title: Identification of functionally variant MDR1 alleles among European Americans and African Americans.
abstract: MDR1 (P-glycoprotein) is an important factor in the disposition of many drugs, and the involved processes often exhibit considerable interindividual variability that may be genetically determined. Single-strand conformational polymorphism analysis and direct sequencing of exonic MDR1 deoxyribonucleic acid from 37 healthy European American and 23 healthy African American subjects identified 10 single nucleotide polymorphisms (SNPs), including 6 nonsynonymous variants, occurring in various allelic combinations. Population frequencies of the 15 identified alleles varied according to racial background. Two synonymous SNPs (C1236T in exon 12 and C3435T in exon 26) and a nonsynonymous SNP (G2677T, Ala893Ser) in exon 21 were found to be linked (MDR1*2 ) and occurred in 62% of European Americans and 13% of African Americans. In vitro expression of MDR1 encoding Ala893 (MDR1*1 ) or a site-directed Ser893 mutation (MDR1*2 ) indicated enhanced efflux of digoxin by cells expressing the MDR1-Ser893 variant. In vivo functional relevance of this SNP was assessed with the known P-glycoprotein drug substrate fexofenadine as a probe of the transporter's activity. In humans, MDR1*1 and MDR1*2 variants were associated with differences in fexofenadine levels, consistent with the in vitro data, with the area under the plasma level-time curve being almost 40% greater in the *1/*1 genotype compared with the *2/*2 and the *1/*2 heterozygotes having an intermediate value, suggesting enhanced in vivo P-glycoprotein activity among subjects with the MDR1*2 allele. Thus allelic variation in MDR1 is more common than previously recognized and involves multiple SNPs whose allelic frequencies vary between populations, and some of these SNPs are associated with altered P-glycoprotein function.
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, USA. richard.kim@mcmail.vanderbilt.edu
authors.forename: R B
authors.initials: RB
authors.lastname: Kim
authors.forename: B F
authors.initials: BF
authors.lastname: Leake
authors.forename: E F
authors.initials: EF
authors.lastname: Choo
authors.forename: G K
authors.initials: GK
authors.lastname: Dresser
authors.forename: S V
authors.initials: SV
authors.lastname: Kubba
authors.forename: U I
authors.initials: UI
authors.lastname: Schwarz
authors.forename: A
authors.initials: A
authors.lastname: Taylor
authors.forename: H G
authors.initials: HG
authors.lastname: Xie
authors.forename: J
authors.initials: J
authors.lastname: McKinsey
authors.forename: S
authors.initials: S
authors.lastname: Zhou
authors.forename: L B
authors.initials: LB
authors.lastname: Lan
authors.forename: J D
authors.initials: JD
authors.lastname: Schuetz
authors.forename: E G
authors.initials: EG
authors.lastname: Schuetz
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000349:Africa / Q000208:ethnology; D000483:Alleles; D018926:Anti-Allergic Agents / Q000493:pharmacokinetics; D019540:Area Under Curve; D044383:Black People / Q000235:genetics*; D003001:Cloning, Molecular; D017931:DNA Primers; D004077:Digoxin / Q000493:pharmacokinetics; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics; D005060:Europe / Q000208:ethnology; D019450:Genes, MDR / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA; D016593:Terfenadine / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D013997:Time Factors; D044465:White People / Q000235:genetics*; D001741:Black or African American
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018926:Anti-Allergic Agents; D017931:DNA Primers; D004791:Enzyme Inhibitors; D004077:Digoxin; D016593:Terfenadine; C093230:fexofenadine