Previously reported eQTL shared between cell types have the same directional effect3. Whilst in general this holds true for our analysis of primary monocytes and B-cells, we observe several eQTL with cell type-dependent directional effects: the same eSNP being associated with opposing directional effects. We identified 197 eSNPs in 35 genes demonstrating significant ‘directional eQTL’ in B-cells and monocytes (permuted p<0.001 both cell types, total opposing directional effect >0.5 in terms of magnitude of mean log2 expression difference between major and minor alleles) (Figure 2a, Supplementary Table 4). To further investigate the significance of these directional findings we estimated the differences in the slopes using z-scores and demonstrated that for 31 of the 35 genes the differences were highly significant (Bonferroni corrected p<1×10−38) (Supplementary Table 4), thus strongly suggesting these were not chance observations. The most significant directional eQTL were noted to the gene DFNA5, previously implicated in familial deafness16 and a target of promoter methylation in gastric cancer17. Other notable genes with directional effect include MCOLN2, encoding a cation channel involved in type I interferon responses18, and SELL (also
