These questions are of particular relevance with respect to GABRA2, given the previous history of association with this gene. GABRA2 was originally associated with adult alcohol dependence in the COGA (Edenberg et al., 2004). This association was subsequently replicated by several independent groups (Covault et al., 2004; Enoch et al., 2006; Fehr et al., 2006; Soyka et al., 2008). Further work in the COGA sample found that GABRA2’s association was not limited to alcohol dependence, but also included illicit drug dependence (Agrawal et al., 2006; Dick et al., 2006b), childhood conduct disorder (Dick et al., 2006b), and adult antisocial behavior (Dick et al., 2006a). Thus, paralleling the twin literature indicating shared genetic influence across externalizing disorders, GABRA2 appeared to be a specific gene predisposing to a spectrum of clinical disorders characterized by a lack of impulse control. The association between GABRA2 and general externalizing behavior has also been extended to a non-clinical, community-based sample, in which individuals carrying the genotype originally associated with adult alcohol dependence in COGA were more likely to evidence an elevated, stable trajectory of externalizing behavior
