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1.  The Emergence of Sex Differences in Risk for Disordered Eating Attitudes During Puberty: A Role for Prenatal Testosterone Exposure 
Journal of abnormal psychology  2013;122(2):420-432.
Research suggests that prenatal testosterone exposure may masculinize (i.e., lower) disordered eating (DE) attitudes and behaviors and influence the lower prevalence of eating disorders in males versus females. How or when these effects become prominent remains unknown, although puberty may be a critical developmental period. In animals, the masculinizing effects of early testosterone exposure become expressed during puberty when gonadal hormones activate sex-typical behaviors, including eating behaviors. This study examined whether the masculinizing effects of prenatal testosterone exposure on DE attitudes emerge during puberty in 394 twins from opposite-sex and same-sex pairs. Twin type (opposite sex vs. same sex) was used as a proxy for level of prenatal testosterone exposure because females from opposite-sex twin pairs are thought to be exposed to testosterone in utero from their male co-twin. Consistent with animal data, there were no differences in levels of DE attitudes between opposite-sex and same-sex twins during pre-early puberty. However, during mid-late puberty, females from opposite-sex twin pairs (i.e., females with a male co-twin) exhibited more masculinized (i.e., lower) DE attitudes than females from same-sex twin pairs (i.e., females with a female co-twin), independent of several “third variables” (e.g., body mass index [BMI], anxiety). Findings suggest that prenatal testosterone exposure may decrease DE attitudes and at least partially underlie sex differences in risk for DE attitudes after mid-puberty.
PMCID: PMC4011635  PMID: 23713501
disordered eating; eating disorder; puberty; sex difference; testosterone
2.  Advanced Paternal Age at Birth: Phenotypic and Etiologic Associations with Eating Pathology in Offspring 
Psychological medicine  2014;44(5):1029-1041.
Advanced paternal age at birth has been linked to several psychiatric disorders in offspring (e.g., schizophrenia), and genetic mechanisms are thought to underlie these associations. This study is the first to investigate whether advanced paternal age at birth is associated with eating disorder risk using a twin study design capable of examining both phenotypic and genetic associations.
In a large, population-based sample of female twins ages 8–17 years in mid-puberty or beyond (N = 1,722), we investigated whether advanced paternal age was positively associated with disordered eating symptoms and an eating disorder history (i.e., anorexia nervosa, bulimia nervosa, or binge eating disorder) in offspring. Biometric twin models examined whether genetic and/or environmental factors underlie paternal age effects for disordered eating symptoms.
Advanced paternal age was positively associated with disordered eating symptoms and an eating disorder history, where the highest level of pathology was observed in offspring born to fathers ≥ 40 years old. Results were not accounted for by maternal age at birth, body mass index, socioeconomic status, fertility treatment, or parental psychiatric history. Twin models indicated decreased genetic, and increased environmental, effects on disordered eating with advanced paternal age.
Advanced paternal age increased risk for the full spectrum of eating pathology, independent of several important covariates. However, contrary to leading hypotheses, environmental rather than genetic factors accounted for paternal age-disordered eating associations. These data highlight the need to explore novel (potentially environmental) mechanisms underlying the effects of advanced paternal age on offspring eating disorder risk.
PMCID: PMC3835756  PMID: 23795717
advanced paternal age; eating disorders; disordered eating; genetic; environmental; twin study
3.  Puberty as a Critical Risk Period for Eating Disorders: A Review of Human and Animal Studies 
Hormones and behavior  2013;64(2):399-410.
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.
PMCID: PMC3761220  PMID: 23998681
puberty; eating disorders; anorexia nervosa; bulimia nervosa; ovarian hormones; estrogen; twin studies
4.  Exploring the Relationship between Negative Urgency and Dysregulated Eating: Etiologic Associations and the Role of Negative Affect 
Journal of abnormal psychology  2013;122(2):433-444.
Negative urgency (i.e., the tendency to engage in rash action in response to negative affect) has emerged as a critical personality trait contributing to individual differences in binge eating. However, studies investigating the extent to which genetic and/or environmental influences underlie the effects of negative urgency on binge eating are lacking. Moreover, it remains unclear whether negative urgency-binge eating associations are simply due to the well-established role of negative affect in the development/maintenance of binge eating. The current study addresses these gaps by examining phenotypic and etiologic associations between negative urgency, negative affect, and dysregulated eating (i.e., binge eating, emotional eating) in a sample of 222 same-sex female twin pairs from the Michigan State Twin Registry. Negative urgency was significantly associated with both dysregulated eating symptoms, even after controlling for the effects of negative affect. Genetic factors accounted for the majority (62–77%) of this phenotypic association, although a significant proportion of this genetic covariation was due to genetic influences in common with negative affect. Non-shared environmental factors accounted for a relatively smaller (23–38%) proportion of the association, but these non-shared environmental effects were independent of negative affect. Findings suggest that the presence of emotion-based rash action, combined with high levels of negative affect, may significantly increase genetic risk for dysregulated eating.
PMCID: PMC3759363  PMID: 23356217
binge eating; emotional eating; impulsivity; negative urgency; negative affect; twin study
5.  Ovarian Hormones and Emotional Eating Associations across the Menstrual Cycle: An Examination of the Potential Moderating Effects of Body Mass Index and Dietary Restraint 
Associations between within-person changes in ovarian hormones and dysregulated eating (binge eating, emotional eating) have been observed across the menstrual cycle. However, studies have not examined moderators that may contribute to differential associations between individuals. We investigated body-weight regulation variables (body mass index (BMI), dietary restraint) that have theoretical relevance by virtue of their associations with both phenotypes.
Women (N = 196) provided emotional eating ratings and saliva samples for 45 days. BMI and restraint were assessed at three time-points and averaged.
Results showed significant estradiol × progesterone interactions in the prediction of within-subject changes in emotional eating. Neither BMI nor restraint moderated these relationships, although a trend-level dietary restraint × estradiol interaction was observed where estradiol’s effects were enhanced in high restraint scorers.
Findings confirm a role for hormones in changes in emotional eating and suggest that restraint might enhance hormone effects in severe groups.
PMCID: PMC3600109  PMID: 23315657
6.  Individual Differences in the Relationship between Ovarian Hormones and Emotional Eating Across the Menstrual Cycle: A Role for Personality? 
Eating behaviors  2013;14(2):161-166.
Within-person changes in estradiol and progesterone predict changes in binge eating tendencies across the menstrual cycle. However, all women have menstrual-cycle fluctuations in hormones, but few experience binge eating. Personality traits may be critical individual difference factors that influence who will engage in emotional eating in the presence of a vulnerable hormonal environment. Women (N=239) provided self-reports of emotional eating and saliva samples for hormone measurement for 45 consecutive days. Negative urgency and negative emotionality were measured once and were examined as moderators of hormone-emotional eating associations. Consistent with prior research, within-person changes in the interaction between estradiol and progesterone predicted emotional eating. Neither negative urgency nor negative emotionality interacted with changes in estradiol and progesterone to predict changes in emotional eating. Additional factors, other than the two personality traits examined, may account for individual differences in within-person associations between hormones and emotional eating.
PMCID: PMC3618657  PMID: 23557813
ovarian hormones; personality; negative urgency; eating disorders; emotional eating
7.  The Interactive Effects of Estrogen and Progesterone on Changes in Emotional Eating Across the Menstrual Cycle 
Journal of abnormal psychology  2012;122(1):131-137.
Studies suggest that within-person changes in estrogen and progesterone predict changes in binge eating across the menstrual cycle. However, samples have been extremely small (maximum N = 9), and analyses have not examined the interactive effects of hormones that are critical for changes in food intake in animals. The aims of the current study were to examine ovarian hormone interactions in the prediction of within-subject changes in emotional eating in the largest sample of women to date (N = 196). Participants provided daily ratings of emotional eating and saliva samples for hormone measurement for 45 consecutive days. Results confirmed that changes in ovarian hormones predict changes in emotional eating across the menstrual cycle, with a significant estradiol x progesterone interaction. Emotional eating scores were highest during the mid-luteal phase, when progesterone peaks and estradiol demonstrates a secondary peak. Findings extend previous work by highlighting significant interactions between estrogen and progesterone that explain mid-luteal increases in emotional eating. Future work should explore mechanisms (e.g., gene-hormone interactions) that contribute to both within- and between-subject differences in emotional eating.
PMCID: PMC3570621  PMID: 22889242
8.  Genetic and Environmental Influences on Thin-Ideal Internalization 
Current research on the etiology of thin-ideal internalization focuses on psychosocial influences (e.g., media exposure). The possibility that genetic influences also account for variance in thin-ideal internalization has never been directly examined. This study used a twin design to estimate genetic effects on thin-ideal internalization and examine if environmental influences are primarily shared or nonshared in origin.
Participants were 343 post-pubertal female twins (ages 12–22; M=17.61) from the Michigan State University Twin Registry. Thin-ideal internalization was assessed using the Sociocultural Attitudes toward Appearance Questionniare-3.
Twin modeling suggested significant additive genetic and nonshared environmental influences on thin-ideal internalization. Shared environmental influences were small and non-significant.
Although prior research focused on psychosocial factors, genetic influences on thin-ideal internalization were significant and moderate in magnitude. Research is needed to investigate possible interplay between genetic and nonshared environmental factors in the development of thin-ideal internalization.
PMCID: PMC3523121  PMID: 23034902
Thin-ideal; internalization; body image; disordered eating; twin study; heritability; Tripartite Model
9.  The Effects of Puberty on Genetic Risk for Disordered Eating: Evidence for a Sex Difference 
Psychological medicine  2011;42(3):627-637.
Differences in genetic influences on disordered eating are present across puberty in girls. Heritability is 0% before puberty, but over 50% during and after puberty. Emerging data suggest that these developmental differences may be due to pubertal increases in ovarian hormones. However, a critical piece of evidence is lacking, namely, knowledge of genetic influences on disordered eating across puberty in boys. Boys do not experience increases in ovarian hormones during puberty. Thus, if pubertal increases in genetic effects are present in boys, then factors in addition to ovarian hormones may drive increases in heritability in girls. The current study was the first to examine this possibility in a sample of 1,006 male and female twins from the Michigan State University Twin Registry.
Disordered eating was assessed with the Minnesota Eating Behaviors Survey. Pubertal development was assessed with the Pubertal Development Scale.
No significant differences in genetic influences on disordered eating were observed in males across any developmental stage. Heritability was 51% in boys during pre-puberty, puberty, and young adulthood. By contrast, in girls, genetic factors accounted for 0% of the variance in pre-puberty, but 51% of the variance during puberty and beyond. Sex differences in genetic effects were only significant during pre-puberty, as the best-fitting models constrained heritability to be equal across all males, pubertal females, and young adult females.
Results highlight sex-specific effects of puberty on genetic risk for disordered eating and provide indirect evidence of a role for ovarian hormones and/or other female-specific factors.
PMCID: PMC3697115  PMID: 21854699
eating disorders; males; genetic; twins; puberty; sex differences
10.  Binge Eating Proneness Emerges during Puberty in Female Rats: A Longitudinal Study 
Journal of abnormal psychology  2011;120(4):948-955.
Puberty is a critical risk period for binge eating and eating disorders characterized by binge eating. Previous research focused almost entirely on psychosocial risk factors during puberty to the relative exclusion of biological influences. The current study addressed this gap by examining the emergence of binge eating during puberty in a rat model. We predicted that there would be minimal differences in binge eating proneness during pre-early puberty, but significant differences would emerge during puberty. Two independent samples of female Sprague-Dawley rats (n = 30 and n = 36) were followed longitudinally across pre-early puberty, mid-late puberty, and adulthood. Binge eating proneness was defined using the binge eating resistant (BER)/binge eating prone (BEP) model of binge eating that identifies BER and BEP rats in adulthood. Across two samples of rats, binge eating proneness emerged during puberty. Mixed linear models showed little difference in palatable food intake between BER and BEP rats during pre-early puberty, but significant group differences emerged during mid-late puberty and adulthood. Group differences could not be accounted for by changes in non-palatable food intake or body weight. Similar to patterns in humans, individual differences in binge eating emerge during puberty in female rats. Findings provide strong confirming evidence for the importance of biological risk factors in developmental trajectories of binge eating risk across adolescence.
PMCID: PMC3697134  PMID: 21574664
binge eating; puberty; animal models; bulimia nervosa; eating disorders
11.  Differential Associations between Ovarian Hormones and Disordered Eating Symptoms across the Menstrual Cycle in Women 
We examined changes in drive for thinness, body dissatisfaction, and dietary restraint across the menstrual cycle and associations between these symptoms and ovarian hormones in two independent samples of women (N = 10 and 8 women, respectively) drawn from the community.
Daily self-report measures of disordered eating and negative affect were completed for 35–65 days. Daily saliva samples were assayed for estradiol and progesterone in Study 2 only.
Levels of body dissatisfaction and drive for thinness were highest during the mid-luteal/pre-menstrual phases in both studies and were negatively associated with estradiol, and positively associated with progesterone. By contrast, dietary restraint showed less variation across the menstrual cycle and weaker associations with ovarian hormones.
Differential associations between ovarian hormones and specific disordered eating symptoms point to distinct etiological processes within the broader construct of disordered eating.
PMCID: PMC3170673  PMID: 21656540
estradiol; progesterone; ovarian hormones; menstrual cycle; eating disorders; disordered eating; drive for thinness; body dissatisfaction; dietary restraint
12.  The Role of Leptin, Melanocortin, and Neurotrophin System Genes on Body Weight in Anorexia Nervosa and Bulimia Nervosa 
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.
Our sample consisted of 745 individuals with AN without a history of BN, 245 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.
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).
To our knowledge, this is the first study to address the issue of clinical heterogeneity in eating disorder genetics 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.
PMCID: PMC4191922  PMID: 24831852
anorexia nervosa; bulimia nervosa; candidate gene association; body weight; melanocortins; neurotrophins
14.  The Quality of the Inter-parental Relationship Does Not Moderate the Etiology of Child Conduct Problems 
Psychological medicine  2014;45(2):319-332.
Although there is a clear phenotypic relationship between the quality of the inter-parental or marital relationship and child conduct problems (CP), the etiology of this association is as yet unclear. One possibility is that this association takes the form of a genotype-environment interaction (GxE), whereby the quality of the inter-parental relationship acts to moderate the etiology of child CP. The current study sought to evaluate this possibility.
We examined multiple measures and informant-reports of the quality of the inter-parental relationship in a sample of more than 700 child twin families from the Michigan State University Twin Registry (MSUTR). Analyses consisted of a series of latent GxE models.
The ‘no moderation’ model provided the best fit to the data in nearly all cases, findings that collectively provide strong evidence against the possibility that the etiology of CP is moderated by the quality of the interparental relationship.
Such findings suggest that, contrary to implicit (and sometimes explicit) assumptions in the field, it is not the case that every environmental risk (or protective) factor exacerbates (or suppresses) genetic influences on CP. Future research should seek to delineate the specific environmental experiences that do serve as etiologic moderators of CP, and to clarify how this gene-environment interplay might change over the course of development.
PMCID: PMC4461551  PMID: 25066424
antisocial behavior; conduct problems; marital relationship; GxE
15.  A Constructive Replication of the Association between the Oxytocin Receptor Genotype and Parenting 
Behavioral genetic studies have robustly indicated that parenting behaviors are heritable – that is, individual differences in parenting are at least partially a function of genetic differences between persons. Few studies, however, have sought to identify the specific genetic variants that are associated with individual differences in parenting. Genes that influence the oxytocin system are of particular interest, given the growing body of evidence that points to the role of oxytocin for social behaviors, including parenting. The current study conducted examinations of associations between a variant in the oxytocin receptor gene (OXTR rs53576) and parental warmth, control, and negativity in a sample of 1,000 twin children and their parents (N=500 families) from the Michigan State University Twin Registry to constructively replicate and extend prior work (Bakermans-Kranenburg & van IJzendoorn, 2008; Michalska et al., 2014). Analyses were conducted both at the level of the child and the level of the parent, allowing us to examine both child-driven (via evocative gene-environment correlation) and parent-driven genetic effects on parenting. Mothers’ OXTR genotype predicted her warmth towards her children, even after controlling for child genotype. This association was not found for fathers. These findings add to the growing body of evidence linking oxytocin functioning to parental behavior and also highlight potential etiological differences in parenting across mothers and fathers.
PMCID: PMC4461003  PMID: 25419912
parenting; genetic; evocative rGE; oxytocin; OXTR
16.  The Effects of Ovariectomy on Binge Eating Proneness in Adult Female Rats 
Hormones and behavior  2011;59(4):585-593.
Ovarian hormones are associated with binge eating in women, however findings are limited by the lack of experimental control inherent in human studies. Animal research that manipulates ovarian hormone status and examines individual differences in extreme binge eating proneness are needed to model clinical phenotypes in humans and to confirm causal effects. The purpose of this study was to examine the effects of adult ovariectomy on overall binge eating risk and extreme binge eating phenotypes using the binge eating resistant (BER)/ binge eating prone (BEP) rat model. We predicted that palatable food consumption would significantly increase after ovariectomy in all rats because ovarian hormones generally suppress food intake. If differences in responsiveness to ovarian hormones underlie BER/BEP phenotypes, then differences in binge eating between BER and BEP rats would be eliminated or diminished after ovariectomy. Changes in palatable food (PF) intake were compared in BER and BEP rats before and after ovariectomy in two samples of adult females. Findings were highly similar in the two samples. PF intake increased significantly following ovariectomy in all rats. However, BEP rats consistently consumed larger amounts of PF than BER rats, both before and after ovariectomy. The consistency of findings across two samples of rats provides strong support for activational effects of ovarian hormones on binge eating. However, the immunity of extreme binge eating phenotypes to ovarian hormone ablation suggests that other, earlier mechanisms (e.g., organizational hormone effects or hormone-independent effects) determine the expression of binge eating phenotypes.
PMCID: PMC3085940  PMID: 21376721
binge eating; bulimia nervosa; ovariectomy; animal models; ovarian hormones
17.  Parental Divorce and Disordered Eating: An Investigation of a Gene-Environment Interaction 
We investigated gene-environment interactions (G×E) for associations between parental divorce and disordered eating (DE).
Participants were 1,810 female twins from the Michigan State University Twin Registry and the Minnesota Twin Family Study. The Minnesota Eating Behaviors Survey was used to assess DE. We tested for G×E by comparing the heritability of DE in twins from divorced versus intact families. It was hypothesized that divorce would moderate the heritability of DE, in that heritability would be higher in twins from divorced than twins from intact families.
As expected, the heritability of body dissatisfaction was significantly higher in twins from divorced than intact families. However, genetic influences were equal in twins from divorced and intact families for all other forms of DE.
Although divorce did not moderate heritability of most DE symptoms, future research should replicate G×Es for body dissatisfaction and identify factors underlying this unique relationship.
PMCID: PMC3058816  PMID: 21312202
Disordered Eating; Parental Divorce; Gene-Environment Interaction; Eating Disorders; Twins
18.  Dietary Restraint Moderates Genetic Risk for Binge Eating 
Journal of abnormal psychology  2011;120(1):119-128.
Dietary restraint is a prospective risk factor for the development of binge eating and bulimia nervosa. Although many women engage in dietary restraint, relatively few develop binge eating. Dietary restraint may only increase susceptibility for binge eating in individuals who are at genetic risk. Specifically, dietary restraint may be a behavioral “exposure” factor that activates genetic predispositions for binge eating. We investigated this possibility in 1,678 young adolescent and adult same-sex female twins from the Minnesota Twin Family Study and the Michigan State University Twin Registry. Twin moderation models were used to examine whether levels of dietary restraint moderate genetic and environmental influences on binge eating. Results indicated that genetic and non-shared environmental factors for binge eating increased at higher levels of dietary restraint. Importantly, these effects were present after controlling for age, body mass index, and genetic and environmental overlap among dietary restraint and binge eating. Results suggest that dietary restraint may be most important for individuals at genetic risk for binge eating, and the combination of these factors could enhance individual differences in risk for binge eating.
PMCID: PMC3057961  PMID: 21171725
binge eating; dietary restraint; gene-environment interactions; twins
19.  Behavior Genetics and the Within-Person Variability of Daily Interpersonal Styles: The Heritability of Flux, Spin and Pulse 
A classical twin study was used to estimate the magnitude of genetic and environmental influences on four measurements of within-person variability: dominance flux, warmth flux, spin and pulse. Flux refers to the variability of an individual’s interpersonal dominance and warmth. Spin measures changes in the tone of interpersonal styles and pulse measures changes in the intensity of interpersonal styles. Daily reports of interpersonal styles were collected from 494 same-sex female twins (142 monozygotic pairs and 105 dizygotic pairs) over 45 days. For dominance flux, warmth flux, and spin, genetic effects accounted for a larger proportion of variance (37%, 24%, and 30%, respectively) than shared environmental effects (14%, 13%, 0%, respectively), with the remaining variance due to the non-shared environment (62%, 50%, 70% respectively). Pulse appeared to be primarily influenced by the non-shared environment, although conclusions about the contribution of familial influences were difficult to draw from this study.
PMCID: PMC4428904  PMID: 25977748
20.  Preliminary Evidence that Estradiol Moderates Genetic Influences on Disordered Eating Attitudes and Behaviors During Puberty 
Psychological medicine  2010;40(10):1745-1753.
Puberty moderates genetic influences on disordered eating attitudes and behaviors, with little genetic influence before puberty but large (≥ 50%) genetic effects during and after puberty. To date, however, nothing is known about the mechanisms that underlie these effects. Estradiol is a particularly promising candidate, as estrogens become elevated at puberty and regulate gene transcription within neurotransmitter systems important for eating-related phenotypes. The aim of this pilot study was to examine whether estradiol levels moderate genetic influences on disordered eating during puberty.
Participants included 198 female twins (ages 10-15 years) from the Michigan State University Twin Registry. Disordered eating attitudes and behaviors were assessed with the total score, weight preoccupation, body dissatisfaction, and binge eating/compensatory behavior subscales of the Minnesota Eating Behavior Survey. Afternoon saliva samples were assayed for estradiol levels. Moderation of genetic effects was examined by comparing twin correlations in low versus high estradiol groups.
In the low estradiol group, monozygotic (MZ) and dizygotic (DZ) twin correlations for all MEBS scales were similar, suggesting little genetic influence. In the high estradiol group, the MZ twin correlation was more than double the DZ twin correlation, indicating the presence of genetic effects. Findings could not be accounted for by age, body mass index, or the physical changes of puberty.
Estradiol may be one important moderator of genetic effects on disordered eating during puberty. Larger twin studies are needed to replicate this pilot work and quantify the extent of genetic moderation.
PMCID: PMC2928391  PMID: 20059800
21.  A Longitudinal Investigation of the Relationship between Disordered Eating Attitudes and Behaviors and Parent-Child Conflict: A Monozygotic Twin Differences Design 
Journal of abnormal psychology  2010;119(2):293-299.
Few studies have examined nonshared environmental risk factors for disordered eating, and none have done so using a longitudinal design. The current project employed a longitudinal, monozygotic twin differences design to examine parent-child conflict as a nonshared environmental risk factor for disordered eating. Participants included 468 monozygotic female twins (234 pairs) from the Minnesota Twin Family Study, followed every three years from ages 11 to 17. Twin differences in disordered eating were assessed with the Total Score, Body Dissatisfaction, Weight Preoccupation and Binge Eating subscales of the Minnesota Eating Behavior Survey. Differences in parent-child conflict were assessed with the Parental Environment Questionnaire. Cross-lagged models were used to examine longitudinal associations among these variables, controlling for within-age associations. Only the longitudinal association between twin differences in disordered eating at age 14 and differences in parent-child conflict at age 17 was significant; twin differences in disordered eating predicted later differences in parent-child conflict rather than the reverse. Findings suggest differences in parent-child conflict between genetically identical twins may be a consequence of, rather than a risk factor for, differences in disordered eating.
PMCID: PMC2941761  PMID: 20455602
22.  A Further Validation of the Minnesota Borderline Personality Disorder Scale 
Personality disorders  2013;5(2):146-153.
Previous research indicates that Borderline Personality Disorder (BPD) is well conceptualized as a dimensional construct that can be represented using normal personality traits. A previous study successfully developed and validated a BPD measure embedded within a normal trait measure, the Minnesota Borderline Personality Disorder Scale (MBPD). The current study performed a further validation of the MBPD by examining its convergent validity, external correlates, and heritability in a sample of 429 female twins. The MBPD correlated strongly with the SCID-II screener for BPD and moderately with external correlates. Moreover, the MBPD and SCID-II screener exhibited very similar patterns of external correlations. Additionally, results indicated that the genetic and environmental influences on MBPD overlap with the genetic and environmental influences on the SCID-II screener, which suggests that these scales are measuring the same construct. This data provide further evidence for the construct validity of the MBPD.
PMCID: PMC4114388  PMID: 24364505
Borderline Personality Disorder; Normal Personality; Nomological Network; Behavioral Genetics
23.  The Possible Influence of Impulsivity and Dietary Restraint on Associations between Serotonin Genes and Binge Eating 
Journal of psychiatric research  2009;43(16):1278-1286.
Although serotonin (5-HT) genes are thought to be involved in the etiology of bulimia nervosa and binge eating, findings from molecular genetic studies are inconclusive. This may be due to limitations of past research, such as a failure to consider the influence of quantitative traits and gene-environment interactions. The current study investigated these issues by examining whether quantitative traits (i.e., impulsivity) and environmental exposure factors (i.e., dietary restraint) moderate 5-HT gene/binge eating associations in a sample of young women (N = 344). Binge eating was assessed using the Minnesota Eating Behaviors Survey and the Dutch Eating Behavior Questionnaire (DEBQ). Impulsivity was assessed with the Barratt Impulsiveness Scale-Version 11. Dietary restraint was measured with a factor score derived from common restraint scales. Saliva samples were genotyped for the 5-HT2a receptor T102C polymorphism and 5-HT transporter promoter polymorphism. As expected, impulsivity and dietary restraint were associated with binge eating. Although the T allele of the 5-HT2a receptor gene and the s allele of the 5-HTT gene were associated with higher levels of impulsivity, there were no main effects of 5-HT genotypes on any binge eating measure, and interactions between genotypes, impulsivity, and dietary restraint were non-significant. In conclusion, we found no evidence to suggest that dietary restraint or impulsivity moderate associations between binge eating and these 5-HT genes. Future research should continue to explore interaction effects by examining larger samples, assessing dietary intake directly, and investigating other genes, traits, and environmental factors that may be related to binge eating and bulimia nervosa.
PMCID: PMC2870529  PMID: 19493540
binge eating; serotonin; impulsivity; dietary restraint; gene-environment interactions
24.  Puberty and the Genetic Diathesis of Disordered Eating Attitudes and Behaviors 
Journal of abnormal psychology  2009;118(4):788-796.
Twin studies from the Minnesota Twin Family Study (MTFS) suggest negligible genetic effects on eating pathology before puberty, but increased genetic effects during puberty. However, an independent study found no pubertal differences in genetic and environmental effects (Rowe et al., 2002). Discrepant results may be due to methodological differences. The MTFS studies divided twins at mid-puberty, while Rowe et al. (2002) divided twins based on menarche alone. We aimed to reconcile discrepant findings by examining differences in etiologic effects for disordered eating attitudes and behaviors (i.e., levels of weight preoccupation, body dissatisfaction, binge eating, compensatory behaviors) using both classification methods in a new sample of 656 female twins. Using the MTFS method, we observed nominal genetic effects in pre-pubertal twins, but significant genetic effects in pubertal and young adult twins. Conversely, genetic effects were moderate and equal in all groups using the Rowe et al. (2002) method. Findings highlight the potentially important role of puberty in the genetic diathesis of disordered eating attitudes and behaviors and the need to use early indicators of pubertal status in studies of developmental effects.
PMCID: PMC2782672  PMID: 19899848
eating disorders; anorexia nervosa; bulimia nervosa; twins; genetic
25.  Prosocial Peer Affiliation Suppresses Genetic Influences on Non-aggressive Antisocial Behaviors during Childhood 
Psychological medicine  2013;44(4):821-830.
Available research has suggested that affiliation with prosocial peers reduces child and adolescent antisocial behavior. However, the etiologic mechanisms driving this association remain unclear. The current study sought to evaluate whether this association takes the form of a gene-environment interaction (GxE) in which prosocial peer affiliation acts to reduce the consequences of genetic risk for non-aggressive antisocial behavior during childhood.
Our sample consisted of 500 twin pairs aged 6 to 10 years from the Michigan State University Twin Registry (MSUTR).
Results robustly supported moderation by prosocial peer affiliation: genetic influences on non-aggressive antisocial behavior were observed to be several-fold larger in those with lower levels of prosocial peer affiliation as compared to those with higher levels of prosocial peer affiliation. This pattern of results persisted even after controlling for gene-environment correlations and deviant peer affiliation, and when restricting our analyses to those twins who share all or nearly all of their friends.
Such findings not only suggest that prosocial peer affiliation moderates genetic influences on non-aggressive antisocial behaviors during childhood, but also provide support for the theoretical notion that protective environmental experiences may exert their influence by promoting resilience to genetic risk.
PMCID: PMC3749251  PMID: 23659437
Non-aggressive antisocial behavior; Rule-breaking; Prosocial Peers; GxE; Resilience

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