Further evidence for family-genetic risk factors in attention deficit hyperactivity disorder. Patterns of comorbidity in probands and relatives psychiatrically and pediatrically referred samples.

We examined 140 probands with attention deficit hyperactivity disorder, 120 normal controls, and their 822 first-degree relatives using "blind" raters and structured diagnostic interviews. Compared with controls, probands with attention deficit hyperactivity disorder were more likely to have conduct, mood, and anxiety disorders. Compared with relatives of controls, relatives of probands with attention deficit hyperactivity disorder had a higher risk for attention deficit hyperactivity disorder, antisocial disorders, major depressive disorder, substance dependence, and anxiety disorders. Patterns of comorbidity indicate that attention deficit hyperactivity disorder and major depressive disorders may share common familial vulnerabilities, that attention deficit hyperactivity disorder plus conduct disorder may be a distinct subtype, and that attention deficit hyperactivity disorder and anxiety disorders are transmitted independently in families. These results extend previous findings indicating family-genetic influences in attention deficit hyperactivity disorder by using both pediatrically and psychiatrically referred proband samples. The distributions of comorbid illnesses in families provide further validation for subgrouping probands with attention deficit hyperactivity disorder by comorbidity.