Common genetic vulnerability for nicotine and alcohol dependence in men

Background: Nicotine and alcohol dependence often occur together. We examin ed data from male twin pairs to determine whether there are genetic or envi ronmental influences common to nicotine and alcohol dependence, and, if so, to estimate the magnitude and correlation of these influences. Methods: Subjects were 3356 male-male twin-pair members of the Vietnam Era Twin Registry who participated in a 1992 telephone administration of the Di agnostic Interview Schedule Version 3 Revised. Genetic model fitting was pe rformed to estimate the magnitude and correlation of genetic and environmen tal contributions to lifetime nicotine and alcohol dependence. Results: The heritability of nicotine dependence was 60.3% (95% confidence interval [CI], 55.4%-65.2%); that of alcohol dependence, 55.1% (95% CI, 49. 7%-60.5%). The best-fitting model for the co-occurrence of lifetime nicotin e and alcohol dependence included a substantial genetic correlation between both disorders (r = 0.68; 95% CI, 0.61-0.74) and a modest unique environme ntal correlation (r = 0.23; 95% CI, 0.14-0.32). Conclusions: These data suggest a common genetic vulnerability to nicotine and alcohol dependence in men. This common genetic influence may partially explain the clinical and epidemiological observations that alcoholics are o ften dependent smokers.