behavioral disinhibition trait make it difficult to extrapolate the magnitude of genetic influences to the covariation among ADHD and alcohol problems. Further, while some evidence for common genes exists, other studies have suggested that environmental influences, rather than genetic, underlie the co-occurrence of disruptive behaviors, particularly ADHD, CD, and oppositional-defiant disorder (Burt et al., 2001, 2005). Additionally, Rose et al. (2004) reported that, at age 14, genetic influences on alcohol dependence were negligible and that the covariation among symptoms of CD and alcohol dependence was due to environmental factors that are common to both phenotypes.
