to be due to an increased rate of comorbid GTS+ADHD among those relatives who also had a diagnosis of GTS. In other words, rates of ADHD alone were not elevated in the relatives of GTS probands who did not themselves also have ADHD, suggesting that the “pure” form of ADHD is not present at an increased frequency in these families [2, 12, 35], but instead exists only when these disorders co-occur in the same individual. Recent work [36] demonstrated that a comorbid diagnosis of GTS and ADHD in a relative of a GTS or ADHD proband was strongly associated with an OCD diagnosis of that proband, and that comorbid GTS and ADHD diagnoses in a relative was associated with some degree of OC symptoms in the same individual [36]. These results suggest that there may be a GTS/OCD/ADHD familial subtype, which might be associated with an increased genetic burden and could represent a more severe form of GTS [37].
