As a next step, we analyzed whether the 3 eQTLs we identified were also associated with SLC1A1 gene expression in neuronal tissue. To this end, we determined genotypes and relative SLC1A1 messenger RNA levels by quantitative polymerase chain reaction in 97 postmortem brain samples from normal, bipolar, and schizophrenic donors, all derived from the dorsolateral prefrontal cortex. There were no significant differences in SLC1A1 expression levels among the 3 diagnosis groups as calculated by analysis of variance (data not shown). We then analyzed all 3 groups jointly for association with eQTLs to have increased power. As shown in Figure 2, rs7858819 and rs301430 were nominally significantly associated with SLC1A1 messenger RNA levels in human brain tissue (P=.02 each). Moreover, the direction of effect (increased expression with increasing number of T alleles at rs7858819 and decreased expression at rs301430) was identical to the data from lymphoblastoid cell line data (Figure 1 and Figure 2).
