Clinical response to antipsychotic drug treatment: association study of polymorphisms in six candidate genes

Clinical Utility and Implementation of Pharmacogenomics for the Personalisation of Antipsychotic Treatments

Decades of pharmacogenetic research have revealed genetic biomarkers of clinical response to antipsychotics. Genetic variants in antipsychotic targets, dopamine and serotonin receptors in particular, and in metabolic enzymes have been associated with the efficacy and toxicity of antipsychotic treatments. However, genetic prediction of antipsychotic response based on these biomarkers is far from accurate. Despite the clinical validity of these findings, the clinical utility remains unclear. Nevertheless, genetic information on CYP metabolic enzymes responsible for the biotransformation of most commercially available antipsychotics has proven to be effective for the personalisation of clinical dosing, resulting in a reduction of induced side effects and in an increase in efficacy. However, pharmacogenetic information is rarely used in psychiatric settings as a prescription aid. Lack of studies on cost-effectiveness, absence of clinical guidelines based on pharmacogenetic biomarkers for several commonly used antipsychotics, the cost of genetic testing and the delay in results delivery hamper the implementation of pharmacogenetic interventions in clinical settings. This narrative review will comment on the existing pharmacogenetic information, the clinical utility of pharmacogenetic findings, and their current and future implementations.

Investigating the Effect of Adherence to Antipsychotic Therapy on the Length of Stay and Number of Hospitalizations in Patients with Schizophrenia - A Descriptive Analysis

Background

Optimizing long-term outcomes in schizophrenia treatment requires effective pharmacological interventions. Medication adherence is known to influence clinical outcomes, yet there is a scarcity of studies examining its correlation with factors like Length of Stay (LOS) and re-hospitalization frequency. These outcomes are crucial indicators of how medication adherence affects overall patient well-being.

Purpose

This study aims to describe the effect of medication adherence on the length of stay (LOS) and number of hospitalizations in patients with schizophrenia.

Patients and Methods

A total of 157 subjects from the West Java Psychiatric Hospital were included in this cross-sectional retrospective study. Data, including demographics, comorbidities, duration of illness, antipsychotic adherence, LOS, and the number of hospitalizations, were collected from the patients' medical records. All the data were analyzed using the Chi-Square (χ²) test with a significance level set at p < 0.05.

Results

Our findings showed that 88% of all schizophrenia inpatients were in the nonadherence group. The highest (40.7%) LOS (>30 days) was found in the non-adherence group with discontinued therapy/stopped therapy group, while the highest percentage of patients with less than five hospitalizations was identified in the obedient and regular therapy group (94.4%). In the statistical results, we observed a significant association between therapy adherence (p = 0.043) and therapy regimen (p = 0.014) with gender. Additionally, the distinction between male and female schizophrenia patients demonstrated statistical significance (p = 0.000).

Conclusion

In this study, therapy adherence and therapy regimen were found to have a significant association with gender, as well as differences between the number of male and female schizophrenia patients that were statistically significant. While other variables may exhibit clinical associations, their statistical significance has not been fully depicted. The results of this study could be preliminary study for subsequent observational studies.

Association of DRD2, DRD4 and COMT genes variants and their gene-gene interactions with antipsychotic treatment response in patients with schizophrenia

Antipsychotic drugs are the first line of treatment in schizophrenia; although antipsychotic responses indicate a wide interindividual variety in patients with schizophrenia. This study aimed to investigate the association between four polymorphisms in DRD2, DRD4 and COMT genes and their gene-gene interactions with antipsychotic treatment response in patients with schizophrenia. A total of 101 patients with schizophrenia were recruited and stratified in treatment responder and treatment resistant groups based on the published criteria of resistant to treatment using PANSS. Clinical and demographic factors were analyzed. Genomic DNA was extracted from whole blood and genotyping for the four polymorphisms were done by ARMS-PCR, PCR-RFLP and gap-PCR. Gene-gene interactions were analyzed by logistic regression. In case of DRD2 A-241G, G allele was significantly associated with resistant to treatment. Regarding DRD4 120-bp duplication, 240/240 genotype was significantly associated with resistant to treatment comparing to other genotypes in a dominant model. The genotype combination of DRD4 240/240 and COMT Val/Val was significantly associated with treatment resistant. Among DRD2 AA genotype, COMT met allele carriers which also had a 120 bp allele of DRD4 had a significantly better response to antipsychotics. Moreover, analysis of clinical and demographic factors demonstrated a significantly longer duration of hospitalization and higher chlorpromazine-equivalent daily dose in resistant to treatment patients. Discovering the polymorphisms which effect treatment response to antipsychotics will provide the possibility of genetic screening before starting an antipsychotic treatment which enhances the chance of responding to antipsychotics and decreases drugs side effects and costs.

Dopaminergic and norepinephrinergic modulation of endogenous event-related potentials: A systematic review and meta-analysis

Event-related potentials (ERPs) represent the cortical processing of sensory, motor or cognitive functions invoked by particular events or stimuli. A current theory posits that the catecholaminergic neurotransmitters dopamine (DA) and norepinephrine (NE) modulate a number of endogenous ERPs during various cognitive processes. This manuscript aims to evaluate a leading neurotransmitter hypothesis with a systematic overview and meta-analysis of pharmacologic DA and NE manipulation of specific ERPs in healthy subjects during executive function. Specifically, the frontally-distributed P3a, N2, and Ne/ERN (or error-related negativity) are supposedly modulated primarily by DA, whereas the parietally-distributed P3b is thought to be modulated by NE. Based on preceding research, we refer to this distinction between frontally-distributed DA-sensitive and parietally-distributed NE-sensitive ERP components as the Extended Neurobiological Polich (ENP) hypothesis. Our systematic review and meta-analysis indicate that this distinction is too simplistic and many factors interact with DA and NE to influence these specific ERPs. These may include genetic factors, the specific cognitive processes engaged, or elements of study design, i.e. session or sequence effects or data-analysis strategies.

The ANKK1/DRD2 gene TaqIA polymorphism (rs1800497) is associated with the severity of extrapyramidal side effects of haloperidol treatment in CYP2D6 extensive metabolizers with schizophrenia spectrum disorders

OBJECTIVES

Extrapyramidal symptoms (EPS) are one of the most prominent side effects of haloperidol. Variability of EPS severity may be associated with the genetic factors, affecting both haloperidol pharmacokinetics (e.g., CYP2D6) and pharmacodynamics (e.g., DRD2, ANKK1). We conducted a 3-week prospective study to investigate the associations of ANKK1/DRD2 TaqIA (rs1800497), DRD2 -141C Ins/Del (rs1799732) polymorphisms and CYP2D6 metabolic phenotype on the efficacy of haloperidol treatment and severity of EPS in patients with schizophrenia spectrum disorders.

METHODS

In total, 57 inpatients with schizophrenia spectrum disorders (24 (42.1%)) females; age -46.7 (11.8) years (M(SD)) of European ancestry were enrolled. BARS and SAS scales were used to assess EPS. PANSS and CGI scales - to assess the efficacy of haloperidol treatment. Genotyping was performed by real-time PCR. CYP2D6 metabolic phenotype was predicted by the CYP2D6 *3, *4, *5, *6, *9, *10, *41 and xN genotypes.

RESULTS

Minor C allele of TaqIA was associated with higher scores of BARS (p=0.029) and SAS (p=0.024) on day 21 and minor Del allele of -141C Ins/Del - with more prominent clinical improvement by CGI scale (p=0.007) but not by PANSS. These differences were observed only in extensive CYP2D6 metabolizers, although no associations with the metabolic type itself were found. General linear model showed that the combination of TaqIA genotype and metabolic type was significantly associated with BARS score on day 21 (p=0.013).

CONCLUSIONS

Our results highlight the importance of using both pharmacokinetic and pharmacodynamic genetic markers for predicting haloperidol treatment response to personalize schizophrenia spectrum disorders treatment.

The genetic influence of the DRD3 rs6280 polymorphism (Ser9Gly) on functional connectivity and gray matter volume of the hippocampus in patients with first-episode, drug-naïve schizophrenia

The D3 dopamine receptor (DRD3) plays a major role in cognitive function and is a candidate gene for schizophrenia. DRD3 is widely distributed in the hippocampus, but whether there are potential associations between the rs6280 genotype, the hippocampus, and cognitive function in first-episode, drug-naïve (FES) patients and healthy controls (HCs) is still poorly understood. First, using functional and structural magnetic resonance imaging data, we calculated the gray matter volume (GMV) and functional connectivity (FC) of the hippocampus. Then, we examined the possible interaction effect of the DRD3 genotype and the disease on the FC and GMV of the hippocampus in 52 FES patients and 51 HCs. Finally, the correlation between the FC and GMV in the hippocampus, influenced by rs6280, and the cognitive performance of subjects was analyzed. A significant interaction effect of diagnostic group by genotype of rs6280 on the GMV of the left hippocampus was found, with lower GMV in FES patients that were C carriers compared with TT homozygotes; the opposite pattern was found in the genetic subgroups of HCs. In the FES group, C carriers performed significantly worse on reasoning and problem-solving tests than TT homozygotes. The left hippocampal GMV positively correlated with reasoning and problem-solving performance in TT homozygotes, but this correlation disappeared in FES patients that were C carriers and in genetic subgroups of HCs. Together, these results suggest that FES patients that are C carriers of rs6280 have lower GMV in the hippocampus, resulting in greater cognitive impairment.

Effects of Glycogen Synthase Kinase-3 Beta Gene Polymorphisms on the Plasma Concentration of Aripiprazole in Chinese Patients with Schizophrenia: A Preliminary Study

This study explored the differences in glycogen synthase kinase-3 beta (GSK3β) gene polymorphisms between patients with schizophrenia and healthy controls and investigated the association between gene polymorphisms and plasma concentration of aripiprazole. We enrolled 127 patients with schizophrenia and 125 healthy controls from southern Fujian. The genotypes of the rs6438552, rs12630592, and rs3732361 loci of GSK3β were evaluated by sequencing with amplified polymerase chain reaction, and the plasma concentration of aripiprazole was determined by high-performance liquid chromatography-tandem mass spectrometry. All three loci of GSK3β had three genotypes each. The genotype distribution in each locus was not significantly different, but there was a significant difference in the allele frequency between the schizophrenia and control groups within each locus. Linkage disequilibrium analyses of the three single-nucleotide polymorphisms (SNPs) revealed strong linkage. The haplotype analysis results showed two haplotypes in the three SNPs of GSK3β. The plasma concentrations, dose-corrected concentrations, and normalized concentrations of aripiprazole were significantly different among the different genotypes of the three SNPs. In conclusion, the rs6438552, rs12630592, and rs3732361 loci of GSK3β may be involved in schizophrenia, and GSK3β gene polymorphism may be correlated with the plasma concentration of aripiprazole.

Pharmacogenetics and Schizophrenia-Can Genomics Improve the Treatment with Second-Generation Antipsychotics?

Schizophrenia (SCZ) is a complex psychiatric disorder of multifactorial origin, in which both genetic and environmental factors have an impact on its onset, course, and outcome. Large variability in response and tolerability of medication among individuals makes it difficult to predict the efficacy of a chosen therapeutic method and create universal and precise guidelines for treatment. Pharmacogenetic research allows for the identification of genetic polymorphisms associated with response to a chosen antipsychotic, thus allowing for a more effective and personal approach to treatment. This review focuses on three frequently prescribed second-generation antipsychotics (SGAs), risperidone, olanzapine, and aripiprazole, and aims to analyze the current state and future perspectives in research dedicated to identifying genetic factors associated with antipsychotic response. Multiple alleles of genes involved in pharmacokinetics (particularly isoenzymes of cytochrome P450), as well as variants of genes involved in dopamine, serotonin, and glutamate neurotransmission, have already been identified as ones of significant impact on antipsychotic response. It must, however, be noted that although currently obtained results are promising, trials with bigger study groups and unified protocols are crucial for standardizing methods and determining objective antipsychotic response status.

Toward Predicting Impact of Common Genetic Variants on Schizophrenia Clinical Responses With Antipsychotics: A Quantitative System Pharmacology Study

CNS disorders are lagging behind other indications in implementing genotype-dependent treatment algorithms for personalized medicine. This report uses a biophysically realistic computer model of an associative and dorsal motor cortico-striatal-thalamo-cortical loop and a working memory cortical model to investigate the pharmacodynamic effects of COMTVal158Met rs4680, 5-HTTLPR rs 25531 s/L and D2DRTaq1A1 genotypes on the clinical response of 7 antipsychotics. The effect of the genotypes on dopamine and serotonin dynamics and the level of target exposure for the drugs was calibrated from PET displacement studies. The simulations suggest strong gene-gene pharmacodynamic interactions unique to each antipsychotic. For PANSS Total, the D2DRTaq1 allele has the biggest impact, followed by the 5-HTTLPR rs25531. The A2A2 genotype improved efficacy for all drugs, with a more complex outcome for the 5-HTTLPR rs25531 genotype. Maximal range in PANSS Total for all 27 individual combinations is 3 (aripiprazole) to 5 points (clozapine). The 5-HTTLPR L/L with aripiprazole and risperidone and the D2DRTaq1A2A2 allele with haloperidol, clozapine and quetiapine reduce the motor side-effects with opposite effects for the s/s genotype. The COMT genotype has a limited effect on antipsychotic effect and EPS. For cognition, the COMT MM 5-HTTLPR L/L genotype combination has the best performance for all antipsychotics, except clozapine. Maximal difference is 25% of the total dynamic range in a 2-back working memory task. Aripiprazole is the medication that is best suited for the largest number of genotype combinations (10) followed by Clozapine and risperidone (6), haloperidol and olanzapine (3) and quetiapine and paliperidone for one genotype. In principle, the platform could identify the best antipsychotic treatment balancing efficacy and side-effects for a specific individual genotype. Once the predictions of this platform are validated in a clinical setting the platform has potential to support rational personalized treatment guidance in clinical practice.

The pharmacogenetics of treatment with olanzapine

Genetic polymorphism in olanzapine-metabolizing enzymes, transporters and drug targets is associated with alterations in safety and efficacy. The aim of this systematic review is to describe all clinically relevant pharmacogenetic information on olanzapine and to propose clinically actionable variants. Two hundred and eighty-four studies were screened; 76 complied with the inclusion criteria and presented significant associations. DRD2 Taq1A (rs1800497) *A1, LEP -2548 (rs7799039) G and CYP1A2*1F alleles were related to olanzapine effectiveness and safety variability in several studies, with a high level of evidence. DRD2 -141 (rs1799732) Ins, A-241G (rs1799978) G, DRD3 Ser9Gly (rs6280) Gly, HTR2A rs7997012 A, ABCB1 C3435T (rs1045642) T and G2677T/A (rs2032582) T and UGT1A4*3 alleles were related to safety, effectiveness and/or pharmacokinetic variability with moderated level of evidence.

Meta-Analysis of Brain Gene Expression Data from Mouse Model Studies of Maternal Immune Activation Using Poly(I:C)

Maternal immune activation (MIA) is a known risk factor for schizophrenia (SCZ) and autism spectrum disorder (ASD) and is often modelled in animal studies in order to study the effect of prenatal infection on brain function including behaviour and gene expression. Although the effect of MIA on gene expression are highly heterogeneous, combining data from multiple gene expression studies in a robust method may shed light on the true underlying biological effects caused by MIA and this could inform studies of SCZ and ASD. This study combined four RNA-seq and microarray datasets in an overlap analysis and ranked meta-analysis in order to investigate genes, pathways and cell types dysregulated in the MIA mouse models. Genes linked to SCZ and ASD and crucial in neurodevelopmental processes including neural tube folding, regulation of cellular stress and neuronal/glial cell differentiation were among the most consistently dysregulated in these ranked analyses. Gene ontologies including K+ ion channel function, neuron and glial cell differentiation, synaptic structure, axonal outgrowth, cilia function and lipid metabolism were also strongly implicated. Single-cell analysis identified excitatory and inhibitory cell types in the cortex, hippocampus and striatum that may be affected by MIA and are also enriched for genes associated with SCZ, ASD and cognitive phenotypes. This points to the cellular location of molecular mechanisms that may be consistent between the MIA model and neurodevelopmental disease, improving our understanding of its utility to study prenatal infection as an environmental stressor.

Association of the genetic polymorphisms of metabolizing enzymes, transporters, target receptors and their interactions with treatment response to olanzapine in chinese han schizophrenia patients

Olanzapine is an atypical antipsychotic drug that has been increasingly used for treatment in schizophrenia. It has been observed that olanzapine responses in schizophrenia patients vary individually, but the reason has not been elucidated. In the study, we aimed to comprehensively explore the relationships between olanzapine responses and genetic polymorphisms of drug metabolizing enzymes, transporters and target receptors, and so as to interpret the reason of good and poor responses of olanzapine. A total of 241 Chinese Han paranoid schizophrenia who treated with olanzapine alone for 4 weeks were recruited. The positive and negative symptom scale (PANSS) was used to evaluate the efficacy of olanzapine. The genetic polymorphisms were detected by improved multiple ligase detection reaction (iMLDR). Multivariate logistic regression analysis suggested that the genetic polymorphisms of CYP1A2 rs762551, UGT1A4 rs2011425, ABCB1 rs1045642, DRD2 rs1799732 and rs1799978, 5-HTR2A rs6311 were significantly associated with olanzapine response. Multifactor dimensionality reduction (MDR) analysis showed that there was a negative interaction between CYP1A2 rs762551, ABCB1 rs1045642, DRD2 rs1799978, 5-HTR2A rs6311 and the interaction model was the optimal model. Our findings could partially explain the different olanzapine outcome and provided evidence for clarifying the predictive indicators of olanzapine response in further.

The polymorphic variants DRD2 rs1800497 and ABCB1 3435C>T are associated with antipsychotic safety parameters in adolescents with an acute psychotic episode: the results of a pilot study

Children and adolescents are more likely than adults to experience adverse side effects when taking antipsychotics. Pharmacogenetic testing allows one to more accurately choose the initial dose of a drug. The genes of pharmacokinetic factors have been shown to be of high prognostic value for the safety of antipsychotics in adults.

Patients and methods. The study enrolled 36 adolescents (58.3% male) (mean age, 14.83±1.84 years). All the patients took an antipsychotic. The follow-up lasted 28 days. On 14 and 28 days of treatment, its efficiency and safety were evaluated using the Children's Global Assessment Scale (CGAS), the Positive and Negative Syndrome Scale (PANSS), the Udvalg for Kliniske Undersњgelser Side Effects Rating Scale (UKU-SERS), the Simpson-Angus Scale (SAS), and the Barnes Akathisia Rating Scale (BARS). The patients were genotyped for CYP3A4*22, CYP3A5*3, CYP2D6*4, *9, *10, ABCB1 1236C>T, 2677G>T/A, 3435C>T, DRD2 rs1800497, DRD4 rs1800955, and HTR2A rs6313.

Results and discussion. The decrease in the mean score of the PANSS subscale “Productive symptoms” was more pronounced in carriers of the DRD2 rs1800497 polymorphic variant (-6.5 [-10.25; -3.75] vs -3 [-6.5; -2 ] on 14 day (p=0.028) and (-11 [-13; -9.5] vs -5 [-9; -3.5] on 28 day (p=0.001) compared to baseline. The carriage of ABCB1 3435CT+TT was associated with worse tolerance to pharmacotherapy on 14 day (the total score of the UKU-SERS M, 8 [3; 11.75] vs M, 2 [1; 6]; p=0.034). The carriers of DRD2 rs1800497 reported a greater severity of antipsychotic-induced neurological disorders (UKU-SERS subscale score M, 1 [0; 2.25] vs M 0 [0; 1]; p=0.029).

Conclusion. The polymorphic variants DRD2 rs1800497 and ABCB1 3435C>T were established to be significantly associated with the efficacy and safety of antipsychotics in adolescents with an acute psychotic episode.

Gene expression and response prediction to amisulpride in the OPTiMiSE first episode psychoses

A fundamental shortcoming in the current treatment of schizophrenia is the lack of valid criteria to predict who will respond to antipsychotic treatment. The identification of blood-based biological markers of the therapeutic response would enable clinicians to identify the subgroup of patients in whom conventional antipsychotic treatment is ineffective and offer alternative treatments. As part of the Optimisation of Treatment and Management of Schizophrenia in Europe (OPTiMiSE) programme, we conducted an RNA-Seq analysis on 188 subjects with first episode psychosis, all of whom were subsequently treated with amisulpride for 4 weeks. We compared gene expression on total RNA from patients' blood before and after treatment and identified 32 genes for which the expression changed after treatment in good responders only. These findings were replicated in an independent sample of 24 patients with first episode psychosis. Six genes showed a significant difference in expression level between good and poor responders before starting treatment, allowing to predict treatment outcome with a predictive value of 93.8% when combined with clinical features. Collectively, these findings identified new mechanisms to explain symptom improvement after amisulpride medication and highlight the potential of combining gene expression profiling with clinical data to predict treatment response in first episode psychoses.

Pharmacogenetics of antipsychotics in adolescents with acute psychotic episode during first 14 days after admission: effectiveness and safety evaluation

Objectives Prediction of the antipsychotic's effectiveness is a relevant topic in the field of personalized medicine. Methods The research design of this study is a prospective observation with posthoc analysis of associations of genetic polymorphisms with safety parameters and effectiveness of antipsychotic therapy. We observed 53 adolescents with an acute psychotic episode which were prescribed antipsychotics for 14 days. We evaluated the effectiveness of antipsychotics with the Positive and Negative Symptoms Scale and the safety with the UKU Side Effects Rating Scale, Simpson-Angus Scale, and Barnes Akathisia rating scale. We genotyped CYP3A4*22 (rs2740574), CYP3A5*3 (6986A>G, rs7767746), CYP2D6*4, *9, *10 (rs3892097, rs1065852), ABCB1 1236C>T (rs1128503), 2677G>T/A (rs2032582), 3435C>T (rs1045642), DRD2 (rs1800497), DRD4 (rs1800955), HTR2A (rs6313) by the real-time polymerase chain reaction method. Results We found significantly more frequent "increased dream activity" between CYP2D6 intermediate metabolizers and normal metabolizers (54 vs. 22%; p=0.043). The «increased duration of sleep» was more often observed in homozygotes TT of ABCB1 2677G>T/A (50 vs. 15.8%, p=0.006) and TT of 3435C>T (41.7 vs. 8.2%, p=0.007). Conclusions We found that CYP2D6 and ABCB1 polymorphisms were associated with the safety of antipsychotics in adolescents with an acute psychotic episode.

Catechol-O-methyltransferase rs4680 and rs4818 haplotype association with treatment response to olanzapine in patients with schizophrenia

Antipsychotic drugs target primarily dopaminergic system which makes catechol-O-methyltransferase (COMT) an interesting target in studies searching for treatment response predictors in schizophrenia. The study assessed the association of the COMT rs4680 and rs4818 polymorphisms with therapeutic response to olanzapine, risperidone, clozapine or other antipsychotic medication after 8 weeks of monotherapy in patients with schizophrenia. 521 Caucasian patients with schizophrenia received a monotherapy with olanzapine (10–20 mg/day; N = 190), risperidone (3–6 mg/day; N = 99), or clozapine (100–500 mg/day; N = 102). The fourth group (N = 130) consisted of patients receiving haloperidol (3–15 mg/day), fluphenazine (4–25 mg/day) or quetiapine (50–800 mg/day). Treatment response was defined as a 50% reduction from the baseline positive and negative syndrome scale (PANSS) total and subscale scores, but also as an observed percentage reduction from the initial PANSS_0–6 total and subscale scores. Carriers of the COMT rs4680 A allele and carriers of the COMT rs4680–rs4818 C-A haplotype block had greater reduction in the PANSS total scores following olanzapine treatment, compared to carriers of the COMT rs4680 GG genotype and other COMT rs4680–rs4818 haplotypes. The COMT rs4680 A allele, and COMT rs4680–rs4818 C-A haplotype, were significantly associated with therapeutic response in patients treated with olanzapine, but not in patients treated with other antipsychotics.

Polygenic risk score for schizophrenia was not associated with glycemic level (HbA1c) in patients with non-affective psychosis: Genetic Risk and Outcome of Psychosis (GROUP) cohort study

INTRODUCTION

Type 2 diabetes (T2D) is a common comorbidity in patients with schizophrenia (SCZ). The underlying pathophysiologic mechanisms are yet to be fully elucidated, although it can be argued that shared genes, environmental factors or their interaction effect are involved. This study investigated the association between polygenic risk score of SCZ (PRS_SCZ) and glycated haemoglobin (HbA1c) while adjusting for polygenic risk score of T2D (PRS_T2D), and clinical and demographic covariables.

METHODS

Genotype, clinical and demographic data of 1129 patients with non-affective psychosis were extracted from Genetic Risk and Outcome of Psychosis (GROUP) cohort study. The glycated haemoglobin (HbA1c) was the outcome. PRS was calculated using standard methods. Univariable and multivariable linear regression analyses were applied to estimate associations. Additionally, sensitivity analysis based on multiple imputation was done. After correction for multiple testing, a two-sided p-value ≤.003 was considered to discover evidence for an association.

RESULTS

Of 1129 patients, 75.8% were male with median age of 29 years. The mean (standard deviation) HbA1c level was 35.1 (5.9) mmol/mol. There was no evidence for an association between high HbA1c level and increased PRS_SCZ (adjusted regression coefficient (aβ) = 0.69, standard error (SE) = 0.77, p-value = .37). On the other hand, there was evidence for an association between high HbA1c level and increased PRS_T2D (aβ = 0.93, SE = 0.32, p-value = .004), body mass index (aβ = 0.20, SE = 0.08, p-value = .01), diastolic blood pressure (aβ = 0.08, SE = 0.04, p-value = .03), late age of first psychosis onset (aβ = 0.19, SE = 0.05, p-value = .0004) and male gender (aβ = 1.58, SE = 0.81, p-value = .05). After multiple testing correction, there was evidence for an association between high HbA1c level and late age of first psychosis onset. Evidence for interaction effect between PRS_scz and antipsychotics was not observed. The multiple imputation-based sensitivity analysis provided consistent results with complete case analysis.

CONCLUSIONS

Glycemic dysregulation in patients with SCZ was not associated with PRS_SCZ. This suggests that the mechanisms of hyperglycemia or diabetes are at least partly independent from genetic predisposition to SCZ. Our findings show that the change in HbA1c level can be caused by at least in part due to PRS_T2D, late age of illness onset, male gender, and increased body mass index and diastolic blood pressure.

Association of Serotonin2c Receptor Polymorphisms With Antipsychotic Drug Response in Schizophrenia

There is conflicting evidence for the association between genetic polymorphisms in the serotonin (5-HT)_2C receptor (HTR2C) and response to antipsychotic drugs (APD) in schizophrenic patients. We tested the association between the HTR2C polymorphisms, Cys23Ser, -759C/T, and -697G/C, and response to APDs (mainly clozapine) in a 6 month prospective study in 171 patients with schizophrenia. Ser23 was significantly associated with treatment response (positive symptoms, X ² = 7.540, p = 0.01; negative symptoms, X ² = 4.796, p = 0.03) in male patients only. A -759C-Ser23 haplotype was similar associated with positive (X ² = 6.648, p = 0.01) and negative (X ² = 6.702, p = 0.01) symptom improvement. Logistic regression, after controlling for covariates, also showed significant haplotypic associations. A meta-analysis of six studies for Ser23 and treatment response showed an overall odds ratio of 2.00 (95%CI, 1.38-2.91, p = 0.0003) or 1.94 (95%CI, 1.27-2.99, p = 0.0024) under fixed or random effect models. These results provide additional evidence that HTR2C polymorphisms are associated with treatment response to APD with HTR2C antagonism or inverse agonism, in male schizophrenic patients.

Pharmacogenetics in Psychiatry

Mental illness represents a major health issue both at the individual and at the socioeconomical level. This is partly due to the current suboptimal treatment options: existing psychotropic medications, including antidepressants, antipsychotics, and mood stabilizers, are effective only in a subset of patients or produce partial response and they are often associated with debilitating side effects that discourage adherence. Pharmacogenetics is the study of how genetic information impacts on drug response/side effects with the goal to provide tailored treatments, thereby maximizing efficacy and tolerability. The first pharmacogenetic studies focused on candidate genes, previously known to be relevant to the pharmacokinetics and pharmacodynamics of psychotropic drugs. Results were mainly inconclusive, but some replicated candidates were identified and included as pharmacogenetic biomarkers in drug labeling and in some commercial kits. With the advent of the genomic revolution, it became possible to study the genetic variation on an unprecedented scale, throughout the whole genome with no need of a priori hypothesis. This may lead to the personalized prescription of existing medications and potentially to the development of innovative ones, thanks to new insights into the genetics of mental illness. Promising findings were obtained, but methods for the generation and analysis of genome-wide and sequencing data are still in evolution. Future pharmacogenetic tests may consist of hundreds/thousands of polymorphisms throughout the genome or selected pathways in order to take into account the complex interactions across variants in a number of genes.

DNA methylation and antipsychotic treatment mechanisms in schizophrenia: Progress and future directions

Antipsychotic response in schizophrenia is a complex, multifactorial trait influenced by pharmacogenetic factors. With genetic studies thus far providing little biological insight or clinical utility, the field of pharmacoepigenomics has emerged to tackle the so-called "missing heritability" of drug response in disease. Research on psychiatric disorders has only recently started to assess the link between epigenetic alterations and treatment outcomes. DNA methylation, the best characterised epigenetic mechanism to date, is discussed here in the context of schizophrenia and antipsychotic treatment outcomes. The majority of published studies have assessed the influence of antipsychotics on methylation levels in specific neurotransmitter-associated candidate genes or at the genome-wide level. While these studies illustrate the epigenetic modifications associated with antipsychotics, very few have assessed clinical outcomes and the potential of differential DNA methylation profiles as predictors of antipsychotic response. Results from other psychiatric disorder studies, such as depression and bipolar disorder, provide insight into what may be achieved by schizophrenia pharmacoepigenomics. Other aspects that should be addressed in future research include methodological challenges, such as tissue specificity, and the influence of genetic variation on differential methylation patterns.

Association study between COMT, DRD2, and DRD3 gene variants and antipsychotic treatment response in Mexican patients with schizophrenia

PURPOSE

The efficacy of schizophrenia treatments using antipsychotics (APs) has long been established, but the benefit obtained by several patients using conventional APs (typical or atypical) has not been enough. Currently, the genetic study of the primary mechanisms of action of the APs has been focused on the dopaminergic pathways. The objective of this study was to determine if the response phenotypes (responder, resistance to treatment, and ultra-resistance to treatment groups) are associated with six single-nucleotide polymorphisms: COMT (Val158Met), DRD2 (A-241G, C376G, C939T, Taq1A), and DRD3 (Ser9Gly).

PATIENTS AND METHODS

We classified the patients through a retrospective/prospective methodology to define response phenotypes.

RESULTS

COMT/Val158Met and DRD3/Ser9Gly were associated with the responder group (P<0.05). The single-nucleotide polymorphism A-241G of DRD2 gene was related with the resistant-to-treatment group (P<0.001). Finally, Met/Met of COMT and Ser/Gly of DRD3 genes showed a predictive effect associated with the resistant-to-treatment phenotype.

CONCLUSION

Further analyses should be performed to validate these genetic markers as mediators for the response to APs.

Genetic Basis of Positive and Negative Symptom Domains in Schizophrenia

Schizophrenia is a highly heritable disorder, the genetic etiology of which has been well established. Yet despite significant advances in genetics research, the pathophysiological mechanisms of this disorder largely remain unknown. This gap has been attributed to the complexity of the polygenic disorder, which has a heterogeneous clinical profile. Examining the genetic basis of schizophrenia subphenotypes, such as those based on particular symptoms, is thus a useful strategy for decoding the underlying mechanisms. This review of literature examines the recent advances (from 2011) in genetic exploration of positive and negative symptoms in schizophrenia. We searched electronic databases PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature using key words schizophrenia, symptoms, positive symptoms, negative symptoms, cognition, genetics, genes, genetic predisposition, and genotype in various combinations. We identified 115 articles, which are included in the review. Evidence from these studies, most of which are genetic association studies, identifies shared and unique gene associations for the symptom domains. Genes associated with neurotransmitter systems and neuronal development/maintenance primarily constitute the shared associations. Needed are studies that examine the genetic basis of specific symptoms within the broader domains in addition to functional mechanisms. Such investigations are critical to developing precision treatment and care for individuals afflicted with schizophrenia.

Classics in Chemical Neuroscience: Aripiprazole

Aripiprazole was the first antipsychotic developed to possess agonist properties at dopamine D₂ autoreceptors, a groundbreaking strategy that presented a new vista for schizophrenia drug discovery. The dopamine D₂ receptor is the crucial target of all extant antipsychotics, and all developed prior to aripiprazole were D₂ receptor antagonists. Extensive blockade of these receptors, however, typically produces extrapyramidal (movement) side effects, which plagued first-generation antipsychotics, such as haloperidol. Second-generation antipsychotics, such as clozapine, with unique polypharmacology and D₂ receptor binding kinetics, have significantly lower risk of movement side effects but can cause myriad additional ones, such as severe weight gain and metabolic dysfunction. Aripiprazole's polypharmacology, characterized by its unique agonist activity at dopamine D₂ and D₃ and serotonin 5-HT_1A receptors, as well as antagonist activity at serotonin 5-HT_2A receptors, translates to successful reduction of positive, negative, and cognitive symptoms of schizophrenia, while also mitigating risk of weight gain and movement side effects. New observations, however, link aripiprazole to compulsive behaviors in a small group of patients, an unusual side effect for antipsychotics. In this review, we discuss the chemical synthesis, pharmacology, pharmacogenomics, drug metabolism, and adverse events of aripiprazole, and we present a current understanding of aripiprazole's neurotherapeutic mechanisms, as well as the history and importance of aripiprazole to neuroscience.

The DRD3 Ser9Gly Polymorphism Predicted Metabolic Change in Drug-Naive Patients With Bipolar II Disorder

Patients with bipolar II disorder (BDII) have a higher prevalence rate of metabolic disturbance. Whether BDII itself, in addition to its current standard treatment, is a risk factor for metabolic syndrome warrants additional study. The dopamine receptor D3 (DRD3) gene, one of the candidate genes for BDII, is also involved in the dopaminergic system. We investigated whether it is related to changes in the metabolic indices of patients with BDII given 12 weeks of standard treatment.Patients with a first diagnosis of BDII (n = 117) were recruited. Metabolic profiles (cholesterol, triglycerides, fasting serum glucose, body mass index) were measured at baseline and at 2, 8, and 12 weeks. The genotype of the DRD3 Ser9Gly polymorphism (rs6280) was determined. Multiple linear regressions with generalized estimating equation methods were used.Seventy-six (65.0%) patients completed the 12-week intervention. Significant differences in triglyceride change were associated with the DRD3 Ser9Gly genotype (P = 0.03). Patients with the Ser/Ser genotype had significantly smaller triglyceride increases and a lower risk of developing metabolic syndrome than did those with the Ser/Gly+Gly/Gly genotype. However, the associations between the DRD3 Ser9Gly polymorphism with changes in triglyceride level become nonsignificant after correcting for multiple comparisons.We conclude that the DRD3 Ser9Gly polymorphism is nominally associated with changes in triglycerides and metabolic syndrome after 12 weeks of standard BDII treatment.

Catechol-O-Methyltransferase Val158Met Polymorphism and Clinical Response to Antipsychotic Treatment in Schizophrenia and Schizo-Affective Disorder Patients: a Meta-Analysis

BACKGROUND

The catechol-O-methyltransferase (COMT) enzyme plays a crucial role in dopamine degradation, and the COMT Val158Met polymorphism (rs4680) is associated with significant differences in enzymatic activity and consequently dopamine concentrations in the prefrontal cortex. Multiple studies have analyzed the COMT Val158Met variant in relation to antipsychotic response. Here, we conducted a meta-analysis examining the relationship between COMT Val158Met and antipsychotic response.

METHODS

Searches using PubMed, Web of Science, and PsycInfo databases (03/01/2015) yielded 23 studies investigating COMT Val158Met variation and antipsychotic response in schizophrenia and schizo-affective disorder. Responders/nonresponders were defined using each study's original criteria. If no binary response definition was used, authors were asked to define response according to at least 30% Positive and Negative Syndrome Scale score reduction (or equivalent in other scales). Analysis was conducted under a fixed-effects model.

RESULTS

Ten studies met inclusion criteria for the meta-analysis. Five additional antipsychotic-treated samples were analyzed for Val158Met and response and included in the meta-analysis (ntotal=1416). Met/Met individuals were significantly more likely to respond than Val-carriers (P=.039, ORMet/Met=1.37, 95% CI: 1.02-1.85). Met/Met patients also experienced significantly greater improvement in positive symptoms relative to Val-carriers (P=.030, SMD=0.24, 95% CI: 0.024-0.46). Posthoc analyses on patients treated with atypical antipsychotics (n=1207) showed that Met/Met patients were significantly more likely to respond relative to Val-carriers (P=.0098, ORMet/Met=1.54, 95% CI: 1.11-2.14), while no difference was observed for typical-antipsychotic-treated patients (n=155) (P=.65).

CONCLUSIONS

Our findings suggest that the COMT Val158Met polymorphism is associated with response to antipsychotics in schizophrenia and schizo-affective disorder patients. This effect may be more pronounced for atypical antipsychotics.

Pharmacological targeting of dopamine D3 receptors: Possible clinical applications of selective drugs

Dopamine D3 receptors have been pharmacologically engaged in humans since the development of the first antipsychotics and ergot-derivative dopamine (DA) agonists, even without knowing it. These agents were generally non-selective, developed primarily to target D2 receptors. In the last 10 years the understanding of the clinical implication of D3 receptors has been progressing also due to the identification of D3 gene polymorphisms, the use of more selective PET ligands such as [(11)C]-(+)-PHNO and the learning regarding the clinical use of the D3-preferential D2/D3 agonists ropinirole and pramipexole. A new specific neuroplasticity role of D3 receptor regarding dendrite arborisation outgrowth in dopaminergic neurons was also proposed to support, at least in part, the slowing of disease observed in subjects with Parkinson׳s Disease treated with DA agonists. Similar mechanisms could be at the basis of the antidepressant-like effects observed with DA agonists when co-administered with standard of care. Severe adverse event occurring with the use of anti-parkinsonian DA agonists in predisposed subjects, i.e., impulse control disorders, are now suggested to be putatively related to overactive D3 receptors. Not surprisingly, blockade of D3 receptors was proposed as treatment for addictive disorders, a goal that could be potentially achieved by repositioning buspirone, an anxiolytic drug with D3-preferential antagonistic features, or with novel selective D3 antagonists or partial agonists currently in development for schizophrenia. At the moment ABT-925 is the only selective D3 antagonist tested in schizophrenic patients in Phase II, showing an intriguing cognitive enhancing effects supported by preclinical data. Finally, exploratory pharmacogenetic analysis suggested that ABT-925 could be effective in a subpopulation of patients with a polymorphism on the D3 receptor, opening to a possible personalised medicine approach.

Association studies of genomic variants with treatment response to risperidone, clozapine, quetiapine and chlorpromazine in the Chinese Han population

Schizophrenia is a widespread mental disease with a prevalence of about 1% in the world population. Continuous long-term treatment is required to maintain social functioning and prevent symptom relapse of schizophrenia patients. However, there are considerable individual differences in response to the antipsychotic drugs. There is a pressing need to identify more drug-response-related markers. But most pharmacogenomics of schizophrenia have typically focused on a few candidate genes in small sample size. In this study, 995 subjects were selected for discovering the drug-response-related markers. A total of 77 single-nucleotide polymorphisms of 25 genes have been investigated for four commonly used antipsychotic drugs in China: risperidone, clozapine, quetiapine, and chlorpromazine. Significant associations with treatment response for several genes, such as CYP2D6, CYP2C19, COMT, ABCB1, DRD3 and HTR2C have been verified in our study. Also, we found several new candidate genes (TNIK, RELN, NOTCH4 and SLC6A2) and combinations (haplotype rs1544325-rs5993883-rs6269-rs4818 in COMT) that are associated with treatment response to the four drugs. Also, multivariate interactions analysis demonstrated the combination of rs6269 in COMT and rs3813929 in HTR2C may work as a predictor to improve the clinical antipsychotic response. So our study is of great significance to improve current knowledge on the pharmacogenomics of schizophrenia, thus promoting the implementation of personalized medicine in schizophrenia.The Pharmacogenomics Journal advance online publication, 18 August 2015; doi:10.1038/tpj.2015.61.

Pharmacogenetics of second-generation antipsychotics

This review considers pharmacogenetics of the so called 'second-generation' antipsychotics. Findings for polymorphisms replicating in more than one study are emphasized and compared and contrasted with larger-scale candidate gene studies and genome-wide association study analyses. Variants in three types of genes are discussed: pharmacokinetic genes associated with drug metabolism and disposition, pharmacodynamic genes encoding drug targets, and pharmacotypic genes impacting disease presentation and subtype. Among pharmacokinetic markers, CYP2D6 metabolizer phenotype has clear clinical significance, as it impacts dosing considerations for aripiprazole, iloperidone and risperidone, and variants of the ABCB1 gene hold promise as biomarkers for dosing for olanzapine and clozapine. Among pharmacodynamic variants, the TaqIA1 allele of the DRD2 gene, the DRD3 (Ser9Gly) polymorphism, and the HTR2C -759C/T polymorphism have emerged as potential biomarkers for response and/or side effects. However, large-scale candidate gene studies and genome-wide association studies indicate that pharmacotypic genes may ultimately prove to be the richest source of biomarkers for response and side effect profiles for second-generation antipsychotics.

Significant association between DRD3 gene body methylation and schizophrenia

The current study was the first one to reveal the contribution of DRD3 methylation to the risk of different (SCZ) subtypes. This study comprised a total of 30 paranoid (15 males and 15 females) and 29 undifferentiated (15 males and 14 females) SCZ patients and 26 age- and gender-matched controls. Our results showed a significant association of CpG2 with SCZ. A breakdown analysis by gender showed that CpG2 and CpG3 methylation were significantly higher in male patients than male controls, and that CpG5 methylation was significantly higher in female patients than female controls. A further breakdown analysis by both gender and SCZ subtype showed that CpG2 and CpG3 methylation were significantly higher in male paranoid SCZ and male undifferentiated SCZ than male controls. In contrast, CpG2 and CpG3 methylation were significantly lower in female undifferentiated SCZ than female controls. Additionally, CpG5 methylation was significantly higher in female paranoid SCZ than female controls. In conclusion, our findings supported that DRD3 gene body hypermethylation was significantly associated with the risk of SCZ. Future study is needed to clarify the mechanisms by which DRD3 gene body hypermethylation contributes to the risk of SCZ.

Meta-analyses of blood homocysteine levels for gender and genetic association studies of the MTHFR C677T polymorphism in schizophrenia

Previous studies suggest that elevated blood homocysteine levels and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism are risk factors for schizophrenia. However, the effects of gender and MTHFR C677T genotypes on blood homocysteine levels in schizophrenia have not been consistent. We first investigated whether plasma total homocysteine levels were higher in patients with schizophrenia than in controls with stratification by gender and by the MTHFR C677T genotypes in a large cohort (N = 1379). Second, we conducted a meta-analysis of association studies between blood homocysteine levels and schizophrenia separately by gender (N = 4714). Third, we performed a case-control association study between the MTHFR C677T polymorphism and schizophrenia (N = 4998) and conducted a meta-analysis of genetic association studies based on Japanese subjects (N = 10 378). Finally, we assessed the effect of plasma total homocysteine levels on schizophrenia by a mendelian randomization approach. The ANCOVA after adjustment for age demonstrated a significant effect of diagnosis on the plasma total homocysteine levels in all strata, and the subsequent meta-analysis for gender demonstrated elevated blood homocysteine levels in both male and female patients with schizophrenia although antipsychotic medication might influence the outcome. The meta-analysis of the Japanese genetic association studies demonstrated a significant association between the MTHFR C677T polymorphism and schizophrenia. The mendelian randomization analysis in the Japanese populations yielded an OR of 1.15 for schizophrenia per 1-SD increase in plasma total homocysteine. Our study suggests that increased plasma total homocysteine levels may be associated with an increased risk of schizophrenia.

B vitamin polymorphisms and behavior: evidence of associations with neurodevelopment, depression, schizophrenia, bipolar disorder and cognitive decline

The B vitamins folic acid, vitamin B12 and B6 are essential for neuronal function, and severe deficiencies have been linked to increased risk of neurodevelopmental disorders, psychiatric disease and dementia. Polymorphisms of genes involved in B vitamin absorption, metabolism and function, such as methylene tetrahydrofolate reductase (MTHFR), cystathionine β synthase (CβS), transcobalamin 2 receptor (TCN2) and methionine synthase reductase (MTRR), have also been linked to increased incidence of psychiatric and cognitive disorders. However, the effects of these polymorphisms are often quite small and many studies failed to show any meaningful or consistent associations. This review discusses previous findings from clinical studies and highlights gaps in knowledge. Future studies assessing B vitamin-associated polymorphisms must take into account not just traditional demographics, but subjects' overall diet, relevant biomarkers of nutritional status and also analyze related genetic factors that may exacerbate behavioral effects or nutritional status.

Association analysis of COMT/MTHFR polymorphisms and major depressive disorder in Chinese Han population

BACKGROUND

In several previous biochemical and genetic studies, the Val158Met polymorphism of the gene encoding catechol-O-methyltransferase (COMT) and the C677T polymorphism of Methylenetetrahydrofolate reductase (MTHFR) have been suggested to be involved in the pathogenesis as well as the treatment response of major depressive disorder (MDD), but the results have been inconsistent. In this study, we investigate the association of COMT/MTHFR and their interactions with MDD and antidepressant response in Chinese Han population.

METHODS

Three hundred and sixty eight depressed patients who met DSM-IV criteria for MDD were recruited for the study. Two hundred and nineteen normal controls were recruited from the local community. Patients and normal controls were genotyped for the functional COMT val158met and MTHFR C677T polymorphisms. Patients were characterized for clinical response to antidepressant treatment as measured by intra-individual changes of Hamilton Depression (HAMD-17) scores over 6 weeks.

RESULTS

The T allele (OR=1.81; CI95%=1.40-2.34, P<0.001) and C/T genotype (OR=3.66; CI95% =2.53-5.28, P<0.001) of MTHFR C677T were significantly different between case and control groups. The COMT Met/Val genotype was more common among depressed individuals than among controls (OR=1.52, CI95%=1.04-2.21, P=0.02).

LIMITATION

There is disequilibrium in age and sex between case and control groups. Though we control the two variables in the statistic analysis, to be more accurate, we need to increase sample size in further study.

CONCLUSION

Individuals with the genotype COMT Met/Val and MTHFR C/T have more probability of suffering from MDD. However, there is no association between gene polymorphism and treatment response.

Pharmacogenetics of clinical response to risperidone

Despite risperidone's proven safety and efficacy, existing pharmacogenetic knowledge could be applied to improve its clinical use. The present work aims to summarize the information about genetic polymorphisms affecting risperidone adverse reactions and efficacy during routine clinical practice. The most relevant genes involved in the metabolism of the drug (i.e., CYP2D6, CYP3A and ABCB1) appear to have the greatest potential to predict differences in plasma concentrations of the drug and its interactions, but also relate to side effects, such as neuroleptic syndrome, weight gain or polydipsia. Other genes that have been found in association at least twice with any adverse reactions including metabolic changes, extrapyramidal symptoms or prolactine increase are: 5HT2A; 5HT2C; 5HT6; DRD2; DRD3; and BDNF. Some of these genes (5HTR2A, DRD2 and DRD3), along with 5-HTTLPR and COMT, have also been reported to be related with negative clinical outcomes. However, there is not yet enough evidence to support their routine screening during clinical practice.

Genetic variation in the human brain dopamine system influences motor learning and its modulation by L-Dopa

Dopamine is important to learning and plasticity. Dopaminergic drugs are the focus of many therapies targeting the motor system, where high inter-individual differences in response are common. The current study examined the hypothesis that genetic variation in the dopamine system is associated with significant differences in motor learning, brain plasticity, and the effects of the dopamine precursor L-Dopa. Skilled motor learning and motor cortex plasticity were assessed using a randomized, double-blind, placebo-controlled, crossover design in 50 healthy adults during two study weeks, one with placebo and one with L-Dopa. The influence of five polymorphisms with established effects on dopamine neurotransmission was summed using a gene score, with higher scores corresponding to higher dopaminergic neurotransmission. Secondary hypotheses examined each polymorphism individually. While training on placebo, higher gene scores were associated with greater motor learning (p = .03). The effect of L-Dopa on learning varied with the gene score (gene score*drug interaction, p = .008): participants with lower gene scores, and thus lower endogenous dopaminergic neurotransmission, showed the largest learning improvement with L-Dopa relative to placebo (p<.0001), while L-Dopa had a detrimental effect in participants with higher gene scores (p = .01). Motor cortex plasticity, assessed via transcranial magnetic stimulation (TMS), also showed a gene score*drug interaction (p = .02). Individually, DRD2/ANKK1 genotype was significantly associated with motor learning (p = .02) and its modulation by L-Dopa (p<.0001), but not with any TMS measures. However, none of the individual polymorphisms explained the full constellation of findings associated with the gene score. These results suggest that genetic variation in the dopamine system influences learning and its modulation by L-Dopa. A polygene score explains differences in L-Dopa effects on learning and plasticity most robustly, thus identifying distinct biological phenotypes with respect to L-Dopa effects on learning and plasticity. These findings may have clinical applications in post-stroke rehabilitation or the treatment of Parkinson's disease.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and age at onset of schizophrenia: no consistent evidence for an association in the Nordic population

Methylenetetrahydrofolate reductase (MTHFR) is an enzyme involved in metabolic pathways of importance for nucleotide synthesis and methylation of DNA, membranes, proteins and lipids. The MTHFR gene includes a common polymorphism (rs1801133 or C677T), which is associated with enzyme activity. The T-allele of the C677T polymorphism has been associated with earlier age at onset of schizophrenia in a Scandinavian population, although no association was found in replication attempts in other populations. Extending the study to five Nordic samples consisting of 2,198 patients with schizophrenia, including the original Scandinavian samples, there was no significant association between MTHFR C677T polymorphism and age at onset in schizophrenia. The present results do not suggest that the investigated MTHFR polymorphism has any significant influence on age at onset of schizophrenia in the Nordic population.

Aberrant dopamine D2-like receptor function in a rodent model of schizophrenia

Based on the observation that antipsychotic medications display antagonist properties at dopamine D2-like receptors, aberrant dopamine signaling has been proposed to underlie psychosis in patients with schizophrenia. Thus, it is not surprising that considerable research has been devoted to understanding the mechanisms involved in the antipsychotic action of these compounds. It is important to note that the majority of these studies have been performed in "normal" experimental animals. Given that these animals do not possess the aberrant neuronal information processing typically associated with schizophrenia, the aim of the current study was to examine the dopamine D2 receptor system in a rodent model of schizophrenia. Here, we demonstrate that methylazoxymethanol acetate (MAM)-treated rats display an enhanced effect of quinpirole on dopamine neuron activity and an aberrant locomotor response to D2-like receptor activation, suggesting changes in postsynaptic D2-like receptor function. To better understand the mechanisms underlying the enhanced response to D2-like ligands in MAM-treated rats, we examined the expression of D2, D3, and dopamine transporter mRNA in the nucleus accumbens and ventral tegmental area by quantitative reverse transcription-polymerase chain reaction. MAM-treated rats displayed a significant increase in dopamine D3 receptor mRNA expression in the nucleus accumbens with no significant changes in the expression of the D2 receptor. Taken together, these data demonstrate robust alterations in dopamine D2-like receptor function in a rodent model of schizophrenia and provide evidence that preclinical studies examining the mechanisms of antipsychotic drug action should be performed in animal models that mirror aspects of the abnormal neuronal transmission thought to underlie symptoms of schizophrenia.