Major findings from these analyses include: (i) parental risk factors, such as parental alcohol dependence and regular smoking, increase risk for externalizing behavior; (ii) prenatal exposures predicted increased symptomatology for HYP/IMP (smoking during pregnancy), INATT and CDP (prenatal alcohol exposure); (iii) after adjusting for measured familial/prenatal risk factors, genetic influences were significant for HYP/IMP, INATT, and CDP; however, similar to earlier reports (Rhee et al., 2003; Rose et al., 2004), genetic effects on alcohol dependence symptoms were negligible, a finding consistent with the fact that, in adolescence, drinking tends to be exploratory and episodic with alcohol dependence symptoms being rarely endorsed (Rose et al., 2004); and (iv) in adolescence, correlated liabilities for conduct and alcohol problems are found in environmental factors common to both phenotypes, while covariation among impulsivity, inattention, and conduct problems is primarily due to genetic influences common to these three behaviors.
