Antipsychotic drug-induced movement disorders in schizophrenics in relation to CYP2D6 genotype

Genetic Factors Associated With Tardive Dyskinesia: From Pre-clinical Models to Clinical Studies

Tardive dyskinesia is a severe motor adverse event of antipsychotic medication, characterized by involuntary athetoid movements of the trunk, limbs, and/or orofacial areas. It affects two to ten patients under long-term administration of antipsychotics that do not subside for years even after the drug is stopped. Dopamine, serotonin, cannabinoid receptors, oxidative stress, plasticity factors, signaling cascades, as well as CYP isoenzymes and transporters have been associated with tardive dyskinesia (TD) occurrence in terms of genetic variability and metabolic capacity. Besides the factors related to the drug and the dose and patients’ clinical characteristics, a very crucial variable of TD development is individual susceptibility and genetic predisposition. This review summarizes the studies in experimental animal models and clinical studies focusing on the impact of genetic variations on TD occurrence. We identified eight genes emerging from preclinical findings that also reached statistical significance in at least one clinical study. The results of clinical studies are often conflicting and non-conclusive enough to support implementation in clinical practice.

CYP2D6 Genotyping and Antipsychotic-Associated Extrapyramidal Adverse Effects in a Randomized Trial of Aripiprazole Versus Quetiapine Extended Release in Children and Adolescents, Aged 12-17 Years, With First Episode Psychosis

PURPOSE/BACKGROUND

The aim of this study was to examine the association between genetically predicted CYP2D6 phenotypes and extrapyramidal symptoms (EPSs).

METHODS/PROCEDURES

Data from the Tolerability and Efficacy of Antipsychotics trial of adolescents with first-episode psychosis randomized to aripiprazole versus quetiapine extended release were studied. Extrapyramidal symptom assessments included the Simpson-Angus Scale and the Barnes Akathisia Rating Scale. Patients were CYP2D6 genotyped. Plasma concentrations of antipsychotics and antidepressants were analyzed.

FINDINGS/RESULTS

One hundred thirteen youths (age, 12-17 years; males, 30%; antipsychotic naive, 51%) were enrolled. Poor metabolizers had a significantly higher dose-adjusted aripiprazole plasma concentration (±SD) compared with normal metabolizers at week 4 (24.30 ± 6.40 ng/mL per milligram vs 14.85 ± 6.15 ng/mL per milligram; P = 0.019), but not at week 12 (22.15 ± 11.04 ng/mL per milligram vs 14.32 ± 4.52 ng/mL per milligram; P = 0.067). This association was not found in the quetiapine extended release group. No association between CYP2D6 genotype groups and global Barnes Akathisia Rating Scale score or Simpson-Angus Scale score was found in any of the treatment arms.

IMPLICATIONS/CONCLUSIONS

Our results do not support routine use of CYP2D6 testing as a predictor of drug-induced parkinsonism or akathisia risk in clinical settings. Further studies with larger samples of CYP2D6 poor metabolizers are needed.

Genetic Testing for Antipsychotic Pharmacotherapy: Bench to Bedside

There is growing research interest in learning the genetic basis of response and adverse effects with psychotropic medications, including antipsychotic drugs. However, the clinical utility of information from genetic studies is compromised by their controversial results, primarily due to relatively small effect and sample sizes. Clinical, demographic, and environmental differences in patient cohorts further explain the lack of consistent results from these genetic studies. Furthermore, the availability of psychopharmacological expertise in interpreting clinically meaningful results from genetic assays has been a challenge, one that often results in suboptimal use of genetic testing in clinical practice. These limitations explain the difficulties in the translation of psychopharmacological research in pharmacogenetics and pharmacogenomics from bench to bedside to manage increasingly treatment-refractory psychiatric disorders, especially schizophrenia. Although these shortcomings question the utility of genetic testing in the general population, the commercially available genetic assays are being increasingly utilized to optimize the effectiveness of psychotropic medications in the treatment-refractory patient population, including schizophrenia. In this context, patients with treatment-refractory schizophrenia are among of the most vulnerable patients to be exposed to the debilitating adverse effects from often irrational and high-dose antipsychotic polypharmacy without clinically meaningful benefits. The primary objective of this comprehensive review is to analyze and interpret replicated findings from the genetic studies to identify specific genetic biomarkers that could be utilized to enhance antipsychotic efficacy and tolerability in the treatment-refractory schizophrenia population.

Genetics of tardive dyskinesia: Promising leads and ways forward

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

CYP450 pharmacogenetic treatment strategies for antipsychotics: a review of the evidence

Although a number of first- and second-generation antipsychotics are available, achieving optimal therapeutic response for patients with schizophrenia can be challenging. The presence of polymorphic alleles for cytochrome P (CYP) 450 may result in lack of expression, altered levels of expression, or altered function of CYP450 enzymes. CYP2D6, CYP1A2, and CYP3A4/5 are major enzymes in the metabolism of antipsychotics and polymorphisms of alleles for these proteins are associated with altered plasma levels. Consequently, standard dosing may result in drug plasma concentrations that are subtherapeutic or toxic in some patients. Patient CYP450 genotype testing can predict altered pharmacokinetics, and is currently available and relatively inexpensive. Evidence-based guidelines provide dose recommendations for some antipsychotics. To date few studies have demonstrated a significant association with genotype-guided antipsychotic use and clinical efficacy. However, many studies have been small, retrospective or cohort designs, and many have not been adequately powered. Numerous studies have shown a significant association between genotype and adverse effects, such as CYP2D6 polymorphisms and tardive dyskinesia. This review summarizes evidence for the role of CYP450 genetic variants in the response to antipsychotic medications and the clinical implications of pharmacogenetics in the management of patients with schizophrenia.

Genetic variability of drug-metabolizing enzymes: the dual impact on psychiatric therapy and regulation of brain function

Polymorphic drug-metabolizing enzymes (DMEs) are responsible for the metabolism of the majority of psychotropic drugs. By explaining a large portion of variability in individual drug metabolism, pharmacogenetics offers a diagnostic tool in the burgeoning era of personalized medicine. This review updates existing evidence on the influence of pharmacogenetic variants on drug exposure and discusses the rationale for genetic testing in the clinical context. Dose adjustments based on pharmacogenetic knowledge are the first step to translate pharmacogenetics into clinical practice. However, also clinical factors, such as the consequences on toxicity and therapeutic failure, must be considered to provide clinical recommendations and assess the cost-effectiveness of pharmacogenetic treatment strategies. DME polymorphisms are relevant not only for clinical pharmacology and practice but also for research in psychiatry and neuroscience. Several DMEs, above all the cytochrome P (CYP) enzymes, are expressed in the brain, where they may contribute to the local biochemical homeostasis. Of particular interest is the possibility of DMEs playing a physiological role through their action on endogenous substrates, which may underlie the reported associations between genetic polymorphisms and cognitive function, personality and vulnerability to mental disorders. Neuroimaging studies have recently presented evidence of an effect of the CYP2D6 polymorphism on basic brain function. This review summarizes evidence on the effect of DME polymorphisms on brain function that adds to the well-known effects of DME polymorphisms on pharmacokinetics in explaining the range of phenotypes that are relevant to psychiatric practice.

Treatment of neurolept-induced tardive dyskinesia

Tardive dyskinesia (TDK) includes orobuccolingual movements and "piano-playing" movements of the limbs. It is a movement disorder of delayed onset that can occur in the setting of neuroleptic treatment as well as in other diseases and following treatment with other drugs. The specific pathophysiology resulting in TDK is still not completely understood but possible mechanisms include postsynaptic dopamine receptor hypersensitivity, abnormalities of striatal gamma-aminobutyric acid (GABA) neurons, and degeneration of striatal cholinergic interneurons. More recently, the theory of synaptic plasticity has been proposed. Considering these proposed mechanisms of disease, therapeutic interventions have attempted to manipulate dopamine, GABA, acetylcholine, norepinephrine and serotonin pathways and receptors. The data for the effectiveness of each class of drugs and the side effects were considered in turn.

Utility and adoption of CYP2D6 and CYP2C19 genotyping and its translation into psychiatric clinical practice

OBJECTIVE

To describe clinical utility and adoption of routinely offered CYP2D6 and CYP2C19 genotyping (CYP test) in daily clinical practice of a psychiatric centre.

METHOD

We described psychiatrists translations of CYP test results in patients with genotypes indicating poor or ultrarapid metabolizer status and treated with at least one CYP-dependent drug based on a retrospective review of medical records. Complementary, we used ethnographic participant observation and qualitative interviews to identify the barriers and incentives for the use of CYP test results.

RESULTS

The cohort study included 101 of 1932 cases genotyped between 2003 and 2009. In 53 of 101 cases, test results were addressed in medical records. The most frequent response was to monitor drug concentrations (23 cases), observe for adverse events (18 cases) and adjust dosage (13 cases). In 33 of 101 cases, results were mentioned in the discharge letter. The ethnographic study indicated a poor adoption of the CYP test in clinical praxis. Test results were lost in workflows and knowledge transfer between laboratory and clinician and were absent from clinical routines, treatment conferences and educational fora.

CONCLUSION

The CYP test has not gained foothold in clinical practice, and its potential clinical benefits are not utilized.

Cytochrome P450 testing for prescribing antipsychotics in adults with schizophrenia: systematic review and meta-analyses

There is wide variability in the response of individuals to standard doses of antipsychotic drugs. It has been suggested that this may be partly explained by differences in the cytochrome P450 (CYP450) enzyme system responsible for metabolizing the drugs. We conducted a systematic review and meta-analyses to consider whether testing for CYP450 single nucleotide polymorphisms in adults starting antipsychotic treatment for schizophrenia predicts and leads to improvements in clinical outcomes. High analytic validity in terms of sensitivity and specificity was seen in studies reporting P450 testing. However, there was limited evidence of the role of CYP2D6 polymorphisms in antipsychotic efficacy, although there was an association between CYP2D6 genotype and extrapyramidal adverse effects. No studies reported on the prospective use of CYP2D6 genotyping tests in clinical practice. In conclusion, evidence of clinical validity and utility of CYP2D6 testing in patients being prescribed antipsychotics is lacking, and thus, routine pharmacogenetic testing prior to antipsychotic prescription cannot be supported at present. Further research is required to improve the evidence base and to generate data on clinical validity and clinical utility.

Pharmacogenetics of debrisoquine and its use as a marker for CYP2D6 hydroxylation capacity

Debrisoquine hydroxylation polymorphism is by far the most thoroughly studied genetic polymorphism of the CYP2D6 drug-metabolizing enzyme. Debrisoquine hydroxylation phenotype has been the most used test in humans to evaluate CYP2D6 activity. Two debrisoquine hydroxylation phenotypes have been described: poor and extensive metabolizers. A group with a very low debrisoquine metabolic ratio within the extensive metabolizers, named ultrarapid metabolizers, has also been distinguished. This CYP2D6 variability can be for a large part alternatively determined by genotyping, which appears to be of clinical importance given CYP2D6 involvement in the metabolism of a large number of commonly prescribed drugs. CYP2D6 pharmacogenetics may then become a useful tool to predict drug-related side effects, interactions or therapeutic failures. However, a number of reasons appear to have made research into this field lag behind. The present review focuses on the relevance of genetics and environmental factors for determining debrisoquine hydroxylation phenotype, as well as the relevance of CYP2D6 genetic polymorphism in psychiatric patients treated with antipsychotic drugs.

Pharmacogenetics of parkinsonism, rigidity, rest tremor, and bradykinesia in African-Caribbean inpatients: differences in association with dopamine and serotonin receptors

We studied the association between polymorphisms of genes coding for dopamine D(2) (DRD2), dopamine D(3) (DRD3), serotonin 2(a) (HTR2A), and serotonin 2(c) (HTR2C) receptors and Antipsychotic-Induced Parkinsonism (AIP), rigidity, bradykinesia, and rest-tremor in African-Caribbeans treated with antipsychotics. Polymorphisms of DRD2 (-141CIns/Del, TaqIA, 957C > T), DRD3 (Ser9Gly), HTR2A (-1438A > G, 102T > C, His452Tyr), and HTR2C (-759C > T, Cys23Ser) genes were determined according to standard protocols. The Unified Parkinson Disease Rating Scale was used for the measurement of AIP, rigidity, bradykinesia, and rest-tremor. Chi-squared or Fisher's exact tests were applied for the association analyses. The t-test was applied for continuous data. Ninety nine males and 27 females met the inclusion criteria (Schizophr Res 1996, 19:195). In males, but not in females, there were significant associations between -141CDel-allele carriership (DRD2) and rigidity (Fisher's Exact Test: P = 0.021) and between 23Ser-allele carriership (HTR2C) and bradykinesia (P = 0.026, chi(2) = 5.0) or AIP (P = 0.008, chi(2) = 7.1). Rest-tremor was not associated with any of the polymorphisms studied. Analyses of the age, chlorpromazine equivalents, benztropine equivalents, the number of patients using anticholinergic medication, and the utilization patterns of the antipsychotic medication did not show statistically significant differences between patients with and without AIP, rigidity, bradykinesia, rest-tremor. Conducting the analysis without gender stratification did not affect our findings considerably, except for the association between bradykinesia and 23Ser-allele which failed to reach statistical significance in the total sample (P = 0.0646, chi(2) = 3.41). Since AIPs subsymptoms (rigidity, bradykinesia, and rest-tremor) may differ pharmacogenetically, our data strongly support symptom-specific analysis of AIP. However, further research is warranted to confirm our findings.

Gene polymorphism influencing treatment response in psychotic patients in a naturalistic setting

RATIONALE

Many patients with psychotic symptoms respond poorly to treatment. Factors possibly affecting treatment response include the presence of polymorphisms in genes coding for various receptor populations, drug-metabolizing enzymes or transport proteins.

OBJECTIVES

To investigate whether genetic polymorphisms could be indicators of treatment response to antipsychotic drugs. The genes of interest were the dopamine D2 receptor gene (DRD2), the serotonin 2A and 2C receptor genes (HTR2A and HTR2C), the P-glycoprotein gene (ABCB1 or MDR1) and the drug-metabolizing cytochrome P450 2D6 gene (CYP2D6).

MATERIAL AND METHODS

Data for this naturalistic, cross-sectional study of patients requiring antipsychotic drugs and attending the Psychosis Outpatient Care clinic in Jönköping, Sweden were obtained from patient interviews, blood samples and information from patient files. Blood samples were genotyped for DRD2 Taq1 A, Ins/Del and Ser311Cys, HTR2A T102C, HTR2C Cys23Ser, ABCB1 1236C>T, 2677G>T/A, 3435C>T and genetic variants of CYP2D6. The patients (n=116) were grouped according to the CANSEPT method regarding significant social and clinical needs and significant side effects.

RESULTS

Patients on olanzapine homozygous for ABCB1 3435T, had more significant social and clinical needs than others. Patients with one or two DRD2 Taq1 A1 alleles had a greater risk of significant side effects, particularly if they were male, Caucasian, had a schizophrenic or delusional disorder or were taking strong dopamine D2-receptor antagonistic drugs.

CONCLUSION

If these results are confirmed, patients carrying the DRD2 Taq1 A1 allele would benefit from using drugs without strong dopamine D2 receptor antagonistic properties.

Impact of CYP2D6 genetic polymorphism on tramadol pharmacokinetics and pharmacodynamics

BACKGROUND AND OBJECTIVE

Tramadol is metabolized by the highly polymorphic enzyme cytochrome P450 (CYP)2D6. Patients with different CYP2D6 genotypes may respond differently to tramadol in terms of pain relief and adverse events. In this study, we compare the pharmacokinetics and effects of tramadol in Malaysian patients with different genotypes to establish the pharmacokinetic-pharmacodynamic relationship of tramadol.

STUDY DESIGN AND SETTING

All patients received an intravenous dose of tramadol 100mg as their first postoperative analgesic. Blood was sampled at 0 minutes and subsequently at 15 and 30 minutes, 1, 2, 4, 8, 16, 20, and 24 hours for serum tramadol and analyzed by high-performance liquid chromatography (HPLC). Patients were genotyped for CYP2D6*1, *3, *4, *5, *9, *10, and *17 alleles and duplication of the gene by means of an allele-specific PCR. Pain was measured using the Visual Analog Scales, and adverse effects were recorded.

RESULTS

About half of the patients had the wild-type allele (CYP2D6*1), with the 'Asian'CYP2D6*10 allele accounting for most of the rest (40%). None of the genotypes predicted poor metabolism. Twenty-seven percent of the patients were intermediate metabolizers (IM) and 2.9% were ultra-rapid (UM) metabolizers; the remaining 70% were extensive metabolizers (EM). The mean total clearance (CL) predicted by the model was lower (19 L/h) and the half-life longer (5.9 hours) than those reported in Western populations. This may due to the high frequency of the CYP2D6*10 allele amongst Malaysian patients. The UM and EM groups had 2.6- and 1.3-times faster CL, respectively, than the IM. CL was 16, 18, 23, and 42 L/h while mean half-lives were 7.1, 6.8, 5.6, and 3.8 hours among the IM, EM1, EM2, and UM groups, respectively. However, the analgesic effects of tramadol were not measured adequately among the postoperative patients to establish its full therapeutic effects. There were significant differences in the adverse-effect profiles amongst the various genotype groups, with the IM group experiencing more adverse effects than the EM, and the EM having more adverse effects than the UM.

CONCLUSION

CYP2D6 activity may play an important role in determining the pharmacokinetics of tramadol and in predicting its adverse effects. If these results can be confirmed in a larger population, genotyping may be an important tool in determining the dose of tramadol.

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.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

The influence of the CYP2D6 polymorphism on psychopathological and extrapyramidal symptoms in the patients on long-term antipsychotic treatment

Poor response to antipsychotics treatment and extrapyramidal side effects (EPS) are the most challenging problems in the treatment of schizophrenia. Several studies were investigating the impact of polymorphic cytochrome P450 2D6 gene (CYP2D6) on EPS but the results were conflicting. There are practically no clinical studies of long-term treatment of schizophrenia and CYP2D6 polymorphism. Our aim was to evaluate the influence of CYP2D6 genotype on psychopathological symptoms and the occurrence of EPS in Slovenian outpatients with schizophrenia or schizoaffective disorder in stable remission, receiving long-term maintenance antipsychotic treatment. In total 131 outpatients meeting the DSM IV criteria for schizophrenia or schizoaffective disorder and receiving maintenance therapy with haloperidol, fluphenazine, zuclopethixole or risperidone were genotyped for 14 polymorphic CYP2D6 alleles. Psychopathological symptoms were assessed with the Positive and Negative Symptom Scale for Schizophrenia (PANSS). EPS were assessed with the Simpson Angus Scale (SAS), the Barnes Akathisia Scale and the Abnormal Involuntary Movement Scale (AIMS). Six patients (4.6%) were genotyped as poor metabolizers (PMs). PMs scored significantly higher on the negative subscale for PANSS. There were no statistically significant differences between the group of PMs and the group of patients with at least one functional CYP2D6 allele in view of patient's characteristics or any of the items of the AIMS, the SAS or the Barnes Akathisia Scale. CYP2D6 genotype may not be the major factor that determines the susceptibility to antipsychotic-induced EPS in Slovenian patients in stable remission and on maintenance therapy with antipsychotics that are mainly CYP2D6 substrates. However, CYP2D6 genotype might be a factor contributing to the persistent negative symptoms of schizophrenia.

The AmpliChip CYP450 genotyping test: Integrating a new clinical tool

The AmpliChip CYP450 Test, which analyzes patient genotypes for cytochrome P450 (CYP) genes CYP2D6 and CYP2C19, is a major step toward introducing personalized prescribing into the clinical environment. Interest in adverse drug reactions (ADRs), the genetic revolution, and pharmacogenetics have converged with the introduction of this tool, which is anticipated to be the first of a new wave of such tools to follow over the next 5-10 years. The AmpliChip CYP450 Test is based on microarray technology, which combines hybridization in precise locations on a glass microarray and a fluorescent labeling system. It classifies individuals into two CYP2C19 phenotypes (extensive metabolizers [EMs] and poor metabolizers [PMs]) by testing three alleles, and into four CYP2D6 phenotypes (ultrarapid metabolizers [UMs], EMs, intermediate metabolizers [IMs], and PMs) by testing 27 alleles, including seven duplications. CYP2D6 is a metabolic enzyme with four activity levels (or phenotypes): UMs with unusually high activity; normal subjects, known as EMs; IMs with low activity; and PMs with no CYP2D6 activity (7% of Caucasians and 1-3% in other ethnic groups). Levels of evidence for the association between CYP2D6 PMs and ADRs are relatively reasonable and include systematic reviews of case-control studies of some typical antipsychotics and tricyclic antidepressants (TCAs). Evidence for other phenotypes is considerably more limited. The CYP2D6 PM phenotype may be associated with risperidone ADRs and discontinuation due to ADRs. Venlafaxine, aripiprazole, duloxetine, and atomoxetine are newer drugs metabolized by CYP2D6 but studies of the clinical relevance of CYP2D6 genotypes are needed. Non-psychiatric drugs metabolized by CYP2D6 include metoprolol, tamoxifen, and codeine-like drugs. CYP2C19 PMs (3-4% of Caucasians and African Americans, and 14-21% of Asians) may require dose adjustment for some TCAs, moclobemide, and citalopram. Other drugs metabolized by CYP2C19 are diazepam and omeprazole. The future of pharmacogenetics depends on the ability to overcome serious obstacles, including the difficulties of conducting and publishing studies in light of resistance from grant agencies, pharmaceutical companies, and some scientific reviewers. Assuming more studies are published, pharmacogenetic clinical applications may be compromised by economic factors and the lack of physician education. The combination of a US FDA-approved test, such as the AmpliChip CYP450 Test, and an FDA definition of CYP2D6 as a 'valid biomarker' makes CYP2D6 genotyping a prime candidate to be the first successful pharmacogenetic test in the clinical environment. One can use microarray technology to test for hundreds of single nucleotide polymorphisms (SNPs) but, taking into account the difficulties for single gene approaches such as CYP2D6, it is unlikely that very complex pharmacogenetic approaches will reach the clinical market in the next 5-10 years.

Investigation of the phenylalanine hydroxylase gene and tardive dyskinesia

Phenylketonuria (PKU), an inborn error of phenylalanine metabolism, has been shown to be a risk factor for tardive dyskinesia (TD). In male psychiatric patients there was a significant relationship between TD and measures of plasma phenylalanine following ingestion of a standardized phenylalanine dose that was indicative of higher brain availability of phenylalanine in patients with TD. In addition, a medical food formulation consisting of branched chain amino acids, which compete with phenylalanine for transport across the blood-brain barrier, has been demonstrated to be an efficacious treatment for TD. Cumulatively these findings suggested that TD was related to phenylalanine metabolism and thus that sequence variants in the gene for phenylalanine hydroxylase (PAH), the rate-limiting enzyme in the catabolism of phenylalanine, could be associated with TD susceptibility. Genetic screening of PAH in a group of 123 psychiatric patients revealed ten sequence polymorphisms and two mutations, but none appeared to be a significant risk factor for TD.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.

Genetic susceptibility to tardive dyskinesia in chronic schizophrenia subjects: III. Lack of association of CYP3A4 and CYP2D6 gene polymorphisms

Tardive dyskinesia is a severe debilitating movement disorder characterized by choreoathetotic movements developing in one-fifth of the patients with schizophrenia. In this study we have investigated the significance of CYP3A4*1B and CYP2D6*4 polymorphisms in TD susceptibility among chronic schizophrenia patients (n = 335) from north India. Tardive dyskinesia was diagnosed in approximately 29% (96/335) of these patients. No significant association of either of the two SNPs with TD (CYP3A4*1B chi2 = 0. 308, df = 1, p = 0.579; CYP2D6*4 chi2 = 0.006, df = 1, p = 0.935) was observed. However a trend towards increased severity of TD in patients heterozygous for the CYP2D6*4 mutation was observed.

CYP2D6 polymorphisms and the risk of tardive dyskinesia in schizophrenia: a meta-analysis

The present study aimed to evaluate whether there is any association between CYP2D6 alleles and susceptibility to tardive dyskinesia in patients with schizophrenia under treatment. A meta-analysis considered case-control studies determining the distribution of genotypes for any CYP2D6 polymorphism in unrelated tardive dyskinesia cases and controls without tardive dyskinesia among patients with schizophrenia who were treated with antipsychotic agents. Loss of function alleles were grouped together in a single comparison, whereas other alleles (2 and 10) were examined separately. Data were available for eight (n=569 patients), three (n=325 patients) and four (n=556) studies evaluating the effect of the loss of function alleles, the 2 allele and the 10 allele, respectively. Summary odds ratios (ORs) suggested that loss of function alleles increased the risk of tardive dyskinesia significantly [OR=1.43, 95% confidence interval (CI) 1.06-1.93, P=0.021], whereas there was no effect for 2 and inconclusive evidence for 10 (OR=0.82, 95% CI 0.50-1.32, P=0.41 and OR=1.19, 95% CI, 0.89-1.60, P=0.24, respectively). Patients who were homozygotes for loss of function alleles (poor metabolizers) had 1.64-fold greater odds of suffering tardive dyskinesia compared to other patients with schizophrenia, but the effect was not formally significant (95% CI 0.79-3.43). For the risk conferred by loss of function alleles, large studies provided more conservative estimates of a genetic effect than smaller studies (P=0.003). CYP2D6 loss of function alleles may predispose to tardive dyskinesia in patients with schizophrenia under treatment, but bias cannot be excluded.

Genetic susceptibility to Tardive Dyskinesia in chronic schizophrenia subjects: I. Association of CYP1A2 gene polymorphism

Understanding the pharmacogenetic basis of developing iatrogenic disorders such as Tardive Dyskinesia (TD) has significant clinical implications. CYP1A2, an inducible gene of the cytochrome P450 family of genes, has been suggested to contribute to the metabolism of typical antipsychotics in subjects with schizophrenia on long-term treatment, and has been considered as a potential candidate gene for development of TD. In this study, we have investigated the significance of CYP1A2 gene polymorphisms in TD susceptibility among chronic schizophrenia sufferers (n=335) from north India. TD was diagnosed in approximately 29% (96/335) of these subjects. Of the 96 TD positives, 28 had been treated with typical antipsychotics alone, 23 with atypical antipsychotics alone and 45 patients had received both classes of drugs during the course of their illness. Out of the six SNPs tested, CYP1A2(*)2, (*)4, (*)5, (*)6 were found to be monomorphic in our population. CYP1A2(*)1C and CYP1A2(*)1F were polymorphic and were analyzed in the study sample. Since these two allelic variants lead to lesser inducibility among smokers, the smoking status of TD patients was also considered for all subsequent analysis. We observed increased severity of TD among TD-Y smokers, who were carriers of CYP1A2(*)1C (G>A) variant allele and had received only typical antipsychotic drugs (F(1,8)=9.203, P=0.016). No significant association of CYP1A2(*)1F with TD was observed irrespective of the class of drug they received or their smoking status. However, we found a significant association of CYP1A2(*)1F with schizophrenia (chi(2)=6.572, df=2, P=0.037).

Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response

Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.

Cytochrome P450 II D6 gene polymorphisms and the neuroleptic-induced extrapyramidal symptoms in Japanese schizophrenic patients

OBJECTIVE

The purpose of this study was to examine whether the neuroleptic-induced extrapyramidal symptoms are associated with the CYP2D6 activity.

METHODS

The CYP2D6 gene polymorphisms (CYP2D6*2, CYP2D6*3, CYP2D6*4, CYP2D6*10, and CYP2D6*12) were genotyped in 196 normal controls and 320 schizophrenic patients receiving neuroleptics. The relationships with susceptibility to extrapyramidal symptoms (EPS) and tardive dyskinesia, and with steady-state serum haloperidol levels in maintenance therapy, were investigated.

RESULTS

The allele frequency of CYP2D6*2 was significantly higher, while that of CYP2D6*10 tended to be higher in the schizophrenic patients susceptible to acute EPS. The steady-state serum haloperidol levels per daily dosage were observed to be significantly higher in schizophrenic patients with the mutant-type homozygote of CYP2D6*2, while this difference was trend level in those of CYP2D6*10. However, no significant difference was observed in the distribution of both CYP2D6*2 (C2938T) and CYP2D6*10 (C188T) polymorphisms between schizophrenic patients with or without tardive dyskinesia.

CONCLUSION

The present results suggest that the homozygotes of CYP2D6*2 and CYP2D6*10 appear to be a susceptibility factor for developing acute EPS in schizophrenic patients and for impaired neuroleptic metabolism in Japanese schizophrenic patients.

Association between CYP2D6 genotype and tardive dyskinesia in Korean schizophrenics

The CYP2D6 gene codes for human cytochrome P450 2D6 enzyme, which is responsible for the metabolism of many psychiatric drugs. In schizophrenic patients treated with neuroleptics, decreased or loss of function CYP2D6 alleles may contribute to the development of tardive dyskinesia (TD), a movement disorder that frequently occurs with chronic neuroleptic treatment. The goal of this study was to determine whether the occurrence of TD is associated with CYP2D6 genotype in a cohort of Korean schizophrenics by employing a CYP450 GeneChip((R)) oligonucleotide microarray and PCR assays to screen for 19 CYP2D6 alleles. Our results revealed that males with at least one decreased or loss of function allele have a moderately greater chance of developing TD than males with only wild-type alleles. Female schizophrenics did not have a significantly greater chance of developing TD. Our results demonstrate the utility of CYP2D6 microarrays to assess genotype status in this Korean cohort.

A perspective on molecular genetic studies of tardive dyskinesia: one clue for individualized antipsychotic drug therapy

Interindividual genetic profile differences related to antipsychotic drug therapy may be determined based on molecular genetic studies of the pathogenesis of schizophrenia and studies of antipsychotic drug responses (therapeutic as well as adverse responses). In the present article, we review molecular genetic studies of tardive dyskinesia (TD), which is a representative adverse response to antipsychotic drugs. Such studies have been performed to explore the gene-associated pharmacokinetic and pharmacodynamic processes of antipsychotic drugs. Positive associations between several genes and TD have been reported. The accumulation of results from such studies will hopefully lead to individualized antipsychotic drug therapies that involve the application of new genomic techniques, including DNA microarrays. Subsequently, antipsychotic drugs may in the future be prescribed for smaller subgroups of patients who have been classified as having a particular genetic profile.

Pharmacogenetics of schizophrenia

Patients display significant differences in response to therapeutic agents which may be caused by a variety of factors. Among them, genetic components presumably play a major role. Pharmacogenetics is the field of research that attempts to unravel the relationship between genetic variation affecting drug metabolism (pharmacokinetic level) or drug targets (pharmacodynamic level) and interindividual differences in pharmacoresponse. In schizophrenia, pharmacokinetic studies have shown the role of genetic variants of the cytochrome P450 enzymes CYP2D6, CYP2C19, and CYP2C9 in the metabolism of neuroleptic drugs. At the level of the drug target, variants of the dopamine D3 and D4, and 5-HT2A and 5-HT2C receptors have been examined. A general problem of pharmacogenetic studies in schizophrenia is the high number of controversial findings which may be related to the lack of standardized phenotype definition. Recently, guidelines for an exact and comparable phenotype characterization have been proposed and will aid in designing and evaluating pharmacogenetic studies in the future. The final goal of pharmacogenetic studies-making a prediction of drug response at the level of the individual patient-will require a simultaneous look at a large number of response-determining genetic variants by applying the tools of pharmacogenomics, e.g. large-scale Single Nucleotide Polymorphism (SNP) detection and genotyping.

Serotonin syndrome and other serotonergic disorders

Serotonin syndrome is an iatrogenic disorder induced by pharmacologic treatment with serotonergic agents that increases serotonin activity. In addition, there is a wide variety of clinical disorders associated with serotonin excess. The frequent concurrent use of serotonergic and neuroleptic drugs and similarities between serotonin syndrome and neuroleptic malignant syndrome can present the clinician with a diagnostic challenge. In this article, we review the pathophysiology, diagnosis, and treatment of serotonin syndrome as well as other serotonergic disorders.

Cytochrome p450 phenotyping/genotyping in patients receiving antipsychotics: useful aid to prescribing?

Many antipsychotics, including perphenazine, zuclopenthixol, thioridazine, haloperidol and risperidone, are metabolised to a significant extent by the polymorphic cytochrome P450 (CYP) 2D6, which shows large interindividual variation in activity. Significant relationships between CYP2D6 genotype and steady-state concentrations have been reported for perphenazine, zuclopenthixol, risperidone and haloperidol when used in monotherapy. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and the occurrence of drug interactions. For many antipsychotics, the role of the different CYPs at therapeutic drug concentrations remains to be clarified. Some studies have suggested that poor metabolisers for CYP2D6 would be more prone to oversedation and possibly parkinsonism during treatment with classical antipsychotics, whereas other, mostly retrospective, studies have been negative or inconclusive. For the newer antipsychotics, such data are lacking. Whether phenotyping or genotyping for CYP2D6 or other CYPs can be used to predict an optimal dose range has not been studied so far. Genotyping or phenotyping can today be recommended as a complement to plasma concentration determination when aberrant metabolic capacity (poor or ultrarapid) of CYP2D6 substrates is suspected. The current rapid developments in molecular genetic methodology and pharmacogenetic knowledge can in the near future be expected to provide new tools for prediction of the activity of the various drug-metabolising enzymes. Further prospective clinical studies in well-defined patient populations and with adequate evaluation of therapeutic and adverse effects are required to establish the potential of pharmacogenetic testing in clinical psychiatry.

Association of the Ser9Gly polymorphism in the dopamine D3 receptor gene with tardive dyskinesia in Korean schizophrenics

Tardive dyskinesia (TD) is usually regarded as one of the most serious side-effects of the long-term usage of neuroleptics due to its high prevalence and potentially irreversible nature. Previously, several genetic polymorphisms were investigated for an association with TD in various ethnic populations. Among them, the Ser9Gly variant in the MscI restriction site of the dopamine D3 receptor gene was reported to be associated with TD. We have investigated the association of Ser9Gly polymorphism of the dopamine D3 receptor gene with TD in Korean schizophrenics. The frequencies of the genotypes of Ser/Ser, Ser/Gly and Gly/Gly in 54 schizophrenic patients without TD were 21 (38.9%), 33 (61.1%) and 0 (0%), while the corresponding frequencies in 59 schizophrenic patients with TD were 25 (42.4%), 28 (47.5%) and 6 (10.1%). We have found a significant genotypic association of the Gly/Gly genotype with TD in Korean schizophrenics (P = 0.028, two-tailed Fisher's exact test). However, there was no significant allelic association of the Ser9Gly allele with TD (chi2 = 0.288, d.f. = 1, P = 0.591) and there was no significant difference in the Abnormal Involuntary Movement Scale score between the three genotypic groups (P = 0.071, anova). In conclusion, we suggest that Gly/Gly homozygotes in the MscI polymorphic site of the dopamine D3 receptor gene may cause some change in the function of the dopamine D3 receptor and may be involved the pathogenesis of TD.

Antipsychotic-induced extrapyramidal syndromes and cytochrome P450 2D6 genotype: a case-control study

To study the association between polymorphism of the cytochrome P450 2D6 gene (CYP2D6) and the risk of antipsychotic-induced extrapyramidal syndromes, as measured by the use of antiparkinsonian medication. Data for this case-control study were obtained from a psychiatric hospital where newly admitted patients are routinely screened for several CYP2D6 mutant alleles. Cases were patients prescribed antiparkinsonian medication during oral antipsychotic drug treatment in the period September 1994 to August 2000. They were divided into those using an antipsychotic drug the metabolic elimination of which depends on the activity of the CYP2D6 enzyme ('CYP2D6-dependent') and those using other antipsychotic drugs. We formed a control group of antipsychotic drug users for both case groups using a matching ratio of 3 : 1 (controls : cases). Control patients were matched on whether or not their prescribed antipsychotic drug was CYP2D6-dependent. Odds ratios for patients who were slow metabolizers versus patients who were extensive metabolizers were calculated using conditional logistic regression and were adjusted for age, gender, dose and other potential confounding factors. We identified 77 case patients who were prescribed a CYP2D6-dependent antipsychotic drug and 54 case patients who were prescribed non CYP2D6-dependent antipsychotic drugs. Among the case- and control-patients using a CYP2D6-dependent antipsychotic drug, the poor metabolizers were more than four times more likely to start with antiparkinsonian medication than the extensive metabolizers (odds ratio 4.44; 95% confidence interval 1.11-17.68). An increased risk was not observed for patients using non CYP2D6-dependent antipsychotic drugs (odds ratio 1.20; 95% confidence interval 0.21-6.79). Genetically impaired CYP2D6 activity can increase the risk of antipsychotic-induced extrapyrimidal syndromes. Poor metabolizers should have their antipsychotic drug dosage reduced when the metabolism of the prescribed drug depends on CYP2D6 activity or should receive an antipsychotic drug that is not CYP2D6-dependent.

Cytochrome P450 polymorphisms and response to antipsychotic therapy

Antipsychotic drugs are used for the treatment of schizophrenia and other related psychotic disorders. The antipsychotics currently available include older or classical compounds and newer or atypical agents. Most antipsychotic drugs are highly lipophilic compounds and undergo extensive metabolism by cytochrome P450 (CYP) enzymes in order to be excreted. There is a wide interindividual variability in the biotransformation of antipsychotic drugs, resulting in pronounced differences in steady-state plasma concentrations and, possibly, in therapeutic and toxic effects, during treatment with fixed doses. Many classical and some newer antipsychotics are metabolized to a significant extent by the polymorphic CYP2D6, which shows large interindividual variation in activity. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and occurrence of drug interactions. No relationship between CYP2D6 genotype or activity and therapeutic effects of classical antipsychotic drugs has been found in the few studies performed. On the other hand, some investigations suggest that poor metabolizers (PMs) of CYP2D6 would be more prone to over-sedation and, possibly, Parkinsonism during treatment with classical antipsychotics, while other studies, mostly retrospective, have been negative or inconclusive. For the newer antipsychotics, such data are lacking. To date, CYP2D6 phenotyping and genotyping appear, therefore, to be clinically useful for dose predicting only in special cases and for a limited number of antipsychotics, while their usefulness in predicting clinical effects must be further explored.

Molecular genetics of CYP2D6: clinical relevance with focus on psychotropic drugs

Cytochrome P450 CYP2D6 is the most extensively characterized polymorphic drug-metabolizing enzyme. A deficiency of the CYP2D6 enzyme is inherited as an autosomal recessive trait; these subjects (7% of Caucasians, about 1% of Orientals) are classified as poor metabolizers. Among the rest (extensive metabolizers), enzyme activity is highly variable, from extremely high in ultrarapid metabolizers, to markedly reduced in intermediate metabolizers. The CYP2D6 gene is highly polymorphic, with more than 70 allelic variants described so far. Of these, more than 15 encode an inactive or no enzyme at all. Others encode enzyme with reduced, "normal" or increased enzyme activity. The CYP2D6 gene shows marked interethnic variability, with interpopulation differences in allele frequency and existence of "population-specific" allelic variants, for instance among Orientals and Black Africans. The CYP2D6 enzyme catalyses the metabolism of a large number of clinically important drugs including antidepressants, neuroleptics, some antiarrhythmics, lipophilic beta-adrenoceptor blockers and opioids. The present-day knowledge on the influence of the genetic variability in CYP2D6 on the clinical pharmacokinetics and therapeutic effects/adverse effects of psychotropic drugs is reviewed.

Functionally gene-linked polymorphic regions and genetically controlled neurotransmitters metabolism

In clinical psychopharmacology, the existence of marked inter-individual differences in both outcome and side effects is a common observation. Consequently, pharmacogenetics has also gained an increasing interest in psychiatry. Recent exciting findings seem to suggest that the growing interest in regulatory regions of candidate genes and neurotransmitters metabolism, together with the application of sophisticated molecular approaches, may offer new opportunities in neuropsychopharmacology. Indeed, quantitative variation of gene expression and/or of neurotransmitters metabolism could better explain both psychopathology and clinical response to psychotropic drugs. Three functional polymorphisms, and their possible relationship with clinical variables, are discussed. The first is the 44-bp insertion/deletion reported in the promoter region of the serotonin transporter gene. A functional repeat polymorphism in the promoter region of the gene encoding for the enzyme monoamine oxidase A represents the second example. The last is a functional polymorphism within the coding region of the gene encoding for the enzyme catechol-O-methyltransferase

Debrisoquine 4-hydroxylase (CYP2D6) genetic polymorphisms and susceptibility to schizophrenia in Chinese patients from Taiwan

Debrisoquine 4-hydroxylase (CYP2D6) is one of the cytochrome P450 enzyme families that metabolize many compounds. Polymorphic activities of debrisoquine 4-hydroxylase were suggested to be associated with some complex diseases, such as cancer and Parkinson's disease. Schizophrenia is also a complex disorder, and hence we are interested in understanding if the CYP2D6 gene is a susceptibility gene for schizophrenia in Chinese. We determined the genotype and allele frequencies of four molecular variants of CYP2D6 gene (i.e. 188C/T, 1934G/A, 2938C/T and 4268C/G) in 162 Chinese schizophrenic patients and 94 non-psychotic control subjects from Taiwan. No significant differences of allele or genotype frequencies of three polymorphisms (i.e. 188T/C, 2938C/T and 4268C/G) were detected between patients and control subjects. The 1934A allele, which accounts for the majority of poor metabolizers in Caucasians, was not detected in either patients or control subjects, indicating that the 1934A allele is very rare in Chinese. Our data suggest that the CYP2D6 gene may not be a susceptibility gene for schizophrenia in Chinese schizophrenic patients.

Lack of association between a functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common side effect of long-term medication with typical neuroleptics. TD presents itself by abnormal involuntary movements and may lead to a potentially disabling and chronic clinical course. A vast majority of patients suffering from schizophrenia are smokers. Smoking has been reported to induce the activity of the CYP1A2 enzyme, which is an established metabolic pathway within the disposition of antipsychotics. Recently, a C-->A genetic polymorphism in the first intron of the CYP1A2 gene was reported to influence CYP1A2 activity in smokers. Subsequently, a pharmacogenetic study in 85 U.S. patients with schizophrenia (44 smokers, 41 individuals with unknown smoking status) showed the C/C genotype to be associated with higher TD severity (measured by the Abnormal Involuntary Movement Scale, AIMS) than the A/C or A/A genotype. This finding prompted us to investigate whether this effect was also present in a larger German sample of 119 patients with schizophrenia (82 smokers, 37 individuals with unknown smoking status). However, we could not replicate the reported association. The median AIMS scores did not differ between individuals with the A/A, A/C, or C/C genotypes. In an additional analysis, we compared the genotypic and allelic distribution among individuals grouped according to the criteria established by Schooler and Kane [1982: Arch Gen Psychiatry 39:486-487] (persistent TD vs. absent TD). We did not observe a differential genotypic or allelic distribution between the two diagnostic groups. Thus, our results do not support the hypothesis that the C-->A polymorphism in the CYP1A2 gene is involved in the etiology of TD in the German population.

Lack of association between serotonin-2A receptor gene (HTR2A) polymorphisms and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a disabling neurological side effect associated with long-term treatment with typical antipsychotics. Family studies and animal models lend evidence for hereditary predisposition to TD. The newer atypical antipsychotics pose a minimal risk for TD which is in part attributed to their ability to block the serotonin-2A (5-HT(2A)) receptor. 5-HT(2A) receptors were also identified in the basal ganglia; a brain region that plays a critical role in antipsychotic-induced movement disorders. We tested the significance of variation in the 5-HT(2A) receptor gene (HTR2A) in relation to the TD phenotype. Three polymorphisms in HTR2A, one silent (C102T), one that alters the amino acid sequence (his452tyr) and one in the promoter region (A-1437G) were investigated in 136 patients refractory or intolerant to treatment with typical antipsychotics and with a DSM-IIIR diagnosis of schizophrenia. We did not find any significant difference in allele, genotype or haplotype frequencies of polymorphisms in HTR2A among patients with or without TD (P > 0.05). Further analysis using the ANCOVA statistic with a continuous measure of the TD phenotype (Abnormal Involuntary Movement Scale (AIMS) score) found that the AIMS scores were not significantly influenced by HTR2A polymorphisms, despite controlling for potential confounders such as age, gender and ethnicity (P > 0.05). Theoretically, central serotonergic function can be subject to genetic control at various other mechanistic levels including the rate of serotonin synthesis (tryptophane hydroxylase gene), release, reuptake (serotonin transporter gene) and degradation (monoamine oxidase gene). Analyses of these other serotonergic genes are indicated. In summary, polymorphisms in HTR2A do not appear to influence the risk for TD. Further studies evaluating in tandem multiple candidate genes relevant for the serotonergic system are warranted to dissect the genetic basis of the complex TD phenotype.

Pharmacogenomics and schizophrenia

Although antipsychotic drugs are effective in alleviating schizophrenic symptoms, individual differences in patient response suggest that genetic components play a major role, and pharmacogenetic studies have indicated the possibility for a more individually based pharmacotherapy. The new field of pharmacogenomics, which focuses on genetic determinants of drug response at the level of the entire human genome, is important for development and prescription of safer and more effective individually tailored drugs. DNA microarray (DNA chip) analysis enables genome-wide scanning, using the high-density single nucleotide polymorphisms map. Pharmacogenomics will aid in understanding how genetics influence disease development and drug response, and contribute to discovery of new treatments. The rate of discovery of those polymorphisms will depend on the quality of the drug response phenotype. Prospective genotyping of schizophrenic patients for the many genes at the level of the drug target, drug metabolism, and disease pathways will contribute to individualized therapy matching the patient's unique genetic make-up with an optimally effective drug.

Tardive dyskinesia is not associated with the serotonin gene polymorphism (5-HTTLPR) in Chinese

Neuroleptics are the mainstay of treatment for schizophrenia, but one of the complications is the development of tardive dyskinesia (TD). The pathophysiology of TD may involve dopamine-serotonin interaction. The serotonin transporter participates in the reuptake and termination of serotonin neurotransmission, and the gene that codes for this protein is thus a candidate gene for the development of TD. There is a functional polymorphism in the transcriptional control region of the serotonin transporter gene, and we investigated the association between this polymorphism and TD in Chinese schizophrenic patients. The patients who did not differ in age and sex distribution did not show variation on the rates of TD and Abnormal Involuntary Movements Scale (AIMS) scores with genotypes. Our findings suggest that 5-HTTLPR polymorphism is not a risk factor for TD in Chinese. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:712-715, 2000.

CYP2D6 genotyping in patients on psychoactive drug therapy

The polymorphic isoenzyme CYP2D6 has a major role in the oxidative metabolism of many deal of psychoactive drugs. Its six mutant alleles (null alleles *3, *4, *5, *6, *7 and *8) encode for inactive enzyme molecules. A carrier of two mutant alleles is considered a poor metabolizer phenotype, while a carrier of only one damaged allele is considered an intermediate metabolizer phenotype. The aim of the study was to assess the prevalence of null alleles in a group of psychiatric patients suffering from depression (n=49) and schizophrenia (n=86) in comparison with healthy individuals (n=145) by the method of multiplex allele specific PCR. Only CYP2D6*3,*4 and *6 mutant alleles were found in the study subjects. No significant difference between the depression and control groups was found for allele prevalence, genotype or phenotype distribution (p>0.05). However, a significant difference was observed between schizophrenic patients and controls for allele frequency (p=0.002), genotype distribution (p=0.016), and phenotype prevalence (p=0.018). The odds ratio of 2.542 for 2D6*4 suggested a significant association between this allele and schizophrenia, significantly contributing to poor metabolizer phenotype (odds ratio=5.020). The relationship between CYP2D6 gene polymorphism and side effects in schizophrenic patients undergoing long-term psychoactive drug therapy was investigated. A significant difference was obtained for allele prevalence (p=0.002), genotype (p=0.029), and phenotype (p=0.002) distribution between patients without and with side effects. A relative risk of 2.626 and 5.333 for 2D6*4 and 2D6*6, respectively, and of 7.08 for poor metabolizer phenotype suggested a significant association between the hereditary susceptibility for a particular type of drug metabolism (defect alleles) and side effects. These preliminary results suggest that the CYP2D6 genotyping appears to be useful for predicting risks for side effects of psychoactive drugs in schizophrenic patients, but their usefulness should be further explored.

Apolipoprotein E epsilon4 and tardive dyskinesia in a Japanese population

The findings that free radicals play a causative role in the occurrence of tardive dyskinesia (TD) and that apolipoprotein E (ApoE) 4 has decreased anti-oxidant activity suggest a potential link between TD and ApoE alleles. We, therefore, examined ApoE allelic frequencies in schizophrenic subjects with TD and non-TD. Serum samples were obtained from 333 DSM IV-diagnosed schizophrenic patients and 191 controls in Japan. The presence of TD was evaluated by research diagnostic criteria for TD. ApoE phenotypes of the serum samples were determined by polyacrylamide gel isoelectricfocusing. A total of 62 TD subjects (31 males, 31 females) were identified among all patients examined. No significant differences in ApoE allelic frequency were found between TD and non-TD groups. ApoE epsilon4 allele frequency, however, was significantly lower in the female TD group than in the male TD group. These findings do not clearly demonstrate a certain association between TD and the epsilon4 allele, but may preliminarily reveal a difference in influence of this allele on the development of TD between males and females.

A functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene: association with tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common and potentially irreversible side effect associated with long-term treatment with typical antipsychotics. Approximately, 80% or more of patients with schizophrenia are smokers. Smoking is a potent inducer of the CYP1A2 enzyme, and is known to cause a significant decrease in plasma concentrations of some antipsychotics. Therefore, person-to-person differences in the extent of CYP1A2 induction by smoking may contribute to risk for the development of TD. Recently, a (C-->A) genetic polymorphism in the first intron of the CYP1A2 gene was found to be associated with variation in CYP1A2 inducibility in healthy volunteer smokers. The aim of this study was to test the clinical importance of the (C-->A) polymorphism in CYP1A2 in relation to TD severity. A total of 85 patients with schizophrenia were assessed for TD severity using the Abnormal Involuntary Movement Scale (AIMS), and were subsequently genotyped for the (C-->A) polymorphism in CYP1A2. The mean AIMS score in patients with the (C/C) genotype (associated with reduced CYP1A2 inducibility) was 2.7- and 3.4-fold greater than in those with the (A/C) or (A/A) genotype, respectively (F[2,82] = 7.4, P = 0.0007). Further, a subanalysis in the 44 known smokers in our sample, revealed a more pronounced effect. The means AIMS score in smokers was 5.4- and 4. 7-fold greater in (C/C) homozygotes when compared to heterozygotes and (A/A) homozygotes, respectively (F[2,41] = 3.7, P = 0.008). These data suggest that the (C-->A) genetic polymorphism in the CYP1A2 gene may serve as a genetic risk factor for the development of TD in patients with schizophrenia. Further studies in independent samples are warranted to evaluate the applicability of our findings to the general patient population receiving antipsychotic medications.

The relevance of ethnic influences on pharmacogenetics to the treatment of psychosis

Interethnic variation amongst the drug metabolising enzymes relevant to the treatment of psychosis is reviewed. The frequency of genetically determined variants at the extremes of enzyme activity is seen to vary considerably between different ethnic groups; in addition, a shift in the frequency distribution giving an overall lower population mean activity may occur. The role of dietary and other environmental influences in the generation of interethnic variation in cytochrome activity is also discussed. Clinical studies pertinent to this variation are reviewed. It is suggested that the reason for conflicting data from some clinical studies is the existence of overlapping substrate specificity, so that one cytochrome is able to substitute for another. Individuals deficient for more than one cytochrome would be likely to show much more pronounced clinical effects than those showing single cytochrome deficiency.

Extension of a pilot study: impact from the cytochrome P450 2D6 polymorphism on outcome and costs associated with severe mental illness

The influence of cytochrome P450 2D6 (CYP2D6) genetic variability was examined in psychiatric inpatients by evaluating adverse drug events (ADEs), hospital stays, and total costs over a 1-year period in an extension of a previously published brief report. One hundred consecutive psychiatric patients from Eastern State Hospital in Lexington, Kentucky, were genotyped for CYP2D6 expression. ADEs were evaluated by a neurologic rating scale, modified Udvalg for Kliniske Undersogelser Side Effect Rating Scale, or chart review. Information on total hospitalization days and total costs were gathered for a 1-year period. Forty-five percent of the patients received medications that were primarily dependent on the CYP2D6 enzyme for their elimination. When the analysis was restricted to just those patients in each group receiving medication heavily dependent on the CYP2D6 enzyme, the following were observed: (1) a trend toward greater numbers of ADEs from medications as one moved from the group with ultrarapid CYP2D6 activity (UM) to the group with absent CYP2D6 activity (PM); (2) the cost of treating patients with extremes in CYP2D6 activity (UM and PM) was on average $4,000 to $6,000 per year greater than the cost of treating patients in the efficient metabolizer (EM) and intermediate metabolizer (IM) groups; and (3) total duration of hospital stay was more pronounced for those in CYP2D6 PM group. Variance of hospital stays and costs calculated from these preliminary data suggests that 1,500 to 2,000 patients must be evaluated over at least a 1-year period to determine whether the CYP2D6 genetic variation significantly alters the duration of hospital stay and costs.

Genetic association analysis between CYP2D6*2 allele and tardive dyskinesia in schizophrenic patients

Previous studies have shown a possible association between tardive dyskinesia (TD) and debrisoquine 4-hydroxylase (CYP2D6) polymorphisms, which result in absent enzyme activity. We have recently found a positive association between TD and the CYP2D6*10 allele, which codes for the intermediate metabolizer (IM) phenotype and is characterized by decreased but not absent CYP2D6 activity in Japanese schizophrenic patients. In addition, the CYP2D6* 2 allele with the HhaI site mutation in exon 6 has also been reported to be an IM allele and a risk factor for Parkinson's disease (PD) in the Japanese population. In the present study, we investigated potential contributions of the CYP2D6*2 allele to TD using case-control and regression analysis in 99 schizophrenic patients. No significant differences in genotypic and allelic frequencies were found between patients with and without TD. Even after using regression analysis to adjust for the confounding variables, there was no significant association of the CYP2D6*2 genotype with either outcome variable, the occurrence of TD or the total AIMS score. These results suggest that the CYP2D6*2 allele may not contribute to the pathogenesis of TD.

Tardive dyskinesia: probing abnormal metabolism with promethazine

Ten in-patients with tardive dyskinesia (TD) (mean AIMS score 16.7) and 8 controls were recruited to the study, and 3 h after oral administration of promethazine a blood sample was taken for assay of levels of promethazine and its immediate metabolites by high-performance liquid chromatography (HPLC). The TD group had a variety of indicators of impaired or slow metabolism compared to the controls. There was a significant difference in the ratio of promethazine to promethazine sulphoxide (P < 0.05) between patients with TD and the control group. The TD group but not the controls showed increasing metabolic impairment with age. This small study confirms the previous reports of impaired neuroleptic metabolism in TD, particularly in the elderly.

The current status of tardive dystonia

Tardive dystonia (TDt), a persistent dystonia associated with exposure to neuroleptic drugs, is an uncommon disorder. It differs from tardive dyskinesia (TDk) in epidemiology, clinical features, risk factors, pathophysiology, course, prognosis, and treatment outcome. TDt seems to develop faster and is more painful, distressing, and disabling than tardive dyskinesia. In this article, evidence is reviewed on the face, descriptive, construct, and predictive validity of this iatrogenic complication of antipsychotic drugs. It is suggested that TDt should not be lumped together with TDk. It deserves a separate nosological status as an independent diagnostic category. The subclassification of TDt into various subtypes based on coexistence of other movement disorders is suggested.