Candidate gene polymorphisms in eating disorders

Psychedelic-Assisted Therapy for People with Eating Disorders

PURPOSE OF REVIEW

A growing body of research suggests psychedelic-assisted therapy (PAT) may be safe and effective for a variety of mental health conditions. Among these, eating disorders have been a recent target of interest. This review provides an up-to-date summary of the potential mechanisms and use of PAT in people diagnosed with eating disorders, with a focus on anorexia nervosa.

RECENT FINDINGS

Classic psychedelics may have transdiagnostic efficacy through several mechanisms relevant to eating disorder pathology. Interest in, and efforts to increase access to PAT are both high. Early clinical trials are focused on establishing the safety and utility of this treatment in eating disorders, and efficacy remains unclear. High-quality published data to support the use of PAT for people with eating disorders remains lacking. Recent studies however suggest PAT has the potential to augment the efficacy of current interventions for these difficult-to-treat conditions.

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.

Contemporary views on the genetics of anorexia nervosa

Anorexia nervosa (AN) is a serious mental illness characterized by severe dietary restriction that leads to high rates of morbidity, chronicity, and mortality. Unfortunately, effective treatment is lacking and few options are available. High rates of familial aggregation and significant heritability suggested that the complex etiology of AN is affected by both genetic and environmental factors. In this paper, we review studies that reported common and rare genetic variation that influence susceptibility of AN through candidate gene studies, genome-wide association studies, and sequencing-based studies. We also discuss gene expression, methylation, imaging genetics, and pharmacogenetics to demonstrate that these studies have collectively advanced our knowledge of how genetic variation contributes to AN susceptibility and clinical course. Lastly, we highlight the importance of gene by environment interactions (G×E) and share our enthusiasm for the use of nutritional genomic approaches to elucidate the interaction among nutrients, metabolic intermediates, and genetic variation in AN. A deeper understanding of how nutrition alters genome stability, how genetic variation influences uptake and metabolism of nutrients, and how response to food components affects disordered eating, will lead to personalized dietary interventions and effective nutraceutical and pharmacological treatments for AN.

[Pathogenesis of anorexia nervosa. Neurobiological risk factors and possible endophenotypes]

Anorexia nervosa is a serious, chronical state of illness which often starts in childhood or adolescence and has serious consequences on the quality of life. This review focuses on the heterogenity of the disease with emphasis on special diagnostic implications in case of childhood onset. Research findings of the last decade showed that genetic and neurobiological vulnerabilities are at least as potent risk factors as psychological, family constellations and sociocultural preferences. The heritability of eating disorders levels those of diseases predominantly influenced by biological factors. The authors give a summary of the most investigated neurobiologic and neurocognitive factors which could be the fundaments of a biological vulnerablilty. To date, no common risk factor could be identified, but some existing adversities can clearly be related to distinct subgroups with the disorder. The concept of endo- and subphenotypes leads to more specific and more efficient methods of therapy in other somatic and psychiatric diseases.

Genetics of eating disorders

Disordered eating behavior is the core symptom of the complex disorders anorexia nervosa and bulimia nervosa. Twin and family studies derive high heritability estimates. Hence, substantial genetic influences on the etiology can be assumed for both. Initially, candidate gene studies pertaining to the monoaminergic neurotransmitter systems and to body weight regulation comprised the core of the genetic analyses. Unfortunately, confirmed, solid findings substantiated in meta-analyses are rare, so that eventually none of these associations is unequivocal. Thus, systematic, genome-wide approaches emerged to identify genes with no a priori evidence for their involvement in eating disorders. Genome-wide association studies have hinted to formerly unknown genetic regions. However, significant genome-wide findings have not yet been reported.

Concurrence of anorexia nervosa and Noonan syndrome

Noonan syndrome (NS) is a genetic disease inherited in an autosomal dominant mode; it presents significant genetic heterogeneity and varying penetrance. Mutations have been identified in several genes, and they account for 75% of all known cases. The majority of reported mutations are localized on PTPN11 gene, which encodes the non-receptor type protein tyrosine phosphatase SHP-2. Diagnosis, however, is mainly established after clinical examination. Anorexia nervosa (AN) is an eating disorder characterized by fear of gaining weight, refusal to maintain normal body weight and distorted perceptions of body image or body shape. AN is independently predicted by female sex and feeding problems in childhood, whereas NS symptoms include feeding difficulties. No comorbidity between NS and AN has been reported to date. The authors reported the case of a 38-year-old female patient with AN who met the van der Burgt criteria for NS with confirmed (a) comorbidity of AN and NS and (b) the absence of the most common mutation in PTPN11 and presence of a novel T > A transversion within intron 8-9.

Do girls with anorexia nervosa have elevated autistic traits?

BACKGROUND

Patients with anorexia may have elevated autistic traits. In this study, we tested test whether patients with anorexia nervosa (anorexia) have an elevated score on a dimensional measure of autistic traits, the Autism Spectrum Quotient (AQ), as well as on trait measures relevant to the autism spectrum: the Empathy Quotient (EQ), and the Systemizing Quotient (SQ).

METHODS

Two groups were tested: (1) female adolescents with anorexia: n = 66, aged 12 to 18 years; and (2) female adolescents without anorexia: n =1,609, aged 12 to 18 years. Both groups were tested using the AQ, EQ, and SQ, via the parent-report adolescent versions for patients aged 12 to 15 years old, and the self-report adult versions for patients aged over 16 years.

RESULTS

As predicted, the patients with anorexia had a higher AQ and SQ. Their EQ score was reduced, but only for the parent-report version in the younger age group. Using EQ-SQ scores to calculate 'cognitive types', patients with anorexia were more likely to show the Type S profile (systemizing (S) better than empathy (E)), compared with typical females.

CONCLUSIONS

Females with anorexia have elevated autistic traits. Clinicians should consider if a focus on autistic traits might be helpful in the assessment and treatment of anorexia. Future research needs to establish if these results reflect traits or states associated with anorexia.

Serotonin Receptor 2A (HTR2A) Gene Polymorphisms Are Associated with Blood Pressure, Central Adiposity, and the Metabolic Syndrome

BACKGROUND

Although the etiology of the metabolic syndrome remains unclear, recent evidence suggests that dysregulation of brain serotonergic activity may partly underlie the covariation of risk factors comprising the syndrome. In addition, prior studies have shown polymorphisms in the serotonin 2A receptor (HTR2A) gene to be associated with two syndrome components, hypertension and central adiposity. We conducted a study to confirm associations of HTR2A polymorphisms with elevated blood pressure and central adiposity and tested for association between these polymorphisms and the metabolic syndrome.

METHODS

The study sample included 934 unrelated individuals of European ancestry. We tested for association of two HTR2A polymorphisms, one in the promoter: (-1438[G/A]) and one in the first intron (2416 [C/T]), individually and as a diplotype, with elevated blood pressure, central adiposity, elevated fasting glucose, triglycerides, high density lipoprotein (HDL) cholesterol and presence of the metabolic syndrome, as defined by the American Heart Association/National Heart, Lung and Blood Institute (AHA/NHLBI) Scientific Statement Executive Summary.

RESULTS

Confirming previous reports, elevated blood pressure (>130/85 mm Hg) was associated with both the -1438 GG and 2416 TT genotypes and the GG/TT diplotype (ORs = 1.39-1.76); high waist circumference was associated with -1438 GG genotype only (OR = 1.57). In addition, both the -1438 GG and 2416 TT genotypes, and the GG/TT diplotype, predicted presence of the metabolic syndrome (ORs = 1.44-1.77). Fasting glucose, triglyceride and HDL cholesterol were not associated with either polymorphism.

CONCLUSIONS

Elevated blood pressure, central adiposity, and the metabolic syndrome are associated with polymorphisms in HTR2A gene.

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.

Animal models of eating disorder traits

Eating disorders, such as anorexia and bulimia nervosa, are psychiatric disorders that are likely determined by a complex interaction between genetic variations, developmental processes, and certain life events. Cross-species analysis of traits related to eating disorders may provide a way to functionally and systematically study neurobiological mechanisms underlying these disorders. Interspecies trait genetics may offer opportunities to identify common neurobiological mechanisms underlying eating disorder characteristics relevant to the initiation, progression, and/or maintenance of the disease, such as cognitive rigidity, increased anxiety levels, and behavioral hyperactivity. These can subsequently be tested directly by studying allelic variation in mice and human subjects and by applying methods that can modify gene expression levels in rodent models. Increasing our knowledge about these traits and their underlying neurobiological mechanisms will be relevant to develop new therapies for patients within the heterogeneous eating disorder populations. Novel mouse genetic and phenotyping tools offer a way to study these neurobehavioral traits under controlled environmental and genetic background conditions.

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.

Focus on HTR2C: A possible suggestion for genetic studies of complex disorders

HTR2C is one of the most relevant and investigated serotonin receptors. Its role in important brain structures such as the midbrain, the lateral septal complex, the hypothalamus, the olfactory bulb, the pons, the choroid plexus, the nucleus pallidus, the striatum and the amygdala, the nucleus accumbens and the anterior cingulated gyrus candidate it as a promising target for genetic association studies. The biological relevance of these brain structures is reviewed by way of the focus on HTR2C activity, with a special attention paid to psychiatric disorders. Evidence from the genetic association studies that dealt with HTR2C is reviewed and discussed alongside the findings derived from the neuronatmic investigations. The reasons for the discrepancies between these two sets of reports are discussed. As a result, HTR2C is shown to play a pivotal role in many different psychiatric behaviors or psychiatric related disrupted molecular balances, nevertheless, genetic association studies brought inconsistent results so far. The most replicated association involve the feeding behavior and antipsychotic induced side effects, both weight gain and motor related: Cys23Ser (rs6318) and -759C/T (rs3813929) report the most consistent results. The lack of association found in other independent studies dampens the clinical impact of these reports. Here, we report a possible explanation for discrepant findings that is poorly or not at all usually considered, that is that HTR2C may exert different or even opposite activities in the brain depending on the structure analyzed and that mRNA editing activity may compensate possible genetically controlled functional effects. The incomplete coverage of the HTR2C variants is proposed as the best cost-benefit ratio bias to fix. The evidence of brain area specific HTR2C mRNA editing opens a debate about how the brain can differently modulate stress events, and process antidepressant treatments, in different brain areas. The mRNA editing activity on HTR2C may play a major role for the negative association results.

Interspecies genetics of eating disorder traits

Family and twin studies have indicated that genetic factors play a role in the development of eating disorders, such as anorexia and bulimia nervosa, but novel views and tools may enhance the identification of neurobiological mechanisms underlying these conditions. Here we propose an integrative genetic approach to reveal novel biological substrates of eating disorder traits analogous in mouse and human. For example, comparable to behavioral hyperactivity that is observed in 40-80% of anorexia nervosa patients, inbred strains of mice with different genetic backgrounds are differentially susceptible to develop behavioral hyperactivity when food restricted. In addition, a list of characteristics that are relevant to eating disorders and approaches to their measurement in humans together with potential analogous rodent models has been generated. Interspecies genetics of neurobehavioral characteristics of eating disorders has the potential to open new roads to identify and functionally test genetic pathways that influence neurocircuits relevant for these heterogeneous psychiatric disorders.

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.

Voluntary exercise prevents the obese and diabetic metabolic syndrome of the melanocortin-4 receptor knockout mouse

Exercise is a mechanism for maintenance of body weight in humans. Morbidly obese human patients have been shown to possess single nucleotide polymorphisms in the melanocortin-4 receptor (MC4R). MC4R knockout mice have been well characterized as a genetic model that possesses phenotypic metabolic disorders, including obesity, hyperphagia, hyperinsulinemia, and hyperleptinemia, similar to those observed in humans possessing dysfunctional hMC4Rs. Using this model, we examined the effect of voluntary exercise of MC4R knockout mice that were allowed access to a running wheel for a duration of 8 wk. Physiological parameters that were measured included body weight, body composition of fat and lean mass, food consumption, body length, and blood levels of cholesterol and nonfasted glucose, insulin, and leptin. At the termination of the experiment, hypothalamic mRNA expression levels of neuropeptide Y (NPY), agouti-related protein (AGRP), proopiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART), orexin, brain-derived neurotropic factor (BDNF), phosphatase with tensin homology (Pten), melanocortin-3 receptor (MC3R), and NPY-Y1R were determined. In addition, islet cell distribution and function in the pancreas were examined. In the exercising MC4R knockout mice, the pancreatic islet cell morphology and other physiological parameters resembled those observed in the wild-type littermate controls. Gene expression profiles identified exercise as having a significant effect on hypothalamic POMC, orexin, and MC3R levels. Genotype had a significant effect on AGRP, POMC, CART, and NPY-Y1R, with an exercise and genotype interaction effect on NPY gene expression. These data support the hypothesis that voluntary exercise can prevent the genetic predisposition of melanocortin-4 receptor-associated obesity and diabetes.

D2 dopamine receptor (DRD2) gene Taq1A polymorphism and the eating-related psychological traits in eating disorders (anorexia nervosa and bulimia) and obesity

OBJECTIVE

Food is considered a reinforcing agent, like a variety of substances such as alcohol and other drugs of abuse that produce pleasure. Psychopathological traits related to food intake are demonstrated in eating disorders as in obesity with different genetic aspects for these diseases. Recently, the prevalence of TaqA1 allele has been associated to alcohol, drug abuse and carbohydrate preference. For this reason, the aim of this study was to evaluate if the presence of A1 allele, in eating disorders and obesity, is associated with some particular psycho-pathological characteristics.

METHODS

We studied the presence of TaqA1 in Italian subjects affected by obesity (n=71), anorexia (n=28), bulimia (n=20) and in control group (n=54). The Eating Disorders Inventory (EDI test) was used to evaluate the psychological profiles. Patients without alcohol and drugs abuse were selected (>125 ml/day).

RESULTS

The A1+ allele, both in A1/A1 and A1/A2 genotypes, was not differently distributed among disease groups; on the contrary two EDI subscales (Drive for thinness and Ineffectiveness) resulted associated with A1+ allele without effect of the eating disease or obesity.

CONCLUSION

These results confirm that the presence of A1+ allele is not simply related to body weight but the A1+ allele might be a marker of a genetic psychological condition in people with high risk to develop pathological eating behaviour.

Pharmacological Characterization of 40 Human Melanocortin-4 Receptor Polymorphisms with the Endogenous Proopiomelanocortin-Derived Agonists and the Agouti-Related Protein (AGRP) Antagonist†,‡

The melanocortin-4 receptor (MC4R) is a G-protein coupled receptor (GPCR) that is expressed in the central nervous system and has a role in regulating energy homeostasis and obesity. Up to a remarkable 6% of morbidly obese adults and children studied possess single nucleotide polymorphisms (SNPs) of the MC4R. Upon stimulation by agonist, the MC4R signals through the intracellular adenylate cyclase signal transduction pathway. Posttranslational modification of the pro-opiomelanocortin (POMC) gene transcript results in the generation of several endogenous melanocortin receptor agonists including alpha-, beta-, gamma-melanocyte stimulating hormones (MSH) and adrenocorticotropin (ACTH) ligands. The endogenous MC4R antagonist, agouti-related protein (AGRP), is expressed in the brain and is only one of two naturally occurring antagonists of GPCRs identified to date. Herein, we have generated 40 hMC4 polymorphic receptors and evaluated their cell surface expression by flow cytometry as well as pharmacologically characterized their functionality using the endogenous agonists alpha-MSH, beta-MSH, gamma2-MSH, ACTH(1-24), the antagonist hAGRP(87-132), and the synthetic agonists NDP-MSH and MTII. This is the first study in which polymorphic hMC4Rs have been pharmacologically characterized simultaneously with multiple endogenous ligands. Interestingly, at the N97D, L106P, and C271Y hMC4Rs beta-MSH was more potent than the other endogenous agonists alpha-MSH, gamma2-MSH, ACTH(1-24). The S58C and R165Q/W hMC4Rs possessed significantly reduced endogenous agonist potency (15- to 90-fold), but the synthetic ligands NDP-MSH and MTII possessed only 2-9-fold reduced potency as compared to the wild-type receptor, suggesting their potential as therapeutic ligands to treat individuals with these polymorphisms.

Impact of violations and deviations in Hardy-Weinberg equilibrium on postulated gene-disease associations

The authors evaluated whether statistically significant violations of Hardy-Weinberg equilibrium (HWE) or the magnitude of deviations from HWE may contribute to the problem of replicating postulated gene-disease associations across different studies. Forty-two gene-disease associations assessed in meta-analyses of 591 studies were examined. Studies with disease-free controls in which HWE was violated gave significantly different results from HWE-conforming studies in five instances. Exclusion of the former studies resulted in loss of statistical significance of the overall meta-analysis in three instances and more than a 10% change in the summary odds ratio in six. Exclusion of HWE-violating studies changed the formal significance of the estimated between-study heterogeneity in three instances. After adjustment for the magnitude of the deviation from HWE for the controls, formal significance was lost in another three instances. Studies adjusted for the magnitude of deviation from HWE tended to become more heterogeneous among themselves, and, for seven gene-disease associations, between-study heterogeneity became significant, while it was not so in the unadjusted analyses. Gene-disease association studies and meta-analyses thereof should routinely scrutinize the potential impact of HWE violations as well as nonsignificant deviations from the exact frequencies expected under HWE. Postulated genetic associations with modest-sized odds ratios and borderline statistical significance may not be robust in such sensitivity analyses.

Uncoupling protein-2/uncoupling protein-3 gene polymorphism is not associated with anorexia nervosa

Energy expenditure abnormalities have been observed in anorexia nervosa (AN). The uncoupling proteins (UCPs) have been implicated as having a role in energy metabolism and thermogenesis, and an association between a marker flanking the UCP-2/UCP-3 gene cluster and AN has been reported. Also known are insertion/deletion and -866G/A polymorphisms in the UCP-2 gene, and the -55C/T polymorphism in the UCP-3 gene. Differences in these alleles are reportedly related to changes in energy expenditure, body mass index, fat tissue accumulation and obesity. Therefore, this case-control association analysis was done to determine whether any of these UCP-2/3 gene polymorphisms are related to a predisposition to AN. In analysis of a cohort of 106 female Japanese AN sufferers and 126 normal female controls, we found no between-group differences in the polymorphism frequencies of these groups. The hypothesis that differences in the UCP-2/3 gene influence the susceptibility to AN was not supported.

Role of brain-derived neurotrophic factor in eating disorders: recent findings and its pathophysiological implications

Eating disorders, which include anorexia nervosa (AN) and bulimia nervosa (BN), are disorders characterized by abnormal patterns of weight regulation and eating behaviors, and by disturbances in attitudes and perceptions toward weight and body shape. Brain-derived neurotrophic factor (BDNF) plays a critical role in regulating neural survival, development, function, and plasticity in the brain. Recent findings using heterozygous BDNF (+/-) knock-out (reduced BDNF levels) mice have provided evidence that BDNF plays a role in regulating eating behaviors. Recently, we found that serum levels of BDNF in patients with eating disorders are significantly decreased compared with normal controls. In addition, an association between the BDNF gene polymorphism and eating disorders has been demonstrated. We reviewed the role of BDNF in the pathophysiology of eating disorders and the BDNF gene as a susceptibility gene for eating disorders. Considering the low levels of BDNF in patients with eating disorders, using drugs that increase the BDNF levels and/or BDNF gene therapy are possible novel therapeutic approaches. Providing confirmation that the BDNF gene is the true susceptibility gene for eating disorders could lead to rapid therapeutic progress in treating these disorders. In addition, a more complete understanding of the signal transduction pathway via the p75 neurotrophin receptor (p75NTR) and TrkB receptors would provide new perspectives for treating eating disorders.

The 5HTTLPR polymorphism, psychopathologic symptoms, and platelet [3H-] paroxetine binding in bulimic syndromes

BACKGROUND

A short (s) allele in the promoter region of the 5-hydroxytryptamine (5-HT) transporter gene (5HTTLPR) has been associated with low transcription of the 5-HT transporter protein, and with clinical manifestations including impulsivity, affective disorder, and bulimia nervosa.

METHODS

We studied implications of the 5HTTLPR s allele for eating symptoms, psychopathologic traits, and platelet [3H-] paroxetine binding in 59 women with bulimia spectrum syndromes.

RESULTS

Compared with those without it, carriers of the s allele of 5HTTLPR showed significantly more affective instability, behavioral impulsivity, interpersonal insecurity, comorbid borderline personality disorder (BPD), and lower density (Bmax) of paroxetine-binding sites.

CONCLUSIONS

Our results suggest that proneness to impulsivity, affective dysregulation, and reduced central 5-HT reuptake may (in part) be codetermined by the 5HTTLPR polymorphism. However, given inconsistent 5HTTLPR expression in different populations, we speculate that we may be observing a phenotype (i.e., eating disorder)-dependent manifestation.

Association between a vasopressin receptor AVPR1A promoter region microsatellite and eating behavior measured by a self-report questionnaire (Eating Attitudes Test) in a family-based study of a nonclinical population

OBJECTIVES

Considerable evidence including twin and family studies suggests that biologic determinants interact with cultural cues in the etiology of anorexia and bulimia nervosa. A gene that makes "biologic sense" in contributing susceptibility to these disorders, and to our knowledge not previously investigated for this phenotype, is the vasopressin receptor (AVPR1A), which we have tested for association with eating pathology.

METHODS

We genotyped 280 families with same-sex siblings for two microsatellites in the promoter region of the AVPR1A gene. Siblings completed the 26-item Eating Attitudes Test (EAT) and the Drive for Thinness (DT) and Body Dissatisfaction (BD) subscales of the Eating Disorders Inventory (EDI). The Quantitative Transmission Disequilibrium Test program (QTDT), which employs flexible and powerful variance-components procedures, was used to test for an association between EAT scores and the two AVPR1A promoter region microsatellites, RS1 and RS3.

RESULTS

A significant association (p = .036) was detected between the RS3 microsatellite and EAT scores. The strongest association was between RS3 and the Dieting subscale of the EAT (p = .011). A significant association was also observed between the EDI-DT and the RS3 microsatellit (p = .0450).

CONCLUSIONS

We demonstrate for the first time an association between a microsatellite polymorphism in the AVPR1A promoter region and scores on the EAT as well as with the EDI-DT. The strongest association was observed between the RS3 microsatellite and the Dieting subscale of the EAT. The relevant phenotype appears to tap severe dietary restriction for weight loss purposes.

Eating disorders: clinical features and pathophysiology

Anorexia nervosa (AN) and bulimia nervosa (BN) are disorders of eating and weight-related behavior that together afflict some 1-3% of women in the United States. One of the remarkable features about each of the eating disorders is how persistent the disordered eating behavior becomes once it has begun. Substantial psychological, social, and physiological disturbances are associated with eating disorders, and it has been very difficult to disentangle those factors that may result from the disturbed behavior from the factors that may have predisposed individuals to, or precipitated the development of, the disorder. This article will briefly review the definitions, phenomenology, and identified risk factors for development of each of the major eating disorders. Pathophysiology will be discussed, with a particular focus on candidate factors that might sustain disordered eating behavior, as informed by clinical and basic science research. Future research directions will be suggested.

The role of leptin in regulating neuroendocrine function in humans

Eating disorders are a group of disease states including anorexia nervosa, bulimia nervosa and binge eating on one end as well as episodic or chronic overeating resulting in obesity at the other end of the spectrum. These disorders are characterized by decreased and/or increased energy intake and are frequently associated with hormonal and metabolic disorders. The discovery of leptin, an adipocyte-secreted hormone acting in the brain to regulate energy homeostasis, and its subsequent study in human physiology have significantly advanced our understanding of normal human physiology and have provided new opportunities for understanding and possibly treating disease states, such as anorexia and bulimia nervosa. It has been recently discovered that leptin levels above a certain threshold are required to activate the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-thyroid axes in men, whereas the hypothalamic-pituitary-adrenal, renin-aldosterone, and growth hormone-IGF-1 axes may be largely independent of circulating leptin levels in humans. In this review, we summarize the latest findings related to the role of leptin in the regulation of several neuroendocrine axes, such as the hypothalamic-pituitary-gonadal and the hypothalamic-pituitary-thyroid axes in humans and discuss its potential pathophysiologic role in eating disorders.

Melanocortin ligands: 30 years of structure-activity relationship (SAR) studies

The challenge of peptide and peptidomimetic research is the development of methods and techniques to improve the biological properties of native peptides and to convert peptide ligands into non-peptide compounds. Improved biological properties of peptides includes enhancement of stability, potency, and receptor selectivity, for both in vivo and in vitro applications. The design of a ligand with specific activity and desired biological properties is a complex task, and, to accomplish this objective, knowledge about putative interactions between a ligand and the corresponding receptor will be valuable. This includes interactions for both the binding and signal transduction processes. Structure-activity relationship (SAR) studies involve systematic modification of a lead peptide and are designed to provide insight into potential interactions involved in the formation of the ligand-receptor complex. It is desirable to have knowledge about both favorable and unfavorable processes that may occur in putative ligand-receptor interactions that result in either receptor stimulation or inhibition. Herein, we discuss various SAR studies that have involved melanocortin peptides over three decades and the information these studies have provided to the melanocortin field.

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.

Association study of cannabinoid receptor gene (CNR1) alleles and anorexia nervosa: differences between restricting and binging/purging subtypes

Anorexia nervosa (AN) is a severe and disabling psychiatric disorder, characterized by profound weight loss and body image disturbance. Family and twin studies indicate a significant genetic contribution to this disorder although no genetic mutation has yet been identified. The endocannabinoid system has recently been implicated in many physiological functions including appetite regulation. We, therefore, undertook a family based study to test the hypothesis whether a polymorphism of the CNR1 gene, which encodes human CB1 receptor, a subclass of the central cannabinoid receptor, contributes to the susceptibility to AN. Fifty two families (parents with one or two affected siblings) were genotyped for the (AAT) trinucleotide repeat of CNR1 gene. Using the haplotype relative risk (HRR) method, the distribution of alleles transmitted to the patients was not found to be significantly different from the non-transmitted parental alleles. However, upon dividing the samples to restricting and binging/purging subtypes of AN, the extended transmission disequilibrium test (ETDT) revealed that there is preferential transmission of different alleles in each of the subtypes. The 14 repeat allele was preferentially transmitted in the binging/purging AN group (P = 0.05) but not in the restricting AN group, whereas the 13 repeat allele was preferentially transmitted in the restricting AN group (almost significant, P = 0.07) but not in the binging/purging AN group. Our study suggests that restricting AN and binging/purging AN may be associated with different alleles of the CNR1 gene.

Evidence of a novel quantitative-trait locus for obesity on chromosome 4p in Mexican Americans

Although several genomewide scans have identified quantitative-trait loci influencing several obesity-related traits in humans, genes influencing normal variation in obesity phenotypes have not yet been identified. We therefore performed a genome scan of body mass index (BMI) on Mexican Americans, a population prone to obesity and diabetes, using a variance-components linkage analysis to identify loci that influence BMI. We used phenotypic data from 430 individuals (26% diabetics, 59% females, mean age +/- SD = 43 +/- 17 years, mean BMI +/- SD = 30.0 +/- 6.7, mean leptin (ng/ml) +/- SD = 22.1 +/- 17.1) distributed across 27 low-income Mexican American pedigrees who participated in the San Antonio Family Diabetes Study (SAFDS) for whom a 10-15-cM map is available. In this genomewide search, after accounting for the covariate effects of age, sex, diabetes, and leptin, we identified a genetic region exhibiting the most highly significant evidence for linkage (LOD 4.5) with BMI on chromosome 4p (4p15.1) at 42 cM, near marker D4S2912. This linkage result has been confirmed in an independent linkage study of severe obesity in Utah pedigrees. Two strong positional candidates, the human peroxisome proliferator-activated receptor gamma coactivator 1 (PPARGC1) and cholecystokinin A receptor (CCKAR) with major roles in the development of obesity, are located in this region. In conclusion, we identified a major genetic locus influencing BMI on chromosome 4p in Mexican Americans.

Combined family trio and case-control analysis of the COMT Val158Met polymorphism in European patients with anorexia nervosa

The high activity Val158 (H) allele of the dopamine-metabolizing enzyme catechol-O-methyltransferase (COMT) was associated with anorexia nervosa (AN) in a recent family trio-based study of patients from Israel. In an attempt to replicate this finding, we performed a combined family trio and case-control study in an European population from seven centers in six different countries (Austria, Germany, Great Britain, Italy [Milan], Italy [Florence], Slovenia, and Spain), together contributing a total of 372 family trios, 684 controls and 266 cases. TDT analyses of high (H) and low (L) alleles in family trios showed that H allele and L allele were each transmitted 101 times (chi(2) = 0, ns). Allele-wise case-control analysis using separate samples simply combined from the centers was also not significant, with the frequencies of the H allele 50% in cases and same in controls. Stratified analysis of data from all centers gave an odds ratio of 0.98 (Cornfield 95% confidence limits 0.78-1.24). Analysis by genotype was likewise not significant (overall chi(2) = 0.42). Because we were not able to support the primary hypothesis that Val158Met is a risk factor for AN, we did not perform secondary analysis of minimum body mass index (mBMI), age at onset or illness subtype (restricting or binge purging anorexia). Overall we found no support for the hypothesis that the Val158 allele of COMT gene is associated with AN in our combined European sample.

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.

Refinement of behavioural traits in animals for the genetic dissection of eating disorders

Both twin and family studies have revealed the involvement of genetic factors in disorders that affect the regulation of body weight, such as obesity and anorexia nervosa. However, pinpointing the genes that contribute to these human disorders has not yet been very successful. In contrast, genetic studies in animals have been basic for the identification of many genes involved in the regulation of various physiological processes of energy metabolism. We thus plan to review here ways in which findings from animal studies and what is known about behavioural diversity in the human population with eating disorders can be combined. This would probably optimise phenotype-based candidate gene analysis in humans.

Eating disorders

Eating disorders rank among the most debilitating psychiatric disturbances that affect young women. Knowledge has increased in recent years about the two major eating disorders, anorexia nervosa (AN) and bulimia nervosa (BN); however, much remains unknown. This review article will provide an overview of the epidemiology, proposed risk factors and clinical features of AN, and BN, as well as current recommendations for evaluation and treatment of these disorders.

Candidate genes for anorexia nervosa in the 1p33-36 linkage region: serotonin 1D and delta opioid receptor loci exhibit significant association to anorexia nervosa

Serotonergic and opioidergic neurotransmitter system alterations have been observed in people with eating disorders; the genes for the serotonin 1D receptor (HTR1D) and the opioid delta receptor (OPRD1) are found on chr1p36.3-34.3, a region identified by our group in a linkage analysis of anorexia nervosa (AN). These candidate genes were evaluated for sequence variation and for linkage and association of this sequence variation to AN in family and case : control data sets. Resequencing of the HTR1D locus and a portion of the OPRD1 locus identified novel SNPs and confirmed existing SNPs. Genotype assay development and genotyping of nine SNPs (four at HTR1D and five at OPRD1) was performed on 191 unrelated individuals fulfilling DSM-IV criteria (w/o amenorrhea criterion) for AN, 442 relatives of AN probands and 98 psychiatrically screened controls. Linkage analysis of these candidate gene SNPs with 33 microsatellite markers in families including relative pairs concordantly affected with restricting AN (N=37) substantially increased the evidence for linkage of this region to restricting AN to an NPL score of 3.91. Statistically significant genotypic, allelic, and haplotypic association to AN in the case : control design was observed at HTR1D and OPRD1 with effect sizes for individual SNPs of 2.63 (95% CI=1.21-5.75) for HTR1D and 1.61 (95% CI=1.11-2.44) for OPRD1. Using genotype data on parents and AN probands, three SNPs at HTR1D were found to exhibit significant transmission disequilibrium (P&<0.05). The combined statistical genetic evidence suggests that HTR1D and OPRD1 or linked genes may be involved in the etiology of AN.

Eating disorders

Eating disorders are an important cause of physical and psychosocial morbidity in adolescent girls and young adult women. They are much less frequent in men. Eating disorders are divided into three diagnostic categories: anorexia nervosa, bulimia nervosa, and the atypical eating disorders. However, the disorders have many features in common and patients frequently move between them, so for the purposes of this Seminar we have adopted a transdiagnostic perspective. The cause of eating disorders is complex and badly understood. There is a genetic predisposition, and certain specific environmental risk factors have been implicated. Research into treatment has focused on bulimia nervosa, and evidence-based management of this disorder is possible. A specific form of cognitive behaviour therapy is the most effective treatment, although few patients seem to receive it in practice. Treatment of anorexia nervosa and atypical eating disorders has received remarkably little research attention.

Diabetes and eating disorders in primary care

OBJECTIVE

To determine the relationship between diabetes and eating disorders among primary care patients.

METHOD

Data on 3,000 patients were obtained from eight primary care and family practice settings, including the PRIME-MD Patient Health Questionnaire (PHQ), self-reported physical illness, and social functioning information. Multivariate logistic regression analyses were used to determine the association between diabetes and eating disorders.

RESULTS

Diabetes was associated with an increased likelihood of eating disorders [OR = 2.3 (1.4, 3.9)], after adjusting for differences in demographic characteristics and comorbid mental disorders. This effect was specific to diabetes. Eating disorder was the only mental disorder associated with a significantly increased risk of diabetes, odds ratio (OR) = 2.4 (1.4, 4.0), after adjusting for demographic characteristics and comorbid mental and physical disorders. Patients with both diabetes and eating disorders had significantly higher levels of comorbid anxiety, panic attacks, and alcohol use disorders, compared with those with one but not both.

DISCUSSION

Consistent with reports from community-based samples, these data suggest that diabetes may be associated with an increased likelihood of eating disorders among patients in primary care. Clinicians who treat patients with diabetes, a common condition in primary care, should screen for eating disorders. In addition, patients with eating disorders may be at risk for the development of diabetes. Further work is needed to determine the generalizability of these findings and to understand the mechanism of this association.

Reduced 5-HT2A receptor binding after recovery from anorexia nervosa

BACKGROUND

Several lines of evidence suggest that a disturbance of serotonin neuronal pathways may contribute to the pathogenesis of anorexia nervosa (AN). This study applied positron emission tomography (PET) to investigate the brain serotonin 2A (5HT2A) receptor, which could contribute to disturbances of appetite and behavior in AN.

METHODS

To avoid the confounding effects of malnutrition, we studied 16 women recovered from AN (REC AN, >1 year normal weight, regular menstrual cycles, no bingeing or purging) compared with 23 healthy control women (CW) using [18F]altanserin, a specific 5-HT2A receptor antagonist on PET imaging.

RESULTS

REC AN women had significantly reduced [18F]altanserin binding relative to CW in mesial temporal (amygdala and hippocampus), as well as cingulate cortical regions. In a subset of subjects (11 CW and 16 REC AN), statistical parametric mapping (SPM) confirmed reduced mesial temporal cortex 5HT2A receptor binding and, in addition, showed reduced occipital and parietal cortex binding.

CONCLUSIONS

This study extends research suggesting that altered 5-HT neuronal system activity persists after recovery from AN and may be related to disturbances of mesial temporal lobe function. Altered 5-HT neurotransmission after recovery also supports the possibility that this may be a trait-related disturbance that contributes to the pathophysiology of AN.

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.

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.