Genetic and environmental contributions to self-report obsessive-compulsive symptoms in Dutch adolescents at ages 12, 14, and 16.

OBJECTIVE To determine the contributions of genetic and environmental influences to variation in self-report of obsessive-compulsive (OC) symptoms in a population-based twin sample of adolescent boys and girls. METHOD Self-report ratings on the eight-item Youth Self-Report Obsessive-Compulsive Scale were collected in Dutch mono- and dizygotic twin pairs who participated at age 12 (N = 746 twin pairs), 14 (N = 963 pairs), or 16 years (N = 1,070 pairs). Structural equation modeling was used to break down the variation in liability to OC symptoms into genetic and environmental components. RESULTS At age 12, no difference in prevalence was found for OC symptoms in boys and girls. At ages 14 and 16, the prevalence was higher in girls. At all ages, genetic factors contributed significantly to variation on OC symptom liability; 27% at the age of 12,57% at the age of 14, and 54% at the age of 16. There were no sex differences in heritability. Only at age 12, environmental factors shared by children from the same family contributed significantly (16%) to individual differences in OC symptom scores. CONCLUSIONS During adolescence, OC symptoms are influenced by genetic and nonshared environmental factors. Sex differences in prevalence, but not heritability, emerge in adolescence. At age 12, shared environmental factors are of importance, but their influence disappears at later ages. This is in line with earlier research at age 12 that used parental ratings of OC symptoms. Thus, between-family factors play a significant role in explaining individual differences in OC symptoms at this age.