title: The major genetic defect responsible for the polymorphism of S-mephenytoin metabolism in humans.
abstract: The metabolism of the anticonvulsant drug mephenytoin exhibits a genetic polymorphism in humans, with the poor metabolizer trait being inherited in an autosomal recessive fashion. There are large interracial differences in the frequency of the poor metabolizer phenotype, with Oriental populations having a 5-fold greater frequency compared to Caucasians. Impaired metabolism of mephenytoin and a number of other currently used drugs results from a defect in a cytochrome P450 enzyme recently identified as CYP2C19. Attempts over the past decade to define the molecular genetic basis of the polymorphism have, however, been unsuccessful. We now report that the principal defect in poor metabolizers is a single base pair (G-->A) mutation in exon 5 of CYP2C19, which creates an aberrant splice site. This change alters the reading frame of the mRNA starting with amino acid 215 and produces a premature stop codon 20 amino acids downstream, which results in a truncated, non-functional protein. We further demonstrate that 7/10 Caucasian and 10/17 Japanese poor metabolizers are homozygous for this defect, indicating that this is the major defect responsible for the poor metabolizer phenotype. Finally, the familial inheritance of the deficient allele was found to be concordant with that of the phenotypic trait.
authors.affiliation: NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: S M
authors.initials: SM
authors.lastname: de Morais
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
authors.forename: J
authors.initials: J
authors.lastname: Blaisdell
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.forename: U A
authors.initials: UA
authors.lastname: Meyer
authors.forename: J A
authors.initials: JA
authors.lastname: Goldstein
mesh_terms: D017398:Alternative Splicing; D001189:Aryl Hydrocarbon Hydroxylases; D044466:Asian People / Q000235:genetics; D001483:Base Sequence; D017124:Conserved Sequence; D065731:Cytochrome P-450 CYP2C19; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D017931:DNA Primers; D005091:Exons; D005260:Female; D006801:Humans; D007438:Introns; D008297:Male; D008617:Mephenytoin / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000235:genetics*; D008969:Molecular Sequence Data; D010375:Pedigree; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D016364:Reading Frames; D013237:Stereoisomerism; D044465:White People / Q000235:genetics
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D008617:Mephenytoin