Differences in the incidence of the CYP2C19 polymorphism affecting the S-mephenytoin phenotype in Chinese Han and Bai populations and identification of a new rare CYP2C19 mutant allele.
The incidence of the S-mephenytoin polymorphism was compared in two Chinese ethnic groups, Han (n = 101) and Bai (n = 202) by phenotype and genotype analysis. The frequency of poor metabolizers (PMs) in Han vs. Bai subjects was 19.8% vs. 13.4%. Han subjects had a higher frequency of the mutant CYP2C19m1 allele (0.366 vs. 0.257, P < .01) and a lower frequency of the wild-type allele (0.559 vs. 0.688, P < .01) than Bai subjects, which is consistent with the difference in the frequencies of PMs between the two ethnic groups. This results in a lower percentage of homozygous wild-type extensive metabolizers of mephenytoin (EMs) in Han subjects than in Bai subjects (40% vs. 59%, P = .005). Therefore, Han subjects may be more susceptible than Bai subjects to the drugs metabolized by the CYP2C19 enzyme. Ratios of urinary S/R-mephenytoin in homozygous EMs were lower than those of heterozygous EMs for both Han and Bai subjects, which shows a gene-dosage effect. Genotype analysis identified all but one PM as homozygous or heterozygous for the two known mutant CYP2C19m1 and/or CYP2C19m2 alleles. A single Bai PM outlier was shown to be heterozygous for CYP2C19m1 and a new mutant CYP2C19 allele containing a single amino acid change of Arg433 --> Trp433. A genotyping test demonstrated that only this one individual carried this rare allele (frequency of 0.0025 in Bai subjects).
Xiao
Z S
ZS
Pharmacogenetics Research Institute, Hunan Medical University, Changsha, People's Republic of China.
Goldstein
J A
JA
Xie
H G
HG
Blaisdell
J
J
Wang
W
W
Jiang
C H
CH
Yan
F X
FX
He
N
N
Huang
S L
SL
Xu
Z H
ZH
Zhou
H H
HH
D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases; D002681:China / Q000208:ethnology; D065731:Cytochrome P-450 CYP2C19; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D006899:Mixed Function Oxygenases / Q000235:genetics*; D009154:Mutation; D010641:Phenotype; D011110:Polymorphism, Genetic
D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19