Further lack of association between the 5-HT2A gene promoter polymorphism and susceptibility to eating disorders and a meta-analysis pertaining to anorexia 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.

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.

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.

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.

Smoking, but not malnutrition, influences promoter-specific DNA methylation of the proopiomelanocortin gene in patients with and without anorexia nervosa

OBJECTIVE

Our pilot study evaluates the impact of environmental factors, such as nutrition and smoking status, on epigenetic patterns in a disease-associated gene.

METHOD

We measured the effects of malnutrition and cigarette smoking on proopiomelanocortin (POMC) promoter-specific DNA methylation in female patients with and without anorexia nervosa (AN). POMC and its derived peptides (alpha melanocyte stimulating hormone and adrenocorticotropic hormone) are implicated in stress and feeding response. Promoter-specific DNA methylation of the POMC gene was determined in peripheral blood mononuclear cells of 54 healthy female control subjects, 40 underweight patients with AN, and 21 weight-restored patients with AN using bisulfite sequencing. Malnutrition was characterized by plasma leptin.

RESULTS

POMC promoter-specific DNA methylation was not affected by diagnosis or nutritional status but significantly negatively associated with cigarette smoking.

CONCLUSIONS

Although malnutrition may be expected to reduce DNA methylation through its effects on one-carbon metabolism, our negative results are in line with several in vitro and clinical studies that did not show a direct relation between gene-specific DNA methylation and folate levels. In contrast, smoking has been repeatedly reported to alter DNA methylation of specific genes and should be controlled for in future epigenetic studies.

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.

Pharmacogenomic implications of variants of monoaminergic-related genes in geriatric psychiatry

Response to psychiatric medications in later life is highly heterogeneous and complex. Monoaminergic-related polymorphisms may influence medication response and susceptibility to side effects in elderly individuals. Individuals with the lower function short (S) allele of the serotonin transporter gene (SLC6A4) insertion/deletion (indel) promoter polymorphism (5-HTTLPR) have both increased the likelihood of adverse drug events and increased the need for higher antidepressant concentrations to obtain maximum antidepressant response. By contrast, carriers of the higher expression homozygous long allele (L/L) genotype may respond at lower concentrations. The differential role of these polymorphisms appears at early stages of treatment rather than in the final antidepressant outcome. Research findings suggest that the rs25531 SNP may influence functional expression of the L allele. Similarly, a variable number of tandem repeats in the second intron of the serotonin transporter gene may influence the expression of SLC6A4 and the implications of these variants may be influenced by aging. Two polymorphisms, rs2242466 (-182T/C) and rs5569 (1287G/A), in the norepinephrine transporter gene (SLC6A2 or NET) have been associated with antidepressant response. Studies in dopamine-related polymorphisms have focused on associations with neuroleptic-induced movement disorders. The rs1800497 variant (Taq1A) of the dopamine receptor D2 (DRD2) gene located in a noncoding 3´ region may regulate expression of D2 receptors. The rs6280 variant (Ser9Gly) of the dopamine receptor 3 (DRD3) gene may influence the binding affinity of D3 receptors as a result of serine to glycine substitution of the receptor protein. A multicenter collaborative research effort would be an effective strategy to increase sample sizes to further investigate how gene variants impact the pharmacodynamics and pharmacokinetics of psychotropic drugs in elderly persons.

The genetics of eating disorders

The eating disorders anorexia nervosa (AN), bulimia nervosa (BN), binge eating disorder and allied diagnoses such as eating disorder not otherwise specified are common, complex psychiatric disorders with a significant genetic component. Aetiology is unknown, but both phenotypic characteristics and genetic factors appear to be shared across these disorders, and indeed patients often change between diagnostic categories. Molecular studies have attempted to define genetic risk factors for these disorders, including case-control and family-based candidate gene association studies and linkage analysis of multiply affected nuclear families. These have used both clinical diagnoses and eating disorder-related intermediate phenotypes such as drive-for-thinness or body dissatisfaction. Candidate gene studies have focussed on neurotransmitter and neurodevelopmental systems [e.g. serotonergic, opioid, cannabinoid and dopaminergic receptors, and brain-derived neurotrophic factor (BDNF)], appetite regulatory peptides and their receptors [leptin, ghrelin, agouti-related protein (AgRP), melanocortin receptors, neuropeptide Y], energy balance systems (e.g. uncoupling proteins), genes implicated in obesity (e.g. FTO) and sex hormone systems (e.g. oestrogen receptors), either identified on the basis of their function alone or as positional candidates from linkage analysis. Of these studies, linkage analysis implicates 1p33-36 for AN, 1q31.3 for quantitative behavioural traits related to anorexia and 10p14 for BN, as well as other behavioural phenotypes across both disorders. Candidate gene association has implicated BDNF, delta 1 opioid receptor (OPDR1) and AgRP. More recently, with the advent of genome-wide association studies (GWAS), analysis with microsatellite markers has implicated novel candidate loci for AN at 1q41 and 11q22, and further GWAS results are expected in the near future.

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.

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.

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.

Serotonin receptor 2A gene polymorphism (-1438A/G) and short-term treatment response to citalopram

The 5-HTR2A gene is a candidate gene for influencing the clinical response to antidepressant treatment. The purpose of this study was to determine the relationship between the -1438A/G polymorphism in the 5-HTR2A gene and the response to citalopram in a Korean population with major depressive disorder (MDD). Citalopram was administered for 4 weeks to the 71 patients who completed this study. We found significant differences in genotype, allele, and carrier distribution between the normal group and MDD patients (genotypes: chi(2) = 6.473, d.f. = 2, p = 0.039; alleles: chi(2) = 5.589, d.f. = 1, p = 0.018; OR = 0.618, 95% CI = 0.414-0.922; allele carriers: chi(2) = 5.383, d.f. = 1, p = 0.020; OR = 0.473, 95% CI = 0.249-0.879). The frequency of the -1438G allele was much higher in MDD patients than in the normal group (allele carriers: chi(2) = 5.383, d.f. = 1, p = 0.020; OR = 0.473, 95% CI = 0.249-0.879). There were also significant differences in response to citalopram according to the -1438A/G variation of 5-HTR2A in MDD patients. The group of remitters carried a higher frequency of the GG allele than of the AA and AG alleles. More of nonremitters carried the A allele than were without it (genotype: chi(2) = 8.016, p = 0.018; allele carrier: chi(2) = 4.512, p = 0.034; OR = 0.324, 95% CI = 0.112-0.936). The response to citalopram differed with the -1438A/G polymorphism genotype and allele carriers. The -1438G/-1438G genotype appeared to be associated with a better response to citalopram, with especially the G allele being related to core depressive symptoms and psychic anxiety improvement (p<0.05). These results suggest that the G allele of the -1438A/G polymorphism in the 5-HTR2A gene is associated with MDD, and that patients with -1438G/-1438G have a better response to citalopram treatment than patients with -1438A/-1438A or -1438A/-1438G.

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.

Meta-analysis of serotonin transporter polymorphisms and affective disorders

Polymorphisms in the promoter region (5-HTTLPR) of the serotonin transporter and a variable number of tandem repeats polymorphism in the second intron have been widely studied. However, the results of association studies examining unipolar depression (MDD) or bipolar disorder depression (BPD) have been mixed. To precisely ascertain small associations with both polymorphisms, a meta-analysis was performed involving several thousand subjects, using random-effects modeling. For MDD, the effect of the 5-HTTLPR genotype was significant (chi2=6.1, P<0.05), with 21% of MDD subjects and 17% of controls homozygous for the short (S) allele (odds ratio, 1.16). Similar findings were noted in BPD, with a higher frequency of S/S genotypes in affected patients, although the results did not reach statistical significance. Results of transmission disequilibrium tests trended in a similar direction but also did not reach statistical significance. No consistent effect of the variable number of tandem repeats polymorphism was revealed for either MDD or BPD. The results suggest that the S allele, or a neighboring allele in linkage disequilibrium, is recessive for MDD and possibly BPD. Notably, the association is very small. With these small associations, confounding issues such as population stratification require addressing. Significant heterogeneity between studies was also evident, possibly reflecting differences in diagnosis, different control populations, and different ethnic populations. These factors should Influence the interpretation of the association found in this analysis.

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.

Psychopathology in the postgenomic era

We are rapidly approaching the postgenomic era in which we will know all of the 3 billion DNA bases in the human genome sequence and all of the variations in the genome sequence that are ultimately responsible for genetic influence on behavior. These ongoing advances and new techniques will make it easier to identify genes associated with psychopathology. Progress in identifying such genes has been slower than some experts expected, probably because many genes are involved for each phenotype, which means the effect of any one gene is small. Nonetheless, replicated linkages and associations are being found, for example, for dementia, reading disability, and hyperactivity. The future of genetic research lies in finding out how genes work (functional genomics). It is important for the future of psychology that pathways between genes and behavior be examined at the top-down psychological level of analysis (behavioral genomics), as well as at the bottom-up molecular biological level of cells or the neuroscience level of the brain. DNA will revolutionize psychological research and treatment during the coming decades.

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.

Re-screening serotonin receptors for genetic variants identifies population and molecular genetic complexity

We have re-screened the genes for the 5-HT1A, 5-HT2A, 5-HT2C, and 5-HT7 serotonin receptors for genetic variants in a large African-American and Caucasian-American population sample. We have identified eight novel variants in these genes including four that are predicted to cause amino acid substitutions. These variants are additional candidates for association studies of behavioral disorders such as depression and schizophrenia as well as quantitative personality traits. We have also detected some, but not all, previously identified variants in these genes suggesting that many previously identified variants are unique to specific populations. The results of this study, and previous screens of serotonin receptors, demonstrate that the genes for serotonin receptors display marked population and molecular genetic complexity. These levels of complexity may have a substantial effect on genetic association studies of human behavioral variability related to these genes. We discuss the implications of these findings and propose methods to address complexity in genetic association studies.

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.

Association of the 5-HT2c gene with susceptibility and minimum body mass index in anorexia nervosa

The association between a non-conservative Cys23Ser in the 5-HT2c gene and anorexia nervosa in females was examined. We used case-controls and family based association analysis in a sample of 118 patients with DSMIV anorexia nervosa, 244 controls and 47 family trios. There was a significant increase in the frequency of the Ser23 allele in the patients by allele (18.8% vs 12.8%; p = 0.026; OR 1.58, 95% CI 1.0-2.4) and genotype (32.2% vs 19.9%; genotype-wise p = 0.027). There was significant correlation between genotype and minimum BMI (r2 = 0.056; p = 0.01), indicating that the Ser23 allele has an effect on severity of illness. We performed TDT analysis using a sub-sample of the cases (58) for whom both parents were available and we found an excess transmission of the Ser23 allele (p = 0.05). Our findings are consistent a role for the Ser23 allele of 5-HT2c in mediating susceptibility to and increasing severity of anorexia nervosa.

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.

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).

The human genetics of eating disorders lessons from the leptin/melanocortin system

Genetic analysis of eating disorders is complex phenotypically and genotypically. As seen in the leptin/melanocortin system, however, the results can lead to a deeper understanding and to new therapies. Benefits are expected for eating disorders that stem from genetic and psychologic causes. Finally, an awareness of possible genetic causes of eating disorders will help determine the causes--and thus the treatments--in children and adolescents with eating disorders, as exemplified by obese patients with mutations in the POMC, PC1, leptin, and MC4R loci.

The children of mothers with eating disorders

There is good evidence that children of parents with psychological disorders are themselves at increased risk of disturbances in their development. Although there has been considerable research on a variety of disorders such as depression and alcohol, research on the children of parents with eating disorders has been relatively recent. This paper aims to review the evidence and covers a number of areas, including genetic factors, pregnancy, the perinatal and postpartum period, infancy, and the early years of life, focusing on feeding and mealtimes, general parenting functions, and growth. This is followed by a consideration of psychopathology in the children, parental attitudes to children's weight and shape, and adolescence. What is clear is that although there are numerous case reports and case series, the number of systematic controlled studies is relatively small, and almost nothing has been written about the children of fathers with eating disorders. What is evident from the available evidence is that children of mothers with eating disorders are at increased risk of disturbance, but that the risk depends on a variety of factors, and that difficulties in the children are far from invariable. The paper concludes by summarizing five broad categories of putative mechanisms, based on the evidence to date, by which eating disturbance in parents can influence child development.

Anorexia nervosa: manifestations and management for the gastroenterologist

Anorexia nervosa is a complex psychiatric disorder with significant morbidity and mortality. It is important for gastroenterologists to be aware of the physiological effects and potential complications of anorexia nervosa, as they are frequently involved in treating patients with this disorder. We review the classic, GI, and neuroendocrinological features of anorexia nervosa. We also discuss gender differences and treatment options in anorexia nervosa. Further studies of GI physiology and pharmacology are needed to determine whether any disturbances may be amenable to therapeutic intervention. Future treatments directed at improving GI sensorimotor function and neurohormonal abnormalities in patients with anorexia nervosa may impact their nutritional rehabilitation and may have important health economic implications as patients avoid hospitalization and are restored to full activities in society. The current team approach, which incorporates psychiatrists, psychologists, nutritionists, pediatricians, internists, and gastroenterologists in the treatment of patients with anorexia nervosa, will continue to be essential.

Drug target discovery by pharmacogenetics: mutations in the melanocortin system and eating disorders

The identification of the genetic defect underlying the obese phenotype of the viable yellow mouse, ectopic overexpression of the agouti protein which acts as antagonist at the melanocortin-4 receptor, together with the demonstration that the brain melanocortin system was one major downstream effector pathway of leptin signaling has put forward melanocortin receptors as drug targets for obesity. The lack of compounds acting as melanocortin receptor antagonists was the reason why pharmacological studies had not recognized melanocortin receptors as important drug targets earlier. Blockade of brain melanocortin receptors results in increased food intake and body weight, whereas stimulation of the brain melanocortin system results in decreased food intake and activation of the hypothalamo-pituitary-adrenal axis. Anorexia nervosa is characterized by decreased body weight and food intake accompanied by changes in neuroendocrine systems such as strong activation of the hypothalamo-pituitary-adrenal axis. Since agouti-related protein suppresses the activity of the melanocortin system, the AgRP gene was investigated as candidate gene in anorexia nervosa. One variant of the AgRP gene was associated with anorexia nervosa, thus putting forward melanocortin receptor blockade as putative pharmacotherapy. Investigating variations in candidate genes in disease populations appears to be a fruitful approach towards the identification of drug targets.

Possible genetic link between eating disorders and seasonal changes in mood and behavior

Studies suggest that there is a seasonal pattern of mood fluctuations and eating behavior in patients with eating disorders. Multiple lines of evidence suggest that serotonergic pathways are involved in the mechanisms of eating disorders and seasonal changes in mood and behavior. Researchers have investigated whether variants of genes related to serotonergic transmission are associated with seasonal affective disorder (SAD) and eating disorders. There is evidence that the -1438G/A promoter polymorphism of the 5-HT2A gene plays a role in the development of SAD and eating disorders. Variation of the tryptophan hydroxylase gene may play a part in eating behavior and weight regulation in females with SAD. The author suggests that there may be a genetic link between SAD and eating disorders. It is possible that there are specific inherited personality types with a predisposition to both eating disorders and SAD.

5-HT2A promoter polymorphism is not associated with anorexia nervosa in Japanese patients

Genetic factors have been implicated in playing a significant role in susceptibility to anorexia nervosa (AN). Among many candidate genes for AN, an association with the A allele of the -1438G/A polymorphism in the promoter region of the 5-HT2A receptor has been reported. However, these findings are controversial and all patients studied to date have been Caucasian. This study was designed to determine whether this association is reproducible in Japanese subjects. This case-control study of a cohort of 75 female Japanese AN sufferers and 127 normal female control subjects revealed no significant association between the 5-HT2A promoter polymorphism and AN. Thus, at least for Japanese subjects, the A-allele of the -1438G/A polymorphism in the promoter region of the 5-HT2A receptor gene does not contribute to a predisposition to AN.

Association between 5HT2A receptor gene promoter region polymorphism and eating disorders in Japanese patients

BACKGROUND

Evidence from family and twin studies suggests a genetic contribution to the etiology of eating disorders (EDs). Recently, researchers have reported genetic associations between the MspI polymorphism (-1438A/G) of the promoter region of the 5HT2A receptor gene and EDs; however, reports of evidence against these findings make the association controversial.

METHODS

The authors examined the prevalence of the -1438A/G polymorphism of the 5HT2A receptor gene among 182 Japanese patients with EDs and 374 normal control subjects. Interactions of the association of this polymorphism with subtypes of anorexia nervosa (AN), bulimia nervosa (BN), and various clinical characteristics were also assessed.

RESULTS

In contrast to previous studies reporting elevated A allele frequencies in patients with AN, the G allele had a significantly higher frequency in patients with BN but not in patients with AN, than in control subjects. Examination of the interactions revealed that the presence of the binge eating and/or purging behavior and comorbid borderline personality disorder (BPD) tended to be associated with increased frequency of the G allele.

CONCLUSIONS

Though preliminary, these results can be interpreted as suggesting that the G allele of the 5HT2A receptor gene -1438A/G polymorphism may be associated with pathological features that EDs and BPD have in common, especially disinhibition in eating behavior and personality trait.

The evolving genetic foundations of eating disorders

Data described earlier are clear in establishing a role for genes in the development of eating abnormalities. Estimates from the most rigorous studies suggest that more than 50% of the variance in eating disorders and disordered eating behaviors can be accounted for by genetic effects. These high estimates indicate a need for studies identifying the specific genes contributing to this large proportion of variance. Twin and family studies suggest that several heritable characteristics that are commonly comorbid with AN and BN may share genetic transmission with these disorders, including anxiety disorders or traits, body weight, and possibly major depression. Moreover, some developmental research suggests that the genes involved in ovarian hormones or the genes that these steroids affect also may be genetically linked to eating abnormalities. Molecular genetic research of these disorders is in its infant stages. However, promising areas for future research have already been identified (e.g., 5-HT2A receptor gene, UCP-2/UCP-3 gene, and estrogen receptor beta gene), and several large-scale linkage and association studies are underway. These studies likely will provide invaluable information regarding the appropriate phenotypes to be included in genetic studies and the genes with the most influence on the development of these disorders.

Association between an agouti-related protein gene polymorphism and anorexia nervosa

Anorexia nervosa (AN) is a life threatening disorder affecting mostly adolescent women. It is a dramatic psychiatric syndrome accompanied by severe weight loss, hyperactivity and neuroendocrine changes (reviewed in Refs 1 and 2). Several studies have shown a strong genetic component in AN (reviewed in Ref 3). Recent advances in unraveling the mechanisms of weight control point to a crucial role of the melanocortin-4 receptor (MC4-r) system in regulating body weight. The orexigenic neuropeptide agouti-related protein (AGRP), a MC4-r antagonist, plays a crucial role in maintaining body weight, by inducing food intake. The sequence of the coding region of the human AGRP gene (AGRP) was determined and the AGRP of 100 patients with AN was screened for variations. Three single nucleotide polymorphisms (SNPs) were identified and screened in a further 45 patients and 244 controls. Two alleles were in complete linkage disequilibrium and were significantly enriched in anorectic patients (11%; P = 0.015) compared to controls (4.5%). These data indicate that variations of AGRP are associated with susceptibility for AN. This is possibly caused by defective suppression of the MC4-r by the variant AGRP, leading to a decreased feeding signal, increasing the risk of developing AN. These results implicate that antagonism of the MC4-r might be considered as pharmacotherapy for patients with AN.

Candidate gene polymorphisms in eating disorders

Anorexia nervosa and bulimia nervosa are complex disorders characterized by disordered eating behaviour. Attitudes towards weight and shape as well as the perception of body shape are disturbed. A substantial genetic influence on these disorders has been suggested by formal genetic studies. Obsessive-compulsive behaviour, perfectionism and anxious personality traits seem to occur premorbidly in several patients. Disturbances of neurotransmitter, neuropeptide and neuroendocrine systems have been reported in acutely ill and followed-up patients. Hence, these systems might be involved in the etiology of these eating disorders.Genetic studies on candidate genes have mainly focussed on the serotonergic system and on genes involved in body weight regulation. Up to now, polymorphisms and variations in various genes (e.g. genes for 5-HT receptors, leptin gene, melanocortin MC(4) receptor gene) have been assessed for association and transmission disequilibrium pertaining to anorexia nervosa and/or bulimia nervosa. Most of the studies yielded negative results. Four studies of a polymorphism (-1438 G/A) within the promoter of the 5-HT(2A) gene (5-HT(2A)) revealed an association of the A-allele to anorexia nervosa. However, three studies could not confirm this result. Furthermore, a meta-analysis did not support the positive association. Currently, combined efforts within the European Union will answer the question of whether or not the A-allele is involved in the predisposition to anorexia nervosa. A transmission disequilibrium test is being performed in about 300 trios consisting of a patient with anorexia nervosa and both parents. As candidate gene approaches did not unequivocally identify susceptibility genes (alleles) for anorexia nervosa or bulimia nervosa, systematic model-free genome-wide screenings should also be performed in order to identify currently unknown genes involved in eating disorders. This kind of approach has already been initiated for anorexia nervosa. Genetic research on eating disorders will hopefully lead to new pharmacological treatment strategies.