For the ABCB1 3435C > T (rs1045642) polymorphism, a previous meta-analysis that included 2 studies founded that MTX treatment toxicity was associated with the ABCB1 C3435T polymorphism in RA when an over-dominant model (TC vs TT + CC) was used (OR 0.483, 95% CI 0.259–0.900, P = 0.022), indicating that heterozygotes (TC) for the polymorphism had a lower risk for developing MTX toxicity than homozygotes (TT and CC).[12] The present meta-analyses included 5 studies with 391 patients with AE and 460 patients without AE. Here, ABCB1 is linked to rheumatoid arthritis.