Supporting its role as a potential endophenotype for EXT, resting state beta activity has been found to be highly heritable (McGuire, Katsanis, Iacono, & McGue, 1998; van Beijsterveldt et al., 1996), and has been linked to the GABRA2 gene, a GABA(A) neurotransmitter receptor gene on chromosome 4p (Edenberg et al., 2004; Porjesz et al., 2002), which itself has also been associated with a number of disorders in the EXT spectrum: alcohol dependence (Edenberg et al., 2004; Enoch, 2008; Soyka et al., 2008), drug dependence (Agrawal et al., 2006; Dick et al., 2006), and conduct disorder (Dick et al., 2006). Thus, there is evidence that the GABRA2 gene may affect both beta frequency EEG power and a predisposition to develop various disorders in the EXT spectrum.
