Moreover, the roles of the other folate-specific transporters (PCFT and RFC) in the kidney remain elusive and require further in vivo studies, particularly, in light of the application of folate-conjugate drugs and antifolates in the treatment of various cancers, chronic inflammatory disorders (e.g., rheumatoid arthritis) [131], and the polycystic kidney. This evidence concerns the gene SLC46A1 and rheumatoid arthritis.