RFC1 and rheumatoid arthritis: In the present study, we only focused on the association between gene polymorphisms and the toxicity to MTX monotherapy in RA patients and did not investigate gene–gene interactions.[65] In addition, combined MTX and biologic disease-modifying anti-rheumatic drug (bDMARD) treatment[66] were excluded from the meta-analysis of the RFC1 80G > A (rs1051266) polymorphism.