Phenotypes and genotypes for CYP2D6 and CYP2C19 in a black Tanzanian population

AIMS: CYP2D6 and CYP2C19 are polymorphically expressed enzymes that show marked interindividual and interethnic variation. The aim of this study was to determine the frequency of the defective alleles in CYP2D6 and CYP2C19 in Africans and to test whether the genotype for CYP2C19 is better correlated with the proguanil/cylcoguanil ratio than the mephenytoin S/R ratio. METHODS: Two hundred and sixteen black Tanzanians were phenotyped for CYP2D6 with the use of sparteine, and for CYP2C19 with the use of mephenytoin and proguanil. Of these 196 subjects were also genotyped for CYP2D6 (including the CYP2D6*1, CYP2D6*3 and CYP2D6*4 alleles) and 195 were genotyped for CYP2C19 (including the CYP2C19*1, CYP2C19*2 and the CYP2C19*3 alleles). Furthermore 100 subjects were examined for the allele duplication in CYP2D6, leading to ultrarapid metabolism, with long PCR. RESULTS: The sparteine metabolic ratio (MR) was statistically significantly higher in the Tanzanian group of homozygous, extensive metabolizers compared to a historical control group of white Danish extensive metabolizers. Only one poor metabolizer for CYP2D6 (MR=124 and genotype CYP2D6*1/CYP2D6*4 ) was found. The gene frequencies were 0.96 for the CYP2D6*1 allele and 0.04 for the CYP2D6*4 allele. No CYP2D6*3 alleles were found. Nine subjects had an allele duplication in CYP2D6 (9%). For CYP2C19 there were seven subjects (3. 6%) who were phenotyped as poor metabolizers, but only three subjects (1.5%) had a genotype (CYP2C19*2/CYP2C19*2 ) indicative of poor metabolism. The gene frequencies were 0.90 for the CYP2C19*1 allele and 0.10 for the CYP2C19*2 allele. No CYP2C19*3 alleles were found. The mephenytoin S/R ratios were not bimodally distributed. CONCLUSIONS: Both the genotyping and phenotyping results show that there is a substantial difference between an African black population and a Caucasian population in the capacity to metabolize drugs via CYP2D6 and CYP2C19.     

Polymorphisms of CYP2C19 and CYP2D6 in Israeli Ethnic Groups

BACKGROUND: The cytochrome P450 isoenzymes CYP2C19 and CYP2D6 catalyze reactions involved in the metabolism of many widely used drugs. Their polymorphisms give rise to important interindividual and interethnic variability in the metabolism and disposition of several therapeutic agents and may cause differences in clinical response to some drugs. Individuals who carry two null alleles of either gene are known as poor metabolizers (PMs), while those who carry more than two copies of the functional CYP2D6 gene are ultrarapid metabolizers (UMs). AIM: The aim of the current study was to genotype Israelis from four different ethnic backgrounds with respect to CYP2C19 and CYP2D6. STUDY DESIGN: Polymorphisms of the CYP2C19 and CYP2D6 genes were determined by genotyping the four ethnic groups using PCR and/or restriction fragment length polymorphism (RFLP) analysis. The groups consisted of three Jewish communities, Yemenite Jews (n = 36), Sephardic Jews (n = 47), Ethiopian Jews (n = 28), and one Arabian population, Bedouins (n = 50). RESULTS: CYP2C19*2 allele frequencies ranged from 12.0 to 19.6% among the four ethnic groups. Within the study population, the CYP2C19*3 gene was only found in one Bedouin individual, in the heterozygous state (CYP2C19*1/*3). In each group, one individual was homozygous for CYP2C19*2, and were predicted to be PMs. The data revealed a high prevalence of CYP2D6*2, *4, *10, *41, and gene duplication, followed by *5 and *17, while *3 was very rare. The frequencies of the CYP2D6*4, *10, and *17 alleles and CYP2D6 gene duplication were significantly different among the four groups. However, the CYP2D6*2, *3, and *5 and *41 alleles showed similar frequencies in the four groups. Four (8.5%) Sephardic Jews and one (2.0%) Bedouin were found with the genotype CYP2D6*4/*4 (two null alleles), and were thus presumably PMs. A total of 15 individuals, distributed in all groups, were found with functional CYP2D6 gene duplications. The frequencies of predicted UMs (duplication of CYP2D6) were 17.8% (5/28) and 12.8% (6/47) in Ethiopian Jews and Sephardic Jews, respectively, which were higher than that of Yemenite Jews (5.6%, 2/36) and Bedouins (4.0%, 2/50). CONCLUSIONS: This is the first study of the CYP2D6 gene polymorphism in Israeli ethnic groups, either Jewish or Arab. Furthermore, this is also the first study of the CYP2C19 gene polymorphism in Jewish or Arab subgroups living in Israel. The frequencies of various alleles for the CYP2D6 gene are significantly different among the ethnic groups in Israel. These new findings may have important clinical implications in administrating drugs metabolized by CYP2D6 and for CYP2D6-related adverse drug reactions in the Israeli population.     

Interferon-beta treatment in patients with multiple sclerosis does not alter CYP2C19 or CYP2D6 activity

AIMS: To determine CYP2C19 and CYP2D6 activity in patients with multiple sclerosis (MS) before and during interferon (IFN)-beta treatment. METHODS: CYP2C19 and CYP2D6 activities were assessed using the probe drugs mephenytoin and debrisoquine, respectively. Urinary mephenytoin (S/R) and debrisoquine (debrisoquine/hydroxy-debrisoquine) metabolic ratios (MR) were determined in 10 otherwise healthy Caucasian multiple sclerosis (MS) patients in the initial stage of the disease, prior to and 1 month after commencing treatment with IFN-beta (Avonex, Rebif or Betaferon). In addition, CYP2C19*2, CYP2C19*3, CYP2D6*3, CYP2D6*4, and CYP2D6*5 genotyping was performed. RESULTS: There was no significant difference in the (S)/(R) mephenytoin ratio (mean difference 0.04; 95% CI -0.03, 0.11) or the debrisoquine MR (mean difference 0.29; 95% CI -0.44, 1.02) before and during regular IFN-beta treatment in extensive metabolizers (EM) (P = 0.5 and P = 0.4 for the respective probe drugs; n = 9 subjects). There were also no differences between the different IFN-beta treatments (P = 0.6 for the (S)/(R) mephenytoin ratio and P = 0.7 for the debrisoquine MR; anova; n = 10). CONCLUSIONS: IFN-beta treatment did not affect the activity of CYP2C19 or CYP2D6. The results suggest that it is safe to administer CYP2C19 or CYP2D6 substrates, without dose adjustment, to patients treated with IFN-beta.     

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.     

Allele and genotype frequencies of CYP2C9, CYP2C19 and CYP2D6 in an Italian population.

The polymorphic cytochrome P450 isoenzymes (CYPs) 2C9, 2C19 and 2D6 metabolise many important drugs, as well as other xenobiotics. Their polymorphism gives rise to important interindividual and interethnic variability in the metabolism and disposition of several therapeutic agents and may cause differences in the clinical response to these drugs. In this study, we determined the genotype profile of a random Italian population in order to compare the CYP2C9, CYP2C19 and CYP2D6 allele frequencies among Italians with previous findings in other Caucasian populations. Frequencies for the major CYP2C9, CYP2C19 and CYP2D6 mutated alleles and genotypes have been evaluated in 360 unrelated healthy Italian volunteers (210 males and 150 females, aged 19-52 years). Genotyping has been carried out on peripheral leukocytes DNA by molecular biology techniques (PCR, RFLP, long-PCR). CYP2C9, CYP2C19 and CYP2D6 allele and genotype frequencies resulted in equilibrium with the Hardy-Weinberg equation. One hundred and fourteen subjects (31.7%) carried one and 23 subjects (6.4%) carried two CYP2C9 mutated alleles. Sixty-eight (18.9%) volunteers were found to be heterozygous and six (1.7%) homozygous for the CYP2C19*2, while no CYP2C19*3 was detected in the evaluated population. Volunteers could be divided into four CYP2D6 genotypes groups: 192 subjects (53.3%) with no mutated alleles (homozygous extensive metabolisers, EM), 126 (35.0%) with one mutated allele (heterozygous EM), 12 (3.4%) with two mutated alleles (poor metabolisers, PM) and 30 (8.3%) with extracopies of a functional gene (ultrarapid metabolisers, UM). Frequencies of both CYP2C9 and CYP2C19 allelic variants, as well as CYP2D6 detrimental alleles, in Italian subjects were similar to those of other Caucasian populations. Conversely, the prevalence of CYP2D6 gene duplication among Italians resulted very high, confirming the higher frequency of CYP2D6 UM in the Mediterranean area compared to Northern Europe.     

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.     

The prevalence of CYP2C19 genotypes in a population of healthy Dutch volunteers and apparent gender differences in phenotypes

We reported the prevalence of poor metabolizers of CYP2C19 to be 1.8% in a sample of the Dutch population ( n =4301; [ 1 ]). These data were obtained by phenotyping. In that study pronounced oral contraceptive related gender differences for CYP2C19 activity were reported. The present study was performed to estimate the prevalence of non-coding mutations of CYP2C19 leading to the poor metabolizer phenotype. Furthermore, the data were analysed for gender differences.
Seven hundred and sixty-five unrelated healthy volunteers were evaluated for their CYP2C19 status. Subjects were phenotyped using mephenytoin. Genotyping was performed by the polymerase chain reaction (PCR) and restriction analysis for the most common null alleles.
For CYP2C19*2 and CYP2C19*3 a frequency of 13.3% and 0.2%, respectively, was observed. The S/R-ratio was significantly higher in heterozygous subjects (S/R-ratio=0.22) compared with homozygous wild type subjects (S/R-ratio=0.11). Comparison of all subjects below 45 years showed a significantly higher S/R-ratio in females compared with males especially in heterozygous subjects (S/R-ratio: 0.39 vs 0.19; P <0.001).
The frequencies of CYP2C19 allelic variants in a population of Dutch healthy volunteers were in accordance with data on other European populations. Assessment of * 2 and * 3 for CYP2C19 predicted the phenotype with an accuracy of over 98.6%. Gene-dose effect existed for CYP2C19. CYP2C19 heterozygous females had a decreased CYP2C19 activity that may be at least partly due to the use of oral contraceptives.     

CYP2C19 genotype and S-mephenytoin 4′-hydroxylation phenotype in a Chinese Dai population

AIMS: To investigate the incidence of the CYP2C19 polymorphism in the Chinese Dai population. METHODS: One hundred and ninety-three healthy Chinese Dai volunteers were identified with respect to CYP2C19 by genotype and phenotype analyses. A polymerase chain reaction-restriction fragment length polymorphism method was performed for genotyping procedures. The 4'-hydroxymephenytoin (4'-OH-MP) and S/R-mephenytoin ( S/R-MP) excreted in the urine were determined by high-performance liquid chromatography and gas chromatography, respectively. RESULTS: Eighteen subjects were identified as poor metabolisers (PMs). The frequency of PMs in the Chinese Dai subjects was 9.3% (95% confidence interval 5.2, 13.4), which is lower than that in the Chinese Han population ( P<0.05). Chinese Dai subjects had a higher frequency of the mutant CYP2C19*2 allele (0.303) and a lower frequency of the mutant CYP2C19*3 allele (0.034). These two mutant alleles could explain all deficiencies of CYP2C19 activity in the Chinese Dai subjects. The frequency of the CYP2C19*3 allele is significantly lower than that in the Chinese Han population ( P<0.05). The mean S/R ratio was lower in the homozygous extensive metabolisers (EMs) compared with that in heterozygous EMs ( P<0.01), and the latter was lower than that in the PMs ( P<0.01). Furthermore, the mean S/R ratio in CYP2C19*3/ CYP2C19*2 heterozygous PMs was possibly lower than that in the CYP2C19*2/ CYP2C19*2 homozygous PMs ( P<0.05). CONCLUSION: The frequencies of PMs and CYP2C19*3 allele in the Chinese Dai population are significantly lower than those in the Han population. The CYP2C19 genotype analysis is largely consistent with the mephenytoin phenotype analysis. The variability of S/R ratios in EMs and PMs shows a gene-dosage effect.     

Polymorphisms in NAT2, CYP2D6, CYP2C19 and GSTP1 and their association with prostate cancer

The development of prostate cancer is dependent on heredity, androgenic influences, and exposure to environmental agents. A high intake of dietary fat is associated with an increased risk of prostate cancer, either through influence on steroid hormone profiles or through production of carcinogenic compounds that require biotransformation by enzymes. The polymorphic glutathione S-transferase (GST), N-acetyltransferase (NAT), and cytochrome P450 (CYP) enzymes are of particular interest in prostate cancer susceptibility because of their ability to metabolize both endogenous and exogenous compounds, including dietary constituents. Association between different NAT2, CYP2D6, CYP2C19 and GSTP1 genotypes and prostate cancer was studied in a Swedish and Danish case-control study comprising 850 individuals. The combined Swedish and Danish study population was analysed by polymerase chain reaction for the NAT2 alleles *4, *5A, *5B, *5C, *6 and *7, and for the CYP2D6 alleles *l, *3 and *4. The Swedish subjects were also analysed for the CYP2C19 alleles *1 and *2, and the GSTP1 alleles *A, *B and *C. No association was found between prostate cancer and polymorphisms in NAT2, CYP2D6, CYP2C19 or GSTP1. An association between CYP2D6 poor metabolism and prostate cancer was seen among smoking Danes; odds ratio 3.10 (95% confidence interval 1.07; 8.93), P = 0.03, but not among smoking Swedes; odds ratio 1.19 (95% confidence interval 0.41; 3.42), P = 0.75. Smoking is not a known risk factor for prostate cancer, and the association between CYP2D6 poor metabolism and prostate cancer in Danish smokers may have arisen by chance.     

Impact of CYP2D6 intermediate metabolizer alleles on single-dose desipramine pharmacokinetics

This study utilized cytochrome P450 2D6 (CYP2D6) genotypes to explain variability of desipramine pharmacokinetics in a cohort of non-poor metabolizer individuals. In an interaction study utilizing desipramine as a probe, genotyping for the CYP2D6*3, *4, *5 and *6 alleles was used to screen out CYP2D6 poor metabolizers. Individuals were categorized according to these and additional alleles (CYP2D6*2, *9, *10, *17, *41 and x2). Genotypes of individuals heterozygous for two or three of *2, *17 and *41 alleles were confirmed by molecular haplotyping. Pharmacokinetic parameters of desipramine were analysed according to CYP2D6 category. Molecular haplotyping was necessary to definitively categorize four of 16 individuals. A subject who had unusually high plasma elimination half-time, exposure and metabolic ratios carried an intermediate metabolizer (IM) *9 allele in combination with a non-functional allele. This combination has a population frequency of less than 1 : 200. Individuals with *1/*1, *1/*2 and *2/*2 genotypes had lower than average plasma elimination half-time, exposure and metabolic ratios. For desipramine, additional genotyping of CYP2D6 IM alleles helped define subgroups of the CYP2D6-positive cohort. This suggests that genotyping for IM alleles will aid in interpretation of clinical trials involving CYP2D6 substrates. Due to the diversity of IM alleles, molecular haplotyping may be necessary to fully characterize CYP2D6 genotype-phenotype relationships.     

Genotypes for the cytochrome P450 enzymes CYP2D6 and CYP2C19 in human longevity Role of CYP2D6 and CYP2C19 in longevity

Objective: To test whether some genotypes for CYP2D6 or CYP2C19 could contribute to longevity, we genotyped 241 Danish nonagenarians and centenarians for CYP2D6 and CYP2C19. Methods: For CYP2D6 we identified the alleles CYP2D6*1, CYP2D6*3 and CYP2D6*4 with allele-specific polymerase chain reaction (PCR). The CYP2D6*5 alleles were identified with a long PCR method. For CYP2C19 we identified the alleles CYP2C19*1, CYP2C19*2 and CYP2C19*3 with an oligonucleotide ligation assay. Results: The four alleles for CYP2D6 did not occur in Hardy-Weinberg proportions. The frequency of poor metabolism was slightly higher (10.2%) than expected [7.7%; odds ratio (OR) = 1.36 (0.75–2.40)]. The genotypes for CYP2C19 occur in Hardy-Weinberg proportions. The frequency of poor metabolism (3.8%) was not significantly different from a young control group [3.1%; OR = 1.21 (0.26–5.75)]. Conclusion: CYP2D6 could play a role in human longevity due to the lack of Hardy-Weinberg proportions. If CYP2D6 only plays a role in longevity by protecting the poor metabolizers from cancer, we should expect a rise in the frequency in these genotypes in Denmark from 7.7% among young adults to 10–11% among very old people. We found a frequency of poor metabolism of 10.2% in the very old group. CYP2C19 is – due to the occurrence of Hardy-Weinberg proportions and the expected number of poor metabolizers – unlikely to contribute to human longevity.     

Polymorphism of CYP2D6, CYP2C19, CYP2C9 and CYP2C8 in the Faroese population

Objective The purpose of the study was to study the distribution of poor and extensive metabolizers of CYP2C19 and CYP2D6 and to genotype for CYP2C8 and CYP2C9 among 312 randomly selected Faroese.Methods and results The participants were phenotyped for CYP2D6 with the use of sparteine. The distribution of the sparteine metabolic ratio (sparteine/didehydrosparteines) was bimodal, and 14.5% (n=44; 95% CI: 10.7–18.9%) of the subjects were phenotyped as poor metabolizers. The frequency of poor metabolizers was higher (P=0.0002; ² test) among the Faroese than in other European populations (7.4%). Genotype analyses for the CYP2D6*3, *4, *6 and *9 alleles were performed using real-time polymerase chain reaction (PCR) (TaqMan, Foster City, CA, USA), and we found 14.6% (n = 45) (95% CI: 10.8–19.0%) with deficient CYP2D6 genes (*3/*4, *4/*4, *4/*6, *6/*6) in the Faroese population. The subjects were phenotyped for CYP2C19 with the use of mephenytoin and 10 subjects, i.e., 3.2% (95% CI: 1.6–5.9%) were phenotyped as poor metabolizers. Genotype analysis for the CYP2C19*2 and *3 alleles was performed by means of PCR analysis, and 2.9% (n=9) (95% CI: 1.3–5.4%) of the Faroese were found to have a deficient CYP2C19 gene all explained by the CYP2C19*2/*2 genotype. The allele frequencies of the CYP2C9*2 and CYP2C9*3 alleles were 8.8% (95% CI: 6.7–11.4%) and 5.3% (95% CI: 3.7–7.4%), respectively, while the CYP2C8*3 allele frequency was 6.9% (95% CI: 5.0–9.2%). Real-time PCR (TaqMan) was used for both CYP2C9 and CYP2C8 genotype analyses.Conclusion The frequency of CYP2D6 poor metabolizers is twofold higher among the Faroese population than other Caucasians, while the frequencies of Faroese subjects with decreased CYP2C19, CYP2C8 and CYP2C9 enzyme activity are the same as seen in other Caucasian populations. A possible consequence might be a higher incidence of side effects among Faroese patients taking pharmaceuticals that are CYP2D6 substrates.     

CYP2D6*10 alleles do not determine plasma fluvoxamine concentration/dose ratio in Japanese subjects

OBJECTIVE: The purpose of the present study was to investigate whether plasma fluvoxamine (FV) concentration is associated with CYP2D6*10 allele polymorphisms. METHODS: Subjects were 46 Japanese patients (21 males) carrying neither *3, *4 nor *5 alleles and treated orally using FV. Venous blood was obtained from each patient for determination of FV concentration/dose (C/D) ratio (plasma concentration of FV divided by daily dose of FV per body weight) and CYP2D6 genotyping. RESULTS: No significant differences in FV C/D ratio were found between subjects with no (n=13), one (n=18) or two (n=15) *10 alleles. CONCLUSION: Our results indicate that CYP2D6*10 genotypes do not exert significant effects on FV C/D ratio. As CYP2D6 genotypes differ with ethnic background, further studies should be conducted in different populations.     

Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan O-demethylation in different CYP2D6 genotypes

AIMS: To determine the frequencies of 11 CYP2D6 mutant alleles (CYP2D6*2, *3, *4, *5, *8, *10, *11, *12, *14, *17 and *18), and their relation to the metabolic capacity of CYP2D6 in Japanese subjects. METHODS: One hundred and sixty-two unrelated healthy Japanese subjects were genotyped with the polymerase chain reaction amplification method and 35 subjects were phenotyped with dextromethorphan. RESULTS: The frequencies of CYP2D6*2,*5, *10 and *14 were 12.9, 6.2, 38.6 and 2.2% in our Japanese subjects, respectively. CYP2D6*3, *4, *8, *11, *12, *17 and *18 were not detected. The mean log metabolic ratio of dextromethorphan in subjects with genotypes predicting intermediate metabolizers was significantly greater than that of heterozygotes for functional and defective alleles. CONCLUSIONS: CYP2D6*5 and CYP2D6*14 are the major defective alleles found in Japanese subjects. In addition, CYP2D6*10 may play a more important role than previously thought for the treatment of Japanese patients with drugs metabolized by CYP2D6.     

Lack of influence of CYP2D6 genotype on the clearance of (R)-, (S)- and racemic-methadone

OBJECTIVE: To investigate the influence of CYP2D6 genotype on the oral clearance of (R)-, (S)- and rac-methadone. METHODS: In this retrospective study, CYP2D6 genotypes were identified in 56 methadone maintained subjects. Plasma concentrations of (R)-, (S)- and rac-methadone were determined by stereoselective HPLC and sufficient data were available to estimate the apparent oral clearances of (R)-, (S)- and rac-methadone using a population kinetic model in 37 of the genotyped subjects. RESULTS: The CYP2D6 allele frequencies were similar to those previously reported in Caucasians, the most common being: CYP2D6*1 (35.2%), CYP2D6*2 (12.0%) and CYP2D6*4 (22.2%). Three unknown SNPs were found in four subjects: 1811G > A (n = 1), 1834C > T (n = 1) and 2720G > C (n = 2). The oral clearances of (R)-, (S)- and rac-methadone varied 5.4-, 6.8- and 6.1-fold, respectively. No significant differences in methadone oral clearance were found between CYP2D6 genotypic PM, IM and EM (p = 0.57, 0.40 and 0.43 for (R)-, (S)- and rac-methadone, respectively). Only 1 subject had duplication of functional CYP2D6 alleles and the oral clearance of the three analytes was not markedly altered. CONCLUSIONS: CYP2D6 poor, intermediate and extensive metabolizer genotypes did not appear to impact on the oral clearance of (R)-, (S)- or rac-methadone. In addition, methadone dosage requirements were not influenced by CYP2D6 genotypes in these subjects. However, the impact of duplication of functional CYP2D6 alleles on oral clearance and dosage requirements requires further investigation.     

CYP2C19 Genetic Polymorphism in Saudi Arabians

The main objective of this study was to evaluate CYP2C19 genetic polymorphism in a Saudi Arabian population by determining the frequencies of CYP2C19*2, *3, *4, *6, *7 and *17 alleles and their relevant genotypes. Genomic DNA was isolated from 192 healthy Saudi Arabians, representing different geographical regions, and genotyping of the selected CYP2C19 variants was carried out by direct sequencing after PCR amplification. The allelic frequency of heterozygous CYP2C19*2 was 8.2% with only one individual found to carry the homozygous genotype of this defective allele. None of the other investigated poor metabolizer alleles (i.e. CYP2C19*3, *4, *6 and *7) was detected in the study population. About 46% of the examined volunteers were found to carry CYP2C19*17 genotype (37.5% heterozygous and 8.1% homozygous of the defective allele) with an overall CYP2C19*17 allelic frequency of 26.9%. In addition, a novel CYP2C19 SNP (G356A) and another very rare SNP (C336T) have been identified in this study with a frequency of about 50% for each. Further studies are required to evaluate the metabolic and clinical relevance of CYP2C19*17, G356A and C336T in the Saudi Arabian population.     

三维凝胶基因芯片法研究中国人群CYP2C9与CYP2C19基因多态性

目的：应用三维凝胶基因芯片方法研究中国人群CYP2C9与CYP2C19基因多态性,为临床合理用药提供新的技术手段与研究方法。方法：提取207名男性健康志愿者基因组DNA,PCR分别扩增包含CYP2C9＊3、＊13与CYP2C19＊2、＊3多态位点目标片段,制备三维凝胶基因芯片,荧光标记探针杂交,芯片扫描并基因分型,用直接测序法对结果进行验证。结果：207人中,11人为CYP2C9＊1/＊3基因型,1人为CYP2C9＊1/＊13基因型,1人为CYP2C9＊3/＊3基因型。2C9＊3、＊13等位基因发生率分别为2.90%、0.24%,慢代谢型发生率为0.48%。CYP2C19突变杂合子有97人,突变纯合子有26人,2C19＊2、＊3等位基因发生率分别为32.85%、3.62%,慢代谢型发生率为12.56%。四种等位基因型分布均符合Hardy-Weinberg平衡。结论：三维凝胶基因芯片方法可为临床快速基因分型提供高效平台。CYP2C9与CYP2C19基因在中国人群存在普遍多态性,检测其基因型可有效指导相关临床治疗药物应用,提高药效,降低不良反应。     

Allele and genotype frequencies of polymorphic cytochromes P450 (CYP2C9, CYP2C19, CYP2E1) and dihydropyrimidine dehydrogenase (DPYD) in the Egyptian population

AIMS: The goal of this study was to determine the frequencies of important allelic variants of CYP2C9, CYP2C19, CYP2E1 and DPYD in the Egyptian population and compare them with the frequencies in other ethnic populations. METHODS: Genotyping of CYP2C9 (*2 and *3), CYP2C19 (*2 and *3), c2 variant of CYP2E1 and DPYD alleles (*2 A-*6 ) was carried out in a total of 247 unrelated Egyptian subjects. An allele-specific fluorogenic 5' nuclease chain reaction assay was applied for detection of CYP2C9 and CYP2C19 variants. Other variants of the CYP2E1 and DPYD genes were determined using polymerase chain reaction (PCR)-restriction fragment length polymorphism and allele-specific PCR based assays. RESULTS: CYP2C9 allele frequencies in 247 Egyptian subjects were 0.820 for CYP2C9*1, 0.120 for CYP2C9*2 and 0.060 for CYP2C9*3. For CYP2C19, the frequencies of the wild type (CYP2C19*1) and the nonfunctional (*2 and *3) alleles were 0.888, 0.110 and 0.002, respectively. CYP2C19*3, which is considered an Asian mutation, was detected in one subject (0.40%) who was heterozygous (*1/*3). Two subjects (0.80%) were homozygous for *2/*2, while no compound heterozygotes (*2/*3) or homozygotes for *3 were detected. For CYP2E1, only four subjects (1.70%) had the rare c2 variant, expressed heterozygously, giving an allele frequency of 0.009. Five variants of DPYD were analysed, with no splice sites (*2 A) or DeltaC1897 (*3) found in this population. The frequencies of other variants were 0.028, 0.115 and 0.090 for *4, *5 and *6, respectively. CONCLUSIONS: Comparing our data with that obtained in several Caucasian, African-American and Asian populations, we found that Egyptians resemble Caucasians with regard to allelic frequencies of the tested variants of CYP2C9, CYP2C19, CYP2E1 and DPYD. Our results may help in better understanding the molecular basis underlying ethnic differences in drug response, and contribute to improved individualization of drug therapy in the Egyptian population.     

Frequency of mutated allele CYP2D6*4 in the Turkish population

The frequency of functionally important mutations and alleles of the gene coding for CYP2D6 shows wide ethnic variations. The present study aimed to determine the most common mutated allele CYP2D6*4 gene in a Turkish population of 100 unrelated subjects, by using real-time PCR with fluorescent probe. CYP2D6*4 allele was not detected in 62 subjects (62%). Among the remaining 38 subjects (38%), 4 (4%) were carriers of two *4 alleles, being homozygous for CYP2D6 and genotyped as CYP2D6*4/*4. 34 subjects (34%) were carriers of one *4 allele, being heterozygous for CYP2D6*4. The frequency of allele *4 was 0.21. These data indicate that 4% of the Turkish individuals living in the city of Bursa are carriers of two nonfunctional mutated alleles *4, being homozygous for CYP2D6*4. It is clinically important to be able to identify those individuals who are likely to have altered pharmacokinetics for CYP2D6 substrates in order to avoid adverse drug reactions.     

CYP2D6 and CYP2C19 activity in a large population of Dutch healthy volunteers: indications for oral contraceptive-related gender differences

OBJECTIVE: We examined a large database containing results on CYP2D6 and CYP2C19 activity of 4301 Dutch volunteers phenotyped in the context of various clinical pharmacology studies. METHODS: The subjects were given 22 mg dextromethorphan, 100 mg mephenytoin and 200 mg caffeine. For CYP2D6, the dextromethorphan/dextrorphan metabolic ratios in urine samples taken for a subsequent 8 h were used. Dextromethorphan and dextrorphan were quantified by reversed-phase high performance liquid chromatography. For CYP2C19 similarly obtained (R)-mephenytoin and (S)-mephenytoin ratios were used. (S)-mephenytoin and (R)-mephenytoin were analysed and quantified by enantioselective capillary gas chromatography. In addition, CYP2C19 poor metabolizer (PM) subjects were reanalysed after acidic pre-treatment of urine samples to confirm the PM status. RESULTS: The investigated population mainly comprised Caucasian (98.9%) males (68%). The age ranged from 18 to 82 years. For CYP2D6, it was found that 8.0% of the subjects were PMs. The average metabolic ratio was 0.014 (0.033) for subjects who showed extensive metabolizing activity (EM) and 5.4 (7.6) for PM subjects. For CYP2C19, it was found that 1.8% of the subjects were PMs. The metabolic ratio was 0.162 (0.124) for EM subjects and 1.076 (0.040) for PM subjects. Within the EM group the metabolic ratio in females was significantly lower for CYP2D6 (-20%) and significantly higher for CYP2C19 (+40%) compared with males. For PMs there was no such difference for CYP2D6 (P = 0.79) or CYP2C19 (P = 0.20). Oral contraceptive (OC) use significantly decreased the CYP2C19 activity by 68% for mephenytoin as compared to non-OC using females. CONCLUSIONS: For CYP2D6, the PM incidence (8.0%) is in accordance with literature data. The CYP2C19, PM incidence (1.8%) is low compared to reports from other European countries. For mephenytoin, the acidification procedure has been shown to be very important for the confirmation of CYP2C19 PMs. In EM females compared to EM males, CYP2D6 activity is increased and CYP2C19 activity is reduced. For CYP2C19 in particular this reduction is substantial and most pronounced in the age range from 18 to 40 years. For CYP2C19, the reduced activity is associated with the use of oral contraceptives.