Increased rates of OCD have been reported in family studies of GTS-ascertained probands. Pauls and colleagues reported increased rates of OCD without tics among relatives of GTS probands even when the probands did not have OCD themselves [25]. In a larger follow-up study, Pauls and colleagues observed that the gender of the proband did not affect the rate of either OCD or tics in the relatives [6]. However, the gender of the relative was associated with the risk of GTS and OCD, such that female relatives were more likely to develop OCD without tics, while male relatives were more likely to develop tic disorders [6]. Subsequent family studies support this finding [7–9, 26, 27], providing evidence that OCD may be a sex-influenced phenotype of GTS or CT. Thus it appears that GTS, CT, and some forms of OCD are likely to have a common underlying susceptibility.
