The differences in drug efficacy and adverse reactions may be caused by genetic variations in drug metabolism between individuals.
The aim of the study was to evaluate the effect of gene polymorphisms on the efficacy of therapy and side effects in patients with rheumatoid arthrit s (RA) treated with methotrexate (MTX).
A total of 273 Caucasian patients with RA were treated with MTX for at least 6 months or stopped MTX because of adverse effects. Seven polymorphisms (RFC-1 c.80G>A, GGH c.-401C>T, MTHFR c.1298A>C and c.677C>T, TYMS 2R/3R, TYMS 6-bp deletion, and TCII c.593T>C) were examined for their effects on MTX efficacy and toxicity. Genomic DNA was obtained from peripheral blood leukocytes.
Of all patients, 53% reported some adverse effects during at least 1 visit, which led to MTX withdrawal in 17% of the patients. Adverse effects were more frequent in patients with the MTHFR 677T allele than in those with the 677CC genotype (odds ratio [OR], 1.97; P = 0.01) and in those with the GGH 401CC genotype than in those with the GGH 401CT and TT genotypes (OR, 3.8; P = 0.05). Furthermore, the MTHFR 677T allele was associated with increased activity of aminotransferases (OR, 3.4; P = 0.02). MTX-related hepatotoxicity and alopecia were more common in patients with the RFC-1 80AA genotype (OR, 3.5, P = 0.01; OR, 2.4, P = 0.04; respectively). A more rapid positive response to MTX therapy was demonstrated in MTHFR 677CC homozygotes (OR, 3.4; P = 0.001). There were no other associations between single -nucleotide polymorphisms and the efficacy of MTX treatment.
The MTHFR 677CC and GGH 401TT and CT genotypes were associated with a reduction in the number of MTX-related adverse events. Future allele and genotype analyses may help identify the subsets of RA patients with an increased risk of adverse effects.