Serotonin subtype 2 receptor genes and clinical response to clozapine in schizophrenia patients

Trace amine associated receptor 1: predicted effects of single nucleotide variants on structure-function in geographically diverse populations

Trace Amine Associated Receptor 1 (TAAR1) is a novel pharmaceutical target under investigation for the treatment of several neuropsychiatric conditions. TAAR1 single nucleotide variants (SNV) have been found in patients with schizophrenia and metabolic disorders. However, the frequency of variants in geographically diverse populations and the functional effects of such variants are unknown. In this study, we aimed to characterise the distribution of TAAR1 SNVs in five different WHO regions using the Database of Genotypes and Phenotypes (dbGaP) and conducted a critical computational analysis using available TAAR1 structural data to identify SNVs affecting ligand binding and/or functional regions. Our analysis shows 19 orthosteric, 9 signalling and 16 micro-switch SNVs hypothesised to critically influence the agonist induced TAAR1 activation. These SNVs may non-proportionally influence populations from discrete regions and differentially influence the activity of TAAR1-targeting therapeutics in genetically and geographically diverse populations. Notably, our dataset presented with orthosteric SNVs D1033.32N (found only in the South-East Asian Region and Western Pacific Region) and T1945.42A (found only in South-East Asian Region), and 2 signalling SNVs (V1253.54A/T2526.36A, found in African Region and commonly, respectively), all of which have previously demonstrated to influence ligand induced functions of TAAR1. Furthermore, bioinformatics analysis using SIFT4G, MutationTaster 2, PROVEAN and MutationAssessor predicted all 16 micro-switch SNVs are damaging and may further influence the agonist activation of TAAR1, thereby possibly impacting upon clinical outcomes. Understanding the genetic basis of TAAR1 function and the impact of common mutations within clinical populations is important for the safe and effective utilisation of novel and existing pharmacotherapies.

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.

Treatment-Resistant Schizophrenia, Clozapine Resistance, Genetic Associations, and Implications for Precision Psychiatry: A Scoping Review

Treatment-resistant schizophrenia (TRS) is often associated with severe burden of disease, poor quality of life and functional impairment. Clozapine is the gold standard for the treatment of TRS, although it is also known to cause significant side effects in some patients. In view of the burgeoning interest in the role of genetic factors in precision psychiatry, we conducted a scoping review to narratively summarize the current genetic factors associated with TRS, clozapine resistance and side effects to clozapine treatment. We searched PubMed from inception to December 2022 and included 104 relevant studies in this review. Extant evidence comprised associations between TRS and clozapine resistance with genetic factors related to mainly dopaminergic and serotoninergic neurotransmitter systems, specifically, TRS and rs4680, rs4818 within COMT, and rs1799978 within DRD2; clozapine resistance and DRD3 polymorphisms, CYP1A2 polymorphisms; weight gain with LEP and SNAP-25 genes; and agranulocytosis risk with HLA-related polymorphisms. Future studies, including replication in larger multi-site samples, are still needed to elucidate putative risk genes and the interactions between different genes and their correlations with relevant clinical factors such as psychopathology, psychosocial functioning, cognition and progressive changes with treatment over time in TRS and clozapine resistance.

Peripheral biomarkers of treatment-resistant schizophrenia: Genetic, inflammation and stress perspectives

Treatment-resistant schizophrenia (TRS) often results in severe disability and functional impairment. Currently, the diagnosis of TRS is largely exclusionary and emphasizes the improvement of symptoms that may not be detected early and treated according to TRS guideline. As the gold standard, clozapine is the most prescribed selection for TRS. Therefore, how to predict TRS in advance is critical for forming subsequent treatment strategy especially clozapine is used during the early stage of TRS. Although mounting studies have identified certain clinical factors and neuroimaging characteristics associated with treatment response in schizophrenia, the predictors for TRS remain to be explored. Biomarkers, particularly for peripheral biomarkers, show great potential in predicting TRS in view of their predictive validity, noninvasiveness, ease of testing and low cost that would enable their widespread use. Recent evidence supports that the pathogenesis of TRS may be involved in abnormal neurotransmitter systems, inflammation and stress. Due to the heterogeneity of TRS and the lack of consensus in diagnostic criteria, it is difficult to compare extensive results among different studies. Based on the reported neurobiological mechanisms that may be associated with TRS, this paper narratively reviews the updates of peripheral biomarkers of TRS, from genetic and other related perspectives. Although current evidence regarding biomarkers in TRS remains fragmentary, when taken together, it can help to better understand the neurobiological interface of clinical phenotypes and psychiatric symptoms, which will enable individualized prediction and therapy for TRS in the long run.

Clozapine's multiple cellular mechanisms: What do we know after more than fifty years? A systematic review and critical assessment of translational mechanisms relevant for innovative strategies in treatment-resistant schizophrenia

Almost fifty years after its first introduction into clinical care, clozapine remains the only evidence-based pharmacological option for treatment-resistant schizophrenia (TRS), which affects approximately 30% of patients with schizophrenia. Despite the long-time experience with clozapine, the specific mechanism of action (MOA) responsible for its superior efficacy among antipsychotics is still elusive, both at the receptor and intracellular signaling level. This systematic review is aimed at critically assessing the role and specific relevance of clozapine's multimodal actions, dissecting those mechanisms that under a translational perspective could shed light on molecular targets worth to be considered for further innovative antipsychotic development. In vivo and in vitro preclinical findings, supported by innovative techniques and methods, together with pharmacogenomic and in vivo functional studies, point to multiple and possibly overlapping MOAs. To better explore this crucial issue, the specific affinity for 5-HT₂R, D1R, α_2c, and muscarinic receptors, the relatively low occupancy at dopamine D2R, the interaction with receptor dimers, as well as the potential confounder effects resulting in biased ligand action, and lastly, the role of the moiety responsible for lipophilic and alkaline features of clozapine are highlighted. Finally, the role of transcription and protein changes at the synaptic level, and the possibility that clozapine can directly impact synaptic architecture are addressed. Although clozapine's exact MOAs that contribute to its unique efficacy and some of its severe adverse effects have not been fully understood, relevant information can be gleaned from recent mechanistic understandings that may help design much needed additional therapeutic strategies for TRS.

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.

Association of Genetic Variants of Dopamine and Serotonin In Schizophrenia

BACKGROUND

Several studies indicated that antipsychotic treatment response and side effect manifestation can be different due to inter-individual variability in genetic variations.

AIM OF THE STUDY

Here we perform a case-control study to explore a potential association between schizophrenia and variants within the antipsychotic drug molecular targets (DRD1, DRD2, DRD3, HTR2A, HTR6) and metabolizing enzymes (CYP2D6, COMT) genes in Armenian population including also analysis of their possible relationship with disease clinical symptoms.

METHODS

A total of 18 SNPs was studied in patients with schizophrenia (n = 78) and healthy control subjects (n = 77) using MassARRAY genotyping.

RESULTS

We found that two studied genetic variants, namely DRD2 rs4436578*C and HTR2A rs6314*A are underrepresented in the group of patients compared to healthy subjects. After the correction for multiple testing, the rs4436578*C variant remained significant while the rs6314*A reported borderline significance. No significant differences in minor allele frequencies for other studied variants were identified. Also, a relationship between the genotypes and age of onset as well as disease duration has been detected.

CONCLUSIONS

The DRD2 rs4436578*C genetic variant might have protective role against schizophrenia, at least in Armenians.

Impact of histamine receptors H1 and H3 polymorphisms on antipsychotic-induced weight gain

OBJECTIVES

A positive correlation between antipsychotic-induced weight gain (AIWG) and the antagonist effect of antipsychotic drugs at the histamine H1 receptor (HRH1) as well as the agonist effect at the histamine H3 receptor (HRH3) in the brain has been consistently demonstrated. We investigated the potential impact of single-nucleotide polymorphisms (SNPs) in HRH1 and HRH3 genes on AIWG.

METHODS

We analysed 40 tagSNPs in HRH1 (n = 34) and HRH3 (n = 6) in schizophrenia/schizoaffective disorder patients (n = 193) primarily treated with clozapine or olanzapine for up to 14 weeks. Linear regression was used to evaluate the association between SNPs and AIWG, with baseline weight and treatment duration as covariates.

RESULTS

In HRH1, a nominal association of rs7639145 with AIWG was observed in patients of European ancestry treated with either clozapine or olanzapine (P= 0.043; β = 1.658; n = 77). We observed nominal association for two HRH1 SNPs rs346074 (P = 0.002; β = -5.024) and rs13064530 (P= 0.004; β = -5.158) in patients of African ancestry treated with either clozapine or olanzapine (n = 37). However, the above associations are not significant after correcting for multiple testing. In HRH3, we did not observe association in either ancestry.

CONCLUSIONS

The current study suggests that SNPs in HRH1 and HRH3 may not have a major role in AIWG.

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.

Clozapine Pharmacogenetic Studies in Schizophrenia: Efficacy and Agranulocytosis

Clozapine is an efficacious atypical antipsychotic for treatment-refractory schizophrenia. Clinical response and appearance of adverse events vary among individual patients receiving clozapine, with genetic and non-genetic factors potentially contributing to individual variabilities. Pharmacogenetic studies investigate associations between genetic variants and drug efficacy and toxicity. To date, most pharmacogenetic studies of clozapine have been conducted through candidate gene approaches. A recent advance in technology made it possible to perform comprehensive genetic mapping underlying clinical phenotypes and outcomes, which allow novel findings beyond biological hypotheses based on current knowledge. In this paper, we will summarize the studies on clozapine pharmacogenetics that have extensively examined clinical response and agranulocytosis. While there is still limited evidence on clozapine efficacy, recent genome-wide studies provide further evidence of the involvement of the human leukocyte antigen (HLA) region in clozapine-induced agranulocytosis.

Biological Predictors of Clozapine Response: A Systematic Review

Background: Clozapine is the recommended antipsychotic for treatment-resistant schizophrenia (TRS) but there is significant variability between patients in the degree to which clozapine will improve symptoms. The biological basis of this variability is unknown. Although clozapine has efficacy in TRS, it can elicit adverse effects and initiation is often delayed. Identification of predictive biomarkers of clozapine response may aid initiation of clozapine treatment, as well as understanding of its mechanism of action. In this article we systematically review prospective or genetic studies of biological predictors of response to clozapine. Methods: We searched the PubMed database until 20th January 2018 for studies investigating "clozapine" AND ("response" OR "outcome") AND "schizophrenia." Inclusion required that studies examined a biological variable in relation to symptomatic response to clozapine. For all studies except genetic-studies, inclusion required that biological variables were measured before clozapine initiation. Results: Ninety-eight studies met the eligibility criteria and were included in the review, including neuroimaging, blood-based, cerebrospinal fluid (CSF)-based, and genetic predictors. The majority (70) are genetic studies, collectively investigating 379 different gene variants, however only three genetic variants (DRD3 Ser9Gly, HTR2A His452Tyr, and C825T GNB3) have independently replicated significant findings. Of the non-genetic variables, the most consistent predictors of a good response to clozapine are higher prefrontal cortical structural integrity and activity, and a lower ratio of the dopamine and serotonin metabolites, homovanillic acid (HVA): 5-hydroxyindoleacetic acid (5-HIAA) in CSF. Conclusions: Recommendations include that future studies should ensure adequate clozapine trial length and clozapine plasma concentrations, and may include multivariate models to increase predictive accuracy.

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.

Pharmacogenetic tests for antipsychotic medications: clinical implications and considerations

Optimizing antipsychotic pharmacotherapy is often challenging due to significant variability in effectiveness and tolerability. Genetic factors influencing pharmacokinetics and pharmacodynamics may contribute to some of this variability. Research studies have characterized these pharmacogenetic relationships, and some genetic markers are now available as clinical tests. These advances in pharmacogenetics research and test availability have great potential to improve clinical outcomes and quality of life in psychiatric patients. For clinicians considering using pharmacogenetics, it is important to understand the clinical implications and also the limitations of markers included in currently available tests. This review focuses on pharmacokinetic and pharmacodynamic gene variants that are currently available in commercial genetic testing panels. Associations of these variants with clinical efficacy and adverse effects, as well as other clinical implications, in antipsychotic pharmacotherapy are discussed.

Clozapine as a Model for Antipsychotic Development

Schizophrenia is a devastating illness that affects up to 1% of the population; it is characterized by a combination of positive symptoms, negative symptoms, and cognitive impairment. Currently, treatment consists of one class of medications known as antipsychotics, which include typical (first-generation) and atypical (second-generation) agents. Unfortunately, antipsychotic medications have limited efficacy, with up to a third of patients lacking a full response. Clozapine, the first atypical antipsychotic developed, is the only medication shown to be superior to all other antipsychotics. However, owing to several life-threatening side effects and required enrollment in a registry with routine blood monitoring, clozapine is greatly underutilized in the US. Developing a medication as efficacious as clozapine with limited side effects would likely become the first-line therapy for schizophrenia and related disorders. In this review, we discuss the history of clozapine, landmark studies, and its clinical advantages and disadvantages. We further discuss the hypotheses for clozapine's superior efficacy based on neuroreceptor binding, and the limitations of a receptor-based approach to antipsychotic development. We highlight some of the advances from pharmacogenetic studies on clozapine and then focus on studies of clozapine using unbiased approaches such as pharmacogenomics and gene expression profiling. Finally, we examine how these approaches could provide insights into clozapine's mechanism of action and side-effect profile, and lead to novel and improved therapeutics.

Treatment-resistant schizophrenia: current insights on the pharmacogenomics of antipsychotics

Up to 30% of people with schizophrenia do not respond to two (or more) trials of dopaminergic antipsychotics. They are said to have treatment-resistant schizophrenia (TRS). Clozapine is still the only effective treatment for TRS, although it is underused in clinical practice. Initial use is delayed, it can be hard for patients to tolerate, and clinicians can be uncertain as to when to use it. What if, at the start of treatment, we could identify those patients likely to respond to clozapine - and those likely to suffer adverse effects? It is likely that clinicians would feel less inhibited about using it, allowing clozapine to be used earlier and more appropriately. Genetic testing holds out the tantalizing possibility of being able to do just this, and hence the vital importance of pharmacogenomic studies. These can potentially identify genetic markers for both tolerance of and vulnerability to clozapine. We aim to summarize progress so far, possible clinical applications, limitations to the evidence, and problems in applying these findings to the management of TRS. Pharmacogenomic studies of clozapine response and tolerability have produced conflicting results. These are due, at least in part, to significant differences in the patient groups studied. The use of clinical pharmacogenomic testing - to personalize clozapine treatment and identify patients at high risk of treatment failure or of adverse events - has moved closer over the last 20 years. However, to develop such testing that could be used clinically will require larger, multicenter, prospective studies.

5-HT2C receptors in psychiatric disorders: A review

5-HT2Rs have a different genomic organization from other 5-HT2Rs. 5HT2CR undergoes post-transcriptional pre-mRNA editing generating diversity among RNA transcripts. Selective post-transcriptional editing could be involved in the pathophysiology of psychiatric disorders through impairment in G-protein interactions. Moreover, it may influence the therapeutic response to agents such as atypical antipsychotic drugs. Additionally, 5-HT2CR exhibits alternative splicing. Central serotonergic and dopaminergic systems interact to modulate normal and abnormal behaviors. Thus, 5HT2CR plays a crucial role in psychiatric disorders. 5HT2CR could be a relevant pharmacological target in the treatment of neuropsychiatric disorders. The development of drugs that specifically target 5-HT2C receptors will allow for better understanding of their involvement in the pathophysiology of psychiatric disorders including schizophrenia, anxiety, and depression. Among therapeutic means currently available, most drugs used to treat highly morbid psychiatric diseases interact at least partly with 5-HT2CRs. Pharmacologically, 5HT2CRs, have the ability to generate differentially distinct response signal transduction pathways depending on the type of 5HT2CR agonist. Although this receptor property has been clearly demonstrated, in vitro, the eventual beneficial impact of this property opens new perspectives in the development of agonists that could activate signal transduction pathways leading to better therapeutic efficiency with fewer adverse effects.

Association of orexin receptor polymorphisms with antipsychotic-induced weight gain

OBJECTIVES

Antipsychotic-induced weight gain (AIWG) is a common side effect of treatment with antipsychotics such as clozapine and olanzapine. The orexin gene and its receptors are expressed in the hypothalamus and have been associated with maintenance of energy homeostasis. In this study, we have analysed tagging single nucleotide polymorphisms (SNPs) in orexin receptors 1 and 2 (HCRTR1 and HCRTR2) for association with AIWG.

METHODS

Schizophrenia or schizoaffective disorder subjects (n = 218), treated mostly with clozapine and olanzapine for up to 14 weeks, were included. Replication was conducted in a subset of CATIE samples (n = 122) treated with either olanzapine or risperidone for up to 190 days. Association between SNPs and AIWG was assessed using analysis of covariance (ANCOVA) with baseline weight and duration of treatment as covariates.

RESULTS

Several SNPs in HCRTR2 were nominally associated with AIWG in patients of European ancestry treated with either clozapine or olanzapine (P<0.05). In the replication analysis two SNPs rs3134701 (P = 0.043) and rs12662510 (P = 0.012) were nominally associated with AIWG. None of the SNPs in HCRTR1 were associated with AIWG.

CONCLUSION

This study provides preliminary evidence supporting the role of HCRTR2 in AIWG. However, these results need to be confirmed in large study samples.

Pharmacogenetics of clozapine response and induced weight gain: A comprehensive review and meta-analysis

Clozapine (CLZ) is the prototype atypical antipsychotic and it has many advantages over other antipsychotic drugs. Several data suggest that both CLZ response and induced weight gain are strongly determined by genetic variability. However, results remain mainly inconclusive. We aim to review the literature data about pharmacogenetics studies on CLZ efficacy, focusing on pharmacodynamic genes. Further, we performed meta-analyses on response when at least three studies for each polymorphism were available. Sensitivity analyses were conducted on Caucasian population when feasible. Electronic literature search was performed to identify pertinent studies published until May 2014 using PubMed, ISI Web of Knowledge and PsycINFO databases. For meta-analyses, data were entered and analyzed through RevMan version 5.2 using a random-effect model. Our literature search yielded 9266 articles on CLZ; among these, we identified 59 pertinent pharmacogenetic studies. Genotype data were retrieved for 14 polymorphisms in 9 genes. Among these, we had available data from at least three independent samples for 8 SNPs in 6 genes to perform meta-analyses: DRD2 rs1799732, DRD3 rs6280, HTR2A rs6313, rs6311, rs6314, HTR2C rs6318, HTR3A rs1062613, TNFa rs1800629. Although literature review provided conflicting results, in meta-analyses three genetic variants within serotonin genes resulted associated to CLZ response: rs6313 and rs6314 within HTR2A gene and rs1062613 within HT3A gene. On the other hand, no clear finding emerged for CLZ-induced weight gain. Our results suggest a possible serotonergic modulation of CLZ clinical response.

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.

Association Study of Serotonin 3 Receptor Subunit Gene Variants in Antipsychotic-Induced Weight Gain

BACKGROUND

Schizophrenia (SCZ) is a chronic severe neuropsychiatric disorder, where pharmacological treatment has been hindered by adverse effects, including antipsychotic-induced weight gain (AIWG) and related complications. Genetic studies have been exploring the appetite regulation and energy homeostasis pathways in AIWG with some promising leads. The serotonin system has been shown to participate in these pathways.

METHODS

In the current study, we examined single nucleotide polymorphisms across the serotonin receptor genes HTR3A and HTR3B. Prospective weight change was assessed for a total of 149 SCZ patients of European ancestry.

RESULTS

We did not find the tested HTR3A or HTR3B gene markers to be associated with AIWG in our sample.

CONCLUSION

Our preliminary findings suggest that these receptors may not play a major role in predicting AIWG.

Variation in Dopamine D2 and Serotonin 5-HT2A Receptor Genes is Associated with Working Memory Processing and Response to Treatment with Antipsychotics

Dopamine D2 and serotonin 5-HT2A receptors contribute to modulate prefrontal cortical physiology and response to treatment with antipsychotics in schizophrenia. Similarly, functional variation in the genes encoding these receptors is also associated with these phenotypes. In particular, the DRD2 rs1076560 T allele predicts a lower ratio of expression of D2 short/long isoforms, suboptimal working memory processing, and better response to antipsychotic treatment compared with the G allele. Furthermore, the HTR2A T allele is associated with lower 5-HT2A expression, impaired working memory processing, and poorer response to antipsychotics compared with the C allele. Here, we investigated in healthy subjects whether these functional polymorphisms have a combined effect on prefrontal cortical physiology and related cognitive behavior linked to schizophrenia as well as on response to treatment with second-generation antipsychotics in patients with schizophrenia. In a total sample of 620 healthy subjects, we found that subjects with the rs1076560 T and rs6314 T alleles have greater fMRI prefrontal activity during working memory. Similar results were obtained within the attentional domain. Also, the concomitant presence of the rs1076560 T/rs6314 T alleles also predicted lower behavioral accuracy during working memory. Moreover, we found that rs1076560 T carrier/rs6314 CC individuals had better responses to antipsychotic treatment in two independent samples of patients with schizophrenia (n=63 and n=54, respectively), consistent with the previously reported separate effects of these genotypes. These results indicate that DRD2 and HTR2A genetic variants together modulate physiological prefrontal efficiency during working memory and also modulate the response to antipsychotics. Therefore, these results suggest that further exploration is needed to better understand the clinical consequences of these genotype-phenotype relationships.

Emerging evidence of insulin-like growth factor 2 as a memory enhancer: a unique animal model of cognitive dysfunction with impaired adult neurogenesis

In the current aging society, cognitive dysfunction is one of the most serious issues that should be urgently resolved. It also affects a wide range of age groups harboring neurological and psychiatric disorders, such as Alzheimer's disease and schizophrenia. Although the molecular mechanism of memory impairment still remains to be determined, neuronal loss and dysfunction has been revealed to mainly attribute to its pathology. The discovery of neural stem cells in the adult brain that are proliferating and able to generate functional neurons has given rise to the idea that neuronal loss could be rescued by manipulating endogenous neural progenitor and stem cells. To this end, we must characterize them in detail and their developmental programming must be better understood. A growing body of evidence has indicated that insulin-like peptides are involved in learning and memory and maintenance of neural progenitor and stem cells, and clinical trials of insulin as a memory enhancer have begun. In contrast to the expectation of insulin and IGF1, the roles of IGF2 in cognitive ability have been poorly understood. However, recent evidence demonstrated in rodents suggests that IGF2 may play a pivotal role in adult neurogenesis and cognitive function. Here, we would like to review the rapidly growing world of IGF2 in cognitive neuroscience and introduce the evidence that its deficit is indeed involved in the impairment of the hippocampal neurogenesis and cognitive dysfunction in the model mouse of 22q11.2 deletion syndrome, which deletes Dgcr8, a critical gene for microRNA processing.

Indicators of response to clozapine treatment

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

Association study of GABAA α2 receptor subunit gene variants in antipsychotic-associated weight gain

Schizophrenia treatment has been hampered by undesirable adverse effects, including weight gain and associated complications. Recent candidate gene studies have been exploring the appetite regulation pathways in antipsychotic-associated weight gain (AAWG) with some promising leads. Genome-wide association studies of obesity have pointed to a number of potential candidate genes, such as MC4R, that were later found to be shared with AAWG. GABAA α2 receptor subunit (GABRA2) was another potential candidate gene for obesity from genome-wide association studies; however, it has not been explored in AAWG. We examined 9 single nucleotide polymorphisms across the GABRA2 gene. Prospective weight change was assessed for a total of 160 schizophrenia patients of European ancestry. The rs279858 marker was associated with percent weight change, with the patients homozygous for the TT genotype experiencing higher percentage weight gain on average than the C allele carriers (P = 0.009). When we performed the analysis considering each clinical site using a meta-analytic method, the results remained statistically significant (P = 1.4e-4). These findings became even more significant when we considered only patients taking clozapine or olanzapine, the 2 medications with higher risk for weight gain (P < 1e-10). GABRA2 genetic variants may play a role in predicting AAWG. However, replication in larger and independent samples is required.

Methylenetetrahydrofolate reductase gene variants and antipsychotic-induced weight gain and metabolic disturbances

Weight gain and metabolic disturbances represent serious side-effects in antipsychotic (AP) treatment, particularly with clozapine and olanzapine. The methylenetetrahydrofolate reductase (MTHFR) gene is a key determinant in the folate metabolism and previous studies reported a significant effect on AP-induced weight gain and related metabolic abnormalities. Thus, we investigated MTHFR gene variants and changes in several important metabolic parameters in AP-treated patients. In this study, two functional MTHFR polymorphisms, rs1801133 (C677T) and rs1801131 (A1298C), were investigated for changes in weight and metabolic parameters. Genotypic associations were evaluated in a large population (n = 347 including 66 first episode psychosis, FEP patients) treated mostly with clozapine and olanzapine. We did not detect any genotypic association with weight changes (p > 0.05) in our total sample and in the sample refined for ancestry and medication. In our allelic analyses, we observed a trend for the 677-C allele to be associated with weight gain in the total sample (p = 0.03). This effect appeared to be driven by the FEP patients where those carrying the C-allele gained, on average, twice as much weight. Exploratory analyses revealed a significant association between the C677T and the A1298C polymorphism with HDL cholesterol serum levels in patients (p = 0.031). Overall we did not detect a major effect of two functional MTHFR gene variants and AP-induced weight gain. However, our findings suggest an effect of the C677T polymorphism in FEP patients and changes in weight and cholesterol levels. Further investigations in a larger sample are required.

Pharmacogenetics in schizophrenia: a review of clozapine studies

OBJECTIVES

Clozapine is quite effective to treat schizophrenia, but its use is complicated by several factors. Although many patients respond to antipsychotic therapy, about 50% of them exhibit inadequate response, and ineffective medication trials may entail weeks of unremitted illness, potential adverse drug reactions, and treatment nonadherence. This review of the literature sought to describe the main pharmacogenetic studies of clozapine and the genes that potentially influence response to treatment with this medication in schizophrenics.

METHODS

We searched the PubMed database for studies published in English in the last 20 years using keywords related to the topic.

RESULTS AND CONCLUSIONS

Our search yielded 145 studies that met the search and selection criteria. Of these, 21 review articles were excluded. The 124 studies included for analysis showed controversial results. Therefore, efforts to identify key gene mechanisms that will be useful in predicting clozapine response and side effects have not been fully successful. Further studies with new analysis approaches and larger sample sizes are still required.

Investigation of melanocortin system gene variants in antipsychotic-induced weight gain

OBJECTIVES

The use of second-generation antipsychotic medications may result in substantial weight gain in a subset of schizophrenia patients. Distinct populations of neurons expressed in the hypothalamus, including the cocaine- and amphetamine-regulated transcript (CART), the polypeptide pro-opiomelanocortin (POMC) and the agouti-related protein (AGRP), have regulatory roles in weight control and energy homeostasis. Thus, we investigated the potential role of CART, POMC and AGRP genetic variants in antipsychotic-induced weight gain (AIWG).

METHODS

Five CART single nucleotide polymorphisms (SNPs) (rs10515115, rs3763153, rs3857384, rs11575893, rs16871471), three POMC SNPs (rs6713532, rs1047521, rs3754860) and one AGRP SNP (rs1338993), were genotyped in 218 patients treated with antipsychotics for chronic schizophrenia and evaluated for AIWG. We compared weight change (%) across genotypic groups using analysis of covariance.

RESULTS

None of the SNPs in POMC, CART, AGRP were significantly associated with AIWG in the refined samples stratified by ethnicity and medication treatment.

CONCLUSIONS

In this exploratory study, we observed that POMC, CART and AGRP gene variants are not a major contributor to AIWG. However larger samples are required to completely rule out their effect on AIWG.

Association of 5-HTR2A and 5-HTR2C serotonin receptor gene polymorphisms with depression risk in patients with coronary heart disease

Associations between 5-HTR2A -1438A/G and 5-HTR2C Cys23Ser polymorphisms and depression and its severity were studied in CHD patients with consideration for the trigger factors, pathogenetic characteristics of CHD, and personal anxiety. The study was carried out in 169 men aged 31-84 (59.0 ± 8.8) years with verified CHD. Depression was more severe (Hamilton score) if it was caused by manifestation or exacerbation of CHD (nosogenic factor) and in the presence of the painful syndrome caused by the cardiac disease, high personal anxiety, and presence of allele G polymorphism - 1438A/G in the genotype. The risk of medium-severe and severe depression in allele G carriers was 2.4-fold higher than in AA genotype carriers. The nosogenic factor modulated the association between allele G and severity of depression symptoms. The risk of medium-severe and severe depression was almost 4-fold higher in carriers of this allele in the presence of this factor.

PTSD and comorbid AUD: a review of pharmacological and alternative treatment options

BACKGROUND

Although posttraumatic stress disorder (PTSD) and alcohol use disorders (AUD) frequently co-occur there are no specific treatments for individuals diagnosed with these comorbid conditions. The main objectives of this paper are to review the literature on pharmacological options for PTSD and comorbid AUD, and to summarize promising behavioral and alternative interventions for those with these dual diagnoses.

METHODS

We conducted a comprehensive search on PsycINFO and MEDLINE/PubMed databases using Medical Subject Headings terms in various combinations to identify articles that used pharmacotherapy for individuals with dual diagnoses of PTSD and AUD. Similar strategies were used to identify articles on behavioral and alternative treatments for AUD and PTSD. We identified and reviewed six studies that tested pharmacological treatments for patients with PTSD and comorbid AUD.

RESULTS

The literature on treatment with US Food and Drug Administration approved medications for patients with dual diagnosis of PTSD and AUD is very limited and inconclusive. Promising evidence indicates that topiramate and prazosin may be effective in reducing PTSD and AUD symptoms in individuals with comorbidity. Seeking safety has had mixed efficacy in clinical trials. The efficacy of other behavioral and alternative treatments (mindfulness-based, yoga, and acupuncture) is more difficult to evaluate since the evidence comes from small, single studies without comparison groups.

CONCLUSION

There is a clear need for more systematic and rigorous study of pharmacological, behavioral, and alternative treatments for patients with dual diagnoses of PTSD and AUD.

Genes and schizophrenia: from a Festschrift Seminar honoring William T. Carpenter Jr, MD

Recent data have begun to elucidate the genetic architecture of schizophrenia, as well as provide new insights into the relationships of specific genetic factors across diagnostic boundaries, with specific symptom domains, and in the prediction of antipsychotic treatment response. Not surprisingly, work conducted at the Maryland Psychiatric Research Center (MPRC), led by Dr William Carpenter, has helped to guide the thinking behind much of this work, as well as contributed valuable data toward these efforts. In this article, I will briefly summarize some of the major findings emerging from these lines of research and highlight the role of the Dr Carpenter and his colleagues at the MPRC in this area.

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.

Role of ethnicity in antipsychotic-induced weight gain and tardive dyskinesia: genes or environment?

Aim: This study explored the role of self-reported ethnicity and genetic ancestry on antipsychotic (AP)-induced weight gain and tardive dyskinesia (TD) in schizophrenia. Patients & methods: Ethnicity was determined by self-report as well as Structure analysis of 190 SNPs selected from HapMap3, genotyped using a customized Illumina BeadChip. Age, gender, baseline weight and AP response using Brief Psychiatric Rating Scale were assessed. Multivariate regression models for AP-induced weight gain and TD, based on the Abnormal Involuntary Movement Scale were constructed. Results: African–American ethnicity (self-report, p = 0.021 and Structure analysis, p = 0.042) predicted AP-induced weight gain but not TD (self-report, p = 0.408 and Structure analysis, p = 0.714). Conclusion: Self-reported African–American ethnicity seemed to better predict AP-induced weight gain in schizophrenia compared with genetic ancestry, suggesting a possible role of environmental in addition to genetic factors. Future larger studies are needed to clarify specific gene–environment mechanisms mediating the effect of ethnicity on AP-induced weight gain.

Original submitted 1 January 2013; Revision submitted 17 June 2013

Scientific challenges and implementation barriers to translation of pharmacogenomics in clinical practice

The mapping of the human genome and subsequent advancements in genetic technology had provided clinicians and scientists an understanding of the genetic basis of altered drug pharmacokinetics and pharmacodynamics, as well as some examples of applying genomic data in clinical practice. This has raised the public expectation that predicting patients' responses to drug therapy is now possible in every therapeutic area, and personalized drug therapy would come sooner than later. However, debate continues among most stakeholders involved in drug development and clinical decision-making on whether pharmacogenomic biomarkers should be used in patient assessment, as well as when and in whom to use the biomarker-based diagnostic tests. Currently, most would agree that achieving the goal of personalized therapy remains years, if not decades, away. Realistic application of genomic findings and technologies in clinical practice and drug development require addressing multiple logistics and challenges that go beyond discovery of gene variants and/or completion of prospective controlled clinical trials. The goal of personalized medicine can only be achieved when all stakeholders in the field work together, with willingness to accept occasional paradigm change in their current approach.

The role of brain-derived neurotrophic factor (BDNF) gene variants in antipsychotic response and antipsychotic-induced weight gain

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has extensive effects on the nervous system including cell survival, differentiation, neuronal growth and maintenance, as well as cell death. Moreover, it promotes synaptic plasticity and interacts with dopaminergic and serotonergic neurons, suggesting an important role on the alteration of brain function with antipsychotic medications and induced weight gain in schizophrenia patients. The differential effects of BDNF gene variants could lead to changes in brain circuitry that would in turn cause variable response to antipsychotic medication. Therefore, we hypothesized that genetic variation in this candidate gene helps in explaining the inter-individual variation observed in antipsychotic drug treatment with respect to response and induced weight gain.

METHOD

We examined four single-nucleotide polymorphisms across the BDNF gene, including Val66Met (rs6265). Prospective BPRS change scores and weight change after six weeks were obtained from a total of 257 schizophrenia patients of European ancestry.

RESULTS

The markers rs11030104 and Val66Met were associated with antipsychotic response (P=0.04; 0.007, respectively). On the other hand, marker rs1519480 was associated with weight gain (P=0.04). Moreover, a two-marker haplotype across rs6265 and rs1519480 was associated with weight change (P=0.001). Results with Val66Met in response, and results with rs6265-rs1519480 haplotypes remained significant at the modified Bonferroni corrected alpha of 0.017.

CONCLUSION

BDNF genetic variants might play an important role in predicting antipsychotic response and antipsychotic-induced weight gain. However, replication in larger and independent samples is required.

Serotonin 2A Receptor Gene Polymorphism in Korean Children with Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

The purpose of this study was to investigate the association between the T102C polymorphism in the serotonin 2A receptor gene and attention-deficit/hyperactivity disorder (ADHD) in Korean patients.

METHODS

A total of 189 Korean children with ADHD as well as both parents of the ADHD children and 150 normal children participated in this study. DNA was extracted from blood samples from all of the subjects, and genotyping was conducted. Based on the allele and genotype information obtained, case-control analyses were performed to compare the ADHD and normal children, and Transmission disequilibrium tests (TDTs) were used for family-based association testing (number of trios=113). Finally, according to the significant finding which was showed in the case-control analyses, the results of behavioral characterastics and neuropsychological test were compared between ADHD children with and without the C allele.

RESULTS

In the case-control analyses, statistically significant differences were detected in the frequencies of genotypes containing the C allele (χ(2)=4.73, p=0.030). In the family-based association study, TDTs failed to detect linkage disequilibrium of the T102C polymorphism associated with ADHD children. In the ADHD children, both the mean reaction time and the standard deviation of the reaction time in the auditory continuous performance test were longer in the group with the C allele compared to the group without the C allele.

CONCLUSION

The results of this study suggest that there is a significant genetic association between the T102C polymorphism in the serotonin 2A receptor gene and ADHD in Korean children.

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

Pharmacogenetic studies have demonstrated significant associations between several candidate genes (DRD2, DRD3, 5HTR2A and 5HTR2C, COMT and MTHFR) and antipsychotic drug response. The present study investigates the effect of nine polymorphisms in these genes for an association with antipsychotic treatment response. 329 Caucasian patients with a non-affective psychotic disorder using antipsychotics were included. All patients participated in the longitudinal GROUP-study in The Netherlands. We genotyped 9 SNPs in 6 candidate genes (DRD2: TaqI_A, -141C; DRD3: Ser9Gly; HTR2A: 102-T/C, His452Tyr; HTR2C: Cys23Ser; COMT: Val158Met; MTHFR: 677-C/T) using standard protocols. Polymorphisms were based on previous studies showing associations with positive symptoms treatment response. The Clinical Global Impression - Improvement (CGI-I) scale was used to assess improvement in positive psychotic symptoms since the start of current antipsychotic treatment. Ordinal regression was used for association analyses. Ninety percent of the patients used second generation antipsychotics, with olanzapine (28%) and risperidone (29%) being the most prescribed drugs. Ser9Gly of the dopamine D3 receptor gene (P value 0.034) and 677-C/T of MTHFR (P value 0.019) were tested statistically significant. Gly-carriers and T-carriers, respectively, showed more clinical improvement on the CGI-I. The other polymorphisms did not show a statistically significant association (P values>0.10). In conclusion, we replicated two out of nine of the previously reported associations between polymorphisms and treatment response. The direction and magnitude of the associations presented here in DRD3 (Ser9Gly) and MTHFR (677-C/T) are in line with previous association studies in Caucasian patients. These polymorphisms may be of value for predicting clinical response.

Association study of 27 annotated genes for clozapine pharmacogenetics: validation of preexisting studies and identification of a new candidate gene, ABCB1, for treatment response

OBJECTIVE

Pharmacogenetic studies on clozapine (CLZ) have provided meaningful insights but have shown redundancies owing to wide interindividual variability and insufficient replication. The present study was designed to validate hitherto suggested candidate genes on CLZ pharmacokinetics and pharmacodynamics and explore new markers through an integrative study.

METHODS

Based on a literature review, a total of 127 variations in 27 candidate genes were selected and analyzed. Ninety-six schizophrenic patients of Korean ethnicity with constant CLZ dosing were recruited, and information on body weight and smoking habits was gathered, as well as plasma drug levels and treatment responses.

RESULTS

Among the pharmacokinetic-related single nucleotide polymorphisms, rs2069521 and rs2069522 in CYP1A2 for CLZ/(dose/weight) and norclozapine/(dose/weight) and rs1135840 in CYP2D6 for norclozapine/CLZ showed borderline associations that were insignificant after correction for multiple testing. Regarding treatment response, significant associations were exhibited in rs7787082 and rs10248420 of ABCB1 (P = 0.0005 and P = 0.0013, respectively) even after correction, and the rs7787082 G and rs10248420 A alleles in ABCB1 were more frequently observed in nonresponders. We also observed a trend in the associations of rs13064530 in HRH1 and rs4938013 in DRD2/ANKK1 with treatment response.

CONCLUSIONS

We could not convincingly replicate most of the previous studies, a result that is possibly due to modest association between the suggested genes. Rather, we found a new candidate gene, ABCB1, for treatment response, which may provide a hypothesis on the relationship between the blood-brain distribution of CLZ and its clinical efficacy.

Association study between variants of AMP-activated protein kinase catalytic and regulatory subunit genes with antipsychotic-induced weight gain

Weight gain and metabolic syndrome are the most common deleterious side effects following treatment with second generation antipsychotic drugs such as clozapine and olanzapine. However, the mechanisms underlying these negative effects of second generation antipsychotic drugs are not fully understood. In this study we investigate whether variants in the genes coding for the α-catalytic (PRKAA1, PRAKAA2) and the β regulatory subunits (PRKAB1 and PRKAB2) of the cellular energy sensor AMP-activated protein kinase (AMPK) are associated with antipsychotic-induced weight gain. To accomplish this, ten polymorphisms in 208 schizophrenia or schizoaffective disorder patients treated with clozapine, haloperidol, risperidone or olanzapine for up to 14 weeks were analyzed. Significant association was observed between rs3766522 in PRKAB2 (AA vs. AT + TT; p = 0.022) and rs10789038 in PRKAA2 (GG + GA vs. AA, p = 0.023) with weight change (%) in patients of European ancestry following treatment with clozapine or olanzapine. Allelic association of the T-allele of rs3766522 (p = 0.019) and the G-allele of rs10789038 (p = 0.041) with weight change (%) was also observed. Analysis of raw weight gain revealed that carriers of the T-allele of rs3766522 (AT + TT, 4.3 kg ± 3.7) gained more weight than the AA-genotype carriers (2.5 kg ± 4.5, p = 0.042). Similarly, carriers of the G-allele of rs10789038 (GG + GA, 4.2 kg ± 4.5) gained more weight than AA-homozygotes (1.5 kg ± 2.9, p = 0.014) under antipsychotic treatment. In conclusion, we observed significant associations between polymorphisms in AMPK subunit genes and weight gain induced by clozapine and olanzapine.

Genetic association study between antipsychotic-induced weight gain and the melanocortin-4 receptor gene

Antipsychotic-induced weight gain (AIWG) may result in the metabolic syndrome in schizophrenia (SCZ) patients. Downstream variants of the melanocortin-4 receptor (MC4R) gene have been associated with obesity in various populations. Thus, we examined single-nucleotide polymorphisms (SNPs) in the MC4R region for association with AIWG in SCZ patients. Four SNPs (rs2229616, rs17782313, rs11872992 and rs8087522) were genotyped in 224 patients who underwent treatment for SCZ and were evaluated for AIWG for up to 14 weeks. We compared weight change (%) across genotypic groups using analysis of covariance for three SNPs (r²≤0.8). European-ancestry patients who were rs8087522 A-allele carriers (AG+AA) on clozapine gained significantly more weight than non-carriers (P=0.027, n=69). These observations were marginal after correction for multiple testing. We performed in vitro electrophoretic mobility-shift assay that suggested that the presence of the A-allele may create a transcription factor-binding site. Further investigation is warranted for both these exploratory findings.

Polymorphisms of the 5-HT2A receptor gene and clinical response to olanzapine in paranoid schizophrenia

BACKGROUND

5-HT2A receptor is strongly implicated in the mode of action of atypical antipsychotic drugs. The aim of the study was to investigate whether the 5-HT2A receptor gene's polymorphisms (His452Tyr and T102C) have an influence on the response to olanzapine in patients with schizophrenia.

METHODS

We studied 99 Caucasian schizophrenia patients treated with olanzapine. Psychopathology was measured before and after 6 weeks of treatment. Clinical improvement was quantified as change in Positive and Negative Syndrome Scale (PANSS) total scores and subscores as shown by percentage improvement below the baseline score. The clinical response to antipsychotic treatment was defined as 30% improvement from baseline in PANSS scores.

RESULTS

The His/Tyr polymorphism was significantly associated with a percentage improvement in PANSS positive symptom subscore (better response in His/His homozygotes; p<0.05) after treatment with olanzapine. As for the T102C polymorphism, a better response in terms of PANSS positive subscore improvement was observed for C/C homozygotes (p<0.01). A significant association of 5-HT2A genotype distribution of the T102C polymorphism with a categorical measure of response, but only in terms of PANSS positive symptom subscores, was observed (p<0.01).

CONCLUSIONS

Variations in the 5-HT2A receptor gene may influence individual and particularly positive symptom response to olanzapine.