This potential complexity is evidenced in the present report by the significant genetic associations between brain electrophysiological endophenotypes from different domains (stimulus-evoked P3 and TF components, and intrinsic, resting state beta activity) and EXT psychopathology. Functionally, a genetic predisposition to disinhibitory disorders has been associated with central nervous system hyperexcitability (Begleiter & Porjesz, 1999). Reduced amplitudes in the brain measures used in the present report theoretically reflect different manifestations of a dysfunction in the capacity for neuronal inhibition and in inhibitory control processes (Begleiter & Porjesz, 1999; Iacono et al., 2000). Additionally, each endophenotype has been linked to different genes, all of which have also been associated with EXT-spectrum disorders (e.g. Chen et al., 2009; Dick et al., 2008; Edenberg et al., 2004; Jones et al., 2004; Williams et al., 1999). Thus, there is theoretical and empirical support for the measures in the present report with regard to their potential collective utility as a multivariate endophenotype for EXT.
