eQTLs are common in the human genome; some eQTLs are shared across tissues and some are tissue-specific [31]–[34]. A recent study integrating GWAS SNPs and gene expression profiles in blood and brain demonstrated that brain tissue is required for eQTL discovery for neurological diseases and psychiatric traits. For example, significant eQTLs that mapped to the Parkinson disease associated gene, MAPT were only detected in post-mortem brains but not in blood [32]. In this study, we detected a consistent cis-regulatory effect on the variability of CHRNA5 mRNA levels in human frontal cortices of African and European ancestry but not in lymphoblastoid cell lines, which supports the importance of examining gene expression in brain, especially for psychiatric traits. Future studies examining other brain regions involved in the reward pathway may further define whether the eQTL for CHRNA5 mRNA expression is limited to frontal cortex or is shared across brain regions.
