The development of alcoholism is influenced by underlying biological susceptibility factors, environmental factors, and complex interactions among genes and environment (Porjesz et al., 2005; Dick and Kendler, 2012). There is a large literature indicating that low P3 amplitude can been considered to be an important genetic marker for the development of alcoholism (Begleiter et al., 1984; Goldman, 1993; Porjesz et al., 2005; Porjesz and Rangaswamy, 2007) and other externalizing disorders (Iacono et al., 2002; Iacono and McGue, 2006). Several genes have been found to be associated with delta and theta EROs underlying P3 (Jones et al., 2004; Jones et al., 2006; Chen et al., 2009; Chen et al., 2010; Zlojutro et al., 2011; Kang et al., 2012), and several of these genes have also been associated with alcoholism (Wang et al., 2004; Luo et al., 2005; Dick et al., 2007; Chen et al., 2009; Chen et al., 2010) and related externalizing disorders as well (Dick, 2007; Dick et al., 2008). Quantitative electrophysiological phenotypes, such as EEG, P3, and related EROs, have served as effective endophenotypes for gene identification in psychiatric
