by the associated genetic factors. The genetic variants associated with BMI were not significantly associated with lifestyle factors and there was no evidence of lifestyle factors mediating the SNP-BMI association.
Our data first confirm the findings for TMEM18 with BMI in a single study on adults and also confirm the findings for FTO and SH2B1. There was no evidence for a direct SNP-lifestyle association.
TMEM18; FTO; SH2B1; lifestyle; obesity
Anorexia nervosa (AN) is a highly heritable young-onset psychiatric illness the etiology of which remains unknown. Estrogen alpha and beta receptors, encoded by ESR1 and ESR2 genes, are involved in food intake regulation and eating behavior, and may have a potential role in AN. We performed a family-based association study of 17 single-nucleotide polymorphisms (SNPs) encompassing ESR1 and ESR2 genes in a cohort of 321 French AN families. We attempted to replicate this finding in a cohort of 41 restrictive AN (RAN) families and in a population-based study of 693 young women. Using the transmission disequilibrium test, a significant over-transmission was detected between AN and ESR1 rs726281 and rs2295193. These SNPs and another among ESR1 were more specifically associated with the RAN subtype (rs726281, p=0.005, odds ratio (OR)=2.1, 95% confidence interval (95% CI)=1.2–3.6; rs3798577, p=0.021, OR=1.6, 95% CI=1.1–2.3; and rs2295193, p=0.007, OR=1.7, 95% CI=1.2–2.5). A large eight-SNPs haplotype of ESR1 gene was also associated with AN (p<0.0001, OR=3.1, 95% CI=1.8–5.1). Association of ESR1 SNPs and RAN was driven by paternal over-transmissions (p<0.0001, OR=3.7, 95% CI=1.9–7.3). Furthermore, we confirmed the preferential paternal over-transmission of the ESR1 rs726281 on the independent German sample of 41 RAN trios (p=0.025, OR=3, 95% CI=1.1–8.3). Finally, rs3798577 was associated with eating disorders in a population-based sample of 693 women (p<0.01). Our findings are strongly in favor of an association between ESR1 polymorphisms and AN. In particular, ESR1 gene confers a high risk of vulnerability to the restrictive subtype of AN, and suggests that the estrogen pathway has to be further analyzed in AN.
anorexia nervosa; restrictive type; binge-eating/purging type; estrogen receptors; transmission disequilibrium test; population-based sample; Eating / Metabolic Disorders; Neurogenetics; Biological Psychiatry; Molecular & Cellular Neurobiology; Anorexia nervosa; estrogen receptors; restrictive type; binge-eating / purging type; transmission disequilibrium test; population-based sample
Heritability of obesity is substantial and recent meta-analyses of genome-wide association studies (GWASs) have been successful in detecting several robustly associated genomic regions for obesity using single-nucleotide polymorphisms (SNPs). However, taken together, the SNPs explain only a small proportion of the overall heritability. Copy number variations (CNVs) might contribute to the ‘missing heritability’. We searched genome-wide for association between common CNVs and early-onset extreme obesity. Four hundred and twenty-four case-parents obesity trios and an independent sample of 453 extremely obese children and adolescents and 435 normal-weight and lean adult controls were genotyped by the Affymetrix Genome-Wide Human SNP Array 6.0. We detected 20 common copy number variable regions (CNVRs) which were associated with obesity. The most promising CNVRs were followed-up in an independent sample of 365 obesity trios, confirming the association for two candidate CNVRs. We identified a common CNVR exclusively covering the three olfactory receptor genes OR4P4, OR4S2 and OR4C6 to be associated with obesity (combined P-value = 0.015 in a total of 789 families; odds ratio for the obesity effect allele = 1.19; 95% confidence interval = 1.016–1.394). We also replicated two common deletions (near NEGR1 and at chromosome 10q11.22) that have previously been reported to be associated with body weight. Additionally, we support a rare CNV on chromosome 16 that has recently been reported by two independent groups. However, rare CNVs had not been the focus of our study. We conclude that common CNVs are unlikely to contribute substantially to the genetic basis of early-onset extreme obesity.
Independent genome-wide association studies (GWAS) showed an obesogenic effect of two single nucleotide polymorphisms (SNP; rs12970134 and rs17782313) more than 150 kb downstream of the melanocortin 4 receptor gene (MC4R). It is unclear if the SNPs directly influence MC4R function or expression, or if the SNPs are on a haplotype that predisposes to obesity or includes functionally relevant genetic variation (synthetic association). As both exist, functionally relevant mutations and polymorphisms in the MC4R coding region and a robust association downstream of the gene, MC4R is an ideal model to explore synthetic association.
We analyzed a genomic region (364.9 kb) encompassing the MC4R in GWAS data of 424 obesity trios (extremely obese child/adolescent and both parents). SNP rs12970134 showed the lowest p-value (p = 0.004; relative risk for the obesity effect allele: 1.37); conditional analyses on this SNP revealed that 7 of 78 analyzed SNPs provided independent signals (p≤0.05). These 8 SNPs were used to derive two-marker haplotypes. The three best (according to p-value) haplotype combinations were chosen for confirmation in 363 independent obesity trios. The confirmed obesity effect haplotype includes SNPs 3′ and 5′ of the MC4R. Including MC4R coding variants in a joint model had almost no impact on the effect size estimators expected under synthetic association.
A haplotype reaching from a region 5′ of the MC4R to a region at least 150 kb from the 3′ end of the gene showed a stronger association to obesity than single SNPs. Synthetic association analyses revealed that MC4R coding variants had almost no impact on the association signal. Carriers of the haplotype should be enriched for relevant mutations outside the MC4R coding region and could thus be used for re-sequencing approaches. Our data also underscore the problems underlying the identification of relevant mutations depicted by GWAS derived SNPs.
Genetic contribution to the development of attention deficit hyperactivity disorder (ADHD) is well established. Seven independent genome-wide linkage scans have been performed to map loci that increase the risk for ADHD. Although significant linkage signals were identified in some of the studies, there has been limited replications between the various independent datasets. The current study gathered the results from all seven of the ADHD linkage scans and performed a Genome Scan Meta Analysis (GSMA) to identify the genomic region with most consistent linkage evidence across the studies. Genome-wide significant linkage (PSR=0.00034, POR=0.04) was identified on chromosome 16 between 64 and 83 Mb. In addition there are nine other genomic regions from the GSMA showing nominal or suggestive evidence of linkage. All these linkage results may be informative and focus the search for novel ADHD susceptibility genes.
ADHD; GSMA; linkage
Meta-analyses of population-based genome-wide association studies (GWAS) in adults have recently led to the detection of new genetic loci for obesity. Here we aimed to discover additional obesity loci in extremely obese children and adolescents. We also investigated if these results generalize by estimating the effects of these obesity loci in adults and in population-based samples including both children and adults. We jointly analysed two GWAS of 2,258 individuals and followed-up the best, according to lowest p-values, 44 single nucleotide polymorphisms (SNP) from 21 genomic regions in 3,141 individuals. After this DISCOVERY step, we explored if the findings derived from the extremely obese children and adolescents (10 SNPs from 5 genomic regions) generalized to (i) the population level and (ii) to adults by genotyping another 31,182 individuals (GENERALIZATION step). Apart from previously identified FTO, MC4R, and TMEM18, we detected two new loci for obesity: one in SDCCAG8 (serologically defined colon cancer antigen 8 gene; p = 1.85×10−8 in the DISCOVERY step) and one between TNKS (tankyrase, TRF1-interacting ankyrin-related ADP-ribose polymerase gene) and MSRA (methionine sulfoxide reductase A gene; p = 4.84×10−7), the latter finding being limited to children and adolescents as demonstrated in the GENERALIZATION step. The odds ratios for early-onset obesity were estimated at ∼1.10 per risk allele for both loci. Interestingly, the TNKS/MSRA locus has recently been found to be associated with adult waist circumference. In summary, we have completed a meta-analysis of two GWAS which both focus on extremely obese children and adolescents and replicated our findings in a large followed-up data set. We observed that genetic variants in or near FTO, MC4R, TMEM18, SDCCAG8, and TNKS/MSRA were robustly associated with early-onset obesity. We conclude that the currently known major common variants related to obesity overlap to a substantial degree between children and adults.
Genome-wide association studies (GWAS) have successfully contributed to the detection of genetic variants involved in body-weight regulation. We jointly analysed two GWAS for early-onset extreme obesity in 2,258 individuals of European origin and followed-up the findings in 3,141 individuals. Evidence for association of markers in two new genetic loci was shown (SDCCAG8 on chromosome 1q43–q44 and between TNKS/MSRA on chromosome 8p23.1). We also re-identified variants in or near FTO, MC4R, and TMEM18 to be associated with extreme obesity. In addition, we assessed the effect of the markers in 31,182 obese, lean, normal weight, and unselected individuals from population-based samples and showed that the variants near FTO, MC4R, TMEM18, and SDCCAG8 were consistently associated with obesity. For variants of TNKS/MSRA, the obesity association was limited to children and adolescents. In summary, we detected two new obesity loci and confirmed that the currently known major common variants related to obesity overlap to a substantial degree between children and adults.
The heritability of obesity and body weight in general is high. A small number of confirmed monogenic forms of obesity—the respective mutations are sufficient by themselves to cause the condition in food abundant societies—have been identified by molecular genetic studies. The elucidation of these genes, mostly based on animal and family studies, has led to the identification of important pathways to the disorder and thus to a deeper understanding of the regulation of body weight. The identification of inborn deficiency of the mostly adipocyte-derived satiety hormone leptin in extremely obese children from consanguineous families paved the way to the first pharmacological therapy for obesity based on a molecular genetic finding. The genetic predisposition to obesity for most individuals, however, has a polygenic basis. A polygenic variant by itself has a small effect on the phenotype; only in combination with other predisposing variants does a sizeable phenotypic effect arise. Common variants in the first intron of the ‘fat mass and obesity associated’ gene (FTO) result in an elevated body mass index (BMI) equivalent to approximately +0.4 kg/m² per risk allele. The FTO variants were originally detected in a genome wide association study (GWAS) pertaining to type 2 diabetes mellitus. Large meta-analyses of GWAS have subsequently identified additional polygenic variants. Up to December 2009, polygenic variants have been confirmed in a total of 17 independent genomic regions. Further study of genetic effects on human body weight regulation should detect variants that will explain a larger proportion of the heritability. The development of new strategies for diagnosis, treatment and prevention of obesity can be anticipated.
Heritability; Genome wide
The polycystic ovary syndrome (PCOS), a common endocrine disorder in women of child-bearing age, mainly characterised by chronic anovulation and hyperandrogenism, is often associated with insulin resistance (IR) and obesity. Its etiology and the role of IR and obesity in PCOS are not fully understood. We examined the influence of validated genetic variants conferring susceptibility to obesity and/or type 2 diabetes mellitus (T2DM) on metabolic and PCOS-specific traits in patients with PCOS.
We conducted an association study in 386 patients with PCOS (defined by the Rotterdam-criteria) using single nucleotide polymorphisms (SNPs) in or in proximity to the fat mass and obesity associated gene (FTO), insulin-induced gene-2 (INSIG2), transcription factor 7-like 2 gene (TCF7L2) and melanocortin 4 receptor gene (MC4R). To compare the effect of FTO obesity risk alleles on BMI in patients with PCOS to unselected females of the same age range we genotyped 1,971 females from the population-based KORA-S4 study (Kooperative Gesundheitsforschung im Raum Augsburg, Survey 4).
The FTO risk allele was associated with IR traits and measures of increased body weight. In addition, the TCF7L2 SNP was associated with body weight traits. For the SNPs in the vicinity of INSIG2 and MC4R and for the other examined phenotypes there was no evidence for an association. In PCOS the observed per risk allele effect of FTO intron 1 SNP rs9939609 on BMI was +1.56 kg/m2, whereas it was +0.46 kg/m2 in females of the same age range from the general population as shown previously.
The stronger effect on body weight of the FTO SNP in PCOS might well have implications for the etiology of the disease.
The orexigenic effects of cannabinoids are limited by activation of the endocannabinoid degrading enzyme fatty acid amide hydrolase (FAAH). The aim of this study was to analyse whether FAAH alleles are associated with early and late onset obesity.
We initially assessed association of five single nucleotide polymorphisms (SNPs) in FAAH with early onset extreme obesity in up to 521 German obese children and both parents. SNPs with nominal p-values ≤ 0.1 were subsequently analysed in 235 independent German obesity families. SNPs associated with childhood obesity (p-values ≤ 0.05) were further analysed in 8,491 adult individuals of a population-based cohort (KORA) for association with adult obesity. One SNP was further analysed in 985 German obese adults and 588 normal and underweight controls. In parallel, we screened the FAAH coding region for novel sequence variants in 92 extremely obese children using single-stranded-conformation-polymorphism-analysis and denaturing HPLC and assessed the implication of the identified new variants for childhood obesity.
The trio analysis revealed some evidence for an association of three SNPs in FAAH (rs324420 rs324419 and rs873978) with childhood obesity (two-sided p-values between 0.06 and 0.10). Although analyses of these variants in 235 independent obesity families did not result in statistically significant effects (two-sided p-values between 0.14 and 0.75), the combined analysis of all 603 obesity families supported the idea of an association of two SNPs in FAAH (rs324420 and rs2295632) with early onset extreme obesity (p-values between 0.02 and 0.03). No association was, however, found between these variants and adult obesity. The mutation screen revealed four novel variants, which were not associated with early onset obesity (p > 0.05).
As we observed some evidence for an association of the FAAH variants rs2295632 rs324420 with early onset but not adult obesity, we conclude that the FAAH variants analyzed here at least do not seem to play a major role in the etiology of obesity within our samples.
Anorexia nervosa (AN) and bulimia nervosa (BN) are complex disorders characterized by disordered eating behavior where the patient’s attitude towards weight and shape, as well as their perception of body shape, are disturbed. Formal genetic studies on twins and families suggested a substantial genetic influence for AN and BN. Candidate gene studies have initially focused on the serotonergic and other central neurotransmitter systems and on genes involved in body weight regulation. Hardly any of the positive findings achieved in these studies were unequivocally confirmed or substantiated in meta-analyses. This might be due to too small sample sizes and thus low power and/or the genes underlying eating disorders have not yet been analyzed. However, some studies that also used subphenotypes (e.g., restricting type of AN) led to more specific results; however, confirmation is as yet mostly lacking. Systematic genome-wide linkage scans based on families with at least two individuals with an eating disorder (AN or BN) revealed initial linkage regions on chromosomes 1, 3 and 4 (AN) and 10p (BN). Analyses on candidate genes in the chromosome 1 linkage region led to the (as yet unconfirmed) identification of certain variants associated with AN. Genome-wide association studies are under way and will presumably help to identify genes and pathways involved in these eating disorders. The elucidation of the molecular mechanisms underlying eating disorders might improve therapeutic approaches.
5-HT2A receptor gene; Melanocortin 4 receptor gene; GWAS
The INSIG2 rs7566605 polymorphism was identified for obesity (BMI≥30 kg/m2) in one of the first genome-wide association studies, but replications were inconsistent. We collected statistics from 34 studies (n = 74,345), including general population (GP) studies, population-based studies with subjects selected for conditions related to a better health status (‘healthy population’, HP), and obesity studies (OB). We tested five hypotheses to explore potential sources of heterogeneity. The meta-analysis of 27 studies on Caucasian adults (n = 66,213) combining the different study designs did not support overall association of the CC-genotype with obesity, yielding an odds ratio (OR) of 1.05 (p-value = 0.27). The I2 measure of 41% (p-value = 0.015) indicated between-study heterogeneity. Restricting to GP studies resulted in a declined I2 measure of 11% (p-value = 0.33) and an OR of 1.10 (p-value = 0.015). Regarding the five hypotheses, our data showed (a) some difference between GP and HP studies (p-value = 0.012) and (b) an association in extreme comparisons (BMI≥32.5, 35.0, 37.5, 40.0 kg/m2 versus BMI<25 kg/m2) yielding ORs of 1.16, 1.18, 1.22, or 1.27 (p-values 0.001 to 0.003), which was also underscored by significantly increased CC-genotype frequencies across BMI categories (10.4% to 12.5%, p-value for trend = 0.0002). We did not find evidence for differential ORs (c) among studies with higher than average obesity prevalence compared to lower, (d) among studies with BMI assessment after the year 2000 compared to those before, or (e) among studies from older populations compared to younger. Analysis of non-Caucasian adults (n = 4889) or children (n = 3243) yielded ORs of 1.01 (p-value = 0.94) or 1.15 (p-value = 0.22), respectively. There was no evidence for overall association of the rs7566605 polymorphism with obesity. Our data suggested an association with extreme degrees of obesity, and consequently heterogeneous effects from different study designs may mask an underlying association when unaccounted for. The importance of study design might be under-recognized in gene discovery and association replication so far.
A polymorphism of the INSIG2 gene was identified as being associated with obesity in one of the first genome-wide association studies. However, this association has since then been highly debated upon inconsistent subsequent reports. We collected association information from 34 studies including a total of 74,000 participants. In a meta-analysis of the 27 studies including 66,000 Caucasian adults, we found no overall association of this polymorphism rs7566605 with obesity, comparing subjects with a body-mass-index (BMI)≥30 kg/m2 with normal BMI subjects (BMI<30 kg/m2). Our data suggested an association of this polymorphism with extreme obesity (e.g., BMI≥37.5 kg/m2) compared to normal controls. Such an association with extreme obesity might induce heterogeneous effects from different study designs depending on the proportion of extreme obesity included by the design. However, further studies would be required to substantiate this finding. The importance of study design might be under-recognized in gene discovery and association replication so far.
Previous studies have suggested that a variant in the melanocortin-4 receptor (MC4R) gene is important in protecting against common obesity. Larger studies are needed, however, to confirm this relation.
We assessed the association between the V103I polymorphism in the MC4R gene and obesity in three UK population based cohort studies, totalling 8,304 individuals. We also did a meta-analysis of relevant studies, involving 10,975 cases and 18,588 controls, to place our findings in context.
In an analysis of all studies, individuals carrying the isoleucine allele had an 18% (95% CI 4-30%, p=0·015) lower risk of obesity compared with noncarriers. There was no heterogeneity among studies and no apparent publication bias.
This study confirms that the V103I polymorphism protects against human obesity at a population level. As such it provides proof of principle that specific gene variants may, at least in part, explain susceptibility and resistance to common forms of human obesity. A better understanding of the mechanisms underlying this association will help determine whether changes in MC4R activity have therapeutic potential.
To identify common variants influencing body mass index (BMI), we analyzed genome-wide association data from 16,876 individuals of European descent. After previously reported variants in FTO, the strongest association signal (rs17782313, P = 2.9 × 10−6) mapped 188 kb downstream of MC4R (melanocortin-4 receptor), mutations of which are the leading cause of monogenic severe childhood-onset obesity. We confirmed the BMI association in 60,352 adults (per-allele effect = 0.05 Z-score units; P = 2.8 × 10−15) and 5,988 children aged 7–11 (0.13 Z-score units; P = 1.5 × 10−8). In case-control analyses (n = 10,583), the odds for severe childhood obesity reached 1.30 (P = 8.0 × 10−11). Furthermore, we observed overtransmission of the risk allele to obese offspring in 660 families (P (pedigree disequilibrium test average; PDT-avg) = 2.4 × 10−4). The SNP location and patterns of phenotypic associations are consistent with effects mediated through altered MC4R function. Our findings establish that common variants near MC4R influence fat mass, weight and obesity risk at the population level and reinforce the need for large-scale data integration to identify variants influencing continuous biomedical traits.
Gastric inhibitory polypeptide (GIP) is postulated to be involved in type 2 diabetes mellitus and obesity. It exerts its function through its receptor, GIPR. We genotyped three GIPR SNPs (rs8111428, rs2302382 and rs1800437) in German families with at least one obese index patient, two case-control studies and two cross-sectional population-based studies.
Genotyping was performed by MALDI-TOF, ARMS-PCR and RFLP. The family-study: 761 German families with at least one extremely obese child or adolescent (n = 1,041) and both parents (n = 1,522). Case-control study: (a) German obese children (n = 333) and (b) obese adults (n = 987) in comparison to 588 adult lean controls. The two cross-sectional population-based studies: KORA (n = 8,269) and SHIP (n = 4,310).
We detected over-transmission of the A-allele of rs2302382 in the German families (pTDT-Test = 0.0089). In the combined case-control sample, we estimated an odd ratio of 1.54 (95%CI 1.09;2.19, pCA-Test = 0.014) for homozygotes of the rs2302382 A-allele compared to individuals with no A-allele. A similar trend was found in KORA where the rs2302382 A-allele led to an increase of 0.12 BMI units (p = 0.136). In SHIP, however, the A-allele of rs2302382 was estimated to contribute an average decrease of 0.27 BMI units (p-value = 0.031).
Our data suggest a potential relevance of GIPR variants for obesity. However, additional studies are warranted in light of the conflicting results obtained in one of the two population-based studies.
A recent genome-wide association (GWA) study of U.S. Caucasians suggested that eight single nucleotide polymorphisms (SNPs) in CTNNBL1 are associated with obesity and increased fat mass. We analysed the respective SNPs in data from our previously published GWA for early onset obesity (case-control design), in GWA data from a population-based cohort of adults, and in an independent family-based obesity study. We investigated whether variants in CTNNBL1 (including rs6013029) and in three other genes (SH3PXD2B, SLIT3 and FLJ42133,) were associated with obesity.
The GWA studies were carried out using Affymetrix® SNP Chips with approximately 500,000 markers each. In the families, SNP rs6013029 was genotyped using the TaqMan® allelic discrimination assay. The German case-control GWA included 487 extremely obese children and adolescents and 442 healthy lean individuals. The adult GWA included 1,644 individuals from a German population-based study (KORA). The 775 independent German families consisted of extremely obese children and adolescents and their parents.
We found no evidence for an association of the reported variants in CTNNBL1 with early onset obesity or increased BMI. Further, in our family-based study we found no evidence for over-transmission of the rs6013029 risk-allele T to obese children. Additionally, we found no evidence for an association of SH3PXD2B, SLIT3 and FLJ42133 variants in our two GWA samples.
We detected no confirmation of the recent association of variants in CTNNBL1 with obesity in a population of Central European ancestry.
Several lines of evidence indicate that the central cannabinoid receptor 1 (CNR1) as well as the major endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH), N-acylethanolamine-hydrolyzing acid amidase (NAAA) and monoglyceride lipase (MGLL) are implicated in mediating the orexigenic effects of cannabinoids. The aim of this study was to analyse whether nucleotide sequence variations in the CNR1, FAAH, NAAA and MGLL genes are associated with anorexia nervosa (AN).
We analysed the association of a previously described (AAT)n repeat in the 3' flanking region of CNR1 as well as a total of 15 single nucleotide polymorphisms (SNPs) representative of regions with restricted haplotype diversity in CNR1, FAAH, NAAA or MGLL in up to 91 German AN trios (patient with AN and both biological parents) using the transmission-disequilibrium-test (TDT). One SNP was additionally analysed in an independent case-control study comprising 113 patients with AN and 178 normal weight controls. Genotyping was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ARMS-PCR or using 3730xl capillary sequencers.
The TDT revealed no evidence for association for any of the SNPs or the (AAT)n repeat with AN (all two-sided uncorrected p-values > 0.05). The lowest p-value of 0.11 was detected for the A-allele of the CNR1 SNP rs1049353 for which the transmission rate was 59% (95% confidence interval 47%...70%). Further genotyping of rs1049353 in 113 additional independent patients with AN and 178 normal weight controls could not substantiate the initial trend for association (p = 1.00).
As we found no evidence for an association of genetic variation in CNR1, FAAH, NAAA and MGLL with AN, we conclude that genetic variations in these genes do not play a major role in the etiology of AN in our study groups.
Background and Objectives
Although more and more genetic information is available, it is unclear whether this information is helpful for patients. Therefore, we assessed the positive and negative effects of informing obese people about the genetic etiology of being overweight.
Two hundred ninety-four obese people were randomized to 2 interventions (a 1-session consultation for obese people on how to manage obesity either including genetic information or not); their results were compared to a control group (116). Subjects were assessed before and after consultation and 6 months later.
Weight, scales on feeling guilty for being overweight, self-control, negative mood (primary endpoint), body acceptance, restraint eating.
Both types of consultations were considered helpful by the participants, and had comparable effects on body weight. The consultation with genetic information was rated superior in terms of leading to new insights (advantage for consultation with genetic information, even 6 months later; p = 0.046). No negative effects (e.g., loss of self-efficacy/self-control, increase of body weight; all p > 0.20 for interaction consultation × time) were observed for informing obese people about the genetic etiology of being overweight. The consultation resulted in long-term improvement of negative mood if it included genetic information in the case of participants with a family history of obesity and if it included no genetic information in the case of obese people without a family history of obesity (p = 0.03 for interaction of group, intervention, and time).
Consultations in obesity can be helpful in general. These consultations should include genetic information if people have a family history of obesity.
obesity; consultation; genetic counseling; MC4R mutation
We have previously identified strong association of six single nucleotide polymorphisms (SNPs) in FTO (fat mass and obesity associated gene) to early onset extreme obesity within the first genome wide association study (GWA) for this phenotype. The aim of this study was to investigate whether the obesity risk allele of one of these SNPs (rs9939609) is associated with weight loss in a lifestyle intervention program. Additionally, we tested for association of rs9939609 alleles with fasting blood parameters indicative of glucose and lipid metabolism.
We initially analysed rs9939609 in a case-control study comprising 519 German overweight and obese children and adolescents and 178 normal weight adults. In 207 of the obese individuals who took part in the outpatient obesity intervention program 'Obeldicks' we further analysed whether carrier status of the obesity risk A-allele of rs9939609 has a differential influence on weight loss after the intervention program. Additionally, we investigated in 480 of the overweight and obese patients whether rs9939609 is associated with fasting blood levels of glucose, triglycerides and HDL and LDL-cholesterol. Genotyping was performed using allele specific polymerase chain reaction (ARMS-PCR). For the association study (case-control approach), the Cochran-Armitage trend test was applied. Blood parameters were analysed using commercially available test kits and the log10-transformed blood parameters and changes in BMI-standard deviation scores (BMI-SDS) were analysed by linear regression with sex and age as covariates under an additive mode of inheritance with the rs9939609 A-allele as risk allele.
We confirmed the association of the risk A-allele of rs9939609 with overweight and early onset obesity (one sided p = 0.036). However, we observed no association of rs9939609 alleles with weight loss or fasting levels of blood glucose, triglycerides and cholesterol.
We confirmed the rs9939609 A-allele as a risk factor for early onset obesity whereas its impact on weight loss or on serum levels of glucose, triglycerides and cholesterol could not be detected in our samples.
This study is registered at clinicaltrials.gov (NCT00435734).
Rare mutations of the low-density lipoprotein receptor gene (LDLR) cause familial hypercholesterolemia, which increases the risk for coronary artery disease (CAD). Less is known about the implications of common genetic variation in the LDLR gene regarding the variability of cholesterol levels and risk of CAD.
Imputed genotype data at the LDLR locus on 1 644 individuals of a population-based sample were explored for association with LDL-C level. Replication of association with LDL-C level was sought for the most significant single nucleotide polymorphism (SNP) within the LDLR gene in three European samples comprising 6 642 adults and 533 children. Association of this SNP with CAD was examined in six case-control studies involving more than 15 000 individuals.
Each copy of the minor T allele of SNP rs2228671 within LDLR (frequency 11%) was related to a decrease of LDL-C levels by 0.19 mmol/L (95% confidence interval (CI) [0.13–0.24] mmol/L, p = 1.5×10−10). This association with LDL-C was uniformly found in children, men, and women of all samples studied. In parallel, the T allele of rs2228671 was associated with a significantly lower risk of CAD (Odds Ratio per copy of the T allele: 0.82, 95% CI [0.76–0.89], p = 2.1×10−7). Adjustment for LDL-C levels by logistic regression or Mendelian Randomisation models abolished the significant association between rs2228671 with CAD completely, indicating a functional link between the genetic variant at the LDLR gene locus, change in LDL-C and risk of CAD.
A common variant at the LDLR gene locus affects LDL-C levels and, thereby, the risk for CAD.
At present pathogenic mechanisms of cancer cachexia are poorly understood. Previous evidence in animal models implicates the melanocortin-4 receptor gene (MC4R) in the development of cancer cachexia. In humans, MC4R mutations that lead to an impaired receptor function are associated with obesity; in contrast, the most frequent polymorphism (Val103Ile, rs2229616; heterozygote frequency approximately 2%) was shown to be negatively associated with obesity. We tested if cancer patients that are homo-/heterozygous for the Val103Ile polymorphism are more likely to develop cachexia and/or a loss of appetite than non-carriers of the 103Ile-allele.
BMI (body mass index in kg/m2) of 509 patients (295 males) with malignant neoplasms was determined; additionally patients were asked about premorbid/pretherapeutical changes of appetite and weight loss. Cachexia was defined as a weight loss of at least 5% prior to initiation of therapy; to fulfil this criterion this weight loss had to occur independently of other plausible reasons; in single cases weight loss was the initial reason for seeing a physician. The average age in years (± SD) was 59.0 ± 14.5 (males: 58.8 ± 14.0, females 59.2 ± 14.0). Blood samples were taken for genotyping of the Val103Ile by PCR- RFLP.
Most of the patients suffered from lymphoma, leukaemia and gastrointestinal tumours. 107 of the patients (21%) fulfilled our criteria for cancer cachexia. We did not detect association between the Val103Ile polymorphism and cancer cachexia. However, if we exploratively excluded the patients with early leucaemic stages, we detected a trend towards the opposite effect (p < 0.05); heterozygotes for the 103Ile-allele developed cancer cachexia less frequently in comparison to the rest of the study group. Changes of appetite were not associated with the 103Ile-allele carrier status (p > 0.39).
Heterozygotes for the 103Ile-allele are not more prone to develop cancer cachexia than patients without this allele; possibly, Ile103 carriers might be more resistant to cancer cachexia in patients with solid tumors. Further studies of the melanocortinergic system in cachexia of patients with solid tumors are warranted.
Obesity is a major health problem. Although heritability is substantial, genetic mechanisms predisposing to obesity are not very well understood. We have performed a genome wide association study (GWA) for early onset (extreme) obesity.
a) GWA (Genome-Wide Human SNP Array 5.0 comprising 440,794 single nucleotide polymorphisms) for early onset extreme obesity based on 487 extremely obese young German individuals and 442 healthy lean German controls; b) confirmatory analyses on 644 independent families with at least one obese offspring and both parents. We aimed to identify and subsequently confirm the 15 SNPs (minor allele frequency ≥10%) with the lowest p-values of the GWA by four genetic models: additive, recessive, dominant and allelic. Six single nucleotide polymorphisms (SNPs) in FTO (fat mass and obesity associated gene) within one linkage disequilibrium (LD) block including the GWA SNP rendering the lowest p-value (rs1121980; log-additive model: nominal p = 1.13×10−7, corrected p = 0.0494; odds ratio (OR)CT 1.67, 95% confidence interval (CI) 1.22–2.27; ORTT 2.76, 95% CI 1.88–4.03) belonged to the 15 SNPs showing the strongest evidence for association with obesity. For confirmation we genotyped 11 of these in the 644 independent families (of the six FTO SNPs we chose only two representing the LD bock). For both FTO SNPs the initial association was confirmed (both Bonferroni corrected p<0.01). However, none of the nine non-FTO SNPs revealed significant transmission disequilibrium.
Our GWA for extreme early onset obesity substantiates that variation in FTO strongly contributes to early onset obesity. This is a further proof of concept for GWA to detect genes relevant for highly complex phenotypes. We concurrently show that nine additional SNPs with initially low p-values in the GWA were not confirmed in our family study, thus suggesting that of the best 15 SNPs in the GWA only the FTO SNPs represent true positive findings.