Genetics of tardive dyskinesia

Genome-wide DNA methylation analysis in schizophrenia with tardive dyskinesia: a preliminary study

BACKGROUND

Tardive dyskinesia (TD) develops in 20-30% of schizophrenia patients and up to 50% in patients > 50 years old. DNA methylation may play an important role in the development of TD.

OBJECTIVE

DNA methylation analyses in schizophrenia with TD.

METHODS

We conducted a genome-wide DNA methylation analysis in schizophrenia with TD using methylated DNA immunoprecipitation coupled with next-generation sequencing (MeDIP-Seq) in a Chinese sample including five schizophrenia patients with TD and five without TD (NTD), and five healthy controls. The results were expressed as the log2FC, fold change of normalized tags between two groups within the differentially methylated region (DMR). For validation, the pyrosequencing was used to quantify DNA methylation levels of several methylated genes in an independent sample (n = 30).

RESULTS

Through genome-wide MeDIP-Seq analysis, we identified 116 genes that were significantly differentially methylated in promotor regions in comparison of TD group with NTD group including 66 hypermethylated genes (top 4 genes are GABRR1, VANGL2, ZNF534, and ZNF746) and 50 hypomethylated genes (top 4 genes are DERL3, GSTA4, KNCN, and LRRK1). Part of these genes (such as DERL3, DLGAP2, GABRR1, KLRG2, LRRK1, VANGL2, and ZP3) were previously reported to be associated with methylation in schizophrenia. Gene Ontology enrichment and KEGG pathway analyses identified several pathways. So far, we have confirmed the methylation of 3 genes (ARMC6, WDR75, and ZP3) in schizophrenia with TD using pyrosequencing.

CONCLUSIONS

This study identified number of methylated genes and pathways for TD and will provide potential biomarkers for TD and serve as a resource for replication in other populations.

Altered DNA methylation of CYP2E1 gene in schizophrenia patients with tardive dyskinesia

BACKGROUND

About 20-30% of patients with schizophrenia develop tardive dyskinesia (TD). Oxidative stress is one potential causes of TD. CYP2E1 is considered as an oxidative stress-related gene, however, no study has been reported on the DNA methylation levels of the CYP2E1 in schizophrenia or TD.

METHODS

A total of 35 schizophrenia patients with TD, 35 schizophrenia patients without TD (NTD), and 35 health controls (HCs) were collected in Beijing, China. DNA was extracted from peripheral blood samples. The promoter methylation levels of CYP2E1 were detected using pyrosequencing. The generalized linear model (GLM) was used to examine the methylation levels of three CpG sites among three diagnostic groups (TD vs. NTD vs. HC).

RESULTS

The average methylation levels were 8.8 ± 10.0, 14.5 ± 11.9 and 15.1 ± 11.3 in TD, NTD and HC groups, respectively. The F-test in GLM revealed overall differences in the average of methylation levels of three CpG sites among three diagnostic groups (p = 0.0227) and in the third CpG site (p = 0.0026). Furthermore, the TD group had lower average methylation levels than HC and NTD groups (p = 0.0115 and 0.0268, respectively). Specifically, TD group showed lower methylation levels in the third CpG site than HC and NTD groups (p = 0.0012 and 0.0072, respectively). Additionally, associations of the methylation levels with clinical features in the TD group were observed using Spearman correlation analysis.

CONCLUSION

This study provides the first evidence of DNA methylation levels in the promoter of CYP2E1 gene associated with schizophrenia and TD. The abnormal DNA methylation might serve as a potential mechanism for TD.

Tardive Dyskinesia Development, Superoxide Dismutase Levels, and Relevant Genetic Polymorphisms

Tardive dyskinesia (TD) is a prevalent movement disorder that significantly impacts patients with schizophrenia (SCZ) due to extended exposure to antipsychotics (AP). Several genetic polymorphisms, including superoxide dismutase (SOD) and DRD3 9ser, have been suggested as explanations why some patients suffer from TD. Methods. A PubMed search was used to search relevant articles using the following keywords: “Tardive Dyskinesia and Superoxide Dismutase”. Fifty-eight articles were retrieved. Among them, 16 were included in this review. Results. Overall, 58 studies were retrieved from PubMed. Most studies investigated the association between TD and the SOD-related polymorphisms. In addition, previous studies reported an association between TD occurrence and other genetic polymorphisms. Conclusion. This study found that the risk of TD is associated with altered SOD levels and several genetic polymorphisms, including VAL 66 Met and DRD3 9ser.

Pharmacogenetics of Antipsychotic Treatment in Schizophrenia

Antipsychotics are the mainstay treatment for schizophrenia. There is large variability between individuals in their response to antipsychotics, both in efficacy and adverse effects of treatment. While the source of interindividual variability in antipsychotic response is not completely understood, genetics is a major contributing factor. The identification of pharmacogenetic markers that predict antipsychotic efficacy and adverse reactions is a growing area of research and holds the potential to replace the current trial-and-error approach to treatment selection in schizophrenia with a personalized medicine approach.In this chapter, we provide an overview of the current state of pharmacogenetics in schizophrenia treatment. The most promising pharmacogenetic findings are presented for both antipsychotic response and commonly studied adverse reactions. The application of pharmacogenetics to schizophrenia treatment is discussed, with an emphasis on the clinical utility of pharmacogenetic testing and directions for future research.

Genome wide study of tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a severe condition characterized by repetitive involuntary movement of orofacial regions and extremities. Patients treated with antipsychotics typically present with TD symptomatology. Here, we conducted the largest GWAS of TD to date, by meta-analyzing samples of East-Asian, European, and African American ancestry, followed by analyses of biological pathways and polygenic risk with related phenotypes. We identified a novel locus and three suggestive loci, implicating immune-related pathways. Through integrating trans-ethnic fine mapping, we identified putative credible causal variants for three of the loci. Post-hoc analysis revealed that SNPs harbored in TNFRSF1B and CALCOCO1 independently conferred three-fold increase in TD risk, beyond clinical risk factors like Age of onset and Duration of illness to schizophrenia. Further work is necessary to replicate loci that are reported in the study and evaluate the polygenic architecture underlying TD.

Pharmacogenetics of antipsychotics: Clinical utility and implementation

Decades of research have produced extensive evidence of the contribution of genetic factors to the efficacy and toxicity of antipsychotics. Numerous genetic variants in genes controlling drug availability or involved in antipsychotic processes have been linked to treatment variability. The complex mechanism of action and multitarget profile of most antipsychotic drugs hinder the identification of pharmacogenetic markers of clinical value. Nevertheless, the validity of associations between variants in CYP1A2, CYP2D6, CYP2C19, ABCB1, DRD2, DRD3, HTR2A, HTR2C, BDNF, COMT, MC4R genes and antipsychotic response has been confirmed in independent candidate gene studies. Genome wide pharmacogenomic studies have proven the role of the glutamatergic pathway in mediating antipsychotic activity and have reported novel associations with antipsychotic response. However, only a limited number of the findings, mainly functional variants of CYP metabolic enzymes, have been shown to be of clinical utility and translated into useful pharmacogenetic markers. Based on the currently available information, actionable pharmacogenetics should be reduced to antipsychotics' dose adjustment according to the genetically predicted metabolic status (CYPs' profile) of the patient. Growing evidence suggests that such interventions will reduce antipsychotics' side-effects and increase treatment safety. Despite this evidence, the use of pharmacogenetics in psychiatric wards is minimal. Hopefully, further evidence on the clinical and economic benefits, the development of clinical protocols based on pharmacogenetic information, and improved and cheaper genetic testing will increase the implementation of pharmacogenetic guided prescription in clinical settings.

Association between the IL10 rs1800896 Polymorphism and Tardive Dyskinesia in Schizophrenia

OBJECTIVE

Interleukin-10 (IL-10) is a major immunoregulatory cytokine and its gene plays a fundamental role in anti-inflammatory and immunosuppressive activity. This study aimed to examine the association between the IL10 gene promoter -1082G/A polymorphism (rs1800896) and tardive dyskinesia (TD) in schizophrenia.

METHODS

Two hundred and eighty unrelated Korean schizophrenic patients participated in this study (105 TD and 175 non-TD patients). TD was diagnosed using the Research Diagnostic Criteria for TD and Abnormal Involuntary Movement Scale (AIMS). Genotyping was performed by RT-PCR and high-resolution melting curve analysis.

RESULTS

The distributions of genotypic frequencies did not differ between patients with and without TD (χ2=4.33, p=0.115). However, allelic frequencies of the two groups were different (χ2=4.45, p=0.035); the A allele frequency was higher in TD. The total AIMS scores of the three genotypes were not different (F=1.33, p=0.266). However, the total AIMS scores of the A allele carrier and the A allele non-carrier were significantly different (t=5.79, p<0.001). Logistic regression analaysis showed that IL10 -1082G/A genotype significantly predicts presence of TD (p=0.045) after adjusting for covariates such as age and treatment duration.

CONCLUSION

This finding suggests that the A allele of rs1800896 may be associated with TD development following a low IL-10 function.

Tardive syndromes

Dopamine receptor-blocking antipsychotics, first introduced into clinical practice in 1952, were hailed as a panacea in the treatment of a number of psychiatric disorders. However, within 5 years, this notion was to be shattered by the recognition of both acute and chronic drug-induced movement disorders which can accompany their administration. Tardive syndromes, denoting the delayed onset of movement disorders following administration of dopamine receptor-blocking (and also other) drugs, have diverse manifestations ranging from the classic oro-bucco-lingual dyskinesia, through dystonic craniocervical and trunk posturing, to abnormal breathing patterns. Although tardive syndromes have been an important part of movement disorder clinical practice for over 60 years, their pathophysiologic basis remains poorly understood and the optimal treatment approach remains unclear. This review summarises the current knowledge relating to these syndromes and provides clinicians with pragmatic, clinically focused guidance to their management.

Pharmacogenomics of Cognitive Dysfunction and Neuropsychiatric Disorders in Dementia

Symptomatic interventions for patients with dementia involve anti-dementia drugs to improve cognition, psychotropic drugs for the treatment of behavioral disorders (BDs), and different categories of drugs for concomitant disorders. Demented patients may take >6–10 drugs/day with the consequent risk for drug–drug interactions and adverse drug reactions (ADRs >80%) which accelerate cognitive decline. The pharmacoepigenetic machinery is integrated by pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes redundantly and promiscuously regulated by epigenetic mechanisms. CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 geno-phenotypes are involved in the metabolism of over 90% of drugs currently used in patients with dementia, and only 20% of the population is an extensive metabolizer for this tetragenic cluster. ADRs associated with anti-dementia drugs, antipsychotics, antidepressants, anxiolytics, hypnotics, sedatives, and antiepileptic drugs can be minimized by means of pharmacogenetic screening prior to treatment. These drugs are substrates, inhibitors, or inducers of 58, 37, and 42 enzyme/protein gene products, respectively, and are transported by 40 different protein transporters. APOE is the reference gene in most pharmacogenetic studies. APOE-3 carriers are the best responders and APOE-4 carriers are the worst responders; likewise, CYP2D6-normal metabolizers are the best responders and CYP2D6-poor metabolizers are the worst responders. The incorporation of pharmacogenomic strategies for a personalized treatment in dementia is an effective option to optimize limited therapeutic resources and to reduce unwanted side-effects.

Pyrosequencing analysis of IRS1 methylation levels in schizophrenia with tardive dyskinesia

Tardive dyskinesia (TD) is a serious side effect of certain antipsychotic medications that are used to treat schizophrenia (SCZ) and other mental illnesses. The methylation status of the insulin receptor substrate 1 (IRS1) gene is reportedly associated with SCZ; however, no study, to the best of the authors' knowledge, has focused on the quantitative DNA methylation levels of the IRS1 gene using pyrosequencing in SCZ with or without TD. The present study aimed to quantify DNA methylation levels of 4 CpG sites in the IRS1 gene using a Chinese sample including SCZ patients with TD and without TD (NTD) and healthy controls (HCs). The general linear model (GLM) was used to detect DNA methylation levels among the 3 proposed groups (TD vs. NTD vs. HC). Mean DNA methylation levels of 4 CpG sites demonstrated normal distribution. Pearson's correlation analysis did not reveal any significant correlations between the DNA methylation levels of the 4 CpG sites and the severity of SCZ. GLM revealed significant differences between the 3 groups for CpG site 1 and the average of the 4 CpG sites (P=0.0001 and P=0.0126, respectively). Furthermore, the TD, NTD and TD + NTD groups demonstrated lower methylation levels in CpG site 1 (P=0.0003, P<0.0001 and P<0.0001, respectively) and the average of 4 CpG sites (P=0.0176, P=0.0063 and P=0.003, respectively) compared with the HC group. The results revealed that both NTD and TD patients had significantly decreased DNA methylation levels compared with healthy controls, which indicated a significant association between the DNA methylation levels of the IRS1 gene with SCZ and TD.

Association Study of the Complement Component C4 Gene in Tardive Dyskinesia

Tardive dyskinesia (TD) is a movement disorder that may develop in schizophrenia patients being treated long-term with antipsychotic medication. TD interferes with voluntary movements and leads to stigma, and can be associated with treatment non-adherence. The etiology of TD is unclear, but it appears to have a genetic component. There is emerging evidence of immune dysregulation in TD. In the current study, we set out to investigate the complex schizophrenia-associated complement component 4 (C4) gene for possible association with TD occurrence and TD severity as assessed by the Abnormal Involuntary Movement Scale (AIMS) in a sample of 129 schizophrenia patients of European ancestry. We have genotyped the copy numbers of long and short forms of C4A and C4B gene variants in 129 European ancestry patients with schizophrenia or schizoaffective disorder. We did not find predicted C4A or C4B expression to be nominally associated with TD risk or severity. However, we found the number of copies of C4BL to be nominally associated with TD severity (p = 0.020).

Putative role of pharmacogenetics to elucidate the mechanism of tardive dyskinesia in schizophrenia

Identifying biomarkers which can be used as a diagnostic tool is a major objective of pharmacogenetic studies. Most mental and many neurological disorders have a compiled multifaceted nature, which may be the reason why this endeavor has hitherto not been very successful. This is also true for tardive dyskinesia (TD), an involuntary movement complication of long-term treatment with antipsychotic drugs. The observed associations of specific gene variants with the prevalence and severity of a disorder can also be applied to try to elucidate the pathogenesis of the condition. In this paper, this strategy is used by combining pharmacogenetic knowledge with theories on the possible role of a dysfunction of specific cellular elements of neostriatal parts of the (dorsal) extrapyramidal circuits: various glutamatergic terminals, medium spiny neurons, striatal interneurons and ascending monoaminergic fibers. A peculiar finding is that genetic variants which would be expected to increase the neostriatal dopamine concentration are not associated with the prevalence and severity of TD. Moreover, modifying the sensitivity to glutamatergic long-term potentiation (and excitotoxicity) shows a relationship with levodopa-induced dyskinesia, but not with TD. Contrasting this, TD is associated with genetic variants that modify vulnerability to oxidative stress. Reducing the oxidative stress burden of medium spiny neurons may also be the mechanism behind the protective influence of 5-HT2 receptor antagonists. It is probably worthwhile to discriminate between neostriatal matrix and striosomal compartments when studying the mechanism of TD and between orofacial and limb-truncal components in epidemiological studies.

New insights into tardive dyskinesia genetics: Implementation of whole-exome sequencing approach

Tardive dyskinesia (TD) is an adverse movement disorder induced by chronic treatment with antipsychotics drugs. The contribution of common genetic variants to TD susceptibility has been investigated in recent years, but with limited success. The aim of the current study was to investigate the potential contribution of rare variants to TD vulnerability. In order to identify TD risk genes, we performed whole-exome sequencing (WES) and gene-based collapsing analysis focusing on rare (allele frequency < 1%) and putatively deleterious variants (qualifying variants). 82 Jewish schizophrenia patients chronically treated with antipsychotics were included and classified as having severe TD or lack of any abnormal movements based on a rigorous definition of the TD phenotype. First, we performed a case-control, exome-wide collapsing analysis comparing 39 schizophrenia patients with severe TD to 3118 unrelated population controls. Then, we checked the potential top candidate genes among 43 patients without any TD manifestations. All the genes that were found to harbor one or more qualifying variants in patients without any TD features were excluded from the final list of candidate genes. Only one gene, regulating synaptic membrane exocytosis 2 (RIMS2), showed significant enrichment of qualifying variants in TD patients compared with unrelated population controls after correcting for multiple testing (Fisher's exact test p = 5.32E-08, logistic regression p = 2.50E-08). Enrichment was caused by a single variant (rs567070433) due to a frameshift in an alternative transcript of RIMS2. None of the TD negative patients had qualifying variants in this gene. In a validation cohort of 140 schizophrenia patients assessed for TD, the variant was also not detected in any individual. Some potentially suggestive TD genes were detected in the TD cohort and warrant follow-up in future studies. No significant enrichment in previously reported TD candidate genes was identified. To the best of our knowledge, this is the first WES study of TD, demonstrating the potential role of rare loss-of-function variant enrichment in this pharmacogenetic phenotype.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

A pharmacogenetic intervention for the improvement of the safety profile of antipsychotic treatments

Antipsychotic drugs fail to achieve adequate response in 30-50% of treated patients and about 50% of them develop severe and lasting side effects. Treatment failure results in poorer prognosis with devastating repercussions for the patients, carers and broader society. Our study evaluated the clinical benefits of a pharmacogenetic intervention for the personalisation of antipsychotic treatment. Pharmacogenetic information in key CYP polymorphisms was used to adjust clinical doses in a group of patients who started or switched treatment with antipsychotic drugs (PharmG+, N = 123), and their results were compared with those of a group of patients treated following existing clinical guides (PharmG-, N = 167). There was no evidence of significant differences in side effects between the two arms. Although patients who had their antipsychotic dose adjusted according to CYPs polymorphisms (PharmG+) had a bigger reduction in side effects than those treated as usual (PharmG-), the difference was not statistically significant (p > 0.05 for all comparisons). However, PharmG+ patients treated with CYP2D6 substrates that were carriers of CYP2D6 UMs or PMs variants showed a significantly higher improvement in global, psychic and other UKU side effects than PharmG- patients (p = 0.02, p = 0.05 and p = 0.01, respectively). PharmG+ clozapine treated patients with CYP1A2 or CYP2C19 UM and PMs variants also showed higher reductions in UKU scores than PharmG- clozapine patients in general. However, those differences were not statistically significant. Pharmacogenetic interventions may improve the safety of antipsychotic treatments by reducing associated side effects. This intervention may be particularly useful when considering treatment with antipsychotics with one major metabolic pathway, and therefore more susceptible to be affected by functional variants of CYP enzymes.

Quantitative DNA Methylation Analysis of DLGAP2 Gene using Pyrosequencing in Schizophrenia with Tardive Dyskinesia: A Linear Mixed Model Approach

Tardive dyskinesia (TD) is a side effect of antipsychotic medications used to treat schizophrenia (SCZ) and other mental health disorders. No study has previously used pyrosequencing to quantify DNA methylation levels of the DLGAP2 gene; while the quantitative methylation levels among CpG sites within a gene may be correlated. To deal with the correlated measures among three CpG sites within the DLGAP2 gene, this study analyzed DNA methylation levels of the DLGAP2 gene using a linear mixed model (LMM) in a Chinese sample consisting of 35 SCZ patients with TD, 35 SCZ without TD (NTD) and 34 healthy controls (HCs) collected in Beijing, China. The initial analysis using the non-parametric Kruskal-Wallis test revealed that three groups (TD, NTD and HC) had significant differences in DNA methylation level for CpG site 2 (p = 0.0119). Furthermore, the average methylation levels among the three CpG sites showed strong correlations (all p values < 0.0001). In addition, using the LMM, three groups had significant differences in methylation level (p = 0.0027); while TD, NTD and TD + NTD groups showed higher average methylation levels than the HC group (p = 0.0024, 0.0151, and 0.0007, respectively). In conclusion, the LMM can accommodate a covariance structure. The findings of this study provide first evidence of DNA methylation levels in DLGAP2 associated with SCZ with TD in Chinese population. However, TD just showed borderline significant differences to NTD in this study.

Investigation of the HSPG2 Gene in Tardive Dyskinesia - New Data and Meta-Analysis

Tardive dyskinesia (TD) is a movement disorder that may occur after extended use of antipsychotic medications. The etiopathophysiology is unclear; however, genetic factors play an important role. The Perlecan (HSPG2) gene was found to be significantly associated with TD in Japanese schizophrenia patients, and this association was subsequently replicated by an independent research group. To add to the evidence for this gene in TD, we conducted a meta-analysis specific to the relationship of HSPG2 rs2445142 with TD occurrence, while also adding our unpublished genotype data. Overall, we found a significant association of the G allele with TD occurrence (p = 0.0001); however, much of the effect appeared to originate from the discovery dataset. Nonetheless, most study samples exhibit the same trend of association with TD for the G allele. Our findings encourage further genetic and molecular studies of HSPG2 in TD.

New findings in pharmacogenetics of schizophrenia

PURPOSE OF REVIEW

This review highlights recent advances in the investigation of genetic factors for antipsychotic response and side effects.

RECENT FINDINGS

Antipsychotics prescribed to treat psychotic symptoms are variable in efficacy and propensity for causing side effects. The major side effects include tardive dyskinesia, antipsychotic-induced weight gain (AIWG), and clozapine-induced agranulocytosis (CIA). Several promising associations of polymorphisms in genes including HSPG2, CNR1, and DPP6 with tardive dyskinesia have been reported. In particular, a functional genetic polymorphism in SLC18A2, which is a target of recently approved tardive dyskinesia medication valbenazine, was associated with tardive dyskinesia. Similarly, several consistent findings primarily from genes modulating energy homeostasis have also been reported (e.g. MC4R, HTR2C). CIA has been consistently associated with polymorphisms in the HLA genes (HLA-DQB1 and HLA-B). The association findings between glutamate system genes and antipsychotic response require additional replications.

SUMMARY

The findings to date are promising and provide us a better understanding of the development of side effects and response to antipsychotics. However, more comprehensive investigations in large, well characterized samples will bring us closer to clinically actionable findings.

Genetics of tardive dyskinesia: Promising leads and ways forward

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

Pharmacogenetics of tardive dyskinesia: an updated review of the literature

Tardive dyskinesia (TD) is a serious and potentially irreversible side effect of long-term exposure to antipsychotic medication characterized by involuntary trunk, limb and orofacial muscle movements. Various mechanisms have been proposed for the etiopathophysiology of antipsychotic-induced TD in schizophrenia patients with genetic factors playing a prominent role. Earlier association studies have focused on polymorphisms in CYP2D6, dopamine-, serotonin-, GABA- and glutamate genes. This review highlights recent advances in the genetic investigation of TD. Recent promising findings were obtained with the HSPG2, DPP6, MTNR1A, SLC18A2, PIP5K2A and CNR1 genes. More research, including collection of well-characterized samples, enhancement of genome-wide strategies, gene–gene interaction and epigenetic analyses, is needed before genetic tests with clinical utility can be made available for TD.

Pharmacogenetics of antipsychotic-induced movement disorders as a resource for better understanding Parkinson's disease modifier genes

Antipsychotic-induced movement disorders are major side effects of antipsychotic drugs among schizophrenia patients, and include antipsychotic-induced parkinsonism (AIP) and tardive dyskinesia (TD). Substantial pharmacogenetic work has been done in this field, and several susceptibility variants have been suggested. In this paper, the genetics of antipsychotic-induced movement disorders is considered in a broader context. We hypothesize that genetic variants that are risk factors for AIP and TD may provide insights into the pathophysiology of motor symptoms in Parkinson’s disease (PD). Since loss of dopaminergic stimulation (albeit pharmacological in AIP and degenerative in PD) is shared by the two clinical entities, genes associated with susceptibility to AIP may be modifier genes that influence clinical expression of PD motor sub-phenotypes, such as age at onset, disease severity, or rate of progression. This is due to their possible functional influence on compensatory mechanisms for striatal dopamine loss. Better compensatory potential might be beneficial at the early and later stages of the PD course. AIP vulnerability variants could also be related to latent impairment in the nigrostriatal pathway, affecting its functionality, and leading to subclinical dopaminergic deficits in the striatum. Susceptibility of PD patients to early development of l-DOPA induced dyskinesia (LID) is an additional relevant sub-phenotype. LID might share a common genetic background with TD, with which it shares clinical features. Genetic risk variants may predispose to both phenotypes, exerting a pleiotropic effect. According to this hypothesis, elucidating the genetics of antipsychotic-induced movement disorders may advance our understanding of multiple aspects of PD and it clinical course, rendering this a potentially rewarding field of study.

Pharmacogenetics of antipsychotic treatment in schizophrenia

Antipsychotics are the mainstay treatment for schizophrenia. There is large variability between individuals in their response to antipsychotics, both in efficacy and adverse effects of treatment. While the source of interindividual variability in antipsychotic response is not completely understood, genetics is a major contributing factor. The identification of pharmacogenetic markers that predict antipsychotic efficacy and adverse reactions is a growing area of research, and holds the potential to replace the current trial-and-error approach to treatment selection in schizophrenia with a personalized medicine approach.In this chapter, we provide an overview of the current state of pharmacogenetics in schizophrenia treatment. The most promising pharmacogenetic findings are presented for both antipsychotic response and commonly studied adverse reactions. The application of pharmacogenetics to schizophrenia treatment is discussed, with an emphasis on the clinical utility of pharmacogenetic testing and directions for future research.

Association study of the vesicular monoamine transporter gene SLC18A2 with tardive dyskinesia

Tardive dyskinesia (TD) is an involuntary movement disorder that can occur in up to 25% of patients receiving long-term first-generation antipsychotic treatment. Its etiology is unclear, but family studies suggest that genetic factors play an important role in contributing to risk for TD. The vesicular monoamine transporter 2 (VMAT2) is an interesting candidate for genetic studies of TD because it regulates the release of neurotransmitters implicated in TD, including dopamine, serotonin, and GABA. VMAT2 is also a target of tetrabenazine, a drug used in the treatment of hyperkinetic movement disorders, including TD. We examined nine single-nucleotide polymorphisms (SNPs) in the SLC18A2 gene that encodes VMAT2 for association with TD in our sample of chronic schizophrenia patients (n = 217). We found a number of SNPs to be nominally associated with TD occurrence and the Abnormal Involuntary Movement Scale (AIMS), including the rs2015586 marker which was previously found associated with TD in the CATIE sample (Tsai et al., 2010), as well as the rs363224 marker, with the low-expression AA genotype appearing to be protective against TD (p = 0.005). We further found the rs363224 marker to interact with the putative functional D2 receptor rs6277 (C957T) polymorphism (p = 0.001), supporting the dopamine hypothesis of TD. Pending further replication, VMAT2 may be considered a therapeutic target for the treatment and/or prevention of TD.

Oxidative stress and tardive dyskinesia: pharmacogenetic evidence

Tardive dyskinesia (TD) is a serious adverse effect of long-term antipsychotic use. Because of genetic susceptibility for developing TD and because it is difficult to predict and prevent its development prior to or during the early stages of medication, pharmacogenetic research of TD is important. Additionally, these studies enhance our knowledge of the genetic mechanisms underlying abnormal dyskinetic movements, such as Parkinson's disease. However, the pathophysiology of TD remains unclear. The oxidative stress hypothesis of TD is one of the possible pathophysiologic models for TD. Preclinical and clinical studies of the oxidative stress hypothesis of TD indicate that neurotoxic free radical production is likely a consequence of antipsychotic medication and is related to the occurrence of TD. Several studies on TD have focused on examining the genes involved in oxidative stress. Among them, manganese superoxide dismutase gene Ala-9Val polymorphisms show a relatively consistent association with TD susceptibility, although not all studies support this. Numerous pharmacogenetic studies have found a positive relationship between TD and oxidative stress based on genes involved in the antioxidant defense mechanism, dopamine turnover and metabolism, and other antioxidants such as estrogen and melatonin. However, many of the positive findings have not been replicated. We expect that more research will be needed to address these issues.

Dystonia, facial dysmorphism, intellectual disability and breast cancer associated with a chromosome 13q34 duplication and overexpression of TFDP1: case report

Background

Dystonia is a movement disorder characterized by involuntary sustained muscle contractions causing twisting and repetitive movements or abnormal postures. Some cases of primary and neurodegenerative dystonia have been associated with mutations in individual genes critical to the G₁-S checkpoint pathway (THAP1, ATM, CIZ1 and TAF1). Secondary dystonia is also a relatively common clinical sign in many neurogenetic disorders. However, the contribution of structural variation in the genome to the etiopathogenesis of dystonia remains largely unexplored.

Case presentation

Cytogenetic analyses with the Affymetrix Genome-Wide Human SNP Array 6.0 identified a chromosome 13q34 duplication in a 36 year-old female with global developmental delay, facial dysmorphism, tall stature, breast cancer and dystonia, and her neurologically-normal father. Dystonia improved with bilateral globus pallidus interna (GPi) deep brain stimulation (DBS). Genomic breakpoint analysis, quantitative PCR (qPCR) and leukocyte gene expression were used to characterize the structural variant. The 218,345 bp duplication was found to include ADPRHL1, DCUN1D2, and TMCO3, and a 69 bp fragment from a long terminal repeat (LTR) located within Intron 3 of TFDP1. The 3' breakpoint was located within Exon 1 of a TFDP1 long non-coding RNA (NR_026580.1). In the affected subject and her father, gene expression was higher for all three genes located within the duplication. However, in comparison to her father, mother and neurologically-normal controls, the affected subject also showed marked overexpression (2×) of the transcription factor TFDP1 (NM_007111.4). Whole-exome sequencing identified an SGCE variant (c.1295G > A, p.Ser432His) that could possibly have contributed to the development of dystonia in the proband. No pathogenic mutations were identified in BRCA1 or BRCA2.

Conclusion

Overexpression of TFDP1 has been associated with breast cancer and may also be linked to the tall stature, dysmorphism and dystonia seen in our patient.

Loss of dopamine neuron terminals in antipsychotic-treated schizophrenia; relation to tardive dyskinesia

The in vivo labeling and brain imaging of dopamine transporters measure the density of dopamine neuron terminals in the human caudate/putamen. A review of such studies shows that the long-term use of antipsychotics had no major effect on the density of the dopamine terminals in individuals who had no tardive dyskinesia, but had reduced the density in those patients with tardive dyskinesia. In addition, the normal loss of dopamine terminals in healthy individuals was approximately 5% per decade. However, this rate of cell loss was apparently increased by approximately three-fold, to about 15% per decade, in schizophrenia patients using antipsychotics on a long-term basis, as measured by the in vivo imaging of the dopamine transporters in the dopamine neuron terminals. While an apparent reduction in dopamine transporters may result from reduced expression of the transporters secondary to antipsychotic treatment, the seemingly increased loss rate is consistent with the accumulation of antipsychotics in the neuromelanin of the substantia nigra, subsequent injury to the dopamine-containing neurons, and the development of extrapyramidal motor disturbances such as tardive dyskinesia or Parkinson's disease.

There is no evidence for an association between the serotonin receptor 3A gene C178T polymorphism and tardive dyskinesia in Korean schizophrenia patients

BACKGROUND

Tardive dyskinesia (TD) is a potential adverse effect of long-term treatment with antipsychotics. Previous studies have suggested a link between brain serotonergic systems and TD vulnerability. A recent report described that a serotonin 3 receptor (5-HTR3) agonist induced rhythmic movements in mice with complete paraplegia. Furthermore, it has been reported that the 5-HTR3 antagonist ondansetron is efficacious in the treatment of Gilles de la Tourette syndrome (GTS).

AIM

The aim of the present study was to determine whether the 5-HTR3A gene C178T polymorphism is associated with antipsychotic-induced TD in Korean schizophrenia patients.

METHODS

We investigated 280 Korean schizophrenia patients. Subjects with TD (n = 105) and without TD (n = 175) were matched for antipsychotic drug exposure and other relevant variables.

RESULTS

The distributions of genotypic (chi-squared = 3.55, p = 0.169) and allelic (chi-squared = 0.40, p = 0.528) frequencies did not differ between patients with and without TD. The total score on the Abnormal Involuntary Movement Scale also did not differ between the two genotype groups (F = 0.94, p = 0.391).

CONCLUSIONS

The findings of the present study do not support the involvement of the 5-HTR3A gene C178T polymorphism in TD in Korean schizophrenia subjects.

Do tardive dyskinesia and L-dopa induced dyskinesia share common genetic risk factors? An exploratory study

Tardive dyskinesia (TD) in schizophrenia patients treated with antipsychotic medications and L-dopa induced dyskinesia (LID) among Parkinson's disease (PD) affected individuals share similar clinical features. Both conditions are induced by chronic exposure to drugs that target dopaminergic receptors (antagonists in TD and agonists in LID) and cause pulsatile and nonphysiological stimulation of these receptors. We hypothesized that the two motor adverse effects partially share genetic risk factors such that certain genetic variants exert a pleiotropic effect, influencing susceptibility to TD as well as to LID. In this pilot study, we focused on 21 TD-associated SNPs, previously reported in TD genome-wide association studies or in candidate gene studies. By applying logistic regression and controlling for relevant clinical risk factors, we studied the association of the SNPs with LID vulnerability in two independent pharmacogenetic samples. We included a Jewish Israeli sample of 203 PD patients treated with L-dopa for a minimum of 3 years and evaluated the existence or absence of LID (LID+ = 128; LID- = 75). An Italian sample was composed of early LID developers (within the first 3 years of treatment, N = 187) contrasted with non-early LID developers (after 7 years or more of treatment, N = 203). None of the studied SNPs were significantly associated with LID susceptibility in the two samples. Therefore, we were unable to obtain proof of concept for our initial hypothesis of an overlapping contribution of genetic risk factors to TD and LID. Further studies in larger samples are required to reach definitive conclusions.

The pharmacogenetics of antipsychotic-induced adverse events

PURPOSE OF REVIEW

Antipsychotic drugs are effective in alleviating a variety of symptoms and are medication of first choice in schizophrenia. However, a substantial interindividual variability in side effects often requires a lengthy 'trial-and-error' approach until the right medication is found for the right patient. Genetic factors have long been hypothesized to be involved and identification of related gene variants could be used to predict and tailor drug treatment.

RECENT FINDINGS

This review highlighting the most recent genetic findings was conducted on the two most common and most well-studied side effects: antipsychotic-induced weight gain and tardive dyskinesia.

SUMMARY

Regarding weight gain, most promising and most consistent findings were obtained in the serotonergic system (HTR2C) and with hypothalamic leptin-melanocortin genes, in particular with one variant close to the melanocortin-4-receptor (MC4R) gene. With respect to tardive dyskinesia, most interesting findings were generally obtained in genes related to the dopaminergic system (dopamine receptors D2 and D3), and more recently with glutamatergic system genes. Overall, genetic studies have been successful in identifying strong findings, in particular for antipsychotic-induced weight gain and to some extent for tardive dyskinesia. Apart from the need for replication studies in larger and well-characterized samples, the next challenge will be to create predictive algorithms that can be used for clinical practice.

Genetic correlates of medical comorbidity associated with schizophrenia and treatment with antipsychotics

PURPOSE OF REVIEW

High comorbidity rates for various medical conditions have been documented in schizophrenia, being explained by factors either inherent to the disease or associated with antipsychotic treatment. The aim of this study is to review the genetic factors contributing to medical comorbidity in schizophrenia.

RECENT FINDINGS

Based on clinical genetic studies in schizophrenia, comorbid impaired glucose tolerance/type 2 diabetes mellitus, most autoimmune disorders and cardiac autonomic dysregulation have the strongest evidence for familial predisposition. Similarly, of antipsychotic-induced adverse drug reactions, tardive dyskinesia, neuroleptic malignant syndrome, and antipsychotic-induced weight gain have some evidence for familial clustering. On the molecular genetic level, schizophrenia seems to share specific genes with type 2 diabetes mellitus and with autoimmune disorders. Various genes have been proposed to account for the reduced incidence of rheumatoid arthritis and cancer in schizophrenic patients and their relatives. Many pharmacogenetic association studies have pinpointed numerous, though often contradictory or poorly replicated, genes of modest effect size for tardive dyskinesia, neuroleptic malignant syndrome, clozapine-induced agranulocytosis, hyperprolactinaemia, antipsychotic-induced weight gain, and antipsychotic-induced QT prolongation.

SUMMARY

Unravelling the genetic underpinnings of medical comorbidity associated with schizophrenia and its treatment is expected to highlight new pathogenetic pathways in both schizophrenia and comorbid medical conditions, and introduce personalized treatment strategies for schizophrenia patients.

No association between PAWR gene polymorphisms and tardive dyskinesia in schizophrenia patients

Tardive dyskinesia (TD) is a hyperkinetic movement disorder associated with the prolonged use of antipsychotic drugs. Since prostate apoptosis response 4 (Par-4) is a key ligand of the dopamine D2 receptor, the Par-4 gene (PAWR) is a good candidate gene to study in the context of TD susceptibility. We examined the association between PAWR gene polymorphisms and TD. Three single nucleotide polymorphisms of PAWR were selected for the analysis: rs7979987, rs4842318, and rs17005769. Two hundred and eighty unrelated Korean schizophrenic patients participated in this study (105 TD and 175 non-TD patients). Genotype/allele-wise and haplotype-wise analyses were performed. There were no significant differences in genotype and allele frequencies between the two groups. Haplotype analysis also did not reveal a difference between the two groups. Within the limitations imposed by the size of the clinical sample, these findings suggest that PAWR gene variants do not significantly contribute to an increased risk of TD.