FAMILIAL TRANSMISSION OF SUBSTANCE DEPENDENCE - ALCOHOL, MARIJUANA, COCAINE, AND HABITUAL SMOKING - A REPORT FROM THE COLLABORATIVE STUDY ON THE GENETICS OF ALCOHOLISM

Background: Alcoholism and substance dependence frequently co-occur. A ccordingly, we evaluated the familial transmission of alcohol, marijua na, and cocaine dependence and habitual smoking in the Collaborative S tudy on the Genetics of Alcoholism. Methods: Subjects (n = 1212) who m et criteria for both DSM-III-R alcohol dependence and Feighner definit e alcoholism and their siblings (n = 2755) were recruited for study. A comparison sample was also recruited (probands, n = 217; siblings, n = 254). Subjects were interviewed with the Semi-Structured Assessment for the Genetics of Alcoholism. The familial aggregation of drug depen dence and habitual smoking in siblings of alcohol-dependent and non-al cohol-dependent probands was measured by means of the Cox proportional hazards model. Results: Rates of alcohol, marijuana, and cocaine depe ndence and habitual smoking were increased in siblings of alcohol-depe ndent probands compared with siblings of controls. For siblings of alc ohol-dependent probands, 49.3% to 50.1% of brothers and 22.4% to 25.0% of sisters were alcohol dependent (lifetime diagnosis), but this elev ated risk was not further increased by comorbid substance dependence i n probands. Siblings of marijuana-dependent probands had an elevated r isk of developing marijuana dependence (relative risk [RR], 1.78) and siblings of cocaine-dependent probands had an elevated risk of develop ing cocaine dependence (RR, 1.71). There was a similar finding for hab itual smoking (RR, 1.77 in siblings of habitual-smoking probands). Con clusions: Alcohol, marijuana, and cocaine dependence and habitual smok ing are all familial, and there is evidence of both common and specifi c addictive factors transmitted in families. This specificity suggests independent causative factors in the development of each type of subs tance dependence.