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

Association between the rs6313 polymorphism in the 5-HTR2A gene and the efficacy of antipsychotic drugs

BACKGROUND

Prescribing the optimal antipsychotic treatment to schizophrenia is very important as it is well established that patients have different sensitivity to the available antipsychotic drugs. The genotype of the HTR2A T102C (rs6313) polymorphism has been suggested to affect the efficacy of antipsychotic drugs, but the results of different studies have been inconsistent METHODS: In this study, a meta-analysis was used to ascertain the association between allele and genotype polymorphism of rs6313 and the efficacy of antipsychotic drugs. Related studies publicated from January 1995 to December 2021 were retrieved from PubMed, Embase, ScienceDirect, and Web of Science databases. The correlations between allele and genotype polymorphism of rs6313 and the responder rate and scale score reduction rate of antipsychotics were analyzed. In addition, subgroup analyses were performed on time, drug, and ethnicity.

RESULTS

A total of 18 studies were included. The meta-analysis showed that allele and genotype polymorphisms at the rs6313 locus overall were not associated with antipsychotic drug responder rate or scale score reduction rate. Ethnicity subgroup analysis showed that antipsychotic drugs were more effective in patients with allele T in the Caucasian population. Indian patients with the TT genotype had the lowest scale score reduction rate and poor drug treatment effect. East Asian patients with the TC genotype had better treatment effect, whereas in patients with the CC genotype, the treatment was less effective. Drug subgroup analysis showed that patients with the TC genotype treated with clozapine had the highest responder rate and score reduction rate.

CONCLUSIONS

The association between rs6313 polymorphism and the efficacy of antipsychotic drugs is mainly influenced by drug and ethnicity. Caucasian patients with the T allele respond better to drug therapy, and Asian patients with TC genotype. The TC genotype was also a good predictor of the efficacy of clozapine treatment.

Functional single nucleotide polymorphisms in dopaminergic receptors D2 predict clinical response to Cariprazine

Cariprazine (CAR) is an antipsychotic drug for the treatment of schizophrenia (SCZ) and bipolar disorder (BD), and it acts as a partial agonist on the dopamine receptors (DR), D2, and D3. Although many single nucleotide polymorphisms (SNPs) in genes coding for these receptors are known to influence response to antipsychotics, to date, no study on CAR pharmacogenetics exists. In this pilot study, we investigated the relationship between SNPs in DRD2 (rs1800497 and rs6277) and DRD3 (rs6280), and response to CAR treatment, evaluated by the psychometric Brief Psychiatric Rating Scale (BPRS), in a cohort of Caucasian patients. We found a significant association between DRD2 rs1800497 and rs6277 and response to CAR treatment. When genotypes were combined into an arbitrary score, the receiver operating characteristic curve analysis showed that using a cut-off value of -2.5 the response to CAR treatment could be predicted with a positive likelihood ratio of 8.0. Our study report, for the first time, a correlation between SNPs in DRD2 and response to CAR treatment. After confirmation in a larger cohort of patients, our results could open the way for the identification of new tools for the provision of response to CAR treatment.

DRD3 Ser9Gly polymorphism and treatment response to antipsychotics in schizophrenia: A meta-analysis

The association between dopamine D3 receptor (DRD3) Ser9Gly polymorphism and treatment response to antipsychotic drugs (APDs) in schizophrenia (SCZ) has been widely reported with inconsistent results, thus we performed an updated meta-analysis to derive a more precise estimation of the relationship. PubMed, Cochrane Library, Medline, Embase, CNKI, Weipu and Wanfang databases were searched for eligible studies published until March 2022. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of the associations in four genetic models. A total of 13 studies with 1769 patients were included in this meta-analysis. Our findings suggested that Ser9Gly polymorphism was significantly associated with treatment response to APDs in SCZ in allele model (Ser vs Gly, OR = 0.72, 95 % CI = 0.58-0.89, P = 0.002), recessive model (Ser/Ser vs Ser/Gly + Gly/Gly, OR = 0.55, 95 % CI = 0.36-0.86, P = 0.008) and co-dominant model (Ser/Ser vs Gly/Gly, OR = 0.57, 95 % CI = 0.33-0.99, P = 0.045) in Caucasians, but not in Asians. meta-regression revealed that the associations were not confounded by mean age, male ratio and treatment duration (P > 0.05). In summary, our results indicated the DRD3 Ser9Gly may influence the efficacy of APDs in specific genetic models, of which Ser allele and Ser/Ser genotype contributed to poor treatment response in Caucasians.

Association of 5-HTR2A T102C and A-1438G polymorphisms with clinical response to atypical antipsychotic treatment in schizophrenia: A meta-analysis

Associations of serotonin 2A receptor (5-HTR2A) gene polymorphisms with clinical response to atypical antipsychotics (AAPs) treatment in schizophrenia (SCZ) were inconsistent. Thus we conducted a meta-analysis to investigate more reliable estimates. The Cochrane Library, Embase, PubMed, Weipu, CNKI and Wanfang databases were searched for eligible studies published up to September 2021. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated in four genetic models. Subgroup analyses were performed by ethnicity and antipsychotic type. Meta-regression was used to evaluate the potential effects of confounding variables. In total, 19 studies were included for the meta-analysis, of which 17 studies containing 2359 patients were identified for T102C polymorphism and 7 studies containing 1408 patients for A-1438G polymorphism. The results showed that A-1438G polymorphism was significantly associated with clinical response to AAPs treatment in SCZ in four genetic models (allele model, A vs. G, OR = 1.87, 95% CI = 1.05-3.33, P = 0.034; recessive model, AA vs. GA + GG: OR = 1.79, 95% CI = 1.17-2.72, P = 0.007; dominant model, AA + GA vs. GG: OR = 3.40, 95% CI = 1.15-10.10, P = 0.027; co-dominant model, AA vs. GG: OR = 3.44, 95% CI = 1.07-11.10, P = 0.039) in Asians, but not in Caucasians. When stratified by antipsychotic type, A-1438G polymorphism was related to the efficacy of olanzapine in recessive model (AA vs. GA + GG, OR = 1.85, 95% CI = 1.18-2.90, P = 0.007), but not in other models. However, neither four genetic models nor subgroup analyses of T102C polymorphism were found any significant associations with AAPs response (P > 0.05). Meta-regression revealed that no association was confounded by mean age, male ratio, treatment duration and illness duration (P > 0.05). The present meta-analysis indicated that 5-HTR2A A-1438G polymorphism, but not T102C polymorphism, was significantly associated with AAPs response in SCZ, especially in Asians and olanzapine-treated patients.

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.

Potential Link between T102C Polymorphism in the Serotonin Receptors (5-HT2A) Gene and Treatment Response of Risperidone on Schizophrenia

BACKGROUND: Schizophrenia affects 1% of population and its molecular etiology remains enigmatic despite enormous study. Approximately one-third of patients failed to respond with treatment. The 5-HT2A receptor appears to be one of important site of action of atypical antipsychotic drugs. It also has been suggested that the T102C gene polymorphism alters promoter activity and expression of 5-HT2A receptors and might be responsible for the associations with the efficacy of typical antipsychotics. AIM: In this study, we aimed to evaluate the potential link between T102C polymorphism in the Serotonin Receptors (5-HT2A) and their response to risperidone. METHODS: We studied 100 schizophrenia patients and 100 healthy volunteers as a comparison of 5-HT2A receptors gene polymorphism distribution, which were all Indonesian. The peripheral blood samples were obtained from all participants. The patients assessed by Positive and Negative Scale (PANSS) and Clinical Global Impression Scale (CGI) when admitted to the hospital. Clinical improvements then assessed 5 times in 4 weeks (when transferred to sub-acute ward, at the 1st, the 2nd, the 3rd, and the 4th week). To analyze the T102C polymorphism of 5-HT2A receptor gene, we used an allele specific polymerase chain reaction based restriction fragment length polymorphism (PCR-RFLP) method. RESULTS: In this study, there were three various polymorphisms of T102C in the serotonin receptor (5-HT2A) gene: T/T, C/C, and T/C. The patients who had homozygous for T/T genotypes were found to give better improvement to risperidone than the patients who were C/C and T/C genotypes (P:0.001). Moreover, the patients with C allele genotype T/C and C/C had minimal response (P:0.001). We found no significant difference distribution of genotypes between schizophrenia patients and healthy volunteers (P:0.498). CONCLUSION: Our result supported that there was a potential link between T102C polymorphism in the serotonin receptor (5-HT2A) gene and treatment response of risperidone. It suggested the importance of genetic screening such as examination of the Serotonin Receptor 5-HT2A (T102C) gene polymorphism to be performed to optimize therapeutic strategies with antipsychotic.

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.

Identification of genetic correlates of response to Risperidone: Findings of a multicentric schizophrenia study from India

Risperidone is most commonly used as an antipsychotic in India for treatment of schizophrenia. However, the response to treatment with risperidone is affected by many factors, genetic factors being one of them. So, we attempted to evaluate the association between dopamine D2 (DRD2) receptor, serotonergic (5HT2A) receptor and CYP2D6 gene polymorphisms and response to treatment with risperidone in persons with schizophrenia from North India. It was a multicentric 12-weeks prospective study, undertaken in patients diagnosed with schizophrenia according to International Classification of Diseases 10th revision, Diagnostic Criteria for Research module (ICD-10 DCR). Patients were treated with incremental dosages of risperidone. Nine gene polymorphisms from three genes viz. DRD2, 5-HT2A and CYP2D6 along with socio-demographical and clinical variables were analyzed to ascertain the association in response to risperidone treatment. The change in the Positive and Negative Syndrome Scale (PANSS) was used to measure the outcome. Significant differences in the frequencies of single nucleotide proteins (SNPs) rs180498 (Taq1D) and rs 6305 (C516T) polymorphisms were found amongst the groups defined according to percent decline in PANSS. The CYP2D6*4 polymorphism differed significantly when drop outs were excluded from analysis. Presence of DRD2 Taq 1 D2D2 and 5-HT2A C516T CT genotypes in patients were more likely to be associated with non-response to risperidone. Ser311Cys (rs1801028) mutation was absent in the North Indian patients suffering from schizophrenia.

Use of combinatorial pharmacogenomic testing in two cases from community psychiatry

This report describes two cases in which pharmacogenomic testing was utilized to guide medication selection for difficult to treat patients. The first patient is a 29-year old male with bipolar disorder who had severe akathisia due to his long acting injectable antipsychotic. The second patient is a 59-year old female with major depressive disorder who was not responding to her medication. In both cases, a proprietary combinatorial pharmacogenomic test was used to inform medication changes and improve patient outcomes. The first patient was switched to a long acting injectable that was not affected by his genetic profile and his adverse effects abated. The second patient had her medications discontinued due to the results of the genetic testing and more intense psychotherapy initiated. While pharmacogenomic testing may be helpful in cases such as these presented here, it should never serve as a proxy for a comprehensive biopsychosocial approach. The pharmacogenomic information may be selectively added to this comprehensive approach to support medication treatment.

A review of genetic alterations in the serotonin pathway and their correlation with psychotic diseases and response to atypical antipsychotics

Serotonin is a neurotransmitter that plays a predominant role in mood regulation. The importance of the serotonin pathway in controlling behavior and mental status is well recognized. All the serotonin elements - serotonin receptors, serotonin transporter, tryptophan hydroxylase and monoamine oxidase proteins - can show alterations in terms of mRNA or protein levels and protein sequence, in schizophrenia and bipolar disorder. Additionally, when examining the genes sequences of all serotonin elements, several single nucleotide polymorphisms (SNPs) have been found to be more prevalent in schizophrenic or bipolar patients than in healthy individuals. Several of these alterations have been associated either with different phenotypes between patients and healthy individuals or with the response of psychiatric patients to the treatment with atypical antipsychotics. The complex pattern of genetic diversity within the serotonin pathway hampers efforts to identify the key variations contributing to an individual's susceptibility to the disease. In this review article, we summarize all genetic alterations found across the serotonin pathway, we provide information on whether and how they affect schizophrenia or bipolar disorder phenotypes, and, on the contribution of familial relationships on their detection frequencies. Furthermore, we provide evidence on whether and how specific gene polymorphisms affect the outcome of schizophrenic or bipolar patients of different ethnic groups, in response to treatment with atypical antipsychotics. All data are discussed thoroughly, providing prospective for future studies.

Pharmacogenomics in psychiatry: the relevance of receptor and transporter polymorphisms

The treatment of severe mental illness, and of psychiatric disorders in general, is limited in its efficacy and tolerability. There appear to be substantial interindividual differences in response to psychiatric drug treatments that are generally far greater than the differences between individual drugs; likewise, the occurrence of adverse effects also varies profoundly between individuals. These differences are thought to reflect, at least in part, genetic variability. The action of psychiatric drugs primarily involves effects on synaptic neurotransmission; the genes for neurotransmitter receptors and transporters have provided strong candidates in pharmacogenetic research in psychiatry. This paper reviews some aspects of the pharmacogenetics of neurotransmitter receptors and transporters in the treatment of psychiatric disorders. A focus on serotonin, catecholamines and amino acid transmitter systems reflects the direction of research efforts, while relevant results from some genome-wide association studies are also presented. There are many inconsistencies, particularly between candidate gene and genome-wide association studies. However, some consistency is seen in candidate gene studies supporting established pharmacological mechanisms of antipsychotic and antidepressant response with associations of functional genetic polymorphisms in, respectively, the dopamine D2 receptor and serotonin transporter and receptors. More recently identified effects of genes related to amino acid neurotransmission on the outcome of treatment of schizophrenia, bipolar illness or depression reflect the growing understanding of the roles of glutamate and γ-aminobutyric acid dysfunction in severe mental illness. A complete understanding of psychiatric pharmacogenomics will also need to take into account epigenetic factors, such as DNA methylation, that influence individual responses to drugs.

Effect of polymorphisms on the pharmacokinetics, pharmacodynamics, and safety of risperidone in healthy volunteers

OBJECTIVE

To identify genetic markers capable of predicting the pharmacokinetics, pharmacodynamics, and adverse effects of risperidone.

METHODS

Genotyping was performed in 70 healthy volunteers receiving a single 1mg oral dose of risperidone. Risperidone and hydroxyrisperidone plasma levels were measured using high-performance liquid chromatography combined with tandem mass spectrometry.Prolactin concentration was quantified by direct chemiluminescence.

RESULTS

Poor CYP2D6 metabolizers showed higher risperidone Cmax, area under the curve (AUC), and t1/2, as well as lower clearance. They also showed lower Cmax and AUC and higher t1/2 for hydroxyrisperidone. Furthermore, individuals with a mutant VKORC1 genotype had a lower risperidone AUC and t1/2 and higher clearance. The hydroxyrisperidone AUC was lower in individuals with the COMT mutant genotype. Risperidone increased prolactin levels (iAUC and iCmax), which were higher in women than in men. The most frequent reactions were somnolence (47.1%), headache (21.4%), and dizziness (17.1%). Women had neurological effects and headache more frequently than men. The incidence of headache was associated with polymorphisms in the AGTR1 and NAT2; neurological effects were associated with CYP2C19.

CONCLUSIONS

Differences in the pharmacokinetics of risperidone are due to polymorphisms in CYP2D6, COMT, and VKORC1. Differences in adverse reactions can be explained by gender and polymorphisms in CYP2C19, AGTR1, and NAT2.

Pharmacogenetics of antipsychotics

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Individualizing clozapine and risperidone treatment for schizophrenia patients

Schizophrenia is a severe disorder that significantly affects the quality of life and total functioning of patients and their caregivers. Clozapine is the first atypical antipsychotic with fewer adverse effects and established efficacy. As a rule of thumb, risperidone is one of the most reliable and effective antipsychotics for newly diagnosed and chronic schizophrenics. Pharmacogenetic studies have identified genomic variants of candidate genes that seem to be important in the way a patient responds to treatment. The recent progress made in pharmacogenomics will improve the quality of treatment, since drug doses will be tailored to the special needs of each patient. In this article, we review the available literature attempting to delineate the role of genomic variations in clozapine and risperidone response in schizophrenic patients of various ethnicities. We conclude that pharmacogenomics for these two drugs is still not ready for implementation in the clinic.

The potential role of dopamine D₃ receptor neurotransmission in cognition

Currently available treatments have limited pro-cognitive effects for neuropsychiatric disorders, such as schizophrenia, Parkinson's disease and Alzheimer's disease. The primary objective of this work is to review the literature on the role of dopamine D₃ receptors in cognition, and propose dopamine D₃ receptor antagonists as possible cognitive enhancers for neuropsychiatric disorders. A literature search was performed to identify animal and human studies on D₃ receptors and cognition using PubMed, MEDLINE and EMBASE. The search terms included "dopamine D₃ receptor" and "cognition". The literature search identified 164 articles. The results revealed: (1) D₃ receptors are associated with cognitive functioning in both healthy individuals and those with neuropsychiatric disorders; (2) D₃ receptor blockade appears to enhance while D₃ receptor agonism seems to impair cognitive function, including memory, attention, learning, processing speed, social recognition and executive function independent of age; and (3) D₃ receptor antagonists may exert their pro-cognitive effect by enhancing the release of acetylcholine in the prefrontal cortex, disinhibiting the activity of dopamine neurons projecting to the nucleus accumbens or prefrontal cortex, or activating CREB signaling in the hippocampus. These findings suggest that D₃ receptor blockade may enhance cognitive performance in healthy individuals and treat cognitive dysfunction in individuals with a neuropsychiatric disorder. Clinical trials are needed to confirm these effects.

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.

Association of common genetic variants with risperidone adverse events in a Spanish schizophrenic population

Risperidone non-compliance is often high due to undesirable side effects, whose development is in part genetically determined. Studies with genetic variants involved in the pharmacokinetics and pharmacodynamics of risperidone have yielded inconsistent results. Thus, the aim of this study was to investigate the putative association of genetic markers with the occurrence of four frequently observed adverse events secondary to risperidone treatment: sleepiness, weight gain, extrapyramidal symptoms and sexual adverse events. A series of 111 schizophrenia inpatients were genotyped for genetic variants previously associated with or potentially involved in risperidone response. Presence of adverse events was the main variable and potential confounding factors were considered. Allele 16Gly of ADRB2 was significantly associated with a higher risk of sexual adverse events. There were other non-significant trends for DRD3 9Gly and SLC6A4 S alleles. Our results, although preliminary, provide new candidate variants of potential use in risperidone safety prediction.

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).

Meta-analysis of the efficacy of adjunctive NMDA receptor modulators in chronic schizophrenia

BACKGROUND

Based on the glutamatergic NMDA receptor hypofunction theory of schizophrenia, NMDA receptor modulators (NMDARMs) may have therapeutic potential in the treatment of schizophrenia.

OBJECTIVE

This meta-analysis aimed to evaluate the potential of modulators of the NMDA receptor as adjunctive therapy for schizophrenia, using the results from published trials.

DATA SOURCES

A primary electronic search for controlled clinical trials using NMDARMs in schizophrenia was conducted on the PubMed, Cochrane Library, EMBASE, CINAHL® and PsycINFO databases. A secondary manual search of references from primary publications was also performed.

STUDY SELECTION

Inclusion criteria were the application of an established method of diagnosis, randomized case assignment, comparison of NMDARM add-on therapy with placebo, and double-blind assessment of symptoms in chronic schizophrenia using standardized rating scales. Results were based on a total sample size of 1253 cases from 29 trials that fulfilled the specified criteria.

DATA EXTRACTION

Scores on rating scales or on their relevant subscales were obtained for all selected studies from published results for the minimum dataset to compute the difference between post- and pre-trial scores and their pooled standard deviation for NMDARM add-on therapy and placebo groups for negative, positive and total symptoms.

RESULTS

A negative standardized mean difference (SMD) indicates therapeutic benefit in favour of NMDARM add-on therapy and all SMD results mentioned here are statistically significant. The overall effect size for NMDARMs as a group was small for negative (SMD -0.27) and medium for total (SMD -0.40) symptoms of chronic schizophrenia. Subgroup analysis revealed medium effect sizes for D-serine and N-acetyl-cysteine (NAC) for negative (SMD -0.53 and -0.45, respectively) and total (SMD -0.40 and -0.64, respectively) symptoms, and for glycine (SMD -0.66) and sarcosine (SMD -0.41) for total symptoms. As adjuvants to non-clozapine antipsychotics, additional therapeutic benefits were observed for NMDARM as a group (SMD -0.14) and glycine (SMD -0.54) for positive symptoms; D-serine (SMD -0.54), NAC (SMD -0.45) and sarcosine (SMD -0.39) for negative symptoms; and NMDARM as a group (SMD -0.38), D-serine (SMD -0.40), glycine (SMD -1.12), NAC (SMD -0.64) and sarcosine (SMD -0.53) for total symptoms. When added to clozapine, none of the drugs demonstrated therapeutic potential, while addition of glycine (SMD +0.56) worsened positive symptoms.

CONCLUSIONS

Taking into consideration the number of trials and sample size in subgroup analyses, D-serine, NAC and sarcosine as adjuncts to non-clozapine antipsychotics have therapeutic benefit in the treatment of negative and total symptoms of chronic schizophrenia. While glycine improves positive and total symptoms as an adjuvant to non-clozapine antipsychotics, it worsens them when added to clozapine.

Genetic variant of HTR2A associates with risk of impulse control and repetitive behaviors in Parkinson's disease

OBJECTIVES

To determine the role of a serotonin 2A receptor gene (=HTR2A) variant in the development of impulse control and repetitive behaviors in Parkinson's disease.

METHODS

We performed a genetic association analysis to a cohort of 404 Korean patients with Parkinson's disease who had been enrolled in a previous study. Presence of impulse control and repetitive behaviors was screened using modified version of Minnesota Impulsive Disorders Interview and genotyping for HTR2A c.102T > C was performed using the TaqMan assay.

RESULTS

The T allele, which is presumably linked to higher receptor expression, was marginally associated with impulse control and repetitive behaviors in Parkinson's disease; the genetic influence was significantly enhanced in the lower levodopa-equivalent-dose group, increasing the risk by 2.8 and 6.9 times in CT and TT carriers, respectively (p-trend = 0.011). There was no significant interaction between the c.102T > C variant and clinical risk variables such as sex, age at onset, total daily levodopa-equivalent-dose, use of dopamine agonist and daily dose of dopamine agonist.

CONCLUSION

Our data support a possible contribution of genetic variation in the HTR2A to the susceptibility to impulse control and repetitive behaviors in Parkinson's disease.

Pharmacogenetics and antipsychotics: therapeutic efficacy and side effects prediction

IMPORTANCE OF THE FIELD

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

AREAS COVERED IN THIS REVIEW

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

WHAT THE READER WILL GAIN

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

TAKE HOME MESSAGE

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

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.

Review: The biological basis of antipsychotic response in schizophrenia

Schizophrenia is a severe mental illness affecting approximately 1% of the population worldwide. Antipsychotic drugs are effective in symptom control in up to two-thirds of patients, but in at least one-third of patients the response is poor. The reason for this is not clear, but one possibility is that good and poor responders have different neurochemical pathologies, and may therefore benefit from different treatment approaches. In this selective review we summarise research findings investigating the biological differences between patients with schizophrenia who show a good or a poor response to treatment with antipsychotic drugs.

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.

HTR2A A-1438G/T102C polymorphisms predict negative symptoms performance upon aripiprazole treatment in schizophrenic patients

RATIONALE

Aripiprazole acts as a partial agonist at dopamine D2 and D3 and serotonin 1A receptors and as an antagonist at serotonin 2A receptors (HTR2A). Since aripiprazole acts as an antagonist at HTR2A, genetic variants of HTR2A may be important in explaining variability in response to aripiprazole.

OBJECTIVES

This study investigated whether the efficacy of aripiprazole can be predicted by functional HTR2A A-1438G/T102C polymorphisms (rs63311/rs6313) as modified by clinical factors in Han Chinese hospitalized patients with acutely exacerbated schizophrenia.

MATERIALS AND METHODS

After hospitalization, the patients (n = 128) were given a 4-week course of aripiprazole. Patients were genotyped for HTR2A A-1438G/T102C polymorphisms via the restriction fragment length polymorphism method. Clinical factors such as gender, age, duration of illness, education level, diagnostic subtype, and medication dosage were noted as well. The researchers measured psychopathology biweekly, using the Positive and Negative Syndrome Scale (PANSS). A mixed model regression approach (SAS Proc MIXED) was used to analyze the effects of genetic and clinical factors on PANSS performance after aripiprazole treatment.

RESULTS

We found that the GG/CC genotype group of HTR2A A-1438G/T102C polymorphisms predicts poor aripiprazole response specifically for negative symptoms. In addition, the clinical factors, including dosage of aripiprazole, age, duration of illness, and diagnostic subtype, were found to influence PANSS performance after aripiprazole treatment.

CONCLUSIONS

The data suggest HTR2A A-1438G/T102C polymorphisms may predict negative symptoms performance upon aripiprazole treatment in schizophrenic patients as modified by clinical factors.

Pharmacogenomic Biomarkers in Neuropsychiatry: The Path to Personalized Medicine in Mental Disorders

Neuropsychiatric disorders and dementia represent a major cause of disability and high cost in developed societies. Most disorders of the central nervous system (CNS) share some common features, such as a genomic background in which hundreds of genes might be involved, genome-environment interactions, complex pathogenic pathways, poor therapeutic outcomes, and chronic disability.

Recent advances in genomic medicine can contribute to accelerate our understanding on the pathogenesis of CNS disorders, improve diagnostic accuracy with the introduction of novel biomarkers, and personalize therapeutics with the incorporation of pharmacogenetic and pharmacogenomic procedures to drug development and clinical practice.

The pharmacological treatment of CNS disorders, in general, accounts for 10–20% of direct costs, and less than 30–40% of the patients are moderate responders to conventional drugs, some of which may cause important adverse drugs reactions (ADRs). Pharmacogenetic and pharmacogenomic factors may account for 60–90% of drug variability in drug disposition and pharmacodynamics. Approximately 60–80% of CNS drugs are metabolized via enzymes of the CYP gene superfamily; 18% of neuroleptics are major substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are major substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are major substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of

CYP3A4. About 10–20% of Caucasians are carriers of defective CYP2D6 polymorphic variants that alter the metabolism of many psychotropic agents. Other 100 genes participate in the efficacy and safety of psychotropic drugs. The incorporation of pharmacogenetic/ pharmacogenomic protocols to CNS research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety. To achieve this goal several measures have to be taken, including: (a) educate physicians and the public on the use of genetic/ genomic screening in the daily clinical practice; (b) standardize genetic testing for major categories of drugs; (c) validate pharmacogenetic and pharmacogenomic procedures according to drug category and pathology; (d) regulate ethical, social, and economic issues; and (e) incorporate pharmacogenetic and pharmacogenomic procedures to both drugs in development and drugs in the market to optimize therapeutics.