We found paternal alcoholism and illicit drug dependence did not predict offspring smoking initiation or regular smoking, but high familial risk for ND was associated with offspring ND. This finding extends our previous analyses demonstrating the specificity of the inter-generational transmission of alcohol dependence and nicotine dependence in a subset of offspring of alcoholic twins (Volk et al. 2007). Our current results are not completely consistent with classical twin models of smoking outcomes in which genetic factors have been shown to contribute to tobacco use, regular smoking and ND. For example, Maes et al. (2004) reported high heritability for initiation of tobacco use, regular smoking, and ND (75%, 80%, and 62%, respectively) and substantial genetic correlations between phenotypes, but found that over one-third of genetic liability was specific to ND (Maes et al. 2004). Investigations of common heritable influences on initiation and persistence of smoking (Madden et al. 2006; True et al. 1997; True et al. 1999) and on initiation and ND (Fagerstrom 1978) are mostly consistent in that genetic factors for regular smoking are not completely accounted for by
