In summary, the current study replicated previous research which found that GABRA2 variation predicted sensation seeking [9] and alcohol problems [15–25], and that disinhibitory personality traits mediated the association between GABRA2 variation and alcohol problems [24]. Findings novel to the current study include the prediction of impulsivity and the mediating role of impulsivity in the relation between GABRA2 and hyperactive–inattentive symptoms and conduct problems. These findings should be viewed with caution until replicated in future studies. Importantly, our results suggest directions for future research. First, because genes predict change in behavior over time [28], future research might attempt to unpack these developmental processes. Second, it is possible that different risk alleles within GABRA2 might be involved in different pathways of risk for externalizing outcomes [4, 69]. If this is true, it might help explain the conflicting directions of associations found in the literature among GABRA2 and externalizing problems. It would also suggest the importance of investigating intermediate phenotypes to better understand the role of GABRA2 on externalizing problems. Finally, our results illustrate the value of examining intermediate phenotypes as mediators
