Correction: Investigation of common, low-frequency and rare genome-wide variation in anorexia nervosa.

The fortieth author's name was listed incorrectly. The correct presentation is A Keski-Rahkonen.

Investigation of common, low-frequency and rare genome-wide variation in anorexia nervosa.

Anorexia nervosa (AN) is a complex neuropsychiatric disorder presenting with dangerously low body weight, and a deep and persistent fear of gaining weight. To date, only one genome-wide significant locus associated with AN has been identified. We performed an exome-chip based genome-wide association studies (GWAS) in 2158 cases from nine populations of European origin and 15 485 ancestrally matched controls. Unlike previous studies, this GWAS also probed association in low-frequency and rare variants. Sixteen independent variants were taken forward for in silico and de novo replication (11 common and 5 rare). No findings reached genome-wide significance. Two notable common variants were identified: rs10791286, an intronic variant in OPCML (P=9.89 × 10-6), and rs7700147, an intergenic variant (P=2.93 × 10-5). No low-frequency variant associations were identified at genome-wide significance, although the study was well-powered to detect low-frequency variants with large effect sizes, suggesting that there may be no AN loci in this genomic search space with large effect sizes.

Evidence for three genetic loci involved in both anorexia nervosa risk and variation of body mass index.

The maintenance of normal body weight is disrupted in patients with anorexia nervosa (AN) for prolonged periods of time. Prior to the onset of AN, premorbid body mass index (BMI) spans the entire range from underweight to obese. After recovery, patients have reduced rates of overweight and obesity. As such, loci involved in body weight regulation may also be relevant for AN and vice versa. Our primary analysis comprised a cross-trait analysis of the 1000 single-nucleotide polymorphisms (SNPs) with the lowest P-values in a genome-wide association meta-analysis (GWAMA) of AN (GCAN) for evidence of association in the largest published GWAMA for BMI (GIANT). Subsequently we performed sex-stratified analyses for these 1000 SNPs. Functional ex vivo studies on four genes ensued. Lastly, a look-up of GWAMA-derived BMI-related loci was performed in the AN GWAMA. We detected significant associations (P-values <5 × 10-5, Bonferroni-corrected P<0.05) for nine SNP alleles at three independent loci. Interestingly, all AN susceptibility alleles were consistently associated with increased BMI. None of the genes (chr. 10: CTBP2, chr. 19: CCNE1, chr. 2: CARF and NBEAL1; the latter is a region with high linkage disequilibrium) nearest to these SNPs has previously been associated with AN or obesity. Sex-stratified analyses revealed that the strongest BMI signal originated predominantly from females (chr. 10 rs1561589; Poverall: 2.47 × 10-06/Pfemales: 3.45 × 10-07/Pmales: 0.043). Functional ex vivo studies in mice revealed reduced hypothalamic expression of Ctbp2 and Nbeal1 after fasting. Hypothalamic expression of Ctbp2 was increased in diet-induced obese (DIO) mice as compared with age-matched lean controls. We observed no evidence for associations for the look-up of BMI-related loci in the AN GWAMA. A cross-trait analysis of AN and BMI loci revealed variants at three chromosomal loci with potential joint impact. The chromosome 10 locus is particularly promising given that the association with obesity was primarily driven by females. In addition, the detected altered hypothalamic expression patterns of Ctbp2 and Nbeal1 as a result of fasting and DIO implicate these genes in weight regulation.

Genome-wide analysis of rare copy number variations reveals PARK2 as a candidate gene for attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurodevelopmental disorder. Genetic loci have not yet been identified by genome-wide association studies. Rare copy number variations (CNVs), such as chromosomal deletions or duplications, have been implicated in ADHD and other neurodevelopmental disorders. To identify rare (frequency ≤1%) CNVs that increase the risk of ADHD, we performed a whole-genome CNV analysis based on 489 young ADHD patients and 1285 adult population-based controls and identified one significantly associated CNV region. In tests for a global burden of large (>500 kb) rare CNVs, we observed a nonsignificant (P=0.271) 1.126-fold enriched rate of subjects carrying at least one such CNV in the group of ADHD cases. Locus-specific tests of association were used to assess if there were more rare CNVs in cases compared with controls. Detected CNVs, which were significantly enriched in the ADHD group, were validated by quantitative (q)PCR. Findings were replicated in an independent sample of 386 young patients with ADHD and 781 young population-based healthy controls. We identified rare CNVs within the parkinson protein 2 gene (PARK2) with a significantly higher prevalence in ADHD patients than in controls (P=2.8 × 10(-4) after empirical correction for genome-wide testing). In total, the PARK2 locus (chr 6: 162 659 756-162 767 019) harboured three deletions and nine duplications in the ADHD patients and two deletions and two duplications in the controls. By qPCR analysis, we validated 11 of the 12 CNVs in ADHD patients (P=1.2 × 10(-3) after empirical correction for genome-wide testing). In the replication sample, CNVs at the PARK2 locus were found in four additional ADHD patients and one additional control (P=4.3 × 10(-2)). Our results suggest that copy number variants at the PARK2 locus contribute to the genetic susceptibility of ADHD. Mutations and CNVs in PARK2 are known to be associated with Parkinson disease.

[Genetic and epigenetic mechanisms in obesity]. / Genetik und Epigenetik der Adipositas.

Obesity is a relevant medical problem. Around 60 % of German adults are overweight, 20 % are obese. The hereditary contribution to the variance of body weight is high. Nevertheless, molecular genetic studies have as yet explained only a small part of the inter-individual variability in the body mass index (BMI). Monogenic forms of obesity, in which loss of a single gene product leads to extreme obesity, are very infrequent. Variance of body weight is commonly explained by a complex interplay of many genetic variants (polygenic obesity). Each variant contributes only a small amount to the body weight. Currently, the largest published analysis of individuals of European origin identified 32 genetic variations (single nucleotide polymorphisms, SNPs) associated with BMI (obesity). Overall, these polygenic obesity variants only explain about 5 % of the variance of the BMI. In addition to the DNA variants epigenetic factors seem to also play a role in body weight regulation. These epigenetic marks can change in the course of life. They might provide an interface between genetic and environmental influences. It is conceivable that in future it will be possible to use epigenetic and genetic markers to detect a predisposition for obesity and to improve prevention and therapy.

Bipolar disorder risk alleles in children with ADHD.

Bipolar disorder (BD) and attention deficit/hyperactivity disorder (ADHD) may share common genetic risk factors as indicated by the high co-morbidity of BD and ADHD, their phenotypic overlap especially in pediatric populations, the high heritability of both disorders, and the co-occurrence in families. We therefore examined whether known polygenic BD risk alleles are associated with ADHD. We chose the eight best SNPs of the recent genome-wide association study (GWAS) of BD patients of German ancestry and the nine SNPs from international GWAS meeting a 'genome-wide significance' level of α = 5 × 10(-8). A GWAS was performed in 495 ADHD children and 1,300 population-based controls using HumanHap550v3 and Human660 W-Quadv1 BeadArrays. We found no significant association of childhood ADHD with single BD risk alleles surviving adjustment for multiple testing. Yet, risk alleles for BD and ADHD were directionally consistent at eight of nine loci with the strongest support for three SNPs in or near NCAN, BRE, and LMAN2L. The polygene analysis for the BP risk alleles at all 14 loci indicated a higher probability of being a BD risk allele carrier in the ADHD cases as compared to the controls. At a moderate power to detect association with ADHD, if true effects were close to estimates from GWAS for BD, our results suggest that the possible contribution of BD risk variants to childhood ADHD risk is considerably lower than for BD. Yet, our findings should encourage researchers to search for common genetic risk factors in BD and childhood ADHD in future studies.

Impact of FTO genotypes on BMI and weight in polycystic ovary syndrome: a systematic review and meta-analysis.

AIMS/HYPOTHESIS: FTO gene single nucleotide polymorphisms (SNPs) have been shown to be associated with obesity-related traits and type 2 diabetes. Several small studies have suggested a greater than expected effect of the FTO rs9939609 SNP on weight in polycystic ovary syndrome (PCOS). We therefore aimed to examine the impact of FTO genotype on BMI and weight in PCOS. METHODS: A systematic search of medical databases (PubMed, EMBASE and Cochrane CENTRAL) was conducted up to the end of April 2011. Seven studies describing eight distinct PCOS cohorts were retrieved; seven were genotyped for SNP rs9939609 and one for SNP rs1421085. The per allele effect on BMI and body weight increase was calculated and subjected to meta-analysis. RESULTS: A total of 2,548 women with PCOS were included in the study; 762 were TT homozygotes, 1,253 had an AT/CT genotype, and 533 were AA/CC homozygotes. Each additional copy of the effect allele (A/C) increased the BMI by a mean of 0.19 z score units (95% CI 0.13, 0.24; p = 2.26 × 10(-11)) and body weight by a mean of 0.20 z score units (95% CI 0.14, 0.26; p = 1.02 × 10(-10)). This translated into an approximately 3.3 kg/m(2) increase in BMI and an approximately 9.6 kg gain in body weight between TT and AA/CC homozygotes. The association between FTO genotypes and BMI was stronger in the cohorts with PCOS than in the general female populations from large genome-wide association studies. Deviation from an additive genetic model was observed in heavier populations. CONCLUSIONS/INTERPRETATION: The effect of FTO SNPs on obesity-related traits in PCOS seems to be more than two times greater than the effect found in large population-based studies. This suggests an interaction between FTO and the metabolic context or polygenic background of PCOS.

The fatty acid amide hydrolase (FAAH) gene variant rs324420 AA/AC is not associated with weight loss in a 1-year lifestyle intervention for obese children and adolescents.

Adult obese carriers of the A allele of SNP rs324420 in the fatty acid amide hydrolase (FAAH) gene lose more weight and improve associated phenotypes better than non-carriers during an intervention. We aimed to replicate this finding in obese children and adolescents undergoing a one year lifestyle intervention (Obeldicks program). A total of 453 overweight and obese children and adolescents (10.8±2.6 years, BMI-SDS 2.4±0.5; 55% girls) were genotyped for rs324420 (C/A) by restriction fragment length polymorphism (RFLP) analysis. Participants were prescribed a balanced diet, containing 55 En% carbohydrates, 30 En% fat, and 15 En% proteins. Moreover, they took part in an exercise therapy once a week. Blood was taken at baseline and after 1 year of intervention. Anthropometric (height, weight, BMI, and BMI-SDS) and plasma parameters (total cholesterol, LDL-cholesterol, HDL-cholesterol, triacylglycerides, glucose, insulin, and HOMA) as well as blood pressure were measured. Both mean BMI and BMI-SDS improved significantly. The mean systolic blood pressure was also lowered and concentrations of HDL-cholesterol increased significantly. However, none of the measured changes were associated with FAAH rs324420 AA/AC genotype. We did not detect evidence for an association of FAAH genotypes with weight reduction in overweight and obese children and adolescents. Hence, the previous finding in adults could not be confirmed. As the length (1 year as compared to 3 months) and mode of treatment (hypocaloric diet in adults vs. physical activity plus balanced meals) of the interventions varied, these parameters might have influenced the inconsistent results.

Genes and lifestyle factors in obesity: results from 12,462 subjects from MONICA/KORA.

BACKGROUND: 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. OBJECTIVE: 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. DESIGN: The association of seven polymorphisms in or near the genes NEGR1, TMEM18, MTCH2, FTO, MC4R, SH2B1 and 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. RESULTS: The minor allele of polymorphism rs6548238 C>T (TMEM18) was associated with lower BMI (-0.418 kg m(-2), P=1.22 × 10(-8)), and of polymorphisms rs9935401 G>A (FTO) and rs7498665 A>G (SH2B1) with increased BMI (0.290 kg m(-2), P=2.85 × 10(-7) and 0.145 kg m(-2), 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 with 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. CONCLUSIONS: 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.

Association between the insulin-induced gene 2 (INSIG2) and weight gain in a German sample of antipsychotic-treated schizophrenic patients: perturbation of SREBP-controlled lipogenesis in drug-related metabolic adverse effects?

Atypical antipsychotics are nowadays the most widely used drugs to treat schizophrenia and other psychosis. Unfortunately, some of them can cause major metabolic adverse effects, such as weight gain, dyslipidemia and type 2 diabetes. The underlying lipogenic mechanisms of the antipsychotic drugs are not known, but several studies have focused on a central effect in the hypothalamic control of appetite regulation and energy expenditure. In a functional convergent genomic approach we recently used a cellular model and demonstrated that orexigenic antipsychotics that induce weight gain activate the expression of lipid biosynthesis genes controlled by the sterol regulatory element-binding protein (SREBP) transcription factors. We therefore hypothesized that the major genes involved in the SREBP activation of fatty acids and cholesterol production (SREBF1, SREBF2, SCAP, INSIG1 and INSIG2) would be strong candidate genes for interindividual variation in drug-induced weight gain. We genotyped a total of 44 HapMap-selected tagging single nucleotide polymorphisms in a sample of 160 German patients with schizophrenia that had been monitored with respect to changes in body mass index during antipsychotic drug treatment. We found a strong association (P=0.0003-0.00007) between three markers localized within or near the INSIG2 gene (rs17587100, rs10490624 and rs17047764) and antipsychotic-related weight gain. Our finding is supported by the recent involvement of the INSIG2 gene in obesity in the general population and implicates SREBP-controlled lipogenesis in drug-induced metabolic adverse effects.

[Genetic determinants of obesity. Current issues]. / Genetische Ursachen der Adipositas. Zum Stand der Forschung.

A small number of confirmed major genes for human obesity has been identified by molecular genetic studies; mutations of these have a strong influence on the development of excessive body weight. However, the underlying mutations are rare and do not explain the current obesity epidemic. The genetic predisposition to common obesity most likely has a polygenic basis, and each single gene variant has only a small influence on body weight. The introduction of genome-wide association scans (GWAS) offers new opportunities for the study of complex diseases. The receptor variant with the amino acid isoleucin (wildtype: valine) at position 103 of the melanocortin-4 receptor (MC4R) represents the first confirmed polygenic variant with an influence on body mass index; additional polymorphisms located 188 kb at the 3' end of the MC4R have also been shown to have an effect on body weight. Variants in the first intron of the "fat mass and obesity associated" gene (FTO) confer the most pronounced polygenic effect on obesity (+0.4 kg/m(2) per allele); these variants were originally detected in 2007 in GWAS pertaining to type 2 diabetes mellitus. Recently, additional SNPs with a polygenic effect on obesity have been identified in three large GWAS. By December 2009, 17 solidly confirmed polygenes for body weight regulation have been reported.

Gain-of-function variants in the melanocortin 4 receptor gene confer susceptibility to binge eating disorder in subjects with obesity: a systematic review and meta-analysis.

The association between coding variants in the melanocortin 4 receptor gene (MC4R) and binge eating disorder (BED) in patients with obesity is controversial. Two independent reviewers systematically searched MEDLINE, Embase, PsycINFO, BIOSIS Previews, Web of Science Core Collection and Google Scholar up to February 2018, using terms describing the MC4R gene and BED. Six of 103 identified references were included. Studies examined associations between at least one coding variant/mutation in MC4R and BED and screened for BED as per the Diagnostic and Statistical Manual of Mental Disorders. Risk of bias was assessed using a modified version of the Q-Genie tool, and overall quality of evidence was assessed using Grading of Recommendations Assessment, Development and Evaluation guidance. Meta-analysis was conducted via logistic regression models. A positive association between gain-of-function (GOF) variants in the MC4R and BED was observed (odds ratio [OR] = 3.05; 95% confidence interval [CI]: 1.82, 5.04; p = 1.7 × 10-5 ), while no association was detected between loss-of-function (LOF) mutations and BED (OR = 1.50; 95% CI: 0.73, 2.96; p = 0.25). Similar results were found after accounting for study quality (GOF variants: OR = 3.15; 95% CI: 1.76, 5.66; p = 1.1 × 10-4 ; LOF mutations: OR = 1.50; 95% CI: 0.73, 2.97; p = 0.25). Our systematic review and meta-analysis provides evidence that GOF variants as opposed to LOF mutations in MC4R are associated with BED in subjects with obesity.

Evidence for an influence of TCF7L2 polymorphism rs7903146 on insulin resistance and sensitivity indices in overweight children and adolescents during a lifestyle intervention.

OBJECTIVE: The T allele of the single-nucleotide polymorphism rs7903146 in TCF7L2 (transcription factor 7 like 2 gene) is associated with type 2 diabetes mellitus. The aim of this study was to analyze whether there is an allele-dosage effect on changes of insulin resistance and sensitivity indices in overweight children participating in a lifestyle intervention. METHODS: We genotyped rs7903146 in 236 overweight children (mean age 10.7 years, mean body mass index (BMI) 28.1 kg/m2) completing a 1-year lifestyle intervention. Degree of overweight as BMI-SDS, homeostasis model assessment for insulin resistance (HOMA-IR) and the insulin sensitivity index QUICKI were measured before and after intervention. RESULTS: Lifestyle intervention resulted in an overweight reduction of -0.29+/-0.02 BMI-SDS. HOMA-IR (-0.63+/-0.22) and QUICKI (+0.008+/-0.003) indices improved significantly (P<0.05) in the course of the intervention in the 155 children with a decrease of BMI-SDS. There was an additive negative effect of T allele on changes of HOMA-IR (P=0.041) and QUICKI (P=0.001) in linear regression analyses adjusted to changes of weight status, age, gender and pubertal stage. CONCLUSION: Overweight children showed a negative dosage-allele effect per T allele at single-nucleotide polymorphism rs7903146 in TCF7L2 concerning an improvement of insulin resistance and sensitivity after overweight reduction in a lifestyle intervention. This finding further suggests that this polymorphism might be involved in glucose metabolism.

A novel non-synonymous mutation in the melanocortin-4 receptor gene (MC4R) in a 2-year-old Austrian girl with extreme obesity.

BACKGROUND: Functionally relevant mutations in the melanocortin-4 receptor gene ( MC4R) currently display the most common major gene/allele effect on extreme obesity. OBJECTIVE: Mutation screen of the MC4R in consecutively ascertained Austrian children and adolescents with severe obesity, to analyse the phenotype of mutation carriers and to functionally characterise novel mutations. SUBJECTS AND METHODS: 102 unrelated extremely obese children and adolescents (mean BMI 33.5+/-7.1 kg/m(2), >97th centile; mean age 13.8+/-4.1 yr) and 109 parents (79 mothers/30 fathers) of 88 of these patients were studied. The MC4R coding region was screened using denaturing high-performance liquid chromatography (dHPLC); PCR products of aberrant dHPLC pattern were re-sequenced. Signal transduction properties of mutant MC4R was investigated by challenge with the highly potent agonist NDP-alpha-MSH. Cell surface expression was determined by ELISA. Magnetic resonance imaging (MRI) of the central nervous system (CNS) was applied to a 2.3 year old index patient. Body fat and bone mineral content were assessed in three of the five mutation carriers by dual energy x-ray absorptiometry (DEXA). Oral glucose tolerance test (OGTT) was applied to some mutation carriers. RESULTS: Heterozygous carriers of two non-synonymous mutations, two polymorphisms and a silent variation were identified within the study group. (1) A novel MC4R non-synonymous mutation (S136F) was detected in a 2.3 year old girl with extreme obesity (BMI 33.2 kg/m(2), >99th centile); (2) a previously described non-synonymous mutation (V253I) was identified in an obese mother (BMI 28.1 kg/m(2)) who did not transmit this mutation to her extremely obese son; (3) two known polymorphisms (V103I and I251L) were also identified; and (4) one obese mother was carrier of a silent variation (c.594C>T; I198). Co-segregation of S136F with the obesity phenotype was shown for three generations. IN VITRO functional studies revealed a complete loss of signal transduction activity of the mutant receptor while cell surface expression was only slightly reduced compared to the wild-type receptor. CONCLUSIONS: We detected a novel non-synonymous mutation (S136F) that leads to a complete loss of MC4R function IN VITRO.

Several mutations in the melanocortin 4 receptor gene are associated with obesity in Chinese children and adolescents.

AIM: To screen mutations in the melanocortin 4 receptor (MC4R) in obese and normal-weight Chinese children and adolescents. METHODS: Three hundred Chinese children and adolescents, including 200 obese and 100 healthy non-obese individuals, were evaluated. The coding region of the MC4R gene was amplified by polymerase chain reaction (PCR) and sequenced. RESULTS: In obese individuals, we detected two novel heterozygous non-synonymous mutations (c.496G>A, resulting in Val166Ile; c.929G>A, resulting in Arg310Lys) and a novel heterozygous non-sense mutation (c.831T>A, resulting in a premature stop codon Cys277Stop). In both obese individuals and controls, a novel heterozygous non-synonymous mutation (c.68T>G, resulting in Leu23Arg, 0.5 and 1%, respectively) and the Val103Ile polymorphism (c.307G>A, 3 and 2%, respectively) were found. There was no difference in alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), cholesterol (CHOL) and whole body insulin sensitivity index (WBISI) between obese individuals with and without mutation. The prevalence for heterozygous MC4R mutations was 1.5% in the obese. CONCLUSIONS: Two novel heterozygous non-synonymous mutations (Val166Ile; Arg310Lys) and a novel heterozygous non-sense mutation (Cys277Stop) were detected in Chinese obese individuals. Leu23Arg variant might be a polymorphism in the Chinese population. There were no differences between clinical and biochemical profiles in the heterozygous mutations and the wild type.

Association of the 103I MC4R allele with decreased body mass in 7937 participants of two population based surveys.

BACKGROUND: The melanocortin-4-receptor gene (MC4R) is part of the melanocortinergic pathway that controls energy homeostasis. In a recent meta-analysis, the MC4R V103I (rs2229616) polymorphism was shown to be associated with body weight regulation. Although no functional differences between the isoleucine comprising receptor and the wild type receptor have been detected as yet, this meta-analysis of 14 case-control studies reported a mild negative association with obesity (odds ratio (OR) 0.69, p = 0.03). However, evidence in a large population based study in a homogeneous population and a significant estimate of the change in quantitative measures of obesity is still lacking. METHODS: We analysed the data of two surveys of a white population with the same high quality study protocol, giving a total of 7937 participants. RESULTS: By linear regression, we found a significant decrease of 0.52 body mass index (BMI) units (95% confidence interval (CI) -0.02 to -1.03, p = 0.043) for carriers of the heterozygote rs2229616G/A genotype, which was observed in 3.7% of the participants. Logistic regression yielded a significantly negative association of the MC4R variant with "above average weight" (BMI > or = median BMI) yielding an OR of 0.75 (95% CI 0.59 to 0.95 p = 0.017). We obtained similar results comparing obese (BMI > or =30 kg/m2, World Health Organization results for 1997) with non-obese (BMI < 30 kg/m2) participants. The results were found for both sexes and each survey separately, and did not depend on the modelling of age, sex, or survey effects. CONCLUSIONS: Our study confirms previous findings of a meta-analysis that the relatively infrequent G/A genotype of the V103I MC4R polymorphism is negatively associated with above average weight and obesity in population based original data of 7937 participants, and extends previous findings by showing for the first time a significantly lower BMI in individuals carrying the infrequent allele of this MC4R variant.

Independent confirmation of a major locus for obesity on chromosome 10.

Linkage results obtained in genome-wide scans for complex phenotypes require confirmation in independent samples. Recently, linkage of obesity to chromosome 10p12 with a maximal multipoint LOD score of 4.85 was reported upon use of an affected sib-pair approach including nuclear families in which the adult index case had a BMI > or = 40 kg/m2 and at least one further sibling had a BMI > or = 27 kg/m2 (Hager et al., 1998, Nat Genet 20:304-8). To attempt to replicate this linkage finding we genotyped 11 markers spanning approximately 23 cM from 10p13 to 10ql1 in a total of 386 individuals stemming from 93 nuclear families with two or more young obese offspring with a BMI > or = 90th age percentile. The highest multipoint maximum likelihood binomial (MLB) LOD score using the extreme concordant sib-pair approach in which one sib had a BMI > or = 95th percentile, and other sibs a BMI > or = 90th percentile was 2.32. Six markers yielded nominal p-values < 0.05, the highest two point MLB-LOD score of 2.45 (nominal p = 0.0004) was obtained for the marker TCF8. Transmission disequilibrium tests for the most frequent parental allele yielded no nominal p-value < 0.05. The linkage results confirm the presence of a major susceptibility locus for obesity in a region near the centromere on chromosome 10.

Systematic mutation screening of the estrogen receptor beta gene in probands of different weight extremes: identification of several genetic variants.

Estrogens are known to have an inhibitory effect on food intake in rodents and primates. Decreased estrogen levels that are found for instance in menopausal woman and in ovarectomized rodents result in body weight gain. Estrogen can act both in the periphery and in the central nervous system via at least two different estrogen receptors (alpha and beta). We systematically screened the coding region and part of the 5' and 3'regions of the estrogen receptor beta gene (ER beta) in 96 extremely obese children and adolescents, 50 patients with anorexia nervosa (AN), 28 patients with bulimia nervosa (BN), and 25 healthy underweight individuals. We detected five different sequence variants in the ER beta: a) A 21 bp deletion (codons 238 to 244) was detected in two obese probands and an underweight individual. b) An 846G-->A transition leading to a nonconservative amino acid substitution (G-250-S) was found in two obese male probands. Both a) and b) were located within the flexible hinge region between DNA and ligand binding domain. c) For a 1082G-->A polymorphism we found suggestive evidence for an association between the more common 1082G-allele and anorexia nervosa (nominal p=0.04). d) One silent mutation (1421T-->C) was found solely in two obese probands. e) A common variant is located in the 3' nontranslated region at position 1730(A-->G). We did not detect association of this polymorphism to any of the analyzed phenotypes. We conclude that the ER beta harbors several different mutations and polymorphisms, none of which can readily be associated with the phenotypes under study.

Systematic mutation screening of the pro-opiomelanocortin gene: identification of several genetic variants including three different insertions, one nonsense and two missense point mutations in probands of different weight extremes.

Pro-opiomelanocortin (POMC) is the precursor of melanocortins (adrenocorticotropin: ACTH, beta-endorphin, beta-lipotropin: beta-LPH, corticotropin like intermediate peptide, alpha-, beta- and gamma-melanocyte-stimulating hormone: alpha-, beta- and gamma-MSH) some of which act in the brain to reduce food intake and are potential mediators of leptin action. Recently, three different mutations in the POMC gene (POMC) were identified in two unrelated children that lead to early-onset extreme obesity, adrenal insufficiency, and red hair pigmentation. In the present study we systematically screened the coding region of POMC in 96 extremely obese children and adolescents, 60 healthy underweight individuals and 46 patients with anorexia nervosa (AN) and identified several variants. a) A 9 and an 18 base pair insertion (9bp and 18bp: AGC AGC GGC and AGC AGC GGC AGC AGC GGC, respectively, between codon 73 and 74; 1,2). These in-frame variants lead to the insertion of three or six amino acids (Ser-Ser-Gly; Ser-Ser-Gly-Ser-Ser-Gly) carboxy-terminal to gamma-MSH. Frequencies of the 9bp insertion allele varied between 3 and 5% among the different study groups (Pearson's chi2 P>0.5). b) Both an out-of-frame 6 bp insertion (within codon 176: GGG CCC) leading to the insertion of two amino acids (Arg-Ala) and a premature stop-codon (G-7316-T: Glu-180-Stop) within the gamma-LPH sequence were maternally inherited in an obese female proband. This proband inherited another missense mutation from her father (Glu-188-Gly). c) A missense mutation (G-7016-A; Asp-80-Asn) was observed in a single patient with AN who also harboured the 9bp insertion on a paternally derived haplotype. d) The allelic co-occurence of two silent mutations (C-6982-T and C-7285-T) was detected in two obese subjects. e) Two further silent mutations (C-3832-T; C-7111-G) were detected in an underweight and an obese subject, respectively. We conclude that the POMC gene harbors several different polymorphisms and mutations, none of which can readily be associated with the phenotypes under study.