An important question to answer with our data is whether and which of the detected xQTLs are brain-specific. However, without tissue samples from the same individuals, distinguishing between subject-specific and tissue-specific effects is not possible. Nonetheless, based on the sparsity of “population-specific” eQTLs27 and a lower replication rate of eQTLs in blood compared to brain, a notable fraction of our eQTLs are likely tissue-specific. For example, when we considered only eQTLs that consist of the top SNP for each gene, we found that, of the 2,416 eQTLs discovered in our cortical tissue study that are testable in the whole-blood dataset26, 433 eQTLs (18%) have an unadjusted p-value >0.05, indicating that this subset of brain eQTLs are unlikely to be present in blood (Figure 2B). As an example, NLRP1 RNA is expressed in both brain and blood (whole blood, monocytes, and T cells), but its expression is only associated with brain-specific eQTL SNPs (Figure 2D). NLRP1 is a member of the inflammasome complex that is implicated in inflammatory response in both immune cells (in particular myeloid cells) and in brain29. Interestingly,
