Association between methylenetetrahydrofolate reductase(MTHFR) gene polymorphism and methotrexate toxicity in Korean patients with rheumatoid arthritis 김성규,Ahmed-El-Sohemy, 성윤경, 이혜순,엄완식,김태환,전재범,유대현,배상철association between methylenetetrahydrofolate reductase(MTHFR) gene polymorphism and methotrexate toxicity in Korean patients with rheumatoid arthritis