Lack of association between the –759C/T polymorphism of the 5-HT2C receptor gene and clozapine-induced weight gain among German schizophrenic individuals

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

5-HT2C receptor gene is viewed as an important candidate gene in pharmacogenetic studies of antipsychotic drug-induced weight gain. However, inconsistent results have been obtained in different populations. We investigated the association between the -759C/T polymorphism of the 5-HT2C receptor gene with early phase (after 4 weeks of treatment) weight gain induced by antipsychotic treatment in Korean schizophrenia patients. The study subjects were eighty-four in-patients receiving monotherapy with one of six antipsychotic drugs. Patients with the variant allele (-759T) were found to be less likely to have substantial (> 5%) weight gain (Fisher's exact test, p=0.030), and this association (t=1.91, df=75, p=0.030) was supported by the repeated measures analysis after controlling for possible confounding effects, i.e., age, sex, baseline BMI, and the type of antipsychotic medicine administered. The variant allele also appeared to have a protective effect against weight gain in a subgroup of patients receiving risperidone. These results support the involvement of the -759C/T polymorphism of the 5-HT2C receptor gene in antipsychotics-induced weight gain in the Korean population.

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.

The association between HTR2C polymorphisms and obesity in psychiatric patients using antipsychotics: a cross-sectional study

The use of antipsychotics is associated with an increased risk of obesity. This consideration makes it important to search for determinants that can predict the risk for antipsychotic-induced obesity. In this cross-sectional study, we investigated whether polymorphisms in the HTR2C gene were associated with obesity (body mass index >30 kg/m2) in patients using antipsychotics. We examined polymorphisms in the promoter region of the HTR2C gene ((HTR2C:c.1-142948(GT)n, rs3813928 (-997 G/A), rs3813929 (-759 C/T), rs518147 (-697 G/C)) and an intragenic polymorphism (rs1414334:C>G). The results of the logistic regression were expressed as adjusted odds ratios (OR). In total, we included 127 patients mainly diagnosed with schizophrenia or schizoaffective disorder (89%). The results indicate that a combined genotype carrying the variant HTR2C:c.1-142948(GT)n 13 repeat allele, the common allele rs3813929 C, the variant allele rs518147 C and the variant allele rs1414334 C is significantly related to an increased risk of obesity (OR 3.71 (95% confidence interval: 1.24-11.12)).

No evidence for binding of clozapine, olanzapine and/or haloperidol to selected receptors involved in body weight regulation

The underlying mechanisms of antipsychotic (AP)-induced weight gain are unknown, but both central and peripheral AP target receptors could potentially be involved. This study used radioligand binding assays to compare the binding affinities of clozapine, olanzapine and haloperidol for candidate receptors potentially involved in AP-induced weight gain. Selected candidates derived from known pathways involved in body weight regulation included receptors classified as anorexigenic (bombesin receptor subtype 3, calcitonin gene-related peptide receptor, cholecystokinin receptor, melanocortin-4 receptor, neurotensin receptor 1) or orexigenic (cannabinoid receptor 1, galanin 1 receptor, melanin-concentrating hormone receptor (MCHR), neuropeptide Y1 receptor) as well as receptors involved in physiological actions related to digestion and fluid homeostasis (angiotensin II type 1 receptor, bradykinin B2 receptor, endothelin receptor, neurokinin 1 receptor, vasoactive intestinal polypeptide receptor 1). Clozapine, olanzapine and haloperidol exhibited negligible affinities to all of these receptors except for the MCHR (Ki=501 nM; haloperidol). With respect to other candidates from (neuro)transmitter systems already suggested to be involved in AP-induced weight gain, the binding profile of olanzapine resembled that of clozapine, with high affinity (Ki<10 nM) for serotonin (5-HT) 5-HT2A, 5-HT2C and 5-HT6, muscarinic M1 and histamine H1 receptors. In contrast, the binding profile of haloperidol was substantially different (high affinity only for the dopamine D1 receptor). In conclusion, we have not identified a novel binding site of the two investigated atypical AP that could contribute to the 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.

An overview of the central control of weight regulation and the effect of antipsychotic medication

Weight regulation is a complex system necessary for maintaining health. Obesity and cachexia are consequences of dysregulation and cause significant physical morbidity and mortality. In the developed world, obesity is a growing epidemic. A greater understanding of the neuroanatomy of weight regulation has been gained through advances in imaging and neural mapping techniques. The neural connections between key hypothalamic and other central nuclei have been elucidated. Advances in molecular biology have led to the identification and cloning of important peripheral and central weight regulating peptides. Weight gain as a consequence of antipsychotic use is increasingly being recognized as a serious clinical issue. The weight regulation system provides a framework upon which antipsychotics exert their weight-inducing effects. Some studies have sought, with inconsistent results, to establish associations between antipsychotic use and levels of weight regulating mediators. The receptor pharmacology of antipsychotics known to increase weight can be studied with a view to establishing genetic variants contributing to the risk. To date, the 5-HT(2C) receptor 759C/T polymorphism shows most promise. Further studies are required to replicate previous findings and establish new associations.

Clustering of metabolic comorbidity in schizophrenia: a genetic contribution?

People with schizophrenia are more likely to develop type 2 diabetes than the general population. Although an increased risk of diabetes has been attributed to environmental determinants such as diet, lifestyle and antipsychotic drugs, the association between these two disorders was noticed well before the advent of current lifestyles and pharmacological interventions, raising the possibility of a shared genetic basis. Schizophrenia and type 2 diabetes are common diseases with a complex mode of inheritance which includes both genetic factors and environmental determinants. As susceptibility genes for both type 2 diabetes and schizophrenia are beginning to be identified there is increasing interest in the possibility of shared susceptibility loci between the two conditions. This article reviews the genetic basis to schizophrenia and type 2 diabetes and discusses the potential for shared loci between both conditions.

C825T polymorphism in the human G protein beta3 subunit gene is associated with long-term clozapine treatment-induced body weight change in the Chinese population

Weight gain, leading to further morbidity and poor treatment compliance, is a common adverse effect of treatment with clozapine. The C825T polymorphism in the human G protein beta3 subunit gene has been noted to be associated with obesity, hypertension and coronary artery disease. Clozapine increases the level of G protein beta3 subunit in the rat striatum. The aim of the present study was to investigate the relationship between G protein beta3 polymorphisms and clozapine-induced body weight change in a Chinese population during long-term treatment. One hundred and thirty-four schizophrenic patients, who were treated with clozapine continuously (13.4+/-0.5 months), were genotyped for G protein beta3 subunit C825T polymorphism. None of these patients received second-generation antipsychotics before clozapine treatment. Body weight was monitored at baseline before clozapine treatment and at the endpoint after clozapine treatment. Patients with the TT type experienced significantly more weight gain (16.2+/-2.5%) compared to those with CT (9.3+/-1.2%) or CC types (5.5+/-2.4%) after long-term clozapine treatment (P = 0.003). Further stratification by gender demonstrated that the effect of C825T polymorphism on weight gain remained significant both in males and females. These findings confirm the importance of genetic factors in body weight change induced by long-term clozapine treatment in patients with schizophrenia, and indicate a role for the G protein beta3 subunit in body weight regulation during long-term clozapine treatment.

Polymorphisms of the 5-HT2C receptor and leptin genes are associated with antipsychotic drug-induced weight gain in Caucasian subjects with a first-episode psychosis

OBJECTIVES

Weight gain, leading to further morbidity and poor treatment adherence, is a common consequence of treatment with antipsychotic drugs. Two recent studies in the same cohort of Chinese Han subjects have shown that polymorphisms of the promoter regions of both the serotonin 5-hydroxytryptamine 2C (5-HT2C) receptor and the leptin genes, are associated with antipsychotic-induced weight gain over 10 weeks. We have investigated whether these effects remain true in a Caucasian population and following longer term treatment.

METHODS

Seventy-three Spanish caucasian patients with a first-episode psychosis and initially drug-naive were genotyped for the 5-HT2C receptor -759C/T and leptin -2548A/G polymorphisms. Body mass index and plasma leptin levels were monitored after 6 weeks, 3 months and 9 months of antipsychotic treatment.

RESULTS

Patients with the -759T variant allele showed significantly less weight gain than those without this allele. This effect held true in the smaller group of patients receiving olanzapine. The -2548 leptin polymorphism was not associated with short-term (6 week and 3 month) weight increases but did show significant association with 9-month antipsychotic-induced weight gain. The 5-HT2C -759 genotype was significantly associated with pre-treatment plasma leptin levels.

CONCLUSIONS

These findings confirm the importance of two genetic factors associated with long-term antipsychotic-induced weight increases in schizophrenia, and implicate a role for leptin in the 5-HT receptor-mediated weight regulation.

Second-generation (atypical) antipsychotics and metabolic effects: a comprehensive literature review

Increasing numbers of reports concerning diabetes, ketoacidosis, hyperglycaemia and lipid dysregulation in patients treated with second-generation (or atypical) antipsychotics have raised concerns about a possible association between these metabolic effects and treatment with these medications. This comprehensive literature review considers the evidence for and against an association between glucose or lipid dysregulation and eight separate second-generation antipsychotics currently available in the US and/or Europe, specifically clozapine, olanzapine, risperidone, quetiapine, zotepine, amisulpride, ziprasidone and aripiprazole. This review also includes an assessment of the potential contributory role of treatment-induced weight gain in conferring risk for hyperglycaemia and dyslipidaemia during treatment with different antipsychotic medications. Substantial evidence from a variety of human populations, including some recent confirmatory evidence in treated psychiatric patients, indicates that increased adiposity is associated with a variety of adverse physiological effects, including decreases in insulin sensitivity and changes in plasma glucose and lipid levels. Comparison of mean weight changes and relative percentages of patients experiencing specific levels of weight increase from controlled, randomised clinical trials indicates that weight gain liability varies significantly across the different second generation antipsychotic agents. Clozapine and olanzapine treatment are associated with the greatest risk of clinically significant weight gain, with other agents producing relatively lower levels of risk. Risperidone, quetiapine, amisulpride and zotepine generally show low to moderate levels of mean weight gain and a modest risk of clinically significant increases in weight. Ziprasidone and aripiprazole treatment are generally associated with minimal mean weight gain and the lowest risk of more significant increases. Published studies including uncontrolled observations, large retrospective database analyses and controlled experimental studies, including randomised clinical trials, indicate that the different second-generation antipsychotics are associated with differing effects on glucose and lipid metabolism. These studies offer generally consistent evidence that clozapine and olanzapine treatment are associated with an increased risk of diabetes mellitus and dyslipidaemia. Inconsistent results, and a generally smaller effect in studies where an effect is reported, suggest limited if any increased risk for treatment-induced diabetes mellitus and dyslipidaemia during risperidone treatment, despite a comparable volume of published data. A similarly smaller and inconsistent signal suggests limited if any increased risk of diabetes or dyslipidaemia during quetiapine treatment, but this is based on less published data than is available for risperidone. The absence of retrospective database studies, and little or no relevant published data from clinical trials, makes it difficult to draw conclusions concerning risk for zotepine or amisulpride, although amisulpride appears to have less risk of treatment-emergent dyslipidaemia in comparison to olanzapine. With increasing data from clinical trials but little or no currently published data from large retrospective database analyses, there is no evidence at this time to suggest that ziprasidone and aripiprazole treatment are associated with an increase in risk for diabetes, dyslipidaemia or other adverse effects on glucose or lipid metabolism. In general, the rank order of risk observed for the second-generation antipsychotic medications suggests that the differing weight gain liability of atypical agents contributes to the differing relative risk of insulin resistance, dyslipidaemia and hyperglycaemia. This would be consistent with effects observed in nonpsychiatric samples, where risk for adverse metabolic changes tends to increase with increasing adiposity. From this perspective, a possible increase in risk would be predicted to occur in association with any treatment that produces increases in weight and adiposity. However, case reports tentatively suggest that substantial weight gain or obesity may not be a factor in up to one-quarter of cases of new-onset diabetes that occur during treatment. Pending further testing from preclinical and clinical studies, limited controlled studies support the hypothesis that clozapine and olanzapine may have a direct effect on glucose regulation independent of adiposity. The results of studies in this area are relevant to primary and secondary prevention efforts that aim to address the multiple factors that contribute to increased prevalence of type 2 diabetes mellitus and cardiovascular disease in populations that are often treated with second-generation antipsychotic medications.

Treatment-refractory schizophrenia

PURPOSE OF REVIEW

The aim of this article is to critically review the current literature on treatment-refractory schizophrenia with an emphasis on emergent themes and key findings.

RECENT FINDINGS

New information continues to emerge on the impact of each second-generation antipsychotic on the treatment-refractory patient population and on the traditionally more difficult-to-treat components (e.g. cognition, suicidality, violence) of the illness. There are continued efforts with pharmacogenetics to predict response and side-effect risk with antipsychotic medications. Polypharmacy continues to be a major and poorly understood treatment practice.

SUMMARY

Our field is advancing the therapeutic nuances of therapy with second-generation antipsychotics in treatment-refractory schizophrenia. Additionally, there is a growing appreciation of the emergent adverse-effect profile of antipsychotic medications and these risk-benefit considerations are more pronounced in severely ill patients.

Clozapine: weight gain in a pair of monozygotic twins concordant for schizophrenia and mild mental retardation

Clozapine is an atypical antipsychotic known to cause considerable weight gain. The extent to which genetic factors determine weight gain is unknown. Here we report on a pair of female monozygotic twins concordant for schizophrenia and mild mental retardation who were treated with clozapine over 5.5 years. One twin gained a total of 53.1 kg and had a weight of 107.5 kg (BMI=38.1 kg/m2) at the end of the observation period. The other twin gained a total of 48.2 kg and finally had a weight of 100.4 kg (BMI=33.8 kg/m2). Because both patients experienced considerable weight gain during treatment, our observation suggests that the antipsychotic-induced weight gain is under strong genetic control.