to genetic factors, and there is fairly strong evidence that a common genetic factor underlies much of the phenotypic association among alcoholism, drug abuse, antisocial personality and CD in late adolescence and adulthood (Hicks et al., 2004; Krueger et al., 2002; Slutske et al., 1998). However, disorder-specific genetic variance also appears important (Blonigen et al., 2005; Dick et al., 2005; Krueger et al., 2002). On the other hand, genetically informative studies of specific relevance to the covariance between alcohol problems and ADHD are surprisingly limited in spite of ample evidence that genetic influences underlie each disorder (e.g. Knopik et al., 2004; Knopik et al., 2005). For instance, Young et al (2000) examined ADHD, CD, substance experimentation (including alcohol, nicotine, and illicit drug use) and novelty seeking in adolescents as indices of a latent behavioral disinhibition trait, which was found to be highly heritable. However, the lack of a direct assessment of alcohol and the additional variables contributing to the latent 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
