Background: We have previously shown that juvenile bipolar disorder (BPD) is a risk for substance use disorders (SUD). Here we examine the expression of both disorders in families of youth with BPD to evaluate the familial risk mechanism.
Methods: We studied 108 adolescent BPD probands with 187 parents (34 with SUD and 58 parents) and 96 control probands with 177 parents with structured interviews. We compared the prevalence of BPD and SUD with Cox proportional hazards models with time to onset of BPD or SUD as the dependent variable and proband diagnosis (Control, BPD, or BPD+SUD) as the independent variable.
Results: The parents of the proband youth with BPD (without SUD) and BPD+SUD were more likely to develop BPD than the parents of control subjects [omnibus test chi2=10.18, p=.006]; we found no differences between the two bipolar groups. Parents of proband youth with BPD and with BPD+SUD were more likely than relatives of control subjects to develop SUD [omnibus test chi2=14.69, p<.001]; however, we found no differences between the parents of the two proband bipolar groups. Within the parents of proband youth with BPD+SUD, we found higher risk of SUD in parents with BPD than in those without BPD [chi2=8.39, p=.004], although the frequency of BPD was low in this group of parents.
Conclusions: Bipolar disorder and SUD are prevalent in the first-degree relatives of adolescents with BPD. Adults with BPD were more likely to manifest SUD with preliminary evidence of BPD and SUD cosegregation.