Xingqun Ni

Association study of 12 polymorphisms spanning the dopamine D2 receptor gene and clozapine treatment response in two treatment refractory/intolerant populations

RationaleDopamine D2 receptor blockade is the major basis for the antipsychotic action of typical antipsychotic drugs (AP) and a necessary but not sufficient basis for the antipsychotic action of atypical APs such as clozapine and other multireceptor antagonists which rely, in part, upon 5-HT2A antagonism. Genetic factors affecting the density and/or function of D2 receptors may therefore affect AP response.ObjectivesThis exploratory study investigates the effect of 12 single nucleotide polymorphisms (SNPs) spanning the entire dopamine D2 gene on clozapine response in two distinct schizophrenic populations (Caucasian and African–American) refractory or intolerant to conventional APs.MethodsThis study included 183 Caucasian and 49 African–American DSM-III-R or DSM-IV schizophrenics. Genotyping was determined by 5′-exonuclease fluorescence assays. Within each population genotype, allele, allele +/−, and haplotype frequencies were compared between responders and non-responders by X2 tests. Linkage disequilibrium analysis was also performed.ResultsIn the Caucasian sample, no significant associations were found for individual SNP tests; however, two haplotypes were identified as having significant protective effects on treatment outcome. In the African–American sample, individual SNP tests identified the Taq1A, Taq1B, and rs1125394 markers as being predictive of clozapine response. Haplotype analyses identified four protective haplotypes containing these SNPs. In addition, no association between the −141C Ins/Del site and clozapine response was found in either population.ConclusionsInterindividual variability in clozapine response among treatment refractory/intolerant patients is still not fully understood and likely involves multiple factors. This exploratory analysis suggests that the D2 receptor gene may be one such factor.

Monoamine oxidase a gene is associated with borderline personality disorder.

Objective Monoamine oxidase A is a mitochondrial enzyme involved in the degradation of certain neurotransmitter amines: serotonin and norepinephrine. As for its role in aggression, impulsivity, suicide and mood liability, monoamine oxidase A can be considered a functional candidate in borderline personality disorder. Methods To test for this hypothesis we genotyped two polymorphic markers in monoamine oxidase A gene, a promoter VNTR and an rs6323 (T941G) in exon 8, in 111 Caucasian borderline personality disorder patients and 289 Caucasian healthy controls. Association analyses using individual marker and haplotype data were performed by a program of COCAPHASE in UNPHASED (MRC Human Genome Mapping Project Resource Centre, Cambridge, UK). Results We found that the borderline personality disorder patients had a high frequency of the high activity VNTR alleles (χ2=4.696, P=0.03) and a low frequency of the low activity haplotype (χ2=5.089, P=0.02). Conclusion These results show that the monoamine oxidase A gene may play an important role in the etiological development of the borderline personality disorder.

Serotonin 2A receptor gene is associated with personality traits, but not to disorder, in patients with borderline personality disorder

Borderline personality disorder (BPD) is a chronic, disabling, and high-risk mental disorder characterized by a pervasive pattern of instability in regulation of emotion, interpersonal relationships, self-image, and impulse control beginning in early adulthood. BPD affects about 1%-2% of the general population and has a high mortality rate as a result of suicide and impulsive behaviour. The serotonin 2A receptor gene (HTR2A) is considered a candidate gene for BPD because multiple lines of evidence suggest that it plays an important role in suicide, impulsivity and emotional liability. To test for an association between HTR2A and BPD, we genotyped four polymorphisms, rs6313 (T102C), rs4941573, rs2296972 and rs6314 (His452Tyr), in 111 Caucasian patients with BPD and 287 Caucasian healthy controls. The program UNPHASED was used to compare allele and haplotype frequencies between cases and controls. We did not find a significant association between HTR2A and BPD based on allele, genotype or haplotype analyses. However, there were significant associations between HTR2A and personality traits in the BPD patients. The C allele of rs6313 and the A allele of rs4941573 associated with a higher Extraversion score. Our results suggest that the serotonin 2A receptor gene may not play a major role in the aetiology of borderline personality disorder, but may have a role in personality traits.

Human p53 tumor suppressor gene (TP53) and schizophrenia: Case–control and family studies

The human p53 tumor suppressor gene (TP53) is considered as a candidate susceptibility gene for schizophrenia because of its functions in neurodevelopment. To test for an association between TP53 and schizophrenia, both the case-control study and the transmission disequilibrium test (TDT) were performed on genotype data from eight polymorphisms in TP53. Our samples included 286 Toronto schizophrenia cases and 264 controls, and 163 Portuguese nuclear families. In the Toronto case-control study significant differences of allele frequencies of the CAA Ins/Del (p=0.027) and the 16bp Ins/Del (p=0.022) were detected. In TDT analysis we found significant differences for transmission of the CAA Ins/Del (p=0.017) in Portuguese schizophrenia families. Haplotype analysis also showed a significant association between TP53 and schizophrenia. These results provide further evidence that TP53 may play a role in the pathogenesis of schizophrenia.

Linkage disequilibrium between dopamine D1 receptor gene (DRD1) and bipolar disorder

BACKGROUND Based on the dopamine hypothesis, the dopamine D1 receptor gene (DRD1) is considered to be a good candidate gene for bipolar disorder (BP). METHODS In our study, three polymorphisms of the DRD1 gene, -800T/C, -48A/G, and 1403T/C, were analyzed in 286 BP trios. Both the transmission disequilibrium test (TDT) and haplotype TDT were performed on the genotype data to test for the presence of linkage disequilibrium between DRD1 and bipolar disorder. With the extended transmission disequilibrium test (ETDT), we also calculated the maternal transmission and paternal transmission for each allele. RESULTS Although no association was found for each individual polymorphism, there is a significant association between DRD1 and BP for haplotype TDT analysis (chi(2) = 16.068, df = 3, p =.0011). CONCLUSIONS These results indicate that DRD1 may play a role in the etiology of bipolar disorder.

COMT158 polymorphism and hostility

The main study was designed primarily to compare the clinical effects of four antipsychotics in 157 patients with schizophrenia or schizoaffective disorder. The secondary genetic study, reported here, is based on a subset of 60 patients who consented to genotyping assays. Based on previous work with the catechol‐O‐methyltransferase (COMT) 158 polymorphism, we hypothesized that the Met–Met homozygotes would be more hostile than the heterozygotes and the Val–Val homozygotes. Hostility ratings at baseline were used to test this hypothesis. The Met–Met homozygotes (N = 7) were found to have significantly higher levels of hostility than the other patients (N = 53). The hypothesis was thus supported. The finding should be replicated in a larger sample.

Connexin 50 gene on human chromosome 1q21 is associated with schizophrenia in matched case–control and family-based studies

Background: The gap junction subunit connexin permits direct intercellular exchange of ions and molecules including glutamate, and plays an important role in the central nervous system. The connexin 40 (Cx40) and connexin 50 (Cx50) genes are located on chromosome 1q21.1, a region strongly linked with schizophrenia. These lines of evidence suggest that Cx40 and Cx50 may play a role in schizophrenia. Methods: Using an allele-specific PCR assay, four polymorphisms each were genotyped for Cx40 and Cx50 in 190 Caucasian patients with schizophrenia and 190 controls matched for sex, age and ethnicity. Following up, Cx50 rs989192 and rs4950495 were investigated in 99 Canadian and 163 Portuguese trios and nuclear families with schizophrenia probands. Hardy–Weinberg equilibrium and linkage disequilibrium (LD) block identification was carried out with HaploView, and association analysis for alleles and haplotypes with a permutation test of 10 000 simulations was carried out using the UNPHASED software program. Results: Distributions of genotype frequencies of all markers were in Hardy–Weinberg equilibrium in Caucasian patients, controls and families. One rs989192-rs4950495 LD block was found in patients but not in controls. We found a significant association between the Cx50 rs989192-rs4950495 haplotype and schizophreniay (χ2 = 29.55, p<0.01). The A-C haplotype had a higher frequency in patients (χ2 = 7.153, p<0.01). Family studies also showed that the A-C haplotype was transmitted more often to patients with schizophrenia (χ2 = 8.43, p<0.01). No association of Cx40 with schizophrenia was found for allele, genotype or haplotype analyses. Conclusions: Our matched case–control and family study indicate that Cx50, but not Cx40, may play a role in the genetic susceptibility to schizophrenia.

The catechol-O-methyl-transferase gene in tardive dyskinesia

Abstract Tardive dyskinesia (TD) is a severe and potentially irreversible motor side effect linked to long-term antipsychotic exposure. Changes in dopamine neurotransmission have been implicated in the etiology of TD, and catechol-O-methyl-transferase (COMT) is an enzyme that metabolizes dopamine. Objectives. We investigated five single-nucleotide polymorphisms in addition to the functional Val158Met variant spanning the COMT gene for association with TD. Methods. We analyzed the six COMT single-nucleotide polymorphisms in a sample of schizophrenia/schizoaffective disorder patients (n=226; 196 Caucasians and 30 African Americans). Results. We found a significant association between the marker rs165599 in the 3′ untranslated region of COMT and TD (AA versus G-carrier: ORAA=2.22, 95% CI:1.23–4.03; P=0.007). The association appeared to be originating from males. We did not find a significant association of the other five tested polymorphisms with TD in our samples. We performed a sex-stratified meta-analysis across all of the published studies (n=6 plus our own data) of COMT and TD, and found an association between ValVal genotype and TD in females (ORValVal=1.63, 95% CI: 1.09–2.45; P=0.019) but not in males. Conclusions. Overall, our results suggest that the COMT gene may have a minor but consistent role in TD, although sex-stratified studies with additional markers in larger clinical samples should be performed.

Family-Based Association Study of the Serotonin-2A Receptor Gene (5-HT2A) and Bipolar Disorder

Objectives: The serotonin 2A receptor gene (5-HT2A) is of great interest for research in neuropsychiatric disorders based on the observation that various neuroleptic agents and antidepressants bind with relatively high affinity at 5-HT2A receptors, and the fact that the receptor density in platelets tends to increase in depression. To test for the presence of association between 5-HT2A and bipolar disorder (BP), we studied a large number of triad families having probands affected with DSM-IV bipolar I (BPI), bipolar II (BPII) or schizoaffective disorder, bipolar type.Methods: Two polymorphisms of 5-HT2A, 102T/C, and His452Tyr were analyzed in the 274 bipolar triad families. Both the transmission disequilibrium test (TDT) and haplotype TDT were performed on the genotype data. We also calculated the maternal transmission and paternal transmission for each allele and compared the mean ages of onset across probands grouped by genotype at each of the two markers.Results: No significant transmission disequilibrium between the alleles of 5-HT2A and BP was found. Separate studies of the sub-phenotypes also failed to demonstrate significant association. However, we found a trend towards transmission disequilibrium with the haplotype 102C.His452 (p=0.0504). This trend may become more significant with a larger sample size.Significance: At present, results of this study suggest that the 5-HT2A is unlikely to play a major role in the genetic susceptibility to BP. Future studies will be directed towards increasing sample size, focusing on subtypes of BP or biochemical measures as phenotypes, and investigating other polymorphisms of 5-HT2A to provide more information at the DNA level.

Haplotype association study between DRD1 gene and bipolar type I affective disorder in two samples from Canada and Sardinia

Based on the dopaminergic hypothesis, the dopamine D1 receptor gene (DRD1) is considered to be a good candidate gene involved in the susceptibility of bipolar disorder (BP). Genetic association between three DRD1 single nucleotide polymorphisms (SNPs) (−800T/C, −48A/G, and 1403T/C) and bipolar type I (BP I) disorder was performed in a case‐control sample of Sardinian origin (170 BP I and 209 controls) and in an enlarged sample (229 families) of BP I trios from Toronto. The haplotype analyses generated significant global chi‐square in both samples (P‐value 0.024 in Toronto and 0.00042 in Sardinian). The main representative haplotypes in both samples were the −800T/−48A/1403C and the −800C/−48G/1403T. Considering each group individually, the −800C/−48G/1403T was transmitted more frequently from parents to BP I probands in Toronto sample (nominally P‐value = 0.047) and was more frequent in cases than in control subjects in Sardinian sample although showing no significant evidence of association (nominally P‐value = 0.16) When the estimated haplotype counts of both samples were combined, the global χ2 was significant (P‐value = 0.00085) and the nominal P‐value for the haplotype −800C/−48G/1403T was 0.01. The fact that the same haplotype shows a similar trend for association in samples originating from different ethnic backgrounds seems to imply that the −800C/−48G/1403T haplotype may be considered as a risk factor for BP I disorder.