Methotrexate (MTX) is a disease-modifying antirheumatic drug used in the treatment of rheumatoid arthritis (RA). Genetic polymorphisms of reduced folate carrier (RFC1 A80G), P-glycoprotein (MDR1 G2677T>A/C and C3435T), 5,10-methylenetetrahydrofolate reductase (MTHFR C677T and A1298C), thymidylate synthase (TS 2R-->3R), methionine synthase (MS A2756G) and methionine synthase reductase (MTRR A66G) modify MTX transport and metabolic effects and may influence the treatment response.
A genotyping approach was used to determine the studied polymorphisms in 213 RA patients.
We observed that 56 (26.3%) patients discontinued MTX treatment due to poor response and/or toxicity. RFC1 A80G and MDR1 C3435T polymorphisms increased the risk for overall MTX toxicity (P = 0.039, OR = 3.574, 95% CI = 1.065-11.993 and P = 0.032, OR = 7.801, 95% CI = 1.194-50.960 respectively), while MTHFR A1298C polymorphism had a protective effect on overall MTX toxicity (P = 0.027, OR = 0.170, 95% CI = 0.035-0.820).
Our results suggest that genetic polymorphisms in the folate metabolic pathway and MTX transporters modify the toxicity but not the efficacy of MTX treatment.