HTR2C haplotypes and antipsychotics-induced weight gain: X-linked multimarker analysis

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.

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.

Weight gain changes in patients with aripiprazole monotherapy compared with aripiprazole-antidepressant polypharmacy in an outpatient sample

OBJECTIVE

This study seeks to evaluate the weight gain effect within a community-based population of patients with diagnoses of depression, mood disorder, and schizophrenia receiving aripiprazole over a period of at least 6 months.

METHOD

The four million members of Kaiser Permanente of Southern California (KPSC) were queried for a four-year period between January 1, 2010 and December 31, 2013. The initial cohort comprised 25,682 KPSC members who received at least one dispense of aripiprazole. This initial cohort was split into those who received aripiprazole as a monotherapy ("Alone" group) and those who were given aripiprazole as part of a combination therapy. The group of patients that received aripiprazole and antidepressant with high serotonin reuptake inhibition we called "High" group while the group receiving aripiprazole and bupropion combination we called "Low" serotonin group. We compared the primary endpoint of mean percent weight change from baseline after 180 days of continuous treatment between the three groups. Three pairwise comparisons were made: High versus Alone, Low versus Alone, and Low versus High, using adjusted and unadjusted linear regression models.

RESULTS

Within this population, patients on aripiprazole monotherapy showed statistically significant weight gain in all three groups. However, there was no statistically significant difference in weight gain between the aripiprazole monotherapy, the high serotonergic combination group, and the low serotonergic combination group. This finding applied even within the subset of patients who were considered obese (body mass index > 30).

CONCLUSIONS

The results suggest that weight gain is unchanged by combination treatments, but further research is required.

The potentially beneficial central nervous system activity profile of ivacaftor and its metabolites

Ivacaftor-lumacaftor and ivacaftor are two new breakthrough cystic fibrosis transmembrane conductance modulators. The interactions of ivacaftor and its two metabolites hydroxymethylivacaftor (iva-M1) and ivacaftorcarboxylate (iva-M6) with neurotransmitter receptors were investigated in radioligand binding assays. Ivacaftor displayed significant affinity to the 5-hydroxytryptamine (5-HT; serotonin) 5-HT2C receptor (pKi=6.06±0.03), β3-adrenergic receptor (pKi=5.71±0.07), δ-opioid receptor (pKi=5.59±0.06) and the dopamine transporter (pKi=5.50±0.20); iva-M1 displayed significant affinity to the 5-HT2C receptor (pKi=5.81±0.04) and the muscarinic M3 receptor (pKi=5.70±0.10); iva-M6 displayed significant affinity to the 5-HT2A receptor (pKi=7.33±0.05). The in vivo central nervous system activity of ivacaftor (40 mg·kg-1 intraperitoneally for 21 days) was assessed in a chronic mouse model of depression. In the forced swim test, the ivacaftor-treated group displayed decreased immobility (52.8±7.6 s), similarly to fluoxetine (33.8±11.0 s), and increased climbing/swimming activity (181.5±9.2 s). In the open field test, ivacaftor produced higher locomotor activity than the fluoxetine group, measured both as mean number of paw touches (ivacaftor 81.1±9.6 versus fluoxetine 57.9±9.5) and total distance travelled (ivacaftor 120.6±16.8 cm versus fluoxetine 84.5±16.0 cm) in 600 s. Treatment of 23 cystic fibrosis patients with ivacaftor-lumacaftor resulted in significant improvements in quality of life (including anxiety) in all five domains of the AweScoreCF questionnaire (p=0.092-0.096). Our findings suggest ivacaftor displays potential clinical anxiolytic and stimulating properties, and may have beneficial effects on mood.

A short history of the 5-HT2C receptor: from the choroid plexus to depression, obesity and addiction treatment

This paper is a personal account on the discovery and characterization of the 5-HT_2C receptor (first known as the 5-HT_1C receptor) over 30 years ago and how it translated into a number of unsuspected features for a G protein-coupled receptor (GPCR) and a diversity of clinical applications. The 5-HT_2C receptor is one of the most intriguing members of the GPCR superfamily. Initially referred to as 5-HT_1CR, the 5-HT_2CR was discovered while studying the pharmacological features and the distribution of [³H]mesulergine-labelled sites, primarily in the brain using radioligand binding and slice autoradiography. Mesulergine (SDZ CU-085), was, at the time, best defined as a ligand with serotonergic and dopaminergic properties. Autoradiographic studies showed remarkably strong [³H]mesulergine-labelling to the rat choroid plexus. [³H]mesulergine-labelled sites had pharmacological properties different from, at the time, known or purported 5-HT receptors. In spite of similarities with 5-HT₂ binding, the new binding site was called 5-HT_1C because of its very high affinity for 5-HT itself. Within the following 10 years, the 5-HT_1CR (later named 5-HT_2C) was extensively characterised pharmacologically, anatomically and functionally: it was one of the first 5-HT receptors to be sequenced and cloned. The 5-HT_2CR is a GPCR, with a very complex gene structure. It constitutes a rarity in the GPCR family: many 5-HT_2CR variants exist, especially in humans, due to RNA editing, in addition to a few 5-HT_2CR splice variants. Intense research led to therapeutically active 5-HT_2C receptor ligands, both antagonists (or inverse agonists) and agonists: keeping in mind that a number of antidepressants and antipsychotics are 5-HT_2CR antagonists/inverse agonists. Agomelatine, a 5-HT_2CR antagonist is registered for the treatment of major depression. The agonist Lorcaserin is registered for the treatment of aspects of obesity and has further potential in addiction, especially nicotine/ smoking. There is good evidence that the 5-HT_2CR is involved in spinal cord injury-induced spasms of the lower limbs, which can be treated with 5-HT_2CR antagonists/inverse agonists such as cyproheptadine or SB206553. The 5-HT_2CR may play a role in schizophrenia and epilepsy. Vabicaserin, a 5-HT_2CR agonist has been in development for the treatment of schizophrenia and obesity, but was stopped. As is common, there is potential for further indications for 5-HT_2CR ligands, as suggested by a number of preclinical and/or genome-wide association studies (GWAS) on depression, suicide, sexual dysfunction, addictions and obesity. The 5-HT_2CR is clearly affected by a number of established antidepressants/antipsychotics and may be one of the culprits in antipsychotic-induced weight gain.

Risperidone-Induced Adverse Drug Reactions and Role of DRD2 (-141 C Ins/Del) and 5HTR2C (-759 C>T) Genetic Polymorphisms in Patients with Schizophrenia

OBJECTIVE

To determine the adverse drug reaction (ADR) profile of risperidone and their association with dopamine (DRD2 - 141 C Ins/Del/rs1799732) and serotonin receptor (5HTR2C -759 C>T/rs3813929) gene polymorphisms in patients with schizophrenia.

MATERIALS AND METHODS

The study was conducted among 289 patients who were diagnosed with schizophrenia and were on treatment with risperidone (4-8 mg/day)-based therapy for a minimum of 4 weeks. Genotyping was carried by real-time quantitative polymerase chain reaction. All the patients were observed for the occurrences of ADRs during the study. Changes in prolactin levels and body weight were analyzed for a subgroup of 102 and 97 patients, respectively.

RESULTS

Risperidone-induced extrapyramidal symptoms (EPSs) were seen in 36.7% of patients. Among them, tremors were the most common symptom 31.8%. Risperidone-induced hyperprolactinemia and weight gain were seen in 87.2% and 53.6% in subgroup patients. Adverse effects such as sedation, gastrointestinal effects, and amenorrhea were seen in 9.7% (28/289), 5.1% (15/289), and 6.1% (7/114), respectively. Occurrence of DRD2 - 141 Ins/Del and Del/Del polymorphisms were significantly associated with increased prolactin levels in response to risperidone (odds ratio [OR] = 10.45; 95% confidence interval = 1.29-84.89, P = 0.004). No such association was observed with 5HTR2C (-759 C>T) polymorphism. Weight gain and EPS were not associated with the above genetic polymorphisms.

CONCLUSION

Hyperprolactinemia, weight gain, and EPSs (>36.7%) were common adverse effects of risperidone. DRD2 - 141C Ins/Del and Del/Del polymorphisms were significantly associated with increased prolactin levels (OR = 10.45) in response to risperidone.

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.

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.

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with increased body mass index and insulin resistance measures in bipolar disorder and schizophrenia

OBJECTIVES

We tested the hypothesis that a common functional variant in brain-derived neurotrophic factor (BDNF), Val66Met, which has been shown to be associated with increased body mass index (BMI) in schizophrenia (SCZ) and schizoaffective disorder (SAD), is also associated with antipsychotic-induced weight gain in bipolar disorder (BPD). Association of Val66Met with other metabolic measures, including high- and low-density cholesterol, triglycerides, total cholesterol, fasting blood glucose, and hemoglobin A1c, was also tested.

METHODS

This was a 12-month, prospective, randomized trial of two atypical antipsychotic drugs (APDs) with moderate (risperidone) or high (olanzapine) risk to cause weight gain. Subjects were diagnosed as having BPD (n = 90) and SCZ or SAD (n = 76).

RESULTS

BMI was significantly greater in all diagnoses for Met66 allele carriers at six months (p = 0.01). Met66 carriers with BPD showed a greater increase in the triglycerides/high-density (HDL) cholesterol ratio (p = 0.01), a key marker for metabolic syndrome related to insulin resistance, and log-triglycerides (p = 0.04), after three or six months of treatment. Met66 carriers had the greatest increase in log-triglycerides (p = 0.03) and triglycerides/HDL cholesterol ratio after three months of treatment with risperidone (p = 0.003), and the highest BMI at six months (p = 0.01).

CONCLUSIONS

The positive association of BNDF Val66Met with high BMI values replicates previous findings in patients with SCZ and indicates the BDNF Val66Met genotype as a potential risk factor for obesity and insulin resistance measures in patients with BPD receiving antipsychotics as well.

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.

Genetic variation in the GCG and in the GLP1R genes and antipsychotic-induced weight gain

Aim: GLP-1 plays a key role in glucose metabolism and influences antipsychotic-induced weight gain (AIWG). Our study is the first to investigate the encoding gene, GCG, and the GLP-1 receptor gene, GLP1R, and association with AIWG. Materials & methods: In 216 schizophrenic patients treated with antipsychotics for up to 14 weeks, we investigated four GCG and 33 GLP1R polymorphisms. Statistical analyses were conducted using SPSS, Haploview 4.2, UNPHASED 3.1.4 and the R-package mbmdr. Results: We observed association of rs13429709 near GCG with AIWG (pcorr = 0.044) in patients of European ancestry receiving olanzapine or clozapine (n = 87). We also found significant gene–gene interaction between rs13429709 and rs2268639 in GLP1R. Only nonsignificant trends were observed for GLP1R polymorphisms with AIWG. Conclusion: We found significant association of rs13429709 with AIWG. Although there was no significant finding for GLP1R, the observed trends and interaction suggest this to be an interesting gene for further examination.

Original submitted 17 October 2013; Revision submitted 11 December 2013

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.

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.

Association study of polymorphisms in leptin and leptin receptor genes with antipsychotic-induced body weight gain

BACKGROUND

Antipsychotic-induced weight gain (AIWG) is a serious side-effect of antipsychotic medication leading to metabolic syndrome and increased cardiovascular morbidity. Unfortunately, there are still no valid predictors to assess an individual's risk to gain weight. Previous studies have indicated an impact of genetic variation in the genes encoding leptin, LEP, and leptin receptor, LEPR, on AIWG, but results have not been conclusive. Thus, we investigated polymorphisms in both genes for an association with AIWG.

METHODS

A total of 181 schizophrenic and schizoaffective patients treated with various antipsychotics were included. In a small subset of patients, leptin plasma levels were additionally obtained. Five polymorphisms in LEP and LEPR (LEP: rs7799039 (-2548G/A polymorphism), rs10954173, rs3828942; LEPR: rs1327120, rs1137101 (Q223R polymorphism) were genotyped using TaqMan assays. Statistical association with % weight change from baseline weight was performed using ANCOVA with baseline weight as covariate.

RESULTS

ANCOVA showed a non-significant trend for genotype association of the rs7799039 marker (p=.068). No significant association of the other LEP and LEPR SNPs with AIWG was detected. However, we found a significant association between a haplotype of LEP rs7799039G-rs10954173G-rs3828942G (p=.035) and AIWG. The rs7799039 G-allele (p=.042) and G-allele of rs3828942 (p=.032) were associated with higher weight gain.

CONCLUSION

Our study supports the hypothesis of an impact of LEP gene variation on AIWG. Limitations of our study include heterogeneous samples, short treatment duration and multiple comparisons. Our findings were compared to previous studies in detail in order to provide the readers with a more conclusive picture. However, further studies are warranted including more gene variants and interaction analyses with other genes of the leptin-melanocortin pathway.

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.

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.

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.

Bioinformatic analyses to select phenotype affecting polymorphisms in HTR2C gene

OBJECTIVE

Single nucleotide polymorphisms (SNPs) in serotonin related genes influence mental disorders, responses to pharmacological and psychotherapeutic treatments. In planning association studies, researchers that want to investigate new SNPs have to select some among a large number of candidates. Our aim is to guide researchers in the selection of the most likely phenotype affecting polymorphisms. Here, we studied serotonin receptor 2C (HTR2C) SNPs because, till now, only relatively few of about 2000 are investigated.

METHODS

We used the most updated and assessed bioinformatic tools to predict which variations can give rise to biological effects among 2450 HTR2C SNPs.

RESULTS

We suggest 48 SNPs that are worth considering in future association studies in the field of psychiatry, psychology and pharmacogenomics. Moreover, our analyses point out the biological level probably affected, such as transcription, splicing, miRNA regulation and protein structure, thus allowing to suggest future molecular investigations.

CONCLUSIONS

Although few association studies are available in literature, their results are in agreement with our predictions, showing that our selection methods can help to guide future association studies.

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.

Functional consequences of two HTR2C polymorphisms associated with antipsychotic-induced weight gain

BACKGROUND

Genetic variation in the promoter region of HTR2C encoding for the 5-HT(2C) receptor is associated with antipsychotic-induced weight gain. Several studies have investigated the regulatory potential of associated variants using gene-reporter systems. Establishing associated polymorphisms as causal variants may aid in the identification of the molecular mechanisms of phenotypic variation.

AIMS & METHODS

To this end we examined the binding of nuclear factors from rat hypothalamus to two polymorphisms in HTR2C, rs3813929 (-759C/T) and rs518147 (-697C/G) using electromobility shift assays. For rs518147, allele-specific RNA folding was also investigated.

RESULTS

Both polymorphisms bound nuclear factors, identifying the sequence fragments as regulatory elements. Importantly, rs3813929 (-759C/T) altered DNA-protein interactions with the weight gain-resistant allele abolishing the formation of two complexes. The formation of allele-specific RNA loops was also observed for rs518147.

CONCLUSION

These data establish rs3813929 (-759C/T) as a functional polymorphism and suggest disruption of DNA-protein interactions as a mechanism by which HTR2C expression is perturbed leading to an influence on antipsychotic-induced weight gain.

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.

Weight gain, schizophrenia and antipsychotics: new findings from animal model and pharmacogenomic studies

Excess body weight is one of the most common physical health problems among patients with schizophrenia that increases the risk for many medical problems, including type 2 diabetes mellitus, coronary heart disease, osteoarthritis, and hypertension, and accounts in part for 20% shorter life expectancy than in general population. Among patients with severe mental illness, obesity can be attributed to an unhealthy lifestyle, personal genetic profile, as well as the effects of psychotropic medications, above all antipsychotic drugs. Novel "atypical" antipsychotic drugs represent a substantial improvement on older "typical" drugs. However, clinical experience has shown that some, but not all, of these drugs can induce substantial weight gain. Animal models of antipsychotic-related weight gain and animal transgenic models of knockout or overexpressed genes of antipsychotic receptors have been largely evaluated by scientific community for changes in obesity-related gene expression or phenotypes. Moreover, pharmacogenomic approaches have allowed to detect more than 300 possible candidate genes for antipsychotics-induced body weight gain. In this paper, we summarize current thinking on: (1) the role of polymorphisms in several candidate genes, (2) the possible roles of various neurotransmitters and neuropeptides in this adverse drug reaction, and (3) the state of development of animal models in this matter. We also outline major areas for future research.

Management of antipsychotic-related weight gain

Despite variations across individuals and agents, antipsychotics are associated with clearly documented weight gain and adverse metabolic effects. Although increased appetite/caloric intake and various receptors, hormones and peptides have been implicated, biological mechanisms contributing to the increase in weight and glucose and lipid abnormalities with antipsychotics are largely unknown. This has hampered the creation of antipsychotics that are free of cardiometabolic effects, even in antipsychotic-naive/early-phase patients, as well as the development of strategies that can prevent or drastically diminish the adverse cardiometabolic effects. In general, three strategies can reduce the cardiometabolic risk of antipsychotics: switching to a less orexigenic/metabolically adverse antipsychotic; adjunctive behavioral treatments; and adjunctive pharmacologic interventions. However, each of these strategies has only been shown to be modestly effective. Among different behavioral interventions (N = 14, n = 746), group and individual treatment, dietary counseling and cognitive-behavioral therapy seem to be similarly effective. Among 15 different pharmacologic strategies (N = 35, n = 1629), only metformin, fenfluramine, sibutramine, topiramate and reboxetine were more effective than placebo, with the most evidence being available for metformin, and no head-to-head trials comparing individual pharmacologic interventions. However, even in the most successful trials the risk reduction was modest. Weight was not decreased to a pretreatment level, and despite superiority compared with placebo, weight gain still often occurred, particularly in antipsychotic-naive patients and when interventions were 'preventively' coinitiated with antipsychotics. Future research should focus on combining treatment modalities or agents and on exploring novel mechanism-based interventions.

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.

Association of HTR2C, but not LEP or INSIG2, genes with antipsychotic-induced weight gain in a German sample

Background: Drug-induced bodyweight gain (BWG) is a serious concern in pharmacotherapy with second-generation antipsychotics. The interindividual variability is likely to be modulated by genetic factors. In the past, pharmacogenetic studies yielded conflicting results, and none of the identified genetic alterations exerts sufficient predictive value for this severe side effect of psychopharmacotherapy. Aim: We aimed to contribute to the replication and extension of prior association findings and investigated the genes encoding serotonin 2C receptor (HTR2C), insulin-induced gene 2 (INSIG2) and leptin (LEP). Patients & methods: We investigated the association of HTR2C, LEP and INSIG2 SNPs with antipsychotic-induced BWG in 128 German schizophrenic patients. Genotyping was performed for nine SNPs (HTR2C: rs498207, rs3813928, rs6318 and rs3813929; INSIG2: rs17587100, rs10490624, rs17047764 and rs7566605; LEP: rs7799039). Association analysis included logistic regression analysis and Pearson´s χ2 tests. Results: We report a significant association of three HTR2C SNPs (rs498207, rs3813928 and rs3813929) and of the respective haplotype with antipsychotic-induced BWG. Regarding the X-chromosomal SNP rs498207, individuals with AA/A genotype gained more weight than those with GG/G genotype. The association observed with the SNP rs498207 was also significant after correcting for multiple testing (p = 0.0196). No association was found for INSIG2 and LEP SNPs. Conclusion: The results contribute to the accumulating evidence for an association of the X-chromosomal HTR2C gene with antipsychotic-induced BWG. The proposed underlying mechanisms include decreased HTR2C gene expression with reduced 5-HT-modulated activation of hypothalamic proopiomelanocortin-neurons, and inverse 5-HT2C agonism in the presence of D2 receptor antagonism.

Psychiatric pharmacogenomic testing in clinical practice

The clinical adoption of psychiatric pharmacogenomic testing has taken place rapidly over the past 7 years. Initially, drug-metabolizing enzyme genes, such as the cytochrome P 4 5 0 2D6 gene (CYP2D6), were identified. Genotyping the highly variable cytochrome P 4 5 0 2D6 gene now provides clinicians with the opportunity to identify both poor metabolizers and ultrarapid metabolizers of 2D6 substrate medications. Subsequently, genes influencing the pharmacodynamic response of medications have been made available for clinical practice. Among the earliest “target genes” was the serotonin transporter gene (SLC6A4) which has variants that have been shown to influence the clinical response of patients of European ancestry when they are treated with selective serotonin reuptake inhibitors. Genotyping of some of the serotonin receptor genes is also available to guide clinical practice. The quantification of the clinical utility of pharmacogenomic testing is evolving, and ethical considerations for testing have been established. Given the increasingly clear cost-effectiveness of genotyping, it has recently been predicted that pharmacogenomic testing will routinely be ordered to guide the selection and dosing of psychotropic medications.

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.

Association between serotonin 5-HT-2C receptor gene (HTR2C) polymorphisms and obesity- and mental health-related phenotypes in a large population-based cohort

OBJECTIVE

Studies have shown that common single-nucleotide polymorphisms (SNPs) in the serotonin 5-HT-2C receptor (HTR2C) are associated with antipsychotic agent-induced weight gain and the development of behavioural and psychological symptoms. We aimed to analyse whether variation in the HTR2C is associated with obesity- and mental health-related phenotypes in a large population-based cohort.

METHOD

Six tagSNPs, which capture all common genetic variation in the HTR2C gene, were genotyped in 4978 men and women from the European Prospective Investigation into Cancer (EPIC)-Norfolk study, an ongoing prospective population-based cohort study in the United Kingdom. To confirm borderline significant associations, the -759C/T SNP (rs3813929) was genotyped in the remaining 16 003 individuals from the EPIC-Norfolk study. We assessed social and psychological circumstances using the Health and Life Experiences Questionnaire. Genmod models were used to test associations between the SNPs and the outcomes. Logistic regression was performed to test for association of SNPs with obesity- and mental health- related phenotypes.

RESULTS

Of the six HTR2C SNPs, only the T allele of the -759C/T SNP showed borderline significant associations with higher body mass index (BMI) (0.23 kg m(-2); (95% confidence interval (CI): 0.01-0.44); P=0.051) and increased risk of lifetime major depressive disorder (MDD) (Odds ratio (OR): 1.13 (95% CI: 1.01-1.22), P=0.02). The associations between the -759C/T and BMI and lifetime MDD were independent. As associations only achieved borderline significance, we aimed to validate our findings on the -759C/T SNP in the full EPIC-Norfolk cohort (n=20 981). Although the association with BMI remained borderline significant (beta=0.20 kg m(-2); 95% CI: 0.04-0.44, P=0.09), that with lifetime MDD (OR: 1.01; 95% CI: 0.94-1.09, P=0.73) was not replicated.

CONCLUSIONS

Our findings suggest that common HTR2C gene variants are unlikely to have a major role in obesity- and mental health-related traits in the general population.

Inflammatory markers in schizophrenia: comparing antipsychotic effects in phase 1 of the clinical antipsychotic trials of intervention effectiveness study

BACKGROUND

C-reactive protein (CRP), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin are systemic inflammatory markers (IM) that positively correlate with cardiovascular (CV) risk. Despite the known CV effects of atypical antipsychotics, there is limited prospective data on IM changes during treatment.

METHODS

The IM outcomes were compared between antipsychotic treatment groups in the CATIE (Clinical Antipsychotic Trials of Intervention Effectiveness) schizophrenia trial phase 1 with subjects with laboratory assessments at baseline and 3 months (n = 789).

RESULTS

There were significant treatment differences in CRP, E-selectin, and ICAM-1 at 3 months, with a differential impact of baseline values on the CRP and ICAM-1 results. In overall comparisons, quetiapine and olanzapine had the highest median levels for CRP, and olanzapine for E-selectin and ICAM-1. Olanzapine was significantly different after baseline adjustment than perphenazine (p = .001) for E-selectin, and in those with low baseline CRP (<1 mg/L), olanzapine was significantly different than perphenazine (p < .001), risperidone (p < .001), and ziprasidone (p = .002) for CRP. Perphenazine had the lowest 3-month ICAM-1 levels in subjects with baseline ICAM-1 above the median, but the differences were not statistically significant versus olanzapine (p = .010), quetiapine (p = .010), and risperidone (p = .006) after controlling for multiple comparisons. The 18-month repeated measures CRP analysis confirmed the significantly higher values for olanzapine in those with low baseline CRP.

CONCLUSIONS

This analysis provides further evidence for differential antipsychotic metabolic liabilities as measured by changes in systemic inflammation. C-reactive protein might emerge as a useful target for CV risk outcomes in schizophrenia patients.

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.

Insulin resistance and secretion in vivo: effects of different antipsychotics in an animal model

Atypical antipsychotics now represent the mainstay of treatment for patients with schizophrenia. Unfortunately, as a class they have also been associated with an increased risk of weight gain and metabolic abnormalities, including type 2 diabetes. We have investigated the diabetogenic effects of a spectrum of antipsychotics, both atypical and typical. Healthy animals were treated acutely with clozapine (10 mg/kg), olanzapine (3.0 mg/kg), risperidone (1 mg/kg), ziprasidone (3 mg/kg) or haloperidol (0.25 mg/kg) and tested using the hyperinsulinemic-euglycemic and hyperglycemic clamp procedures. Clozapine and olanzapine had a rapid and potent effect on insulin sensitivity by lowering the glucose infusion rate and increasing hepatic glucose production. Both clozapine and olanzapine, as well as risperidone, decreased peripheral glucose utilization. Neither ziprasidone nor haloperidol had a significant impact on insulin sensitivity. In the hyperglycemic clamp, clozapine and olanzapine impaired beta cell function as reflected by a decrease in insulin secretion. Results confirm that 1) antipsychotic medications have an immediate impact on metabolic parameters and 2) the various atypical antipsychotics differ in their propensity to acutely induce metabolic side effects. Our data also support the preclinical use of these clamp procedures in screening putative antipsychotics.