The multidrug-resistance protein 4 polymorphism is a new factor accounting for thiopurine sensitivity in Japanese patients with inflammatory bowel disease

Background Multidrug resistance protein 4 (MRP4) functions as an efflux pump of nucleoside monophosphate analogs, such as 6-mercaptopurine (6-MP) and 6-thioguanine nucleotide (6-TGN). A single-nucleotide polymorphism in human MRP4 (rs3765534) dramatically reduces MRP4 function and results in the intracellular accumulation of 6-TGN. In this study, we investigated the association between MRP4 G2269A polymorphism and thiopurine sensitivity in Japanese IBD patients.