Interaction of genes from influx-metabolism-efflux pathway and their influence on methotrexate efficacy in rheumatoid arthritis patients among Indians.

Objective Methotrexate (MTX) is the drug of choice for rheumatoid arthritis (RA) but is effective only in around 60% of treated patients. Bioavailability of MTX may be a major determinant of response status and this may be governed by variations in MTX receptor and transporter genes and genes responsible for polyglutamation and deconjugation. We investigated the contribution of single nucleoticle polymorphisms (SNPs) in RFC, FOLR1, FPGS, GGH and MDR1 genes to MTX response in RA patients from North India. Methods RA patients recruited using American College of Rheumatology criteria, were categorized into good and poor responders to MTX, based on disease activity score. A total of 17 SNPs from the above mentioned genes were genotyped and tested for association with MTX response using chi(2) test; logistic regression along with clinical variables; and gene-gene interaction using multifactor dimensionality reduction (MDR). Results One novel synonymous SNP Ala324Ala (972 G >A) was identified in RFC gene. The CT genotype of C3435T in MDR1 gene conferred almost twice the risk of poor response [chi(2) =5.85, P=0.01, odds ratio (95% confidence interval)=1.97 (1.13-3.42)] and was retained in binary logistic regression [B=0.66, P=0.025, adjusted odds ratio (95% confidence interval)= 1.93(1.09-3.42)]. Significant interaction between SNPs in GGH and MDR1 genes seems promising. Conclusion Interactions between genes coding for deconjugation and transporter seem to be important determinants of MTX response in RA but replication and functional studies would be confirmatory. Pharmacogenetics and Genomics 18:1041-1049 (C) 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins.