Identification and functional characterization of new potentially defective alleles of human CYP2C19.

CYP2C19 is a clinically important enzyme responsible for the metabolism of a number of therapeutic drugs, such as mephenytoin, omeprazole, diazepam, proguanil, propranolol and certain antidepressants. Genetic polymorphisms in this enzyme result in poor metabolizers of these drugs. There are racial differences in the incidence of the poor metabolizer trait, which represents 13-23% of Asians but only 3-5% of Caucasians. In this study, single nucleotide polymorphisms (SNPs) in CYP2C19 were identified by direct sequencing of genomic DNA from 92 individuals from three different racial groups of varied ethnic background, including Caucasians, Asians and blacks. Several new alleles were identified containing the coding changes Arg114 His (CYP2C199), Pro227 Leu (CYP2C1910), Arg150 His (CYP2C1911), stop491 Cys (CYP2C1912), Arg410 Cys (CYP2C1913), Leu17 Pro (CYP2C1914) and Ile19 Leu (CYP2C1915). When expressed in a bacterial cDNA expression system, CYP2C199 exhibited a modest decrease in the V(max) for 4'-hydroxylation of -mephenytoin, and no alteration in its affinity for reductase. CYP2C1910 exhibited a dramatically higher K(m) and lower V(max) for mephenytoin. CYP2C1912was unstable and expressed poorly in a bacterial cDNA expression system. Clinical studies will be required to confirm whether this allele is defective in vivo. CYP2C199, CYP2C1910 and CYP2C19*12 all occurred in African-Americans, or individuals of African descent, and represent new potentially defective alleles of CYP2C19 which are predicted to alter risk of these populations to clinically important drugs.