CYP2D6 Gene Polymorphisms Research Articles

Characterization of the CYP2D6 Gene Locus and Metabolic Activity in Indo- and Afro-Trinidadians: Discovery of Novel Allelic Variants

The highly polymorphic CYP2D6 gene has extensively been studied in many populations, but there is a void of knowledge regarding CYP2D6 pharmacogenetics and activity in populations with unique ancestries and admixture, such as those residing in Trinidad and Tobago. 167 healthy Indo- and 103 Afro-Trinidadians were phenotyped with dextromethorphan and extensively genotyped. Gene resequencing was performed to resolve cases with genotype/phenotype discordance. CYP2D6 activity did not differ between the Indo-Trinidadians and Afro-Trinidadians. Poor metabolizers were, however, more frequent in the Indo-Trinidadians (4.19 vs 1.94%), and unique allele frequency patterns were observed. Two novel nonfunctional allelic variants were found among the Indo-Trinidadians in two discordant cases. CYP2D6*100 is characterized by a single nucleotide deletion and CYP2D6*101 by a 19-bp deletion; both cause frameshifts. Our study underscores the importance of thoroughly characterizing the genetic make up of unique populations when considering pharmacogenetic testing for individualized therapy.

Alcohol withdrawal investigation of Cytochrome P450 CYP1A2, CYP2D6, CYP2E1 and CYP3A4 expression and gene polymorphism

Alcohol withdrawal investigation of Cytochrome P450 CYP1A2, CYP2D6, CYP2E1 and CYP3A4 expression and gene polymorphism

Genetic Variants of CYP2D6 Gene and Cancer Risk: A HuGE Systematic Review and Meta-analysis

Genetic polymorphisms in metabolic enzymes are associated with numerous cancers. A large number of single nucleotide polymorphisms (SNPs) in the CYP2D6 gene have been reported to associate with cancer susceptibility. However, the results are controversial. The aim of this Human Genome Epidemiology (HuGE) review and meta-analysis was to summarize the evidence for associations. Studies focusing on the relationship between CYP2D6 gene polymorphisms and susceptibility to cancer were selected from the Pubmed, Cochrane library, Embase, Web of Science, Springerlink, CNKI and CBM databases. Data were extracted by two independent reviewers and the meta-analysis was performed with Review Manager Version 5.1.6 and STATA Version 12.0 software. Odds ratios (ORs) with 95% confidence intervals (95%CIs) were calculated. According to the inclusion criteria, forty-three studies with a total of 7,009 cancer cases and 9,646 healthy controls, were included in the meta-analysis. The results showed that there was a positive association between heterozygote (GC) of rs1135840 and cancer risk (OR=1.92, 95%CI: 1.14-3.21, P=0.01). In addition, we found that homozygote (CC) of rs1135840 might be a protective factor for cancer (OR=0.58, 95%CI: 0.34-0.97, P=0.04). Similarly, the G allele and G carrier (AG + GG) of rs16947 and heterozygote (A/del) of rs35742686 had negative associations with cancer risk (OR=0.69, 95%CI: 0.48-0.99, P=0.04; OR=0.60, 95%CI: 0.38-0.94, P=0.03; OR=0.50, 95%CI: 0.26-0.95, P=0.03; respectively). This meta-analysis suggests that CYP2D6 gene polymorphisms are involved in the pathogenesis of various cancers. The heterozygote (GC) of rs1135840 in CYP2D6 gene might increase the risk while the homozygote (CC) of rs1135840, G allele and G carrier (AG + GG) of rs16947 and heterozygote (A/del) of rs35742686 might be protective factors.

Clinical Response and Side Effects of Metoclopramide

Metoclopramide is associated with variable efficacy and side effects when used in the treatment of gastroparesis. To determine associations of clinical and pharmacogenetic parameters with response and side effects to metoclopramide in patients with upper gastrointestinal symptoms suggestive of gastroparesis. Gastroparetic patients treated with metoclopramide were enrolled. Clinical parameters recorded were age, sex, weight, diabetic status, gastric emptying result, daily dose, effectiveness, and side effects. DNA was isolated from salivary samples; 20 single nucleotide polymorphisms were genotyped in 8 candidate genes (ABCB1, ADRA1D, CYP1A2, CYP2D6, DRD2, DRD3, HTR4, KCNH2). One hundred gastroparetic patients treated with metoclopramide participated. Dose averaged 33±16 mg/d for 1.1±1.7 years. Responders (53 of 100 patients) were older (48±15 vs. 38±11 y; P=0.0004) and heavier (body mass index of 28±7 vs. 25±7; P=0.0125). Efficacy was associated with polymorphisms in KCNH2 (rs1805123, P=0.020) and ADRA1D (rs2236554, P=0.035) genes. Side effects, occurred in 64 patients, were more common in females (83% vs. 64%; P=0.037), nondiabetics (77% vs. 47%; P=0.004), and patients with normal gastric emptying (41% vs. 17%; P=0.015). Side effects were associated with polymorphisms in CYP2D6 (rs1080985, P=0.045; rs16947, P=0.008; rs3892097, P=0.049), KCNH2 (rs3815459, P=0.015), and serotonin 5-HT4 receptor HTR4 gene (rs9325104, P=0.026). Side effects to metoclopramide were more common in nondiabetic patients with normal gastric emptying. Polymorphisms in CYP2D6, KCNH2, and 5-HT4 receptor HTR4 genes were associated with side effects, whereas polymorphisms in KCNH2 and ADRA1D genes were associated with clinical response. Clinical parameters and pharmacogenetic testing may be useful in identifying patients before treatment with metoclopramide to enhance efficacy and minimize side effects.

Influence of ABCB1 genetic polymorphisms on the pharmacokinetics of risperidone in healthy subjects with CYP2D6*10/*10

The objective of this study was to investigate the combined influence of genetic polymorphisms in ABCB1 and CYP2D6 genes on risperidone pharmacokinetics. Seventy-two healthy Korean volunteers receiving a single oral dose of 2 mg risperidone were included in this study. Significant differences were observed between the ABCB1 3435C>T genotypes for the pharmacokinetic parameters (peak serum concentration) of risperidone and the active moiety (risperidone and its main metabolite, 9-hydroxyrisperidone). There were no significant differences in the area under the serum concentration-time curves of risperidone and the active moiety among the ABCB1 2677G>T/A and 3435C>T genotypes. However, the peak serum concentration and area under the serum concentration-time curves were significantly different among the ABCB1 3435C>T genotypes in CYP2D6*10/*10. These findings indicate that polymorphisms of ABCB1 3435C>T in individuals with CYP2D6*10/*10, which has low metabolic activity, could play an important role in the potential adverse effects or toxicity of risperidone.

High Correlation Between Serum and Cerebrospinal Fluid Olanzapine Concentrations in Patients With Schizophrenia or Schizoaffective Disorder Medicating With Oral Olanzapine as the Only Antipsychotic Drug

The primary aim of the present study was to investigate the relationship between steady state serum and cerebrospinal fluid (CSF) concentrations of olanzapine (OLA) and its metabolite 4'-N-desmethylolanzapine (DMO) in patients with schizophrenia or schizoaffective disorder treated with oral OLA as the only antipsychotic drug. The influence of smoking, gender, age, as well as polymorphisms in cytochrome P450 CYP2D6, CYP1A2, and ABCB1 genes on the serum and CSF drug levels was also analyzed. Thirty-seven white outpatients (10 smokers and 27 nonsmokers) were included. From 29 of them, CSF was collected successfully. A strong correlation (Spearman rank correlation [rs] = 0.93; P < 0.05) was found between serum and CSF concentrations of OLA and a somewhat weaker correlation (rs = 0.5; P < 0.05) between those of DMO. The CSF concentrations of OLA and DMO were on average 12% and 16% of those in serum. Extensive metabolizers of CYP2D6 had higher (P < 0.05) daily doses than poor metabolizers when the influence of smoking was taken into account. Smokers had lower (P < 0.01) concentration-to-dose ratios of OLA in serum (mean, 2.23 ng/mL per mg vs 3.32 ng/mL per mg) and CSF (0.27 ng/mL per mg vs 0.41 ng/mL per mg) than nonsmokers. The concentration-to-dose ratio for serum DMO decreased with increasing age (rs = -0.41; P < 0.05). Carriers of ABCB1 1236T/2677T/3435T haplotype had higher serum (mean, 37.7 ng/mL vs 22.5 ng/mL; P = 0.035) and CSF (4.7 ng/mL vs 2.6 ng/mL; P = 0.018) OLA concentrations than patients without this haplotype. The present study shows a strong correlation between serum and CSF concentrations of OLA, indicating that concentrations of OLA in serum reflect those in CSF.

CYP1A1 and CYP2D6 Gene Polymorphisms in Israeli Jewish Women With Cervical Cancer

To assess the frequency distribution of the CYP1A1 and CYP2D6 gene polymorphisms in Israeli Jewish women with cervical cancer. Forty-three Israeli Jewish women with cervical cancer and 123 healthy Israeli Jewish women were assessed. CYP1A1 (2 alleles) and CYP2D6 polymorphism was analyzed using an allele-specific, polymerase chain reaction-based method. The allele frequency and genotype distribution for the CYP1A1 (2 alleles) and CYP2D6 polymorphism did not reach a level of significance. Smoking was the only independent risk factor for cervical cancer (P = 0.0003). CYP1A1 and CYP2D6 mutations are not related to an increased risk for cervical cancer in the Jewish Israeli population.

Molecular Diversity at the CYP2D6 Locus in Healthy and Schizophrenic Southern Brazilians

The delineation of allele distribution and frequency is required to effectively translate pharmacogenetics to the clinic and given the paucity of CYP2D6 data in the Brazilian population, the purpose of this research was to characterize CYP2D6 alleles and genotype frequencies in Brazilians of European and African ancestries. Moreover, since it is suggested in the literature that CYP2D6 poor metabolism might be involved with susceptibility to schizophrenia, we included data from Brazilian schizophrenic patients to verify if CYP2D6 poor metabolism phenotypes are associated with susceptibility to schizophrenia. We investigated 24 CYP2D6 polymorphisms, gene deletions and gene multiplications in 179 healthy individuals from Brazil, 92 of European descent and 87 African Brazilians. CYP2D6 gene polymorphisms were genotyped by a MassARRAY SNP genotyping system. A total of 19 different alleles and five allele duplications were identified in African and European Brazilians. No significant differences in CYP2D6 allele function or poor metabolizer predicted phenotype frequencies were observed between healthy controls and schizophrenic patients, but the predicted metabolic phenotype distribution showed a significant higher frequency of intermediate metabolizers in African Brazilians than in European Brazilians (p = 0.001). CYP2D6 poor metabolizer genotype seems not to be a determining factor of schizophrenia susceptibility in Brazilians. The characterization of CYP2D6 variability will be very useful for future pharmacogenetic studies in the Brazilian population.

Genetic polymorphism, linkage disequilibrium, haplotype structure and novel allele analysis of CYP2C19 and CYP2D6 in Han Chinese

The cytochrome P450 2C19 and 2D6 enzymes are predominantly found in the human liver, and have important functions in the metabolism of many different classes of commonly used drugs. Their genetic polymorphisms give rise to both important interethnic variability in metabolism and the risk of treatment failure or dose-dependent drug toxicity. To investigate genetic polymorphisms in CYP2C19 and CYP2D6 genes in Han Chinese, we sequenced regions of the 5' flanking region, exon, intron and 3' UTR from these two genes using 100 unrelated healthy Chinese Hans. We detected 48 genetic variants in CYP2C19. A total of 15 of them are novel, including two polymorphisms in putative transcriptional factor-binding sites. The CYP2C19*1, *2, *3, *4, *17, *23, *24 and *25 alleles have frequencies of 67.5, 25.5, 2, 0.5, 3, 0.5, 0.5 and 0.5%, respectively. Based on computational predictions, three novel alleles (CYP2C19*23, *24 and *25) are deleterious mutations of the CYP2C19 protein. In CYP2D6, we identified 84 different polymorphisms, including 18 novel single-nucleotide polymorphisms. One novel polymorphism is located in a potential cis-regulatory element of the gene. The allele frequencies of CYP2D6*1, *2, *4, *5, *6, *10, *14, *21, *36, *41, *43, *52 and *71 are 18.5, 14, 1, 7, 0.5, 49, 1.5, 0.5, 1, 4, 0.5, 1 and 1.5%, respectively. The occurrence of CYP2D6 duplication is 0.5%. The novel CYP2D6*71 is anticipated as a putative poor metabolizer allele. We also performed linkage disequilibrium analysis and observed strong linkage disequilibrium spanning of the CYP2C19 and CYP2D6 regions. In addition, network analysis showed that 15 haplotypes of CYP2C19 and 22 of CYP2D6 are classified into five and three groups, respectively. Comparisons of allele frequency distributions revealed significant interethnic and intraethnic differences in these two genes. In conclusion, this study revealed that CYP2C19 and CYP2D6 have a complicated allele composition and distinct frequency distribution in Han Chinese.

Polymorphisms in genes encoding drugs and xenobiotic metabolizing enzymes in a Brazilian population

Polymorphic variations of several genes associated with drugs and xenobiotic metabolism have been linked to the factors that predispose to the carcinogenesis process. As considerable interindividual and interethnic variation in metabolizing enzyme activity has been associated with polymorphic alleles, we evaluated the frequency of the polymorphisms of CYP2D6, EPHX1 and NQO1 genes in 361 Brazilian individuals separated by ethnicity (European and African ancestry), using the polymerase chain reaction-restriction fragment length (PCR-RFLP) method. The allele frequencies of the variants *3 and *4 for the gene CYP2D6 were 0.04 and 0.14 for white subjects and 0.03 and 0.10 for black individuals, respectively. For the both variants of the gene EPHX1, we found higher allele frequencies among white individuals compared with mulatto subjects (0.62 vs 0.54 and 0.18 vs 0.14, respectively); however, these differences were not statistically significant (p = 0.39 and 0.56, respectively). For the NQO1 gene we observed a higher frequency of the homozygous genotype among black individuals (7.9%) compared with white subjects (6.3%) (p = 0.003). The genotype frequencies were within the Hardy–Weinberg equilibrium. We concluded that the allele frequencies of CYP2D6, EPHX1 and NQO1 gene polymorphisms in this Brazilian population showed ethnic variability when compared with those observed in other populations.

Drug dosing error with drops—severe clinical course of codeine intoxication in twins

In spite of the lack of evidence for its efficacy, and of sporadic reports of severe adverse events, codeine is still widely used as an antitussive agent in children. A 3-year-old boy (twin 1) was found lying in vomit and apnoeic at night; he was resuscitated and immediately transferred to our paediatric intensive care unit (PICU). Two and a half hours later, his twin brother (twin 2) was found dead in his bed at home. Twin 1 required mechanical ventilation for 3 days, but he eventually made a full recovery; autopsy in twin 2 showed massive aspiration of gastric content. History revealed that the monozygotic twins had an upper respiratory tract infection for several days and had both been given codeine at a dose of "10 drops per day" by their mother. The blood of both twins was found to contain high levels of codeine and its metabolites. The weight of "10 drops" was determined experimentally and was found to range from 494 to 940 mg. Thus, the highest possible dose given by mother was 23.5 mg of codeine instead of the recommended 10 mg. The twins had identical CYP2D6 gene polymorphisms corresponding to the "extensive metaboliser" type. Because of the variability of drop size drug dosage, dosage "by drops" is unprecise and may result in accidental overdose. The combination of repeated overdosing and extensive metabolism to morphine is likely to have caused apnoea in these twins. These cases illustrate the danger of codeine as an antitussive in young children.

Clinical Pharmacogenetics and Potential Application in Personalized Medicine

The current 'fixed-dosage strategy' approach to medicine, means there is much inter-individual variation in drug response. Pharmacogenetics is the study of how inter-individual variations in the DNA sequence of specific genes affect drug responses. This article will highlight current pharmacogenetic knowledge on important drug metabolizing enzymes, drug transporters and drug targets to understand interindividual variability in drug clearance and responses in clinical practice and potential use in personalized medicine. Polymorphisms in the cytochrome P450 (CYP) family may have had the most impact on the fate of pharmaceutical drugs. CYP2D6, CYP2C19 and CYP2C9 gene polymorphisms and gene duplications account for the most frequent variations in phase I metabolism of drugs since nearly 80% of drugs in use today are metabolised by these enzymes. Approximately 5% of Europeans and 1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant drug metabolising enzyme that demonstrates genetic variants. Studies into CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and CYP2C9*3 alleles. Extensive polymorphism also occurs in a majority of Phase II drug metabolizing enzymes. One of the most important polymorphisms is thiopurine S-methyl transferases (TPMT) that catalyzes the S-methylation of thiopurine drugs. With respect to drug transport polymorphism, the most extensively studied drug transporter is P-glycoprotein (P-gp/MDR1), but the current data on the clinical impact is limited. Polymorphisms in drug transporters may change drug's distribution, excretion and response. Recent advances in molecular research have revealed many of the genes that encode drug targets demonstrate genetic polymorphism. These variations, in many cases, have altered the targets sensitivity to the specific drug molecule and thus have a profound effect on drug efficacy and toxicity. For example, the beta (2)-adrenoreceptor, which is encoded by the ADRB2 gene, illustrates a clinically significant genetic variation in drug targets. The variable number tandem repeat polymorphisms in serotonin transporter (SERT/SLC6A4) gene are associated with response to antidepressants. The distribution of the common variant alleles of genes that encode drug metabolizing enzymes, drug transporters and drug targets has been found to vary among different populations. The promise of pharmacogenetics lies in its potential to identify the right drug at the right dose for the right individual. Drugs with a narrow therapeutic index are thought to benefit more from pharmacogenetic studies. For example, warfarin serves as a good practical example of how pharmacogenetics can be utilized prior to commencement of therapy in order to achieve maximum efficacy and minimum toxicity. As such, pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and licensed drugs.

Naturalistic pharmacogenetic study of treatment resistance to typical neuroleptics in European–Brazilian schizophrenics

This study aimed to explore the influence of variation in DRD2, DRD3, CYP2D6, CYP3A4, and CYP3A5 genes on treatment resistance to typical neuroleptics in a Brazilian sample of patients with schizophrenia. One polymorphism at DRD2 gene, five at DRD3, 24 at CYP2D6, nine at CYP3A4 gene, and one at CYP3A5 gene were genotyped in a sample of 186 patients with schizophrenia. From the nine studied CYP3A4 single nucleotide polymorphisms, only the -392A>G was polymorphic, and significant associations were observed between this single nucleotide polymorphism and efficacy of neuroleptic treatment. Homozygous individuals for the -392A variant [P=0.014, odds ratio (OR)=3.32] were more frequent in the treatment-resistant group, compared with carriers of one copy of the -392G variant. The CYP3A5 low expressor genotype (CYP3A5*3/CYP3A5*3) was found to be associated with refractoriness to neuroleptic treatment (P=0.003, OR=3.16). Among the haplotypes observed in DRD3 gene, the T/A/G/A/C haplotype showed an association with refractoriness to neuroleptics (chi=5.342, P=0.021, OR=1.75). This association showed that carriers of one copy of this haplotype presented intermediate values between noncarriers and homozygous individuals for the haplotype. No association was observed with polymorphisms in DRD2 and CYP2D6 genes. Multiple logistic regression analyses showed that the number of copies of DRD3 T/A/G/A/C haplotype and CYP3A5 low expressor genotype were predictors of refractoriness to neuroleptic after controlling for selected risk factors. CYP3A5*3 individuals carrying at least one copy of the T/A/G/A/C haplotype showed a higher risk to be refractory to neuroleptics than CYP3A5*3 homozygotes+non-T/A/G/A/C carriers (chi=5.533, P=0.019, OR=2.32, 95% confidence interval=1.08-5.02). No significant associations were observed with DRD2 and CYP2D6 polymorphisms. Our results suggest a role for CYP3A5 and DRD3 gene variants on refractoriness to neuroleptic treatment in Brazilians with schizophrenia.

Role of CYP2D6 gene polymorphism in individual's ability to quit smoking

In 1980, we published two papers of importance for the future of our research: (i) it was shown that the two polymorphic hydroxylations of debrisoquine and sparteine are catalysed by a common enzyme now called CYP2D6 and (ii) that this polymorphic enzyme also catalysed the metabolism of the tricyclic antidepressant nortriptyline. Later, it was shown that most antidepressants are metabolized by CYP2D6. There are many allelic variants of CYP2D6 causing decreased (e.g. CYP2D6*10 in Asians) or no (*4 in Caucasians) activity of the enzyme. We have identified duplication and amplification of a CYP2D6 gene as a cause of ultrarapid metabolism. There are pronounced interethnic differences in these allelic variants. When nortriptyline was given as single doses to healthy subjects, there was a close relationship between the rate of 10-hydroxylation and the number of functional CYP2D6 genes.Most neuroleptic drugs are also metabolized by CYP2D6. Exceptions are the atypical neuroleptics clozapine and olanzapine, which are mainly metabolized by CYP1A2. When haloperidol was given as a single oral dose to a panel of healthy Swedish Caucasians, PM of debrisoquine eliminated the drug slower than EM (PM=poor, EM=extensive metabolisers). Among eight patients treated with i.m. injection of haloperidol decanoate every 4 weeks, one patient having the genotype CYP2D6*4/*4 and thus a PM, had the highest plasma concentration of haloperidol, highest dopamine D2-receptor occupancy and most pronounced extrapyramidal side-effects. In Japan, plasma concentrations of haloperidol per dose unit have been shown to be related to the CYP2D6*10 allele. In Koreans, this relationship was confirmed at doses of haloperidol below 20 mg per day, but not at higher doses. These and other studies taken together show that at low doses haloperidol is metabolized by CYP2D6, while at high doses, this enzyme is saturated and then enzymes with a higher capacity, e.g. CYP3A4, are taking over.CYP2D6 catalyzes the metabolism of a large number of psychotropic drugs and the pronounced variation in its activity between individuals and populations contributes to the variation in treatment response and side effects. Also, it must be emphasized that when two drugs, both of which are substrates of CYP2D6, are co-administrated they may increase each others' plasma concentrations and potentiate therapeutic effects and adverse drug reactions.

Implication of Xenobiotic Metabolizing Enzyme gene (CYP2E1, CYP2C19, CYP2D6, mEH and NAT2) Polymorphisms in Breast Carcinoma

BackgroundXenobiotic Metabolizing Enzymes (XMEs) contribute to the detoxification of numerous cancer therapy-induced products. This study investigated the susceptibility and prognostic implications of the CYP2E1, CYP2C19, CYP2D6, mEH and NAT2 gene polymorphisms in breast carcinoma patients.MethodsThe authors used polymerase chain reaction and restriction enzyme digestion to characterize the variation of the CYP2E1, CYP2C19, CYP2D6, mEH and NAT2 gene in a total of 560 unrelated subjects (246 controls and 314 patients).ResultsThe mEH (C/C) mutant and the NAT2 slow acetylator genotypes were significantly associated with breast carcinoma risk (p = 0.02; p = 0.01, respectively). For NAT2 the association was more pronounced among postmenopausal patients (p = 0.006). A significant association was found between CYP2D6 (G/G) wild type and breast carcinoma risk only in postmenopausal patients (p = 0.04). Association studies of genetic markers with the rates of breast carcinoma specific overall survival (OVS) and the disease-free survival (DFS) revealed among all breast carcinoma patients no association to DFS but significant differences in OVS only with the mEH gene polymorphisms (p = 0.02). In addition, the mEH wild genotype showed a significant association with decreased OVS in patients with axillary lymph node-negative patients (p = 0.03) and with decreasesd DFS in patients with axillary lymph node-positive patients (p = 0.001). However, the NAT2 intermediate acetylator genotype was associated with decreased DFS in axillary lymph node-negative patients.ConclusionThe present study may prove that polymorphisms of some XME genes may predict the onset of breast carcinoma as well as survival after treatment.

The CYP2D6 gene locus in South African Coloureds: unique allele distributions, novel alleles and gene arrangements

The highly polymorphic CYP2D6 gene locus has been extensively scrutinised in the major ethnic populations, but little is known about the locus for many indigenous and unique admixed populations, including the Coloureds of South Africa. This study aimed at characterising the CYP2D6 gene locus in Coloured subjects and predict their phenotype status. CYP2D6 genotyping was performed on 99 Coloured subjects by long-range polymerase chain reaction (PCR) and PCR restriction fragment length polymorphism (RFLP). Testing included 25 allelic variants as well as gene duplications. Novel alleles were cloned and sequenced. A novel strategy for CYP2D7/2D6 hybrid gene detection is described. Thirteen alleles had a frequency of = 1%, three were infrequent (<1%) and 16 of the tested alleles were not detected. CYP2D6*5 had a frequency of 17.2%, one of the highest ever observed in any population. Two novel alleles, CYP2D6*64 and *65, were identified. In addition, four samples carried CYP2D7/2D6 hybrid genes, of which one matched the CYP2D6*66 allele of a resequenced Caucasian control subject. CYP2D6*66 is similar to CYP2D6*16, but its putative recombination point is further upstream. Genotyping identified three poor metabolisers (3%; predicted incidence 6.6%), and 12% of the population had an activity score of 0.5 indicative of intermediate metabolism. The Coloured population has a unique composition of alleles and a distinct frequency distribution. The preliminary data presented suggest decreased CYP2D6 activity compared with Caucasians. Follow-up studies including both genotyping and phenotyping will need to be conducted to further assess the relationship between genotype and phenotype in this population of complex ancestry.

Exogenous and Endogenous Determinants of Blood Trihalomethane Levels after Showering

BackgroundWe previously conducted a study to assess whether household exposures to tap water increased an individual’s internal dose of trihalomethanes (THMs). Increases in blood THM levels among subjects who showered or bathed were variable, with increased levels tending to cluster in two groups.ObjectivesOur goal was to assess the importance of personal characteristics, previous exposures, genetic polymorphisms, and environmental exposures in determining THM concentrations in blood after showering.MethodsOne hundred study participants completed a health symptom questionnaire, a 48-hr food and water consumption diary, and took a 10-min shower in a controlled setting. We examined THM levels in blood samples collected at baseline and 10 and 30 min after the shower. We assessed the significance of personal characteristics, previous exposures to THMs, and specific gene polymorphisms in predicting postshower blood THM concentrations.ResultsWe did not observe the clustering of blood THM concentrations observed in our earlier study. We found that environmental THM concentrations were important predictors of blood THM concentrations immediately after showering. For example, the chloroform concentration in the shower stall air was the most important predictor of blood chloroform levels 10 min after the shower (p < 0.001). Personal characteristics, previous exposures to THMs, and specific polymorphisms in CYP2D6 and GSTT1 genes were significant predictors of both baseline and postshowering blood THM concentrations as well as of changes in THM concentrations associated with showering.ConclusionThe inclusion of information about individual physiologic characteristics and environmental measurements would be valuable in future studies to assess human health effects from exposures to THMs in tap water.

Genetic variability and opioid efficacy

Summary A number of clinical observations suggest that patients' genetic disposition influences their response to opioids. This position is strengthened because data from basic research agree with data obtained in human studies. However, a clinical relevance for genetic variability was only established for the CYP2D6 gene polymorphisms and the mu-opioid receptor gene A118G polymorphism. For other opioids or other candidate genes, clinical data are either not available or the data are yet too limited to reach a definitive conclusion. Still, the results obtained so far strongly indicate that opioid efficacy is related to inborn properties caused by genetic variability related to opioid metabolism, opioid receptors, opioid signaling, and opioid transporters. In addition, clinical effects are influenced by variations in other biological systems that modify the effects induced by opioid agonists. Clinical data are lacking for most opioids and little is known about the exact mechanisms by which genetic variability interacts with opioid signaling. Further research should combine basic and clinical research with the end goal of obtaining improved and individualized pain treatment.

Clinical Implications of CYP2D6 Genetic Polymorphism During Treatment with Antipsychotic Drugs

CYP2D6 is described as the most relevant enzyme in the metabolism of many antipsychotic drugs. Its contribution to the interindividual differences in drug response is reviewed here highlighting its role in the kinetics of antipsychotic drugs and the occurrence of drug interactions. The activity of CYP2D6 is inherited as a monogenetic trait and the CYP2D6 gene appears highly polymorphic in humans. The polymorphic alleles may lead to altered activity of the CYP enzymes causing absent, decreased (poor), or increased (ultrarapid) metabolism that in turn influence the disposition of the antipsychotic drugs. Antipsychotic drug biotransformation is mainly determined by genetic factors mediating CYP2D6 gene polymorphism, however the importance of environmental factors (dietary, smoking, diseases, etc.) is also recognized. Additionally, the potential interaction between CYP2D6 and the endogenous metabolism must be taken into consideration. The present review summarizes the relevance of physiological and environmental factors in CYP2D6 hydroxylation capacity, the inhibition of CYP2D6 activity during treatment, the use of drug/metabolite ratio as a tool to evaluate CYP2D6 hydroxylation capacity in a patient, and the relevance of CYP2D6 for drug plasma concentration and for QTc interval lengthening during treatment with antipsychotic drugs.

Association of CYP2D6 gene polymorphism and anxiety on Spielberger Trait Anxiety Index with smoking behaviour

Waga, Chikakoa; Murayama, Ohoshib; Sand, Akihiroc; Yoshihara, Eijia; Ikeda, Kazutakad; Iwahash, Kazuhikoa Author Information