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 with only 3.2% of the relatives of OCD probands without tics [28], though this finding was not fully replicated in a subsequent sample [31]. Thus results from OCD family studies suggest that there may be different types of OCD (adult onset and childhood-onset), with only the childhood-onset form likely to share common genetic factors with GTS. However it is still unclear whether there is an additional subtype of early onset OCD that is unrelated to tics.
