Further evidence for co-segregation between pediatric obsessive compulsive disorder and attention deficit hyperactivity disorder: a familial risk analysis.

Background: To examine the relationship between obsessive compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) in children and adolescents using familial risk analysis. Methods: We assessed for ADHD and OCD in the 1057 first-degree relatives of three groups of index children: those with OCD and ADHD, those with OCD but no ADHD and matched controls with neither disorder. Results: The age-corrected risk for OCD was similarly elevated in families of OCD youth with (14.8%) and without ADHD (17.5%) (p = .78), and both groups had significantly higher rates of OCD compared with controls (.5%) (p < .001). In contrast, the risk for ADHD was significantly elevated only among relatives of youth who had ADHD (15.3%) compared with controls (4.6%) (p < .001). Relatives affected with ADHD also had a significantly elevated risk for OCD compared to relatives unaffected by ADHD (20% vs. 4.9%, hazard ratio 4.8) (p < .001) and the two disorders occurred together with higher than expected frequency in affected relatives of OCD+ADHD probands (p < .001) suggesting co-segregation between these two disorders. There was no evidence of nonrandom mating between OCD- and ADHD-affected spouses. Conclusions: These results extend previous findings regarding the familiality of both OCD and ADHD and provide further evidence of a familial relationship between ADHD and pediatric OCD which best fit the hypothesis of a unique familial subtype.