The structure of genetic and environmental risk factors for three measures of disordered eating

Associations Between Attention Deficit Hyperactivity Disorder Symptom Dimensions and Disordered Eating Symptoms in Adolescence: A Population-Based Twin Study

Although bivariate associations between attention-deficit/hyperactivity disorder (ADHD) and eating disorders in adolescent girls and boys have been previously identified, the mechanistic link underlying the symptom-level associations remains unclear. We evaluated shared genetic and environmental influences on ADHD symptoms and disordered eating in 819 female and 756 male twins from the Swedish TCHAD cohort using bivariate models. Common additive genetic and unique environmental effects accounted for majority of ADHD and disordered eating associations in a differential manner. For girls, the strongest genetic correlation was observed for cognitive/inattention problems-bulimia (0.54), with genetic factors accounting for 67% of the phenotypic correlation. For boys, the strongest genetic correlations were observed for conduct problems-bulimia and hyperactivity-bulimia (~ 0.54), accounting for 83% and 95% of the phenotypic correlation, respectively. As per our findings, the risk of comorbidity and shared genetics highlights the need for preventative measures and specialized treatment for ADHD and disordered eating in both sexes.

Association of etiological factors across the extreme end and continuous variation in disordered eating in female Swedish twins

BACKGROUND

Accumulating evidence suggests that many psychiatric disorders etiologically represent the extreme end of dimensionally distributed features rather than distinct entities. The extent to which this applies to eating disorders (EDs) is unknown.

METHODS

We investigated if there is similar etiology in (a) the continuous distribution of the Eating Disorder Inventory-2 (EDI-2), (b) the extremes of EDI-2 score, and (c) registered ED diagnoses, in 1481 female twin pairs at age 18 years (born 1992-1999). EDI-2 scores were self-reported at age 18. ED diagnoses were identified through the Swedish National Patient Register, parent-reported treatment and/or self-reported purging behavior of a frequency and duration consistent with DSM-IV criteria. We differentiated between anorexia nervosa (AN) and other EDs.

RESULTS

The heritability of the EDI-2 score was 0.65 (95% CI 0.61-0.68). The group heritabilities in DeFries-Fulker extremes analyses were consistent over different percentile-based extreme groups [0.59 (95% CI 0.37-0.81) to 0.65 (95% CI 0.55-0.75)]. Similarly, the heritabilities in liability threshold models were consistent over different levels of severity. In joint categorical-continuous models, the twin-based genetic correlation was 0.52 (95% CI 0.39-0.65) between EDI-2 score and diagnoses of other EDs, and 0.26 (95% CI 0.08-0.42) between EDI-2 score and diagnoses of AN. The non-shared environmental correlations were 0.52 (95% CI 0.32-0.70) and 0.60 (95% CI 0.38-0.79), respectively.

CONCLUSIONS

Our findings suggest that some EDs can partly be conceptualized as the extreme manifestation of continuously distributed ED features. AN, however, might be more distinctly genetically demarcated from ED features in the general population than other EDs.

The Anorexia Nervosa Genetics Initiative: Study description and sample characteristics of the Australian and New Zealand arm

OBJECTIVES

Anorexia nervosa is a severe psychiatric disorder with high mortality rates. While its aetiology is poorly understood, there is evidence of a significant genetic component. The Anorexia Nervosa Genetics Initiative is an international collaboration which aims to understand the genetic basis of the disorder. This paper describes the recruitment and characteristics of the Australasian Anorexia Nervosa Genetics Initiative sample, the largest sample of individuals with anorexia nervosa ever assembled across Australia and New Zealand.

METHODS

Participants completed an online questionnaire based on the Structured Clinical Interview Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) eating disorders section. Participants who met specified case criteria for lifetime anorexia nervosa were requested to provide a DNA sample for genetic analysis.

RESULTS

Overall, the study recruited 3414 Australians and 543 New Zealanders meeting the lifetime anorexia nervosa case criteria by using a variety of conventional and social media recruitment methods. At the time of questionnaire completion, 28% had a body mass index ⩽ 18.5 kg/m². Fasting and exercise were the most commonly employed methods of weight control, and were associated with the youngest reported ages of onset. At the time of the study, 32% of participants meeting lifetime anorexia nervosa case criteria were under the care of a medical practitioner; those with current body mass index < 18.5 kg/m² were more likely to be currently receiving medical care (56%) than those with current body mass index ⩾ 18.5 kg/m² (23%). Professional treatment for eating disorders was most likely to have been received from general practitioners (45% of study participants), dietitians (42%) and outpatient programmes (42%).

CONCLUSIONS

This study was effective in assembling the largest community sample of people with lifetime anorexia nervosa in Australia and New Zealand to date. The proportion of people with anorexia nervosa currently receiving medical care, and the most common sources of treatment accessed, indicates the importance of training for general practitioners and dietitians in treating anorexia nervosa.

Genetic and environmental associations between body dissatisfaction, weight preoccupation, and binge eating: Evidence for a common factor with differential loadings across symptom type

OBJECTIVE

Prior twin studies provide support for a single "common factor" that contributes genetic and environmental risk to a range of disordered eating symptoms. However, the common factor may be indexed less well by binge eating (BE) than other symptoms of eating disorders [i.e., body dissatisfaction (BD) and weight preoccupation (WP)]. We sought to explore the presence of a common factor and test whether loadings differed across three key symptoms (i.e., BE, BD, WP).

METHOD

Disordered eating was assessed via self-report in 631 female twin pairs from the Michigan State University Twin Registry.

RESULTS

We detected a common disordered eating factor that was influenced primarily by additive genetic and nonshared environmental influences. However, we observed different loadings on this common factor by symptom type, as factor loadings for BD and WP were stronger than that for BE. Moreover, the residual environmental and/or genetic variances (i.e., those that are independent of the common factor) were larger in BE than those of BD or WP.

DISCUSSION

Although all three symptoms share a common set of genetic and environmental influences, risk for BE may involve additional genetic, biological, and environmental factors that are not shared with other symptoms of eating pathology. © 2016 Wiley Periodicals, Inc.(Int J Eat Disord 2017; 50:157-161).

Genetic variants associated with disordered eating

OBJECTIVE

Although the genetic contribution to the development of anorexia nervosa (AN) has long been recognized, there has been little progress relative to other psychiatric disorders in identifying specific susceptibility genes. Here, we have carried out a genome-wide association study on an unselected community sample of female twins surveyed for eating disorders.

METHOD

We conducted genome-wide association analyses in 2,564 female twins for four different phenotypes derived from self-report data relating to lifetime presence of 15 types of disordered eating: AN spectrum, bulimia nervosa (BN) spectrum, purging via substances, and a binary measure of no disordered eating behaviors versus three or more. To complement the variant level results, we also conducted gene-based association tests using VEGAS software.

RESULTS

Although no variants reached genome-wide significance at the level of p < 10(-8), six regions were suggestive (p < 5 × 10(-7)). The current results implicate the following genes: CLEC5A, LOC136242, TSHZ1, and SYTL5 for the AN spectrum phenotype; NT5C1B for the BN spectrum phenotype; and ATP8A2 for the disordered eating behaviors phenotype.

DISCUSSION

As with other medical and psychiatric phenotypes, much larger samples and meta-analyses will ultimately be needed to identify genes and pathways contributing to predisposition to eating disorders.

Sex differences in the physiology of eating

Hypothalamic-pituitary-gonadal (HPG) axis function fundamentally affects the physiology of eating. We review sex differences in the physiological and pathophysiological controls of amounts eaten in rats, mice, monkeys, and humans. These controls result from interactions among genetic effects, organizational effects of reproductive hormones (i.e., permanent early developmental effects), and activational effects of these hormones (i.e., effects dependent on hormone levels). Male-female sex differences in the physiology of eating involve both organizational and activational effects of androgens and estrogens. An activational effect of estrogens decreases eating 1) during the periovulatory period of the ovarian cycle in rats, mice, monkeys, and women and 2) tonically between puberty and reproductive senescence or ovariectomy in rats and monkeys, sometimes in mice, and possibly in women. Estrogens acting on estrogen receptor-α (ERα) in the caudal medial nucleus of the solitary tract appear to mediate these effects in rats. Androgens, prolactin, and other reproductive hormones also affect eating in rats. Sex differences in eating are mediated by alterations in orosensory capacity and hedonics, gastric mechanoreception, ghrelin, CCK, glucagon-like peptide-1 (GLP-1), glucagon, insulin, amylin, apolipoprotein A-IV, fatty-acid oxidation, and leptin. The control of eating by central neurochemical signaling via serotonin, MSH, neuropeptide Y, Agouti-related peptide (AgRP), melanin-concentrating hormone, and dopamine is modulated by HPG function. Finally, sex differences in the physiology of eating may contribute to human obesity, anorexia nervosa, and binge eating. The variety and physiological importance of what has been learned so far warrant intensifying basic, translational, and clinical research on sex differences in eating.

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

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

Genetic and environmental influences on disordered eating: An adoption study

Twin studies indicate significant genetic, but little shared environmental, influences on eating disorders. However, critics argue that study limitations constrain the conclusions that can be drawn. Adoption studies avoid many of these limitations, but to date, no adoption studies of eating pathology have been conducted. The current study was the first adoption study to examine genetic/environmental effects for disordered eating. Participants included 123 adopted and 56 biological female sibling pairs. Disordered eating (i.e., overall eating pathology, body dissatisfaction, weight preoccupation, binge eating) was assessed with the Minnesota Eating Behaviors Survey (Klump, McGue, & Iacono, 2000; von Ranson, Klump, Iacono, & McGue, 2005). Biometric model fitting indicated significant genetic influences (59%-82%) on all forms of disordered eating, with nonshared environmental factors accounting for the remaining variance. Shared environmental factors did not contribute significantly to any disordered eating symptom. Our findings bolster those from twin studies and provide critical evidence of significant genetic effects on disordered eating symptoms.

Do weight and shape concerns exhibit genetic effects? Investigating discrepant findings

OBJECTIVE

Unlike twin studies of general weight and shape concerns, studies examining the heritability of the undue influence of weight and shape concerns on self-evaluation have found little evidence for genetic effects. The present study sought to resolve these discrepancies by examining the heritability of both types of weight and shape concerns in a young adult twin sample.

METHOD

Participants included 270 female twins from the Michigan State University Twin Registry. General weight and shape concerns were assessed with subscales from the Eating Disorder Examination Questionnaire (EDEQ). Similar to previous research, the undue influence of weight and shape on self-evaluation was assessed using averaged scores from two EDEQ items.

RESULTS

The heritability of all weight and shape measures was estimated at 49-66%.

DISCUSSION

General weight and shape concerns and the undue influence of these concerns on self-evaluation are influenced by genetic factors in young adult female twins.

The heritability of eating disorders: methods and current findings

Family, twin, and adoption studies of anorexia nervosa (AN), bulimia nervosa (BN), binge-eating disorder (BED), and the proposed purging disorder presentation (PD) have consistently demonstrated that genetic factors contribute to the variance in liability to eating disorders. In addition, endophenotypes and component phenotypes of eating disorders have been evaluated and provide further insight regarding genetic factors influencing eating disorders and eating disorder diagnostic criteria. Many of these phenotypes have demonstrated substantial heritability. This chapter reviews biometrical genetic methods and current findings from family and twin studies that investigate the role of genes and environment in the etiology of eating disorders. We review the methodology used to estimate heritability, the results of these studies, and discuss the implications of this research for the basic conceptualization of eating disorders and the future value of twin modeling in the molecular genetic era.

Genetic risk factors for disordered eating in adolescent males and females

The etiologic role of genetic and environmental factors on disordered eating was examined in a sample of 15- to 17-year-old female-female, male-male, and opposite-sex twin pairs. Also assessed was whether a single factor is underlying 3 facets (body dissatisfaction, drive for thinness, bulimia) of disordered eating, including the possible importance of sex differences. Univariate model-fitting analyses indicated that genetic factors are more important for girls and environment more important for boys for body dissatisfaction and drive for thinness. A multivariate common factor analysis indicated that a single factor accounted for the association among these 3 facets of disordered eating in both sexes. However, only 50% of the genetic risk for this factor is shared between the sexes.

Recurrent binge eating (RBE) and its characteristics in a sample of young women in Germany

OBJECTIVE

To examine the characteristics of recurrent binge eating (RBE) in a non-treatment-seeking sample from the general population. RBE individuals are described in terms of socio-economic status, general psychopathology, and comorbidity rates of mental disorders.

METHOD

Participants were 1877 German females aged 18-24 years from a population-based epidemiological study.

RESULTS/DISCUSSION

The point prevalence of RBE in our sample was 0.9% (N = 17). Compared to healthy women, subjects with RBE suffered more often from comorbid mental disorders and also exhibited more general psychopathology: They were similar to women with other mental disorders and other eating disorders (EDs). RBE seems to be a syndrome of clinical significance itself and might be an important risk factor for the development of further EDs, especially binge eating disorder (BED) and other mental disorders.

Genetics of food intake and eating behavior phenotypes in humans

This review summarizes the research advances of the past decade regarding the role of human genetic differences in energy and nutrient intake as well as in eating behavior phenotypes and selected eating disorders. The evidence for familial aggregation and heritability based on twin and nuclear family study designs is summarized. Genome-wide linkage scans and quantitative trait loci identified to date are discussed. DNA sequence variants in candidate genes are reviewed. Single genes associated with classical eating disorders are also incorporated. Epigenetic events will need to be incorporated in future studies designed to investigate the effects of DNA variants on dietary phenotypes. Understanding the relative contribution of global genetic variation and of DNA sequence variants in specific genes is important in the effort to influence dietary habits in a healthier direction.

Genetics in eating disorders: extending the boundaries of research

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

A transdiagnostic approach to understanding eating disorders

Categorical models dominate the eating disorder field, but the tandem use of categorical and dimensional models has been proposed. A transdiagnostic dimensional model, number of lifetime eating disorder behaviors (LEDB), was examined with respect to (1) its relationship to a variety of indicators of the individual's functioning, (2) the degree to which it was influenced by genetic and environmental risk factors, and (3) exposure to specific environmental risk factors. Data from self-report and interview from 1002 female twins (mean age = 34.91 years, SD = 2.09) were examined. While 15.4% women met criteria for a lifetime eating disorder, 29% had at least one LEDB. The dimensional measure provided an indicator of associated functioning, and was influenced primarily by the nonshared environment. The number of LEDB was associated with the degree of impaired functioning. This impairment was associated with conflict between parents and criticism from parents when growing up.

Variance components analyses of multiple asthma traits in a large sample of Australian families ascertained through a twin proband

BACKGROUND

Intermediate phenotypes are often measured as a proxy for asthma. It is largely unclear to what extent the same set of environmental or genetic factors regulate these traits.

OBJECTIVE

Estimate the environmental and genetic correlations between self-reported and clinical asthma traits.

METHODS

A total of 3,073 subjects from 802 families were ascertained through a twin proband. Traits measured included self-reported asthma, airway histamine responsiveness (AHR), skin prick response to common allergens including house dust mite (Dermatophagoides pteronyssinus [D. pter]), baseline lung function, total serum immunoglobulin E (IgE) and eosinophilia. Bivariate and multivariate analyses of eight traits were performed with adjustment for ascertainment and significant covariates.

RESULTS

Overall 2,716 participants completed an asthma questionnaire and 2,087 were clinically tested, including 1,289 self-reported asthmatics (92% previously diagnosed by a doctor). Asthma, AHR, markers of allergic sensitization and eosinophilia had significant environmental correlations with each other (range: 0.23-0.89). Baseline forced expiratory volume in 1 s (FEV(1)) showed low environmental correlations with most traits. Fewer genetic correlations were significantly different from zero. Phenotypes with greatest genetic similarity were asthma and atopy (0.46), IgE and eosinophilia (0.44), AHR and D. pter (0.43) and AHR and airway obstruction (-0.43). Traits with greatest genetic dissimilarity were FEV(1) and atopy (0.05), airway obstruction and IgE (0.07) and FEV(1) and D. pter (0.11).

CONCLUSION

These results suggest that the same set of environmental factors regulates the variation of many asthma traits. In addition, although most traits are regulated to great extent by specific genetic factors, there is still some degree of genetic overlap that could be exploited by multivariate linkage approaches.

Gender differences in associations of eating pathology between mothers and their adolescent offspring

OBJECTIVE

To study the association of eating pathology between mothers and their adolescent offspring in a population sample.

RESEARCH METHODS AND PROCEDURES

The participants were 481 women (mean age, 47+/-SD 5 years; BMI, 25+/-4 kg/m2) and their 481 adolescent children 16 to 17 years old (BMI, 21+/-3 kg/m2) of the Stockholm Weight Development Study. Assessment methods were the Three-Factor Eating Questionnaire Revised 18 and the Eating Disorder Inventory 2.

RESULTS

A higher body weight was most related to cognitive restraint for adolescents and to emotional eating for adult women. A mother-daughter link could be identified for eating pathology, with the strongest link found for emotional eating. No mother-son link could be identified. Age subgroup analyses revealed a stronger mother-daughter link for body attitudes in younger mothers and for cognitive restraint in older mothers.

DISCUSSION

Gender differences revealed that eating pathology was shared by mothers and daughters but not by mothers and sons. A psychological strategy such as eating as a response to negative emotions was most interrelated between mothers and daughters. Younger mothers shared more attitudes toward the body with their daughters, whereas older mothers shared more restrictive eating behaviors with their daughters. The mother-daughter links found may be due to gender-specific genetic and psychological family transmission and gender-specific environmental influences. The sons' eating behaviors seem to be more independent and would be formed by other factors than for the girls.

Genes and/or Jeans?

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

Genetics in eating disorders: state of the science

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

Genetic analysis of bulimia nervosa: methods and sample description

OBJECTIVE

Twin and family studies suggest that genetic variants contribute to the pathogenesis of bulimia nervosa (BN) and anorexia nervosa (AN). The Price Foundation has supported an international, multisite study of families with these disorders to identify these genetic variations. The current study presents the clinical characteristics of this sample as well as a description of the study methodology.

METHOD

All probands met modified criteria for BN or bulimia nervosa with a history of AN (BAN) as defined in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; American Psychiatric Association, 1994). All affected relatives met DSM-IV criteria for BN, AN, BAN, or eating disorders not otherwise specified (EDNOS). Probands and affected relatives were assessed diagnostically using both trained-rater and self-report assessments. DNA samples were collected from probands, affected relatives, and available biologic parents.

RESULTS

Assessments were obtained from 163 BN probands and 165 BAN probands. Overall, there were 365 relative pairs available for linkage analysis. Of the affected relatives of BN probands, 62 were diagnosed as BN (34.8%), 49 as BAN (27.5%), 35 as AN (19.7%), and 32 as EDNOS (18.0%). For the relatives of BAN probands, 42 were diagnosed as BN (22.5%), 67 as BAN (35.8%), 48 as AN (25.7%), and 30 as EDNOS (16.0%).

DISCUSSION

This study represents the largest genetic study of eating disorders to date. Clinical data indicate that although there are a large number of individuals with BN disorders, a range of eating pathology is represented in the sample, allowing for the examination of several different phenotypes in molecular genetic analyses.

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.

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.

Eating disorders: relations with inconsistent discipline, anxiety, and drinking among college women

Since as many as 20% of all college women report symptoms of eating disorders, the present study examined the relationship between self-reported eating disorder symptoms. anxiety, drinking, and retrospective reports of inconsistent parenting during childhood. 101 college women, 85% Euro-Americans of mean age 19 yr., completed an anonymous survey including questions from the Eating Disorder Index-1, the Retrospective Family Unpredictability Scale, the Trait Anxiety Scale, and measures of drinking in the previous month. Eating disorder symptoms correlated with self-reported drinking quantity, anxiety, and retrospective ratings of inconsistent discipline. This appears to be the first time eating disorder symptoms have been associated with inconsistent discipline. Implications for etiology and treatment of eating disorders are discussed.

Does environment matter? A review of nonshared environment and eating disorders

OBJECTIVE

Nonshared environmental influences are experiences that are unique to siblings reared in the same family. We review studies highlighting the importance of nonshared factors for the development of eating disorders and suggest areas for future research.

METHODS

Findings from behavioral genetic studies of eating disorders as well as methodological issues are reviewed.

RESULTS

Twin studies suggest that approximately 17%-46% of the variance in both anorexia nervosa (AN) and bulimia nervosa (BN) can be accounted for by nonshared environmental factors. Studies directly examining these influences are scarce, although initial data indicate that differential paternal relationships, body weight teasing, peer group experiences, and life events may account for the development of eating pathology in one sibling versus another.

DISCUSSION

Additional research is needed to identify specific nonshared environmental influences on eating disorders such as differential parental and sibling treatment, disparate peer group characteristics, and differential experience of life events such as physical and sexual abuse.

The children of mothers with eating disorders

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

The evolving genetic foundations of eating disorders

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