5-HT2A receptor gene polymorphisms in anorexia nervosa and bulimia nervosa

Association of serotonin receptor gene polymorphisms with anorexia nervosa: a systematic review and meta-analysis

PURPOSE

Several studies have investigated the association between anorexia nervosa and polymorphisms of genes regulating serotonin neurotransmission, with a focus on the rs6311 polymorphism of 5-HTR2A. However, inconsistent results of these studies and conflicting conclusions of existing meta-analyses complicate the understanding of a possible association. We have updated these results and evaluated the involvement of other serotonin receptor gene polymorphisms in anorexia nervosa.

METHODS

Adhering to PRISMA guidelines, we have searched studies on anorexia nervosa and serotonin-regulating genes published from 1997 to 2022, selected those concerning receptor genes and meta-analyzed the results from twenty candidate gene studies on the 5-HTR2A rs6311 polymorphism and the 5-HTR2C rs6318 polymorphism.

RESULTS

Present analyses reveal an association for the 5-HTR2A rs6311 polymorphism, with G and A alleles, across eighteen studies (2049 patients, 2877 controls; A vs. G allele, Odds Ratio = 1.24; 95% Confidence Interval = 1.06-1.47; p = 0.009). However, after geographic subgrouping, an association emerged only in a Southern European area, involving five studies (722 patients, 773 controls; A vs. G allele, Odds Ratio = 1.82; 95% Confidence Interval = 1.41-2.37; p < 0.00001). No association was observed for the 5-HTR2C rs6318 polymorphism across three studies.

CONCLUSIONS

To date, the involvement in the pathophysiology of anorexia nervosa of the 5-HTR2A rs6311 polymorphism appears limited to a specific genetic and/or environmental context, while that of the 5-HTR2C rs6318 polymorphism seems excluded. Genome-wide association studies and epigenetic studies will likely offer deeper insights of genetic and environmental factors possibly contributing to the disorder.

LEVEL OF EVIDENCE

III Evidence obtained from well-designed cohort or case-control analytic studies. Clinical trial registration PROSPERO registration number: CRD42021246122.

Ketamine as a Treatment for Anorexia Nervosa: A Narrative Review

Anorexia nervosa (AN) is a highly complex disorder to treat, especially in severe and enduring cases. Whilst the precise aetiology of the disorder is uncertain, malnutrition and weight loss can contribute to reductions in grey and white matter of the brain, impairments in neuroplasticity and neurogenesis and difficulties with cognitive flexibility, memory and learning. Depression is highly comorbid in AN and may be a barrier to recovery. However, traditional antidepressants are often ineffective in alleviating depressive symptoms in underweight patients with AN. There is an urgent need for new treatment approaches for AN. This review gives a conceptual overview for the treatment of AN with ketamine. Ketamine has rapid antidepressant effects, which are hypothesised to occur via increases in glutamate, with sequelae including increased neuroplasticity, neurogenesis and synaptogenesis. This article provides an overview of the use of ketamine for common psychiatric comorbidities of AN and discusses particular safety concerns and side effects. Potential avenues for future research and specific methodological considerations are explored. Overall, there appears to be ample theoretical background, via several potential mechanisms, that warrant the exploration of ketamine as a treatment for adults with AN.

Association of 5-HTR2A -1438A/G polymorphism with anorexia nervosa and bulimia nervosa: A meta-analysis

Although a number of studies have been conducted on the association of -1438A/G polymorphism in serotonin 2A receptor (5-HTR2A) gene with anorexia nervosa (AN) and bulimia nervosa (BN), the results remained inconsistent. We thus performed a meta-analysis to clarify the effects of -1438A/G polymorphism on the risk of AN and BN. PubMed, Embase, the Cochrane Library, CNKI, Weipu and Wanfang databases were searched for eligible studies. Pooled odds ratio (OR) and 95 % confidence interval (CI) were calculated to estimate the strength of the association. Subgroup analysis was also performed by ethnicity. In total, 17 studies were included for the meta-analysis, of which 15 studies containing 2028 cases and 2725 controls were used for AN analysis and 7 studies containing 505 cases and 1129 controls for BN analysis. The results showed -1438A/G polymorphism was significantly associated with the risk of AN in four genetic models (allele model, A vs. G: OR = 1.31, 95 % CI = 1.11-1.64, P = 0.003; recessive model, AA vs. GA + GG: OR = 1.69, 95 % CI = 1.28-2.23, P = 0.000; dominant model, AA + GA vs. GG: OR = 1.35, 95 % CI = 1.02-1.79, P = 0.037; co-dominant model, AA vs. GG: OR = 1.94, 95 % CI = 1.29-2.92, P = 0.002) in Caucasians, but not in Asians. We failed to observe a significant association between -1438A/G polymorphism and the risk of BN either in overall or in Caucasian population. The present meta-analysis indicated that A allele and AA genotype of 5-HTR2A -1438A/G polymorphism may contribute to higher risk of AN, especially in Caucasians. However, this polymorphism was not associated with the susceptibility to BN.

5-HT2AR and BDNF gene variants in eating disorders susceptibility

Evidence from family and twin studies points to a genetic contribution to the etiology of eating disorders (EDs), confirmed by the association of several single nucleotide polymorphisms (SNPs) with this group of disorders. Previous reports have suggested that the serotonin receptor (5-HT2AR) and brain-derived neurotrophic factor (BDNF) genes could be both involved in EDs susceptibility. In order to provide further evidence about such association, we focused our attention on two SNPs located in these genes carrying out a genetic association study on a large Italian cohort composed of 556 ED patients and 355 controls (CTRs). Obtained results confirm the presence of an association between 5-HT2AR and BDNF genes and the susceptibility to EDs.

Genetic association analysis of 5-HTR2A gene variants in eating disorders in a Mexican population

INTRODUCTION

The 5-HTR2A gene has been implicated as candidate gene for eating disorders. The aim of the present study was to analyze the association of rs6311 and rs6313 polymorphisms of 5-HTR2A gene with eating disorders in Mexican population, and to evaluate if the polymorphisms of 5-HTR2A gene were associated with comorbidities in eating behavior.

METHODS

We conducted a case-control analysis with 460 subjects. We included 168 patients with eating disorders and 292 controls; two polymorphisms of 5-HTR2A gene were genotyped. We assessed the association by allele, genotype, and inheritance models. Psychiatric comorbidities were analyzed by genotype in patients with eating disorders.

RESULTS

We found an association between rs6311 and eating disorders in a Mexican population by allele (OR = 8.09; 95% CI = 5.99-11.03; p = 2.2e-16) and genotype (OR = 76.14; 95% CI = 35.61-177.18; p = 2.2e-16). Individuals who carried GG genotype showed increased risk for suicide attempted (OR = 2.14; CI = 1.10-4.26; p = 0.035) as comorbidity associated with eating disorders. No positive associations were observed for rs6313 polymorphism.

CONCLUSION

Our results showed an association of rs6311 (A1438G) polymorphism of 5-HTR2A gene with eating disorders, and these polymorphic variants could increase the risk of psychiatric comorbidities. However, more studies are required to replicate the results and to reach to a conclusive association between eating disorders and rs6311.

Association of the 5-HT2A receptor gene promoter polymorphism-1438G/A with anorexia nervosa and psychopathological traits in the Chinese Han population: A preliminary study

OBJECTIVE

The aim of the study was to explore the possible role of the 5-HT_2A -1438G/A polymorphism in the susceptibility to anorexia nervosa (AN) in the Chinese Han population.

METHODS

The -1438G/A polymorphism of 249 female AN patients, 228 matched healthy controls, and 198 trios was genotyped using SNaP shot assay. Psychopathological traits of eating-disordered behaviors in AN subjects were examined using the Chinese version of the Eating Disorder Examination Questionnaire.

RESULTS

Neither the case-control analysis nor the transmission disequilibrium test revealed significant associations between the -1438G/A polymorphism and AN (P > .05). However, AA homozygote patients with AN had lower weight and shape concern scores of the EDE-Q6.0 than those of GA heterozygotes (P < .05).

DISCUSSION

Our findings suggested that female AN patients with 5-HT_2A -1438AA genotype may be characterized by less severe eating-disordered psychopathological traits in the Chinese Han population.

Anxiolytic-like effects of leptin on fixed interval responding

Leptin has been shown to affect energy homeostasis, learning and memory, and some models of anxiolytic action. However, leptin has produced inconsistent results in previous non-operant behavioural tests of anxiety. Here, we test the anxiolytic potential of leptin in an operant paradigm that has produced positive results across all classes of anxiolytic so far tested. Rats were tested in the Fixed Interval 60 Seconds (FI60) task following administration of 0/0.5/1.0mg/kg (i.p.) leptin or an active anxiolytic control of 5mg/kg (i.p.) chlordiazepoxide (CDP). By the end of the 14days of testing in the FI60 task, 0.5mg/kg leptin released suppressed responding in a manner similar to CDP, and 1.0mg/kg leptin produced a relative depression in responding, a similar outcome pattern to previously tested 5HT-agonist anxiolytics. This suggests that leptin behaves similarly to established serotonergic anxiolytics such as buspirone and fluoxetine; with the delay in development of effect during testing, and the inverted-U dose-response curve explaining the inconsistent behaviour of leptin in behavioural tests of anxiety, as this type of pattern is common to serotonergic anxiolytics.

Pharmacological manipulations in animal models of anorexia and binge eating in relation to humans

Eating disorders, such as anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorders (BED), are described as abnormal eating habits that usually involve insufficient or excessive food intake. Animal models have been developed that provide insight into certain aspects of eating disorders. Several drugs have been found efficacious in these animal models and some of them have eventually proven useful in the treatment of eating disorders. This review will cover the role of monoaminergic neurotransmitters in eating disorders and their pharmacological manipulations in animal models and humans. Dopamine, 5-HT (serotonin) and noradrenaline in hypothalamic and striatal regions regulate food intake by affecting hunger and satiety and by affecting rewarding and motivational aspects of feeding. Reduced neurotransmission by dopamine, 5-HT and noradrenaline and compensatory changes, at least in dopamine D2 and 5-HT(2C/2A) receptors, have been related to the pathophysiology of AN in humans and animal models. Also, in disorders and animal models of BN and BED, monoaminergic neurotransmission is down-regulated but receptor level changes are different from those seen in AN. A hypofunctional dopamine system or overactive α2-adrenoceptors may contribute to an attenuated response to (palatable) food and result in hedonic binge eating. Evidence for the efficacy of monoaminergic treatments for AN is limited, while more support exists for the treatment of BN or BED with monoaminergic drugs.

Preliminary evidence for the role of HTR2A variants in binge eating in young women

We examined the association between 15 single nucleotide polymorphisms (SNPs) in HTR2A and characteristics of disordered eating, including weight/shape concerns, binge eating (with or without loss of control), and compensatory behaviors (purging and nonpurging). Whether a lifetime history of major depressive disorder (MDD) moderated or mediated this association was also investigated. A sample of 1533 twin women of White descent that were part of the Missouri Adolescent Female Twin Study was used. Data were collected using self-report responses to a semistructured interview. Logistic regression analyses were used to examine the association between weight/shape concerns, binge eating, and compensatory behaviors and SNPs (where carriers of the minor allele were coded as 1). Two SNPs, rs6561333 and rs2296972, showed a protective influence against binge eating, with rs2296972 being significant at a trend level after application of the false discovery rate. The SNP was not associated with MDD nor did MDD moderate its putative relation with binge eating. Pending replication, our analyses provide preliminary evidence for intronic SNPs in HTR2A and their association with binge eating. Given the well-documented role of serotonergic dysfunction in eating psychopathology, this report warrants considerable further study.

Pharmacogenetics of the G protein-coupled receptors

Pharmacogenetics investigates the influence of genetic variants on physiological phenotypes related to drug response and disease, while pharmacogenomics takes a genome-wide approach to advancing this knowledge. Both play an important role in identifying responders and nonresponders to medication, avoiding adverse drug reactions, and optimizing drug dose for the individual. G protein-coupled receptors (GPCRs) are the primary target of therapeutic drugs and have been the focus of these studies. With the advance of genomic technologies, there has been a substantial increase in the inventory of naturally occurring rare and common GPCR variants. These variants include single-nucleotide polymorphisms and insertion or deletions that have potential to alter GPCR expression of function. In vivo and in vitro studies have determined functional roles for many GPCR variants, but genetic association studies that define the physiological impact of the majority of these common variants are still limited. Despite the breadth of pharmacogenetic data available, GPCR variants have not been included in drug labeling and are only occasionally considered in optimizing clinical use of GPCR-targeted agents. In this chapter, pharmacogenetic and genomic studies on GPCR variants are reviewed with respect to a subset of GPCR systems, including the adrenergic, calcium sensing, cysteinyl leukotriene, cannabinoid CB1 and CB2 receptors, and the de-orphanized receptors such as GPR55. The nature of the disruption to receptor function is discussed with respect to regulation of gene expression, expression on the cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (altered ligand binding, G protein coupling, constitutive activity). The large body of experimental data generated on structure and function relationships and receptor-ligand interactions are being harnessed for the in silico functional prediction of naturally occurring GPCR variants. We provide information on online resources dedicated to GPCRs and present applications of publically available computational tools for pharmacogenetic studies of GPCRs. As the breadth of GPCR pharmacogenomic data becomes clearer, the opportunity for routine assessment of GPCR variants to predict disease risk, drug response, and potential adverse drug effects will become possible.

A debate on current eating disorder diagnoses in light of neurobiological findings: is it time for a spectrum model?

BACKGROUND

Sixty percent of eating disorders do not meet criteria for anorexia- or bulimia nervosa, as defined by the Diagnostic and Statistical Manual version 4 (DSM-IV). Instead they are diagnosed as 'eating disorders not otherwise specified' (EDNOS). Discrepancies between criteria and clinical reality currently hampering eating disorder diagnoses in the DSM-IV will be addressed by the forthcoming DSM-V. However, future diagnoses for eating disorders will rely on current advances in the fields of neuroimaging and genetics for classification of symptoms that will ultimately improve treatment.

DISCUSSION

Here we debate the classification issues, and discuss how brain imaging and genetic discoveries might be interwoven into a model of eating disorders to provide better classification and treatment. The debate concerns: a) current issues in the classification of eating disorders in the DSM-IV, b) changes proposed for DSM-V, c) neuroimaging eating disorder research and d) genetic eating disorder research.

SUMMARY

We outline a novel evidence-based 'impulse control' spectrum model of eating disorders. A model of eating disorders is proposed that will aid future diagnosis of symptoms, coinciding with contemporary suggestions by clinicians and the proposed changes due to be published in the DSM-V.

Life beyond kinases: structure-based discovery of sorafenib as nanomolar antagonist of 5-HT receptors

Of great interest in recent years has been computationally predicting the novel polypharmacology of drug molecules. Here, we applied an "induced-fit" protocol to improve the homology models of 5-HT(2A) receptor, and we assessed the quality of these models in retrospective virtual screening. Subsequently, we computationally screened the FDA approved drug molecules against the best induced-fit 5-HT(2A) models and chose six top scoring hits for experimental assays. Surprisingly, one well-known kinase inhibitor, sorafenib, has shown unexpected promiscuous 5-HTRs binding affinities, K(i) = 1959, 56, and 417 nM against 5-HT(2A), 5-HT(2B), and 5-HT(2C), respectively. Our preliminary SAR exploration supports the predicted binding mode and further suggests sorafenib to be a novel lead compound for 5HTR ligand discovery. Although it has been well-known that sorafenib produces anticancer effects through targeting multiple kinases, carefully designed experimental studies are desirable to fully understand whether its "off-target" 5-HTR binding activities contribute to its therapeutic efficacy or otherwise undesirable side effects.

Eating Disorders: From Twin Studies to Candidate Genes and Beyond

Substantial effort has been put into the exploration of the biological background of eating disorders, through family, twin and molecular genetic studies. Family studies have shown that anorexia (AN) and bulimia nervosa (BN) are strongly familial, and that familial etiologic factors appear to be shared by both disorders. Twin studies often focus on broader phenotypes or subthreshold eating disorders. These studies consistently yielded moderate to substantial heritabilities. In addition, there has been a proliferation of molecular genetic studies that focused on Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) AN and BN. Seven linkage regions have been identified in genome-wide screens. Many genetic association studies have been performed, but no consistent association between a candidate gene and AN or BN has been reported. Larger genetic association studies and collaborations are needed to examine the involvement of several candidate genes and biological pathways in eating disorders. In addition, twin studies should be designed to assist the molecular work by further exploring genetic determinants of endophenotypes, evaluating the magnitude of contribution to liability of measured genotypes as well as environmental risk factors related to eating disorders. In this manner twin and molecular studies can move the field forward in a mutually informative way.

Contemporary thinking about the role of genes and environment in eating disorders

Objective – To review recent literature documenting how family, twin and molecular genetic studies of eating disorders have revolutionized our conceptualizations of anorexia and bulimia nervosa. Methods – We summarized extant litera-ture on genetic epidemiology of eating disorders. Results – Results of extant studies highlight the underlying biological vulnera- bilities associated with these conditions. Genetic research has also opened up new avenues and approaches for exploring how the environment exerts its influence on risk. Conclusions – We discuss state-of-the-science findings in the genetics of eating disorders, explore various mechanisms of gene-environment interplay, and discuss implications of this research for science, practice, families and individuals with eating disorders.

Evidence of complex involvement of serotonergic genes with restrictive and binge purge subtypes of anorexia nervosa

OBJECTIVES

There is mixed evidence of association of serotoninergic genes with anorexia nervosa (AN), but substantial evidence for the involvement of serotonergic mechanisms in appetite control. This study was designed to investigate possible associations between the two subtypes of AN (Restricting-RAN, and Binge-purging-BPAN) and polymorphisms within five genes encoding for proteins involved in the serotoninergic system.

METHODS

In order to carry out this investigation we have conducted a case-control association study on 226 females meeting the criteria for AN, and 678 matched healthy females.

RESULTS

Our data show a significant association between polymorphisms with the gene encoding HTR2A with both AN subtypes, an association between polymorphisms within the genes encoding HTR1D and HTR1B with RAN, and an association between polymorphisms within the gene encoding HTR2C with BPAN. No associations were found for any polymorphisms of the serotonin transporter gene. This outcome indicates a substantial and complex inter-relationship between serotoninergic genes and AN.

CONCLUSIONS

Given these data we hypothesis that the expression or control of expression of several genes of the serotoninergic system, and interactions between these genes, could exert considerable influence over the specific symptomatology of the subtypes of AN.

Conceptualizing the role of estrogens and serotonin in the development and maintenance of bulimia nervosa

Serotonergic dysregulation is thought to underlie much of the pathology in bulimia nervosa (BN). The purpose of this review is to expand the serotonergic model by incorporating specific and nonspecific contributions of estrogens to the development and maintenance of bulimic pathology in order to guide research from molecular genetics to novel therapeutics for BN. Special emphasis is given to the organizing theory of general brain arousal which allows for integration of specific and nonspecific effects of these systems on behavioral endpoints such as binge eating or purging as well as arousal states such as fear, novelty seeking, or sex. Regulation of the serotonergic system by estrogens is explored, and genetic, epigenetic, and environmental estrogen effects on bulimic pathology and risk factors are discussed. Genetic and neuroscientific research support this two-system conceptualization of BN with both contributions to the developmental and maintenance of the disorder. Implications of an estrogenic-serotonergic model of BN are discussed as well as guidelines and suggestions for future research and novel therapeutic targets.

Associations between the serotonin-1A receptor C(-1019)G polymorphism and disordered eating symptoms in female adolescents

The purpose of this study was to examine the relationship between the C(-1019)G polymorphism of the serotonin-1A receptor gene and eating behavior in female adolescents. A total of 204 post-menarche, adolescent women, aged 16-17 years, were recruited from two neighboring high schools in Seoul. Polymerase chain reaction (PCR) was used to isolate and examine the C(-1019)G polymorphism in the serotonin-1A receptor genes (rs6295) of all participants. The Bulimia Investigatory Test, Edinburgh (BITE) and the Eating Attitude Test-26 (EAT-26) were administered to all participants. The total score of the EAT-26 differed significantly among the three genotype groups [CC, CG, GG (F = 4.844, p = 0.009)]. Both the EAT-26 (F = 9.69, p = 0.002) and the BITE (F = 5.22, p = 0.023) scores were higher in the participants who were G allele carriers than in the non-carrier group. The dieting subscale of the EAT-26 was higher among the G allele carriers (F = 12.941, p < 0.001), and these results were maintained even after adjusting for depression and anxiety. These findings suggest that the C(-1019)G polymorphism in the 5-HT1A receptor gene is associated with disordered eating symptoms in Korean female adolescents.

Eating disorders: the current status of molecular genetic research

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.

Genetic findings in anorexia and bulimia nervosa

Anorexia nervosa (AN) and bulimia nervosa (BN) are complex disorders associated with disordered eating behavior. Heritability estimates derived from twin and family studies are high, so that substantial genetic influences on the etiology can be assumed for both. As the monoaminergic neurotransmitter systems are involved in eating disorders (EDs), candidate gene studies have centered on related genes; additionally, genes relevant for body weight regulation have been considered as candidates. Unfortunately, this approach has yielded very few positive results; confirmed associations or findings substantiated in meta-analyses are scant. None of these associations can be considered unequivocally validated. Systematic genome-wide approaches have been performed to identify genes with no a priori evidence for their relevance in EDs. Family-based scans revealed linkage peaks in single chromosomal regions for AN and BN. Analyses of candidate genes in one of these regions led to the identification of genetic variants associated with AN. Currently, an international consortium is conducting a genome-wide association study for AN, which will hopefully lead to the identification of the first genome-wide significant markers.

The possible influence of impulsivity and dietary restraint on associations between serotonin genes and binge eating

Although serotonin (5-HT) genes are thought to be involved in the etiology of bulimia nervosa and binge eating, findings from molecular genetic studies are inconclusive. This may be due to limitations of past research, such as a failure to consider the influence of quantitative traits and gene-environment interactions. The current study investigated these issues by examining whether quantitative traits (i.e., impulsivity) and environmental exposure factors (i.e., dietary restraint) moderate 5-HT gene/binge eating associations in a sample of young women (N = 344). Binge eating was assessed using the Minnesota Eating Behavior Survey and the Dutch Eating Behavior Questionnaire (DEBQ). Impulsivity was assessed with the Barratt Impulsiveness Scale-Version 11. Dietary restraint was measured with a factor score derived from common restraint scales. Saliva samples were genotyped for the 5-HT2a receptor T102C polymorphism and 5-HT transporter promoter polymorphism. As expected, impulsivity and dietary restraint were associated with binge eating. Although the T allele of the 5-HT2a receptor gene and the s allele of the 5-HTT gene were associated with higher levels of impulsivity, there were no main effects of 5-HT genotypes on any binge eating measure, and interactions between genotypes, impulsivity, and dietary restraint were non-significant. In conclusion, we found no evidence to suggest that dietary restraint or impulsivity moderate associations between binge eating and these 5-HT genes. Future research should continue to explore interaction effects by examining larger samples, assessing dietary intake directly, and investigating other genes, traits, and environmental factors that may be related to binge eating and bulimia nervosa.

Genetic variation and effects on human eating behavior

Feeding is a physiological process, influenced by genetic factors and the environment. In recent years, many studies have been performed to unravel the involvement of genetics in both eating behavior and its pathological forms: eating disorders and obesity. In this review, we provide a condensed introduction on the neurological aspects of eating and we describe the current status of research into the genetics of eating behavior, primarily focused on specific traits such as taste, satiation, and hunger. This is followed by an overview on the genetic studies done to unravel the heritable background of obesity and eating disorders. We examine the discussion currently taking place in the field of genetics of complex disorders and phenotypes on how to perform good and powerful studies, with the use of large-scale whole-genome association studies as one of the possible solutions. In the final part of this review, we give our view on the latest developments, including endophenotype approaches and animal studies. Studies of endophenotypes of eating behavior may help to identify core traits that are genetically influenced. Such studies would yield important knowledge on the underlying biological scaffold on which diagnostic criteria for eating disorders could be based and would provide information to influence eating behavior toward healthier living.

The serotonin 2A receptor gene in alcohol dependence and tobacco smoking

Alcohol and nicotine abuse and dependence are multifactorial traits that frequently co-occur, where 80-90% of alcohol-dependent individuals who seek treatment smoke. Nicotine is the main compound of tobacco and one of its effects is to increase the release of serotonin. Variations in the serotonergic system may influence some aspects of smoking. The serotonin receptor gene HTR2A has been a candidate gene with some evidence for association with alcohol and nicotine dependencies. The polymorphism HTR2A A-1438G is a functional SNP, and the presence of the A allele increases the transcriptional activity of the gene. The aim of the present study was to test for possible associations between the A-1438G polymorphism in the serotonin receptor gene (HTR2A) with tobacco smoking combined or not with alcohol dependence. The polymorphic site was genotyped in three groups of European-derived Brazilians: individuals with co-occurrence of alcohol dependence and tobacco smoking (n=113), non-alcoholic smokers (n=120) and non-smoking controls (n=115). A higher frequency of the A allele was observed in the two groups of smokers than in the non-smoking controls (chi(2)=6.53, p=0.04). Combining these groups in comparison with the control group, the difference is more significant (chi(2)=6.45, p=0.01). These results support previous evidence for association between HTR2A polymorphisms and substance use disorders.

Genetic susceptibility to eating disorders: associated polymorphisms and pharmacogenetic suggestions

Anorexia nervosa (AN), bulimia nervosa (BN) and binge-eating disorder (BED) are characterized by abnormal eating behaviors often resulting in dramatic physical consequences for the patients. The etiology of eating disorders (EDs) is currently unknown; however, a strong genetic contribution is likely to be involved. To date, the majority of genetic studies have focused on candidate genes, and polymorphic variants of genes coding for substances likely to be involved in the etiopathogenesis of EDs have been assessed for association with AN, BN, BED and/or ED-related phenotypic traits. Results have been generally inconsistent and cannot be considered conclusive because of several methodological flaws and differences, such as small sample sizes, ethnic heterogeneity of studied populations, lack of statistical correction for multiple testing, adoption of different diagnostic criteria and population stratification. Although, at present, no convincing evidence for associations of candidate genes with EDs has been provided, the 5-HT2A receptor gene and the BDNF gene seem to be promising candidates for genetic influences on AN, since polymorphic variants of these genes have been found quite consistently, although not specifically, linked to AN restricting subtype in large sample studies. Moreover, pharmacogenetic investigations have suggested a possible role of some gene polymorphisms in predicting the response to treatment with selective serotonin reuptake inhibitors in BN, but results are still preliminary. The heterogeneity of ED phenotypes is believed to represent the most relevant variable responsible for contradictory and not conclusive results. Future studies should focus on more homogeneous subgroups, either relying on specific ED traits or identifying endophenotypes. This will be useful also for prevention and treatment of EDs.

No differences are seen in the regional cerebral blood flow in the restricting type of anorexia nervosa compared with the binge eating/purging type

AIMS

Anorexia nervosa (AN) is subdivided into the restricting type (AN-R) and the binge-eating/purging type (AN-BP), but differences in cerebral blood flow between patients with these types of AN and healthy controls have not been investigated.

METHODS

The present study was designed to elucidate any such differences using resting single photon emission computed tomography (SPECT) studies to compare the differences in cerebral perfusion among both types of AN and a healthy control group. Resting regional cerebral blood flow was assessed using SPECT with technetium-99m hexamethylpropyleneamine oxime in 13 female AN-R patients, 13 female AN-BP patients, and 10 healthy women as controls with 3-D stereotactic surface projections.

RESULTS

The analytic program of the SPECT images showed bilateral decreased perfusion of the subcallosal gyrus (SCG), midbrain and posterior cingulate gyrus (PCG) in both AN-R and AN-BP patients, as compared with the controls. There were no clear differences between the AN-R and AN-BP groups. There were no significant differences in cerebral blood flow between patients with AN-R and AN-BP.

CONCLUSIONS

Abnormalities of the neuronal circuits containing the SCG, midbrain and PCG are possibly relevant to trait-related AN.

G protein-coupled receptor pharmacogenetics

Common G protein-coupled receptor (GPCR) gene variants that encode receptor proteins with a distinct sequence may alter drug efficacy without always resulting in a disease phenotype. GPCR genetic loci harbor numerous variants, such as DNA insertions or deletions and single-nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to interindividual differences in disease susceptibility/progression and drug responses. In this chapter, these pharmacogenetic phenomena are reviewed with respect to a limited sampling of GPCR systems, including the beta(2)-adrenergic receptors, the cysteinyl leukotriene receptors, and the calcium-sensing receptor. In each example, the nature of the disruption to receptor function that results from each variant is discussed with respect to the regulation of gene expression, expression on cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (by altering ligand binding, G protein coupling, and receptor constitutive activity). Despite the breadth of pharmacogenetic knowledge available, assessment for genetic variants is only occasionally applied to drug development projects involving pharmacogenomics or to optimizing the clinical use of GPCR drugs. The continued effort by the basic science of pharmacogenetics may draw the attention of drug discovery projects and clinicians alike to the utility of personalized pharmacogenomics as a means to optimize novel GPCR drug targets.

Visual hallucinations in Parkinson's disease are not influenced by polymorphisms of serotonin 5-HT2A receptor and transporter genes

Psychiatric disorders are common in Parkinson's disease (PD) and hallucinations are observed in nearly 40% of PD patients. The involvement of dopaminergic system in the pathogenesis of psychosis has been sustained by most of the authors even if several evidences indicate that multiple neurochemical substrates might underlie psychosis in PD. In PD there is an extensive loss of serotoninergic raphe neurons and serotonin dysfunction had been implicated in the pathogenesis of many psychiatric disorders such as depression, schizophrenia, and in psychosis of patients with Alzheimer disease. The association of a serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the 5-HT2A receptor T102C polymorphism with psychosis in a group of patients with PD was investigated. No significant differences in the distribution of allele and genotype frequencies of the 5-HTTLPR (p>0.01) and 5-HT2A T102C (p>0.05) were found between patients and controls as well as between the patients' subgroups without and with psychosis. These data might suggest that 5-HTTLPR and 5-HT2A polymorphisms are not major susceptibility factors of psychotic symptoms in PD patients.

Genetics in eating disorders: extending the boundaries of research

OBJECTIVE: To review the recent literature relevant to genetic research in eating disorders and to discuss unique issues which are crucial for the development of a genetic research project in eating disorders in Brazil. METHOD: A computer literature review was conducted in the Medline database between 1984 and may 2005 with the search terms "eating disorders", "anorexia nervosa", "bulimia nervosa", "binge eating disorder", "family", "twin" and "molecular genetic" studies. RESULTS: Current research findings suggest a substantial influence of genetic factors on the liability to anorexia nervosa and bulimia nervosa. Genetic research with admixed populations should take into consideration sample size, density of genotyping and population stratification. Through admixture mapping it is possible to study the genetic structure of admixed human populations to localize genes that underlie ethnic variation in diseases or traits of interest. CONCLUSIONS: The development of a major collaborative genetics initiative of eating disorders in Brazil and South America would represent a realistic possibility of studying the genetics of eating disorders in the context of inter ethnic groups, and also integrate a new perspective on the biological etiology of eating disorders.

Allele C-specific methylation of the 5-HT2A receptor gene: evidence for correlation with its expression and expression of DNA methylase DNMT1

Differential DNA methylation has been suggested to contribute to differential activity of alleles C and T and thereby to genetic associations between the C/T(102) polymorphism in the 5-HT2A receptor gene (5HT2AR) and psychiatric disorders. We surveyed methylation in two CpG sites, which are specific to allele C. The majority of allele C-specific CpG sites were methylated in human temporal cortex and peripheral leukocytes and levels of methylation varied between individuals. Levels of methylation in the promoter correlated significantly with the expression of 5HT2AR. Methylation of allele C-specific CpG sites in the first exon correlated significantly with the expression of DNA methylase 1 (DNMT1) but not S-adenosylhomocysteine hydrolase (AHCY). These findings support the hypothesis that allele-specific DNA methylation is involved in regulation of 5HT2AR expression, influencing expression differences between alleles C and T.

The 5-HT2A -1438 A/G and 5-HTTLPR polymorphisms and personality dimensions in adolescent anorexia nervosa: association study

Disturbances of serotonergic neurotransmission and temperamental vulnerability have both been implicated in the pathogenesis of anorexia nervosa (AN). We genotyped the -1438 A/G polymorphism in the 5-HT2A receptor gene and serotonin transporter linked-polymorphic region (5-HTTLPR) in 132 adolescent subjects with AN and in 93 healthy controls. Personality dimensions in AN patients were assessed with the Temperament and Character Inventory. In a case-control model, we tested the hypothesis that these genetic variants confer susceptibility to AN. We also analyzed whether two polymorphisms show association with temperamental and character traits. No significant difference was found in the 5-HTTLPR frequency between AN patients and controls; however, there was a statistical trend towards a higher frequency of the A allele of the -1438 A/G polymorphism in patients than in controls (64.9 vs. 56.7%, chi2 test, p=0.08). We also found a significant association between the A allele of this polymorphism and two temperamental traits. Patients homozygous for the A allele showed lower reward dependence than G/G homozygotes, and A/A homozygotes showed lower harm avoidance than heterozygotes. Low reward dependence and harm avoidance were more characteristic of the restrictive-type AN than of other subtypes of the disorder. No association of 5-HTTLPR with personality dimensions in AN patients was observed. Our results may suggest that the A allele of the -1438 A/G polymorphism confers some genetic risk for adolescent AN patients, especially in those with personality traits, which are typical of the restrictive-type AN.

The G protein-coupled receptors: pharmacogenetics and disease

Genetic variation in G-protein coupled receptors (GPCRs) is associated with a wide spectrum of disease phenotypes and predispositions that are of special significance because they are the targets of therapeutic agents. Each variant provides an opportunity to understand receptor function that complements a plethora of available in vitro data elucidating the pharmacology of the GPCRs. For example, discrete portions of the proximal tail of the dopamine D1 receptor have been discovered, in vitro, that may be involved in desensitization, recycling and trafficking. Similar in vitro strategies have been used to elucidate naturally occurring GPCR mutations. Inactive, over-active or constitutively active receptors have been identified by changes in ligand binding, G-protein coupling, receptor desensitization and receptor recycling. Selected examples reviewed include those disorders resulting from mutations in rhodopsin, thyrotropin, luteinizing hormone, vasopressin and angiotensin receptors. By comparison, the recurrent pharmacogenetic variants are more likely to result in an altered predisposition to complex disease in the population. These common variants may affect receptor sequence without intrinsic phenotype change or spontaneous induction of disease and yet result in significant alteration in drug efficacy. These pharmacogenetic phenomena will be reviewed with respect to a limited sampling of GPCR systems including the orexin/hypocretin system, the beta2 adrenergic receptors, the cysteinyl leukotriene receptors and the calcium-sensing receptor. These developments will be discussed with respect to strategies for drug discovery that take into account the potential for the development of drugs targeted at mutated and wild-type proteins.

Olanzapine reduces physical activity in rats exposed to activity-based anorexia: possible implications for treatment of anorexia nervosa?

BACKGROUND

Anorexia nervosa (AN) patients often show extreme hypophagia and excessive physical activity. Activity-based anorexia (ABA) is considered an animal model of AN and mimics food restriction and hyperactivity in rats. This study investigated whether treatment with olanzapine (Zyprexa) reduces the development of ABA in rats. The effect of olanzapine treatment in AN patients was also evaluated in a small open-label study.

METHODS

Rats were chronically (1 week) infused with olanzapine (7.5 mg/kg) and exposed to the ABA model or ad libitum feeding. Hyperactive AN patients were followed for up to 3 months of olanzapine treatment (5 mg/kg).

RESULTS

Olanzapine treatment reduced development of ABA in rats by reducing running wheel activity, starvation-induced hypothermia and activation of the hypothalamus-pituitary-adrenal axis. Olanzapine treatment reduced activity levels of AN patients compared with untreated AN patients, without affecting body weight and plasma leptin levels.

CONCLUSIONS

Olanzapine treatment reduced wheel running and thereby diminished development of ABA in rats. Olanzapine treatment also reduced physical activity in hyperactive AN patients in a small open-label study. These data support the need for controlled studies investigating the putative beneficial effects of olanzapine treatment in AN patients.

A review and primer of molecular genetic studies of anorexia nervosa

Recent research on anorexia nervosa (AN) has focused on examining the genetic underpinnings of its etiology. The current article reviews molecular genetic studies that have focused on this aspect of AN development. Medline and PsychInfo literature searches, in addition to close inspection of study reference sections, were used to identify studies that examined the genetic diathesis for AN. Findings from association studies indicate some role for the serotonin system in the development of AN. Genomic regions on chromosomes 1 and 10 are also likely to harbor susceptibility genes for AN as well as a range of eating pathologies. Findings corroborate those of neurobiologic studies suggesting that alterations in serotonergic functioning may contribute to the pathogenesis of AN. Nonetheless, future molecular genetic research would benefit from larger and more sustained investigations of candidate genes in homogeneous phenotypes.

Association of the promoter polymorphism -1438G/A of the 5-HT2A receptor gene with behavioral impulsiveness and serotonin function in women with bulimia nervosa

Separate lines of research suggest that the functional alterations in the serotonin (5-HT) 2A receptor are associated with 5-HT tone, behavioral impulsiveness, and bulimia nervosa (BN). We explored the effect of allelic variations within the 5-HT2A receptor gene promoter polymorphism -1438G/A on trait impulsiveness and serotonin function in women with BN. Participants included women with BN having the A allele (i.e., AA homozygotes and AG heterozygotes, BNA+, N = 21); women with BN but without the A allele (i.e., GG homozygotes, BNGG, N = 12), and normal eater control women having the A allele (NEA+, N = 19) or without the A allele (NEGG; N = 9). The women were assessed for psychopathological tendencies and eating disorder symptoms, and provided blood samples for measurement of serial prolactin responses following oral administration of the post-synaptic partial 5-HT agonist meta-chlorophenylpiperazine (m-CPP). The BNGG group had higher scores than the other groups on self-report measures of non-planning and overall impulsiveness and had blunted prolactin response following m-CPP. The bulimic groups did not differ from each other on current eating symptoms or on frequencies of other Axis I mental disorders. Findings indicate that women with BN who are GG homozygotes on the -1438G/A promoter polymorphism are characterized by increased impulsiveness and lower sensitivity to post-synaptic serotonin activation. These findings implicate the GG genotype in the co-aggregation of impulsive behaviors and alterations of post-synaptic 5-HT functioning in women with BN.

HTR2A: association and expression studies in neuropsychiatric genetics

Over the last decade the gene encoding 5-hydroxytryptamine (serotonin) receptor 2A (HTR2A) has been implicated as a functional candidate in many neuropsychiatric phenotypes including: schizophrenia, attention deficit hyperactivity disorder (ADHD), affective disorders, eating disorders, anxiety disorders, obsessive-compulsive disorder, suicide and Alzheimer's disease (AD). Different studies have tested for genetic association (case-control and family-based studies), protein expression (receptor binding assays), transcriptional expression (mRNA assays) and allelic expression. In this review we examine and summarize these findings in various neuropsychiatric phenotypes.

Psychopathological traits and 5-HT2A receptor promoter polymorphism (-1438 G/A) in patients suffering from Anorexia Nervosa and Bulimia Nervosa

Various studies have evaluated the possible role of the -1438G/A polymorphism within the 5-HT2A receptor gene in the susceptibility to Eating Disorders (EDs). One hundred and forty-eight ED patients (EDp) and 89 control subjects were interviewed by means of the Eating Disorder Examination (EDE) and analyzed for distribution of the -1438G/A polymorphism. Patients with the AA genotype suffering from Anorexia Nervosa and Bulimia Nervosa showed higher Weight and Shape Concern (P = 0.003 and P = 0.010, respectively) scores and greater overall severity of the ED psychopathology (EDE total score) (P = 0.012). The obtained preliminary data suggest the use of dimensional psychopathological measures in ED genetic studies.

Genes and/or Jeans?

Eating disorders are prevalent among young adult females and pose serious psychological and medical risks. Notwithstanding important advances, efforts to develop effective means of preventing and treating eating disorders have been limited by an incomplete understanding of their multifactorial etiology. Whereas epidemiologic data strongly suggest the influence of socio-cultural context in moderating risk, many hypotheses about how these effects are exerted have remained empirically unevaluated. Specifically, experimental and observational data suggest that social transition (e.g., transnational migration, urbanization, modernization), Western media exposure, and certain peer environments (involving social comparison and teasing) may all contribute to risk. With respect to genetic influences on etiology, family and twin studies have supported a genetic diathesis to eating disorders. Whereas, molecular genetic studies have generated interesting leads- with the most promising findings emerging for genes related to the function of serotonin-they have yet to identify well-replicated susceptibility loci. This paper reviews the data supporting both socio-cultural and genetic contributions for eating disorders and suggests productive future strategies for continuing to unravel their likely multiple and complex interactions.

Genetics in eating disorders: state of the science

Eating disorders have been viewed as psychiatric illnesses that are strongly influenced by societal pressures towards thinness and attractiveness. Although the environmental context of these disorders must not be neglected, recent research in the area of genetic epidemiology suggests a substantial influence of genetic factors on liability to eating disorders. This review presents a synthesis of current knowledge about genetic factors implicated in the etiology of eating disorders.

Analysis of the −1438 G/A polymorphism of the 5-HT2A serotonin receptor gene in bulimia nervosa patients with or without a history of anorexia nervosa

A single nucleotide polymorphism (-1438 G/A) located 1438 base pairs upstream of the consensus start site of the 5-HT2A receptor gene has been reported. The hypothesis that this gene polymorphism may be a susceptibility factor in bulimia nervosa was explored in a female population of purgative bulimics. Bulimia nervosa patients who have suffered preceding anorexia nervosa episodes formed the so-called previous anorexia nervosa bulimic patient group. At variance with some previous reports, when the frequency distribution of genotypes and alleles was compared in patients and controls, no differences were detected regardless of whether the bulimia nervosa patients had suffered prior anorexia nervosa episodes.

Coming to Terms With Risk Factors for Eating Disorders: Application of Risk Terminology and Suggestions for a General Taxonomy

The aims of the present review are to apply a recent risk factor approach (H. C. Kraemer et al., 1997) to putative risk factors for eating disorders, to order these along a timeline, and to deduce general taxonomic questions. Putative risk factors were classified according to risk factor type, outcome (anorexia nervosa, bulimia nervosa, binge-eating disorder, full vs. partial syndromes), and additional factor characteristics (specificity, potency, need for replication). Few of the putative risk factors were reported to precede the onset of the disorder. Many factors were general risk factors; only few differentiated between the 3 eating disorder syndromes. Common risk factors from longitudinal and cross-sectional studies were gender, ethnicity, early childhood eating and gastrointestinal problems, elevated weight and shape concerns, negative self-evaluation, sexual abuse and other adverse experiences, and general psychiatric morbidity. Suggestions are made for the conceptualization of future risk factor studies.

No association between two polymorphisms at the 5HT2A gene and bipolar affective puerperal psychosis

OBJECTIVE

To examine whether variation at two common polymorphisms, T102C and -1438AG, of the serotonin 2A gene (5HT2A) are involved in the puerperal triggering mechanism of bipolar affective puerperal psychosis.

METHOD

A total of 242 parous women diagnosed with bipolar disorder were genotyped for the two polymorphisms. Of these, 165 women had experienced a manic or psychotic episode, according to DSM-IV criteria, within 6 weeks of childbirth (the puerperal psychosis group). The comparison group comprised of 77 parous women who had not experienced psychiatric disturbance following childbirth.

RESULTS

No significant differences between genotype or allelic frequencies were found between the two groups for either polymorphism.

CONCLUSION

The results indicate that variation at two common polymorphisms of the 5HT2A gene does not appear to play a major role in the development of bipolar affective puerperal psychosis.

The serotonin 2A -1438 G/A receptor polymorphism in a group of Swedish male criminals

Studies have shown that genetic components to some extent underlie behavioral disorders such as impulsive aggression and violence, and that central serotonergic mechanisms are involved in the development of such behavior. In the present study, we analyzed a polymorphism in the gene encoding the serotonin 2A receptor (5-HT2A -1438 G/A) in a group of Swedish criminals (n=97) and in a group of healthy Swedish blood donors (n=202). The 5-HT2A -1438 GG genotype was lower in the criminal group than in the control group (P=0.034). In accordance with previous results, no associations were found between the 5-HT2A -1438 G/A polymorphism and personality as measured by Karolinska Scales of Personality. Neither were there any associations between the studied polymorphism and the type of crime committed.

The physiological-psychological dichotomy in the study of food intake

Human food intake is driven by necessity. We eat to live, but as Brillat-Savarin and others have noted throughout history, in affluent societies eating is a pleasure and becomes more than a means to an end. Eating signifies lifestyle choice and it has considerable meaning in our society beyond the acquisition of essential energy and nutrients. Thus, it is that the study of human food intake, particularly food choice, in contrast to food intake in other animals, tends to be skewed towards measures of behavioural, social and environmental influences rather than on precise physiological processes reflecting metabolism and nutrient partitioning. The dichotomy between physiological and psychological measures is a false one, since all behaviours are necessarily expressed through physiological systems. However, in the field of human food intake research the dichotomy refers to the divergent strands of interest in either psychological or physiological processes underlying intake and appetite. The present review considers both psychological and physiological measures in promoting our understanding of the human appetite system. The overall conclusion is that the burgeoning interest in identifying appetite suppressant drugs to combat obesity and in genotyping alongside behavioural phenotyping will close the gap between psychological and physiological perspectives on human food intake.

5-HT2A receptor gene promoter polymorphism in relation to abdominal obesity and cortisol

OBJECTIVE

There is considerable evidence that cortisol secretion is associated with obesity. The regulation of the 5-hydroxytryptamine receptor 2A (5-HT2A) gene might play an essential role because it is involved in the control of cortisol secretion. Therefore, we examined the potential impact of the 5-HT2A -1438G/A promoter polymorphism on obesity and estimates of insulin, glucose, and lipid metabolism as well as circulating hormones, including salivary cortisol, in 284 unrelated Swedish men born in 1944.

RESEARCH METHODS AND PROCEDURES

The subjects were genotyped by using polymerase chain reaction amplification of the promoter region of the gene for 5-HT2A followed by digestion of the reaction product with the restriction enzyme MspI.

RESULTS

The frequencies were 0.39 for allele -1438A and 0.61 for allele -1438G. Homozygotes for the -1438G allele had, in comparison with -1438A/A subjects, higher body mass index, waist-to-hip ratio, and abdominal sagittal diameter. Moreover, cortisol escape from 0.25-mg dexamethasone suppression was found in subjects with the -1438A/G genotype. Serum leptin, fasting insulin, and glucose, as well as serum lipids, were not different across the -1438G/A genotype groups.

DISCUSSION

From these results, we suggest the possibility that an abnormal production rate of the 5-HT2A gene product might lead to the development of abdominal obesity. The pathophysiology could involve stress factors that destabilize the serotonin-hypothalamic-pituitary-adrenal system in those with genetic vulnerability in the serotonin receptor gene.

Association of 5-HT(2A) receptor gene polymorphism with major affective disorders: the case of a subgroup of bipolar disorder with low suicide risk

BACKGROUND

The implication of serotonin in suicide and affective disease explains why the 5-HT(2A) receptor gene has been proposed as a candidate gene in these disorders, although with conflicting results.

METHODS

We analysed the distribution of the 5-HT(2A)-1438A/G genetic polymorphism in 192 patients with major affective disorder (127 bipolar disorders and 65 unipolar disorders) compared to 142 healthy control subjects.

RESULTS

We found a higher frequency of the A allele in affected patients than in control subjects (p =.034), this difference being particularly striking for the subgroup of patients with type I bipolar disorder (p =.015). Patients with no personal and/or familial history of suicide attempts mainly accounted for the excess of the A allele in affected patients.

CONCLUSIONS

The association detected in this study suggests that the 5-HT(2A) receptor gene may play a role in the genetic susceptibility to bipolar disorder, through a specific subgroup of bipolar type I patients with lower risk of suicidal behavior.

5-HT2A receptor gene polymorphism and eating disorders

Recent studies have reported a genetic association between the -1438 G/A polymorphism within the promoter region of the 5-HT(2A) receptor gene and eating disorders (ED), with conflicting results. To clarify the role of the -1438 G/A polymorphism in different ED categories we have analyzed the genotype and allele frequency distribution in 54 Italian patients with Binge ED (BED) compared to 132 obese non-BED subjects. No significant differences were found between obese BED and obese non-BED individuals, suggesting that this polymorphism does not genetically distinguish these two phenotypes. Moreover, the evaluation of 148 patients with anorexia nervosa and 86 patients with bulimia nervosa revealed an association of the A allele with both these disorders.

The 5-HT(2A) -1438G/A polymorphism in anorexia nervosa: a combined analysis of 316 trios from six European centres

Several case-control association studies have raised the possibility that the A allele of a -1438 G/A polymorphism in the type 2A serotonin receptor (HTR2A) gene may be a risk factor for anorexia nervosa. However the absence of linkage and the existence of negative association studies raise the possibility of false positive findings, resulting from population stratification or lack of statistical power. To address this controversy we recruited a sample of 316 patients with anorexia nervosa from six European centres, and utilised a family-based transmission disequilibrium (TDT) approach to analyse the HTR2A-1438 G/A polymorphism. Age at onset and minimal BMI were also taken into consideration in order to detect clinical heterogeneity or a quantitative trait effect. The TDT approach showed that the A allele was transmitted 133 times and not transmitted 148 times (McNemar chi(2) = 0.29, df = 1, P = 0.59). Also, the haplotype-based haplotype relative risk method showed no evidence for association of the A allele, in samples from each centre (chi(2) < 2.15, df = 1, P > 0.14) and in the total sample (chi(2) = 0.55, df = 1; P = 0.46). Furthermore, we found no evidence for heterogeneity of the A allele frequency between samples (chi(2) = 2.54, df = 4, P = 0.64), either according to minimal-BMI (F1/242 = 2.14, P = 0.45) or age at onset (F1/224 = 2.39; P = 0.12). QTL-TDT analyses also showed no direct role of the A allele on these traits. We thus found no evidence for a significant role of the 5-HT(2A) gene in anorexia nervosa. Previous results may have been exposed to stratification bias (which we controlled by the TDT method) and/or the risk of type 1 error (from which we were less exposed because of the sample size).