CYP2D6 gene test in psychiatric patients and healthy volunteers

CYP2C19 and CYP2D6 Genotypes and Metabolizer Status Distribution in a Bulgarian Psychiatric Cohort

CYP2D6 and CYP2C19 are enzymes of essential significance for the pharmacokinetics of a multitude of commonly used antidepressants, antipsychotics, antiemetics, β-blockers, opioids, antiestrogen, antacids, etc. Polymorphisms in the respective genes are well established as resulting in functional differences, which in turn can impact safety and efficacy. Importantly, the prevalence of genetic CYP2D6 and CYP2C19 variability differs drastically between populations. Drawing on the limited information concerning genotype frequencies in Bulgaria, we here analyzed 742 Bulgarian psychiatric patients predominantly diagnosed with depression and/or anxiety. Specifically, we analyzed frequencies of CYPC19*2, *4 and *17, as well as of CYP2D6*2, *3, *4, *5, *6, *10 and *41. In total, 571 out of 742 patients (77%) carried at least one variant which impacts metabolizer status. Overall, 48.6% of the studied individuals were classified as non-normal metabolizers of CYP2D6 with most exhibiting reduced function (38.2% intermediate metabolizers and 6.6% poor metabolizers). In contrast, for CYP2C19, the majority of non-normal metabolizers showed increased functionality (28.9% rapid and 5.5% ultrarapid metabolizers), while reduced activity metabolizer status accounted for 25.6% (23.8% intermediate and 1.8% poor metabolizers). These results provide an important resource to assess the genetically encoded functional variability of CYP2D6 and CYP2C19 which may have significant implications for precision medicine in Bulgarian psychiatry practice.

The potential impact of CYP2D6 (*2/*4/*10) gene variants among Egyptian epileptic children: A preliminary study

BACKGROUND

The cytochrome P450 (CYP) isoenzymes have an indispensable role in the metabolic phase of different medications during the treatment of multiple neuropsychiatric disorders. The foremost goal of this study is to evaluate the correlation of the allelic variants within CYP2D6 (*2/*4/*10) gene with the susceptibility for epileptic syndrome as well as the assessment the degree of resistance towards antiepileptic drugs (AEDs).

METHODS

This work was designed based on the involvement of 200 participants [100 unrelated healthy controls, 50 AEDs responsive, and 50 AEDs resistant]. Genomic DNA for the CYP2D6 variants was genotyped utilizing the T-ARMS-PCR technique.

RESULTS

The distributions of the CYP2D6*2 (rs16947; c.886C > T) and CYP2D6*4 (rs3892097; c.506-1G > A) variants were significantly correlated with elevated risk among epileptic patients compared to healthy controls (P-value < 0.05). Furthermore, the CYP2D6*2 variant was statistically associated with disease risk among AEDs responsive patients, while the CYP2D6*4 variant was statistically correlated with disease risk among AEDs resistant patients (P-value < 0.05). Interestingly, the allelic variants of the CYP2D6*4 (A allele) and CYP2D6*10 (T allele) were associated with elevated risk among AEDs resistant compared to AEDs responsive patients (P-value = 0.008 and 0.040, respectively).

CONCLUSIONS

The CYP2D6*2 and CYP2D6*4 variants were recognized as independent risk factors among epileptic patients, but not the CYP2D6*10 variant.

Population pharmacogenomics: an update on ethnogeographic differences and opportunities for precision public health

Both safety and efficacy of medical treatment can vary depending on the ethnogeographic background of the patient. One of the reasons underlying this variability is differences in pharmacogenetic polymorphisms in genes involved in drug disposition, as well as in drug targets. Knowledge and appreciation of these differences is thus essential to optimize population-stratified care. Here, we provide an extensive updated analysis of population pharmacogenomics in ten pharmacokinetic genes (CYP2D6, CYP2C19, DPYD, TPMT, NUDT15 and SLC22A1), drug targets (CFTR) and genes involved in drug hypersensitivity (HLA-A, HLA-B) or drug-induced acute hemolytic anemia (G6PD). Combined, polymorphisms in the analyzed genes affect the pharmacology, efficacy or safety of 141 different drugs and therapeutic regimens. The data reveal pronounced differences in the genetic landscape, complexity and variant frequencies between ethnogeographic groups. Reduced function alleles of CYP2D6, SLC22A1 and CFTR were most prevalent in individuals of European descent, whereas DPYD and TPMT deficiencies were most common in Sub-Saharan Africa. Oceanian populations showed the highest frequencies of CYP2C19 loss-of-function alleles while their inferred CYP2D6 activity was among the highest worldwide. Frequencies of HLA-B*15:02 and HLA-B*58:01 were highest across Asia, which has important implications for the risk of severe cutaneous adverse reactions upon treatment with carbamazepine and allopurinol. G6PD deficiencies were most frequent in Africa, the Middle East and Southeast Asia with pronounced differences in variant composition. These variability data provide an important resource to inform cost-effectiveness modeling and guide population-specific genotyping strategies with the goal of optimizing the implementation of precision public health.

Meta-analysis of probability estimates of worldwide variation of CYP2D6 and CYP2C19

Extensive migration has led to the necessity of knowledge regarding the treatment of migrants with different ethnical backgrounds. This is especially relevant for pharmacological treatment, because of the significant variation between migrant groups in their capacity to metabolize drugs. For psychiatric medications, CYP2D6 and CYP2C19 enzymes are clinically relevant. The aim of this meta-analysis was to analyze studies reporting clinically useful information regarding CYP2D6 and CYP2C19 genotype frequencies, across populations and ethnic groups worldwide. To that end, we conducted a comprehensive meta-analysis using Embase, PubMed, Web of Science, and PsycINFO (>336,000 subjects, 318 reports). A non-normal metabolizer (non-NM) probability estimate was introduced as the equivalent of the sum-prevalence of predicted poor, intermediate, and ultrarapid metabolizer CYP2D6 and CYP2C19 phenotypes. The probability of having a CYP2D6 non-NM predicted phenotype was highest in Algeria (61%) and lowest in Gambia (2.7%) while the probability for CYP2C19 was highest in India (80%) and lowest in countries in the Americas, particularly Mexico (32%). The mean total probability estimates of having a non-NM predicted phenotype worldwide were 36.4% and 61.9% for CYP2D6 and CYP2C19, respectively. We provide detailed tables and world maps summarizing clinically relevant data regarding the prevalence of CYP2D6 and CYP2C19 predicted phenotypes and demonstrating large inter-ethnic differences. Based on the documented probability estimates, pre-emptive pharmacogenetic testing is encouraged for every patient who will undergo therapy with a drug(s) that is metabolized by CYP2D6 and/or CYP2C19 pathways and should be considered in case of treatment resistance or serious side effects.

Single nucleotide and structural variants of CYP2D6 gene in Kinh Vietnamese population

CYP2D6 genetic variations could result in alteration of CYP2D6 enzyme activity, leading to dissimilarity among individuals in regard of drug metabolism.This study aims to detect all genetic variants, allele, and genotype frequencies of CYP2D6 gene in 136 unrelated healthy Kinh Vietnamese volunteers. All single nucleotide variants (SNVs) and structural variations (SVs) of CYP2D6 gene were identified by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) assay.Totally, 30 SNVs and 9 SVs including a whole gene deletion, 8 hybrid structures, and tandem arrangements were identified. Of the 7 novel SNVs detected, the 3157G>T (R329L) substitution was predicted to be deleterious by PROVEAN; the 3851G>A (W358X) variant resulted in a truncated protein; and the 2988G>A variant located in the intron 6 was predicted to be capable of modifying splicing motif by Human Splicing Finder. We determined 29 different genotypes of CYP2D6 from 136 individuals. The most common alleles were the CYP2D6*10 (43.75%), *1 (18.75%), and tandem arrangement *36-*10 (12.13%).This study provides best information on CYP2D6 polymorphism comprising the newly discovered SNVs, structural variations, and their frequencies in Kinh Vietnamese. These new data would be valuable in view of precise dosing of CYP2D6 metabolized drugs and giving better treatment outcome.

CYP2D6 allele frequencies in Korean population, comparison with East Asian, Caucasian and African populations, and the comparison of metabolic activity of CYP2D6 genotypes

Cytochrome P450 (CYP) 2D6 is present in less than about 2% of all CYP enzymes in the liver, but it is involved in the metabolism of about 25% of currently used drugs. CYP2D6 is the most polymorphic among the CYP enzymes. We determined alleles and genotypes of CYP2D6 in 3417 Koreans, compared the frequencies of CYP2D6 alleles with other populations, and observed the differences in pharmacokinetics of metoprolol, a prototype CYP2D6 substrate, depending on CYP2D6 genotype. A total of 3417 unrelated healthy subjects were recruited for the genotyping of CYP2D6 gene. Among them, 42 subjects with different CYP2D6 genotypes were enrolled in the pharmacokinetic study of metoprolol. The functional allele *1 and *2 were present in frequencies of 34.6 and 11.8%, respectively. In decreased functional alleles, *10 was the most frequent with 46.2% and *41 allele was present in 1.4%. The nonfunctional alleles *5 and *14 were present at 4.5 and 0.5% frequency, respectively. The *X × N allele was present at a frequency of 1.0%. CYP2D6*1/*1, *1/*2 and *2/*2 genotypes with normal enzyme activity were present in 12.1%, 8.6% and 1.4% of the subjects, respectively. CYP2D6*5/*5, *5/*14, and *14/*14 genotypes classified as poor metabolizer were only present in 4, 2, and 1 subjects, respectively. Mutant genotypes with frequencies of more than 1% were CYP2D6*1/*10 (32.0%), *10/*10 (22.3%), *2/*10 (11.7%), *5/*10 (3.7%), *1/*5 (2.5%), and *10/*41 (1.2%). The relative clearance of metoprolol in CYP2D6*1/*10, *1/*5, *10/*10, *5/*10, and *5/*5 genotypes were 69%, 57%, 24%, 14% and 9% of CYP2D6*wt/*wt genotype, respectively. These results will be very useful in establishing a strategy for precision medicine related to the genetic polymorphism of CYP2D6.

CYP2D6 and CYP2C19 genotyping in psychiatric patients on psychotropic medication in the former Dutch Antilles

AIM

This study was aimed to asses the prevalence of CYP2D6 and CYP2C19 polymorphisms in psychiatric patients and in volunteers from Dutch caribbean origin.

METHODS

In total, 435 individuals were genotyped for CYP2D6 and CYP2C19. Of these, 269 were psychiatric patients on psychotropic medication, living in Curaçao and 166 were volunteers from the Dutch Caribbean population.

RESULTS

No differences in prevalence of alleles were found.

CONCLUSION

Although prevalence of alleles appeared to be very different from African and Caucasian populations, the distribution into predicted phenotypes shows an equal distribution as in Caucasians.

Pharmacogenetic testing revisited: 5' nuclease real-time polymerase chain reaction test panels for genotyping CYP2D6 and CYP2C19

Due to their involvement in the metabolization of commonly prescribed psychopharmaceutical drugs, the cytochrome oxidase genes CYP2D6 and CYP2C19 are extensive targets for pharmacogenetic testing. The existence of common allelic variants allows the prediction of a metabolic phenotype based on a genotype result, hereby supplying a clinical tool for optimizing prescription and minimizing adverse effects. In this study, we present the development of two 5' nuclease real-time polymerase chain reaction (PCR) test panels, capable of detecting eight of the most clinically relevant alleles of the CYP2D6 gene (*2, *3, *4, *6, *9, *10, 17, *41) and the three most common nonfunctional alleles of CYP2C19 (*2, *3, *4). The assays have been thoroughly validated using a large collection of reference samples, by parallel testing and by DNA sequencing. The reanalysis of reference samples provided the calculation of the frequency of the CYP2D6*4K allele in a population, not previously reported. Furthermore, original test results from CYP2D6*41, generated based on the presence of the 2850T and the lack of the -1584G single-nucleotide polymorphism (SNP), were compared with genotyping based on the current acknowledged founder SNP 2988G of this allele. These results indicate that up to 17.7% of the patients originally tested as carriers of the CYP2D6*41 allele may have had an incorrect phenotypic result assigned. The two 5' nuclease real-time PCR test panels have subsequently been optimized for use in the clinical laboratory, using a standard real-time PCR instrument and software.

Pharmacogenetics of Cytochrome P450 Enzymes in American Indian and Caucasian Children Admitted to a Psychiatric Hospital

OBJECTIVE

The cytochrome P450 (CYP450) enzyme system metabolizes many psychiatric medications. We compare frequencies of alleles and phenotypes for CYP2D6, CYP2C9, and CYP2C19 in American Indian (AI) and Caucasian youth treated at a psychiatric hospital in the Northwestern United States.

METHODS

A retrospective chart review evaluated CYP450 pharmacogenetic (PGx) data from the Shodair Children's Hospital Clinical Genetic Laboratory between 2006 and 2014. CYP2D6 genotyping was performed using the xTAG® CYP2D6 Kit (Luminex, Austin, TX). CYP2C9 and CYP2C19 genotyping was performed by laboratory-developed assays using allele-specific quantitative polymerase chain reaction (qPCR) and/or melt-curve analysis.

RESULTS

A total of 123 AIs and 688 Caucasians met criteria for inclusion. The overall prevalence of CYP2D6 poor metabolizers was 8.3% (95% Confidence Interval [CI] 6.1%, 10.4%), 9.3% in Caucasians (95% CI 7.1%, 11.5%), and 2.4% in AIs (95% CI 0%, 5.2%). The overall prevalence of CYP2D6 ultrarapid metabolizers was 1.6% (95% CI 0.7%, 2.5%), 1.6% in the Caucasians (95% CI 0.7%, 2.5%), and 1.6% in AIs (95% CI 0%, 3.9%). The overall prevalence of CYP2C9 poor metabolizers was 3% (95% CI 1.7%, 4.2%), 3.2% in Caucasians (95% CI 1.8%, 4.6%), and 1.8% in AIs (95% CI 0%, 4.2%). The overall prevalence of CYP2C19 poor metabolizers was 2.5% (95% CI 1.3%, 3.6%), 2.9% in Caucasians (95% CI 1.6%, 4.2%), and 0% in AIs. The overall prevalence of CYP2C19 ultrarapid metabolizers was 1.5% (95% CI 0.6%, 2.4%), 1.6% in Caucasians (95% CI 0.6%, 2.6%), and 0.9% in AIs (95% CI 0%, 2.6%).

CONCLUSIONS

This study is the first to identify differences in polymorphism frequencies of the CYP450 system in AIs and Caucasian youth admitted to a psychiatric hospital. Our findings warrant further study of these populations to determine if these differences are generalizable to the larger population of Caucasian and AI/Alaska Native youth in the Northwestern United States.

Frequency of CYP450 enzyme gene polymorphisms in the Greek population: review of the literature, original findings and clinical significance

The cytochrome P450 (CYP450) enzyme family is involved in the oxidative metabolism of many therapeutic drugs and various endogenous substrates. These enzymes are highly polymorphic. Prevalence of CYP450 enzyme gene polymorphisms vary among different populations and substantial inter- and intra-ethnic variability in frequency of CYP450 enzyme gene polymorphisms has been reported. This paper provides an overview and investigation of CYP450 genotypic and phenotypic reports published in the Greek population.

Does pharmacogenetic testing for CYP450 2D6 and 2C19 among patients with diagnoses within the schizophrenic spectrum reduce treatment costs?

The effect of pharmacogenetic testing for CYP450 2D6 and 2C19 on treatment costs have not yet been documented. This study used Danish patient registers to calculate healthcare costs of treating patients with diagnoses within the schizophrenic spectrum for 1 year with or without pharmacogenetic testing for polymorphisms in the genes for the CYP2D6 and CYP2C19 enzymes. In a randomized, controlled trial, stratified with respect to metabolizer genotype, 104 patients were assigned to treatment based on pharmacogenetic testing and 103 patients to treatment as usual. Random exclusion of extensive and intermediate metabolizers was used to increase the frequency of extreme metabolizers (poor metabolizers and ultrarapid metabolizers for CYP2D6) to 20% in both groups. Cost differences were analysed at several levels including (i) overall healthcare expenditure, (ii) psychiatric hospital cost (iii) nonpsychiatric hospital cost, (iv) primary care spending and (v) pharmaceuticals. Statistically significant differences in costs of psychiatric care dependent on metabolizer status were found between intervention groups. Pharmacogenetic testing significantly reduced costs among the extreme metabolizers (poor metabolizers and ultrarapid metabolizers) to 28%. Use of primary care services and pharmaceuticals was also affected by the intervention.This study confirms earlier findings that extreme metabolizers (poor and ultrarapid metabolizers) incur higher costs than similar patients with a normal metabolizer genotype. However, this study shows that these excess costs can be reduced by pharmacogenetic testing. Pharmacogenetic testing for CYP2D6 and CYP2C19 could thus be considered as a means of curtailing high psychiatric treatment costs among extreme metabolizers.

Do guidelines recommending pharmacogenetic testing of psychiatric patients affect treatment costs and the use of healthcare services?

Aim: To identify the effects of local recommendations of pharmacogenetic testing in psychiatry with respect to treatment costs. Methods: Based on Danish patient registers, individual treatment costs within a 365-day period at three psychiatric hospitals recommending and using pharmacogenetic testing is compared retrospectively with treatment costs at other Danish psychiatric hospitals using alternate treatment strategies. Primary outcome of interest is total direct costs analyzed by multilevel modelling. Secondary outcome measures are healthcare consumption within specific sectors analyzed by Tobitregressions. Results: Costs among patients treated at hospitals recommending and using pharmacogenetic testing were not found to be statistically significantly different from costs among patients treated at sites using alternate treatment strategies. In spite of recommendations to test all patients the uptake of the test was, however, low (26—31 %). Treatment practice using routine therapeutic drug monitoring (in Ãrhus) shows a trend towards lower costs. Conclusions: Based on this natural experiment we were not able to document statistically significant differences in total costs between treatment sites that had guidelines recommending pharmacogenetic testing, relative to sites without such guidelines, over a period of one year. However, guidelines of pharmacogenetic testing and possibly also therapeutic drug monitoring seem to lead to reductions in costs for primary care services. In the case of the former, reductions do, however, seem to be outweighed by increases in costs for psychiatric and non-psychiatric inpatient stays. In conclusion, no statistically significant differences in total direct costs across sites with different treatment strategies were found.

Genotyping of the cytochrome P450 2D6 4469 C>T polymorphism using SimpleProbes™

BACKGROUND

Genotyping of human cytochrome P450s is a pharmacogenetic approach to diagnosing inherited deficiencies in drug metabolizing enzymes that influence therapeutic responses. The P450 CYP2D6 (debrisoquine hydroxylase) metabolizes numerous antidepressants and neuroleptic agents and there is evidence of a relationship between gene polymorphism and variant therapeutic response. Polymorphism in CYP2D6 causes poor, intermediate, efficient or ultrarapid metabolization of substrate drugs affecting pharmacokinetic parameters and requiring dose adjustments. Predictive genotyping for broader clinical application is reliant on fast, technically simple analyses. A new genotyping method was explored. It identifies the single nucleotide polymorphism (SNP) 4469 C>T (NCBI access no. M33388) with one fluorescent hybridization probe (SimpleProbes; SP) using the LightCycler (LC). This SNP is found in 21 alleles, comprising 30% in Caucasian populations and encoding enzymes with poor, intermediate or efficient activity. The remaining 65 known alleles either harbour a C in position 4469 or are deletion mutants.

METHODS

Comparative detection of C>T polymorphism was done using a well-established polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique and PCR followed by melting-point (T(m)) analysis with an SP covering the SNP position in 144 samples encompassing alleles *2 and *41 with a T, alleles *1,*3, *4, *6, *9, *10, *15 with a C and the deletion mutant allele *5.

RESULTS

C>T polymorphism was detected with complete concordance. T(m) of SP/target heteroduplex complexes for C was: T(m) 67, 89 degrees C to 68, 62 degrees C and for T: T(m) 60, 70 degrees C to 61, 51 degrees C.

CONCLUSION

By one-step SP methodology it proved possible within 2 h to identify an SNP in genotypes comprising >90% in Caucasian populations.

Estimating the Danish populations' preferences for pharmacogenetic testing using a discrete choice experiment. The case of treating depression

OBJECTIVE

The objective is to estimate willingness-to-pay (WTP) for pharmacogenetic testing in the treatment of depression.

METHODS

In a web-based discrete choice questionnaire, four attributes were included: 1) number of changes in antidepressants before symptom relief; 2) time with dosage adjustments due to adverse side effects and/or lack of effects; 3) cost of pharmacogenetic testing; 4) probability of benefits from pharmacogenetic testing. Respondents were asked to choose between two scenarios; 1) pharmacogenetic testing; and 2) an opt-out option reflecting a scenario without pharmacogenetic testing. The indirect utility model was assumed to be multiplicative in probability of benefits and reduced time with dosage adjustments as well as reduced number of antidepressant changes.

RESULTS

Most coefficients had the expected signs and were statistically significant. WTP for avoidance of one change in antidepressant medication is 1571 Danish Krone (DKK), whereas WTP for reducing the period with dosage-adjustments by 1 month is DKK604. Both were statistically significantly different from zero.

CONCLUSION

If diagnosed with depression, peoples' WTP for pharmacogenetic testing appears to exceed its price as long as there is a reasonable probability for improvements in treatment (in the present case 10%). Utility is associated with outcomes only. Hence, other modes of provision of similar improvements in treatment may be valued equally highly. WTP estimates and the associated policy implications appear to be robust because they were unaffected by estimation model.

DNA microarray technology in the clinical environment: the AmpliChip CYP450 test for CYP2D6 and CYP2C19 genotyping

INTRODUCTION

An important technological advance in genetic testing is the DNA microarray, which allows for the simultaneous testing of thousands of DNA sequences. The AmpliChip CYP450 Test employs this microarray technology for cytochrome P450 (CYP) 2D6 and CYP2C19 genotyping. Isoenzymes encoded by these genes are responsible for the metabolism of many widely prescribed drugs. The objectives of this study were to identify CYP2D6 and CYP2C19 alleles and phenotypes in a psychiatric patient population in Kentucky, and to describe practical issues associated with DNA microarray technology.

METHODS

A total of 4,532 psychiatric patients were recruited from three state hospitals in Kentucky. Whole blood, buccal swabs, or saliva samples were genotyped with the AmpliChip CYP450 Test to derive a predicted phenotype.

RESULTS

In this cohort, the overall prevalence of CYP2D6 poor metabolizers was 7.6% (95% CI 7%, 8.3%), 8.2% in the Caucasians (95% CI 7.4%, 9.%) and 1.8% in the African Americans (95% CI 0.9%, 3.5%). The overall prevalence of CYP2D6 ultrarapid metabolizers was 1.5% (95% CI 1.2%, 1.9%), 1.5% in the Caucasians (95% CI 1.1%, 1.9%) and 2.0% in the African Americans (95% CI 1.1%, 3.7%). The overall prevalence of CYP2C19 poor metabolizers was 2.0% (95% CI 1.8%, 2.7%), 2.2% in Caucasians (95% CI 1.6%, 2.5%) and 4.0% in African Americans (95% CI 2.6%, 6.1%).

CONCLUSION

We also propose a numeric system for expression of CYP2D6 and CYP2C19 enzyme activity to aid clinicians in determining treatment strategy for patients receiving therapeutics that are metabolized by the CYP2D6 or CYP2C19 gene products.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Identification of CYP2D6 null variants among long-stay, chronic psychiatric inpatients: is it strictly necessary?

We identified the null variants *3,*4,*5,*6,*7 and *8 of the CYP2D6 gene [encoding for cytochrome P450 (debrisoquine hydroxylase)] in a group of 84 chronic-stay psychiatric inpatients with severe schizophrenia or related disorders and receiving treatment with one or more CYP2D6 substrates for years. We also studied a group of 100 healthy controls of similar ethnic origin (Spanish Caucasians). Three patients were poor metabolizers (PMs) for antipsychotic drugs according to their CYP2D6 genotype (i.e. homozygous for the *4 allele) but they exhibited no adverse drug reaction over the years despite chronic treatment with CYP2D6 substrates. We suggest that CYP2D6 genetic screening is more useful in other type of psychiatric patients, particularly in younger ones starting treatment protocols.

Pharmacogenetic basis for therapeutic optimization in Alzheimer's disease

Alzheimer's disease is a major health problem in developed countries. Approximately 10-15% of direct costs in dementia are attributed to pharmacological treatment, and only 10-20% of the patients are moderate responders to conventional antidementia drugs, with questionable cost effectiveness. The phenotypic expression of Alzheimer's disease is characterized by amyloid deposition in brain tissue and vessels (amyloid angiopathy), intracellular neurofibrillary tangle formation, synaptic and dendritic loss, and premature neuronal death. Primary pathogenic events underlying this neurodegenerative process include genetic factors involving more than 200 different genes distributed across the human genome, accompanied by progressive cerebrovascular dysfunction, and diverse environmental factors. Mutations in genes directly associated with the amyloid cascade (APP, PSEN1, PSEN2) are present in less than 5% of the Alzheimer's disease population; however, the presence of the epsilon4 allele of the apolipoprotein E gene (APOE) represents a major risk factor for more than 40% of patients with dementia. Genotype-phenotype correlation studies and functional genomics studies have revealed the association of specific mutations in primary loci and/or APOE-related polymorphic variants with the phenotypic expression of biological traits. It is estimated that genetics accounts for between 20% and 95% of the variability in drug disposition and pharmacodynamics. Recent studies indicate that the therapeutic response in Alzheimer's disease is genotype specific, depending on genes associated with Alzheimer's disease pathogenesis and/or genes responsible for drug metabolism (e.g. cytochrome P450 [CYP] genes). In monogenic studies, APOEepsilon4/epsilon4 genotype carriers are the worst responders to conventional treatments. Some cholinesterase inhibitors currently being use in the treatment of Alzheimer's disease are metabolized via CYP-related enzymes. These drugs can interact with many other drugs that are substrates, inhibitors or inducers of the CYP system, this interaction eliciting liver toxicity and other adverse drug reactions. CYP2D6 enzyme isoforms are involved in the metabolism of more than 20% of drugs used in CNS disorders. The distribution of the CYP2D6 genotypes in the European population of the Iberian peninsula differentiates four major categories of CYP2D6-related metabolizer types: (i) extensive metabolizers (EM) [51.61%]; (ii) intermediate metabolizers (IM) [32.26%]; (iii) poor metabolizers (PM) [9.03%]; and (iv) ultra-rapid metabolizers (UM) [7.10%]. PMs and UMs tend to show higher transaminase activity than EMs and IMs. EMs and IMs are the best responders, and PMs and UMs are the worst responders to pharmacologic treatments in Alzheimer's disease. At this early stage of the development of pharmacogenomic/pharmacogenetic procedures in Alzheimer's disease therapeutics, it seems very plausible that the pharmacogenetic response in Alzheimer's disease depends on the interaction of genes involved in drug metabolism and genes associated with Alzheimer's disease pathogenesis.

Pharmacogenomics and therapeutic prospects in dementia

Dementia is a major problem of health in developed countries. Alzheimer's disease (AD) is the main cause of dementia, accounting for 50-70% of the cases, followed by vascular dementia (30-40%) and mixed dementia (15-20%). Approximately 10-15% of direct costs in dementia are attributed to pharmacological treatment, and only 10-20% of the patients are moderate responders to conventional anti-dementia drugs, with questionable cost-effectiveness. Primary pathogenic events underlying the dementia process include genetic factors in which more than 200 different genes distributed across the human genome are involved, accompanied by progressive cerebrovascular dysfunction and diverse environmental factors. Mutations in genes directly associated with the amyloid cascade (APP, PS1, PS2) are only present in less than 5% of the AD population; however, the presence of the APOE-4 allele in the apolipoprotein E (APOE) gene represents a major risk factor for more than 40% of patients with dementia. Genotype-phenotype correlation studies and functional genomics studies have revealed the association of specific mutations in primary loci (APP, PS1, PS2) and/or APOE-related polymorphic variants with the phenotypic expression of biological traits. It is estimated that genetics accounts for 20-95% of variability in drug disposition and pharmacodynamics. Recent studies indicate that the therapeutic response in AD is genotype-specific depending upon genes associated with AD pathogenesis and/or genes responsible for drug metabolism (CYPs). In monogenic-related studies, APOE-4/4 carriers are the worst responders. In trigenic (APOE-PS1-PS2 clusters)-related studies the best responders are those patients carrying the 331222-, 341122-, 341222-, and 441112- genomic profiles. The worst responders in all genomic clusters are patients with the 441122+ genotype, indicating the powerful, deleterious effect of the APOE-4/4 genotype on therapeutics in networking activity with other AD-related genes. Cholinesterase inhibitors of current use in AD are metabolized via CYP-related enzymes. These drugs can interact with many other drugs which are substrates, inhibitors or inducers of the cytochrome P-450 system; this interaction elicits liver toxicity and other adverse drug reactions. CYP2D6-related enzymes are involved in the metabolism of more than 20% of CNS drugs. The distribution of the CYP2D6 genotypes differentiates four major categories of CYP2D6-related metabolyzer types: (a) Extensive Metabolizers (EM)(*1/*1, *1/*10)(51.61%); (b) Intermediate Metabolizers (IM) (*1/*3, *1/*4, *1/*5, *1/*6, *1/*7, *10/*10, *4/*10, *6/*10, *7/*10) (32.26%); (c) Poor Metabolizers (PM) (*4/*4, *5/*5) (9.03%); and (d) Ultra-rapid Metabolizers (UM) (*1xN/*1, *1xN/*4, Dupl) (7.10%). PMs and UMs tend to show higher transaminase activity than EMs and IMs. EMs and IMs are the best responders, and PMs and UMs are the worst responders to pharmacological treatments in AD. It seems very plausible that the pharmacogenetic response in AD depends upon the interaction of genes involved in drug metabolism and genes associated with AD pathogenesis. The establishment of clinical protocols for the practical application of pharmacogenetic strategies in AD will foster important advances in drug development, pharmacological optimization and cost-effectiveness of drugs, and personalized treatments in dementia.

Patient preferences for pharmacogenetic screening in depression

Objectives:The aims of this study were to estimate preferences and willingness-to-pay (WTP) for genetic screening for CYP2D6 polymorphisms among a group of former and currently depressed patients.

Methods:A Web-based discrete choice questionnaire was sent to 89 respondents, age 18–65. Four attributes were included: (i) shifts in antidepressant medication before symptom relief, (ii) time with antidepressant medication without symptom relief, (iii) time with antidepressant medication without symptoms but with adverse side-effects, (iv) cost of genetic screening. We used a switching model with two scenarios, one representing patients’ own treatment history and the other a treatment scenario with genetic screening.

Results:In a main-effects model involving the four attributes all coefficients had the expected sign, indicating that as the number of shifts, price or time without symptom relief, and/or dosage-adjustments increased, the likelihood of choosing the screening test decreased. Price and number of shifts in medicine were significant. Marginal WTP for 5 percent probability of a reduction of one in antidepressant shifts was DKK2,599 (€350).

Conclusions:Patients value reductions in shifts in antidepressants and price when choosing between genetic screening and no screening. They do not focus on how the reductions are provided, nor do they value the genetic information the test provides irrespective of its effect on outcome. Given, that the test is able to provide a reduction of one shift in the number of antidepressant shifts with a probability of 5 percent, WTP for the test exceeds its cost.

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

Individualizing antipsychotic drug therapy in schizophrenia: the promise of pharmacogenetics

The first- and second-generation antipsychotic drugs have become mainstay drug treatment for schizophrenia. However, patients who receive antipsychotic drugs differ with respect to treatment response and drug-induced adverse events. The biological predictors of treatment response are being researched worldwide, with emphasis on molecular genetic predictors of treatment response. Because of the rapid and exciting developments in the field, we reviewed the recent studies of the molecular genetic basis of treatment response in schizophrenia. The accumulating data suggest that DNA information in the pathways for drug metabolism and drug target sites may be an important predictor of treatment response in schizophrenia. The data suggest that clinicians may soon be using a patient's genotype to decide initial choice of antipsychotic drug treatment in schizophrenia. The pharmacogenetics of schizophrenia can improve the prospects of individualized treatment and drug discovery. Pharmacogenetic investigations of schizophrenia susceptibility loci, and genes controlling drug target site receptors, drug-metabolizing enzymes, the blood-brain barrier systems, and epigenetic mechanisms could lead to a molecular classification of treatment response and adverse events of psychotropic drugs.

Genetic polymorphisms of drug-metabolizing enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 in the Greek population

The aim of the present study was to determine the prevalence of the most common allelic variants of the polymorphic cytochrome P450 (CYP) enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 and to predict the genotype frequency for each polymorphism in the Greek population. DNA isolated from peripheral blood samples derived from 283 non-related Greek ethnic subjects was used to determine the frequency of CYP2D6*3, CYP2D6*4, CYP2C9*2, CYP2C9*3 and CYP3A5*3 allelic variants by the polymerase chain reaction (PCR)-restriction fragment length polymorphism method, CYP2C19*2 and CYP2C19*3 with allelic specific amplification (PCR-ASA), and CYP2D6*2 (gene duplications) by long PCR analysis. The allelic frequencies (out of a total of 566 alleles) for CYP2D6*3 and CYP2D6*4, were 2.3% and 17.8%, respectively, while gene duplications (CYP2D6*2) were found in 7.4% of the subjects tested. For CYP2C9*2 and CYP2C9*3 polymorphisms the allelic frequencies were 12.9% and 8.13% respectively. For CYP2C19, the *2 polymorphism was present at an allelic frequency of 13.1%, while no subjects were found carrying the CYP2C19*3 allele. Finally, the CYP3A5*3 allele was abundantly present in the Greek population with an allelic frequency of 94.4%. Overall our results show that the frequencies of the common defective allelic variants of CYP2C9, CYP2C19 and CYP3A5 in Greek subjects are similar to those reported for several other Caucasian populations. Finally, a high prevalence of CYP2D6 gene duplication among Greeks was found, a finding that strengthens the idea that a South/North gradient exists in the occurrence of CYP2D6 ultrarapid metabolizers in European populations.