CFTR and cystic fibrosis: The higher ABCC1 mRNA levels induced by the plasma of CF patients may be related to the development of multidrug resistance to CF therapy; the increased activity of ABCC1 may complement diminished CFTR. Although we confirmed the eQTL effect of rs504348 on plasma-induced ABCC1 expression in PBMCs, there was no correlation between CF phenotypes and rs504348 genotypes.