title: Genetic polymorphism of (S)-mephenytoin 4'-hydroxylation in populations of African descent.
abstract: OBJECTIVE
  The frequency of CYP2C19 poor metabolizers (PMs) in populations of African descent has been reported to range from 1.0% to 35.4%. In order to determine with greater certainty the frequency of CYP2C19 PMs in such black populations we have performed a meta-analysis of the studies.
  
  
  METHODS
  Relevant data on the frequency of both the PM phenotype of probe drugs (mephenytoin, omeprazole, and proguanil), and the distribution frequencies of CYP2C19 alleles and genotypes in black populations were summarized and reanalysed using a meta-analytical approach.
  
  
  RESULTS
  Of nine reported studies two were excluded because of significant heterogeneity (chi2=115, P<0.0001). The combined data from the remaining seven studies showed that the frequency of the PM phenotype in 922 healthy unrelated black Africans and black Americans ranged from 1.0% to 7.5% (n=7 for combined data) with an overall frequency being 3.9% (36 of 922; 95%CI: 2.7%-5.2%). The frequency of the PM genotypes in blacks was 3.7% (36 of 966; 95%CI: 2.5%-4.9%), in agreement with the frequency of the PM phenotype. In the extensive metabolizers (EMs) 29% (271 of 930) were heterozygotes (wt/m ). The observed frequencies of the three Mendelian genotypes were 0.68 for wt/wt, 0.28 for wt/m, and 0.04 for m/m. The allelic distribution was appropriate at 82.3% (95%CI: 80.5%-83.9%) for CYP2C19*1, 17.3% (95%CI:15.7%-19.0%) for CYP2C19*2 (m1 ), and 0.4% (95%CI: 0.1%-0.7%) for CYP2C19*3 (m2 ) in these populations.
  
  
  CONCLUSIONS
  We conclude that subjects of African ancestry have a low frequency of the CYP2C19 PM phenotype and genotype; that the defective CYP2C19 alleles are uncommon, and that a small proportion of heterozygotes exists in the EM subpopulation.
authors.affiliation: Division of Clinical Pharmacology, Departments of Medicine and Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232-6602, USA.
authors.forename: H G
authors.initials: HG
authors.lastname: Xie
authors.forename: R B
authors.initials: RB
authors.lastname: Kim
authors.forename: C M
authors.initials: CM
authors.lastname: Stein
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
authors.forename: A J
authors.initials: AJ
authors.lastname: Wood
mesh_terms: D000349:Africa; D001189:Aryl Hydrocarbon Hydroxylases; D044383:Black People / Q000235:genetics*; D065731:Cytochrome P-450 CYP2C19; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D006900:Hydroxylation; D008617:Mephenytoin / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D011110:Polymorphism, Genetic; D001741:Black or African American
chemical_list: 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