The estimated heritability of the TOCS total score was 74%, which was higher than estimates for OC symptoms from previous twin studies using existing OC measures6,8,9,35–37. The TOCS also had higher heritability estimates than the CBCL-OCS, an established heritable OC measure9, supporting the utility of the TOCS in genetic research. Each OC trait dimension was heritable, a finding that converges with previous studies of youth and adults15–17,36,38,39. Environmental factors contributed significantly to only the Cleaning/Contamination dimension, suggesting a distinct etiological mechanism. This finding is consistent with a previous study in an adolescent population-based sample that also reported low additive genetic effects for this dimension17. The effect of common environment on Cleaning/Contamination may result from family values, education or parental modeling.
