Single nucleotide polymorphisms in the leptin receptor gene: studies in anorexia nervosa

Brain and gut microbiota disorders in the psychopathology of anorexia nervosa

Studies of pathophysiological mechanisms involved in eating disorders (EDs) have intensified over the past several years, revealing their unprecedented and unanticipated complexity. Results from many articles highlight critical aspects in each member of ED family. Notably, anorexia nervosa (AN) is a disorder due to undefined etiology, frequently associated with symptoms of depression, anxiety, obsessive-compulsiveness, accompanied by endocrine alterations, altered immune response, increased inflammation, and dysbiosis of the gut microbiota. Hence, an advanced knowledge of how and why a multisystem involvement exists is of paramount importance to understand the pathogenetic mechanisms of AN. In this review, we describe the change in the brain structure/function focusing on hypothalamic endocrine disorders and the disequilibrium of gut microbiota in AN that might be responsible for the psychopathological complication.

A review on association and correlation of genetic variants with eating disorders and obesity

Background

Now, eating disorders and obesity and their correlations are danger signal in worldwide which is caused by multifactor and associated with significant mortality and morbidity.

Main body

Every aspect of a patient’s life is influenced by eating disorders and obesity and their correlations. Due to frequent seeing of obese patients, eating disorders have been included in the review as they can sometimes be associated with obesity. However, it should be noted that most patients having eating disorder are at risk to be obese or overweight. This research explores the risk factors for the two disorders, as well as the assessment of medical complications and treatment recommendations for the disorders. In these two disorders, there is also a correlation. The essential consideration is that eating disorders are impulse-control disorders which are similar to addictive behaviors in some aspects. So it is a crying need to treat a patient with obesity and eating disorders simultaneously to ensure success. Genome-wide association studies (GWASs) have increased our knowledge of the pathophysiology of eating disorders (EDs) and obesity and their correlation.

Conclusion

This review enlightens on the summary of eating disorder, obesity, genotypic traits, molecular relations, interaction, correlation, and effect of eating disorder and obesity which outline potential future directions and clinical implications for patients with EDs and obesity.

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.

The use of animal models to decipher physiological and neurobiological alterations of anorexia nervosa patients

Extensive studies were performed to decipher the mechanisms regulating feeding due to the worldwide obesity pandemy and its complications. The data obtained might be adapted to another disorder related to alteration of food intake, the restrictive anorexia nervosa. This multifactorial disease with a complex and unknown etiology is considered as an awful eating disorder since the chronic refusal to eat leads to severe, and sometimes, irreversible complications for the whole organism, until death. There is an urgent need to better understand the different aspects of the disease to develop novel approaches complementary to the usual psychological therapies. For this purpose, the use of pertinent animal models becomes a necessity. We present here the various rodent models described in the literature that might be used to dissect central and peripheral mechanisms involved in the adaptation to deficient energy supplies and/or the maintenance of physiological alterations on the long term. Data obtained from the spontaneous or engineered genetic models permit to better apprehend the implication of one signaling system (hormone, neuropeptide, neurotransmitter) in the development of several symptoms observed in anorexia nervosa. As example, mutations in the ghrelin, serotonin, dopamine pathways lead to alterations that mimic the phenotype, but compensatory mechanisms often occur rendering necessary the use of more selective gene strategies. Until now, environmental animal models based on one or several inducing factors like diet restriction, stress, or physical activity mimicked more extensively central and peripheral alterations decribed in anorexia nervosa. They bring significant data on feeding behavior, energy expenditure, and central circuit alterations. Animal models are described and criticized on the basis of the criteria of validity for anorexia nervosa.

Genetics and Epigenetics of Eating Disorders

Eating disorders (EDs) are serious psychiatric conditions influenced by biological, psychological, and sociocultural factors. A better understanding of the genetics of these complex traits and the development of more sophisticated molecular biology tools have advanced our understanding of the etiology of EDs. The aim of this review is to critically evaluate the literature on the genetic research conducted on three major EDs: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). We will first review the diagnostic criteria, clinical features, prevalence, and prognosis of AN, BN, and BED, followed by a review of family, twin, and adoption studies. We then review the history of genetic studies of EDs covering linkage analysis, candidate gene association studies, genome-wide association studies, and the study of rare variants in EDs. Our review also incorporates a translational perspective by covering animal models of ED-related phenotypes. Finally, we review the nascent field of epigenetics of EDs and a look forward to future directions for ED genetic research.

The outcome of treatment for anorexia nervosa inpatients who required urgent hospitalization

Background

This study was done to determine which psychosocial factors are related to the urgent hospitalization of anorexia nervosa patients (AN) due to extremely poor physical condition and to evaluate their outcome after inpatient treatment.

Methods

133 hospitalized AN patients were classified into an urgent hospitalization (n = 24) or a planned hospitalization (n = 109) group. Multiple regression analysis was done of clinical features, body mass index (BMI), psychological tests [The Minnesota Multiphasic Personality Inventory (MMPI), alexithymia, relationship with parents, and the Eating Disorder Inventory (EDI)]. The effectiveness of treatment was prospectively determined two years after discharge by the Global Clinical Score (GCS). The hospitalized weight gain and the frequency of outpatient visits were evaluated.

Results

Of the factors assessed, only BMI at admission was related to the necessity of urgent hospitalization (β = − 1.063, P = 0.00). The urgent group had significantly more weight loss after discharge and poorer social adaptation on the GCS, even when the patient had a sufficient increase in body weight during inpatient treatment and an equivalent number of outpatient consultations.

Conclusion

None of the parameters of the psychosocial tests studied were significantly different between the groups. The outcome of the urgent group was poor. Two years after discharge they had difficulty maintaining weight and continued to have poor social adaptation.

The role of leptin, melanocortin, and neurotrophin system genes on body weight in anorexia nervosa and bulimia nervosa

OBJECTIVE

Although low weight is a key factor contributing to the high mortality in anorexia nervosa (AN), it is unclear how AN patients sustain low weight compared with bulimia nervosa (BN) patients with similar psychopathology. Studies of genes involved in appetite and weight regulation in eating disorders have yielded variable findings, in part due to small sample size and clinical heterogeneity. This study: (1) assessed the role of leptin, melanocortin, and neurotrophin genetic variants in conferring risk for AN and BN; and (2) explored the involvement of these genes in body mass index (BMI) variations within AN and BN.

METHOD

Our sample consisted of 745 individuals with AN without a history of BN, 245 individuals with BN without a history of AN, and 321 controls. We genotyped 20 markers with known or putative function among genes selected from leptin, melanocortin, and neurotrophin systems.

RESULTS

There were no significant differences in allele frequencies among individuals with AN, BN, and controls. AGRP rs13338499 polymorphism was associated with lowest illness-related BMI in those with AN (p = 0.0013), and NTRK2 rs1042571 was associated with highest BMI in those with BN (p = 0.0018).

DISCUSSION

To our knowledge, this is the first study to address the issue of clinical heterogeneity in eating disorder genetic research and to explore the role of known or putatively functional markers in genes regulating appetite and weight in individuals with AN and BN. If replicated, our results may serve as an important first step toward gaining a better understanding of weight regulation in eating disorders.

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.

Genetic variation of the ghrelin activator gene ghrelin O-acyltransferase (GOAT) is associated with anorexia nervosa

The gastrointestinal peptide hormone ghrelin promotes food intake and increases body weight and adiposity through activation of the growth hormone secretagogue receptor (GHSR1a). To promote its biological action ghrelin is acylated at its serine 3 residue by the recently discovered ghrelin O-acyltransferase (GOAT, a.k.a. membrane-bound O-acyltransferase 4, MBOAT4). Plasma levels of total and acyl-ghrelin are negatively correlated with body-mass-index (BMI); as lower the BMI as higher plasma levels of total and acylated ghrelin and vice versa. Accordingly, plasma levels of total and acyl-ghrelin are elevated in patients with anorexia nervosa (AN) and decline upon weight regain. The importance of the endogenous Goat/ghrelin system in the neuroendocrine adaptation to fasting was recently highlighted by the observation that acyl-ghrelin mediated elevation of growth hormone (GH) release prevents starvation induced hypoglycemia in Goat(-/-) mice. The aim of this study was to test if genetic variation of GOAT is implicated in the etiology of AN. We therefore assessed association of 6 tagging single nucleotide polymorphisms (tagSNPs), which were predicted to cover 96% the common genetic variability of GOAT plus 50 kb of the 5' and 3' flanking region, in 543 German patients with AN and 612 German normal and underweight healthy controls. Based on a recessive mode of inheritance we observed some evidence for association of the G/G genotype at SNP rs10096097 with AN (nominal two-sided p = 0.031). Based on our results we conclude that genetic variation in GOAT might be implicated in the etiology of AN.

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.

Molecular mechanisms underlying anorexia nervosa: focus on human gene association studies and systems controlling food intake

Anorexia nervosa (AN) is a complex multi-factorial disease with high heritability. The psychological AN symptoms are poorly connected with specific molecular mechanisms. Here we review the molecular basis of AN with the focus on human genetic association studies; we put these in the experimental biological context with emphasis on molecular systems controlling food intake and body weight in a direct or indirect manner. We systematically searched for human genetic studies related to AN and grouped data into main categories/systems reflecting their major known roles: (1) Systems related to mental disorders (serotonin, brain-derived neurotrophic factor (BDNF), norepinephrine (NE), glutamate (NMDA) receptor and SK3 channel, KCCN3). (2) Hunger regulatory systems (leptin, AGRP, MSH, melanocortin 4 receptor (MC4R), NPY, ghrelin, cholecystokinin (CCK). (3) Feeding motivation- and reward-related systems (opioids, OPRD1, cannabinoids (anandamide (AEA), THC, CBR1), dopamine, DRD2, DRD3, DRD4, catecholamine-O-methyl transferase (COMT). (4) Systems regulating energy metabolism (uncoupling proteins 2 and 3 (UCP2 and UCP3). (5) Neuroendocrine systems with emphasis on sex hormones (estrogen receptor-beta (ESR2). (6) The immune system and inflammatory response (tumor necrosis factor-alpha (TNF-alpha)). Overall, we found that in total 175 association studies have been performed on AN cohorts on 128 different polymorphisms related to 43 genes. We review the strongest associations, identify some genes that have an important role in regulating BMI whose possible relationship to AN has not been investigated and discuss the potential targets for pharmacological interventions.

Lack of association of genetic variants in genes of the endocannabinoid system with anorexia nervosa

BACKGROUND

Several lines of evidence indicate that the central cannabinoid receptor 1 (CNR1) as well as the major endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH), N-acylethanolamine-hydrolyzing acid amidase (NAAA) and monoglyceride lipase (MGLL) are implicated in mediating the orexigenic effects of cannabinoids. The aim of this study was to analyse whether nucleotide sequence variations in the CNR1, FAAH, NAAA and MGLL genes are associated with anorexia nervosa (AN).

METHODS

We analysed the association of a previously described (AAT)n repeat in the 3' flanking region of CNR1 as well as a total of 15 single nucleotide polymorphisms (SNPs) representative of regions with restricted haplotype diversity in CNR1, FAAH, NAAA or MGLL in up to 91 German AN trios (patient with AN and both biological parents) using the transmission-disequilibrium-test (TDT). One SNP was additionally analysed in an independent case-control study comprising 113 patients with AN and 178 normal weight controls. Genotyping was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ARMS-PCR or using 3730xl capillary sequencers.

RESULTS

The TDT revealed no evidence for association for any of the SNPs or the (AAT)n repeat with AN (all two-sided uncorrected p-values > 0.05). The lowest p-value of 0.11 was detected for the A-allele of the CNR1 SNP rs1049353 for which the transmission rate was 59% (95% confidence interval 47%...70%). Further genotyping of rs1049353 in 113 additional independent patients with AN and 178 normal weight controls could not substantiate the initial trend for association (p = 1.00).

CONCLUSION

As we found no evidence for an association of genetic variation in CNR1, FAAH, NAAA and MGLL with AN, we conclude that genetic variations in these genes do not play a major role in the etiology of AN in our study groups.

Genetic susceptibility to eating disorders: associated polymorphisms and pharmacogenetic suggestions

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

Relevance of animal models to human eating disorders and obesity

BACKGROUND AND RATIONALE

This review addresses the role animal models play in contributing to our knowledge about the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN) and obesity.

OBJECTIVES

Explore the usefulness of animal models in complex biobehavioral familial conditions, such as AN, BN, and obesity, that involve interactions among genetic, physiologic, psychological, and cultural factors.

RESULTS AND CONCLUSIONS

The most promising animal model to mimic AN is the activity-based anorexia rodent model leading to pathological weight loss. The paradigm incorporates reward elements of the drive for activity in the presence of an appetite and allows the use of genetically modified animals. For BN, the sham-feeding preparation in rodents equipped with a gastric fistula appears to be best suited to reproduce the postprandial emesis and the defects in satiety. Animal models that incorporate genes linked to behavior and mood may clarify biobehavioral processes underlying AN and BN. By contrast, a relative abundance of animal models has contributed to our understanding of human obesity. Both environmental and genetic determinants of obesity have been modeled in rodents. Here, we consider single gene mutant obesity models, along with models of obesigenic environmental conditions. The contributions of animal models to obesity research are illustrated by their utility for identifying genes linked to human obesity, for elucidating the pathways that regulate body weight and for the identification of potential therapeutic targets. The utility of these models may be further improved by exploring the impact of experimental manipulations on the behavioral determinants of energy balance.

Eating disorders: an overview of treatment responses and the potential impact of vulnerability genes and endophenotypes

Anorexia nervosa (AN), bulimia nervosa (BN) and binge-eating disorder (BED) are the three main eating disorders. Antidepressants, antipsychotics, anticonvulsants, prokinetic agents, opiate antagonists, appetite suppressants, tetrahydrocannabinol, cyproheptadine, zinc and ondansetron have been tested, and are frequently associated with psychological treatment. Selective serotonin reuptake inhibitors have a proven efficacy in BN and binge eating disorder. Other treatments, such as atypical antipsychotics in AN, anticonvulsants in BN and BED, and naltrexone and ondansetron in BN, may be promising, but lack the appropriate trials. The development of genetic researches in eating disorders may help the clinician to choose the most appropriate treatment in forthcoming years, using genetic polymorphisms of vulnerability genes, those linked to endophenotypes, or genes implicated in the metabolism of the drug treatment.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

The transcript expression profile of the leptin receptor-coding gene assayed with the oligonucleotide microarray technique--could this be an anorexia nervosa marker?

Anorexia nervosa is a serious eating disorder with the highest mortality rate of any psychiatric disorder. The DSM-IV classification differentiates two AN types: the restricting type (AN-R) and the binge-eating/purging type (AN-BP). Leptin (LEP) levels can be thought of as a signal to the body of its energy reserves. The leptin receptor (including all its mRNA isoforms) is expressed in many tissues. Our aim was to discover the transcript expression profile of the LEP receptor-coding gene in the peripheral blood mononuclears in AN-R and AN-BP patients. Three young women suffering from Anorexia nervosa (one with AN-BP and two with AN-R) took part in the study, along with three non-anorexic subjects as our reference group. LEP receptor gene expression was examined using the oligonucleotide microarray method (HG-U133A, Affymetrix). The results were normalized using RMAExpress. Next, the accumulation analysis method was used (clustering). Hierarchical clustering resulted in three groups of separate clusters. The first group (cluster I) consisted of AN-R patients. The next group (cluster II) consisted of reference group patients suffering from different psychic disorders not related to eating disorders. Cluster III consisted of two patients--the first with AN-BP and the second with an adaptive disorder.