Association study of adrenergic beta3 receptor (Trp64Arg) and G-protein beta3 subunit gene (C825T) polymorphisms and weight change during clozapine treatment

Adrenoceptors: A Focus on Psychiatric Disorders and Their Treatments

Research into the involvement of adrenoceptor subtypes in the cause(s) of psychiatric disorders is particularly challenging. This is partly because of difficulties in developing animal models that recapitulate the human condition but also because no evidence for any causal links has emerged from studies of patients. These, and other obstacles, are outlined in this chapter. Nevertheless, many drugs that are used to treat psychiatric disorders bind to adrenoceptors to some extent. Direct or indirect modulation of the function of specific adrenoceptor subtypes mediates all or part of the therapeutic actions of drugs in various psychiatric disorders. On the other hand, interactions with central or peripheral adrenoceptors can also explain their side effects. This chapter discusses both aspects of the field, focusing on disorders that are prevalent: depression, schizophrenia, anxiety, attention-deficit hyperactivity disorder, binge-eating disorder, and substance use disorder. In so doing, we highlight some unanswered questions that need to be resolved before it will be feasible to explain how changes in the function of any adrenoceptor subtype affect mood and behavior in humans and other animals.

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.

Pharmacogenetic Correlates of Antipsychotic-Induced Weight Gain in the Chinese Population

Antipsychotic-induced weight gain (AIWG) is a common adverse effect of this treatment, particularly with second-generation antipsychotics, and it is a major health problem around the world. We aimed to review the progress of pharmacogenetic studies on AIWG in the Chinese population to compare the results for Chinese with other ethnic populations, identify the limitations and problems of current studies, and provide future research directions in China. Both English and Chinese electronic databases were searched to identify eligible studies. We determined that > 25 single-nucleotide polymorphisms in 19 genes have been investigated in association with AIWG in Chinese patients over the past few decades. HTR2C rs3813929 is the most frequently studied single-nucleotide polymorphism, and it seems to be the most strongly associated with AIWG in the Chinese population. However, many genes that have been reported to be associated with AIWG in other ethnic populations have not been included in Chinese studies. To explain the pharmacogenetic reasons for AIWG in the Chinese population, genome-wide association studies and multiple-center, standard, unified, and large samples are needed.

Visceral Fat Dysfunctions in the Rat Social Isolation Model of Psychosis

Medication with neuroleptics has been associated with adipose tissue dysfunctions and, in particular, with increased visceral fat amount. However, several studies suggested that antipsychotic treatment might not be the main responsible of fat mass accumulation, as this has been also described in not treated psychotic patients. One of the most used “drug-free” rodent models of psychosis is the social isolation rearing of young adult rats, which provides a non-pharmacologic method of inducing long-term alterations reminiscent of symptoms seen in psychotic patients. Recent data highlighted a crucial role of redox imbalance in adipose tissue dysfunctions, in terms of decreased antioxidant defense and increased reactive oxygen species (ROS). Here, we investigated possible oxidative stress-related biomolecular alterations associated with visceral fat increase in 7 week isolated rats. To this purpose, we quantified total and visceral fat amount by using dual-energy X-ray (DEXA) absorptiometry. On visceral fat, we analyzed the expression of specific ROS-producer genes (Nox1, Nox4, Hmox-1), antioxidant enzymes (Prdx1 and Ucp-1) and oxidative stress-induced damage markers (Cidea, Slc2a4, and Acacb). The impact of oxidative stress on beta3-adrenergic receptors (Adrb3), at both mRNA and protein level, was also assessed. We found that 7 weeks of social isolation induced an increase in total and visceral fat, associated with a decrease in Prdx1 (mRNA and protein) as well as Ucp-1 mRNA levels and an enhanced expression of Nox1 (mRNA and protein) and Hmox-1 mRNA. No differences were detected in Nox4 mRNA levels between grouped and isolated animals. Elevations in Cidea, Slc2a4, and Acacb expression in visceral fat of isolated animals accounted for oxidative stress-related damage in this tissue, further associated with a significant increase in Adrb3 mRNA and protein. Our results provide a novel understanding of the pathological link existing among psychosocial stress-induced psychosis, adipose tissue dysfunctions and redox imbalance, opening new therapeutic perspectives for the treatment of alterations in peripheral tissues associated with this mental disorder.

Genetic variants impacting metabolic outcomes among people on clozapine: a systematic review and meta-analysis

Clozapine is the gold standard medication for treatment refractory schizophrenia, but unfortunately, its use is also associated with many adverse metabolic side effects. There may be a strong genetic component to the development of these adverse effects. We undertook a systematic review to examine the evidence for genetic variation being associated with secondary metabolic outcomes in patients with schizophrenia on clozapine, under both longitudinal and cross-sectional study designs. We limited studies to those examining patients definitely taking clozapine, unlike prior reviews that have examined metabolic effects of patients taking a range of antipsychotic medications. We found associations with outcomes such as increases in BMI and metabolic syndrome for variants in genes such as LEP and HTR2C. Meta-analysis of rs381328 in HTR2C revealed that the presence of the T allele led to a 0.63 kg/m² (95% CI - 1.06 to - 0.19; p = 0.005) decrease in BMI compared to the C allele. Study and population heterogeneity and lack of statistical power among reviewed articles mean that evidence is lacking to warrant prophylactic genotyping of patients commencing clozapine to predict those at increased risk of developing adverse metabolic effects. Further efforts to establish collaborative consortia, consensus around study design and replication studies in independent populations should be encouraged.

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.

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

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

Pharmacogenetics in schizophrenia: a review of clozapine studies

OBJECTIVES

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

METHODS

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

RESULTS AND CONCLUSIONS

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

Association of the C825T polymorphism in the GNB3 gene with obesity and metabolic phenotypes in a Taiwanese population

The relationship between obesity and a single nucleotide polymorphism (SNP), rs5443 (C825T), in the guanine nucleotide binding protein beta polypeptide 3 (GNB3) gene is currently inconsistent. In this study, we aimed to reassess whether the GNB3 rs5443 SNP could influence obesity and obesity-related metabolic traits in a Taiwanese population. A total of 983 Taiwanese subjects with general health examinations were genotyped. Based on the criteria defined by the Department of Health in Taiwan, the terms "overweight" and "obesity" are defined as 24 ≦ BMI < 27 and BMI ≧ 27, respectively. Compared to the carrier of the combined CT + TT genotypes of the GNB3 rs5443 polymorphism, triglyceride was significantly higher for the carrier of CC genotype in the complete sample population (128.2 ± 93.2 vs. 114.3 ± 79.1 mg/dl; P = 0.041). In addition, the carriers of CC variant had a higher total cholesterol than those with the combined CT + TT variants (194.5 ± 36.8 vs. 187.9 ± 33.0 mg/dl; P = 0.019) in the complete sample population. In the normal controls, both triglyceride (P = 0.018) and total cholesterol (P = 0.011) were also significantly higher in the CC homozygotes than in the combined CT + TT genotypes. However, the GNB3 rs5443 SNP did not exhibit any significant association with obesity or overweight among the subjects. Our study indicates that the CC genotype of the GNB3 rs5443 SNP may predict higher obesity-related metabolic traits such as triglyceride and total cholesterol in non-obese Taiwanese subjects (but not in obese subjects).

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).

Genetic interactions in the adrenergic system genes: analysis of antipsychotic-induced weight gain

Atypical antipsychotics (AP) have high affinity for many neurotransmitter receptors. Among these receptors, APs are antagonist at α-adrenergic and β-adrenergic receptors, and this pharmacological property has been postulated to be involved in the mechanism of action of these drugs with respect to both clinical response and adverse effects.

OBJECTIVE

We tested the hypotheses that AP-induced weight gain is associated with genetic variation in adrenergic receptors and pathway enzymes. We analyzed nine genetic polymorphisms across seven adrenergic genes (ADRA1A, ADRA2A, ADRA2C, ADRB3, DBH, MAOA and COMT).

METHODS

One hundred thirty-nine patients with schizophrenia were prospectively assessed for AP-induced weight gain. The HelixTree software (Golden Helix, Bozeman, MT, USA) was employed to detect differences in genotypic distribution between weight gainer and non-weight gainer groups. Furthermore, for the dopamine β-hydroxylase haplotype, we were able to obtain both the molecular and the statistical phases, analyzing the phenotype considering both phases.

RESULTS

Weight gain was not associated with any adrenergic gene.

CONCLUSIONS

Our results suggest that genetic polymorphisms in the adrenergic system may not play a major role in AP-induced weight gain; however, adrenergic 2A receptor gene that produced previously the most consistent associations with this phenotype showed a significant interaction with the monoamine oxidase A in weight gainers.

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.

Variation in GNB3 predicts response and adverse reactions to antidepressants

There is substantial inter-individual variation in response and adverse reactions to antidepressants, and genetic variation may, in part, explain these differences. GNB3 encodes the β3 subunit of the G protein complex, which is involved in the downstream signalling cascade following monoamine receptor activation. A functional polymorphism in this gene (C825T) has been associated with response to antidepressants. Several lines of evidence suggest that GNB3 moderates improvement in the neurovegetative symptoms of depression (such as sleep and appetite) and related adverse reactions independently of change in core mood symptoms. We here report analysis of data from GENDEP, a part-randomized pharmacogenomic trial, on the outcome of 811 subjects with major depression undergoing treatment with either escitalopram or nortriptyline in which the C825T SNP and three further SNPs in GNB3 were genotyped. The TT genotype was significantly associated with a superior response to nortriptyline and these effects were specific to improvements in neurovegetative symptoms. In addition, the same genotype predicted fewer incidents of treatment-emergent insomnia and greater weight gain on the same drug. Our results are consistent with previous associations with GNB3 and emphasize the importance of signalling genes in antidepressant response.

Pharmacogenetics and antipsychotics: therapeutic efficacy and side effects prediction

IMPORTANCE OF THE FIELD

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

AREAS COVERED IN THIS REVIEW

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

WHAT THE READER WILL GAIN

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

TAKE HOME MESSAGE

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

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

A positive association between homeostasis model assessment of insulin resistance score and the Trp64Arg polymorphism of the β3-Adrenergic receptor gene in schizophrenia patients in Taiwan

OBJECTIVE

To investigate the possible association between the Trp64Arg polymorphism of the β3-adrenergic receptor gene and the homeostasis model assessment of insulin resistance (HOMA-IR) index in schizophrenia patients in Taiwan.

METHOD

A total of 203 inpatients who met DSM-IV diagnostic criteria for schizophrenia were recruited from a psychiatry center in Taiwan from September 2002 to August 2003. All patients had been treated with antipsychotics for at least 6 months. The genotyping of the Trp64Arg polymorphism of the β3-adrenergic receptor gene was done by the polymerase chain reaction-restriction fragment length polymorphism method with the restriction enzyme MvaI. The HOMA-IR index was used to indicate the degree of insulin resistance.

RESULTS

After adjusting for sex, age, and body mass index status, the association between the HOMA-IR index and the Trp64Arg polymorphism of the β3-adrenergic receptor gene was still positive (regression coefficient = -0.65, P = .033).

CONCLUSIONS

The polymorphism of the β3-adrenergic receptor gene may be related to the development of insulin resistance in chronic schizophrenia patients in Taiwan.

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 of the α2A adrenergic receptor -1291C/G polymorphism and antipsychotic-induced weight gain in European–Americans

Aims: To investigate the -1291 C/G promoter polymorphism (rs1800544) of the adrenergic α-2A receptor (ADRA2A) with clozapine-/olanzapine-induced weight gain in European–Americans and African–Americans. The α-adrenergic receptors inhibit lipolysis in the adipose tissue and are involved in weight gain regulation. Moreover, two previous studies indicated an association with antipsychotic-induced weight gain with the same polymorphism in Asian populations. Materials & methods: We analyzed a relatively large (n = 129) and well-characterized group of patients and monitored them for a period of 6–14 weeks. Our refined sample consisted of 60 European–Americans and 39 African–Americans on clozapine or olanzapine, prospectively. Results: In European–Americans, we observed a significant difference in weight gain across the genotypic categories (p = 0.046). The carriers of the C allele gained more weight compared with the subjects homozygous for the GG allele (CC + CG vs GG; 3.73 ± 4.13 kg vs 0.23 ± 2.92 kg; p = 0.013). We did not find a significant association in African–Americans, although the sample size was probably too small. Conclusion: Our observations suggest a possible role of ADRA2A polymorphisms in clozapine-/olanzpaine-induced weight gain in subjects of European descent.

G-protein beta3 Subunit Gene 825C/T Polymorphism Is Not Associated with Olanzapine-Induced Weight Gain in Korean Schizophrenic Patients

OBJECTIVE

Weight gain is a possible adverse effect of the use of antipsychotics, and is an important factor for long-term health and treatment compliance. Olanzapine is an atypical antipsychotic known to cause considerable weight gain. A relationship between weight gain and the G protein beta3 subunit gene (GNB3) 825C/T polymorphism has been reported. We therefore examined this possible association in a Korean schizophrenic patient group receiving olanzapine treatment.

METHODS

Weight and height measurements were obtained prior to starting olanzapine and measured again after long-term treatment. Genotyping for the 825C/T polymorphism was performed using a PCR-based method.

RESULTS

We found that long-term treatment with olanzapine resulted in mean gains in weight and body mass index (BMI) of 5.2 kg and 1.93 kg/m(2), respectively. There was a no significant difference in the mean body weight change from baseline to the endpoint after olanzapine treatment between the genotype groups (p=0.796). There were also no significant differences in genotype or allele frequencies between the severe weight-gain (more than 10%) and minimal weight-gain (less than 10%) groups (chi(2)=0.037, p=0.98; chi(2)=0.020, p=0.89).

CONCLUSION

The finding from this study thus does not support a relationship between the GNB3 825C/T polymorphism and weight gain in Korean schizophrenic patients receiving olanzapine treatment.

Association of antipsychotic induced weight gain and body mass index with GNB3 gene: a meta-analysis

It has been reported that C825T variant in the gene encoding the G-protein subunit beta3 (GNB3) is associated with antipsychotic-induced weight gain and obesity. We investigated the association of the GNB3 and antipsychotic-induced weight gain as well as body mass index (BMI) using meta-analytical techniques. Our analysis of 402 schizophrenia subjects showed a trend (p=0.072) only under a fixed-model. As it was observed heterogeneity among the studies (p=0.007), we re-analyzed using a random-effects framework and no significance was found (p=0.339). No evidence for bias publication was reported (p=0.868). Our analysis of 18,903 subjects showed a trend (p=0.053) associating CC and lower BMI under a fixed model. Although no significant association was found, the same pattern (CC and lower antipsychotic-induced weight gain) was observed. Our meta-analysis indicates that firmly establishing the role of pharmacogenetics in clinical psychiatry requires much larger sample sizes that have been reported.

Performance of a neuro-fuzzy model in predicting weight changes of chronic schizophrenic patients exposed to antipsychotics

Artificial intelligence has become a possible solution to resolve the problem of loss of information when complexity of a disease increases. Obesity phenotypes are observable clinical features of drug-naive schizophrenic patients. In addition, atypical antipsychotic medications may cause these unwanted effects. Here we examined the performance of neuro-fuzzy modeling (NFM) in predicting weight changes in chronic schizophrenic patients exposed to antipsychotics. Two hundred and twenty inpatients meeting DSMIV diagnosis of schizophrenia, treated with antipsychotics, either typical or atypical, for more than 2 years, were recruited. All subjects were assessed in the same study period between mid-November 2003 and mid-April 2004. The baseline and first visit's physical data including weight, height and circumference were used in this study. Clinical information (Clinical Global Impression and Life Style Survey) and genotype data of five single nucleotide polymorphisms were also included as predictors. The subjects were randomly assigned into the first group (105 subjects) and second group (115 subjects), and NFM was performed by using the FuzzyTECH 5.54 software package, with a network-type structure constructed in the rule block. A complete learned model trained from merged data of the first and second groups demonstrates that, at a prediction error of 5, 93% subjects with weight gain were identified. Our study suggests that NFM is a feasible prediction tool for obesity in schizophrenic patients exposed to antipsychotics, with further improvements required.

Possible association between G-protein β3 subunit C825T polymorphism and antipsychotic-induced restless legs syndrome in schizophrenia

OBJECTIVE

The incidence of restless legs syndrome (RLS) is presumed to be higher among people with schizophrenia who take antipsychotic medication, most of which blocks the dopamine D2 receptor. The purpose of this study was to determine whether the G-protein β3 subunit (GNB3) C825T polymorphism is associated with antipsychotic-induced RLS in schizophrenia.

METHODS

We examined 178 Korean patients with schizophrenia. All of the subjects were evaluated using the diagnostic criteria of the International Restless Legs Syndrome Study Group and the International Restless Legs Scale. Genotyping was performed for the C825T polymorphism in the GNB3 gene.

RESULTS

The genotype distribution did not differ significantly between antipsychotic-induced RLS patients and patients who had no-RLS symptoms (χ 2 = 4.30, p = 0.116). The genotypes of the C825T single-nucleotide polymorphism (SNP) were classified into two groups: C+ (CC and CT genotypes) and C- (TT genotype). The presence of the C allele (C+) was associated with an increased likelihood of RLS (χ 2 = 4.14, p = 0.042; odds ratio = 2.56, 95% confidence interval = 1.02-6.47).

CONCLUSIONS

These results suggest that the GNB3 C825T SNP is associated with RLS in schizophrenia. However, confirming this association requires future larger scale studies in which the effects of medication are strictly controlled.

Pharmacogenetics and pharmacogenomics of schizophrenia: a review of last decade of research

The last decade of research into the pharmacogenetics of antipsychotics has seen the development of genetic tests to determine the patients' metabolic status and the first attempts at personalization of antipsychotic treatment. The most significant results are the association between drug metabolic polymorphisms, mainly in cytochrome P450 genes, with variations in drug metabolic rates and side effects. Patients with genetically determined CYP2D6 poor metabolizer (PMs) status may require lower doses of antipsychotic. Alternatively, CYP2D6 ultrarapid matabolizers (UMs) will need increased drug dosage to obtain therapeutic response. Additionally, polymorphisms in dopamine and serotonin receptor genes are repeatedly found associated with response phenotypes, probably reflecting the strong affinities that most antipsychotics display for these receptors. In particular, there is important evidence suggesting association between dopamine 2 receptor (D2) polymorphisms (Taq I and -141-C Ins/Del) and a dopamine 3 receptor (D3) polymorphism (Ser9Gly) with antipsychotic response and drug-induced tardive dyskinesia. Additionally, there is accumulating evidence indicating the influence of a 5-HT2C polymorphism (-759-T/C) in antipsychotic-induced weight gain. Application of this knowledge to clinical practice is slowly gathering pace, with pretreatment determination of individual's drug metabolic rates, via CYP genotyping, leading the field. Genetic determination of patients' metabolic status is expected to bring clinical benefits by helping to adjust therapeutic doses and reduce adverse reactions. Genetic tests for the pretreatment prediction of antipsychotic response, although still in its infancy, have obvious implications for the selection and improvement of antipsychotic treatment. These developments can be considered as successes, but the objectives of bringing pharmacogenetic and pharmacogenomic research in psychiatric clinical practice are far from being realized. Further development of genetic tests is required before the concept of tailored treatment can be applied to psychopharmatherapy. This review aims to summarize the key findings from the last decade of research in the field. Current knowledge on genetic prediction of drug metabolic status, general response and drug-induced side effects will be reviewed and future pharmacogenomic and epigenetic research will be discussed.

Genetics of antipsychotic treatment emergent weight gain in schizophrenia

Classic and modern antipsychotics can induce substantial weight gain causing diabetes, lipid abnormalities and psychological distress. Treatment emergent weight gain varies within the broad class of antipsychotics; however, an individual's propensity to develop weight gain largely depends on genetic factors. The first part of this review highlights current ideas and concepts related to antipsychotic-induced weight gain, including principles on energy homeostasis. The second part summarizes genetic findings emphasizing studies published after 2003 as prior studies have been reviewed in detail elsewhere. Candidate gene studies have produced significant findings in the 5-hydroxytryptamin 2C (5HT2C) and adrenergic alpha2a (ADRalpha2a) receptor genes, as well as in the leptin, guanine nucleotide binding protein (GNB3) and synaptomal-associated protein 25kDa (SNAP25) genes. Results from genome-wide association and linkage studies point to several chromosomal regions (e.g., 12q24) and some specific genes (e.g., promelanin concentrating hormone [PMCH], polycyctic kidney and hepatic disease 1 [PKHD1], peptidylglycine alpha-amidating monooxygenase [PAM]). However, more efforts are needed before risk prediction and personalized medicine can be made available for antipsychotic-induced weight gain.

Pharmacogenetics of schizophrenia

There is substantial unexplained interindividual variability in the drug treatment of schizophrenia. A substantial proportion of patients respond inadequately to antipsychotic drugs, and many experience limiting side effects. As genetic factors are likely to contribute to this variability, the pharmacogenetics of schizophrenia has attracted substantial effort. The approaches have mainly been limited to association studies of polymorphisms in candidate genes, which have been indicated by the pharmacology of antipsychotic drugs. Although some advances have been made, particularly in understanding the pharmacogenetics of some limiting side effects, genetic prediction of symptom response remains elusive. Nevertheless, with improvements in defining the response phenotype in carefully assessed and homogeneous subject groups, the near future is likely to see the identification of genetic predictors of outcome that may inform the choice of pharmacotherapy.

Clozapine-induced weight gain: a study in monozygotic twins and same-sex sib pairs

To assess the relative contribution of genetic factors in antipsychotic-induced weight gain, we explored the similarity in body mass index (BMI) (kg/m(2)) change under clozapine only (clozapine DeltaBMI) and upon additional inclusion of BMI change under prior antipsychotic medication (total DeltaBMI) of five monozygotic twins in comparison with seven same-sex sibs. Twin and sib pairs were identified by a telephone screening of 786 office-based psychiatrists. Measured data on weight and other clinical variables were obtained cross-sectionally and retrospectively from medical records. We found greater similarity in total DeltaBMI in monozygotic twins (intrapair difference 2.78+/-3.41 kg/m(2)) than in same-sex sibs (5.55+/-4.35 kg/m(2)), resulting in heritability estimates of h(2)=0.8 and A=0.45 (ACE twin model). However, intrapair differences in clozapine DeltaBMI were similar between twins (4.18+/-4.27 kg/m(2)) and sibs (4.68+/-4.88 kg/m(2)). We hypothesize that the weight plateau achieved under clozapine is influenced by genetic factors. The weight gain achieved during pretreatment with other antipsychotics seems to limit clozapine-induced weight gain, thus presumably explaining why heritability/similarity in monozygotic twins in comparison with same-sex sibs is greater for total DeltaBMI than for clozapine DeltaBMI. An important caveat is that, owing to the sample size, the heritability estimates have a large standard error and thus have to be interpreted with caution.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.