Overall, these results resoundingly confirm the prior findings with respect to GABRA2. The haplotypes designated as the risk factors correspond exactly to those reported by Edenberg and colleagues (i.e., rs279871 is A, rs279845 is T, see Table 2 from Edenberg and colleages) [1]. This work also extends those findings by demonstrating that the risk conferred by GABRA2 haplotypes is not just limited to AD and can be observed using a sample that was not collected because of the occurrence of alcohol related problems. Rather, in this adoption sample, we find significant relationships between genetic variation at GABRA2 with respect to all three common forms of SUD in our population which suggests that this locus be considered as a risk for SUDs in general, rather than just a locus for AD. Alternatively, these data could be interpreted to suggest that substance use disorders may be an overlapping syndrome with common causes whose manifestation may reflect interactions between genetic vulnerability and environmental factors such as substance exposure and availability [20, 21].
