In the DSM-5, hoarding is considered both a possible symptom of OCD and a symptom of a distinct hoarding disorder18. In our study, Hoarding did not correlate as well phenotypically with the other dimensions or the TOCS total score but was genetically correlated with all other OC trait dimensions. Hoarding also differed from the other dimensions in that genetic influences contributed significantly to both shared and dimension-specific variance. Excluding Hoarding from the independent pathway model did not affect model fit, suggesting that Hoarding was not obscuring a latent OC trait that accounted for the other OC dimensions. A study of adult twins also showed that hoarding had both specific and unique genetic effects and that an independent model fit the data best with or without the hoarding dimension15. In another previous adult twin study, hoarding and total OC symptoms were not highly genetically correlated but did share additive genetic effects20. Probable hoarding disorder and OC symptoms also shared genetic effects in another sample of adult twins19. Classifying hoarding as a distinct condition is useful in the clinic and may help
