Genetic and environmental influences on problematic masturbatory behavior in children: a study of same-sex twins.

Child sexual behavior problems, such as excessive or public masturbation, are often judged to result from environmental stress or trauma. We studied the relative importance of genetic and environmental factors for problematic masturbatory behavior among nonreferred prepubertal children. All twins born in Sweden in 1985-86 were identified from the Swedish Twin Registry. Parents, mainly mothers, completed Child Behavior Checklist (CBCL) ratings (Achenbach, 1991) for 401 monozygotic (MZ) and 248 dizygotic (DZ) same-sex twin pairs (male-male or female-female) at age 7-9 years. Scores of two CBCL items concerning specific sexual behavior problems (Plays with own sex parts in public and Plays with own sex parts too much) were summed and the influence of genetic and environmental factors on variability assessed. The prevalence of problematic child masturbatory behavior was low and associated with other emotional and behavioral problems. The degree of problematic child masturbatory behavior resemblance was higher within MZ twin pairs as compared to DZ same-sex twin pairs. Model fitting indicated that genetic factors substantially influenced the studied behaviors (77%, 95% CI = 9-96%), although family environment also played a role. Our results suggest that hereditary factors should be considered together with stressful experiences such as sexual victimization in the evaluation of elementary school children presenting with problematic masturbatory behaviors. When interpreting the findings, the very brief measure of sexual problem behavior and low statistical power, precluding the analysis of possible coinheritance with other symptoms or disorders, should be borne in mind.