rs1236423, which is located in a conserved suppressor region of DRD2, is of particular interest because it was shown by Zhang et al. (2007) to influence the expression of DRD2 in postmortem brain tissues. The minor allele of rs12364283 confers higher transcriptional activity compared with the major allele; a gain-of-function such as this might be expected to have functional consequences even in heterozygotes. The minor G allele enhances expression of DRD2 (Zhang et al., 2007), and imaging studies show that enhanced DRD2 expression is associated with better performance on inhibition tasks (for a review, see Cropley et al., 2006). These data are consistent with our finding that participants with genotypes A/G or G/G performed better on the stop RT in comparison with the A/A group. Analysis of the Block 2 haplotype was no better than rs12364283 alone at accounting for variability in stop RT. These data are consistent with the hypothesis that rs12364283 influences behavior because of its effect on DRD2 gene expression.
