Lack of Association between the C3435T Polymorphism in the Human Multidrug Resistance (MDR1) Gene and Response to Antiepileptic Drug Treatment

Purpose: P‐glycoprotein (P‐gp) has been implicated in the causation of refractory epilepsy. The expression and efflux efficiency of P‐gp is influenced by a polymorphism (C3435T) in the encoding gene (MDR1). Recent evidence suggests that the homozygous C‐variant, which is associated with higher expression and increased activity of P‐gp, is more common in patients with pharmacoresistant epilepsy. We have investigated the prevalence of this polymorphism in a series of patients attending a specialist epilepsy clinic. Methods: DNA samples were obtained from 400 patients, irrespective of seizure type or drug treatment. Genotype of the C3435T polymorphism was determined by traditional polymerase chain reaction (PCR) followed by restriction digest. Classification of response to treatment was determined in a blinded fashion by an independent physician. Results were expressed as genotype and allele frequencies per response group and compared by logistic regression analysis. Results: In total, 170 patients were classified as responders, with ≥12 months seizure freedom on current treatment. The remaining 230 patients were classified as nonresponders. Comparison of responders and nonresponders revealed no significant difference in allele frequency (C vs. T; odds ratio, 1.03; 95% CI, 0.78–1.37; p = 0.83) or genotype frequency (CC vs TT; odds ratio, 1.07; 95% CI, 0.60–1.91; p = 0.81). Subanalyses of individual seizure types were similarly unremarkable. Conclusions: This study failed to corroborate a previously reported association between the C3435T polymorphism in the human MDR1 gene and pharmacoresistant epilepsy. Whether the C3435T polymorphism can act as a marker for the natural history of treated epilepsy remains to be determined.