Heterogeneity of childhood conduct disorder: further evidence of a subtype of conduct disorder linked to bipolar disorder.

Background: Although a small literature suggests that conduct disorder (CD) co-occurs with bipolar disorder (BPD), little is known about this overlap. Thus, we investigated the familial association of antisocial disorders (CD and/or antisocial personality disorder (ASPD)) and BPD among the first degree relatives of children with CD with and without comorbid BPD.
Methods: We compared relatives of four proband groups defined by the presence or absence of CD and BPD in the proband: (1) CD+BPD (N=26 probands, 92 relatives; (2) BPD without CD (BPD) (N=19 probands, 53 relatives); (3) CD without BPD (CD) (N=16 probands, 58 relatives); and (4) controls without BPD or CD (N=102 probands, 338 relatives). All subjects were evaluated with structured diagnostic interviews. Diagnoses of relatives were made blind to the diagnoses of probands.
Results: The results show high rates of antisocial disorders and BPD in relatives of children with CD+BPD. Moreover, antisocial disorders and BPD cosegregated among the relatives of children with CD+BPD. While relatives of both CD proband groups with and without BPD had high rates of CD/ASPD, the combined condition CD/ASPD+BPD was found exclusively among relatives of probands with CD+BPD.
Limitations: Since we pooled two datasets, subjects were not all evaluated at the same time. Also, the lack of direct psychiatric interviews with children younger than 12 may have decreased the sensitivity of some diagnoses.
Conclusions: These family-genetic findings suggest that CD and BPD represent separate disorders. Furthermore, they suggest that the comorbid condition of CD+BPD may be a distinct nosological entity. This suggests that clinicians treating CD or BPD children should consider the treatment implications of this comorbid condition.