In conclusion, we replicate the association between GABRA2 and externalizing behavior (Dick et al., 2009) in a large sample of adolescents and young adults. However, we find that association is only detected with subclinical levels of externalizing behavior, as indexed by Achenbach’s self-report scales. There was no evidence of association with diagnostic level symptoms of externalizing disorders — alcohol dependence, illicit drug dependence, conduct disorder, or antisocial personality disorder — in these young adult and adolescent samples. Furthermore, we extend this association by exploring whether ‘impulsivity’ may be involved in the association between GABRA2 and externalizing behavior, and what specific aspects of impulsivity are most relevant. We find evidence for association with sensation-seeking and extraversion in the adolescent sample only. There was not robust association with the BIS or low conscientiousness and GABRA2. These results help us understand the pathways by which GABRA2 conveys risk (and conversely, does not convey risk) to externalizing behavior. This information will be critical to identifying those individuals most at risk for the eventual development of problems and to intervene and disrupt gene-disorder relationships. Additionally,
