Common and specific factors in the familial transmission of substance dependence

Alcohol dependence is frequently complicated by other substance dependence. Evidence from family and twin studies support both common and specific addictive factors predisposing one to alcohol and other substance dependence. This is a report of a linkage study of alcohol, marijuana, and cocaine dependence and habitual smoking in families of alcoholics to search for common and specific genetic factors. Subjects were part of the Collaborative Study on the Genetics of Alcoholism (COGA). Individuals who met criteria for both DSM-III-R al-cohol dependence and Feighner definite alcoholism were identified in substance abuse treatment settings, and their relatives were recruited as a sample at high risk for substance dependence. All subjects were interviewed using a semi- structured interview (SSAGA) that evaluated alcohol and substance dependence, and other psychiatric disorders. Male and female probands had high rates of other substance dependence (marijuana dependence: 47% men 40% women; cocaine dependence: 47% men 51% women; habitual smoking 63% men 55% women). A genomic screen for loci linked to the development of each disorder was undertaken. There was evidence of linkage of alcohol, marijuana, and cocaine dependence at the same locus on Chromosome 1. This locus was not linked to the development of habitual smoking. There was evidence of linkage to both habitual smoking and alcohol dependence on Chromosome 2, and the comorbid phenotype of habitual smoking and alcohol dependence gave the strongest evidence of linkage.