Spiliopoulou A, et al. - Researchers examined whether localization of genetic effects on response to tumour necrosis factor inhibitors (TNFi) in rheumatoid arthritis (RA) could be done by considering known genetic susceptibility loci for relevant traits. In addition, they determined the utility of these genetic loci for stratifying drug response. They quantified TNFi response by change in swollen joint counts (ΔSJC) and erythrocyte sedimentation rate, and studied its relation with locus-specific scores that were constructed from genome-wide assocation study summary statistics in 2938 genotyped individuals: 37 scores for RA; scores for 19 immune cell traits; scores for expression or methylation of 93 genes with previously reported associations between transcript level and drug response. ΔSJC showed a statistically significant association with the RA score at the CD40 locus and an inverse association with the score for expression of CD39 on CD4 T cells. As patients with RA are often prescribed TNFi after failing to respond to methotrexate, it is difficult to interpret the association with the CD39 trait. Findings suggest the possible relevance of the CD39 and CD40 pathways for targeting drug therapy.