Abstract
We used familial risk analysis to clarify the diagnostic comorbidity between pediatric BP-I disorder and ADHD, testing the hypothesis that pediatric-BP-I disorder comorbid with ADHD represents a distinct subtype. Structured diagnostic interviews were used to obtain DSM-IV psychiatric diagnoses on first-degree relatives (n = 726) of referred children and adolescents satisfying diagnostic criteria for BP-I disorder (n = 239). For comparison, diagnostic information on the first-degree relatives (N = 511) of non-bipolar ADHD children (N = 162) and the first degree relatives (N = 411) of control children (N = 136) with neither ADHD nor BP-I disorder were examined. BP-I disorder and ADHD in probands bred true irrespective of the comorbidity with the other disorder. We also found that the comorbid condition of BP-I disorder plus ADHD also bred true in families, and the two disorders co-segregated among relatives. This large familial risk analysis provides compelling evidence that pediatric BP-I disorder comorbid with ADHD represents a distinct familial subtype.