Pharmacogenomic and metabolic biomarkers in the folate pathway and their association with methotrexate effects during dosage escalation in rheumatoid arthritis

Arthritis Rheum. 2006 Oct;54(10):3095-103. doi: 10.1002/art.22129.


Objective: To evaluate the contribution of metabolites (methotrexate [MTX] and folate polyglutamate [PG] levels) and pharmacogenetic biomarkers in the folate pathway to the effects of MTX in patients with rheumatoid arthritis not previously treated with this antifolate.

Methods: Forty-eight MTX-naive adult patients were enrolled in a prospective longitudinal study. MTX therapy was initiated at 7.5 mg/week and was increased every 4-6 weeks until a therapeutic response was achieved. Response was assessed using the Disease Activity Score in 28 joints (DAS28). Red blood cell (RBC) MTX and folate PG levels were measured with 9 common polymorphisms in the folate pathway. Statistical analyses consisted of generalized linear models and multivariate regressions.

Results: After 6 months of therapy, the median weekly MTX dosage was 17.5 mg and the median decrease in the DAS28 was 2.0. There was a large interpatient variability in RBC MTXPG levels (median 35 nmoles/liter [interquartile range 28-51] at month 6). Patients with a lesser decrease in the DAS28 (fewer improvements) had lower RBC MTXPG levels (P < 0.05) despite the higher MTX dose administered (P < 0.05). RBC folate PG levels decreased significantly during treatment, and a lesser decrease in RBC folate PGs was associated with a lesser decrease in the DAS28 (P < 0.05). Primary side effects were gastrointestinal and neurologic in nature. Risk genotypes associated with toxicity were in gamma-glutamyl hydrolase (-401CC), 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (347GG), methylenetetrahydrofolate reductase (1298AC/CC), methionine synthase (2756AA), and methionine synthase reductase (66GG).

Conclusion: RBC MTXPG levels are a useful means by which to monitor therapy. The genetic associations presented generate hypotheses, and confirmation in independent cohorts is warranted.

MeSH terms

  • Alleles
  • Arthritis, Rheumatoid / blood
  • Arthritis, Rheumatoid / drug therapy*
  • Arthritis, Rheumatoid / genetics
  • Arthritis, Rheumatoid / physiopathology
  • Dose-Response Relationship, Drug
  • Enzymes / genetics
  • Folic Acid Antagonists / adverse effects
  • Folic Acid Antagonists / pharmacology
  • Folic Acid Antagonists / therapeutic use*
  • Humans
  • Longitudinal Studies
  • Methotrexate / adverse effects
  • Methotrexate / blood
  • Methotrexate / pharmacology
  • Methotrexate / therapeutic use*
  • Middle Aged
  • Multivariate Analysis
  • Pharmacogenetics
  • Polymorphism, Genetic
  • Prospective Studies
  • Pteroylpolyglutamic Acids / blood*
  • Pteroylpolyglutamic Acids / genetics
  • Severity of Illness Index


  • Enzymes
  • Folic Acid Antagonists
  • Pteroylpolyglutamic Acids
  • Methotrexate