Comorbidity of bipolar I disorder and conduct disorder: a familial risk analysis

Objective To investigate the association between pediatric bipolar I (BP-I) disorder and conduct disorder (CD) using familial risk analysis. Method We compared diagnoses in relatives of youth in four proband groups defined by the presence or absence of BP-I and CD: (1) probands with neither CD nor BP-I (probands: N = 550; relatives: N = 1656), (2) probands with CD and without BP-I (probands: N = 40; relatives: N = 127), (3) probands with BP-I and without CD (probands: N = 197; relatives: N = 579), and (4) probands with both CD and BP-I (probands: N = 176; relatives: N = 488). All subjects were evaluated with structured diagnostic interviews, and diagnoses of relatives were made blind to the diagnoses of probands. Results Relatives of probands with BP-I disorder had high rates of BP-I, and relatives of probands with CD had high rates of CD irrespective of the comorbidity with the other disorder. Relatives of probands with the combined condition of CD and BP-I had high rates of the combined condition. Conclusion The finding of cosegregation between BP-I disorder and CD is consistent with the hypothesis that the combined condition represents a distinct subtype of either disorder.