2005; Enoch, 2008; Soyka et al., 2008] is associated with CD symptoms and externalizing behavior in adolescents [Dick et al., 2006, 2009], providing evidence that variations in one gene can manifest as different conditions at different stages of the life cycle. Electrophysiological endophenotypes, which are thought to index genetic vulnerability to psychiatric phenotypes, are also shared across substance use disorders and conduct disorder [Iacono et al., 1999; Porjesz et al., 2005]. For example, a reduced P3 event-related potential amplitude has been found among adolescents with both substance use disorders and externalizing disorders [Iacono et al., 2002]. Suicide attempts are also considerably elevated in individuals with alcohol dependence and conduct disorder [Kessler et al., 1999]. A recent study by Conner et al. [2009], found that proactive aggression (unemotional aggression executed for reward) is associated with both suicide attempts and suicidal ideation among inpatient substance abuse patients. Furthermore, in the COGA adult sample, unplanned suicide attempts among persons with alcohol dependence are associated with externalizing behaviors, including antisocial behavior and alcohol-related aggression [Conner et al., 2007]. Suicidal behavior is influenced by genetic factors [Bondy et al., 2006], and it is thought that the predisposition to suicidal behavior reflects a heritable liability to
