-759 C/T polymorphism of 5-HT2C receptor gene and early phase weight gain associated with antipsychotic drug treatment

Identification of four novel loci associated with psychotropic drug-induced weight gain in a Swiss psychiatric longitudinal study: A GWAS analysis

Patients suffering from mental disorders are at high risk of developing cardiovascular diseases, leading to a reduction in life expectancy. Genetic variants can display greater influence on cardiometabolic features in psychiatric cohorts compared to the general population. The difference is possibly due to an intricate interaction between the mental disorder or the medications used to treat it and metabolic regulations. Previous genome wide association studies (GWAS) on antipsychotic-induced weight gain included a low number of participants and/or were restricted to patients taking one specific antipsychotic. We conducted a GWAS of the evolution of body mass index (BMI) during early (i.e., ≤ 6) months of treatment with psychotropic medications inducing metabolic disturbances (i.e., antipsychotics, mood stabilizers and some antidepressants) in 1135 patients from the PsyMetab cohort. Six highly correlated BMI phenotypes (i.e., BMI change and BMI slope after distinct durations of psychotropic treatment) were considered in the analyses. Our results showed that four novel loci were associated with altered BMI upon treatment at genome-wide significance (p < 5 × 10-8): rs7736552 (near MAN2A1), rs11074029 (in SLCO3A1), rs117496040 (near DEFB1) and rs7647863 (in IQSEC1). Associations between the four loci and alternative BMI-change phenotypes showed consistent effects. Replication analyses in 1622 UK Biobank participants under psychotropic treatment showed a consistent association between rs7736552 and BMI slope (p = 0.017). These findings provide new insights into metabolic side effects induced by psychotropic drugs and underline the need for future studies to replicate these associations in larger cohorts.

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.

Effect of 5-HT2C receptor gene polymorphism (HTR2C-759C/T) on metabolic adverse effects in Thai psychiatric patients treated with risperidone

BACKGROUND

The use of Atypical antipsychotics (AAPs) is related to metabolic disturbances, which put psychiatric patients at risk for cardiovascular morbidity and mortality. Evidence is emerging of genetic risk factors. The HTR2C gene is an essential candidate in pharmacogenetic studies of antipsychotic-induced metabolic effects. Nevertheless, there were inconsistent results among studies.

OBJECTIVE

To investigate the relationship between -759C/T, functional polymorphism of the HTR2C gene and metabolic adverse effects in Thai psychiatric patients treated with risperidone monotherapy.

METHOD

In this cross-sectional study, 108 psychiatric patients treated with risperidone monotherapy for ≥3 months were recruited. Anthropometric measurements and laboratory tests were obtained upon enrollment and history of treatment was reviewed from medical records. Weight gain was defined as an increase ≥7% of baseline weight. Metabolic syndrome was evaluated according to the 2005 International Diabetes Federation (IDF) Asia criteria. The -759C/T, polymorphism was genotyped. The associations between -759C/T polymorphism and metabolic side effects were analyzed. Multiple logistic regression was used for determining potential confounders.

RESULTS

Neither weight gain nor metabolic syndrome was significantly associated with -759C/T allelic and genotype variants of HTR2C. However, T allele of -759C/T polymorphism significantly associated with the hypertension. This association was not affected by possible confounding factors such as gender, risperidone dose, duration of treatment and family history of hypertension.

CONCLUSION

Our findings suggest that psychiatric patients with T allele of -759C/T polymorphism may be at higher risk for hypertension. Further study with prospective design with larger patient groups are needed.

The Burden of Antipsychotic-Induced Weight Gain and Metabolic Syndrome in Children

Antipsychotic medications are critical to child and adolescent psychiatry, from the stabilization of psychotic disorders like schizophrenia, bipolar disorder, and psychotic depression to behavioral treatment of autism spectrum disorder, tic disorders, and pediatric aggression. While effective, these medications carry serious risk of adverse events-most commonly, weight gain and cardiometabolic abnormalities. Negative metabolic consequences affect up to 60% of patients and present a major obstacle to long-term treatment. Since antipsychotics are often chronically prescribed beginning in childhood, cardiometabolic risk accumulates. An increased susceptibility to antipsychotic-induced weight gain (AIWG) has been repeatedly documented in children, particularly rapid weight gain. Associated cardiometabolic abnormalities include central obesity, insulin resistance, dyslipidemia, and systemic inflammation. Lifestyle interventions and medications such as metformin have been proposed to reduce risk but remain limited in efficacy. Furthermore, antipsychotic medications touted to be weight-neutral in adults can cause substantial weight gain in children. A better understanding of the biological underpinnings of AIWG could inform targeted and potentially more fruitful treatments; however, little is known about the underlying mechanism. As yet, modest genetic studies have nominated a few risk genes that explain only a small percentage of the risk. Recent investigations have begun to explore novel potential mechanisms of AIWG, including a role for gut microbiota and microbial metabolites. This article reviews the problem of AIWG and AP metabolic side effects in pediatric populations, proposed mechanisms underlying this serious side effect, and strategies to mitigate adverse impact. We suggest future directions for research efforts that may advance the field and lead to improved clinical interventions.

Association of the HTR2C-759C/T polymorphism and antipsychotic-induced weight gain: a meta-analysis

Background

Antipsychotic-induced weight gain (AIWG) is a crucial factor for the medication cessation of patients with schizophrenia. Multiple studies have shown that the functional polymorphism -759 C/T (rs3813929) in the HTR2C promoter region could possibly be correlated with AIWG.

Aim

To evaluate the genetic association of the HTR2C-759C/T polymorphism and AIWG in patients with schizophrenia with antipsychotic drugs (APDs) administration.

Methods

Eligible studies were identified by searching the following databases: PubMed, Embase, Web of Science, China Nation Knowledge Infrastructure (CNKI), VIP, Wanfang Data, Chinese Biomedical Literature Database (CBM) and the Airiti Library. The quality of studies was evaluated based on the Newcastle-Ottawa Scale. The pooled OR and 95% CI were calculated for the dominant (CT/TT/T vs CC/C) mode, and subgroup analyses were performed based on ethnicity, antipsychotic medication and gender; all statistical analyses were performed using the statistical software STATA V.12.0.

Result

A total of 17 studies with 3170 patients with schizophrenia were included in our meta-analysis. The result of the meta-analysis has shown that the association between the -759 C/T polymorphism and AIWG is statistically significant (OR 0.34, 95% CI: 0.20 to 0.57, z=4.11, p<0.001). The subgroup analyses revealed significant correlations between the -759 C/T polymorphism and AIWG in the Caucasian population (OR 0.33, 95% CI: 0.14 to 0.77, z=2.55, p=0.011), the Asian population (OR 0.31, 95% CI: 0.18 to 0.52, z=4.46, p<0.001), the patients with APDs administration (CT/TT/T vs CC/C: OR 0.63, 95% CI: 0.40 to 1.00, z=1.97, p=0.049) and the patients with atypical antipsychotic drug administration (CT/TT/T vs CC/C: OR 0.21, 95% CI: 0.09 to 0.47, z=3.83, p<0.001). The sensitivity analysis showed that the results were stable. Begg’s test (after correction z=1.07, p=0.287) and Egger’s test (t=−2.41, p=0.029) show that the included articles have no significant publication bias.

Conclusion

There is a significant genetic association between HTR2C-759C/T and AIWG, and patients with T allele are less likely to have AIWG.

Progress in Genetic Polymorphisms Related to Lipid Disturbances Induced by Atypical Antipsychotic Drugs

Metabolic side effects such as weight gain and disturbed lipid metabolism are often observed in the treatment of atypical antipsychotic drugs (AAPDs), which contribute to an excessive prevalence of metabolic syndrome among schizophrenic patients. Great individual differences are observed but the underlying mechanisms are still uncertain. Research on pharmacogenomics indicates that gene polymorphisms involved in the pathways controlling food intake and lipid metabolism may play a significant role. In this review, relevant genes (HTR2C, DRD2, LEP, NPY, MC4R, BDNF, MC4R, CNR1, INSIG2, ADRA2A) and genetic polymorphisms related to metabolic side effects of AAPDs especially dyslipidemia were summarized. Apart from clinical studies, in vitro and in vivo evidence is also analyzed to support related theories. The association of central and peripheral mechanisms is emphasized, enabling the possibility of using peripheral gene expression to predict the central status. Novel methodological development of pharmacogenomics is in urgent need, so as to provide references for individualized medication and further to shed some light on the mechanisms underlying AAPD-induced lipid disturbances.

Psychotropic drug-induced genetic-epigenetic modulation of CRTC1 gene is associated with early weight gain in a prospective study of psychiatric patients

BACKGROUND

Metabolic side effects induced by psychotropic drugs represent a major health issue in psychiatry. CREB-regulated transcription coactivator 1 (CRTC1) gene plays a major role in the regulation of energy homeostasis and epigenetic mechanisms may explain its association with obesity features previously described in psychiatric patients. This prospective study included 78 patients receiving psychotropic drugs that induce metabolic disturbances, with weight and other metabolic parameters monitored regularly. Methylation levels in 76 CRTC1 probes were assessed before and after 1 month of psychotropic treatment in blood samples.

RESULTS

Significant methylation changes were observed in three CRTC1 CpG sites (i.e., cg07015183, cg12034943, and cg 17006757) in patients with early and important weight gain (i.e., equal or higher than 5% after 1 month; FDR p value = 0.02). Multivariable models showed that methylation decrease in cg12034943 was more important in patients with early weight gain (≥ 5%) than in those who did not gain weight (p = 0.01). Further analyses combining genetic and methylation data showed that cg12034943 was significantly associated with early weight gain in patients carrying the G allele of rs4808844A>G (p = 0.03), a SNP associated with this methylation site (p = 0.03).

CONCLUSIONS

These findings give new insights on psychotropic-induced weight gain and underline the need of future larger prospective epigenetic studies to better understand the complex pathways involved in psychotropic-induced metabolic side effects.

Pharmacogenomics in Asia: a systematic review on current trends and novel discoveries

While early pharmacogenomic studies have primarily been carried out in Western populations, there has been a notable increase in the number of Asian studies over the past decade. We systematically reviewed all pharmacogenomic studies conducted in Asia published before 2016 to highlight trends and identify research gaps in Asia. We observed that pharmacogenomic research in Asia was dominated by larger developed countries, notably Japan and Korea, and mainly driven by local researchers. Studies were focused on drugs acting on the CNS, chemotherapeutics and anticoagulants. Significantly, several novel pharmacogenomic associations have emerged from Asian studies. These developments are highly encouraging for the strength of regional scientific and clinical community and propound the importance of discovery studies in different populations.

Pharmacogenetic Associations of Antipsychotic Drug-Related Weight Gain: A Systematic Review and Meta-analysis

Although weight gain is a serious but variable adverse effect of antipsychotics that has genetic underpinnings, a comprehensive meta-analysis of pharmacogenetics of antipsychotic-related weight gain is missing. In this review, random effects meta-analyses were conducted for dominant and recessive models on associations of specific single nucleotide polymorphisms (SNP) with prospectively assessed antipsychotic-related weight or body mass index (BMI) changes (primary outcome), or categorical increases in weight or BMI (≥7%; secondary outcome). Published studies, identified via systematic database search (last search: December 31, 2014), plus 3 additional cohorts, including 222 antipsychotic-naïve youth, and 81 and 141 first-episode schizophrenia adults, each with patient-level data at 3 or 4 months treatment, were meta-analyzed. Altogether, 72 articles reporting on 46 non-duplicated samples (n = 6700, mean follow-up = 25.1wk) with 38 SNPs from 20 genes/genomic regions were meta-analyzed (for each meta-analysis, studies = 2-20, n = 81-2082). Eleven SNPs from 8 genes were significantly associated with weight or BMI change, and 4 SNPs from 2 genes were significantly associated with categorical weight or BMI increase. Combined, 13 SNPs from 9 genes (Adrenoceptor Alpha-2A [ADRA2A], Adrenoceptor Beta 3 [ADRB3], Brain-Derived Neurotrophic Factor [BDNF], Dopamine Receptor D2 [DRD2], Guanine Nucleotide Binding Protein [GNB3], 5-Hydroxytryptamine (Serotonin) Receptor 2C [HTR2C], Insulin-induced gene 2 [INSIG2], Melanocortin-4 Receptor [MC4R], and Synaptosomal-associated protein, 25kDa [SNAP25]) were significantly associated with antipsychotic-related weight gain (P-values < .05-.001). SNPs in ADRA2A, DRD2, HTR2C, and MC4R had the largest effect sizes (Hedges' g's = 0.30-0.80, ORs = 1.47-1.96). Less prior antipsychotic exposure (pediatric or first episode patients) and short follow-up (1-2 mo) were associated with larger effect sizes. Individual antipsychotics did not significantly moderate effect sizes. In conclusion, antipsychotic-related weight gain is polygenic and associated with specific genetic variants, especially in genes coding for antipsychotic pharmacodynamic targets.

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.

Pharmacogenetics of second-generation antipsychotics

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

HTR2C polymorphisms, olanzapine-induced weight gain and antipsychotic-induced metabolic syndrome in schizophrenia patients: a meta-analysis

OBJECTIVE

To conduct meta-analyses of all published association studies on the HTR2C -759C/T (rs3813829) polymorphism and olanzapine-induced weight gain in schizophrenia patients and on the HTR2C -759C/T, -697G/C (rs518147) and rs1414334:C> G polymorphisms and olanzapine/clozapine/risperidone-induced metabolic syndrome in schizophrenia patients.

METHODS

Eligible studies were identified by searching PubMed and Web of Science databases. Meta-analyses were performed using Cochrane Review Manager (RevMan, version 5.2) to calculate the pooled odds ratio (OR) and its corresponding 95% confidence interval (CI).

RESULTS

Our meta-analyses revealed both a significant positive association between the rs1414334 C allele and olanzapine/clozapine/risperidone-induced metabolic syndrome and a marginally significant positive association between the -697C allele and the induced metabolic syndrome in schizophrenia patients, but no significant association between the -759C/T polymorphism and the induced metabolic syndrome in schizophrenia patients. Our analysis further revealed a pronounced trend toward a significant negative association between the -759T allele and high olanzapine-induced weight gain and a trend toward a significant positive association between the -759C allele and high olanzapine-induced weight gain in Caucasian schizophrenia patients.

CONCLUSIONS

Our results support that HTR2C polymorphisms play a role in antipsychotic-induced metabolic disturbance. More association studies are needed to further elucidate association of different HTR2C polymorphisms and antipsychotic-induced metabolic disturbance.

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.

Clinical validity of cytochrome P450 metabolism and serotonin gene variants in psychiatric pharmacotherapy

Adverse events, response failures and medication non-compliance are common in patients receiving medications for the treatment of mental illnesses. A systematic literature review assessed whether pharmacokinetic (PK) or pharmacodynamic (PD) responses to 26 commonly prescribed antipsychotic and antidepressant medications, including efficacy or side effects, are associated with nucleotide polymorphisms in eight commonly studied genes in psychiatric pharmacotherapy: CYP2D6, CYP2C19, CYP2C9, CYP1A2, CYP3A4, HTR2C, HTR2A, and SLC6A4. Of the 294 publications included in this review, 168 (57%) showed significant associations between gene variants and PK or PD outcomes. Other studies that showed no association often had insufficient control for confounding variables, such as co-medication use, or analysis of medications not substrates of the target gene. The strongest gene-outcome associations were for the PK profiles of CYP2C19 and CYP2D6 (93% and 90%, respectively), for the PD associations between HTR2C and weight gain (57%), and for SLC6A4 and clinical response (54%), with stronger SLC6A4 response associations for specific drug classes (60-83%). The preponderance of evidence supports the validity of analyzing nucleotide polymorphisms in CYP and pharmacodynamic genes to predict the metabolism, safety, or therapeutic efficacy of psychotropic medications commonly used for the treatment of depression, schizophrenia, and bipolar illness.

Determinants of physical health parameters in individuals with intellectual disability who use long-term antipsychotics

Individuals with intellectual disability frequently use antipsychotics for many years. This may have detrimental health effects, including neurological symptoms and metabolic and hormonal dysregulation, the latter possibly affecting bone metabolism. There is large variability in the degree in which antipsychotic agents lead to these health problems. In the current study we investigated potential determinants of physical symptoms and biological parameters known to be associated with use of antipsychotics in a convenience sample of 99 individuals with intellectual disability who had used antipsychotics for more than one year for behavioural symptoms. We focused on extrapyramidal symptoms; on overweight and presence of components of the metabolic syndrome; and on elevated plasma prolactin and bone turnover parameters. As predictor variables, we used patient (sex, age, genetic polymorphisms, and severity of intellectual disability) and medication use (type and dosage) characteristics. We found extrapyramidal symptoms to be present in 53%, overweight or obesity in 46%, and the metabolic syndrome in 11% of participants. Hyperprolactineaemia and one or more elevated bone turnover markers were present in 17% and 25%, respectively. Higher age and more severe intellectual disability were associated with dyskinesia and a higher dosage of the antipsychotic drug was associated with parkinsonism. Less severe intellectual disability was related to higher Body Mass Index. Use of atypical antipsychotics was associated with higher diastolic blood pressure and elevated fasting glucose. Clinicians who prescribe antipsychotics in individuals with intellectual disability should carefully balance the potential benefits of prolonged treatment against the risk of health hazards associated with the use of antipsychotics.

Effects of controlled discontinuation of long-term used antipsychotics on weight and metabolic parameters in individuals with intellectual disability

Antipsychotics are frequently prescribed agents in individuals with intellectual disability, often for behavioral symptoms. Efficacy of antipsychotics for this is ambiguous, so discontinuation should be considered. Weight gain and metabolic dysregulation are well-known adverse effects of antipsychotics which increase the risk of the metabolic syndrome. We performed a discontinuation study in 99 adults with intellectual disability, living in residential facilities who used antipsychotics for behavioral symptoms for more than 1 year. The aim of the present study was to investigate the effects of discontinuation of long-term used antipsychotics on weight, body mass index (BMI), and parameters of the metabolic syndrome and to investigate the influence of genetic polymorphisms and medication factors on these outcomes. Discontinuation of antipsychotics led to a mean decrease of 4 cm waist circumference, of 3.5 kg weight, 1.4 kg/m2 BMI, and 7.1 mm Hg systolic blood pressure. In those participants who had not completely discontinued use of antipsychotics we found a decrease in weight and BMI and an increase in fasting glucose. The presence of the C-allele of serotonin 5-hydroxytryptamine receptor polymorphism rs141334 was associated with higher waist circumference and higher plasma levels of triglycerides and lower levels of high-density lipoprotein. Achievement of complete discontinuation predicted a larger decrease in waist circumference and BMI. In conclusion, results of the study show the beneficial effects of discontinuation of long-term used antipsychotics on metabolic outcomes.

759C/T Variants of the Serotonin (5-HT2C) Receptor Gene and Weight Gain in Children and Adolescents in Long-Term Risperidone Treatment

BACKGROUND

Great inter-individual variability exists in the susceptibility to gain weight during antipsychotic treatment. Thus, we examined whether the -759C/T variants in the promoter region of the 5HT2C receptor gene were differentially associated with weight gain in children and adolescents in long-term risperidone treatment.

METHODS

Medically healthy 7 to 17 year-olds, treated with risperidone for ≥ six months, were enrolled. Anthropometric measurements, laboratory tests, and treatment history were obtained upon enrollment and from medical records. The effect of the genotype on the trajectory of age-sex-adjusted weight and body mass index (BMI) z scores before and after the onset of risperidone treatment was investigated.

RESULTS

In 124 subjects (90% males, mean age: 11.8 years) treated with risperidone for a mean of 2.8 years, weight and BMI z scores significantly increased after starting risperidone. This change was similar across the two genotype groups as were changes in several cardiometabolic variables.

CONCLUSION

In contrast to other reports, the T allele failed to confer protection against excessive weight gain or cardiometabolic abnormalities in this group of children and adolescents chronically treated with risperidone.

Personalized medicine in psychiatry: problems and promises

The central theme of personalized medicine is the premise that an individual's unique physiologic characteristics play a significant role in both disease vulnerability and in response to specific therapies. The major goals of personalized medicine are therefore to predict an individual's susceptibility to developing an illness, achieve accurate diagnosis, and optimize the most efficient and favorable response to treatment. The goal of achieving personalized medicine in psychiatry is a laudable one, because its attainment should be associated with a marked reduction in morbidity and mortality. In this review, we summarize an illustrative selection of studies that are laying the foundation towards personalizing medicine in major depressive disorder, bipolar disorder, and schizophrenia. In addition, we present emerging applications that are likely to advance personalized medicine in psychiatry, with an emphasis on novel biomarkers and neuroimaging.

Genetic variations in the serotoninergic system contribute to body-mass index in Chinese adolescents

OBJECTIVE

Obesity has become a worldwide health problem in the past decades. Human and animal studies have implicated serotonin in appetite regulation, and behavior genetic studies have shown that body mass index (BMI) has a strong genetic component. However, the roles of genes related to the serotoninergic (5-hydroxytryptamine,5-HT) system in obesity/BMI are not well understood, especially in Chinese subjects.

SUBJECTS AND DESIGN

With a sample of 478 healthy Chinese volunteers, this study investigated the relation between BMI and genetic variations of the serotoninergic system as characterized by 136 representative polymorphisms. We used a system-level approach to identify SNPs associated with BMI, then estimated their overall contribution to BMI by multiple regression and verified it by permutation.

RESULTS

We identified 12 SNPs that made statistically significant contributions to BMI. After controlling for gender and age, four of these SNPs accounted for 7.7% additional variance of BMI. Permutation analysis showed that the probability of obtaining these findings by chance was low (p = 0.015, permuted for 1000 times).

CONCLUSION

These results showed that genetic variations in the serotoninergic system made a moderate contribution to individual differences in BMI among a healthy Chinese sample, suggesting that a similar approach can be used to study obesity.

Pharmacogenetics of antipsychotics: recent progress and methodological issues

INTRODUCTION

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

This article reviews the recent progress in pharmacogenetic research of antipsychotic drugs since 2010, focusing on two areas: antipsychotic-induced weight gain and clozapine-induced agranulocytosis. The article also provides discussion on the important methodological issues in this area of research. The specific aim of this article is to provide the reader with up-to-date evidence in pharmacogenetic research, and for them to gain familiarity to the issues and challenges facing the field.

EXPERT OPINION

Pharmacogenetic studies of antipsychotic drugs are promising despite many challenges. Recent advances as reviewed in this article push the field closer to routine clinical utilization of pharmacogenetic testing. Progress in genomic technology and bioinformatics, larger sample sizes, better phenotype characterization, and careful consideration of study design issues will help to elevate antipsychotic pharmacogenetics to its next level.

Pharmacogenetics of antipsychotic-induced weight gain: review and clinical implications

Second-generation antipsychotics (SGAs), such as risperidone, clozapine and olanzapine, are the most common drug treatments for schizophrenia. SGAs presented an advantage over first-generation antipsychotics (FGAs), particularly regarding avoidance of extrapyramidal symptoms. However, most SGAs, and to a lesser degree FGAs, are linked to substantial weight gain. This substantial weight gain is a leading factor in patient non-compliance and poses significant risk of diabetes, lipid abnormalities (that is, metabolic syndrome) and cardiovascular events including sudden death. The purpose of this article is to review the advances made in the field of pharmacogenetics of antipsychotic-induced weight gain (AIWG). We included all published association studies in AIWG from December 2006 to date using the Medline and ISI web of knowledge databases. There has been considerable progress reaffirming previous findings and discovery of novel genetic factors. The HTR2C and leptin genes are among the most promising, and new evidence suggests that the DRD2, TNF, SNAP-25 and MC4R genes are also prominent risk factors. Further promising findings have been reported in novel susceptibility genes, such as CNR1, MDR1, ADRA1A and INSIG2. More research is required before genetically informed, personalized medicine can be applied to antipsychotic treatment; nevertheless, inroads have been made towards assessing genetic liability and plausible clinical application.

Atypical antipsychotic-induced weight gain: insights into mechanisms of action

Prescriptions for second-generation antipsychotics (SGAs) have surpassed those for first-generation agents in the treatment of schizophrenia and bipolar disorder. While SGAs have the benefit of a much reduced risk of causing movement disorders, they have been associated with weight gain and metabolic effects. These adverse reactions are not uncommon, and threaten to have a significant impact on the patient's health over the long-term treatment that the patient requires. Currently, the aetiology of these effects is not known. This article reviews the data exploring the weight gain phenomenon. The literature was reviewed from searches of PubMed and the references of major articles in the field. The SGAs present a heterogeneous risk for weight gain. In addition, different individuals receiving the same drug can exhibit substantially different weight changes. This pattern suggests that a group of factors are associated with the weight gain phenomenon rather than a single mechanism. Coupled with the genetic profile that the patient brings to the treatment, the risk for SGA-induced weight gain will be different for different drugs and different individuals. Targets for exploration of the weight gain phenomenon include receptor interactions involving serotonin, histamine, dopamine, adrenergic, cannabinoid and muscarinic receptors. The association of SGA-induced weight gain and the role of orexigenic and anorexigenic peptides are reviewed. Also, a brief discussion of genetic factors associated with SGA-induced weight gain is presented, including that of the serotonin 5-HT(2C) receptor gene (HTR2C) and the cannabinoid 1 receptor gene (CNR1). The most promising data associated with SGA-induced weight gain include investigations of the histamine H(1), 5-HT(2A), 5-HT(2C), muscarinic M(3) and adrenergic receptors. In addition, work in the genetic area promises to result in a better understanding of the variation in risk associated with different individuals.

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).

Role of 5-HT(2C) receptor gene variants in antipsychotic-induced weight gain

Antipsychotic-induced weight gain is a serious side effect of antipsychotic medication that can lead to increased morbidity, mortality, and non-compliance in patients. Numerous single nucleotide polymorphisms have been studied for association with antipsychotic-induced weight gain in an attempt to find genetic predictors of this side effect. An ability to predict this side effect could lead to personalized treatment plans for predisposed individuals, which could significantly decrease the prevalence and severity of weight gain. Variations in the serotonin receptor 2c gene (HTR2C) have emerged as promising candidates for prediction of antipsychotic-induced weight gain. Specifically, the well-studied −759C/T promoter polymorphism has been associated with weight gain in diverse populations, although some studies have reported no association. This discrepancy is likely due to heterogeneity in study design with respect to ethnicity, treatment duration, and other variables. Notably, the association between HTR2C and antipsychotic-induced weight gain appears strongest in short-term studies on patients with limited or no previous antipsychotic treatment. Other, less extensively studied promoter polymorphisms (−697C/G, −997G/A, and −1165A/G) have also emerged as potential predictors of antipsychotic-induced weight gain. Conversely, the well-studied intronic polymorphism Cys23Ser does not appear to be associated. With further research on both HTR2C and other genetic and environmental predictors of antipsychotic-induced weight gain, a predictive test could one day be created to screen patients and provide preventative or alternative treatment for those who are predisposed to this serious side effect.

Pharmacogenetic testing to predict antipsychotic-induced weight gain: a systematic review

Weight gain is an important side effect of antipsychotic drugs. Since the high interindividual difference in weight gain suggests that genetic factors play a role in this weight gain, studies have tried to identify these factors. Most of these studies were carried out in the past few years and focussed largely on receptor polymorphisms, although some tried to explain the variation in weight gain by differences in pharmacokinetics. Unfortunately, the results of these association studies are often conflicting, which makes it hard to apply this genetic knowledge in daily clinical practice. This article summarizes the findings of these association studies and focuses on differences in study methodology in an attempt to explain why study results could have been conflicting. Furthermore, the feasibility of genetic testing in today’s clinical practice is discussed, using a model that consists of four components; analytical validity, clinical validity, clinical utility and ethical, legal and social issues.

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.

Polymorphisms of the HTR2C gene and antipsychotic-induced weight gain: an update and meta-analysis

AIMS

This study aims to test for possible associations between the gene coding for the 5-HT2C receptor and antipsychotic-induced weight gain.

MATERIALS & METHODS

Four HTR2C polymorphisms (rs498207, C-759T, G-697C and Ser23Cys) were investigated in our sample of 205 chronic schizophrenia patients.

RESULTS

Significant over-representation of the C-G-Cys23 haplotype in patients with weight gain (OR: 1.93; 95% CI: 1.04-3.56; p = 0.0015) was found. Similarly, haplotype analyses of percentage weight change were also significant (p = 0.029) for the C-G-Cys23 haplotype associated with the highest average percent weight gain. Observations in the polymorphisms are consistent with previous studies. An updated meta-analysis of nine previous studies plus our current sample suggest that the -759C allele is associated with antipsychotic-induced weight gain.

CONCLUSION

Additional studies, including the resequencing of the region surrounding the HTR2C promoter, and functional studies of the promoter polymorphisms, may elucidate the mechanism underlying this genetic association.

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.

Risperidone-induced weight gain in referred children with autism spectrum disorders is associated with a common polymorphism in the 5-hydroxytryptamine 2C receptor gene

Weight gain is an important adverse effect of risperidone, but predictors of significant weight gain have yet to be identified in pediatric patients. Here, we investigated differences between age- and gender-normed body mass index-standardized z scores at baseline and after 8 weeks of open-label, flexible-dose risperidone treatment (mean dose: 1.70  mg/day) in 32 youths with pervasive developmental disorder (mean age = 8.74, range = 5-16 years) in relation to -759C/T 5-hydroxytryptamine 2C receptor (HTR2C) promoter and rs1414334 HTR2C intragenic C/G alleles, along with gender, age, and risperidone dose, using repeated measures analyses of variance. Carriers of the HTR2C promoter T allele gained an average of 0.043 ± 0.017 body mass index-standardized z scores (1.84 ± 1.51  kg) versus 0.64 ± 0.35 z (3.23 ± 1.47  kg) for non-T-allele carriers (p < 0.001). Presence of the rs1414334 C allele played no significant role. Further, weight gain appeared to be associated with younger age and higher doses of risperidone. The current preliminary findings suggest that the variant T allele of the -759C/T HTR2C promoter polymorphism is protective against risperidone-induced weight gain. Younger children and those treated with higher doses of risperidone may be at higher risk for weight gain.

MTHFR genotype and differential evolution of metabolic parameters after initiation of a second generation antipsychotic: an observational study

Most second-generation antipsychotics (SGAs) induce metabolic disturbances, but large differences exist in the degree to which individual patients develop these. Little is known about genetic factors associated with differential liability. Cross-sectional studies suggested an association between polymorphisms in 5,10-methylenetetraydrofolate reductase (MTHFR) and metabolic syndrome in patients with schizophrenia. This study aimed to assess whether the C677T (rs1801133) or A1298C (rs1801131) polymorphism in the MTHFR gene predict differential evolution of metabolic parameters over the course of a 3-month follow-up period after initiation of an SGA. One hundred and four patients with schizophrenia initiated on a SGA were measured at baseline, 6 weeks and 3 months. MTHFR A1298C, but not C677T, genotype predicted pos-baseline increases in weight [beta=2.5, standard error (SE)=0.92, P=0.006], waist circumference (beta=2.0, SE=1.0, P=0.050), fasting glucose (beta=2.8, SE=1.2, P=0.024) and glucose at 120 min during the Oral Glucose Tolerance Test (beta=10.7, SE=4.5, P=0.018) following a de novo metabolic challenge with a specific SGA. A1298C allele carriers consistently displayed the most unfavorable evolution of metabolic parameters. Thus, MTHFR A1298C genotype may explain part of the individual liability to metabolic disturbances in patients with schizophrenia.

Lack of Association between Glutathione S-Transferase-M1, -T1, and -P1 Polymorphisms and Olanzapine-Induced Weight Gain in Korean Schizophrenic Patients

OBJECTIVE

Oxidative stress may be an important pathogenic mechanism in the obesity and metabolic syndrome. The aims of this study was to assess the possible association between the oxidative stress related Glutathione S-Transferase genes (GST-M1, GST-T1, and GST-P1) variants and the olanzapine-induced weight gain in Korean schizophrenic patients.

METHODS

We categorized 78 schizophrenic patients into two groups the more than 7% weight gain from baseline (weight gain >/=7%) and the less weight gain (weight gain <7%) groups according to weight change between before and after long-term olanzapine treatment (440+/-288 days). All participants were genotyped for the GST-M1, GST-T1 and GST-P1 genes. Differences in allele frequencies between cohorts with different body weight changes were evaluated by a chi-square analysis and Fisher's exact test. The multifactor dimensionality reduction (MDR) approach was used to analyze gene-gene interactions.

RESULTS

Mean body weight gain was 5.42 kg. There was no difference in the null genotype distribution of GST-M1 and -T1 between subjects with body weight gain >/=7% compared to subjects with body weight gain <7% (p>0.05). No significant difference in GST-P1 genotype and allele frequencies were observed between the groups (p>0.05). MDR analysis did not show a significant interaction between the three GST gene variants and susceptibility to weight gain (p>0.05).

CONCLUSION

These findings do not support a relationship between the genetic variants of three GST genes (GST-M1, -T1 and -P1) and weight gain in Korean schizophrenic patients receiving olanzapine treatment.

Pharmacogenetics of antipsychotic-induced side effects

Currently available antipsychotic drugs (APDs) carry significant, though highly variable, liability to neurologic and metabolic side effects. Pharmacogenetics approaches offer the possibility of identifying patient-specific biomarkers for predicting risk of these side effects. To date, a few single nucleotide polymorphisms (SNPs) in a handful of genes have received convergent support across multiple studies. The primary focus has been on SNPs in dopamine and serotonin receptor genes: persuasive meta-analytic evidence exists for an effect of the dopamine D2 and D3 receptor genes (DRD2 and DRD3) in risk for tardr inesia (TD) and for an effect of variation at the receptor gene (HTR2C) for liability to APD-inducec gain. However, effect sizes appear to be modest, and pharmacoeconomic considerations have not been sufficiently studied, thereby limiting clinical applicability at this time. Effects of these genes and others on risk for TD, extrapyramidal side effects, hyperprolactinemia, and weight gain are revieved in this article.

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.

Pharmacogenetics of risperidone therapy in autism: association analysis of eight candidate genes with drug efficacy and adverse drug reactions

Little has been reported on the factors, genetic or other, that underlie the variability in individual response, particularly for autism. In this study we simultaneously explored the effects of multiple candidate genes on clinical improvement and occurrence of adverse drug reactions, in 45 autistic patients who received monotherapy with risperidone up to 1 year. Candidate genes involved in the pharmacokinetics (CYP2D6 and ABCB1) and pharmacodynamics (HTR2A, HTR2C, DRD2, DRD3, HTR6) of the drug, and the brain-derived neurotrophic factor (BDNF) gene, were analysed. Using the generalized estimating equation method these genes were tested for association with drug efficacy, assessed with the Autism Treatment Evaluation Checklist, and with safety and tolerability measures, such as prolactin levels, body mass index (BMI), waist circumference and neurological adverse effects, including extrapyramidal movements. Our results confirm that risperidone therapy was very effective in reducing some autism symptoms and caused few serious adverse effects. After adjusting for confounding factors, the HTR2A c.-1438G>A, DRD3 Ser9Gly, HTR2C c.995G>A and ABCB1 1236C>T polymorphisms were predictors for clinical improvement with risperidone therapy. The HTR2A c.-1438G>A, HTR2C c.68G>C (p.C33S), HTR6 c.7154-2542C>T and BDNF c.196G>A (p.V66M) polymorphisms influenced prolactin elevation. HTR2C c.68G>C and CYP2D6 polymorphisms were associated with risperidone-induced increase in BMI or waist circumference. We thus identified for the first time several genes implicated in risperidone efficacy and safety in autism patients. Although association results require replication, given the small sample size, the study makes a preliminary contribution to the personalized therapy of risperidone in autism.

Focus on HTR2C: A possible suggestion for genetic studies of complex disorders

HTR2C is one of the most relevant and investigated serotonin receptors. Its role in important brain structures such as the midbrain, the lateral septal complex, the hypothalamus, the olfactory bulb, the pons, the choroid plexus, the nucleus pallidus, the striatum and the amygdala, the nucleus accumbens and the anterior cingulated gyrus candidate it as a promising target for genetic association studies. The biological relevance of these brain structures is reviewed by way of the focus on HTR2C activity, with a special attention paid to psychiatric disorders. Evidence from the genetic association studies that dealt with HTR2C is reviewed and discussed alongside the findings derived from the neuronatmic investigations. The reasons for the discrepancies between these two sets of reports are discussed. As a result, HTR2C is shown to play a pivotal role in many different psychiatric behaviors or psychiatric related disrupted molecular balances, nevertheless, genetic association studies brought inconsistent results so far. The most replicated association involve the feeding behavior and antipsychotic induced side effects, both weight gain and motor related: Cys23Ser (rs6318) and -759C/T (rs3813929) report the most consistent results. The lack of association found in other independent studies dampens the clinical impact of these reports. Here, we report a possible explanation for discrepant findings that is poorly or not at all usually considered, that is that HTR2C may exert different or even opposite activities in the brain depending on the structure analyzed and that mRNA editing activity may compensate possible genetically controlled functional effects. The incomplete coverage of the HTR2C variants is proposed as the best cost-benefit ratio bias to fix. The evidence of brain area specific HTR2C mRNA editing opens a debate about how the brain can differently modulate stress events, and process antidepressant treatments, in different brain areas. The mRNA editing activity on HTR2C may play a major role for the negative association results.

Obesity, serious mental illness and antipsychotic drugs

The prevalence of overweight and obesity is higher in people with mental illness than in the general population. Body weight is tightly regulated by a complex system involving the cortex and limbic system, the hypothalamus and the gastrointestinal tract. While there are justifiable concerns about the weight gain associated with antipsychotic medication, it is too simplistic to ascribe all obesity in people with serious mental illness (SMI) to their drug treatment. The development of obesity in SMI results from the complex interaction of the genotype and environment of the person with mental illness, the mental illness itself and antipsychotic medication. There are dysfunctional reward mechanisms in SMI that may contribute to poor food choices and overeating. While it is clear that antipsychotics have profound effects to stimulate appetite, no one receptor interaction provides an adequate explanation for this effect, and many mechanisms are likely to be involved. The complexity of the system regulating body weight allows us to start to understand why some individuals appear much more prone to weight gain and obesity than others.

Association between the insulin-induced gene 2 (INSIG2) and weight gain in a German sample of antipsychotic-treated schizophrenic patients: perturbation of SREBP-controlled lipogenesis in drug-related metabolic adverse effects?

Atypical antipsychotics are nowadays the most widely used drugs to treat schizophrenia and other psychosis. Unfortunately, some of them can cause major metabolic adverse effects, such as weight gain, dyslipidemia and type 2 diabetes. The underlying lipogenic mechanisms of the antipsychotic drugs are not known, but several studies have focused on a central effect in the hypothalamic control of appetite regulation and energy expenditure. In a functional convergent genomic approach we recently used a cellular model and demonstrated that orexigenic antipsychotics that induce weight gain activate the expression of lipid biosynthesis genes controlled by the sterol regulatory element-binding protein (SREBP) transcription factors. We therefore hypothesized that the major genes involved in the SREBP activation of fatty acids and cholesterol production (SREBF1, SREBF2, SCAP, INSIG1 and INSIG2) would be strong candidate genes for interindividual variation in drug-induced weight gain. We genotyped a total of 44 HapMap-selected tagging single nucleotide polymorphisms in a sample of 160 German patients with schizophrenia that had been monitored with respect to changes in body mass index during antipsychotic drug treatment. We found a strong association (P=0.0003-0.00007) between three markers localized within or near the INSIG2 gene (rs17587100, rs10490624 and rs17047764) and antipsychotic-related weight gain. Our finding is supported by the recent involvement of the INSIG2 gene in obesity in the general population and implicates SREBP-controlled lipogenesis in drug-induced metabolic adverse effects.

Classifying antipsychotic agents : need for new terminology

Converging data from multiple lines of research provide growing understanding of the pharmacological basis of the efficacy and tolerability of antipsychotic agents. This review highlights some of the drawbacks of the current practice of classifying antipsychotic agents into first- and second-generation agents, and argues that much of what is known about an antipsychotic agent in terms of its efficacy and tolerability can be predicted from its binding affinity at different receptors. This makes a case for a new system of classification that reflects the receptor binding affinity profiles of individual antipsychotic agents. In its quest to make a compelling case, the review provides detailed explanations for the pharmacological basis of antipsychotic efficacy, antipsychotic-induced weight gain and diabetes mellitus, cognitive effects and other adverse effects.

Association between HTR2C and HTR2A polymorphisms and metabolic abnormalities in patients treated with olanzapine or clozapine

Serotonin 2C and 2A receptor (5-HT2C and 5-HT2A) antagonisms are hypothesized to play a role in the metabolic adverse effects induced by olanzapine and clozapine. Associations between polymorphisms in 5-HT2C and 5-HT2A receptor coding genes, HTR2C and HTR2A, with antipsychotic-induced weight gain have been reported. The impact of HTR2C and HTR2A polymorphisms on body mass index (BMI), glucose-insulin homeostasis, and blood lipid levels was evaluated in 46 patients with schizophrenia or schizoaffective disorder and treated with olanzapine (n = 28) or clozapine (n = 18) for at least 6 months. Olanzapine-treated patients with HTR2C haplotype C (-759C, -697C, and 23Ser) had higher BMI (P = 0.029) and C peptide levels (P = 0.029) compared with patients with haplotype B (-759T, -697C, and 23Cys). The frequency of patients homozygous for the HTR2C haplotype A (-759C, -697G, and 23Cys) was significantly higher among clozapine-treated patients with obesity (BMI >/= 30 kg/m) compared with nonobese patients (P = 0.015; odds ratio, 28; 95% confidence interval, 2-380). Patients carrying the HTR2A haplotype 2 (-1438A, 102T, and 452His) had significantly higher C peptide levels compared with haplotype 3 (-1438A, 102T, and 452Tyr) carriers in the olanzapine group (P = 0.034) and in the overall study population (P = 0.019). None of the haplotypes were associated with serum levels of insulin, triglycerides, and cholesterol or with homeostasis model assessment index for insulin resistance. In conclusion, both HTR2C and HTR2A gene polymorphisms seem to be associated with the occurrence of metabolic abnormalities in patients treated with olanzapine or clozapine.

Pharmacogenetics of risperidone response and induced side effects

Risperidone is an atypical antipsychotic that has been effectively used to treat several psychiatric diseases. Atypical antipsychotics present some advantages over conventional antipsychotics, primarily because they offer effective treatment alternatives that are relatively free of extrapyramidal symptoms. However, as with all antipsychotics, there are wide individual differences in response to risperidone, both regarding therapeutic effects and adverse effects, imposing some limitations with respect to the therapeutic use of the drug. Genetic factors are thought to play an important role in determining the variability to drug response. A growing number of studies are investigating how genetic polymorphisms of enzymes involved in drug metabolism or of receptors targeted by antipsychotic agents influence drug treatment of several neuropsychiatric diseases. In this article we will review the genetic variability in both the pharmacokinetics of risperidone action and in pharmacodynamic structures mediating risperidone effects, as well as the pharmacogenetic studies performed for these genes.

Searching susceptibility genes for antipsychotic-induced weight gain: is the 5-HT2C receptor gene a promising candidate?

Evaluation of: de Luca V, Mueller DJ, de Bartolomeis A, Kennedy JL: Association of the HTR2C gene and antipsychotic induced weight gain: a meta-analysis. Int. J. Neuropsychopharmacol. (2007) (Epub ahead print) [1] . Weight gain is a major adverse effect of the second-generation antipsychotics that are widely prescribed in psychiatric practice. Given its variability among patients and indirect evidence of its heritability, antipsychotic-induced weight gain has become a major target of pharmacogenetic studies. The protective effect of the T allele of the 5-HT2C receptor gene -759C/T promoter polymorphism on antipsychotic-induced weight gain has been repeatedly reported in independent studies. However, negative results have also been obtained, especially in subjects treated with clozapine. Recently, de Luca and colleagues investigated the association between the 5-HT2C receptor gene -759C/T promoter polymorphism and antipsychotic-induced weight gain using a meta-analytical approach [1] . The pooled data of eight studies (total 588 subjects) showed a trend of association between the -759T allele and lower weight gain, with evidence of significant between-study heterogeneity. Publication bias and the influence of confounding variables, such as age, gender, ethnicity, clozapine-treated patient proportions, durations of observation and the effect of weight gain cutoff criteria on effect size, were also evaluated in their meta-analysis. To clarify the contribution of the 5-HT2C receptor gene to a complex trait such as antipsychotic-induced weight gain, a greater number of independent studies with larger sample size that carefully consider various confounding factors and gene-environment interactions are required.