Association of candidate genes with phenotypic traits relevant to anorexia nervosa

Higher-Order Inputs Involved in Appetite Control

The understanding of the neural control of appetite sheds light on the pathogenesis of eating disorders such as anorexia nervosa and obesity. Both diseases are a result of maladaptive eating behaviors (overeating or undereating) and are associated with life-threatening health problems. The fine regulation of appetite involves genetic, physiological, and environmental factors, which are detected and integrated in the brain by specific neuronal populations. For centuries, the hypothalamus has been the center of attention in the scientific community as a key regulator of appetite. The hypothalamus receives and sends axonal projections to several other brain regions that are important for the integration of sensory and emotional information. These connections ensure that appropriate behavioral decisions are made depending on the individual's emotional state and environment. Thus, the mechanisms by which higher-order brain regions integrate exteroceptive information to coordinate feeding is of great importance. In this review, we will focus on the functional and anatomical projections connecting the hypothalamus to the limbic system and higher-order brain centers in the cortex. We will also address the mechanisms by which specific neuronal populations located in higher-order centers regulate appetite and how maladaptive eating behaviors might arise from altered connections among cortical and subcortical areas with the hypothalamus.

Fear and food: Anxiety-like behavior and the susceptibility to weight loss in an activity-based anorexia rat model

Anorexia nervosa (AN) is a severe psychiatric disorder characterized by energy restriction, low body weight, a fear of gaining weight, and often excessive physical activity. Anxiety disorders appear to constitute a major risk factor for developing AN and are the most frequent comorbidity. Here, the influence of anxiety‐like behavior prior to food restriction on increased physical activity, leading to greater susceptibility to weight loss, was tested in rats. Furthermore, the possible anxiolytic effect of starvation itself was analyzed. A chronic starvation model activity‐based anorexia (ABA) was applied to mimic physiological and behavioral characteristics of AN. During the induction of starvation and acute starvation, food intake was reduced by 70% and the rats lost 25% of their body weight, which was kept stable to imitate chronic starvation. Anxiety‐like behavior was quantified before and after chronic starvation using the elevated plus maze, based on rodents’ aversion to open spaces. Anxiety‐related behavior before food restriction was associated with increased running‐wheel activity during habituation and during the induction of starvation, and predicted faster weight loss in ABA rats. Additionally, food‐restricted animals showed less anxiety‐like behavior after chronic starvation. Animals showing more anxiety‐like behavior appear to be more susceptible to weight loss, partially mediated by increased physical activity. Anxiety‐related behavior was associated with increased physical activity, which in turn was associated with more rapid weight loss. Our data let us assume that food restriction has an anxiolytic effect. These findings demonstrate the importance of considering anxiety disorders in patients with AN.

Genetic Markers in Psychiatry

Psychiatric disorders such as addiction (substance use and addictive disorders), depression, eating disorders, schizophrenia, and post-traumatic stress disorder (PTSD) are severe, complex, multifactorial mental disorders that carry a high social impact, enormous public health costs, and various comorbidities as well as premature morbidity. Their neurobiological foundation is still not clear. Therefore, it is difficult to uncover new set of genes and possible genetic markers of these disorders since the understanding of the molecular imbalance leading to these disorders is not complete. The integrative approach is needed which will combine genomics and epigenomics; evaluate epigenetic influence on genes and their influence on neuropeptides, neurotransmitters, and hormones; examine gene × gene and gene × environment interplay; and identify abnormalities contributing to development of these disorders. Therefore, novel genetic approaches based on systems biology focused on improvement of the identification of the biological underpinnings might offer genetic markers of addiction, depression, eating disorders, schizophrenia, and PTSD. These markers might be used for early prediction, detection of the risk to develop these disorders, novel subtypes of the diseases and tailored, personalized approach to therapy.

Development of an AmpliSeqTM Panel for Next-Generation Sequencing of a Set of Genetic Predictors of Persisting Pain

Background: Many gene variants modulate the individual perception of pain and possibly also its persistence. The limited selection of single functional variants is increasingly being replaced by analyses of the full coding and regulatory sequences of pain-relevant genes accessible by means of next generation sequencing (NGS).

Methods: An NGS panel was created for a set of 77 human genes selected following different lines of evidence supporting their role in persisting pain. To address the role of these candidate genes, we established a sequencing assay based on a custom AmpliSeq^TM panel to assess the exomic sequences in 72 subjects of Caucasian ethnicity. To identify the systems biology of the genes, the biological functions associated with these genes were assessed by means of a computational over-representation analysis.

Results: Sequencing generated a median of 2.85 ⋅ 10⁶ reads per run with a mean depth close to 200 reads, mean read length of 205 called bases and an average chip loading of 71%. A total of 3,185 genetic variants were called. A computational functional genomics analysis indicated that the proposed NGS gene panel covers biological processes identified previously as characterizing the functional genomics of persisting pain.

Conclusion: Results of the NGS assay suggested that the produced nucleotide sequences are comparable to those earned with the classical Sanger sequencing technique. The assay is applicable for small to large-scale experimental setups to target the accessing of information about any nucleotide within the addressed genes in a study cohort.

Molecular bases of anorexia nervosa, bulimia nervosa and binge eating disorder: shedding light on the darkness

Eating-disorders (EDs) consequences to human health are devastating, involving social, mental, emotional, physical and life-threatening aspects, concluding on impairment and death in cases of extreme anorexia nervosa. It also implies that people suffering an ED need to find psychiatric and psychological help as soon as possible to achieve a fully physical and emotional recovery. Unfortunately, to date, there is a crucial lack of efficient clinical treatment to these disorders. In this review, we present an overview concerning the actual pharmacological and psychological treatments, the knowledge of cells, circuits, neuropeptides, neuromodulators and hormones in the human brain- and other organs- underlying these disorders, the studies in animal models and, finally, the genetic approaches devoted to face this challenge. We will also discuss the need for new perspectives, avenues and strategies to be developed in order to pave the way to novel and more efficient therapeutics.

Relationships Between Self-Reported and Observed Parenting Behaviour, Adolescent Disordered Eating Attitudes and Behaviours, and the 5-HTTLPR Polymorphism: Data From the Australian Temperament Project

This study examined whether self-reported and observationally measured parental behaviours were associated with disordered eating, and investigated possible moderation by a serotonin-transporter polymorphism (5-HTTLPR). Study 1 included 650 adolescents from the Australian Temperament Project who completed the Eating Disorder Inventory-2 Drive for Thinness and Bulimia scales at 15/16 years and were genotyped for 5-HTTLPR. Parents completed an Australian Temperament Project-devised measure of parental warmth and harsh punishment. Study 2 included a subgroup of 304 participants who also engaged in a video-recorded family interaction, with observed parental warmth and hostility coded by the Iowa Family Interaction Rating Scale. Greater self-reported parental warmth was associated with lower bulimia scores. Conversely, observationally measured parental warmth was associated with lower drive for thinness, but not bulimia. Self-reported parental harsh punishment was associated with bulimia only, with observed parental hostility associated with neither outcome. 5-HTTLPR genotype did not moderate the relationship between parent behaviours and adolescent disordered eating. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.

Effects of single genetic variants and polygenic obesity risk scores on disordered eating in adolescents - The HUNT study

PURPOSE

Improving the understanding of the role of genetic risk on disordered eating (DE).

METHODS

A case-control study including 1757 (F: 979, M: 778) adolescents (aged 13-19 years) from the Nord-Trøndelag Health Study (HUNT), an ethnically homogenous Norwegian population based study. Cases and controls were defined using a shortened version of the Eating Attitude Test. Logistic regression was employed to test for associations between DE phenotypes and 24 obesity and eating disorder susceptibility SNPs, and the joint effect of a subset of these in a genetic risk score (GRS).

RESULTS

COMT was shown to be associated with poor appetite/undereating (OR: 0.6, CI 95%: 0.43-0.83, p = 0.002). Independent of obesity associations, the weighted GRS was associated to overeating in 13-15 year old females (OR: 2.07, CI 95%: 1.14-3.76, p = 0.017). Additionally, a significant association was observed between the GRS and loss of control over eating in the total sample (OR: 1.62, CI 95%: 1.01-2.61, p = 0.046).

CONCLUSIONS

The COMT variant (rs4680) was associated with poor appetite/undereating. Our study further confirms prior findings that obesity risk also confers risk for loss of control over eating; and overeating amongst girls.

BDNF-Val66Met variant and adolescent stress interact to promote susceptibility to anorexic behavior in mice

There is an urgent need to identify therapeutic targets for anorexia nervosa (AN) because current medications do not impact eating behaviors that drive AN's high mortality rate. A major obstacle to developing new treatments is the lack of animal models that recapitulate the pattern of disease onset typically observed in human populations. Here we describe a translational mouse model to study interactions between genetic, psychological and biological risk factors that promote anorexic behavior. We combined several factors that are consistently associated with increased risk of AN-adolescent females, genetic predisposition to anxiety imposed by the BDNF-Val66Met gene variant, social isolation stress and caloric restriction (CR). Approximately 40% of the mice with all of these risk factors will exhibit severe self-imposed dietary restriction, sometimes to the point of death. We systematically varied the risk factors outlined above to explore how they interact to influence anorexic behavior. We found that the Val66Met genotype markedly increases the likelihood and severity of abnormal feeding behavior triggered by CR, but only when CR is imposed in the peri-pubertal period. Incidence of anorexic behavior in our model is dependent on juvenile exposure to social stress and can be extinguished by adolescent handling, but is discordant from anxiety-like behavior. Thus, this study characterized gene × environment interactions during adolescence that could be the underlying driver of abnormal eating behavior in certain AN patients, and represents a promising system to identify possible targets for therapeutic intervention.

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.

Overview of genetic research in anorexia nervosa: The past, the present and the future

BACKGROUND

Even though the evidence supporting the presence of a heritable component in the aetiology of anorexia nervosa (AN) is strong, the underlying genetic mechanisms remain poorly understood. The recent publication of a genome-wide association study (GWAS) of AN (Boraska, Mol Psychiatry, 2014) was an important step in genetic research in AN.

OBJECTIVE

To briefly sum up strengths and weaknesses of candidate-gene and genome-wide approaches, to discuss the genome-wide association studies of AN and to make predictions about the genetic architecture of AN by comparing it to that of schizophrenia (since the diseases share some similarities and genetic research in schizophrenia is more advanced).

METHOD

Descriptive literature review.

RESULTS

Despite remarkable efforts, the gene-association studies in AN did not advance our knowledge as much as had been hoped, although some results still await replication.

DISCUSSION

Continuous effort of participants, clinicians and researchers remains necessary to ensure that genetic research in AN follows a similarly successful path as in schizophrenia. Identification of genetic susceptibility loci provides a basis for follow-up studies.

Genetic neuropathology of obsessive psychiatric syndromes

Anorexia nervosa (AN), bulimia nervosa (BN) and obsessive-compulsive disorder (OCD) are complex psychiatric disorders with shared obsessive features, thought to arise from the interaction of multiple genes of small effect with environmental factors. Potential candidate genes for AN, BN and OCD have been identified through clinical association and neuroimaging studies; however, recent genome-wide association studies of eating disorders (ED) so far have failed to report significant findings. In addition, few, if any, studies have interrogated postmortem brain tissue for evidence of expression quantitative trait loci (eQTLs) associated with candidate genes, which has particular promise as an approach to elucidating molecular mechanisms of association. We therefore selected single-nucleotide polymorphisms (SNPs) based on candidate gene studies for AN, BN and OCD from the literature, and examined the association of these SNPs with gene expression across the lifespan in prefrontal cortex of a nonpsychiatric control cohort (N=268). Several risk-predisposing SNPs were significantly associated with gene expression among control subjects. We then measured gene expression in the prefrontal cortex of cases previously diagnosed with obsessive psychiatric disorders, for example, ED (N=15) and OCD/obsessive-compulsive personality disorder or tics (OCD/OCPD/Tic; N=16), and nonpsychiatric controls (N=102) and identified 6 and 286 genes that were differentially expressed between ED compared with controls and OCD cases compared with controls, respectively (false discovery rate (FDR) <5%). However, none of the clinical risk SNPs were among the eQTLs and none were significantly associated with gene expression within the broad obsessive cohort, suggesting larger sample sizes or other brain regions may be required to identify candidate molecular mechanisms of clinical association in postmortem brain data sets.

Purging behavior modulates the relationships of hormonal and behavioral parameters in women with eating disorders

BACKGROUND/AIMS

There is ample consensus that there is a neurophysiological basis for eating disorders (ED). Traits of personality translate into behavioral traits, purging being a well-defined transversal example. The direct implication of steroid hormones on ED has seldom been studied, despite their effects on behavior.

METHODS

After psychological interview analysis, 57 ED female patients (31 purgative and 26 nonpurgative) and 17 female controls were studied. Metabolic parameters and analysis of androgen, estrogen and glucocorticoid hormones were determined in parallel to the psychopathological profile (EDI-2 and SCL-90-R) and anthropometric measurements.

RESULTS

Psychometric tests showed clear differences between ED and controls, but there were few hormonal-metabolic significant differences. In purgative ED there were repeated (significant) positive correlations with corticosteroid-binding globulin (CBG) and negative correlations with sex hormone-binding globulin (SHBG) versus eating and general psychopathology. In nonpurging ED there were positive correlations for deoxycortisol, free fatty acids and albumin and negative for aspartate aminotransferase and psychopathological traits.

CONCLUSION

The data suggest that CBG/corticosteroids and sexual hormones/SHBG are involved in purging behavior and its psychopathology and severity scores. Correlations of selected psychometric data and the CBG/SHBG levels in purging may eventually result in clinical markers. This approach may provide additional clues for understanding the pathogenesis of ED.

Evidence for the role of EPHX2 gene variants in anorexia nervosa

Anorexia nervosa (AN) and related eating disorders are complex, multifactorial neuropsychiatric conditions with likely rare and common genetic and environmental determinants. To identify genetic variants associated with AN, we pursued a series of sequencing and genotyping studies focusing on the coding regions and upstream sequence of 152 candidate genes in a total of 1205 AN cases and 1948 controls. We identified individual variant associations in the Estrogen Receptor-ß (ESR2) gene, as well as a set of rare and common variants in the Epoxide Hydrolase 2 (EPHX2) gene, in an initial sequencing study of 261 early-onset severe AN cases and 73 controls (P=0.0004). The association of EPHX2 variants was further delineated in: (1) a pooling-based replication study involving an additional 500 AN patients and 500 controls (replication set P=0.00000016); (2) single-locus studies in a cohort of 386 previously genotyped broadly defined AN cases and 295 female population controls from the Bogalusa Heart Study (BHS) and a cohort of 58 individuals with self-reported eating disturbances and 851 controls (combined smallest single locus P<0.01). As EPHX2 is known to influence cholesterol metabolism, and AN is often associated with elevated cholesterol levels, we also investigated the association of EPHX2 variants and longitudinal body mass index (BMI) and cholesterol in BHS female and male subjects (N=229) and found evidence for a modifying effect of a subset of variants on the relationship between cholesterol and BMI (P<0.01). These findings suggest a novel association of gene variants within EPHX2 to susceptibility to AN and provide a foundation for future study of this important yet poorly understood condition.

Loss of control over eating: a description of the eating disorder/obesity spectrum in women

GOALS

This study aimed to analyse the association, commonalities and differences between obesity and eating disorders (ED).

METHOD

A total of 150 female patients [50 obese with bulimia nervosa (OB + BN), 50 obese with binge eating disorders (OB + BED), 50 obese without eating disorders (OB)] and 50 female healthy-eating/weight control (CG) volunteers participated in this study.

ASSESSMENT

All participants were assessed by the Eating Disorders Inventory-2 (EDI-2), the Symptom Checklist-Revised (SCL-90-R) and the Temperament and Character Inventory-Revised.

RESULTS

In general, all the groups differed significantly and showed linear trends (OB + BN > OB + BED > OB > CG) on general and eating psychopathology (SCL-90-R and EDI-2). Regarding personality traits, statistically significant differences across all four groups were found on Harm Avoidance and Self-Directedness. Whereas some symptoms were shared in extreme weight conditions, others were specifically related to ED.

CONCLUSIONS

The presence of binge and purge symptomatology in obese patients is clinically relevant. These findings help to understand the relationship between Obesity and ED.

Puberty as a critical risk period for eating disorders: a review of human and animal studies

This article is part of a Special Issue "Puberty and Adolescence". Puberty is one of the most frequently discussed risk periods for the development of eating disorders. Prevailing theories propose environmentally mediated sources of risk arising from the psychosocial effects (e.g., increased body dissatisfaction, decreased self-esteem) of pubertal development in girls. However, recent research highlights the potential role of ovarian hormones in phenotypic and genetic risk for eating disorders during puberty. The goal of this paper is to review data from human and animal studies in support of puberty as a critical risk period for eating disorders and evaluate the evidence for hormonal contributions. Data are consistent in suggesting that both pubertal status and pubertal timing significantly impact risk for most eating disorders in girls, such that advanced pubertal development and early pubertal timing are associated with increased rates of eating disorders and their symptoms in both cross-sectional and longitudinal research. Findings in boys have been much less consistent and suggest a smaller role for puberty in risk for eating disorders in boys. Twin and animal studies indicate that at least part of the female-specific risk is due to genetic factors associated with estrogen activation at puberty. In conclusion, data thus far support a role for puberty in risk for eating disorders and highlight the need for additional human and animal studies of hormonal and genetic risk for eating disorders during puberty.

Lifetime obesity in patients with eating disorders: increasing prevalence, clinical and personality correlates

OBJECTIVES

The aims of our study were to examine the lifetime prevalence of obesity rate in eating disorders (ED) subtypes and to examine whether there have been temporal changes among the last 10 years and to explore clinical differences between ED with and without lifetime obesity.

METHODS

Participants were 1383 ED female patients (DSM-IV criteria) consecutively admitted, between 2001 and 2010, to Bellvitge University Hospital. They were assessed by means of the Eating Disorders Inventory-2, the Symptom Checklist-90-Revised, the Bulimic Investigatory Test Edinburgh and the Temperament and Character Inventory-Revised.

RESULTS

The prevalence of lifetime obesity in ED cases was 28.8% (ranging from 5% in anorexia nervosa to 87% in binge-eating disorders). Over the last 10 years, there has been a threefold increase in lifetime obesity in ED patients (p < .001). People with an ED and obesity had higher levels of childhood and family obesity (p < .001), a later age of onset and longer ED duration; and had higher levels of eating, general and personality symptomatology.

CONCLUSIONS

Over the last 10 years, the prevalence of obesity associated with disorders characterized by the presence of binge episodes, namely bulimic disorders, is increasing, and this is linked with greater clinical severity and a poorer prognosis.

Association analysis of 94 candidate genes and schizophrenia-related endophenotypes

While it is clear that schizophrenia is highly heritable, the genetic basis of this heritability is complex. Human genetic, brain imaging, and model organism studies have met with only modest gains. A complementary research tactic is to evaluate the genetic substrates of quantitative endophenotypes with demonstrated deficits in schizophrenia patients. We used an Illumina custom 1,536-SNP array to interrogate 94 functionally relevant candidate genes for schizophrenia and evaluate association with both the qualitative diagnosis of schizophrenia and quantitative endophenotypes for schizophrenia. Subjects included 219 schizophrenia patients and normal comparison subjects of European ancestry and 76 schizophrenia patients and normal comparison subjects of African ancestry, all ascertained by the UCSD Schizophrenia Research Program. Six neurophysiological and neurocognitive endophenotype test paradigms were assessed: prepulse inhibition (PPI), P50 suppression, the antisaccade oculomotor task, the Letter-Number Span Test, the California Verbal Learning Test-II, and the Wisconsin Card Sorting Test-64 Card Version. These endophenotype test paradigms yielded six primary endophenotypes with prior evidence of heritability and demonstrated schizophrenia-related impairments, as well as eight secondary measures investigated as candidate endophenotypes. Schizophrenia patients showed significant deficits on ten of the endophenotypic measures, replicating prior studies and facilitating genetic analyses of these phenotypes. A total of 38 genes were found to be associated with at least one endophenotypic measure or schizophrenia with an empirical p-value<0.01. Many of these genes have been shown to interact on a molecular level, and eleven genes displayed evidence for pleiotropy, revealing associations with three or more endophenotypic measures. Among these genes were ERBB4 and NRG1, providing further support for a role of these genes in schizophrenia susceptibility. The observation of extensive pleiotropy for some genes and singular associations for others in our data may suggest both converging and independent genetic (and neural) pathways mediating schizophrenia risk and pathogenesis.