While blood-cell-composition SNPs22 comprised 21% of the tested SNPs, they represented the majority (64%) of trans-eQTL SNPs. Many of the identified trans-eQTL SNPs may regulate the abundance of a specific blood cell type and could result in trans-eQTL effects on genes specifically expressed in that cell type. Although we corrected the individual expression datasets for cell-type composition effects using PCs (Methods, Supplementary Note), the fact that numerous trans-eQTLs emanate from known blood-cell-composition SNPs suggested a residual effect of cell composition.
