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.

Amygdala volume analysis in female twins with major depression.

BACKGROUND: Previous research examining the amygdala volumes in major depressive disorder (MDD) has found conflicting evidence for association. Furthermore, few of these studies have examined differences in individuals with an onset during childhood or adolescence. This study examined amygdala volume and its potential association with early onset major depression. METHODS: A community-based sample of 47 right-handed young adult female monozygotic and dizygotic twin pairs was examined. For 29 twin pairs, one twin per pair had a lifetime history of MDD, while 18 age-matched control twin pairs had no lifetime history of MDD or other Axis I disorder. Core, noncore, and total amygdala volumes were estimated based on a combination of manual tracing, automated segmentation, and expert rater regional boundary definitions. RESULTS: No significant differences were found in amygdala volumes between depressed, high-risk, or control subjects. However, analyses comparing control monozygotic twins to randomly created control subject pairs suggest that there are familial, perhaps genetic, influences on core and total amygdala volumes. CONCLUSIONS: Findings suggest that although there were no significant differences in amygdala volumes between groups, familial factors influence amygdala volumes. Discrepancies between studies measuring amygdala volume in MDD may be due to differences in amygdala boundary definitions.

Season of birth and disordered eating in female college students.

OBJECTIVE: Earlier studies have suggested relationships between season of birth and eating disorders. These studies have found that women with anorexia nervosa (AN) and bulimia nervosa (BN) are more likely to be born in the first 6 months rather than in the last 6 months of the year. The current study examines relationships between season of birth and general disordered eating in female college students. METHOD: Subjects included 155 female twin and triplet participants from the Michigan Twin Study. Disordered eating was assessed with subscales from the Minnesota Eating Disorders Inventory (M-EDI) and the Eating Disorders Examination Questionnaire (EDEQ). Both a two-group comparison and a three-group comparison of M-EDI and EDEQ scores were conducted. The two-group comparison comprised subjects born between January and June and subjects born between July and December. The three-group comparison comprised subjects born between January and April, between May and August, and between September and December. RESULTS: No significant differences in M-EDI or EDEQ scores were observed in any of the group comparisons. DISCUSSION: The lack of significant differences across birth periods suggests that season of birth effects may not generalize to general disordered eating characteristics in nonclinical samples.