The purpose of this study was to examine the hypothesis that prenatal exposure to sex hormones affects the risk for developing eating disorder symptoms, full syndrome eating disorders, other psychiatric disorders with known sex differences, and temperament traits in members of opposite sex (OS) versus same sex (SS) twin pairs. Female (N=9433) and male (N=7025) twins from the Swedish Twin Registry with known co-twin sex and zygosity completed questionnaires assessing eating disorder attitudes and behaviors, lifetime history of other psychiatric disorders (including alcohol abuse, substance use, mood disorders, anxiety disorders, and autism/Aspergers), and temperament traits. Females were analyzed separately using logistic regressions and analysis of variance with generalized estimating equations applied to control for the correlated nature of the data. All comparisons were across monozygotic SS twins, dizygotic SS twins, and dizygotic OS twins. Additional analyses were conducted with the full sample to assess whether a linear trend existed across female and male OS and SS twins. After controlling for multiple comparisons, no significant differences were found. Presumed prenatal exposure to sex hormones was not associated with risk or protection for developing eating disorder behaviors, full syndromes, other psychiatric disorders, or temperament traits in this sample
