Phenotypic heterogeneity in the TOCS, demonstrated by six OC dimensions, also reflected some etiological heterogeneity. Genetic factors contributed considerably to all OC dimensions, although less so for Cleaning/Contamination. All OC dimensions were also co-heritable indicating that they share some genetic influences. However, the degree to which genetic effects influenced the variance shared by dimensions (Ac) rather than the dimensions individually (As) varied by dimension. For many OC dimensions, shared effects (Ac) accounted for genetic influences with the other dimensions, suggesting that similar genetic factors played an important role across phenotypically separate, but correlated, OC dimensions. By contrast, what made the OC dimensions different was accounted for mostly by unique environment (Es) rather than genetic factors (As). A notable exception was Hoarding that had considerable genetic effects that were shared with the other dimensions (Ac) but also had considerable Hoarding-specific genetic influences (As). A similar pattern was observed for Superstition. Unlike our study, a previous study of female adults15 reported dimension-specific genetic effects for most OC dimensions. However, both ours and this previous study reported that unique environment accounted for most
