Finally, and somewhat surprisingly, and in contrast to previous family studies, we did not find evidence for increased heritability of the less severe phenotypes of CMVT and OCB in combination with the more severe phenotypes of TS and OCD. This may be due to the fact that the sample consists of nuclear families rather than multigenerational pedigrees, where the co-segregation of these phenotypes has been more clearly established11, 24. However, it does suggest that the inclusion of CMVT and/or OCB would not provide a significant advantage, and may in fact be a disadvantage, at least in genetic studies of nuclear families or other samples (such as case-control studies) where there is not clearly a strong genetic loading.
