ABCG2 and rheumatoid arthritis: When comparing healthy Japanese adults with Japanese RA patients, there were no significant differences in allelic frequencies of the MTHFR 1298A > C, TYMS 3'-UTR (−6/+6), RFC1 80G > A, RFC1−43 T > C, FPGS 1994G > A, GGH 452C > T, GGH−401C > T, ABCB1 3435C > T, ABCC2 IVS 23 + 56 T > C, and ABCG2 914C > A polymorphisms in 299 healthy Japanese adults and 159 Japanese RA patients.