A controlled family study of attention-deficit/hyperactivity disorder and Tourette's disorder

OBJECTIVE: Although attention-deficit/hyperactivity disorder (ADHD) is frequently comorbid with Tourette's disorder (TD), it is unclear whether they have a common genetic etiology. Familial relationships between DSM-IV ADHD and TD are studied in TD+ADHD, TD-only (TD-ADHD), ADHD-only (ADHD-TD), and control groups. METHOD: Case-control, direct-interview family study of 692 relatives of 75 TD+ADHD, 74 TD-only, 41 ADHD-only, and 49 control probands collected between 1999 and 2004. Age-corrected prevalence rates, odds ratios, and predictors of TD, ADHD, and OCD among relatives are estimated from blinded best-estimate diagnoses using survival Kaplan-Meier and generalized estimating equation regression analyses. RESULTS: In relatives of the TD-only group, although ADHD exceeded control rates (p=.03), ADHD-TD (p=.51) rates were not increased. In the ADHD-only group, TD was increased (p=.004) but TD-ADHD rates were not increased (p=.18). Comorbid ADHD+TD diagnoses in relatives were elevated in all case groups (p