Genetics of comorbid mood disorder and alcohol dependence

Objectives: To assess genetic vulnerability factors related to comorbid mood disorder and alcohol dependence. Methods: We analyzed family studies of bipolar affective disorder for familiality of comorbid alcohol dependence. We then analyzed family studies of alcohol dependence for familiality (and genetic linkage characteristics) of comorbid depression and mania. Results: Alcohol dependence was increased in subjects with mood disorder diagnoses within a series of families ascertained for bipolar illness. Comorbid alcohol dependence was found to be familial (Relative Risk = 1.5, p <.002). Similarly, comorbid depression and mania are familial within a series of families ascertained for alcohol dependence. Alcohol dependence and depression appear to be linked to markers on chromosome 1p; they are also associated with the gene coding for the M2 muscarinic receptor on chromosome 7q (CHRM2). Conclusions: There are specific genetic vulnerability factors related to comorbid alcohol dependence and depression. Family studies suggest that such specific factors may also be identified for alcohol dependence and mania.