be largely attributed to common genetic factors (Hicks, Krueger, Iacono, McGue, & Patrick, 2004; Kendler et al., 2003). The high heritability and common genetic influence across these disorders suggest that a behavioral/clinical phenotype based on this EXT factor may be a better target in the search for genes underlying SUDs and related behavioral disinhibitory disorders in this spectrum than any of the disorders individually.
