Examining the relationship between obsessive-compulsive disorder and attention-deficit/hyperactivity disorder in...

To use family study methodology to examine the relationship between obsessive-compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD) in children and adolescents.

We assessed for ADHD and OCD in the 1533 first-degree relatives of three groups of index children: those with ADHD and OCD, those with ADHD but no OCD, and matched controls with neither disorder.

The risk for ADHD was similarly elevated in families of ADHD youth with (18.9%) and without OCD (20.1%; p = .91), and both groups had significantly higher rates of ADHD compared with controls (4.6%; p < or = .001), which was consistent with previous research showing a strong familial risk for ADHD. The risk for OCD was significantly elevated only among relatives of youth with ADHD plus comorbid OCD (13.0%) compared with controls (.5%; p < or = .001) and was consistent with previous research showing a strong familial risk for OCD. Relatives affected with ADHD had a significantly elevated risk for OCD compared with relatives unaffected by ADHD (7.4% vs. 1.3%; p < .001), suggestive of co-segregation between these disorders. There was no evidence of nonrandom mating between ADHD- and OCD-affected spouses.

These results extend previously reported findings regarding the heritability of both ADHD and OCD and provide new evidence of a familial relationship between ADHD and pediatric OCD that best fits the hypothesis of a unique familial subtype.