for those in brain. Liu et al.14 extended the stratified linkage disequilibrium (LD) score regression method to estimate genetic correlation (rg) of gene expression between tissues at all SNPs in local or distal regions and showed that the mean estimate of pairwise rg at all local SNPs (i.e. cis-genetic correlation) was ~0.75 in 11 GTEx tissues but they did not estimate rg between brain and blood. In this study, we use a summary-data-based method to estimate the correlation of effect sizes of the top-associated cis-eQTLs (or cis-mQTLs) between blood and brain for genes expressed (or CpG sites methylated) in both tissues, accounting for errors in their estimated effects. We demonstrate by simulation and analysis of real data the gain of power by using cis-eQTL or cis-mQTL effects estimated in blood as proxies of those in brain to identify putative functional genes for brain-related complex traits and diseases.
