Allele Frequencies Of CYP2C19 Research Articles

Characterisation of CYP2C8, CYP2C9 and CYP2C19 polymorphisms in a Ghanaian population

BackgroundGenetic influences on drug efficacy and tolerability are now widely known. Pharmacogenetics has thus become an expanding field with great potential for improving drug efficacy and reducing toxicity. Many pharmacologically-relevant polymorphisms do show variability among different populations. Knowledge of allelic frequency distribution within specified populations can be useful in explaining therapeutic failures, identifying potential risk groups for adverse drug reactions (ADRs) and optimising doses for therapeutic efficacy. We sought to determine the prevalence of clinically relevant Cytochrome P450 (CYP) 2C8, CYP2C9, and CYP2C19 variants in Ghanaians. We compared the data with other ethnic groups and further investigated intra country differences within the Ghanaian population to determine its value to pharmacogenetics studies.MethodsRFLP assays were used to genotype CYP2C8 (*2, *3, *4) variant alleles in 204 unrelated Ghanaians. CYP2C9*2 and CYP2C19 (*2 and *3) variants were determined by single-tube tetra-primer assays while CYP2C9 (*3, *4, *5 and *11) variants were assessed by direct sequencing.ResultsAllelic frequencies were obtained for CYP2C8*2 (17%), CYP2C8*3 (0%), CYP2C8*4 (0%), CYP2C9*2 (0%), CYP2C9*3 (0%), CYP2C9*4 (0%), CYP2C9*5 (0%), CYP2C9*11 (2%), CYP2C19*2 (6%) and CYP2C19*3 (0%).ConclusionAllele frequency distributions for CYP2C8, CYP2C9 and CYP2C19 among the Ghanaian population are comparable to other African ethnic groups but significantly differ from Caucasian and Asian populations. Variant allele frequencies for CYP2C9 and CYP2C19 are reported for the first time among indigenous Ghanaian population.

CYP2C9*8 is Prevalent Among African–Americans: Implications for Pharmacogenetic Dosing

Although the frequencies of pharmacogenetic variants differ among racial groups, most pharmacogenetic algorithms for genotype-guided warfarin dosing only include two CYP2C9 alleles (*2 and *3) and a single VKORC1 allele (g.-1639G>A or g.1173C>T) commonly found among Caucasians. Therefore, this study sought to identify other CYP2C9 and VKORC1 alleles important in warfarin dose variability and to determine their frequencies in different racial and ethnic groups. The CYP2C9 and VKORC1 genes were sequenced in selected sensitive (< 21 mg/week) and resistant (> 49 mg/week) individuals with discrepant therapeutic and algorithm-predicted warfarin doses based on prior CYP2C9 and VKORC1 genotyping. The CYP2C9 and VKORC1 allele frequencies were determined in healthy, racially self-identified blood donors. Sequencing identified an African-American male with a lower than predicted therapeutic warfarin dose (14.4 mg/week), previously genotyped as CYP2C9*1/*1, who was homozygous for CYP2C9*8 (c.449G>A; p.R150H). Genotyping 600 African-American alleles identified CYP2C9*8 as their most frequent variant CYP2C9 allele (0.047), and the combined allele frequency of CYP2C9*2, *3, *5, *6, *8 and *11 was 0.133. Given most warfarin pharmacogenetic dosing algorithms only include CYP2C9*2 and *3, the inclusion of CYP2C9*8 alone could reclassify the predicted metabolic phenotypes of almost 10% of African-Americans, or when combined with CYP2C9*5, *6 and *11, more than 15%. In addition, the African-American VKORC1 g.-1639A allele frequency was 0.108 and three g.1331G>A (p.V66M) carriers were identified. CYP2C9*8 is prevalent among African-Americans ( approximately 1 in 11 individuals). Thus, in this racial group, the incorporation of CYP2C9*8 into genotyping panels may improve dose prediction of CYP2C9-metabolized drugs, including warfarin.

Frequencies of genotypes and alleles of the functional SNPs in CYP2C19 and CYP2E1 in mainland Chinese Kazakh, Uygur and Han populations

CYP2C19 and CYP2E1 show great genetic differences between Orientals and Caucasians. The objective of this study was to investigate the genotype and allele distribution patterns of CYP2C19 and CYP2E1 polymorphisms among healthy participants in mainland Chinese Kazakh, Uygur and Han populations by the PCR-restriction fragment length polymorphism technique. The allele frequencies of CYP2C19 2, CYP2E1 5B and CYP2E1 6 were significantly lower in the Chinese Kazakh (15.4, 11.2 and 14.5%, respectively) (P<0.05) and Uygur (16.1, 12.1 and 18.8%) (P<0.05) populations than that in the Chinese Han population (28.8, 19.4 and 26.2%), but the frequencies of CYP2C19 3 were similar among the three populations (8.0, 9.4 and 7.2%). Frequencies of the three combined genotypes, one for predicted CYP2C19 poor metabolizers and two for predicted high levels of CYP2E1 transcription, were significantly lower in the Chinese Kazakh (7.5, 19.6 and 28.0%, respectively) (P<0.05, chi(2)-test) and Uygur (8.1, 22.8 and 33.6%) (P<0.05) populations compared with the Chinese Han population (16.5, 35.9 and 44.7%). The present research shows that frequencies of the functional single-nucleotide polymorphisms in the CYP2C19 and CYP2E1 genes vary in the Chinese Kazakh, Uygur and Han populations, suggesting that disease susceptibilities or drug responses associated with enzyme activities of CYP2C19 and CYP2E1 may differ in the diverse ethnic populations in mainland China.

Prevalence of CYP2C9 polymorphisms in the south of Europe

CYP2C9 is a major liver enzyme responsible of the metabolism of many clinically important drugs. The presence of CYP2C9 genetic polymorphisms has been associated with marked interindividual variability in its catalytic activity that could result in drug toxicity. Here we present frequencies of the most common CYP2C9 coding variants CYP2C9*2 (C430T) and CYP2C9*3 (A1075C) in representative samples of four regions from Spain (Basque Country, n=358; Catalonia, n=240; Central Spain, n=190 and Galicia, n=288) and one northern Italian region, (Verona, n=164), which range between 0.125 and 0.165 in the case of CYP2C9*2 and between 0.071 and 0.085 for CYP2C9*3. No significant differences between CYP2C9 allele frequencies were found comparing all the sampled populations. A more extensive comparative analysis using allele frequency data of populations widely spread over Europe was performed, showing significant differences in the CYP2C9*2 allele frequencies distribution between some of the regions, being quite homogeneous in the case of CYP2C9*3 variant. The results obtained show that above 40% of our samples carry a mutate allele, which can result in a poor metabolization of low therapeutic index drugs as oral anticoagulants (warfarin, acenocoumarol), oral antidiabetic drugs and some non-steroidal anti-inflammatory drugs. Our study constitutes both a large (n=1240) and robust allele frequency database on CYP2C9 polymorphisms, which represents one of the most numerous CYP2C9*2 and *3 database existing to date.

Comparisons of CYP2C19 Genetic Polymorphisms Between Korean and Vietnamese Populations

It is well known that CYP2C19 is an enzyme showing genetic polymorphism that may cause marked interindividual and interethnic variation in the metabolism and disposition of its substrates. This study compared the frequency distribution of CYP2C19*1, *2, and *3 alleles in Korean and Vietnamese populations, representing Far Eastern and Southwestern Asian populations, respectively. The presence of the CYP2C19 variant alleles was analyzed in 377 Korean and 165 Vietnamese healthy subjects using a new pyrosequencing method. The respective allele frequencies of CYP2C19*1, *2, and *3 were 64%, 28%, and 8% in Koreans and 69%, 24%, and 5% in Vietnamese. The frequency of poor metabolizer genotype (*2/*2, *2/*3, *3/*3) in Korean (12.5%, 95% confidence interval 11.4-13.6) was not significantly different from that of Vietnamese population (7.2%, 95% confidence interval 6.2-8.2) (P = 0.074). These results obtained from a large number of subjects can be used in comparative studies with other ethnic groups in future clinical research.

CYP2C19 Polymorphism in Korean patients on warfarin therapy

This study was designed to assess the effect of CYP2C19 polymorphism on warfarin dosage requirements and bleeding complications in the Korean population. Patients were placed into one of four groups according to the dose of warfarin they received and the presence of bleeding complications: regular dose control, regular dose bleeding, low dose control, and low dose bleeding. Genotyping for CYP2C19*2 and CYP2C19*3 was performed by the restriction fragment length polymorphism method for each patient and each study group. The measured internal normalized ratio (INR) in each dose group was similar even though the administered dosage was significantly different. A total of 66 patients were evaluated for CYP2C19 polymorphism. Among them 25 patients (37.9%) were homozygous wild type. Four patients (6.1%) had heterozygous mutations at both loci. Others had mutations on either the CYP2C19*2 or *3 locus. Higher genetic variation was observed in CYP2C19*2 than in CYP2C19*3 among Korean patients on warfarin therapy. Our data suggested that there is a higher incidence of bleeding complications in patients who have a higher allele frequency of CYP2C19. It was also revealed that the distribution of CYP2C19 polymorphism among Asian populations is more similar than of the distribution among Caucasian populations.

Frequency of CYP2C9 Genotypes among Omani Patients Receiving Warfarin and Its Correlation with Warfarin Dose

Objectives: This study was conducted to determine the frequency of CYP2C9 alleles in Omani patients receiving warfarin and to correlate genotyping data with warfarin dosage. The Omani population has Asian and African ethnicities. Methods: CYP2C9 genotypes were determined by the polymerase chain reaction restriction fragment length polymorphism method. Non-parametric Kruskal-Wallis test was used to compare groups of continuous data for significance differences. Results: Genotyping data showed that 12.7 and 5.8% of the samples were heterozygous for the CYP2C9*2 and CYP2C9*3 alleles, respectively. The CYP2C9*2 allele frequency was 0.074 in our population. It was 0.029 for CYP2C9*3. Conclusion: This is the first report on the presence of CYP2C9*2 allele homozygocity in any Asian or African population.

Allele variants of the cytochrome P450 2C9 genotype in white subjects from the netherlands with serious gastroduodenal ulcers attributable to the use of NSAIDs

Background: The most common serious adverse effects (AEs) associated with NSAID therapy are bleeding and perforated gastroduodenal ulcers. These AEs are dose related, and reduced oral clearance of NSAIDs associated with polymorphisms of cytochrome P450 (CYP) would, theoretically, increase the risk for AEs. Objective: The purpose of this study was to determine whether polymorphisms of the CYP2C9 genotype are associated with the development of serious complications of NSAID-related ulcers. Methods: We examined the records of patients with complications of serious NSAID-related ulcers who were hospitalized from November 2001 to December 2003. Diagnosis was confirmed by endoscopy or abdominal surgery, and a group of consecutive subjects was identified for genetic analysis. CYP2C9 allele frequencies were determined and compared with those in a matched cohort of subjects receiving stable weekly maintenance doses of oral coumarin anticoagulants. Allele frequencies also were compared with those in matched cohorts from earlier studies. Results: All 26 subjects with serious NSAID-related ulcers were white, 15 (58%) were female, and the median age was 74.5 years (range, 32–96 years). All 87 subjects in the reference group were white, 24 (28 %) were female, and the median age was 69 years (range, 48–81 years). CYP2C9 genotype frequencies did not differ significantly between subjects with serious complications of NSAID-related ulcers and subjects using oral coumarin anticoagulants. The genotype frequencies in both groups were similar to those reported in previous studies in white subjects. Conclusion: The CYP2C9 genotype was not a significant or clinically relevant risk factor in the development of serious NSAID-related ulcers in this group of subjects.

Frequency of CYP2C9 polymorphisms affecting warfarin metabolism in a large anticoagulant clinic cohort

Objectives: To assess allele frequency and genotype distribution of CYP2C9 polymorphisms in patients ( n = 189) attending an anticoagulant clinic in comparison to control patients ( n = 177) and also to assess if the patients with variant genotypes require lower doses of warfarin. Methods: Genotyping of the common CYP2C9 variants *2 and *3 was carried out by multiplexed PCR-RFLP while the *5 and *6 allele variants were genotyped by singleton PCR-RFLP. DNA sequencing was used to confirm genotype in all specimens with *3, *4 and *6 alleles. Results: CYP2C9 allele frequencies in patients were 0.81 for *1, 0.11 for *2 and 0.08 for *3, compared to 0.88, 0.08 and 0.04, respectively, in controls. Patients with *1/*3 and *X/ *X (where * X is *2 or *3) genotypes required 32 to 67% less warfarin in comparison to patients with the normal *1/*1 genotype. Other alleles were observed in less than 1% of subjects. Conclusions: Allele frequencies and genotypes for CYP2C9*2 and *3 variants in patients on warfarin are not statistically different from controls whether or not they are stratified for ethnicity. Less common genotypes (*4, *5, *6) do not contribute significantly to warfarin sensitivity among patients attending a routine anticoagulation clinic. CYP2C9 genotype predicts warfarin dosage even in an uncontrolled, retrospective survey of unselected patients on warfarin therapy.

CYP2C19 Genetic Polymorphism in Thai, Burmese and Karen Populations

The genetic polymorphism of CYP2C19 was examined in three Southeast Asian populations. This study was conducted in 774 Thais, 127 Burmeses and 131 Karens. Genomic DNA was extracted from leucocytes and analyzed by the PCR-RFLP technique. Genotype analysis revealed that the allele frequencies of CYP2C19*1, CYP2C19*2 and CYP2C19*3 in the Thais were 0.68, 0.29 and 0.03, respectively, and those of the Burmese population were 0.66, 0.30 and 0.04, respectively. For Karens, the minority ethnic in Mynmar, the allele frequencies of CYP2C19*1, CYP2C19*2 and CYP2C19*3 were 0.71, 0.28 and 0.01, respectively. The prevalence of PM estimated from genotype data among these three ethnic populations were 9.2%, 11.0%, and 8.4%, respectively. The PM phenotype and the frequencies of CYP2C19 defective alleles, particularly CYP2C19*3 among these three Southeast Asian ethnics appeared to be lower than other Asian populations. Lower prevalence of CYP2C19 PM suggests that these ethnics may have different capacity to metabolize drugs that are substrates of CYP2C19. Certain drug dosage regiments should be considered differently for Asian populations.

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Association between genetic polymorphisms of CYP2C19 and CYP2C9 and phenytoin serum concentration

To investigate the relationship between the genetic polymorphism of cytochrome CYP2C19 and CYP2C9 and the serum concentration of phenytoin (PHT) in patients with epilepsy. The peripheral blood samples of 200 patients with epilepsy aged 2 - 68, were collected to undergo PCR. Denaturing high performance liquid chromatography (DHPLC) was used to detect the PCR products so as to examined the 2 common CYP2C19 allele variants and one CYP2C9 allele. The patients were treated with PHT of the dosage of 1.00 - 18.02 mg/kg alone. After 5 half-life periods venous blood was collected before the administration. Fluorescence polarization immunoassay was used to measure the PHT serum concentration standardized by dosage and body weight. The allele frequencies of CYP2C19 * 2, CYP2C19 * 3, and CYP2C9 * 3 were 31%, 8%, and 6% respectively. Thirty-two patients with CYP2C19 and/or CYP2C9 allele variants were classified into 3 groups: extensive metabolizer (EM, n = 11) homozygous for CYP2C19 * 1/* 1 combined with CYP2C9 * 1/* 1 alleles, intermediate metabolizer (IM, n = 14) heterozygous for CYP2C19 * 1/* 2 or CYP2C19 * 1/* 3 alleles, and poor metabolizer (PM, n = 7) with the genotype of CYP2C19 * 2/* 2 or CP2C19 * 2/* 3, or CYP2C19 * 1/* 2 combined with CYP2C9 * 1/* 3. The genotype distribution rates of EM, IM, and PM were 34%, 44%, and 22% respectively. The PHT serum concentration of the PM group was (4.0 +/- 0.9) Css, significantly higher than that of the IM group [(3.0 +/- 0.9) Css, P < 0.05] and that of the EM group [(2.6 +/- 0.8) Css, P < 0.01] without a significant difference between the IM group and EM group. Phenytoin is metabolized via CYP2C19 and CYP2C9. The PHT serum concentration of the PM is significantly higher. Genotyping helps predict the clinical response to PHT administration.

Lower frequency of CYP2C9*2 in Mexican-Americans compared to Spaniards

Interethnic differences in cytochrome P450 polymorphism might be responsible, at least in part, for the variations in drug disposition between ethnic groups. Of the various CYP2C9 alleles, CYP2C9*2 and CYP2C9*3 have been reported to have altered catalytic activities compared to the wild-type CYP2C9*1. The present study is aimed at analysing the CYP2C9 polymorphism in a Mexican-American compared with a Spanish population. Differences between the two populations of healthy volunteers, Mexican-Americans (n=98 subjects) and Spaniards (n=102 subjects), regarding the CYP2C9 allele frequencies have been found. CYP2C9 genotypes among the studied Mexican-American population are in equilibrium. The 95% CI were, respectively, 0.81-0.90 for CYP2C9*1 (n=169), 0.05-0.13 for CYP2C9*2 (n=16) and 0.031-0.10 for CYP2C9*3 (n=11). CYP2C9*4, *5 and *6 were found in none of the studied subjects. The frequency of CYP2C9*2 was lower among Mexican-Americans compared to Spaniards (P<0.05). The obtained frequency of CYP2C9 alleles is compatible with the genomic assembly of the constitutive potential ethnic origin of this population, and supports the need of pharmacogenetic studies for optimizing the recommended drug dosages to Mexican-Americans.

Cytochrome P4502C9 (CYP2C9) genotypes in a Nordic population in Denmark.

The human CYP2C is a subfamily of P450 enzymes that metabolize approximately 20% of clinically used drugs (Goldstein 2001). The four members of the subfamily are: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 is an enzyme of major importance in human drug metabolism. Substrates for CYP2C9 include phenytoin (Banpai et al. 1996), S-warfarin (Rettie et al. 1992), acenocoumarol (Verstuyft et al. 2003a), losartan (Stearns et al. 1995), tolbutamide (Miners & Birkett 1996), glipizide (Kidd et al. 1999), fluvastatin (Kirchheiner et al. 2003) and some NSAIDs (Miners & Birkett 1998). Six different human CYP2C9 cDNA sequences have been reported to make the enzyme polymorphic (Stubbins et al. 1996). Since the wildtype CYP2C9*1 and the single nucleotide polymorphisms CYP2C9*2 and CYP2C9*3 were discovered first, they have undergone more thorough investigation showing that the allelic variants CYP2C9*2 and CYP2C9*3 encode enzymes with decreased substrate turnover (Craig et al. 2002; Kirchheiner et al. 2002; Shon et al. 2002). The CYP2C9*2 allele, which is derived from a C430→T single nucleotide polymorphism in exon 3, encodes the Arg144→Cys substitution, whereas a A1075→C single nucleotide polymorphism in exon 7 results in the substitution Ile359→Leu for CYP2C9*3 (Stubbins et al. 1996). The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 and the genotype frequencies of CYP2C9*1/*1, CYP2C9*1/*2, CYP2C9*1/*3, CYP2C9*2/*2, CYP2C9*2/*3 and CYP2C9*3/*3 for a Nordic population in Denmark were determined. Two hundred seventy-six healthy Nordic (mainly Danish) volunteers of Caucasian origin were enrolled in the study. The 154 males and 122 females aged 19–42 were primarily students at the University of Southern Denmark. The protocol was approved by The Scientific Ethical Committee for Vejle and Funen Counties. A written informed consent to participate in the study was obtained from the volunteers. Two×10 ml venous blood was obtained with EDTA as anticoagulant from each volunteer. The DNA from peripheral leukocytes was isolated by PUREGENETM genomic DNA purification kit by Gentra Systems, Minnesota 55441, USA, according to the guidelines of the manufacturer. Genotyping of variants was performed by allelic discrimination based on fluorescent PCR (Verstuyft et al. 2003b). Table 1 shows the genotype and allele frequencies of CYP2C9 for the population. Table 2 shows the comparison of allele and genotype frequencies of CYP2C9 in populations from different European studies. The CYP2C9 genetic polymorphism has been well studied in Caucasians and the frequencies of CYP2C9*1,CYP2C9*2 and CYP2C9*3 alleles found in the Nordic population were similar to those found in other European populations. The allelic frequencies were 83% (79–86%) for CYP2C9*1, 12% (9.5–15%) for CYP2C9*2 and 5.3% (3.5–7.5%) for CYP2C9*3. The expected frequency of CYP2C9*3/*3 in the Nordic population according to the Hardy-Weinberg law is (5.3%)2=0.28%. The expected number of CYP2C9*3/*3 in the Nordic population of 276 individuals is therefore 0.8. Not surprisingly, no CYP2C9*3/*3 was found in the population. The CYP2C9 polymorphism is of clinical relevance for drugs which are metabolized almost exclusively by the enzyme that has a small therapeutic index and for which clinical dose titration is not feasible. Warfarin is a very likely candidate, and clinical studies (Scordo et al. 2002) have shown that the CYP2C9 genotype is a major determinant of maintenance dose and metabolic clearance of S-warfarin. However, even within the 6 genotypes in table 1 and 2 Scordo et al. (2002) reported a considerable interindividual variability. Thus further studies are warranted before CYP2C9 genotyping can be recommended previous to warfarin treatment.

Association between the CYP2C9 polymorphism and the drug metabolism phenotype.

CYP2C9, an isoform of the cytochrome P450 enzyme, is involved in the metabolism of most of the drugs of choice for the treatment of thromboembolic disorders. Functional polymorphism is associated with two variant alleles (alleles *2 and *3) encoding CYP2C9 enzymes with a potentially different catalytic activity. The aim of the study was to determine the frequency of the CYP2C9 polymorphism in a representative sample of the Croatian population (n = 177) and to assess the association between the CYP2C9 polymorphism and the warfarin dose in patients with thromboembolism (n = 181). The CYP2C9 genotype was determined by polymerase chain reaction-restriction fragment length poymorphism (PCR-RFLP). According to the CYP2C9 genotype distribution, 31.2% of the healthy subjects were identified with a heterozygous or homozygous CYP2C9 variant genotype. The frequency of 2C9*2 and 2C9*3 alleles was 12.4% and 3.7%, respectively. There was no gender-related genotype or allele difference. In thromboembolism patients, the frequency of CYP2C9 alleles *2 and *3 was 17.4% and 6.6%, respectively, and did not differ significantly from the control group. Almost half (42.5%) of the patients carried at least one variant CYP2C9 genotype. The allele difference between patient subgroups receiving warfarin doses lower and higher than the optimal warfarin dose (4.1 mg/day) was significant (p = 0.027), especially for allele 2C9*3 (p = 0.019; OR 3.250, 95%, CI 1.263-8.413). Comparison of the warfarin dose between patients with different genotypes yielded a significant dose difference between the patients with wild-type genotype and those with variant genotypes (Kruskall-Wallis, chi2 = 9.745, p = 0.008). The results of the association of each of five genotype combinations with the warfarin maintenance dose revealed it to be significantly related to the genotype (Kruskall-Wallis, chi2 = 12.854, p = 0.025). Expressed as percentage of the mean dose in patients with wild-type alleles, the mean warfarin maintenance dose was 92% in 2C9*2 heterozygotes, 74% in 2C*3 heterozygotes, 61% in 2C9*2 homozygotes, 34% in 2C9*3 homozygotes and 63% in compound heterozygotes for 2C9*2 and 2C9*3. Although the mean maintenance dose in homozygous *2/*2 and compound *2/*3 genotype patients was markedly lower (mean 2.66 mg and 2.75 mg, respectively, vs. 4.37 mg), statistical analysis yielded no significance because of the small number of patients carrying these genotypes. A significantly lower maintenance dose was observed in the subgroup of heterozygous *1/*3 genotype patients (p = 0.022). These preliminary results suggest a significant association of the CYP2C9 polymorphism with the warfarin dose and underline the importance of pre-therapeutic genotyping to identify the subjects likely to develop undesirable drug effects.

CYP2C9 gene and susceptibility to major depressive disorder

Alteration of monoaminergic neurotransmission has been implicated in the pathophysiology of mood disorders, and CYP2C9 enzyme activity has been shown to be modulated by serotonin in vitro. The present study was aimed at analysing the frequency of CYP2C9 alleles (*1, *2, *3) among patients suffering from major depressive disorder. In all, 70 such suffering psychiatric outpatients were studied. The CYP2C9 genotypes were determined by allele-specific PCR. The CYP2C9*3 allele frequency was higher (P<0.01) among the patients suffering from major depression than in a population of 89 schizophrenic patients (odds ratio=3.3) and 138 healthy volunteers (odds ratio=2.8). The results suggest that CYP2C9 genetic polymorphism may be related to a major depressive disorder due to an alteration in endogenous metabolism, although a linkage between CYP2C9 and some other gene related to depression cannot be ruled out.

The effect of CYP2C19 and CYP2D6 genotypes on the metabolism of clomipramine in Japanese psychiatric patients.

In this study, the authors investigated the relationship between the metabolism of clomipramine (C) and the genotypes of cytochrome P450 (CYP) CYP2C19 and CYP2D6. Fifty-one Japanese patients (18 men and 33 women) were administered 10 to 250 mg/day of C by mouth and maintained on the same daily dose of C for at least 2 weeks to obtain steady-state concentrations. Plasma levels of C and its metabolites N-desmethylclomipramine (DC), 8-hydroxyclomipramine, and 8-hydroxy-N-desmethylclomipramine (HDC) were determined by high-performance liquid chromatography. The allele frequencies of CYP2C19*2, CYP2C19*3, CYP2D6*5, and CYP2D6*10 were 27.5%, 12.8%, 2.9%, and 43.1%, respectively. Subjects who were homozygous for mutated alleles of CYP2C19 showed approximately 75% higher concentrations of C corrected by dose and body weight compared with those who were homozygous for wild-type alleles. Also, subjects who were homozygous for mutated alleles of CYP2C19 showed an approximately 68% higher value of C/DC compared with those who were homozygous for wild-type alleles. No significant difference in the ratio of DC/HDC was observed between subjects who were homozygous for mutated alleles of CYP2D6 and those who were homozygous for wild-type alleles. These results suggest that genotyping CYP2C19 is useful for grossly predicting the risk of getting high plasma concentrations of C and the low individual capacity to demethylate C because there is marked interindividual variability within each genotype. However, the genotyping of CYP2D6 is not useful for predicting the individual capacity to hydroxylate DC.

Phenytoin metabolic ratio: a putative marker of CYP2C9 activity in vivo.

CYP2C9 mediates the oxidative metabolism of approximately 10% of drugs, some of which are characterized by a narrow therapeutic index. We aimed to validate genotype method and phenotype methodology, for evaluation of CYP2C9 activity in vivo. Thirty-one healthy subjects (22 male) received a single 300 mg dose of phenytoin. Blood was drawn periodically and urine was collected at intervals for 96 h. Plasma phenytoin and 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) and urine S and R enantiomers of p-HPPH were determined by high-performance liquid chromatography. CYP2C9 genotyping was obtained by polymerase chain reaction followed by digestion with Sau96I and StyI for the identification of CYP2C9*2 and CYP2C9*3, respectively. Eighteen subjects were CYP2C9*1 homozygous, seven were CYP2C9*2 heterozygous, four were CYP2C9*3 heterozygous, one was CYP2C9*2 homozygous and one was compound CYP2C9*2/CYP2C9*3 heterozygous. The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 were 0.76 [95% confidence interval (CI) 0.73-0.79], 0.16 (95% CI 0.13-0.19) and 0.08 (95% CI 0.05-0.11), respectively. The CYP2C9-mediated production of (S)-p-HPPH represented the major metabolic pathway of phenytoin biotransformation as its excretion accounted for 95.6 + 0.9% of 'total' p-HPPH excretion over the 96 h collection interval. Phenytoin metabolic clearance to produce (S)-p-HPPH (PMC), correlated significantly with (S)-p-HPPH (or 'total' p-HPPH) content in 0-8, 0-12 and 0-24 urine collections (r = 0.88, 0.85 and 0.89, respectively) and with phenytoin metabolic ratio (PMR) defined as the ratio of urine (S)-p-HPPH (or 'total' p-HPPH) to mid-interval plasma phenytoin (r = 0.90, 0.88 and 0.94, respectively). PMC and PMR exhibited a gene-dose effect so that the highest and lowest values were noted in homozygous subjects CYP2C9*1 and subjects carrying two defective alleles, respectively, whereas heterozygous subjects had intermediate values. CYP2C9 genotyping and several phenytoin metabolic indices are correlated with CYP2C9 activity in vivo. The utility of phenytoin to predict the metabolism of other CYP2C9 substrates justifies further evaluation.

Interindividual variability in sensitivity to warfarin--Nature or nurture?

Interindividual variability in responses to warfarin is attributed to dietary vitamin K, drug interactions, age, or genetic polymorphism in the cytochrome P4502C9 enzyme (CYP2C9) (allelic variants 2C9*2 and 2C9*3 ) linked with impaired metabolism of the potent enantiomere S-warfarin. We quantified the relative effects of age and of simultaneously determined CYP2C9 genotype, plasma warfarin and vitamin K concentrations, and concurrent medications on warfarin maintenance doses in 156 patients at optimized stable anticoagulation. Allele frequencies for CYP2C9*1, CYP2C9*2, and CYP2C9*3 were 0.84, 0.10, and 0.06. Warfarin doses were 6.5 +/- 3.2, 5.2 +/- 2.4, and 3.3 +/- 2.0 mg/d in the 3 genotype groups (P < .0001). Warfarin doses decreased with age as follows: 7.7 +/- 3.7 versus 4.9 +/- 2.9 mg/d at < 50 years and >66 years (P < .001), mainly as a result of decreased plasma warfarin clearance (2.8 +/- 1.4 mL/min versus 1.9 +/- 0.8 mL/min; P < .001). Vitamin K (1.6 +/- 1.1 ng/mL) did not differ among the age or genotype groups. Patients >or=66 years old with the CYP2C9*3 allele required only 2.2 +/- 1.2 mg/d compared with 7.9 +/- 3.7 mg/d in those <or=65 years old bearing the CYP2C9*1 allele (P < .001). On multiple regression, warfarin maintenance doses were independently associated with plasma warfarin (reflecting its metabolic clearance) (r (2) = 0.26), age (possibly reflecting increased intrinsic sensitivity) (r (2) = 0.12), and genotype (reflecting S-warfarin levels) (r (2) = 0.10) but not with plasma vitamin K. At optimized steady state, individual sensitivity to warfarin is determined by CYP2C9 genotype and age with no effect of vitamin K. Prospective studies will determine the impact of these findings in clinical practice.

Frequency of cytochrome P450 2C9 mutant alleles in a Korean population.

To determine the frequencies of CYP2C9 variants in the Korean population and compare them with the frequencies in other ethnic populations. Genotyping of CYP2C9*2 and CYP2C9*3 allelic variants was carried out in 574 Korean subjects by PCR and restriction fragment length pattern analysis. Thirteen of 574 subjects (2.3%) were heterozygous for CYP2C9*3 (Ile359Leu), but no subjects with a CYP2C9*2 allele or homozygous for CYP2C9*3 were identified. The allele frequency of CYP2C9*3 in Korean subjects (0.0113, 95% CI 0.0066-0.0193) was similar to that of other East Asian populations, but was considerably lower than that of Caucasian populations. CYP2C9*3 seems to be an allelic variant related to the functional polymorphism of CYP2C9, but this variant is rarely seen among Koreans compared with Caucasians. Routine genotyping of the CYP2C9*2 allele is considered to be unnecessary in Korean and East Asians, because this allele appears to be extremely rare or absent in these populations.