Pharmacogenetics of antipsychotic treatment: lessons learned from clozapine

Prescribing of clozapine and olanzapine: dosage, polypharmacy and patient ethnicity

Aims and Method

The aim of this study was to determine the existence and extent of differences in prescribing practice for patients according to ethnic group, with two widely used atypical antipsychotics, olanzapine and clozapine. All in-patient prescription charts were screened and patients receiving olanzapine and clozapine identified. Dosage, antipsychotic co-prescription and race were recorded, along with demographic details, and evaluated using comparative statistical analysis.

Results

Overall, 1441 prescriptions were screened; 328 patients received olanzapine and 200 clozapine. Details of ethnic origin were available for 287 of those prescribed olanzapine and 188 of those prescribed clozapine. There was no significant difference between ethnic groups in age or gender, for either drug. For clozapine, dosage and extent of antipsychotic co-prescription did not differ significantly between ethnic groups; for olanzapine, there was no significant difference in daily dose between the groups, but co-prescription was significantly more common in Black (33%) than in White patients (20%; P=0.023).

Clinical Implications

Important differences in the prescription of olanzapine and clozapine between ethnic groups are uncommon, but demand further investigation. Larger studies incorporating additional baseline details such as diagnosis and body weight are called for.

Indicators of response to clozapine treatment

Since its initial landmark trial against chlorpromazine in 1988, clozapine has been the drug of choice for the treatment of refractory schizophrenia. However, variability in clinical response to clozapine treatment is unequivocal. In an effort to preselect patients who are most likely to benefit from clozapine, a number of patient and disease variables and select genetic differences have been studied for their association with positive treatment response to clozapine. Because of small trial sizes and the heterogeneity of study design, findings have resulted in no generalizable conclusion. Future pharmacogenetic studies hold the promise of antipsychotic treatment personalization.

Fluorescence of neutrophil granulocytes as a biomarker for clozapine use

Non-adherence to medication is a major issue in the treatment of schizophrenia in general and in particular for those treated with clozapine. A reliable tool to quantify patients long-term adherence to clozapine is currently unavailable. Enhanced FL3 neutrophil granulocyte fluorescence was serendipitously observed in a small population of schizophrenic patients treated with clozapine. The present study was aimed at assessing the association between clozapine use and FL3-fluorescence. A cross-sectional study was performed using data from the Utrecht Patient Oriented Database (UPOD). A total of 38,390 inpatients were included, of which 124 (0.33%) used clozapine. FL3-fluorescence was significantly higher (U=240,179, P<0.001) in clozapine users (mean (SD)=90.5 (11.8)) than in non-users (mean (SD)=69.8 (3.3)). Observed FL3-fluorescence was found to increase with increasing clozapine dose. The area under the receiver operating characteristic curve was 0.95. Our results confirm the association between use of clozapine and elevated FL3-fluorescence. Further research is needed to unravel the underlying mechanism and to investigate the true potential of FL3-fluorescence as a clozapine-adherence biomarker in clinical practice.

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.

Influence of serotonin transporter gene polymorphisms on clozapine response in Brazilian schizophrenics

Schizophrenia is a severe mental illness affecting around 1% of adults with a high degree of morbidity and mortality. Affected individuals are at increased risk for unemployment, handicap, obesity, diabetes mellitus, hearth attack and suicide. Antipsychotic drugs are the best treatment for this disease, but about 20% of patients display drug resistance, or refractoriness, and may receive a special neuroleptic named Clozapine. Despite its superiority from other neuroleptics, only 30-60% of drug-resistant patients are responsive to clozapine. Clozapine's action results from interactions between dopaminergic and serotonergic neurotransmitter systems and since clozapine appears to exert its effect strongly through the serotonergic systems, alterations in serotonin synaptic levels may influence antipsychotic response. The serotonin transporter (5-HTT) is responsible for pre-synaptic re-uptake of serotonin, making this transporter a logical candidate gene for prediction of clozapine response and to increase understanding about mechanisms of refractoriness. Therefore, we investigated the influence of two polymorphisms in the 5-HTT gene (HTTLPR/rs25531 and VNTR Stin2) in clozapine response in a sample of 116 schizophrenic individuals of European descent from South-Brazil. Significant differences between responders and non-responders to clozapine were observed for the HTTLPR/rs25531 polymorphism. Nonresponders to clozapine showed a higher frequency of S'-allele (P = 0.01) and also were more likely to be S'/S' homozygous or S'/L' heterozygous than those who did respond (P = 0.04). After controlling for confounding variables, logistic regression analyses confirmed this association (OR = 3.15; 95% CI: 1.13-8.80). The observed association suggests that increased availability of extracellular serotonin concentrations at all synapses may reduce clozapine effect.

Genetic association between TNF-alpha -308 G>A polymorphism and longitudinal weight change during clozapine treatment

OBJECTIVE

The aim of the study was to investigate the association between genetic variation in the tumor necrosis factor-alpha (TNF-alpha) gene and longitudinal weight change during long-term clozapine treatment.

METHODS

Fifty-five patients with refractory schizophrenia treated with clozapine for 8 years were recruited. Gender, age, treatment response to clozapine in the first 14 months, baseline BMI, clozapine dose, concomitant use of mood stabilizers and other antipsychotics, and -308 G > A polymorphism in the human TNF-alpha gene were analyzed using generalized estimating equations.

RESULTS

In addition to having a lower baseline BMI (p = 0.0013) and a longer treatment time (p = 0.050), the -308 GG carriers gained significantly more weight than the -308 A allele carriers (p = 0.0084) during 8 years of clozapine treatment, after controlling for other non-genetic factors.

CONCLUSIONS

The -308 G > A genetic variant of the TNF-alpha gene is associated with longitudinal weight change during clozapine treatment. Follow-up duration is an important factor to consider when performing pharmacogenetic study of clozapine-induced weight gain.

Cholinesterase inhibitors in Alzheimer's disease and Lewy body spectrum disorders: the emerging pharmacogenetic story

This review provides an update on the current state of pharmacogenetic research in the treatment of Alzheimer's disease (AD) and Lewy body disease (LBD) as it pertains to the use of cholinesterase inhibitors (ChEI). AD and LBD are first reviewed from clinical and pathophysiological perspectives. This is followed by a discussion of ChEIs used in the symptomatic treatment of these conditions, focusing on their unique and overlapping pharmacokinetic and pharmacodynamic profiles, which can be used to identify candidate genes for pharmacogenetics studies. The literature published to date is then reviewed and limitations are discussed. This is followed by a discussion of potential endophenotypes which may help to refine future pharmacogenetic studies of response and adverse effects to ChEIs.

The efficacies of clozapine and haloperidol in refractory schizophrenia are related to DTNBP1 variation

OBJECTIVE

The prototypical atypical antipsychotic agent, clozapine, is more efficacious for refractory schizophrenia than the 'typical' antipsychotics, but the mechanism underlying this enhanced efficacy is still under investigation. Since 2002, at least 22 association studies have shown that the DTNBP1 can be associated with the risk for schizophrenia. We hypothesized that DTNBP1 might also influence the response to antipsychotic treatments. This study aimed to investigate the relationship between the DTNBP1 and the effects of clozapine and haloperidol on refractory schizophrenia.

METHODS

Patients with refractory schizophrenia were assigned to clozapine (n=85) or haloperidol (n=96) and followed for 3 months. Symptom improvement was evaluated by Positive and Negative Syndrome Scale score. Six markers at DTNBP1 and 38 ancestry-informative markers were genotyped in all participants. The relationships between the effects of antipsychotics and the diplotypes, haplotypes, genotypes, and alleles of DTNBP1 were tested by analysis of covariance, analysis of variance, and t-test.

RESULTS

Patients with diplotype ACCCTC/GTTGCC, genotypes T/T+T/C, or allele T of marker rs742105 (P1333) have better response to clozapine (0.005< or =P< or =0.049), and patients with diplotype ACCCTC/GCCGCC, genotype A/G, or allele A of marker rs909706 (P1583) have better response to haloperidol (0.007< or =P< or =0.080) in European-Americans, African-Americans, and/or the combined sample; European-American patients with diplotype ACCCTC/GCCGCC have worse response to clozapine on positive symptoms (P=0.011).

CONCLUSION

This study shows that the DTNBP1 gene modulates the effects of both the atypical antipsychotic clozapine and the typical antipsychotic haloperidol. Participants with different DTNBP1 diplotypes, haplotypes, genotypes, or alleles might have different responses to these antipsychotics.

Overview of pharmacogenetics

Pharmacogenetics is the study of relationships between genetic variation and inter-individual differences with respect to drug response. As the field has matured over the past 15 years, a remarkable diversity of pathways, variation types, and mechanisms have been found to be relevant pharmacogenetic factors. Today, pharmacogenetics is becoming more important in pharmacology for target validation, lead optimization, and understanding of idiosyncratic toxicity. This unit provides an overview of the history of pharmacogenetics and current research applications in drug discovery, as well as a discussion of research quality issues relevant for human subjects research in the pharmacogenetics laboratory.

Pharmacogenetic testing in schizophrenia and posttraumatic stress disorder

Genotyping patients prior to beginning psychiatric pharmacological therapy can serve to inform practitioners as to each patient's likelihood of therapeutic response and their relative risk of experiencing toxicity and other adverse side effects from certain drugs. Such information could arm physicians with the knowledge they need to make appropriate drug and dosing decisions and avoid the lengthy trial-and-error process with which they are faced today. This article describes the current state of pharmacogenetic testing in schizophrenia and posttraumatic stress disorder.

Pharmacogenetics in psychiatry: are we ready for widespread clinical use?

There are high expectations about the capabilities of pharmacogenetics to tailor psychotropic treatment and "personalize" treatment. While a large number of associations, with generally small effect size, have been discovered, a "test" with widespread use and adoption is still missing. A more realistic picture, recognizing the important contribution of clinical and environmental factors toward overall clinical outcome has emerged. In this emerging view, genetic findings, if considered individually, may have limited clinical applications. Thus, in recent years, combinations of information in several genes have been used for the selection of appropriate therapeutic doses and for the prediction of agranulocytosis, hyperlipidemia, and response to antipsychotic and antidepressant medications. While these tests based on multiple genes show greater predictive ability than individual allele tests, their net impact on clinical consequence and costs is limited, thus leading to limited penetration into widespread clinical use. As one looks at other branches of medicine, there are successful examples of pharmacogenetic tests guiding treatment, and thus, it is reasonable to hope that with the incorporation of clinical and environmental information and the identification of new genes drawn from genome-wide analysis, will improve the predictive utility of these tests leading to their increased use by clinicians.

Off-target effects of psychoactive drugs revealed by genome-wide assays in yeast

To better understand off-target effects of widely prescribed psychoactive drugs, we performed a comprehensive series of chemogenomic screens using the budding yeast Saccharomyces cerevisiae as a model system. Because the known human targets of these drugs do not exist in yeast, we could employ the yeast gene deletion collections and parallel fitness profiling to explore potential off-target effects in a genome-wide manner. Among 214 tested, documented psychoactive drugs, we identified 81 compounds that inhibited wild-type yeast growth and were thus selected for genome-wide fitness profiling. Many of these drugs had a propensity to affect multiple cellular functions. The sensitivity profiles of half of the analyzed drugs were enriched for core cellular processes such as secretion, protein folding, RNA processing, and chromatin structure. Interestingly, fluoxetine (Prozac) interfered with establishment of cell polarity, cyproheptadine (Periactin) targeted essential genes with chromatin-remodeling roles, while paroxetine (Paxil) interfered with essential RNA metabolism genes, suggesting potential secondary drug targets. We also found that the more recently developed atypical antipsychotic clozapine (Clozaril) had no fewer off-target effects in yeast than the typical antipsychotics haloperidol (Haldol) and pimozide (Orap). Our results suggest that model organism pharmacogenetic studies provide a rational foundation for understanding the off-target effects of clinically important psychoactive agents and suggest a rational means both for devising compound derivatives with fewer side effects and for tailoring drug treatment to individual patient genotypes.

Clinical aspects of super-refractory schizophrenia: a 6-month cohort observational study

OBJECTIVE

Approximately 30% of treatment-resistant schizophrenic patients do not fully respond to Clozapine and such patients are termed Clozapine non-responders or super-refractory schizophrenics. The aim of this study was to characterize patients with super-refractory schizophrenia according to demographic and psychopathological variables, as compared with patients with refractory schizophrenia or non-refractory subjects.

METHOD

One hundred two outpatients meeting DSM-IV criteria for schizophrenia were followed-up for 6 months. Subjects were classified into 3 groups: non-refractory (n=25), refractory (n=43) and super-refractory (n=34). Psychopathology was assessed by the Positive and Negative Syndrome Scale, the Schedule for Deficit Syndrome, the Calgary Depression Scale and the Quality of Life Scale. Patients were rated at 2-month intervals.

RESULTS

Higher levels of severity at the disease onset as well as higher severity of positive symptoms were found to be predictive of super-refractoriness.

CONCLUSIONS

The super-refractory schizophrenia patients have psychopathological predictive factors that need studies comparing brain images, genetical features and other clinical comparisons.

Could HTR2A T102C and DRD3 Ser9Gly predict clinical improvement in patients with acutely exacerbated schizophrenia? Results from treatment responses to risperidone in a naturalistic setting

OBJECTIVE

This study seeks to replicate previous results indicating that T102C in the serotonin 2A receptor (HTR2A) and Ser9Gly in the dopamine D3 receptor (DRD3) were associated with a risperidone response to acutely exacerbated schizophrenia, and to determine whether possession of these alleles predicts clinical improvement in a naturalistic setting.

METHODS

We consecutively recruited 100 schizophrenia patients and assessed clinical improvement after 4 weeks of risperidone treatment.

RESULTS

The patients with T/T in the HTR2A gene showed less clinical improvement than did those with T/C or C/C (p = 0.044). In the case of the DRD3 gene, we did not find statically significant association with clinical improvement (p = 0.061). When patients were categorized into responders and nonresponders, the C allele was more frequent in responders (OR = 2.28, 95%CI = 1.06-4.91, p = 0.039). When combinations of the two polymorphisms were considered, patients who had T/T in the HTR2A gene and encoded Ser/Ser or Ser/Gly from DRD3 gene had a higher propensity to non-responsiveness compared to other subjects (OR = 3.57, 95%CI = 1.10-11.62, p = 0.039).

CONCLUSIONS

Our findings suggest that the HTR2A T102C could be a potential indicator of clinical improvement after risperidone treatment.

Pharmacogenetics of antiparkinsonian drug treatment: a systematic review

Pharmacotherapy is the mainstay in the treatment of Parkinson's disease and the armamentarium of drugs available for the therapy of this disease is still expanding. Anti-Parkinson's disease drugs are effective in reducing the physical symptoms, such as hypokinesia, bradykinesia, rigidity and tremor. However, there is a large interindividual variability in response to anti-Parkinson's disease drugs with respect to both drug efficacy and toxicity. It is thought that genetic variability in genes encoding drug-metabolizing enzymes, drug receptors and proteins involved in pathway signaling is an important factor in determining interindividual variability in drug response. Pharmacogenetics aims at identifying genetic markers associated with drug response. Ideally, knowledge of these genetic markers will enable us to predict an individual's drug response in terms of both efficacy and toxicity. The role of pharmacogenetics in the treatment of Parkinson's disease is relatively unexplored. Therefore, we aim to present a systematic review of the published pharmacogenetic studies in Parkinson's disease and to describe polymorphic genes of interest for future research.

Investigation of possible association between Ser9Gly polymorphism of the D3 dopaminergic receptor gene and response to typical antipsychotics in patients with schizophrenia

Typical antipsychotics have a high affinity for dopamine receptors. It is therefore of interest to investigate such loci in pharmacogenetic studies on psychosis. We investigated the hypothesis that Ser9Gly polymorphism of the DRD3 gene may play a role in the differences in individual response to typical antipsychotics between schizophrenic patients. The sample was composed of 53 good responders and 59 poor ones. No significant differences between the good and poor responders were found in the allelic distribution (good responders: Ser9 61.32%, Gly9 38.67%; poor responders: Ser9 64.40%, Gly9 35.59%; odds ratio, OR = 0.88, 0.49 < OR < 1.56; chi2 = 0.23, 1 degree of freedom, df, p = 0.63) and genotype distribution (good responders: Ser9/Ser9 37.73%, Ser9/Gly9 47.16%, Gly9/Gly9 15.09%; poor responders: Ser9/Ser9 42.37%, Ser9/Gly9 44.06%, Gly9/Gly9 13.55%; chi2 = 0.25, 2 df, p = 0.88). Nor was there any association with homozygosity (good responders: homozygous: 52.82%, heterozygous: 47.16%; poor responders: homozygous: 55.92%, heterozygous: 44.06%; odds ratio, OR = 0.88, 0.39 < OR < 1.99; chi2 = 0.11, 1 df, p = 0.74). The results did not support the hypothesis that Ser9Gly polymorphism of the DRD3 gene influences the response to typical antipsychotics in our sample of schizophrenics.

Serum concentrations of clozapine and norclozapine in the prediction of relapse of patients with schizophrenia

Schizophrenic outpatients (n=102) whose condition had stabilized with clozapine (CLZ) therapy and were being maintained on CLZ were followed for 1 year. Clinical status and concentrations of serum clozapine (CLZ) and its metabolite norclozapine (NCLZ) were evaluated periodically or when relapse occurred. Relapse was defined as a significant exacerbation of psychotic symptoms or hospitalization. Thirty-three patients relapsed and 69 did not. Relapse patients displayed significantly lower serum concentrations of CLZ and a sum of CLZ and NCLZ at endpoint than non-relapses (CLZ: 162 ng/ml vs. 237 ng/ml, p<0.001; CLZ+NCLZ: 225 ng/ml vs. 301 ng/ml, p<0.001). When all subjects were pooled together, a significant inverse correlation was observed between percent increase in the total score on the Brief Psychiatric Rating Scale (BPRS) from baseline and serum levels of CLZ alone (r=0.404, p<0.001) and the sum of CLZ and NCLZ (r=0.364, p<0.001). Relapses and non-relapses were well separated by a threshold CLZ serum concentration of 200 ng/ml with a sensitivity of 73% and a specificity of 80%. The threshold value represented about a 40% lower serum CLZ level than concentration achieved in acute treatment. Survival analysis showed a similarity of the relapse risk over time defined by the CLZ serum threshold and by symptomatic criteria. These results suggest that effective relapse prevention may require maintenance of patients at CLZ serum concentrations above 200 ng/ml and above 60% of the acute-phase level during long-term maintenance treatment of schizophrenia.

Translocation of AIF in the human and rat striatum following protracted haloperidol, but not clozapine treatment

Loss of mitochondrial membrane integrity and consequent release of apoptogenic factors may be involved in mediating striatal neurodegeneration after prolonged treatment with the typical antipsychotic drug haloperidol. Apoptosis-inducing factor (AIF), an intramitochondrial protein, may have a large influence on mediating haloperidol-induced striatal neuron destruction. Translocation of this protein from mitochondria to the nucleus promotes cell death independently of the caspase cascade. To examine how AIF may contribute to haloperidol-induced apoptosis, AIF translocation was observed in three haloperidol treatment paradigms. SH-SY5Y cells were treated with both haloperidol and clozapine and examined for AIF immunofluorescence. Immunohistochemistry was also performed on human striatal sections obtained from the Stanley Foundation Neuropathology Consortium and on rat brain sections following 28 days of antipsychotic drug treatment. In the cellular model haloperidol, but not clozapine treatment increased the nuclear AIF immunofluorescent signal and decreased cell viability. Corollary to these findings, striatal sections from patients who had taken haloperidol and rats who were administered haloperidol both had an elevated nuclear AIF signal. The results provide novel evidence implicating the involvement of AIF in haloperidol-associated apoptosis and its relevance to the development of typical antipsychotic drug-related adverse effects such as tardive dyskinesia.

Dopamine D4 receptor gene exon III polymorphism and interindividual variation in response to clozapine

To investigate the relationship between 48 bp variant number tandem repeat polymorphism in dopamine D4 receptor gene and response to clozapine in schizophrenic patients, the authors included 81 inpatients with a DSM-IV diagnosis of schizophrenia and patients meeting criteria for refractory to treatment were excluded. This study found that the frequencies of five 48 bp repeats homozygous genotype and five 48 bp repeats allele were significantly less in the responders than the nonresponders, which divided by improving total schizophrenic symptom. The results of this study suggest that inherited variants of D4 may explain some of the interindividual variation seen in patient response to clozapine.

Apolipoprotein D is associated with long-term outcome in patients with schizophrenia

Accumulating evidence implicates deficiencies in apolipoprotein D (ApoD) function and arachidonic acid signaling in schizophrenic disorders. We addressed two hypotheses in relation to ApoD: first, polymorphisms in the ApoD gene confer susceptibility to or are markers of disease, and, second, genetic variation in the ApoD is associated with long-term clinical outcome to antipsychotic treatment. We genotyped two single-nucleotide polymorphisms in the ApoD gene in 343 chronic patients with schizophrenia spectrum disorders (ICD-10) and 346 control subjects of Danish origin. We did not find ApoD alleles, genotypes or haplotypes to be associated with disease. However, we did find that long-term clinical outcome was associated with the ApoD polymorphism rs7659 (P = 0.041) following adjustment for lifetime clinical global impression, age at first admission and gender.

Pharmacogenetic testing in the clinical management of schizophrenia: a decision-analytic model

Clinical application of pharmacogenetic testing has been proposed as a means of improving treatment outcomes in psychiatry. The identification of a putative genetic test for better clozapine response in schizophrenia offers an opportunity to evaluate the cost-effectiveness of such testing. The authors performed a cost-effectiveness analysis of a genetic test that may identify individuals with greater likelihood of responding to clozapine treatment. We modeled a target population of schizophrenia patients in an acute psychotic episode, using a lifetime time horizon and societal perspective. Outcome measures included life expectancy, quality-adjusted life expectancy, costs, and incremental cost-effectiveness. Effects of variations in testing parameters were also examined. For a 30-year-old with schizophrenia, applying the pharmacogenetic test and treating those predicted to respond to clozapine with clozapine-first cost US $47,705 per additional quality-adjusted life-year, compared with treating all patients with conventional agents and reserving clozapine for treatment-resistant patients. In 1-way sensitivity analyses, test sensitivity and cost had the greatest impact on the incremental cost-effectiveness. We conclude that pharmacogenetic tests may achieve utility in clinical psychiatry, although their cost-effectiveness depends on several clinical parameters. More consistent reporting of test parameters such as sensitivity and specificity would greatly facilitate assessment of future pharmacogenetic studies.

Predictors and markers of clozapine response

RATIONALE

With other atypical antipsychotics now available, having predictors of clozapine response would be of considerable value, offering clinicians guidance in their decision as to when, and if, a trial of clozapine is warranted.

OBJECTIVES

The aim was to review existing evidence regarding identified predictors and markers of clozapine response.

METHODS

Relevant studies were identified through PUBMED searches (1975-June 2004) and cross-referencing of reviews and included studies. The data were summarized under two main categories: clinical (general, neurological, cognitive/neuropsychological, clozapine levels) and biological (biochemical, endocrine, genetic, metabolic, morphological, dopamine D2 receptor occupancy). 'Reliable' predictors/markers were defined a priori as those with support of at least two independent reports that addressed overall response, with no contradictory findings to date. 'Potential' predictors/markers had the support of a single report that addressed overall response and at least one other evaluating treatment outcome but not directly addressing response status.

RESULTS AND CONCLUSIONS

Higher baseline clinical symptoms and functioning in the previous years and low cerebrospinal homovanillic acid/5-hydroxyindoleacetic acid levels were identified as reliable. Three potential measures were identified: reduction of frontal cortex metabolic activity, reduction of caudate volume, and improvement in P50 sensory gating.

Pharmacogenetic studies of response to risperidone and other newer atypical antipsychotics

Risperidone and other newer atypical antipsychotics are becoming the mainstay for schizophrenia treatment. Recent studies suggest that the 5-hydroxytryptamine receptor 2A (5-HT2A) gene (HTR2A) T102C and G-1438A polymorphisms may influence treatment response of risperidone or olanzapine for schizophrenia's negative symptoms (e.g., blunted affect and social withdrawal). In addition, the HTR6 T267C polymorphism has been linked to risperidone response for positive symptoms (delusions and hallucinations). The dopamine D2 receptor (DRD2) Ser311Cys polymorphism may also play a role in determining risperidone efficacy for positive, negative and cognitive symptoms, the DRD2 Ins-A2/Del-A1 diplotype may predict better risperidone response, and the DRD3 Ser311Cys variant may affect general treatment response of several atypical agents. Although investigators have started to explore genetic effects on cognitions of schizophrenia patients receiving antipsychotics, future larger sized pharmacogenetic studies on both psychotic symptoms and cognitive functions are warranted.

The role of atypical antipsychotics in glucose/insulin dysregulation and the evolving role of the psychiatrist in a new era of drug treatment options

This article examines the issue of atypical antipsychotics, glucose/insulin, and other metabolic derangements (ie, metabolic syndrome), including a general introduction to the health concerns of our patients, a review of the literature, possible mechanisms of antipsychotic induced glucose dysregulation, monitoring approaches, and management and prevention of metabolic syndrome. Literature review leads to mechanism hypotheses and risk estimations, leading to guidelines for monitoring and treatment. The patient population suffers from a higher degree of baseline metabolic dysregulation resulting in cardiovascular disease through components of the metabolic syndrome, and this risk increases with administration of atypical antipsychotic medication at different rates, depending on both drug and patient risk factors. The growing knowledge of mechanisms behind drug induced glucose/insulin and other metabolic dysregulation, as well as advances in pharmacogenomics, will help refine drug selection and monitoring for adverse, life-threatening metabolic effects.

GENETIC TESTING IN PRIMARY CARE

Rapid advances in genetic research are leading to an expanding array of genetic tests. Primary care providers will increasingly be challenged to identify patients whose symptoms, physical findings, or family history indicate the need for genetic testing, and to determine how to use genetic information most effectively to improve disease prevention. In addressing these challenges, practitioners will need to consider the range of different uses of genetic testing, including diagnosis in symptomatic and asymptomatic people, risk assessment, reproductive decision-making, and population screening. They will need a set of core skills and knowledge to evaluate family history and to recognize clinical findings that indicate genetic risk. At the same time, the primary care perspective will contribute to the evaluation of appropriate uses of genetic testing. A partnership between medical genetics and primary care will help to ensure the development of effective policies, educational tools, and practice guidelines for the coming era of genomic health care.

Differential display polymerase chain reaction reveals increased expression of striatal rat glia-derived nexin following chronic clozapine treatment

Clozapine is considered a prototype of the 'so-called' atypical antipsychotic drug class. It has affinity for a broad range of receptors and, in comparison to typical antipsychotic drugs, produces less extrapyramidal side effects. However, its mechanism of action remains unclear. Differential display polymerase chain reaction (ddPCR) was implemented in this study to contribute to the current understanding of this mechanism at the genetic level and to identify novel genes regulated by clozapine. This technique generated approximately 2400 gene sequences that were analyzed for differential gene expression following protracted clozapine treatment. One of these sequences, originally termed Clozapine Regulated Gene (CRG), was shown to be significantly upregulated following the treatment. Northern hybridization confirmation of this finding revealed that chronic clozapine administration caused a five-fold increase in CRG mRNA. Elongation of the 5'- and 3'-ends of CRG indicated that the fragment was in fact rat glia-derived nexin mRNA. Western blotting demonstrated that levels of the mRNA's associated protein also increased comparably (three-fold) following chronic treatment with the antipsychotic drug. This study presents a possible neuroprotective role of nexin in clozapine treatment, particularly in the prevention of neuronal proteolytic degradation, since nexin has been shown to be a protease inhibitor.

Effect of DRD2, 5-HT2A, and COMT genes on antipsychotic response to risperidone

Risperidone is a widely used atypical antipsychotic with certain advantages over typical antipsychotics. Although variations in the efficacy of treatment with risperidone have been observed, no specific predictable marker has been identified as of yet. In all, 73 Japanese patients with schizophrenia were given risperidone for 8 weeks, and clinical symptoms were evaluated using the Positive and Negative Syndrome Scale (PANSS). Six candidate polymorphisms (HTR2A -1438G>A, 102T>C, H452Y; DRD2 -141delC, Taq I A; COMT V158M) were genotyped. The diplotype configuration for each individual was estimated by the maximum-likelihood method. Multiple linear regressions were used to analyze the effects of these haplotypes/genotype and other prognostic factors on PANSS scale performance. After adjustment for the effects of patient-related variables, HTR2A diplotype and COMT genotype, as well as other potential prognostic factors, did not significantly influence the clinical performance. A DRD2 haplotype tended to correlate with better clinical performance. Compared with patients who had Ins-A2/Ins-A2 diplotype (n=25), PANSS total scores of patients with Ins-A2/Del-A1 diplotype (n=10) showed 40% greater improvement (P=0.03). The PANSS total scores of patients with HTR2A A-T/A-T diplotype (n=22) tended to show 15% worse improvement compared with A-T/G-C diplotype (n=33) (P=0.06). These results should be treated with caution because of limitations due to small sample size, heterogeneity of patients with respect to past antipsychotic use history, and no correction for multiple corrections. However, the present findings generate important hypotheses in a sample of Japanese schizophrenia patients that may lay the foundation for future pharmacogenomics investigations in other populations.

Quetiapine in hospitalized patients with schizophrenia refractory to treatment with first-generation antipsychotics: a 4-week, flexible-dose, single-blind, exploratory, pilot trial

This short-term, single-blind, pilot trial was initiated to investigate the usefulness of quetiapine therapy in the treatment of schizophrenic patients refractory to first-generation antipsychotics. Following a neuroleptic-free period prior to study entry (at least 1 week for oral formulations and 6 weeks for depot formulations), quetiapine was started at 50 mg/day and titrated up to 500 mg/day by Day 6. This 500 mg daily dose was then maintained or increased up to a maximum of 750 mg/day, at the discretion of the treating physician, who was aware of the antipsychotic prescribed. Efficacy measures were represented by changes in total and component PANSS score from baseline to different intervals. Safety and tolerability were evaluated by monitoring the spontaneously referred moderate-to-severe adverse events, changes from baseline in SAS, BARS, and AIMS scores, supplementary use of flurazepam, lorazepam, and benztropine, clinically relevant physical changes, abnormalities in vital signs, blood chemistry, and hematology, and modifications in QTc interval and body weight. Rating scale assessments, categorization of adverse events, determination of physical examination, vital signs, and body weight were performed by a qualified physician blind to the particular antipsychotic under investigation and the aims of the study. All 12 patients completed the 4-week quetiapine treatment course. Mean total PANSS scores were significantly reduced between baseline and study endpoint (p=0.006). Five out of six PANSS subcomponent scores also showed significant decreases (p < 0.05). Six patients showed a reduction of > or = 20% in PANSS total score by the final day of quetiapine treatment, so were classified as responders. There were responders in all schizophrenia diagnostic subgroups (undifferentiated, paranoid, and disorganized). Two patients reported moderate adverse events. One patient received 3 days of benztropine therapy for EPS and five received flurazepam for insomnia. Weight change was minimal and mean SAS, BARS, and AIMS scores all showed nonsignificant decreases between baseline and endpoint. The 50% quetiapine response rate reported here in refractory patients is comparable with those previously reported for other atypical antipsychotics in populations of both refractory and intolerant patients.

A neurobehavioral screening of the ckr mouse mutant: implications for an animal model of schizophrenia

A model of schizophrenia, the chakragati (ckr) mouse was serendipitously created as a result of a transgenic insertional mutation. The apparent loss-of-function of an endogenous gene produced mice that, when homozygous, displayed an abnormal circling behavior phenotype. To determine whether this phenotype could be corrected by atypical antipsychotics, we compared the effects of clozapine and olanzapine on rotational turns and hyperactivity. Both of these drugs successfully ameliorated circling behavior and hyperactivity in homozygous mice. The increased motor activity of these mutant mice was both qualitatively and quantitatively similar to that observed in wild-type animals treated with dizocilpine, an N-methyl-D-aspartate receptor antagonist that produces behaviors resembling positive symptoms of schizophrenia. Mice either homozygous or heterozygous for the mutation also displayed enlargement of the lateral ventricles, which was accompanied only in the homozygous genotype by a loss of individual myelinated axons in the striatum and agenesis of the corpus callosum. These structural brain deficits were selective in that the nigro-striatal dopamine system was normal in these homozygous mice. In addition, two types of interneurons in the neostriatum, namely those producing acetylcholine or nitric-oxide synthase were also devoid of significant structural abnormalities. These results indicate that the ckr mouse mutant could be used as a possible animal model to study the pathophysiology of schizophrenia and suggest possible strategies for treating the behavioral aspects of this brain disease.

Role of dopamine D3 receptor (DRD3) and dopamine transporter (DAT) polymorphism in cognitive dysfunctions and therapeutic response to atypical antipsychotics in patients with schizophrenia

Molecular components of the dopaminergic system may play an important role in the pathophysiology of schizophrenia. In this study, we investigated the relationship of the Ser9Gly (S/G) polymorphism of the dopamine D3 receptor (DRD3) and the variable number of tandem repeats (VNTR) polymorphism of the dopamine transporter (DAT) with therapeutic response to atypical antipsychotics (clozapine, olanzapine, quetiapine, risperidone) and cognitive functions. No associations were found between the DRD3 and DAT polymorphisms and schizophrenia. The S/S genotype and the S allele were more frequent in the non-responder patients (n = 28) than in the group of responders (n = 47) (cut-off: >20-point improvement in Global Assessment of Functioning (GAF) scale). The patients with S/S genotype completed fewer categories and had more perseverative errors in the Wisconsin Card Sorting Test (WCST) compared with the S/G patients. The S/S and S/G patients did not differ in positive and negative symptoms, GAF scores, WCST failure to maintain set, and verbal learning. No differences in symptoms or WCST measures were observed in the patients with different DAT genotypes. These results suggest that the S/S genotype of the DRD3 is associated with worse therapeutic response and more severe executive dysfunctions in patients with schizophrenia.

Predictors of clinical outcome in schizophrenic patients responding to clozapine

Many of the patients who respond better to clozapine (CLZ) than to typical antipsychotics still have residual psychopathology, but CLZ drug resistance data are lacking. The aim of this study was to evaluate the possible predictive factors of a clinical response to CLZ in a group of 20 schizophrenic patients (DSM-IV: 13 males and 7 females with a mean age of 35.5 years +/- 7.1 SD) resistant to typical antipsychotics but CLZ responders as assessed by the Brief Psychiatric Rating Scale (BPRS) (>20% improvement). After a 1-week washout period, CLZ was started at a dose of 25 mg/d, which was increased by the third week up to a maximum of 600 mg/d (mean 365.00 +/- 129.88 mg/d SD) and remained unchanged until the end of the study (week 8). The patients showed a significant improvement in the mean scores of the rating scales for positive (SAPS) and negative symptoms of schizophrenia (Scale for the Assessment of Negative Symptoms, SANS) (P < 0.003, P < 0.02). All of the patients included in the study were BPRS responders; 65% were also SAPS and 75% SANS responders (>20% improvement). The improvement in the SANS score was significantly greater among the female patients (P < 0.05). The SAPS and SANS responders had a significantly higher mean metabolic ratio [MR = (NCLZ/CLZ)] than the nonresponders (P < 0.01), and the percentage of improvement significantly correlated with the increase in MR. This finding suggests that the individual pharmacogenetics indicated by metabolic capacity may be related to clinical response. All of the patients showed a reduction in white blood cell counts, but this was significantly less in the SANS responders than the SANS nonresponders (P = 0.047). The SAPS responders had significantly lower neutrophil counts than the nonresponders (P = 0.03). Our results seem to suggest the importance of pharmacodynamic, constitutional, and genetic data over strict pharmacokinetics in determining the clinical response to CLZ.

Genetic predisposition to neuroleptic malignant syndrome : implications for antipsychotic therapy

The pathogenetic mechanism of neuroleptic malignant syndrome (NMS), a potentially lethal adverse effect of antipsychotics, is not well understood. In addition to acquired risk factors, clinical observations suggest a number of genetic factors predisposing patients to NMS. Recent findings in pharmacogenetics indicate that the genetic polymorphisms for drug-metabolizing enzymes, drug transporters, and possibly drug-targeting molecules, are associated with the interindividual differences in drug responses concerning both efficacy and adverse reactions. Genetic association studies have sought to identify polymorphisms influencing susceptibility to NMS, especially with respect to the dopamine D(2) receptor, serotonin receptor, and cytochrome p450 2D6. While a few candidate polymorphisms were associated with NMS, a large controlled study is needed to attain statistical power. On the other hand, NMS might include heterogeneous conditions with common characteristic symptoms but different causative mechanisms. Further analysis of individuals with identified genetic mutations or polymorphisms should advance our understanding of mechanisms underlying NMS.

Pharmacogenomics of psychiatric drug treatment

It is the goal of pharmacogenomics in psychiatry to establish predictive relationships between polymorphisms of candidate genes and therapeutic response to drug treatment. Polymorphisms of candidate genes related to drug mechanisms and pathophysiology of illness and defined clinical phenotype are the foundations for pharmacogenomic studies. Pharmacogenomic studies of antipsychotic response have focused on polymorphisms of genes for dopamine and serotonin receptors with most positive results reported for polymorphisms of genes of the 5HT2a and 5HT2c serotonin receptor subtypes. Although the goal of establishing individualized medicine predicated on an individual patient's genetic code has yet to be achieved, the fundamentals are now in place for second-generation investigation and more application to health care.

Genetic predictors of therapeutic response to clozapine: current status of research

Clozapine is one of the most clinically potent drugs currently available for treating the symptoms of schizophrenia. Compared with conventional antipsychotics it surpasses its predecessors in its ability to treat a wider range of symptoms in otherwise refractory patients, while possessing a low propensity to produce extrapyramidal symptoms. Despite its significant advantages, not all patients benefit from treatment. Some patients react adversely to therapy while others fail to respond adequately. If those most likely to benefit from clozapine could be identified prior to treatment, this would significantly improve the clinical management of these patients. Genetic alterations in drug-metabolising enzymes have previously been demonstrated to influence the efficacy of clinically relevant drugs. It is possible that similar alterations in these and other systems may influence the response variability of patients to clozapine. Pharmacogenetic studies are at present investigating genes encoding drug receptors, drug-metabolising enzymes and neurotransmitter transporters to identify genetic variants that may be important. To date polymorphisms within serotonergic and dopaminergic pathways have been implicated, though the involvement of similar variants in other candidate systems is also likely. This information will ultimately enable the genetic prediction of patients most likely to benefit from the drug, and in the process would alleviate the unnecessary exposure of predisposed individuals to potentially serious adverse effects.

Discovery and utilization of haplotypes for pharmacogenetic studies of psychotropic drug response

The treatment of seriously mentally ill patients is complicated by variability in individual response to psychotropic drugs. Some patients remain treatment refractory even after two to three therapeutic modalities. Other patients experience adverse events that range from mild discomfort, to poor compliance, to life threatening. Genaissance Pharmaceuticals is actively engaged in a candidate gene-based haplotype (HAP Marker) approach to the pharmacogenetics of drug response and adverse events. In the present article, we review reasons why HAP Markers are more useful than single nucleotide polymorphisms (SNPs) for discovering genetic correlations to clinical response. In addition, we review our approach to HAP Marker discovery, which involves discovering SNPs in the functional regions of genes by sequencing, organizing these SNPs into HAP Markers for an index population of ethnically diverse individuals and calculating population frequencies for these HAP Markers. For clinical correlations, HAP Markers are defined and correlated to clinical data using the in-house DecoGen Informatics System. This approach has clear implications for the discovery of psychiatric disease-associated genes as well as for the development of safer, more efficacious psychiatric drugs.

Pharmacogenetics of bipolar disorder

To review the pharmacogenetics of bipolar disorders, the authors searched databases for genetic association and linkage studies involving response to long-term prophylactic lithium treatment, as well as treatment with antidepressants or clozapine. Significant ethnic variations in the metabolism and efficacy of antidepressants, as well as clozapine, have been reported by several groups. Systematic studies suggest that that genetic factors affect the response to prophylactic lithium treatment. Numerous associations between the three traits of interest and candidate gene polymorphisms have been proposed. Among these, an association between the serotonin transporter gene and response to serotonin reuptake inhibitors appears robust. Considerable interest has also focused on serotonergic gene polymorphisms and response to clozapine. Response to pharmacotherapy in bipolar disorders may be mediated by genetic factors, but the role played by heritability is unknown.

Psychiatric pharmacogenetics: personalizing psychostimulant therapy in attention-deficit/hyperactivity disorder

There is a substantial amount of variation in response and adverse drug reactions to psychostimulant therapy in attention-deficit/hyperactivity disorder (ADHD). Psychiatric pharmacogenetics is a rapidly developing field, which can be applied to identify genetic predictors of this variability in outcome to psychostimulant medications. This article will briefly review ADHD and its pharmacotherapy. This will be followed by an overview of the pharmacokinetics and pharmacodynamics of methylphenidate, the most commonly used psychostimulant in the US. Then the field of psychiatric pharmacogenetics will be introduced and its methodology will be described. This will be followed by a discussion about how pharmacogenetics can be applied to children afflicted with ADHD. The future of psychiatric pharmacogenetics will then be presented with an emphasis being placed on developing prospects that will ensure the continued advancement of this field.

Pharmacogenetics: the therapeutic drug monitoring of the future?

Genetic variability in drug response occurs as a result of molecular alterations at the level of drug-metabolising enzymes, drug targets/receptors, and drug transport proteins. In this paper, we discuss the possibility that therapeutic drug monitoring (TDM) in the future will involve not the mere measurement and interpretation of drug concentrations but will include both traditional TDM and pharmacogenetics-oriented TDM. In contrast to traditional TDM, which cannot be performed until after a drug is administered to the patient. pharmacogenetics-oriented TDM can be conducted even before treatment begins. Other advantages of genotyping over traditional TDM include, but are not limited to, the following: (i) it does not require the assumption of steady-state conditions (or patient compliance) for the interpretation of results; (ii) it can often be performed less invasively (with saliva, hair root or buccal swab samples); (iii) it can provide predictive value for multiple drugs [e.g. a number of cytochrome P450 (CYP) 2D6, CYP2C 19 or CYP2C9 substrates] rather than a single drug; (iv) it provides mechanistic, instead of merely descriptive, information; and (v) it is constant over an individual's lifetime (and not influenced by concurrent drug administration, alteration in hormonal levels or disease states). Pharmacogenetic information can be applied a priori for initial dose stratification and identification of cases where certain drugs are simply not effective. However, traditional TDM will still be required for all of the reasons that we use it now. In current clinical practice, pharmacogenetic testing is performed for only a few drugs (e.g. mercaptopurine, thioguanine, azathioprine, trastuzumab and tacrine) and in a limited number of teaching hospitals and specialist academic centres. We propose that other drugs (e.g. warfarin, phenytoin, codeine, oral hypoglycaemics, tricyclic antidepressants, aminoglycosides, digoxin, cyclosporin, cyclophosphamide, ifosfamide, theophylline and clozapine) are potential candidates for pharmacogenetics-oriented TDM. However, prospective studies of phaymacogenetics-oriented TDM must be performed to determine its efficacy and cost effectiveness in optimising therapeutic effects while minimising toxicity. In the future, in addition to targeting a patient's drug concentrations within a therapeutic range, pharmacists are likely to be making dosage recommendations for individual drugs on the basis of the individual patient's genotype. As we enter the era of personalised drug therapy, we will be able to identify not only the best drug to be administered to a particular patient, but also the most effective and safest dosage from the outset of therapy.

Pharmacogenetics in affective disorders

Pharmacogenetics will be of substantial help in the field of affective disorders pharmacotherapy. The possible definition of a genetic liability profile for drug side-effects and efficacy will be of great help in treatments that need weeks to months to be effective. During the last few years, a number of groups have reported possible liability genes. The efficacy and time of onset of selective serotonin reuptake inhibitors have been associated with a polymorphism in the promoter region of the transporter (SERTPR) in many independent studies, while variants at the tryptophan hydroxylase gene, 5-HT2a receptor and G-protein beta3 have been associated with them in pilot studies. Lithium long-term prophylactic efficacy has been associated with SERTPR, TPH and inositol polyphosphate 1-phosphatase variants, though in unreplicated samples. A number of further candidate genes were not associated with these treatments. In conclusion, both acute and long-term treatments appear to be, at least to some extent, under genetic influence and preliminary data have identified possible liability genes.

Association analysis for NMDA receptor subunit 2B (GRIN2B) genetic variants and psychopathology and clozapine response in schizophrenia

It is known that a syndrome resembling schizophrenia is produced by the N-methyl-d-aspartate receptor antagonists. It has also been demonstrated that the level of an ionotropic N-methyl-d-aspartate 2B subunit (GRIN2B) of the glutamate receptor tends to increase after subchronic administration of clozapine, suggesting that GRIN2B may play an active role in the pathogenesis of schizophrenia and the function of clozapine medication. We studied 100 schizophrenic patients, investigating the associations for the GRIN2B genetic variants, and psychiatric symptoms and clozapine response. No significant differences were demonstrated comparing these three groups in terms of the baseline Brief Psychiatric Rating Scale (BPRS) score (P = 0.441). The percentage of patients scoring within 20% of baseline BPRS after clozapine treatment was similar for the three genotype groups (P = 0.132). A marginally higher mean clozapine dosage was revealed, however, for patients bearing the 2664C/C genotype (P = 0.013). Although replication of this research is required to confirm the results, an association for the GRIN2B C2664T polymorphism and clozapine treatment is suggested from our findings, which may assist in the prediction of optimal dosage for schizophrenic patients.

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

Treatment-resistance to clozapine in association with ultrarapid CYP1A2 activity and the C-->A polymorphism in intron 1 of the CYP1A2 gene: effect of grapefruit juice and low-dose fluvoxamine

Antipsychotic response to clozapine varies markedly among patients with schizophrenia. The disposition of clozapine is dependent, in part, on the cytochrome P-450 (CYP) 1A2 enzyme in vivo. In theory, a very high CYP1A2 activity may lead to subtherapeutic concentrations and treatment resistance to clozapine. This prospective case study evaluates the clinical significance of ultrarapid CYP1A2 activity and a recently discovered single nucleotide (C --> A) polymorphism in intron 1 of the CYP1A2 gene (CYP1A2*F) for treatment resistance to clozapine. In addition, we describe the effect of grapefruit juice or low-dose fluvoxamine (25-50 mg/d) coadministration on clozapine and active metabolite norclozapine steady-state plasma concentration and antipsychotic response.