A Controlled Family Study of Attention-Deficit/Hyperactivity Disorder and Tourette's Disorder

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. 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. 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 ≤ .03). TD in relatives predicted comorbid ADHD (p < .001), and ADHD in relatives predicted comorbid TD (p < .001). OCD in relatives predicted both ADHD (p = .002) and TD (p < .001) in relatives. TD and ADHD are not alternate phenotypes of a single underlying genetic cause. There is an increased risk of comorbid ADHD and TD in affected families, possibly reflecting some overlapping neurobiology or pathophysiology.