Karen S. Mitchell

Eating disorder symptomatology and substance use disorders: prevalence and shared risk in a population based twin sample.

Objective: Research shows a significant association between eating disorders (ED) and substance use disorders (SUD). The objective of this study is to examine the prevalence, chronology, and possibility of shared familial risk between SUD and ED symptomatology. Method: Subjects included 1,206 monozygotic and 877 dizygotic adult female twins. ED symptomatology included anorexia (AN) and bulimia nervosa (BN) diagnosis, symptoms associated with diagnostic criteria, and BN symptom count. SUD included alcohol, illicit drug, and caffeine abuse/dependence. Generalized estimated equation modeling was used to examine phenotypic associations, and Choleksy decompositions were used to delineate the contribution of genes and environment to comorbidity. Results: There were no significant differences between SUD prevalence in women with AN and BN. Women with BN reported BN preceded SUD development while the reverse was true for AN. Twin analyses showed possible familial overlap between BN symptomatology and all SUD examined. Discussion: Results suggest an important difference in the chronology of EDs and SUDs. Women with BN may be turning to substances to dampen bulimic urges. Women with AN may be engaging in substance use initially in an effort to lose weight. Results also suggest familial factors contribute to the comorbidity between BN and SUD.

Assessing the heritability of anorexia nervosa symptoms using a marginal maximal likelihood approach.

BACKGROUNDnAssessment of eating disorders at the symptom level can facilitate the refinement of phenotypes. We examined genetic and environmental contributions to liability to anorexia nervosa (AN) symptoms in a population-based twin sample using a genetic common pathway model.nnnMETHODnParticipants were from the Norwegian Institute of Public Health Twin Panel (NIPHTP) and included all female monozygotic (MZ; 448 complete pairs and four singletons) and dizygotic (DZ; 263 complete pairs and four singletons) twins who completed the Composite International Diagnostic Interview (CIDI) assessing DSM-IV Axis I and ICD-10 criteria. Responses to items assessing AN symptoms were included in a model fitted using the marginal maximum likelihood (MML) approach.nnnRESULTSnHeritability of the overall AN diagnosis was moderate [a2=0.22, 95% confidence interval (CI) 0.0-0.50] whereas heritabilities of the specific items varied. Heritability estimates for weight loss items were moderate (a2=0.31-0.34) and items assessing weight concern when at a low weight were smaller (0.18-0.29). Additive genetic factors contributed little to the variance of amenorrhea, which was most strongly influenced by unshared environment (a2=0.16, e2=0.71).nnnCONCLUSIONSnAN symptoms are differentially heritable. Specific criteria such as those related to body weight and weight loss history represent more biologically driven potential endophenotypes or liability indices. The results regarding weight concern differ somewhat from those of previous studies, highlighting the importance of assessing genetic and environmental influences on variance of traits within specific subgroups of interest.

Binge eating disorder: a symptom-level investigation of genetic and environmental influences on liability.

BACKGROUNDnRecent behavioral genetic studies have emphasized the importance of investigating eating disorders at the level of individual symptoms, rather than as overall diagnoses. We examined the heritability of binge eating disorder (BED) using an item-factor analytic approach, which estimates contributions of additive genetic (A), common environmental (C), and unique environmental (E) influences on liability to BED as well as individual symptoms.nnnMETHODnParticipants were 614 monozygotic and 410 dizygotic same-sex female twins from the Mid-Atlantic Twin Registry who completed a self-report measure of BED symptoms based upon DSM-IV criteria. Genetic and environmental contributions to BED liability were assessed at the diagnostic and symptom levels, using an item-factor approach.nnnRESULTSnLiability to BED was moderately heritable; 45% of the variance was due to A, with smaller proportions due to C (13%), and E (42%). Additive genetic effects accounted for 29-43% of the variance in individual items, while only 8-14% was due to C.nnnCONCLUSIONSnResults highlight the relevance of examining eating disorders at the symptom level, rather than focusing on aggregate diagnoses.

Evaluation of a Structural Model of Objectification Theory and Eating Disorder Symptomatology among European American and African American Undergraduate Women

This study evaluated a structural equation model of objectification theory among European American (EA; n = 408) and African American women (AA; n = 233). Modeling results indicated a particularly strong association between thin-ideal internalization/body monitoring and eating disorder symptoms, with weaker relationships among body dissatisfaction, depression, anxiety, and eating disorder symptoms. The measurement model was not equivalent for EAs and AAs; however, the structural model was invariant, suggesting that the relationships among these variables may be similar for both groups. Thus, objectification theory does appear to be applicable to AA women, although specification of relevant constructs and refinement of assessment instruments is warranted.

A twin study of specific bulimia nervosa symptoms

BACKGROUNDnTwin studies have suggested that additive genetic factors significantly contribute to liability to bulimia nervosa (BN). However, the diagnostic criteria for BN remain controversial. In this study, an item-factor model was used to examine the BN diagnostic criteria and the genetic and environmental contributions to BN in a population-based twin sample. The validity of the equal environment assumption (EEA) for BN was also tested.nnnMETHODnParticipants were 1024 female twins (MZ n=614, DZ n=410) from the population-based Mid-Atlantic Twin Registry. BN was assessed using symptom-level (self-report) items consistent with DSM-IV and ICD-10 diagnostic criteria. Items assessing BN were included in an item-factor model. The EEA was measured by items assessing similarity of childhood and adolescent environment, which have demonstrated construct validity. Scores on the EEA factor were used to specify the degree to which twins shared environmental experiences in this model.nnnRESULTSnThe EEA was not violated for BN. Modeling results indicated that the majority of the variance in BN was due to additive genetic factors. There was substantial variability in additive genetic and environmental contributions to specific BN symptoms. Most notably, vomiting was very strongly influenced by additive genetic factors, while other symptoms were much less heritable, including the influence of weight on self-evaluation. These results highlight the importance of assessing eating disorders at the symptom level.nnnCONCLUSIONSnRefinement of eating disorder phenotypes could ultimately lead to improvements in treatment and targeted prevention, by clarifying sources of variation for specific components of symptomatology.

ANXIETY, ALEXITHYMIA, AND DEPRESSION AS MEDIATORS OF THE ASSOCIATION BETWEEN CHILDHOOD ABUSE AND EATING DISORDERED BEHAVIOR IN AFRICAN AMERICAN AND EUROPEAN AMERICAN WOMEN

This study evaluated structural equation models of the associations among family functioning, childhood abuse, depression, anxiety, alexithymia, and eating disorder symptomatology in a sample of 412 European American and 192 African American female undergraduates. Additionally, the specific roles of anxiety, depression, and alexithymia as mediators were assessed. Each of these variables was a significant mediator of the association between childhood abuse and disordered eating. Finally, a test of invariance between the African American and European American subsamples was significant, highlighting the need for additional cross-cultural eating disorder research.

Rural adolescent attitudes toward smoking and weight loss : Relationship to smoking status

Perceptions that smoking contributes to weight loss are widespread among youth. We examined the association between weight loss and smoking to determine whether supportive attitudes were associated with smoking status and whether this is a particular problem in rural areas. High school students (N=730) completed a survey assessing smoking-related characteristics and behaviors. Attitudes assessed included perceptions of whether weight concerns were the reasons others smoke and personal beliefs about tobaccos effect on weight gain. Smoking status was categorized as never (44%), experimental (42%), and current (14%). Multinomial logistic regressions investigated relationships between attitudes and smoking, adjusting for weight goals, gender, ethnicity, parent/peer smoking, and body mass index. Both attitudinal measures were associated with smoking (p< .05). Nonsmokers and experimental smokers were more likely than current smokers to believe that people smoke to lose weight. Although current smokers were less likely to report that others smoke for weight control, they believed they would gain weight if they quit. Conversely, nonsmokers and experimental smokers were less likely to believe they would gain weight if they do not smoke compared with current smokers. Thus personal attitudes differ from attitudes toward others with respect to weight loss and smoking. Moreover, endorsement of these attitudes can reliably distinguish current versus experimental smokers and may help better clarify the transition to current smoker. Because weight concerns are a significant factor in youth smoking, these issues should be included in intervention efforts, particularly in rural communities where smoking rates are higher and age at initiation is earlier.

An Investigation of a Measure of Twins’ Equal Environments

The equal environments assumption, which holds that trait-relevant environments are equally correlated among monozygotic (MZ) and dizygotic (DZ) twin pairs, is essential to twin designs. Violations of this assumption could lead to biased parameter estimates in twin models. A variety of methods and measures have been used to test this assumption. No studies to date have evaluated the measurement invariance of such items or examined the distribution of the underlying equal environments trait. The current study was an investigation of the psychometric properties of a self-report measure of twins equal environments. Exploratory and confirmatory factor analysis results indicated that items loaded onto child and teen equal environments factors. Factor loadings and factor variances and their covariance were invariant for MZ and DZ twins; however, DZ twins had significantly lower factor means than MZ twins. Further, these items demonstrated adequate test-retest reliability. Lastly, the child and teen factors may be bimodally distributed, particularly for MZ twin pairs. Measurement invariance issues, as well as distributions of equal environments traits, should be considered when evaluating the equal environments assumption, in order to produce accurate parameter estimates in twin models.

An Investigation of Weight Suppression in a Population-Based Sample of Female Twins

OBJECTIVEnWeight suppression (WS), maintaining a body weight below ones maximum adult weight, is associated with bingeing, purging, and weight gain in clinical samples.nnnMETHODnWe investigated associations between eating disorder-related variables and WS and additive genetic (A), common (C), and unique (E) environmental contributions to WS in a population-based sample of 1,503 female adult twins.nnnRESULTSnModeling results were similar for participants reporting no binge eating (NBE) and those reporting binge eating plus loss of control (BE + LOC): 20-25% of the variance in WS was due to A and 70-75% due to E. Among NBE participants, restraint, drive for thinness, body dissatisfaction, and dieting during child/adulthood were related to WS. Restraint, disinhibition, and dieting during childhood were significantly associated with WS in the BE + LOC subsample.nnnDISCUSSIONnAlthough maintaining lower body weight could be advantageous, interventionists should take care when addressing weight suppression in individuals vulnerable to eating disorder symptomatology.

Characteristics of Monozygotic Male and Female Twins Discordant for Overweight: A Descriptive Study

OBJECTIVESnBMI is highly heritable. Yet, trends in obesity highlight environmental influences on body weight. Monozygotic (MZ) twins discordant for overweight offer a unique opportunity to examine these factors.nnnMETHODSnMZ male (n=8 pairs) and female twins (n=10 pairs) discordant for overweight (defined as the BMI of one twin being at least 24.5, and the BMI of his/her co-twin being below 24.5 and at least three points lower) were identified from the Mid-Atlantic Twin Registry. Variables were assessed via self-report questionnaires.nnnRESULTSnOne overweight and two non-overweight females met criteria for bulimia nervosa. Rates of dieting and binge eating were high among all males and females. Hunger scores were higher among non-overweight females; disinhibition scores were higher among overweight males. Only one non-overweight and three overweight males smoked; 90% of non-overweight and 40% of overweight females smoked.nnnCONCLUSIONSnAssessing tobacco use and eating disorders may be important when sampling on the basis of family members who are discordant for BMI. Finally, results suggest possibilities for interventions in individuals at-risk for overweight.