Tardive Dyskinesia In Schizophrenia Research Articles

Associations between Catechol-O-methyltransferase (COMT) polymorphisms and cognitive impairments, psychiatric symptoms and tardive dyskinesia in schizophrenia

IntroductionCatechol-O-methyltransferase (COMT) is a crucial enzyme involved in dopamine metabolism and has been implicated in the etiology of tardive dyskinesia (TD). We aimed to investigate the associations between COMT gene polymorphisms and the occurrence and severity of TD in a Chinese population, as well as the impact on the psychiatric symptoms and cognitive impairments observed in TD patients. MethodsA total of 216 chronic schizophrenia patients, including 59 TD patients and 157 NTD patients, were recruited for this study. Three SNPs of the COMT gene (rs4680, rs165599 and rs4818) were selected and genotyped using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). TD severity, psychopathology and cognitive functioning were assessed using the Abnormal Involuntary Movement Scale (AIMS), the Positive and Negative Syndrome Scale (PANSS) and the Repeated Battery for Assessment of Neuropsychological Status (RBANS), respectively. ResultsIn TD patients, total AIMs scores were higher in carriers of the rs4680 AA genotype than in carriers of the AG and GG genotypes (p = 0.01, 0.006), carriers of the rs4818 GC and CC genotypes had higher orofacial scores than in GG genotypes (p = 0.032, 0.002). In male TD patients, carriers of the rs165599 GA genotype scored lower in the extremities and trunk scores than AA genotype carriers (p = 0.015). Moreover, in male TD patients, COMT rs4818 was associated with cognition, since the C allele carriers had significantly higher immediate memory (p = 0.043) and verbal function (p = 0.040) scores than the G allele carriers. In addition, rs165599 genotype interacted with TD diagnosis on depressed factor (p = 0.031). ConclusionWithin the Chinese population, COMT gene polymorphisms could potentially serve as biomarkers for the symptoms and prognosis of TD patients.

Association between the IL10 rs1800896 Polymorphism and Tardive Dyskinesia in Schizophrenia.

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

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.

Adjunctive Melatonin for Tardive Dyskinesia in Patients with Schizophrenia: A Meta-Analysis.

BackgroundTardive dyskinesia (TD) is characterized by abnormal and involuntary movements. Importantly, TD could cause considerable personal suffering and social and physical disabilities.AimsThis meta-analysis based on randomized controlled trials (RCTs) systematically assessed the therapeutic effect and tolerability of melatonin for TD in schizophrenia.MethodsA computerized and systematical search of both Chinese (Wanfang Data, Chinese National Knowledge Infrastructure (CNKI), SINOMED) and English (PubMed, PsycINFO, Embase, Cochrane Library databases) databases, from their inception until June 8, 2017, was conducted by two independent authors. The severity of TD symptoms were the primary outcome measure and analyzed using a random effects model by the Review Manager (RevMan) Version 5.3. Quality evaluation of included RCTs was conducted using the Cochrane risk of bias and Jadad scale. The GRADE (Grades of Recommendation, Assessment, Development, and Evaluation) system recommendation grading method was used to assess the overall quality level of meta-analytic outcomes.ResultsFour RCTs (n=130) were identified and analyzed. Three RCTs used double blind and 1 RCT used masked assessors using the Cochrane risk of bias, and 3 RCTs were rated as high quality based on Jadad scale. Compared with the control group, adjunctive melatonin was superior in reducing the severity of TD as measured by the Abnormal Involuntary Movement Scale (AIMS) (4 RCTs, n=130, weighted mean difference (WMD): -1.52 (95% confidence intervals (CI): -3.24, 0.20), p=0.08; I2=0%) although the improvement did not reach a significant level. The overall evidence quality of the improvement of TD symptoms, according to GRADE approach, was rated as “Low”. The data on the ADRs and cognitive effect were limited.ConclusionsThis meta-analysis shows that melatonin has potential for improving TD symptoms in schizophrenia. Future higher quality and larger RCTs are warranted to confirm the findings.

Extract of Ginkgo biloba for Tardive Dyskinesia: Meta-analysis of Randomized Controlled Trials.

Free radicals may be involved in the pathogenesis of tardive dyskinesia (TD). We conducted this meta-analysis to systematically examine the efficacy of extract of Ginkgo biloba (EGb), a potent antioxidant possessing free radical-scavenging properties, as a treatment for TD in schizophrenia using randomized controlled trial (RCT) data. Drawn from English and Chinese databases, 3 RCTs of EGb augmentation of antipsychotics (APs) vs. AP plus placebo or AP monotherapy were identified. 2 evaluators extracted data. The primary outcome measure was the severity of TD symptoms assessed by the Abnormal Involuntary Movement Scale (AIMS). Weighted mean difference (WMD) and risk ratio (RR) ±95% confidence intervals (CI) were calculated. Statistical analyses were performed using Review Manager (version 5.1.7.0) and STATA (version 12.0). The 3 RCTs (n=299) from China, of 12 weeks duration, involved schizophrenia patients with TD of 55.9±13.4 years old. EGb (240 mg/day) outperformed the control group in reducing the severity of TD and clinical symptoms as measured by the AIMS (trials=3, n=299, WMD: -2.30 (95%CI: - 3.04, -1.55), P<0.00001) and the adverse drug reactions as assessed by the Treatment Emergent Symptom Scale (TESS) (trials=2, n=142, WMD: -2.38 (95%CI: -4.01, -0.74), P=0.004). Both the Positive and Negative Syndrome Scale (PANSS) total score (trials=2, n=239, P=0.87) and all-cause discontinuation (trials=3, n=299, P=0.21) were similar between the EGb and control group. This meta-analysis suggests that adjunctive EGb appeared to be an effective and safe option for improving TD in the treatment of schizophrenia patients. However, better RCTs are needed to demonstrate its efficacy and safety especially on cognitive function in TD. CRD42015024930.

Polymorphisms of genes of oxidative stress and glutamate excitotoxicity in patients with tardive dyskinesia in schizophrenia

Polymorphisms of genes of oxidative stress and glutamate excitotoxicity in patients with tardive dyskinesia in schizophrenia

Possible association between DBH 19 bp insertion/deletion polymorphism and clinical symptoms in schizophrenia with tardive dyskinesia

Overactivity of dopaminergic neurotransmission is a putative mechanism of tardive dyskinesia (TD). Previous studies have found dysfunction in plasma dopamine beta-hydoxylase (DBH) in schizophrenia with TD. Moreover, DBH, whose activity and levels are strongly controlled by the DBH gene, is a key enzyme in the conversion of dopamine (DA) to norepinephrine (NE) associated with excited behavior. This study examined whether the DBH5'-insertion/deletion (Ins/Del) polymorphism was associated with excited behavior in schizophrenia with TD. The presence of the DBH5'-Ins/Del polymorphism was determined in 741 schizophrenia with TD (n = 345) and without TD (n = 396). The Abnormal Involuntary Movement Scale and Positive and Negative Syndrome Scale were used to assess the severity of TD and psychopathology of schizophrenia. There was no significant difference in the allelic and genotypic frequencies of the DBH5'-Ins/Del polymorphism between schizophrenia with and without TD (both p > 0.05). However, the excited symptoms score was significantly different to the DBH5'-Ins/Del genotypic groups in schizophrenia with TD (p < 0.05) but not in the two groups of non-TD and total patients (both p > 0.05). The excited symptoms score was higher in TD patients with the Del/Del genotype than those with Ins alleles (p = 0.015). Our findings suggest that the DBH5'-Ins/Del polymorphism may not contribute directly to the development of TD in schizophrenia, but it may be involved in the excited behavior of TD patients.

Tardive dyskinesia in schizophrenia

Sarró et al report grey matter deficits associated with tardive dyskinesia in schizophrenia. Much evidence suggests that the intrinsic pathophysiology of schizophrenia contributes to predisposition to tardive dyskinesia. The possibility that antipsychotics might play a causal role in the grey matter deficits cannot be excluded, but the evidence is tenuous.

Structural brain changes associated with tardive dyskinesia in schizophrenia

The pathological basis of tardive dyskinesia is unknown. Although its clinical features implicate the basal ganglia, imaging studies have not found clear evidence that it is associated with volume changes in these or other brain structures. To determine, using voxel-based structural imaging, whether there are regions of grey matter volume change in people with schizophrenia who also have tardive dyskinesia compared with those without tardive dyskinesia. A total of 81 people with chronic schizophrenia, 32 with tardive dyskinesia and 49 without, were examined using magnetic resonance imaging (MRI) and whole-brain, optimised voxel-based morphometry. A comparison group of 61 healthy controls was also examined. Compared with those without tardive dyskinesia, patients with tardive dyskinesia showed a pattern of volume reductions in predominantly subcortical regions, including the basal ganglia and the thalamus. Within the basal ganglia, volume reductions were seen in the caudate nucleus, to a lesser extent in the putamen, and only marginally in the globus pallidus. The patients with tardive dyskinesia, but not those without, showed significant volume reductions in the basal ganglia compared with the healthy controls but both groups had smaller volumes than controls in other affected areas. The pathological process or processes that underlie the development of tardive dyskinesia are not just neurochemical in nature, but affect brain structure.

Association of the dopamine β‐hydroxylase 19 bp insertion/deletion polymorphism with positive symptoms but not tardive dyskinesia in schizophrenia

Overactivity of dopaminergic neurotransmission is a putative mechanism of tardive dyskinesia (TD). Dopamine beta-hydroxylase (DBH) is a key enzyme in the conversion of dopamine to norepinephrine, and plasma DBH activity is altered in TD patients. This study examined whether the functional DBH 5'-Ins/Del polymorphism was associated with TD severity in Chinese patients with schizophrenia. We compared the rate of this polymorphism in patients with (n = 312) and without TD (n = 435), and healthy controls (n = 625). The severity of TD was assessed using the Abnormal Involuntary Movement Scale (AIMS) and psychopathology using the Positive and Negative Syndrome Scale (PANSS). There were no significant differences in the distribution of the allele and genotype frequencies between the patients and controls, or between the patients with and without TD. Also, there was no significant difference in the AIMS total score between the three genotype groups. However, the PANSS positive symptom subscore was significantly higher in patients with Del/Del genotype (13.2 ± 5.2) than those with Ins/Del (11.2 ± 4.9) and Ins/Ins (11.1 ± 3.1) genotypes (both p < 0.05). These results suggest that although the DBH 5'-Ins/Del polymorphism was not associated with susceptibility to TD in patients with schizophrenia, it might be related to positive symptoms of schizophrenia.

Association between TNF-α promoter −308A/G polymorphism and tardive dyskinesiain Chinese Han patients with schizophrenia

Previous studies have indicated that the immune may be involved in the pathogenesis of tardive dyskinesia (TD). Some genetic polymorphisms in the human leukocyte antigen (HLA) I and II regions have been associated with TD, and the tumor necrosis factor-α (TNF-α) gene is located in the HLA III region. TNF-α levels in the striatum significantly increased in haloperidol-induced TD in rats. The TNF-α gene -308A/G single nucleotide polymorphism (SNP) has been shown to directly influence TNF-α expression. The genetic association between the TNF-α gene -308A/G SNP and TD is unclear. The present study investigated whether this variation is associated with clinical phenotypes and TD in schizophrenia in a genetically homogeneous northern Chinese Han population. We genotyped the TNF-α gene -308A/G SNP in patients with schizophrenia with TD (n=350) and without TD (n=410). The Abnormal Involuntary Movement Scale (AIMS) and Positive and Negative Syndrome Scale (PANSS) were used to assess the severity of TD and psychopathology of schizophrenia, respectively. The allele and genotype frequencies did not significantly differ between patients with schizophrenia with and without TD (p>0.05). No significant difference was found in the total AIMS score between the genotypes (p>0.05). However, the PANSS negative symptom subscore was associated with risk for TD (p=0.004), and a significant difference was found in total AIMS score between the genotypes in TD patients (p=0.013). The TNF-α gene -308A/G polymorphism does not appear to play a major role in the susceptibility to TD in patients with schizophrenia in a northern Chinese Han population. However this polymorphism may play a role in the TD severity.

Analysis of genetic variations in the dopamine D1 receptor (DRD1) gene and antipsychotics-induced tardive dyskinesia in schizophrenia

Dyskinesia is a kind of abnormal involuntary movement disorder that increases with age. The pathogenesis of dyskinesia may result from divergent changes in dopamine D1 receptors (DRD1) and dopamine D2 receptors (DRD2) in the brain while aging. Tardive dyskinesia (TD), a kind of dyskinesia, may develop after long-term antipsychotic treatment. Because the prevalence of TD also steadily increased with age, TD has been suggested to be the consequence of an imbalance between DRD1 and DRD2. We supposed that patients who develop TD may have genetic variants of DRD1 that cause the excitatory effects of DRD1 overwhelming the attenuated inhibitory effects of DRD2 after antipsychotic treatment. In the present study, schizophrenic inpatients receiving long-term antipsychotic treatment were first assessed using the Abnormal Involuntary Movement Scale (AIMS), and only patients who were either free of any abnormal involuntary movements (non-TD group, AIMS =0) or who showed persistent TD (TD group) were enrolled. Finally, 382 patients were recruited (TD=220, non-TD=162) and three single nucleus polymorphisms (SNPs; rs5326, rs4532 and rs265975) of DRD1 were genotyped for each subject. Genotype frequency (%; AA/AG/GG) of rs4532 (TD: non-TD) was 61.4/35.8/2.8: 74.2/24.5/1.3. After genetic analyses, genotype GG showed significant association with TD (if OR=2.0, power (%)=98.5; if OR=1.5, power (%)=63.7; P=0.033). Haplotype frequency (%) CGC of rs5326-rs4532-rs265975 (TD: non-TD) was 19.0:13.7; and after haplotype-based analyses, haplotype CGC also showed significant association with TD (OR=1.4, permutation P=0.027). Our results indicate that the genotypic variants of DRD1 might play a role in the susceptibility of TD. Further replication in other countries or other populations is highly expected.

Extract ofGinkgo bilobaTreatment for Tardive Dyskinesia in Schizophrenia

Free radicals may be involved in the pathogenesis of tardive dyskinesia (TD). Extract of Ginkgo biloba (EGb) is a potent antioxidant possessing free radical-scavenging activities. The aim of the study was to evaluate the efficacy of EGb-761, a standardized extract given in capsule form, in treating TD in schizophrenia patients. Inpatients with DSM-IV-diagnosed schizophrenia and TD (n = 157) in a mainland China Veterans Affairs psychiatric hospital were randomly assigned to 12 weeks of treatment with either EGb-761, 240 mg/d (n = 78) or a placebo (n = 79) in a double-blind manner. Primary outcome measures were (1) change from baseline in the Abnormal Involuntary Movement Scale (AIMS) score and (2) proportion of patients with a ≥ 30% reduction in their AIMS total score at week 12. Secondary outcome measures included the Positive and Negative Syndrome Scale (PANSS) and cognitive performance as measured by the Continuous Performance Test-37 Version and the 3-card Stroop task. Patients were recruited for the study between December 2006 and May 2007. Of the 157 patients who were randomly assigned, 152 (96.8%) completed the study. EGb-761 treatment significantly decreased the AIMS total score in patients with TD compared to those who were given a placebo (2.13 ± 1.75 vs -0.10 ± 1.69; P < .0001), with 40 (51.3%) and 4 (5.1%) patients achieving response in the EGb-761 and placebo treatment groups, respectively. There were no between-group differences in the PANSS total score or cognitive measures from baseline to week 12. EGb-761 appears to be an effective treatment for reducing the symptoms of TD in schizophrenia patients, and improvement may be mediated through the well-known antioxidant activity of this extract. clinicaltrials.gov identifier: NCT00672373.

Drs. Nelson and Papakostas Reply

Drs. Nelson and Papakostas Reply

Non‐therapeutic risk factors for onset of tardive dyskinesia in schizophrenia: A meta‐analysis

A meta-analysis of prospective studies with schizophrenia patients was conducted to examine whether the evidence exists for risk factors for the emergence of Tardive Dyskinesia (TD) in schizophrenia. A computer assisted Medline/PubMed and Embase search was conducted in January 2008 for the years 1985-2007. Selected were truly prospective studies of incident cases of TD in a population with at least 80% patients with schizophrenia. Measures of relative risk were collected from the individual studies, either directly or by calculating the relative risk from the cox- or logistic regression coefficient provided in the article. Hazard Ratio's and Odds Ratio's were pooled using fixed and random effect models in case of multiple studies using the same measure of risk and outcome. Only eight studies satisfied the inclusion criteria reporting on 25 different single estimate risk factors. Of 25 risk factors, six concerned replicated estimates suitable for meta-analysis. Of these, non-white ethnic group and early extrapyramidal symptoms qualified as risk factors for the emergence of TD in schizophrenia. The association with older age was suggestive but inconclusive. Despite many reported risk factors for TD in schizophrenia, little conclusive evidence exists to corroborate this. However, the fact that early EPS predicts onset of TD has important clinical and research implications.

Gender differences in the prevalence, risk and clinical correlates of tardive dyskinesia in Chinese schizophrenia

Despite extensive use of antipsychotic drug treatment, few studies address the prevalence of tardive dyskinesia (TD) in homogeneous ethnic groups such as the Chinese. This study examined gender-specific relationships between TD and symptom levels in schizophrenia among Han Chinese, which have previously received little systematic study. Five hundred and twenty-two inpatients with schizophrenia receiving long-term treatment with antipsychotics were evaluated with the AIMS. The patient's psychopathology was assessed with the Positive and Negative Syndrome Scale (PANSS). Demographic and clinical data were collected from a detailed questionnaire and medical records. The overall TD prevalence was 33.7% with rates of 39.2% (138/352) in males and 22.4% (38/170) in females (chi (2) = 14.6, df = 1, p < 0.0001; adjust odds ratio 2.06; CI, 1.32-3.16). The AIMS score in patients with TD was lower in females than males (5.3 +/- 3.9 vs 6.7 +/- 3.7, t = 2.52, p < 0.01) after adjustment for the significant covariates. TD was associated with the negative symptoms on the PANSS in both genders, and with age, PANSS total and positive symptoms in men, not women. Our present findings suggest that there are gender differences in the prevalence, risk, and clinical correlates of TD in schizophrenia. Although this study is limited by cross-sectional designs, the magnitude of these gender-specific differences is substantial and deservers further prospective study.

Analysis of genetic variations in the RGS9 gene and antipsychotic‐induced tardive dyskinesia in schizophrenia

Some patients treated chronically with antipsychotics develop tardive dyskinesia (TD), an abnormal involuntary movement disorder. Typical antipsychotics block D(2) dopamine receptors (D(2)DR) and produce D(2)DR supersensitivity. On contrary, regulators of G-protein signaling (RGS) can enhance the signal termination of G-protein-coupled D(2)DR. Besides, after prolonged inhibition of dopaminergic transmission, dopaminergic agonists induced severe dyskinesia only in RGS9 knock-out mice but not in normal mice. Therefore, variety in the human RGS9 gene may be related to susceptibility to TD. In this study, schizophrenic inpatients receiving long-term antipsychotic treatment were assessed using the Abnormal Involuntary Movement Scale twice over a 3-month interval. Only patients in whom abnormal involuntary movements were absent (non-TD group) and those who showed persistent TD (TD group) were enrolled. There were 407 patients in the study sample (TD = 252; non-TD = 155) and seven single nucleus polymorphisms (SNPs) in the RGS9 gene were genotyped for each subject. Genotype and allelic distributions of SNPs did not differ between the TD and non-TD groups in this study, with the exception that a weak trend of allelic association was seen with rs4790953 (P = 0.0399). In the haplotype analysis, a significant association of the AGG haplotype (rs8077696-rs8070231-rs2292593) of the RGS9 gene was found (permutation P = 0.007), and this is worthy of replication and further study.

Val158Met Polymorphism in the Catechol-O-Methyltransferase (COMT) Gene Is Not Associated with Tardive Dyskinesia in Schizophrenia

Objective: This study investigated whether the catechol-O-methyltransferase (COMT) gene V158M single-nucleotide polymorphism (SNP) influences susceptibility to tardive dyskinesia (TD). Methods: We examined 209 Korean schizophrenic patients using the Abnormal Involuntary Movement Scale (AIMS), with genotyping performed for the COMT gene V158M SNP. Results: The logistic regression analysis showed that old age [p = 0.032, OR = 1.40 (OR corresponds to 10-year), 95% CI = 1.03–1.90] was a risk factor for TD, but there was no significant association between the COMT genotype and TD. The heterozygotes (MV genotype) of the COMT gene polymorphism tended to develop TD less than homozygotes (MM and VV); however, the risk did not reach statistical significance (p = 0.050, OR = 1.81, 95% CI = 1.00–3.29). Conclusions: These results suggest that the V158M SNP of the COMT gene is not associated with TD in schizophrenia. However, there is a tendency that the heterozygous genotype of the COMT gene polymorphism has a protective effect against TD. Further investigations are warranted to evaluate a molecular heterosis of this polymorphism in development of TD in a large sample of subjects.

No evidence for an association between G protein β3 subunit gene C825T polymorphism and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic. We evaluated candidate functional polymorphism of the G protein beta3 subunit (GNB3) gene for association with drug-induced TD in the Korean schizophrenic patients. We investigated whether the C825T polymorphism of the GNB3 gene is associated with the TD in a Korean sample of schizophrenic patients with (n = 83) and without TD (n = 126), matched for antipsychotic drug exposure and other relevant variables. The distribution of genotypes and allele frequencies of GNB3 were not different between schizophrenic patients with TD and without TD (p > 0.05). Within the limitations imposed by the size of the clinical sample, these findings suggest that the GNB3 825 C/T single nucleotide polymorphism (SNP) does not contribute significantly to risk for TD.

Association analysis of polymorphisms in the N-methyl- d-aspartate (NMDA) receptor subunit 2B ( GRIN2B) gene and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a neurological disorder characterized by irregular, non-rhythmic, choreoathetotic and involuntary movements in single or multiple body regions. Chronic administration of typical antipsychotic agents, which predominantly act on dopamine receptors, implicates the dopamine system in susceptibility to TD. An alternative to this dopaminergic supersensivity hypothesis in understanding the pathogenesis of TD is the glutamatergic neurotoxicity hypothesis, which implicates the N-methyl- d-aspartate (NMDA) receptor in TD pathogenesis. In the present study, the association between three polymorphisms (T-200G, C366G and C2664T) of the GRIN2B gene, which encodes the 2B subunit of the NMDA receptor, and the occurrence and severity of TD were investigated in 273 Chinese schizophrenic patients receiving long-term antipsychotic treatment (TD: 142, non-TD: 133). There was no significant association between patients' genotype and allele frequencies and TD occurrence. Among the TD patients, the differences in the total scores on the Abnormal Involuntary Movement Scale (AIMS) among the three genotypes of each polymorphism were not significant. Because the three studied markers are in weak linkage disequilibrium with each other, haplotype-based association was not carried out. We conclude that genetic variations in the human GRIN2B gene probably do not play a major role in susceptibility to, or severity of TD.