Background: Attention deficit disorder with or without hyperactivity (ADD) is present in 49% to 83% of patients with Tourette's syndrome (TS), and up to 50% of children with attention-deficit hyperactivity disorder (ADHD) have chronic tics or a family history of chronic tics. Two explanations have been offered for this association: (1) ADHD is part of the pleiotropic expression of the Gilles de la Tourette (Gts) gene(s), or (2) the presence of ADHD in TS is due to ascertainment bias.
Method: To avoid ascertainment bias, we examined 338 first-degree relatives of 131 TS probands utilizing a structured questionnaire and the DSM-III criteria for ADD and DSM-III-R criteria for ADHD. All probands and many relatives were personally interviewed.
Results: Of the relatives with TS, 61% had ADD and 36% had ADHD. Of the relatives with chronic tics, 41% had ADD and 26% had ADHD. Log-linear analysis showed a major, significant association between tics and ADHD.
Conclusion: These results indicate that ADHD is part of the pleiotropic expression of the Gts gene(s).