It is well known now that the hydroxylative metabolism of S-MP is catalized by cytochrome P450 2C19(CYP 2C19). For genotyping
analysis, DNA was isolated from the blood of 16 Chinese normal subjects who had been previously phenotyped(9 were S-MP EMs and 7 were S-MPPMs). Then the specific DNA fragment of CYP 2C19 was amplified by technique of PCR and digested with restrictive endoclease Sma I.000 Our results demonstrated that among the 16 subjects,4 were
homozygous for the wild-type gene(CYP 2C19 wt/wt), 4 of them were homozygous for mutant gene(CYP 2C19 m/m)and 9 others were heterozygous(CYP 2C19 wt/m). Thus, the CYP 2C19m defect accounted for 11 of 14 alleles(80%)in Chinese poor metabolizers and could explain about 60% PMs phenotypes. This defect was not able to explain all PMs.It is therefore indicated the existence of another, yet unidentified
mutation. DNA from two individuals, including 1 homozygous EMs and 1 hormozygous PMs was amplifled, subcloned into pGEM-T vector and sequenced.Our results indicated that only CYP 2C19 intron4/exon5 was amplified in the genotyping test. The principal defect in poor metabolizer is a single base pair(G→A)mutation in exon5 of CYP2C19, which created an aberrant splicing site and resulted in a non-functional enzyme protein, but the nucleotide sequence of intron 4 of the mutated gene is identical to that of the normal gene.