The relationship between alcoholism and bipolar affective disorder: Association in families of comorbid probands

Objective: Maier and Merikangas [1996], among others, have suggested a familial relationship between bipolar disorder and alcoholism, but results have been inconsistent. We hypothesized that alcoholism would be associated with bipolar affective disorder (BPAD) in families of probands with both disorders, but not in other families. Methods: Among 116 BPI probands ascertained at Johns Hopkins, 42 were comorbid for alcoholism while 74 were not. We analyzed data on 250 first-degree relatives of comorbid probands and 391 first-degree relatives of non-comorbid probands. Every subject was interviewed by a psychiatrist, and family history and medical records were also taken into account. BPAD in the relatives was defined as BPI, BPII, schizoaffective disorder, or recurrent major depression. Alcoholism was defined by either RDC criteria or DSM III-R criteria for abuse or dependence. Results: In the families of comorbid probands, 46% of relatives with BPAD had alcoholism, while 29% of the relatives without BPAD had alcoholism (chi-square = 6.9, df = 1, P < .009; OR = 2.1). In families of BPI, nonalcoholic probands, 27% of relatives with BPAD had alcoholism, while 29% of relatives without BPAD had alcoholism (OR = 0.9, P = ns). Conclusion: BPAD and alcoholism are associated in a sample of families of probands who are comorbid for the two disorders. This association is not seen in families of BPI probands who do not have alcoholism. The possibility that the observed association is due to a shared genetic locus will be explored in further analyses.