The familial aggregation of alcohol dependence, habitual smoking, and major depressive disorder in the collaborative study of the genetics of alcoholism

Twin studies demonstrate that shared genetic components influence the development of alcohol dependence, smoking, and major depressive disorder. We examined the familial aggregation of these three disorders in subjects from the Collaborative Study of the Genetics of Alcoholism (COGA). Individuals who met criteria for DSM-III-R alcohol dependence and Feighner definite alcoholism were identified in treatment centers, and their first-degree family members were enrolled as a high risk population. Control families were recruited at each site. All subjects were interviewed using the SSAGA, a semi-structured interview that evaluated alcohol dependence, smoking, and major depressive disorder. The familial aggregation of these disorders was analyzed in 1432 alcohol dependent and control probands and their 3015 siblings. Alcohol dependence, habitual smoking, and major depressive disorder more commonly occurred in the siblings of alcohol dependent individuals compared to controls (alcohol dependence 35% vs 11%; habitual smoking 35% vs 11%; major depressive disorder 19%; vs 8%). Siblings of an affected proband were more likely to express the same disorder (risk ratio: alco-hol dependence given proband with alcohol dependence 3.2; habitual smoking given proband with habitual smoking 1.8; major depressive disorder given proband with major depressive disorder 1.2). While there was evidence of cross transmission of alcohol dependence and habitual smoking (risk ratio: habitual smoking given proband with alcohol dependence 1.9), there was no evidence of cross transmission of alcohol dependence and major depressive disorder or habitual smoking and major depressive disorder. These findings confirm and extend similar results from the Health and Adjustment of Young Adults Study.