Family studies of co-occurring bipolar disorder and substance abuse

Bipolar affective disorder often co-occurs with substance abuse. Investigations of this population however are confounded by the inclusion of patients with bipolar disorder secondary to substance usage. For this reason we were es-pecially interested families in the Bipolar Genetics Project. Probands with bipolar disorder in this project have heavy genetic loading and are therefore more likely to have a primary bipolar disorder. We previously reported that substance abuse was associated with an earlier onset of illness and a greater morbid risk for bipolar disorder in family members. Further analysis revealed that the onset of bipolar disorder before or after the onset of substance abuse did not change the results. Moreover a substance abuse history increased the morbid risk of bipolar disorder in relatives regardless of whether all relatives or only first-degree relatives were included in the analysis. Also a substance history in the probands doubled the risk of substance abuse in affected relatives. Other clinical outcome measures suggest that the probands with substance abuse may have a poorer clinical course. These findings are generally consistent with a model that assumes a common genetic basis for bipolar disorder and substance abuse in family members with strong family histories of bipolar disorder.