Reduced amplitude of the P3 event-related potential (ERP) has long been associated with alcoholism and familial risk of developing alcoholism (Begleiter, Porjesz, Bihari, & Kissin, 1984; Hill, 2004; 1994). This association between P3 amplitude reduction (P3-AR) and alcoholism, however, has recently been extended to encompass a spectrum of disorders characterized by behavioral disinhibition. In addition to alcoholism, this disinhibition spectrum includes disorders such as conduct disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and substance use disorders (Bauer & Hesselbrock, 2003; Iacono, Carlson, Malone, & McGue, 2002; Justus, Finn, & Steinmetz, 2001). Large-scale epidemiological studies with twins have shown that the common comorbidity among these disorders can be accounted for by an underlying “externalizing” factor that is highly heritable (Kendler, Prescott, Myers, & Neale, 2003; Krueger et al., 2002; Young, Stallings, Corley, Krauter, & Hewitt, 2000). Recently, P3-AR was shown to be associated with this externalizing factor (Patrick et al., 2006), and this association is accounted for by shared genetic effects (Hicks et al., 2007). These findings support the hypothesis that P3-AR is an endophenotype for general vulnerability to the spectrum of externalizing disorders, rather than for any one disorder specifically.
