BDNF gene is a genetic risk factor for schizophrenia and is related to the chlorpromazine-induced extrapyramidal syndrome in the Chinese population. Pharmacogenet Genomics. 2008;18:449-457. [PMID: 18408624 DOI: 10.1097/fpc.0b013e3282f85e26]

Morphogenetic theory of mental and cognitive disorders: the role of neurotrophic and guidance molecules

Mental illness and cognitive disorders represent a serious problem for the modern society. Many studies indicate that mental disorders are polygenic and that impaired brain development may lay the ground for their manifestation. Neural tissue development is a complex and multistage process that involves a large number of distant and contact molecules. In this review, we have considered the key steps of brain morphogenesis, and the major molecule families involved in these process. The review provides many indications of the important contribution of the brain development process and correct functioning of certain genes to human mental health. To our knowledge, this comprehensive review is one of the first in this field. We suppose that this review may be useful to novice researchers and clinicians wishing to navigate the field.

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.

Effects of BDNF Val66Met Polymorphism on White Matter Microalterations of the Corpus Callosum in Patients with Panic Disorder in Korean Populations

OBJECTIVE

The brain-derived neurotrophic factor (BDNF) Val66Met (rs6265) polymorphism is suggested to be associated with the pathophysiology of anxiety disorders, including panic disorder (PD). Although the fronto-limbic white matter (WM) microstructures have been investigated, the corpus callosum (CC) has not yet been studied regarding its relationship with BDNF Val66Met polymorphism in PD.

METHODS

Ninety-five PD patients were enrolled. The Neuroticism, the Anxiety Sensitivity Inventory-Revised, Panic Disorder Severity Scale, and Beck Depression Inventory-II (BDI-II) were administered. Voxel-wise statistical analysis of diffusion tensor imaging data was performed within the CC regions using Tract-Based Spatial Statistics.

RESULTS

The GG genotype in BDNF Val66Met polymorphism has significantly higher fractional anisotropy (FA) values of the body and splenium of the CC, neuroticism and depressive symptom scale scores than the non-GG genotype in PD. The FA values of the body of the CC in the two groups were significantly different independent of age, sex, neuroticism, and BDI-II.

CONCLUSION

Our findings demonstrate that the BDNF Val66Met polymorphism is associated with WM connectivity of the body and splenium of the CC, and may be related to neuroticism and depressive symptoms in PD. Additionally, the CC connectivity according to BDNF polymorphism may play a role in the pathophysiology of PD.

BDNF Val66Met polymorphism and clinical response to antipsychotic treatment in schizophrenia and schizoaffective disorder patients: a meta-analysis

Brain-derived neurotrophic factor (BDNF) plays an important role in dopaminergic and serotonergic neurotransmission by modulating dopaminergic neuron differentiation and establishment. Multiple studies have analyzed the functional BDNF Val66Met variant in relation to antipsychotic response in schizophrenia (SCZ) patients, yielding mixed results. A meta-analysis was thus performed to examine the relationship between this variant and symptom improvement during antipsychotic treatment. Searches using PubMed, Web of Science, and PsycInfo until October 2017 yielded 11 studies that met inclusion criteria (total n = 3774). These studies investigated the BDNF Val66Met variant and antipsychotic response in patients with SCZ or schizoaffective disorder. Responders to antipsychotics were defined using the original criteria applied in each study. Effect sizes were computed using odds ratios, which were pooled according to the Mantel-Haenszel method. The BDNF Val66Met variant was not associated with the total number of responders and non-responders (p > 0.05) under dominant, recessive, or allelic models. Secondary analyses stratifying for individuals of each ethnicity and drug type also revealed no significant associations. Our findings suggest that the BDNF Val66Met variant is not associated with response to antipsychotics in individuals with SCZ. However, considering the current sample size, small effects cannot be ruled out. Moreover, recent studies have suggested that Val66Met forms haplotypes with other BDNF variants. Future studies should examine the Val66Met variant in conjunction with these other variants in relation to antipsychotic response. Moreover, since illness duration appears to influence BDNF levels in SCZ patients, future studies should aim to control for this potential confounding factor in response analyses.

Critical Issues in BDNF Val66Met Genetic Studies of Neuropsychiatric Disorders

Neurotrophins have been implicated in the pathophysiology of many neuropsychiatric diseases. Brain-derived neurotrophic factor (BDNF) is the most abundant and widely distributed neurotrophin in the brain. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a common and functional single-nucleotide polymorphism (SNP) affecting the activity-dependent release of BDNF. BDNF Val66Met transgenic mice have been generated, which may provide further insight into the functional impact of this polymorphism in the brain. Considering the important role of BDNF in brain function, more than 1,100 genetic studies have investigated this polymorphism in the past 15 years. Although these studies have reported some encouraging positive findings initially, most of the findings cannot be replicated in following studies. These inconsistencies in BDNF Val66Met genetic studies may be attributed to many factors such as age, sex, environmental factors, ethnicity, genetic model used for analysis, and gene–gene interaction, which are discussed in this review. We also discuss the results of recent studies that have reported the novel functions of this polymorphism. Because many BDNF polymorphisms and non-genetic factors have been implicated in the complex traits of neuropsychiatric diseases, the conventional genetic association-based method is limited to address these complex interactions. Future studies should apply data mining and machine learning techniques to determine the genetic role of BDNF in neuropsychiatric diseases.

Theranostic Biomarkers for Schizophrenia

Schizophrenia is a highly heritable, chronic, severe, disabling neurodevelopmental brain disorder with a heterogeneous genetic and neurobiological background, which is still poorly understood. To allow better diagnostic procedures and therapeutic strategies in schizophrenia patients, use of easy accessible biomarkers is suggested. The most frequently used biomarkers in schizophrenia are those associated with the neuroimmune and neuroendocrine system, metabolism, different neurotransmitter systems and neurotrophic factors. However, there are still no validated and reliable biomarkers in clinical use for schizophrenia. This review will address potential biomarkers in schizophrenia. It will discuss biomarkers in schizophrenia and propose the use of specific blood-based panels that will include a set of markers associated with immune processes, metabolic disorders, and neuroendocrine/neurotrophin/neurotransmitter alterations. The combination of different markers, or complex multi-marker panels, might help in the discrimination of patients with different underlying pathologies and in the better classification of the more homogenous groups. Therefore, the development of the diagnostic, prognostic and theranostic biomarkers is an urgent and an unmet need in psychiatry, with the aim of improving diagnosis, therapy monitoring, prediction of treatment outcome and focus on the personal medicine approach in order to improve the quality of life in patients with schizophrenia and decrease health costs worldwide.

BDNF Val66Met and clinical response to antipsychotic drugs: A systematic review and meta-analysis

BACKGROUND

The polymorphic brain-derived neurotrophic factor (BDNF) gene has been postulated to be involved in inter-individual variability response to antipsychotic drugs.

PURPOSE

To perform a qualitative and quantitative synthesis of studies evaluating the influence of BDNF genetic variation on clinical response to antipsychotics.

METHODS

The review protocol was published in the PROSPERO database (Reg. n(o) CRD42015024614). A comprehensive search was performed through PubMed, Web of Knowledge and Cochrane databases up to July 2015. The methodological quality of identified studies was assessed using the MINORS criteria. Publication bias was estimated and potential sources of heterogeneity were investigated via meta-regression, subgroup and sensitivity analyses.

RESULTS

Nine studies including a total of 2461 antipsychotic-treated patients fulfilled inclusion criteria for meta-analysis of BDNF Val66Met. Using the random-effects model, the pooled results showed no significant association with antipsychotic response for the dominant (Met carriers vs Val/Val, OR: 0.93, 95% CI: 0.72-1.19, P=0.55), codominant (Met/Met vs Val/Val, OR: 0.82, 95% CI: 0.59-1.15, P=0.25), recessive (Met/Met vs Val carriers, OR: 0.81, 95% CI 0.60-1.10, P=0.18) or the allelic contrast (Met vs Val, OR: 0.92, 95% CI 0.76-1.10, P=0.34). Visual inspection of funnel plots and further evaluation with Egger's test did not suggest evidence of publication bias. Despite lack of significant heterogeneity in most comparisons, no evidence of association also emerged in the subgroup and sensitivity analyses conducted.

CONCLUSION

The present meta-analysis excludes a clinically relevant effect of BDNF Val66Met on antipsychotic drug response per se. Nevertheless, further investigation is still needed to clarify in well-designed, large sample-based studies, the impact of BDNF haplotypes containing the Val66Met polymorphism.

Research in China on the molecular genetics of schizophrenia

Schizophrenia is a complex disease caused by genetic and environmental factors with a global heritability of more than 80%. By the end of the 1970s, Chinese scientists reported a heritability of schizophrenia of 82.9% in the Chinese Han population. Continuous improvements in research techniques and the recruitment of larger samples have made it possible for Chinese scientists to identify a number of candidate susceptibility genes for schizophrenia. This article reviews the results in genetic research of schizophrenia by Chinese scientists over the last five decades

Pharmacogenetics of drug response in Parkinson's disease

Parkinson's disease (PD) is a debilitating, demoralizing and financially devastating condition affecting 1% of population at the age of 60 years. Thus, very important issue to address is individual therapy optimization. Recent results have shown evidence that variable efficacy of treatment and risk of motor and mental complications could have genetic origin. Significant roles in that process play (pharmaco)genomic/genetic studies of PD. Variability in genes coding for drug-metabolizing enzymes, drug receptors and proteins involved in drug pathway signaling is an important factor determining inter-individual variability in drug responses. Interpersonal differences in drug responses are clearly documented although individualized treatment of PD is not widely known. Treatment with antiparkinsonian drugs is associated with the development of complications, such as L-DOPA-induced dyskinesia (LID), hallucinations and excessive daytime sleepiness. Carriers of specific genetic polymorphisms are particularly susceptible to development of some of these drug adverse effects. Pharmacogenomics aims to understand the relationship between genetic factors and inter-individual variations in drug responses, and to translate this information in therapy tailored to individual patient genetics. Relatively few efforts have been made to investigate the role of pharmacogenetics in the individual response to anti-PD drugs. Thus, many genetic variations and polymorphisms in myriad of different proteins can influence individual response to anti-PD drugs.

Association between the brain-derived neurotrophic factor Val66Met polymorphism and therapeutic response to olanzapine in schizophrenia patients

RATIONALE

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a major role in neurogenesis and neuroplasticity, and in the modulation of several neurotransmitter systems including the dopaminergic system. There are mixed reports about the association between the BDNF Val66Met polymorphism, schizophrenia, and treatment response to antipsychotic drugs.

OBJECTIVES

The present study evaluated the association of the BDNF Val66Met polymorphism with treatment response to atypical antipsychotic olanzapine in schizophrenia and the possible predictive value of the BDNF Val66Met genotype status in treatment response to antipsychotic medication.

METHODS

The study included 590 ethnically homogenous Caucasian patients with schizophrenia (diagnosed using the SCID), 40.2 ± 12.0 years old, treated with olanzapine monotherapy (10-20 mg/day), or with other antipsychotics such as risperidone (3-6 mg/day), clozapine (100-500 mg/day), haloperidol (3-115 mg/day), fluphenazine (4-25 mg/day), and quetiapine (50-800 mg/day). Patients were subdivided into responders and non-responders according to a 50 % reduction in the Positive and Negative Syndrome Scale (PANSS) total and subscale scores after 8 weeks of treatment.

RESULTS

The results, corrected for possible effects of gender and age, showed a significant association between the BDNF Val66Met polymorphism and treatment response to olanzapine in patients. The Val/Val genotype was observed more frequently in treatment responders to olanzapine, and this genotype was associated with an improvement in clinical symptoms.

CONCLUSIONS

Our results suggest that BDNF Val66Met variants might influence the response to 8 weeks of monotherapy with olanzapine, in a relatively large sample of patients with schizophrenia.

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.

Brain-derived neurotrophic factor as a potential biomarker of cognitive recovery in schizophrenia

Brain-derived neurotrophic factor (BDNF) has been proposed as a biomarker of schizophrenia and, more specifically, as a biomarker of cognitive recovery. Evidence collected in this review indicates that BDNF is relevant in the pathophysiology of schizophrenia and could play a role as a marker of clinical response. BDNF has been shown to play a positive role as a marker in antipsychotic treatment, and it has been demonstrated that typical antipsychotics decrease BDNF levels while atypical antipsychotics maintain or increase serum BDNF levels. Furthermore, BDNF levels have been associated with severe cognitive impairments in patients with schizophrenia. Consequently, BDNF has been proposed as a candidate target of strategies to aid the cognitive recovery process. There is some evidence suggesting that BDNF could be mediating neurobiological processes underlying cognitive recovery. Thus, serum BDNF levels seem to be involved in some synaptic plasticity and neurotransmission processes. Additionally, serum BDNF levels significantly increased in schizophrenia subjects after neuroplasticity-based cognitive training. If positive replications of those findings are published in the future then serum BDNF levels could be definitely postulated as a peripheral biomarker for the effects of intensive cognitive training or any sort of cognitive recovery in schizophrenia. All in all, the current consideration of BDNF as a biomarker of cognitive recovery in schizophrenia is promising but still premature.

Analysis of schizophrenia and hepatocellular carcinoma genetic network with corresponding modularity and pathways: novel insights to the immune system

Background

Schizophrenic patients show lower incidences of cancer, implicating schizophrenia may be a protective factor against cancer. To study the genetic correlation between the two diseases, a specific PPI network was constructed with candidate genes of both schizophrenia and hepatocellular carcinoma. The network, designated schizophrenia-hepatocellular carcinoma network (SHCN), was analysed and cliques were identified as potential functional modules or complexes. The findings were compared with information from pathway databases such as KEGG, Reactome, PID and ConsensusPathDB.

Results

The functions of mediator genes from SHCN show immune system and cell cycle regulation have important roles in the eitology mechanism of schizophrenia. For example, the over-expressing schizophrenia candidate genes, SIRPB1, SYK and LCK, are responsible for signal transduction in cytokine production; immune responses involving IL-2 and TREM-1/DAP12 pathways are relevant for the etiology mechanism of schizophrenia. Novel treatments were proposed by searching the target genes of FDA approved drugs with genes in potential protein complexes and pathways. It was found that Vitamin A, retinoid acid and a few other immune response agents modulated by RARA and LCK genes may be potential treatments for both schizophrenia and hepatocellular carcinoma.

Conclusions

This is the first study showing specific mediator genes in the SHCN which may suppress tumors. We also show that the schizophrenic protein interactions and modulation with cancer implicates the importance of immune system for etiology of schizophrenia.

Genetic variation and the risk of haloperidol-related parkinsonism in elderly patients: a candidate gene approach

Factors that influence the variation in occurrence of antipsychotic-related parkinsonism in elderly have not been well elucidated. The aim of this study was to investigate whether previous identified and studied genetic polymorphisms at DRD2, ANKK1, DRD3, HTR2A, HTR2C, RGS2, COMT, and BDNF genes are associated with antipsychotic-related parkinsonism in elderly patients.This cross-sectional study included 150 inpatients aged 65 years and older who were treated with haloperidol. Parkinsonism assessed by the Simpson Angus Scale was present in 46% of the included patients. The investigated predictors were polymorphisms in DRD2 (141CIns/Del and C957T), ANNK1 (TaqIA), DRD3 (Ser9Gly), HTR2A (-1438G>A and His452Tyr), HTR2C (Cys23Ser and -759C/T), RGS2 (+2971C>G), COMT (G158A), and BDNF (Val66Met). Frequencies of the -759 T allele of the HTR2C gene and the 158A allele of the COMT gene were significantly higher in patients without antipsychotic-induced parkinsonism (AIP) (nominal P = 0.03 and P = 0.02, respectively). -759 T allele carriership in females was associated with a lower risk of AIP (adjusted odds ratio, 0.31; 95% confidence interval, 0.11-0.85). The decrease in risk of AIP in carriers of the COMT 158A allele did not reach statistical significance. No significant associations were found between AIP and the remaining selected polymorphisms.Although validation is needed, this study suggests that carriership of the -759 T allele of the HTR2C gene in females may be protective against development of parkinsonism in elderly patients during treatment with haloperidol.

Reprint of: Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

The pharmacogenetics of symptom response to antipsychotic drugs

Antipsychotic drugs are limited in their efficacy by the relatively poor response of negative and cognitive symptoms of schizophrenia as well as by the substantial variability in response between patients. Pharmacogenetic studies have sought to identify the genetic factors that underlie the individual variability in response to treatment, with a past emphasis on dopamine and serotonin receptors as candidate genes. Few studies have separated effects on positive and negative symptoms, despite the established differences in response to drug treatment between these syndromes. Where this has been done most findings are consistent with the conclusion that dopamine receptor polymorphisms relate to positive symptom response, while negative symptom improvement is influenced by polymorphisms of genes involved in 5-HT neurotransmission. A wide range of polymorphisms in other candidate genes have been investigated, with some positive findings in those genes associated with glutamatergic transmission and/or risk factors for schizophrenia. However, there remains a lack of good replicated findings; furthermore there is little evidence to support drug-specific genetic associations with treatment response. While most past studies focused on single candidate genes, technology now permits genome-wide association studies with response to antipsychotics. Although not without major limitations, these "hypothesis-free" approaches are beginning to identify further important risk factors for treatment response. Again there is little consistency between various studies, although some of the polymorphisms identified are in genes involved in neurodevelopment, which is increasingly being recognized as important in the pathophysiology of schizophrenia.

Neurotoxic/neuroprotective activity of haloperidol, risperidone and paliperidone in neuroblastoma cells

The neurotoxicity of antipsychotic (AP) drugs seems to be linked with neurological side effects like extrapyramidal symptoms (EPS). On the other hand, neuroprotective effects can mitigate or slow the progressive degenerative structural changes in the brain leading to improved outcome of schizophrenia. First and second-generation antipsychotics may differ in their neurotoxic and neuroprotective properties. The aim of this study was to compare the neurotoxic/neuroprotective activity of haloperidol, a first-generation antipsychotic, and risperidone, a second-generation one, with paliperidone, a relatively new second-generation antipsychotic, in SK-N-SH cells. Haloperidol, risperidone and paliperidone (10, 50, 100 μM) were administered, either alone or in combination with dopamine (100 μM), to human neuroblastoma SK-N-SH. We examined the effects of the drugs on cell viability (measured by alamarBlue®), caspase-3 activity (measured by fluorimetric assay) and cell death (by measuring the externalization of phosphatidylserine). Haloperidol significantly decreased cell viability and increased caspase-3 activity and cell death. Risperidone and paliperidone did not affect cell viability or cell death. Both second-generation APs decreased caspase-3 activity, especially paliperidone. In cells treated with dopamine in combination with antipsychotics, only paliperidone (10 μM) induced a slight improvement in cell viability. While haloperidol potentiated the dopamine-induced increase in caspase-3 activity, risperidone and paliperidone reduced this effect. The results indicate that haloperidol induces apoptosis, whereas risperidone and paliperidone may afford protection against it. Of the APs tested, paliperidone always showed the strongest neuroprotective effect. The different antipsychotic effects on survival and cell death might be related to differences in their capacity to induce EPS.

The pharmacogenetics of antipsychotic treatment

There is substantial interindividual variability in the effects of treatment with antipsychotic drugs not only in the emergence of adverse effects but also in symptom response. It is becoming increasingly clear that much of this variability is due to genetic factors; pharmacogenetics is the study of those factors, with the eventual goal of identifying genetic predictors of treatment effects. There have been many reported associations of single nucleotide polymorphisms (SNPs) in candidate genes with the consequences of antipsychotic drug treatment. Thus variations in dopaminergic and serotoninergic genes may influence positive and negative symptom outcome, respectively. Among the adverse effects, tardive dyskinesia and weight gain have been the most studied, with some consistent associations of functional SNPs in genes relating to pharmacological mechanisms. Technological advance has permitted large-scale genome-wide association studies (GWAS), but as yet there are few reports that replicate prior findings with candidate genes. Nevertheless, GWAS may identify associations which provide new clues relating to underlying mechanisms.

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).

Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

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.

Pharacogenetic effects of dopamine transporter gene polymorphisms on response to chlorpromazine and clozapine and on extrapyramidal syndrome in schizophrenia

A number of studies have investigated the effectiveness of the dopamine transporter (SLC6A3) Gene as an antipsychotic target. However, the focus has mainly been on a 40-bp variable number of a tandem repeat (VNTR) in the 3'-region and results have been inconsistent. To fully evaluate SLC6A3 as a therapeutic antipshycotic target we investigated association of the gene with responses to chlorpromazine and clozapine and with chlorpromazine-induced extrapyramidal syndrome (EPS) in the Chinese schizophrenia population. Six polymorphisms across the whole region of this gene were analyzed, namely rs2652511 (T-844C) and rs2975226 (T-71A) in the 5'-regulatory region, rs2963238 (A1491C) in intron 1, a 30-bp VNTR in intron 8, rs27072 and the 40-bp VNTR in the 3'-region. We found that the polymorphic marker, rs2975226, showed significant association of allele and genotype frequencies with response to clozapine (allele-wise: adjusted p=0.00404; genotype-wise: adjusted p=0.024), and that patients with the T allele had a better response to the drug. The haplotype block constructed from the first three markers near the 5'-region showed significant association with response to clozapine (for haplotype T-T-A: p=0.0085; for haplotype C-A-C: p=0.0092). We did not identify any significant association of the six genetic variants or haplotypes with EPS after Bonferoni correction. Our findings suggest that the 5'-regulatory region of SLC6A3 plays an important role in response to clozapine and that its role in EPS needs to be replicated in a large-scale well designed study.

Acute D2 receptor blockade induces rapid, reversible remodeling in human cortical-striatal circuits

Structural remodeling has been observed in the human brain over periods of weeks to months, but the molecular mechanisms governing this process remain incompletely characterized. Using multimodal pharmaco-neuroimaging, we found that acute D2 receptor blockade induced reversible striatal volume changes and structural-functional decoupling in motor circuits within hours; these alterations predicted acute extrapyramidal motor symptoms with high precision. Our findings suggest a role for D2 receptors in short-term neural plasticity and identify a potential biomarker for neuroleptic side effects in humans.

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.

Genetic variants in the BDNF gene and therapeutic response to risperidone in schizophrenia patients: a pharmacogenetic study

Risperidone is a widely used atypical antipsychotic agent that produces considerable interindividual differences in patient response. We investigated the pharmacogenetic relationship between the brain-derived neurotrophic factor (BDNF) gene and response to risperidone in 127 Han Chinese schizophrenic patients. Three functional polymorphisms, (GT)(n) dinucleotide repeat polymorphism, C-270T, and the rs6265G/A single-nucleotide polymorphism (SNP), were genotyped and analyzed for association, with reduction of Brief Psychiatric Rating Scale (BPRS) scores following an 8-week period of risperidone monotherapy. For individual polymorphic analysis, we found that the frequency of the 230-bp allele of the (GT)(n) polymorphism was much higher in responders (47.95%) than in nonresponders (32.41%) and the difference was statistically significant even after Bonferroni's adjustment (for the 230-bp allele: adjusted P=0.039). For haplotype-based analyses of the three polymorphisms, no positive finding was observed in the global test, but in specific haplotype tests, two haplotypes were also significantly related to response to risperidone (for haplotype 230-bp/C-270/rs6265G: P=0.0009; for haplotype 234-bp/C-270/rs6265A: P=0.043), indicating that patients with the 230-bp allele of the (GT)(n) polymorphism or the 230-bp/C-270/rs6265G haplotype responded better to risperidone than those with other alleles or haplotypes, and that the positive effect of the individual haplotype 230-bp/C-270/rs6265G was mainly driven by the 230-bp allele. These findings demonstrate that the individual and combinatorial genetic variants in the BDNF gene might have a role in the therapeutic response to risperidone in the Han Chinese population.

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.