Results from family studies of OCD-ascertained families have also supported this conclusion, though the relationship is more complex. It has been observed that childhood onset OCD in probands is associated with greater rates of GTS and tics in their relatives [28, 29]. Furthermore, individuals with early onset of OCD appear more likely to have a tic disorder than individuals with adult-onset OCD [28, 30], and relatives of female OCD probands have a greater risk of developing tic disorders [28]. These investigators have also observed a much higher rate of GTS and tics among relatives of OCD probands who had family histories of OCD (7.4% vs. 1.4%) compared to relatives of probands without a family history of OCD [28], suggesting that non-familial OCD is not associated with tic disorders. However, in contrast to the family studies of GTS summarized above in which all GTS families had higher rates of OCD regardless of whether the proband had GTS and OCD, some OCD family studies have demonstrated that OCD probands with tics have higher rates of tics in first degree relatives (10.6%), compared
