title: Association of multidrug resistance in epilepsy with a polymorphism in the drug-transporter gene ABCB1.
abstract: BACKGROUND
  One third of patients with epilepsy have drug-resistant epilepsy, which is associated with an increased risk of death and debilitating psychosocial consequences. Because this form is resistant to multiple antiepileptic drugs, the mode of resistance must be nonspecific, involving drug-efflux transporters such as ATP-binding cassette sub-family B member 1 (ABCB1, also known as MDR1 and P-glycoprotein 170). We hypothesized that the CC genotype at the ABCB1 C3435T polymorphism, which is associated with increased expression of the protein, influences the response to antiepileptic-drug treatment.
  
  
  METHODS
  ABCB1 3435 was genotyped in 315 patients with epilepsy, classified as drug-resistant in 200 and drug-responsive in 115, and 200 control subjects without epilepsy. Recently devised methods were used to control for population stratification, and linkage disequilibrium was calculated across the gene.
  
  
  RESULTS
  As compared with patients with drug-responsive epilepsy, patients with drug-resistant epilepsy were more likely to have the CC genotype at ABCB1 3435 than the TT genotype (odds ratio, 2.66; 95 percent confidence interval, 1.32 to 5.38; P=0.006). There was no genetic stratification between the two groups of patients. The polymorphism fell within an extensive block of linkage disequilibrium spanning much or all of the gene, implying that the polymorphism may not itself be causal but rather may be linked with the causal variant.
  
  
  CONCLUSIONS
  These pharmacogenomic results identify a genetic factor associated with resistance to antiepileptic drugs.
authors.affiliation: Department of Molecular Pathogenesis, Institute of Neurology, London, UK.
authors.forename: Asra
authors.initials: A
authors.lastname: Siddiqui
authors.forename: Reinhold
authors.initials: R
authors.lastname: Kerb
authors.forename: Michael E
authors.initials: ME
authors.lastname: Weale
authors.forename: Ulrich
authors.initials: U
authors.lastname: Brinkmann
authors.forename: Alice
authors.initials: A
authors.lastname: Smith
authors.forename: David B
authors.initials: DB
authors.lastname: Goldstein
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Wood
authors.forename: Sanjay M
authors.initials: SM
authors.lastname: Sisodiya
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D016022:Case-Control Studies; D018432:Drug Resistance, Multiple / Q000235:genetics*; D004827:Epilepsy / Q000188:drug therapy / Q000235:genetics*; D005787:Gene Frequency; D019450:Genes, MDR; D005838:Genotype; D006801:Humans; D015810:Linkage Disequilibrium; D011110:Polymorphism, Genetic
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1