Polymorphisms of dopamine receptors and tardive dyskinesia among Chinese patients with schizophrenia

Tardive dyskinesia in Asia- current clinical practice and the role of neurologists in the care pathway

Tardive dyskinesia (TD) is a movement disorder that can arise as a side effect of treatment with dopamine receptor-blocking agents (DRBAs), including antipsychotic drugs (APDs) used to manage psychotic illnesses. Second-generation APDs (SGAs) are often preferred to first-generation drugs due to their lower propensity to cause TD, however many SGAs-treated patients still develop the condition. Although TD is a global health concern, evidence regarding the occurrence of TD and how it is managed in Asian countries is currently limited. This article reports the results of a systematic review of the published literature on TD focusing on its prevalence, types of patients, knowledge of the condition, causative factors, and usual treatment pathways in clinical practice in Asian countries. Epidemiological data suggest that the prevalence of TD is increasing globally due to an overall rise in APD use, contributing factors being polypharmacy with multiple APDs, the use of higher than necessary doses, and off-label use for non-psychotic indications. Although exact prevalence figures for TD in Asian countries are difficult to define, there is a similar pattern of rising APD use which will result in increasing numbers of TD patients in this region. These issues need to be addressed and strategies developed to minimize TD risk and manage this disabling condition which impacts patients' quality of life and daily functioning. To date, both research into TD has been predominantly psychiatry focused and the perspectives from neurologists regarding the clinical management of this challenging condition are scarce. However, neurologists have an essential role in managing the movement disorders manifestations that characterize TD. Optimum management of TD, therefore, should ideally involve collaboration between psychiatrists and neurologists in joint care pathways, wherever practical. Collaborative pathways are proposed in this article, and the challenges that will need to be addressed in Asian countries to improve the care of people with TD are highlighted, with a focus on the neurologist's viewpoint and the implications for the management of TD globally.

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.

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.

[Pharmacogenetic-based risk assessment of antipsychotic-induced extrapyramidal symptoms]

"Typical" antipsychotics remain the wide-prescribed drugs in modern psychiatry. But these drugs are associated with development of extrapyramidal symptoms (EPS). Preventive methods of EPS are actively developed and they concentrate on personalized approach. The method of taking into account genetic characteristics of patient for prescribing of treatment was proven as effective in cardiology, oncology, HIV-medicine. In this review the modern state of pharmacogenetic research of antipsychotic-induced EPS are considered. There are pharmacokinetic and pharmacodynamic factors which impact on adverse effects. Pharmacokinetic factors are the most well-studied to date, these include genetic polymorphisms of genes of cytochrome P450. However, evidence base while does not allow to do the significant prognosis of development of EPS based on genetic testing of CYP2D6 and CYP7A2 polymorphisms. Genes of pharmacodynamics factors, which realize the EPS during antipsychotic treatment, are the wide field for research. In separate part of review research of such systems as dopaminergic, serotonergic, adrenergic, glutamatergic, GABAergic, BDNF were analyzed. The role of oxidative stress factors in the pathogenesis of antipsychotic-induced EPS was enough detailed considered. The system of those factors may be used for personalized risk assessment of antipsychotics' safety in the future. Although there were numerous studies, the pharmacogenetic-based prevention of EPS before prescribing of antipsychotics was not introduced. However, it is possible to distinguish the most perspectives markers for further research. Furthermore, brief review of new candidate genes provides here, but only preliminary results were published. The main problem of the field is the lack of high- quality studies. Moreover, the several results were not replicated in repeat studies. The pharmacogenetic-based research must be standardized by ethnicity of patients. But there is the ethnical misbalance in world literature. These facts explain why the introduction of pharmacogenetic testing for risk assessment of antipsychotic-induced EPS is so difficult to achieve.

Clinical significance of pharmacogenomic studies in tardive dyskinesia associated with patients with psychiatric disorders

Pharmacogenomics is the study of the effects of genetic polymorphisms on medication pharmacokinetics and pharmacodynamics. It offers advantages in predicting drug efficacy and/or toxicity and has already changed clinical practice in many fields of medicine. Tardive dyskinesia (TD) is a movement disorder that rarely remits and poses significant social stigma and physical discomfort for the patient. Pharmacokinetic studies show an association between cytochrome P450 enzyme-determined poor metabolizer status and elevated serum antipsychotic and metabolite levels. However, few prospective studies have shown this to correlate with the occurrence of TD. Many retrospective, case-control and cross-sectional studies have examined the association of cytochrome P450 enzyme, dopamine (receptor, metabolizer and transporter), serotonin (receptor and transporter), and oxidative stress enzyme gene polymorphisms with the occurrence and severity of TD. These studies have produced conflicting and confusing results secondary to heterogeneous inclusion criteria and other patient characteristics that also act as confounding factors. This paper aims to review and summarize the pharmacogenetic findings in antipsychotic-associated TD and assess its clinical significance for psychiatry patients. In addition, we hope to provide insight into areas that need further research.

BDNF Val66Met polymorphism and antipsychotic-induced tardive dyskinesia occurrence and severity: a meta-analysis

BACKGROUND

Tardive dyskinesia (TD) is a serious long-term consequence of antipsychotic treatment. Since brain-derived neurotrophic factor (BDNF) has potent neurotrophic activity, genetic alterations in the BDNF gene may affect antipsychotic-induced TD.

METHODS

Searching PubMed and Web of Science until 05/31/13, we conducted a systematic review and a meta-analysis of the effects of BDNF Val66Met polymorphism on antipsychotic-induced TD. Pooled odds ratio was calculated to assess the effects of BDNF Val66Met polymorphism on TD occurrence. Additionally, pooled standardized mean differences (Hedges' g) were calculated to assess the effects on Abnormal Involuntary Movement Scale (AIMS) total score.

RESULTS

Out of 699 potentially eligible hits, 6 studies (N=1740, mean age=46.0±10.4years; males=73.1%; Asians=80.5%, Caucasians=19.5%; schizophrenia=96.2%) were included in this meta-analysis. Pooling data from all studies, no significant associations were found between BDNF Val66Met polymorphism and TD (p=0.82) or AIMS total scores (p=0.11). However, in studies including only Caucasians (n=339), Met allele carriers had significantly higher AIMS total scores (Hedges' g=0.253, 95% confidence interval=0.030 to 0.476, p=0.026) and non-significantly higher TD occurrence (p=0.127). Conversely, there was no association between BDNF and AIMS scores (p=0.57) or TD (p=0.65) in Asians.

CONCLUSION

Although there was no significant association between BDNF Val66Met polymorphism and TD or AIMS scores across all patients, our results suggest that BDNF Val66Met polymorphism affects severity and, possibly, TD development in Caucasians. Since the number of studies and patients was still small, additional data are needed to confirm genotype-racial interactions. Furthermore, BDNF enhancing treatments for TD may require further study, especially in Caucasians.

Pharmacogenetics of antipsychotics

OBJECTIVE

During the past decades, increasing efforts have been invested in studies to unravel the influence of genetic factors on antipsychotic (AP) dosage, treatment response, and occurrence of adverse effects. These studies aimed to improve clinical care by predicting outcome of treatment with APs and thus allowing for individualized treatment strategies. We highlight most important findings obtained through both candidate gene and genome-wide association studies, including pharmacokinetic and pharmacodynamic factors.

METHODS

We reviewed studies on pharmacogenetics of AP response and adverse effects published on PubMed until early 2012. Owing to the high number of published studies, we focused our review on findings that have been replicated in independent studies or are supported by meta-analyses.

RESULTS

Most robust findings were reported for associations between polymorphisms of the cytochrome P450 system, the dopamine and the serotonin transmitter systems, and dosage, treatment response, and adverse effects, such as AP-induced weight gain or tardive dyskinesia. These associations were either detected for specific medications or for classes of APs.

CONCLUSION

First promising and robust results show that pharmacogenetics bear promise for a widespread use in future clinical practice. This will likely be achieved by developing algorithms that will include many genetic variants. However, further investigation is warranted to replicate and validate previous findings, as well as to identify new genetic variants involved in AP response and for replication of existing findings.

Oxidative stress and tardive dyskinesia: pharmacogenetic evidence

Tardive dyskinesia (TD) is a serious adverse effect of long-term antipsychotic use. Because of genetic susceptibility for developing TD and because it is difficult to predict and prevent its development prior to or during the early stages of medication, pharmacogenetic research of TD is important. Additionally, these studies enhance our knowledge of the genetic mechanisms underlying abnormal dyskinetic movements, such as Parkinson's disease. However, the pathophysiology of TD remains unclear. The oxidative stress hypothesis of TD is one of the possible pathophysiologic models for TD. Preclinical and clinical studies of the oxidative stress hypothesis of TD indicate that neurotoxic free radical production is likely a consequence of antipsychotic medication and is related to the occurrence of TD. Several studies on TD have focused on examining the genes involved in oxidative stress. Among them, manganese superoxide dismutase gene Ala-9Val polymorphisms show a relatively consistent association with TD susceptibility, although not all studies support this. Numerous pharmacogenetic studies have found a positive relationship between TD and oxidative stress based on genes involved in the antioxidant defense mechanism, dopamine turnover and metabolism, and other antioxidants such as estrogen and melatonin. However, many of the positive findings have not been replicated. We expect that more research will be needed to address these issues.

Pharmacogenetics of response to antipsychotics in patients with schizophrenia

This review presents the findings of pharmacogenetic studies exploring the influence of gene variants on antipsychotic treatment response, in terms of both symptom improvement and adverse effects, in patients with schizophrenia. Despite numerous studies in the field, replicating findings across different cohorts that include subjects of different ethnic groups has been challenging. It is clear that non-genetic factors have an important contribution to antipsychotic treatment response. Differing clinical, demographic and environmental characteristics of the cohorts studied have added substantial complexity to the interpretation of the positive and negative findings of many studies. Pharmacogenomic genome-wide investigations are beginning to yield interesting data although they have failed to replicate the most robust findings of candidate gene studies, and are limited by the sample size, especially given the need for studying homogeneous cohorts. Most of the studies conducted on cohorts treated with single antipsychotics have investigated clozapine, olanzapine or risperidone response. These studies have provided some of the most replicated associations with treatment efficacy. Serotonergic system gene variants are significantly associated with the efficacy of clozapine and risperidone, but may have less influence on the efficacy of olanzapine. Dopamine D3 receptor polymorphisms have been more strongly associated with the efficacy of clozapine and olanzapine, and D2 genetic variants with the efficacy of risperidone. Serotonin influences the control of feeding behaviour and has been hypothesized to have a role in the development of antipsychotic-induced weight gain. Numerous studies have linked the serotonin receptor 2C (5-HT2C) -759-C/T polymorphism with weight gain. The leptin gene variant, -2548-G/A, has also been associated with weight gain in several studies. Pharmacogenetic studies support the role of cytochrome P450 enzymes and dopamine receptor variants in the development of antipsychotic-induced movement disorders, with a contribution of serotonergic receptors and other gene variants implicated in the mechanism of action of antipsychotics. Clozapine-induced agranulocytosis has been associated with polymorphisms in the major histocompatibility complex gene (HLA).

Ethical and Policy Considerations in the Application of Pharmacogenomic Testing for Tardive Dyskinesia: Case Study of the Dopamine D3 Receptor

Tardive dyskinesia (TD) is a serious adverse effect often associated with the first generation antipsychotic medications used in the management of mental health disorders such as schizophrenia. Pharmacogenomics is the study of human genomic variation in relation to individual and population variability in medication response and side effects. Neuropsychiatry is one of the clinical domains in which pharmacogenomic approaches have been extensively studied. In the late 1990s, the Glycine9 (Gly9) allele of the Serine-9-Glycine (Ser9Gly) polymorphism in dopamine D3 receptor gene (DRD3) was found to be associated with both a liability to, and worsened severity of, TD in schizophrenic patients treated with typical antipsychotics. This initial discovery has been subsequently replicated and testing for the Ser9Gly polymorphism has now become commercially available. The question that currently presents itself is whether its use should be encouraged for patients who may be prescribed a typical or atypical antipsychotic medication. However, the translation of this new technology to clinical practice presents multiple social, ethical and policy challenges. Though pharmacogenomic testing holds much promise in this scenario, many important questions remain to be answered before its widespread use can be medically and ethically justified. This article highlights the key advances in our understanding of the role of human genetic variation in the D3 receptor in relation to TD. Then, issues of uncertainty, consent, confidentiality, and access are considered with respect to the use of DRD3 polymorphism testing in risk stratification for susceptibility to tardive dyskinesia. We propose three recommendations that may help bring this technology into the clinic: 1) prospective pharmacogenomic studies of DRD3 polymorphism and TD risk should be conducted; 2) the design of such studies should be influenced by scientists, ethicists and policy makers to protect potentially vulnerable patients; and 3) appropriate knowledge transfer to front-line health care workers must take place.

Pharmacogenetics and antipsychotics: therapeutic efficacy and side effects prediction

IMPORTANCE OF THE FIELD

Antipsychotic drug is the mainstay of treatment for schizophrenia, and there are large inter-individual differences in clinical response and side effects. Pharmacogenetics provides a valuable tool to fulfill the promise of personalized medicine by tailoring treatment based on one's genetic markers.

AREAS COVERED IN THIS REVIEW

This article reviews the pharmacogenetic literature from early 1990s to 2010, focusing on two aspects of drug action: pharmacokinetics and pharmacodynamics. Genetic variants in the neurotransmitter receptors including dopamine and 5-HT and metabolic pathways of drugs including CYP2D6 and COMT were discussed in association with clinical drug response and side effects.

WHAT THE READER WILL GAIN

Readers are expected to learn the up-to-date evidence in pharmacogenetic research and to gain familiarity to the issues and challenges facing the field.

TAKE HOME MESSAGE

Pharmacogenetic research of antipsychotic drugs is both promising and challenging. There is consistent evidence that some genetic variants can affect clinical response and side effects. However, more studies that are designed specifically to test pharmacogenetic hypotheses are clearly needed to advance the field.

No Evidence for an Association between Dopamine D2 Receptor Polymorphisms and Tardive Dyskinesia in Korean Schizophrenia Patients

OBJECTIVE

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic. Dopaminergic activity in the nigrostriatal system have been proposed to be involved in development of TD and dopamine D2 receptors (DRD2) has been regarded as a candidate gene for TD because the antipsychotics have potent antagonism DRD2. This study was aimed to find the relationship between DRD2 gene and antipsychotic-induced TD.

METHODS

We evaluated whether 5 DRD2 single nucleotide polymorphisms (-141Cins>del/TaqID/NcoI/Ser311Cys/TaqIA) are associated with antipsychotic-induced TD in 263 Korean schizophrenia patients with (n=100) and without TD (n=163) who were matched for antipsychotic drug exposure and other relevant variables. Haplotype analyses were also performed.

RESULTS

None of 5 polymorphisms were found to be significantly associated with TD and with TD severity as measured by Abnormal Involuntary Movement Scale. Overall haplotype (-141Cins>del/TaqID/NcoI/Ser311Cys/TaqIA) frequency was also not significantly different between TD and non-TD groups, although one rare haplotype (I-D1-T-G-A1) showed significantly different frequency between TD and non-TD groups (2.7% vs. 8.5%, respectively, p=0.031).

CONCLUSION

The present study does not support that DRD2 gene may be involved in TD in the Korean population, although further studies are warranted.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

The DRD3 rs6280 polymorphism and prevalence of tardive dyskinesia: a meta-analysis

To elucidate a widely suspected but inconclusive association between rs6280 in the dopamine receptor 3 gene (DRD3) and prevalence of tardive dyskinesia (TD), we conducted a meta-analysis of studies obtained in a systematic search of several bibliographic systems. We conducted several analyses of funnel plot asymmetry, overall heterogeneity, and study characteristics in analyses analogous to general, dominant and recessive inheritance models with the prevalence odds ratio (POR) as the measure of association. Thirteen eligible studies were identified with publication dates between 1997 and 2008. Evidence of funnel plot asymmetry was discerned in the dominant and general model analyses, but not in the recessive model analysis. Stratified analyses indicated that publication year, TD assessment method (Schooler-Kane criteria or other) and TD assessment frequency (single or repeated) were important study characteristics associated with heterogeneous PORs across studies. Studies conducted among patients with older age, fewer women or European (compared with Asian) ancestry reported stronger average PORs. Summary POR estimates under the dominant and general inheritance models were not warranted due to funnel plot asymmetry and heterogeneity. Under the recessive model, the summary estimate was POR = 0.93 (95% confidence interval: 0.70-1.23). We conclude that there is no or little association between DRD3 rs6280 polymorphisms and prevalence of TD.

The role of dopamine D3, 5-HT2A and 5-HT2C receptor variants as pharmacogenetic determinants in tardive dyskinesia in African-Caribbean patients under chronic antipsychotic treatment: Curacao extrapyramidal syndromes study IX

Tardive dyskinesia (TD) is associated with polymorphisms of the dopamine D(3), serotonin 2A and 2C receptors (DRD3, HTR2A and HTR2C, respectively). This study investigated the possible relationship between TD and the polymorphisms Ser9Gly (DRD3), 102T>C (HTR2A), -1438G>A(HTR2A) and Cys23Ser (HTR2C) in African-Caribbean inpatients. One hundred and twenty-six patients under chronic antipsychotic treatment were genotyped. The assessment of TD was carried out with the abnormal involuntary movement scale (AIMS). The relationships between the carriership of the least frequent alleles and the respective orofaciolingual dyskinesia (TDof) (sum of the items 1-4 of the AIMS), limb-truncal dyskinesia (TDlt) (sum of items 5-7 of the AIMS) and TD (sum of items 1-7 of the AIMS) were analyzed with ANCOVA, comparing means with age as a covariate and stratification for carriers and non-carriers of the mutations. In addition, we conducted pre-planned t-tests to compare AIMS values of carriers of the combinations of alleles versus the corresponding non-carriers. In the study population, females with 9Ser carriership exhibited higher AIMS values than non-carriers. Male subjects with 9Ser carriership in combination with 23Ser or -1438A carriership exhibited higher AIMS values. In male patients also, the combination of 23Ser and -1438A carriership increased TD. The study clearly shows that the African-Caribbean population differs from the Caucasian population with regard to the association of TD with the polymorphisms studied and suggests that the association of TD with the studied polymorphisms of the 5-HT(2C) and probably of the 5-HT(2A) receptor are the result of a changed susceptibility of the patients, independent of the action of the antipsychotics on these receptors.

Genetic underpinnings of tardive dyskinesia: passing the baton to pharmacogenetics

Manifestation of tardive dyskinesia (TD) among schizophrenia subjects on long-term antipsychotic treatment with typical drugs has been a clinical concern. Despite its association with extrapyramidal symptoms, typical drugs are still routinely prescribed globally though marginally superior atypical drugs have long been available. The genetic component in the etiology of TD is well documented. Search for these determinants has led to a few consensus associations of CYP2D6 *10, CYP1A2*1F, DRD2 Taq1A (rs1800497), DRD3 Ser9Gly (rs6280) and MnSOD Ala9Val (rs4880) variants with TD. However, translation of these observations into the clinic has not been achieved so far. This review discusses the salient features of TD etiopathology, current status of TD genetics, interactions between genetic and nongenetic factors, some major drawbacks, challenges and expected focus in TD research over the next decade, with emphasis on pharmacogenetics.

Association study between glutathione S-transferase GST-M1, GST-T1, and GST-P1 polymorphisms and tardive dyskinesia

OBJECTIVES

Data from several studies suggest that oxidative stress may play a role in the pathophysiology of tardive dyskinesia (TD). Glutathione S-transferase (GST) enzymes play important roles in protecting cells against oxidative stress. In the present study, we investigated the hypothesis that polymorphisms in genes for these detoxifying enzymes can influence susceptibility to TD in patients with schizophrenia.

METHODS

The GST-M1, GST-T1, and GST-P1 loci were analyzed by polymerase chain reaction (PCR)-based methods in 83 schizophrenic patients with TD and 126 schizophrenic without TD who were matched for antipsychotic drug exposure and other relevant variables. The multifactor dimensionality reduction (MDR) approach was used to analyze gene-gene interactions.

RESULTS

There were no significant differences in the distributions of the GST-M1, GST-T1, and GST-P1 genotypes between the TD and non-TD groups (p > 0.05). However, in comparison of the severity of TD among genotypes using Poisson regression showed that Ile/Ile genotype of GST-P1 had higher AIMS score compared to Ile/Val + Val/Val genotypes (X(2) = 7.13, p = 0.008). MDR analysis did not show a significant interaction between the three GST gene variants and susceptibility to TD (p > 0.05).

CONCLUSIONS

These results suggest that GST gene polymorphisms do not confer increased susceptibility to TD in patients with schizophrenia but TD severity might be related with GST-P1 variants.

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.

Association between dopamine-related polymorphisms and plasma concentrations of prolactin during risperidone treatment in schizophrenic patients

Hyperprolactinemia is an inevitable consequence of treatment with antipsychotic agents to some extent because prolactin response to antipsychotics is related to dopamine blockade. Recent studies have suggested that polymorphisms of the dopamine receptors are associated with therapeutic response to antipsychotics. Thus, we studied the effects of major polymorphisms of dopamine-related genes on plasma concentration of prolactin. Subjects were 174 schizophrenic patients (68 males, 106 females) receiving 3 mg twice daily of risperidone for at least 4 weeks. Sample collections were conducted 12 h after the bedtime dosing. Five dopamine-related polymorphisms (Taq1A, -141C ins/del for DRD2, Ser9Gly for DRD3, 48 bp VNTR for DRD4, Val158Met for COMT) were identified. The mean (+/-SD) plasma concentration of prolactin in females was significantly higher than males (54.3+/-27.2 ng/ml versus 126.8+/-70.2 ng/ml, p<0.001). No dopamine-related polymorphisms differed the plasma concentration of prolactin in males or females. Multiple regression analyses including plasma drug concentration and age revealed that plasma concentration of prolactin correlated with gender (standardized partial correlation coefficients (beta)=0.551, p<0.001) and negatively with age (standardized beta=-0.202, p<0.01). No correlations were found between prolactin concentration and dopamine-related polymorphisms. These findings suggest that plasma prolactin concentrations in females are much higher than in males but the dopamine-related variants are not predominantly associated with plasma concentration of prolactin.

Antipsychotic-induced tardive dyskinesia and polymorphic variations in COMT, DRD2, CYP1A2 and MnSOD genes: a meta-analysis of pharmacogenetic interactions

Despite accumulating evidence pointing to a genetic basis for tardive dyskinesia, results to date have been inconsistent owing to limited statistical power and limitations in molecular genetic methodology. A Medline, EMBASE and PsychINFO search for literature published between 1976 and June 2007 was performed, yielding 20 studies from which data were extracted for calculation of pooled estimates using meta-analytic techniques. Evidence from pooled data for genetic association with tardive dyskinesia (TD) showed (1) in COMT(val158met), using Val-Val homozygotes as reference category, a protective effect for Val-Met heterozygotes (OR=0.63, 95% CI: 0.46-0.86, P=0.004) and Met carriers (OR=0.66, 95% CI: 0.49-0.88, P=0.005); (2) in Taq1A in DRD2, using the A1 variant as reference category, a risk-increasing effect for the A2 variant (OR=1.30, 95% CI: 1.03-1.65, P=0.026), and A2-A2 homozygotes using A1-A1 as reference category (OR=1.80, 95% CI: 1.03-3.15, P=0.037); (3) in MnSOD Ala-9Val, using Ala-Ala homozygotes as reference category, a protective effect for Ala-Val (OR=0.37, 95% CI: 0.17-0.79, P=0.009) and for Val carriers (OR=0.49, 95% CI: 0.24-1.00, P=0.047). These analyses suggest multiple genetic influences on TD, indicative of pharmacogenetic interactions. Although associations are small, the effects underlying them may be subject to interactions with other loci that, when identified, may have acceptable predictive power. Future genetic research will take advantage of new genomic knowledge. Molecular Psychiatry (2008) 13, 544-556; doi:10.1038/sj.mp.4002142; published online 8 January 2008.

No association between the DRD3 Ser9Gly polymorphism and schizophrenia

OBJECTIVE

To investigate the association between a Ser9Gly polymorphism of the dopamine D3 receptor gene (DRD3) and schizophrenia.

METHODS

408 schizophrenic patients and 172 control subjects were compared with regard to their DRD3 Ser9Gly genotypic and allelic frequencies. In addition, we carried out a family-based association study including 183 pedigrees (472 subjects) using the transmission disequilibrium test (TDT).

RESULTS

No significant differences of genotype or homozygosity distribution were identified between patients and controls. When patients were stratified according to gender, response to treatment, age at onset, no significant differences were observed. Neither allele A (Ser), or G (Gly) were preferentially transmitted from parents to affected offspring.

CONCLUSION

The hypothesis that the DRD3 Ser9Gly polymorphism plays a predisposing role in schizophrenia is not supported by this study.

Molecular mechanisms of schizophrenia

Schizophrenia is a complex disorder, where family, twin and adoption studies have been demonstrating a high heritability of the disease and that this disease is not simply defined by several major genes but rather evolves from addition or potentiation of a specific cluster of genes, which subsequently determines the genetic vulnerability of an individual. Linkage and association studies suggest that a genetic vulnerablility, is not forcefully leading to the disease since triggering factors and environmental influences, i.e. birth complications, drug abuse, urban background or time of birth have been identified. This has lead to the assumption that schizophrenia is not only a genetically defined static disorder but a dynamic process leading to dysregulation of multiple pathways. There are several different hypothesis based on several facets of the disease, some of them due to the relatively well-known mechanisms of therapeutic agents. The most widely considered neurodevelopmental hypothesis of schizophrenia integrates environmental influences and causative genes. The dopamine hypothesis of schizophrenia is based on the fact that all common treatments involve antidopaminergic mechanisms and genes such as DRD2, DRD3, DARPP-32, BDNF or COMT are closely related to dopaminergic system functioning. The glutamatergic hypothesis of schizophrenia lead recently to a first successful mGlu2/3 receptor agonistic drug and is underpinned by significant findings in genes regulating the glutamatergic system (SLC1A6, SLC1A2 GRIN1, GRIN2A, GRIA1, NRG1, ErbB4, DTNBP1, DAAO, G72/30, GRM3). Correspondingly, GABA has been proposed to modulate the pathophysiology of the disease which is represented by the involvement of genes like GABRA1, GABRP, GABRA6 and Reelin. Moreover, several genes implicating immune, signaling and networking deficits have been reported to be involved in the disease, i.e. DISC1, RGS4, PRODH, DGCR6, ZDHHC8, DGCR2, Akt, CREB, IL-1B, IL-1RN, IL-10, IL-1B. However, molecular findings suggest that a complex interplay between receptors, kinases, proteins and hormones is involved in schizophrenia. In a unifying hypothesis, different cascades merge into another that ultimately lead to the development of symptoms adherent to schizophrenic disorders.

No association between dopamine D4 receptor gene -521 C/T polymorphism and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotics. We evaluated whether a candidate functional polymorphism of the dopamine D4 receptor (DRD4) gene is associated with drug-induced TD in 209 Korean schizophrenic patients with TD (n = 83) and without TD (n = 126) who were matched for antipsychotic drug exposure and other relevant variables. There was no significant association of the genotype and allele frequencies determined by the -521 C/T SNP of DRD4 between TD and non-TD patients. In addition, there was no significant difference in terms of total Abnormal Involuntary Movement Scale scores among the 3 genotype groups. Within the limitations imposed by the size of the clinical sample, these findings suggest that the DRD4 -521 C/T SNP does not contribute significantly to the risk for TD.

Association study of tardive dyskinesia and twelve DRD2 polymorphisms in schizophrenia patients

Tardive dyskinesia (TD) is a side-effect of chronic antipsychotic medication. Abnormalities in dopaminergic activity in the nigrostriatal system have been most often suggested to be involved because the agents which cause TD share in common potent antagonism of dopamine D2 receptors (DRD2), that notably is not balanced by effects such as more potent serotonin (5-HT)2A antagonism. Thus, a number of studies have focused on the association of dopamine system gene polymorphisms and TD. The most consistent findings have been found with the Ser9Gly polymorphism of the DRD3 gene. Although DRD2 has long been hypothesized to be the main target for antipsychotics, only a few polymorphisms in DRD2 have been investigated for their potential involvement in the aetiology of TD. In the present study, we investigated 12 polymorphisms spanning the DRD2 gene and their association with TD in our European Caucasian (n=202) and African-American (n=30) samples. Genotype frequencies for a functional polymorphism, C957T (Duan et al., 2003; Hirvonen et al., 2004), and the adjacent C939T polymorphism were found to be significantly associated with TD (p=0.013 and p=0.022 respectively). DRD2 genotypes were not significantly associated with TD severity as measured by AIMS (Abnormal Involuntary Movement Scale) with the exception of a trend for C939T (p=0.071). Both TD and total AIMS scores were found to be significantly associated with two-marker haplotypes containing C939T and C957T (p=0.021 and p=0.0087 respectively). Preliminary results indicated that C957T was also associated with TD in our African-American sample (p=0.047). Taken together, the present study suggests that DRD2 may be involved in TD in the Caucasian population, although further studies are warranted.

Polymorphisms in dopamine receptor DRD1 and DRD2 genes and psychopathological and extrapyramidal symptoms in patients on long-term antipsychotic treatment

DRD(1) and DRD(2) receptor gene variants have been associated with clinical aspects of schizophrenia; however only specific features were analyzed in different samples. To assess the complex interaction between genetic and clinical factors, we studied the possible cross-interactions between DRD1 and DRD2 dopamine receptor gene polymorphisms, symptomatology of schizophrenia and schizoaffective disorders, and the occurrence of treatment induced side effects taking into consideration possible clinical confounding variables. One hundred thirty one outpatients in stable remission meeting the DSMIV criteria for schizophrenia spectrum disorders and receiving long-term maintenance therapy with haloperidol, fluphenazine, zuclopenthixole, or risperidone were genotyped for DRD1 A-48G, DRD2 Ins-141CDel, and DRD2 Ser311Cys polymorphisms. Psychopathological symptoms were assessed with the positive and negative syndrome scale for schizophrenia (PANSS). Extrapyramidal side effects were assessed with the Simpson-Angus extrapyramidal side effects scale (EPS), the Barnes Akathisia scale (BARS), and the abnormal involuntary movement scale (AIMS). Drug dosage was included as covariant because it was associated with the severity of symptomatology, akathisia, and parkinsonism. No association was observed for DRD1 and DRD2 polymorphisms and extrapyramidal side effects, or with the other clinical variables considered. Our study suggests that DRD1 and DRD2 variants are not liability factors for tardive dyskinesia.

Pharmacogenetics and pharmacogenomics of schizophrenia: a review of last decade of research

The last decade of research into the pharmacogenetics of antipsychotics has seen the development of genetic tests to determine the patients' metabolic status and the first attempts at personalization of antipsychotic treatment. The most significant results are the association between drug metabolic polymorphisms, mainly in cytochrome P450 genes, with variations in drug metabolic rates and side effects. Patients with genetically determined CYP2D6 poor metabolizer (PMs) status may require lower doses of antipsychotic. Alternatively, CYP2D6 ultrarapid matabolizers (UMs) will need increased drug dosage to obtain therapeutic response. Additionally, polymorphisms in dopamine and serotonin receptor genes are repeatedly found associated with response phenotypes, probably reflecting the strong affinities that most antipsychotics display for these receptors. In particular, there is important evidence suggesting association between dopamine 2 receptor (D2) polymorphisms (Taq I and -141-C Ins/Del) and a dopamine 3 receptor (D3) polymorphism (Ser9Gly) with antipsychotic response and drug-induced tardive dyskinesia. Additionally, there is accumulating evidence indicating the influence of a 5-HT2C polymorphism (-759-T/C) in antipsychotic-induced weight gain. Application of this knowledge to clinical practice is slowly gathering pace, with pretreatment determination of individual's drug metabolic rates, via CYP genotyping, leading the field. Genetic determination of patients' metabolic status is expected to bring clinical benefits by helping to adjust therapeutic doses and reduce adverse reactions. Genetic tests for the pretreatment prediction of antipsychotic response, although still in its infancy, have obvious implications for the selection and improvement of antipsychotic treatment. These developments can be considered as successes, but the objectives of bringing pharmacogenetic and pharmacogenomic research in psychiatric clinical practice are far from being realized. Further development of genetic tests is required before the concept of tailored treatment can be applied to psychopharmatherapy. This review aims to summarize the key findings from the last decade of research in the field. Current knowledge on genetic prediction of drug metabolic status, general response and drug-induced side effects will be reviewed and future pharmacogenomic and epigenetic research will be discussed.

Tardive dyskinesia and essential fatty acids

Tardive dyskinesia (TD) is a movement disorder described in individuals who have been treated with anti-dopaminergic agents. The pathophysiology of this condition remains to be fully elucidated. Several mechanisms like dopaminergic supersensitivity, dysfunction of striatonigral, GABAergic neurons and disturbed balance between dopaminergic and cholinergic systems have been described. Essential fatty acids (EFAs) are important components of neuronal membrane and the EFA content of these membranes can significantly influence neuronal functioning. Lower levels of EFAs have been reported in red blood cells (RBC) and plasma of individuals with moderate to severe TD. Supplementation with EFAs (omega-3 and omega-6 and ethyl-EPA) have been tried to alleviate TD in open and double-blind clinical trials and in some animal models of TD. In addition, antioxidants (Vitamin E) and melatonin have been tried. However, smaller numbers of patients and shortened length of clinical studies make it difficult to draw any definitive conclusions. Large multi-centre studies with sound methodology of both EFAs and antioxidants are needed.

Antipsychotic-induced tardive dyskinesia and the Ser9Gly polymorphism in the DRD3 gene: a meta analysis

BACKGROUND

A polymorphic site in the gene encoding the dopamine 3 receptor (DRD3) resulting in a serine (Ser) into glycine (Gly) substitution has been shown to affect dopamine binding affinity, and may contribute to individual differences in susceptibility to antipsychotic-induced tardive dyskinesia (TD).

METHODS

A Medline, EMBASE and PsychINFO search of literature published between 1976 and March 2005 yielded 11 studies from which data were extracted for calculation of pooled estimates using meta-analytic techniques.

RESULTS

The Gly allele increased the risk relative to the Ser allele (OR=1.17; 95% CI: 1.01-1.37) with evidence of publication bias. No significant genotype effects were apparent.

CONCLUSIONS

TD may be associated with functional variation in the DRD3 allele. However, caution is required in interpreting this finding, as there is evidence of publication bias, genetic methodology has shortcomings, and the relation between antipsychotics, schizophrenia and TD is complex.

The effect of chronic administration of sarizotan, 5-HT1A agonist/D3/D4 ligand, on haloperidol-induced repetitive jaw movements in rat model of tardive dyskinesia

Dyskinesia is the most troublesome side effect in long-term treatment of both Parkinson's disease (PD) and schizophrenia. The 5-HT1A agonist and D3/D4 ligand sarizotan [Bartoszyk, G.D., van Amsterdam, C., Greiner, H.E., Rautenberg, W., Russ, H., Seyfried, C.A., 2004. Sarizotan, a serotonin 5-HT1A receptor agonist and dopamine receptor ligand. 1. Neurochemical profile. J. Neural Transm. 111, 113-126.] is in clinical development for the treatment of PD-associated dyskinesia. Because 5-HT1A agonists are known to counteract antipsychotic-induced motor side effects, sarizotan was investigated for its effects in two rat models of tardive dyskinesia (TD). The acute administration of sarizotan (0.17-13.5 mg/kg i.p.) reduced episodes of SKF 38393-induced repetitive jaw movements (RJM) in rats with a maximal effect at 1.5 mg/kg. In a chronic study, sarizotan (0.04-9 mg/kg/day), administered in the drinking water for 7 weeks during withdrawal from chronic haloperidol treatment (1.5 mg/kg/day), dose-dependently reversed haloperidol-induced RJM, significant at the doses of 1.5 and 9 mg/kg. Agonism at 5-HT1A receptors may be mediating the inhibitory effect of sarizotan on RJM in rat models of tardive dyskinesia.

Genetic susceptibility to tardive dyskinesia among schizophrenia subjects: IV. Role of dopaminergic pathway gene polymorphisms

OBJECTIVE

Tardive dyskinesia (TD) is an antipsychotic induced side effect observed in 20-30% of schizophrenia subjects on long-term typical antipsychotic treatment. We tested the possible association of 24 polymorphisms from six dopaminergic genes: namely, dopamine receptors D1, D2, D3, D4; the dopamine transporter (DAT); and the catalyzing enzyme catechol-O-methyltransferase (COMT), with TD.

METHODS

Multiple SNP/VNTR markers from candidate genes were analyzed using suitable approaches and allelic, genotypic and haplotypic associations were tested.

RESULTS

120 bp duplication marker, 1.2 kb upstream from initiation codon of DRD4 gene showed a significant genotypic association [chi2 = 9.29, P = 0.009; OR (95% CI) = 0.52 (0.31-0.86) for genotype 120 dup/120 dup]. In the COMT gene, a significant allelic [chi2 = 13.87, P = 0.0002] as well as genotypic association [chi2 = 16.08, P = 0.0003; OR (95% CI) = 0.24 (0.11-0.55) for genotype GG] was observed with the 408 C>G (exon 4) single nucleotide polymorphism and a significant genotypic association [chi2 = 6.32, P = 0.04; OR (95% CI) = 0.50 (0.33-0.92) for genotype GG] was observed with 472 G > A (exon 4, Val 158 Met) SNP. 120 bp dup-T-repeat 3 in DRD4 and G-C-A-insC in COMT genes were observed to be TD associated haplotypes.

CONCLUSIONS

Our study presents a detailed analysis of the possible role of dopaminergic genes in the genesis of TD. DRD4 and COMT genes were observed to be the most important candidates in North Indian schizophrenia subjects. These suggestive associations need to be investigated in replicate studies.

Pharmacogenetics as a tool in the therapy of schizophrenia

AIM

This review summarises the present knowledge of associations between pharmacogenetics and therapeutic efficacy and side effects of antipsychotics to enable pharmacists to judge the applicability for a more tailor made therapy in patients with schizophrenia. Polymorphisms of Cytochrome P450 isoenzymes and neurotransmitter receptors involved in the efficacy and side effects of antipsychotics are highlighted in this review.

METHOD

A search was performed in Medline and EMBASE for the period 1995-August 2002. Also relevant references from the selected papers were incorporated.

RESULTS

Poor metabolism with respect to CYP2D6 seems to be related with more pronounced extrapyramidal symptoms and more specifically with a higher incidence of tardive dyskinesia. The C/C-genotype for CYP1A2 results in smokers in a reduction of enzyme activity, but an effect on the incidence of tardive dyskinesia is controversial. For dopamine D2 receptors the effect of the -141C Ins/Del polymorphism on efficacy is not clear yet, although the Taq I polymorphism is associated with greater improvement of positive, but not negative symptoms in acute psychosis. The Gly9-allele of the dopamine D3 receptor is associated with the response to clozapine, but in studies in which the choice of antipsychotics is not restricted, the role of this polymorphism is unclear. The reverse is applicable to the dopamine D(4.2/4.7) polymorphism. For the 5-HT2A receptor the His452Tyr polymorphism is associated with response to clozapine, the 102 T/C polymorphism leads to equivocal results. The polymorphism studied for 5-HT5A, 5-HT6, alpha1A- and alpha2A-receptors give no clear associations with the response to clozapine. The polymorphism studied of the dopamine D2 and D4 receptor are not related to extrapyramidal adverse effects and side effects, respectively. The 9Gly-variant of the dopamine D3 receptor, the 102C-variant, but not the His452Tyr polymorphism of the 5-HT2A-receptor and the 23Ser-variant (for females only) of the 5-HT2C receptor seem to increase the susceptibility to tardive dyskinesia. Weight gain induced by antipsychotics seems to be associated with the -759C-allele of the 5-HT2C receptor.

CONCLUSION

The results show the first careful steps toward application of pharmacogenetics in a more individualised, tailor-made, pharmacotherapy. A pre-condition seems to be a multifactorial approach, as can be expected for multifactorial processes.

Neuropsychiatric pharmacogenetics: moving toward a comprehensive understanding of predicting risks and response

Pharmacogenetic research in the area of neuropsychiatric illnesses is rapidly evolving. Due to the complexity of the human brain, it is not surprising that our knowledge about the interaction between genetics and the treatment of these illnesses is very small. The Human Genome Project (HGP) has identified > 30,000 genes; several thousand of which have been found to occur in the brain or serve a role that enhances the brain’s function. Much of the research in the post-HGP era is being driven by a desire to use genetics to predict which patients deviate from the norm in terms of drug response or side effects. By identifying these people, we will be able to direct clinical practice such that therapies for these disorders can be individualized. With this in mind, the following review is intended to cover a broad understanding of CNS pharmacogenetics with the goal of summarizing available literature on promising candidate gene targets, which may eventually help us predict clinical outcomes in patients taking medications commonly used to treat neuropsychiatric disorders.

Polymorphisms of dopamine degradation enzyme (COMT and MAO) genes and tardive dyskinesia in patients with schizophrenia

Several lines of evidence suggest that tardive dyskinesia (TD) may be associated with altered dopaminergic neurotransmission. We hypothesized that deranged dopamine degradation enzyme activities might be related to the susceptibility to TD through altered dopaminergic neurotransmission in the central nervous system. In the present study, we investigated the relationship between the gene polymorphisms of three dopamine degradation enzymes and TD. We genotyped the valine/methionine polymorphism of codon 108/158 in the catechol-O-methyltransferase (COMT) gene, the 30-bp repeat polymorphism in the promoter of the monoamine oxidase A (MAOA) gene, and the A/G polymorphism in intron 13 of the monoamine oxidase B (MAOB) gene in 206 Japanese patients with schizophrenia. No significant difference was found in total scores on the Abnormal Involuntary Movement Scale (AIMS) among the subject groups, sorted according to the COMT, MAOA and MAOB genotypes. Moreover, no significant difference was found in allele frequencies between patients with TD and patients without TD for any of the polymorphisms. As both COMT and MAO genes are involved in degrading catecholamines, we also sought evidence for additive and epistatic effects, but none was observed. Our data, therefore, do not support the hypothesis that polymorphisms in COMT, MAOA, and MAOB genes are involved individually or in combination in the predisposition to TD.

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.