Familial rates of affective and substance use disorders in patients with first-episode mania.

Background: One explanation for the high co-occurrence between bipolar and substance use disorders is that substance abuse may precipitate affective symptoms in patients who otherwise may have not had the genetic risk for developing an affective illness. Previous studies comparing familial rates of affective illness between bipolar patients with and without alcohol use have provided conflicting results. We hypothesized that patients with bipolar disorder and antecedent alcohol abuse would have lower familial rates of affective illness than bipolar patients without antecedent alcohol abuse.

Methods: Family history data were obtained on 275 first-degree relatives of 51 patients hospitalized for a first manic episode using the Family History Research Diagnostic Criteria.

Results: Patients with bipolar disorder and antecedent alcohol abuse had lower familial rates of affective illness than patients with bipolar disorder without antecedent alcohol abuse (two-tailed Fisher's exact, P = 0.003). There was no statistically significant difference in the familial rates of affective illness between bipolar patients with and without antecedent drug abuse (other than alcohol). Patients with bipolar disorder and antecedent alcohol abuse had a significantly older age of onset of affective illness (27.6 years) than patients with bipolar disorder without antecedent alcohol abuse (20.6 years, z = 3.3, df = 1, P = 0.0009). There was no statistical difference in age of onset of affective illness between the patients with antecedent drug abuse and the patients without antecedent drug abuse.

Limitations: Future studies with a larger number of bipolar patients, direct structured interviews of family members and better differentiation between substance abuse and dependence syndromes are needed to extend and replicate this pilot study.

Conclusions: Our study suggests that there may be a subset of bipolar patients who have antecedent alcohol abuse and a subset who develop alcohol abuse after the onset of bipolar disorder. We further speculate that alcohol abuse may precipitate mania in some patients with bipolar disorder.