Genetic influences on disordered eating behaviour are largely independent of body mass index

Exploring the possibility of parents' broad internalizing phenotype acting through passive gene-environment correlations on daughters' disordered eating

Twin studies demonstrate significant environmental influences and a lack of genetic effects on disordered eating before puberty in girls. However, genetic factors could act indirectly through passive gene-environment correlations (rGE; correlations between parents' genes and an environment shaped by those genes) that inflate environmental (but not genetic) estimates. The only study to explore passive rGE did not find significant effects, but the full range of parental phenotypes (e.g., internalizing symptoms) that could impact daughters' disordered eating was not examined. We addressed this gap by exploring whether parents' internalizing symptoms (e.g., anxiety, depressive symptoms) contribute to daughters' eating pathology through passive rGE. Participants were female twin pairs (aged 8-14 years; M = 10.44) in pre-early puberty and their biological parents (n = 279 families) from the Michigan State University Twin Registry. Nuclear twin family models explored passive rGE for parents' internalizing traits/symptoms and twins' overall eating disorder symptoms. No evidence for passive rGE was found. Instead, environmental factors that create similarities between co-twins (but not with their parents) and unique environmental factors were important. In pre-early puberty, genetic factors do not influence daughters' disordered eating, even indirectly through passive rGE. Future research should explore sibling-specific and unique environmental factors during this critical developmental period.

Elucidating factors underlying parent-offspring similarity in eating pathology in pre- and early puberty: Exploring the possibility of passive gene-environment correlation

Familial resemblance in eating pathology is typically attributed to parents providing an environment that leads to the development of eating pathology. However, offspring raised by biological parents receive both their environment and genes from their parents, raising the possibility that genetic influences, environmental influences, and/or gene-environment interplay may account for familial resemblance. Past studies have not explored the possibility of parents' genes influencing the environment they provide (i.e., passive gene-environment correlations or "passive rGE"). If present, passive rGE is most likely to "hide" in estimates of shared environmental influence in classical twin models. The current study used a nuclear twin family design to explore the possibility of passive rGE during pre- and early puberty when past studies have demonstrated the importance of shared environmental influence. Additionally, the present study explored whether sibling-specific (i.e., influences specific to the twin generation) or family-specific (i.e., "cultural" influences within the home) environmental influences account for shared environmental influences found in past studies. Participants included preearly pubertal same-sex female twins and their biological parents (N = 547 families) from the Minnesota Twin Family Study and the Michigan State University Twin Registry. Disordered eating was assessed with self-report measures in the twins and parents. Pubertal status was determined using an established cut-off on a self-report measure. Passive rGE was not indicated in this study of pre- and early pubertal twins. Instead, sibling-specific shared environmental and nonshared environmental influences were most influential. Future research should work to identify the sibling-specific environmental influences that contribute to sibling similarity in disordered eating. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Etiological influences on continuity and co-occurrence of eating disorders symptoms across adolescence and emerging adulthood

OBJECTIVE

The role of common and symptom-specific genetic and environmental influences in maintaining eating disorder symptoms across development remains unclear. This study investigates the continuity and change of etiological influences on drive for thinness, bulimia, and body dissatisfaction symptoms and their co-occurrence, across adolescence and emerging adulthood.

METHOD

In total, 2,629 adolescent twins (mean age = 15.20, SD = 1.95) reported eating disorders symptoms across three waves of data collection. Biometric common pathways model was fitted to estimate genetic and environmental contributions to the continuity of each symptom over time, as well as time- and symptom-specific influences.

RESULTS

Drive for thinness and body dissatisfaction symptoms showed a pattern of high continuity across development and high correlations with each other, whereas bulimia symptoms were moderately stable and less associated with the other two symptoms. Latent factors reflecting continuity of each symptom were largely under genetic influence (A_l  = 0.60-0.82). New genetic influences contributing to change in the developmental course of symptoms were observed in emerging adulthood. Genetic influences correlated considerably between the three symptoms. Non-shared environmental influences were largely time-and symptom-specific, but some contributed moderately to the continuity across development (E_l  = 0.18-0.40). The etiological overlap was larger between drive for thinness and body dissatisfaction symptoms than with bulimia symptoms.

DISCUSSION

The results provide preliminary evidence that stable as well as newly emerging genetic influences contribute to the co-occurrence of drive for thinness, bulimia, and body dissatisfaction symptoms across adolescence and emerging adulthood. Conversely, environmental influences were less stable and contributed to change in symptoms over time.

Sex Differences in Binge Eating: Gonadal Hormone Effects Across Development

Eating disorders are highly sexually differentiated disorders that exhibit a female predominance in risk. Most theories focus on psychosocial explanations to the exclusion of biological/genetic influences. The purpose of this descriptive review is to evaluate evidence from animal and human studies in support of gonadal hormone effects on sex differences in binge eating. Although research is in its nascent stages, findings suggest that increased prenatal testosterone exposure in males appears to protect against binge eating. Although pubertal testosterone may exert additional protective effects, the prenatal period is likely critical for the decreased risk observed in males. By contrast, studies indicate that, in females, it is the lack of prenatal testosterone coupled with the organizational effects of pubertal ovarian hormones that may lead to increased binge eating. Finally, twin data suggest that changes in genetic risk may underlie these hormone influences on sex differences across development.

The effects of puberty on genetic risk for disordered eating: evidence for a sex difference

BACKGROUND

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 1006 male and female twins from the Michigan State University Twin Registry.

METHOD

Disordered eating was assessed with the Minnesota Eating Behavior Survey. Pubertal development was assessed with the Pubertal Development Scale.

RESULTS

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.

CONCLUSIONS

The 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.

Bivariate analysis of disordered eating characteristics in adolescence and young adulthood

OBJECTIVE

We examined the etiology of two disordered eating characteristics.

METHOD

Participants included 1,470 female adolescent and young adult twins and their female nontwin siblings. Phenotypic factor analyses of a seven-item eating pathology screening tool yielded two factors: weight and shape concerns and behaviors (WSCB) and binge eating (BE). Univariate and bivariate extended twin analyses (including cotwins and nontwin siblings) were used to estimate the magnitude of genetic and environmental influences on these characteristics.

RESULTS

Analyses indicated that individual differences in WSCB and BE could be explained by additive genetic influences (a² = 0.43 (95% CI: 0.33-0.52) and 0.49 (95% CI: 0.36-0.58), respectively), with the remaining variance due to nonshared environmental influences. The genetic correlation between WSCB and BE was estimated at 0.64; the nonshared environmental correlation was estimated at 0.27.

DISCUSSION

These results corroborate previous findings on genetic and environmental influences on disordered eating characteristics and suggest that findings can be extended to nontwin populations.

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 influence of gender and puberty on the heritability of disordered eating symptoms

Eating disorders and disordered eating symptoms are clearly heritable, but recent research has suggested that genetic and environmental influences on disordered eating symptoms vary as a function of gender and development. Data are limited, but evidence suggests that gender may moderate the type of genetic risk, rather than the magnitude of genetic effects, on disordered eating symptoms. Only a moderate proportion of the genetic influences on disordered eating symptoms are shared between males and females. In females, at least some of the unique genetic risk may be related to puberty and ovarian hormone regulation. The heritability of disordered eating symptoms in females increases with both pubertal development and increasing levels of estradiol. Although much more research is needed to elucidate specific mechanisms, gonadal hormones may be promising candidates for understanding sex and developmental effects and the ways in which genes exert their influence on disordered eating.