Association of catechol-O-methyltransferase gene polymorphisms with schizophrenia and negative symptoms in a Chinese population

Genotypic and Haplotypic Association of Catechol-O-Methyltransferase rs4680 and rs4818 Gene Polymorphisms with Particular Clinical Symptoms in Schizophrenia

Catechol-O-methyl transferase (COMT) gene variants are involved in different neuropsychiatric disorders and cognitive impairments, associated with altered dopamine function. This study investigated the genotypic and haplotypic association of COMT rs4680 and rs4618 polymorphisms with the severity of cognitive and other clinical symptoms in 544 male and 385 female subjects with schizophrenia. COMT rs4818 G carriers were more frequent in male patients with mild abstract thinking difficulties, compared to CC homozygotes or C allele carriers. Male carriers of COMT rs4680 A allele had worse abstract thinking (N5) scores than GG carriers, whereas AA homozygotes were more frequent in male subjects with lower scores on the intensity of the somatic concern (G1) item, compared to G carriers. Male carriers of COMT rs4818-rs4680 GA haplotype had the highest scores on the G1 item (somatic concern), whereas GG haplotype carriers had the lowest scores on G2 (anxiety) and G6 (depression) items. COMT GG haplotype was less frequent in female patients with severe disturbance of volition (G13 item) compared to the group with mild symptoms, while CG haplotype was more frequent in female patients with severe then mild symptoms. These findings suggest the sex-specific genotypic and haplotypic association of COMT variants with a severity of cognitive and other clinical symptoms of schizophrenia.

Emerging evidence for astrocyte dysfunction in schizophrenia

Schizophrenia is a complex, chronic mental health disorder whose heterogeneous genetic and neurobiological background influences early brain development, and whose precise etiology is still poorly understood. Schizophrenia is not characterized by gross brain pathology, but involves subtle pathological changes in neuronal populations and glial cells. Among the latter, astrocytes critically contribute to the regulation of early neurodevelopmental processes, and any dysfunctions in their morphological and functional maturation may lead to aberrant neurodevelopmental processes involved in the pathogenesis of schizophrenia, such as mitochondrial biogenesis, synaptogenesis, and glutamatergic and dopaminergic transmission. Studies of the mechanisms regulating astrocyte maturation may therefore improve our understanding of the cellular and molecular mechanisms underlying the pathogenesis of schizophrenia.

The inconsistent mediating effect of catechol O methyl transferase Val158Met polymorphism on the sex difference of cognitive impairment in schizophrenia patients

OBJECTIVE

Schizophrenia is a multifaceted mental disorder characterized by heterogeneous positive/negative symptoms and cognitive deficits. Sex differences have been reported in various aspects of the disease. However, the underlying genetic reasons remain unelucidated. Recent studies show that the influence of COMT Val158Met (rs4680) variation is sexually dimorphic. Thus, this study aims to explore whether there is an effect of the interaction between COMT Val158Met (rs4680) polymorphism and sex on patients' clinical characteristics and cognitive function.

MATERIALS AND METHODS

We recruited 367 in patients with chronic schizophrenia (246 males and 121 females) and 419 healthy controls (172 males and 247 females). The cognitive performance was assessed by Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), and the COMT Val158Met (rs4680) polymorphism is genotyped. The psychopathological symptoms of the patients were assessed by the Positive and Negative Syndrome Scale (PANSS).

RESULTS

We find that male patients had a significantly higher proportion of carrying the Val allele and Val/Val carriers exhibited more severe positive symptoms and cognitive impairment than Met carriers. COMT Val158Met (rs4680) polymorphism inconsistently mediated the relationship between sex and cognitive performance in schizophrenia patients.

CONCLUSION

These findings suggest that COMT Val158Met (rs4680) polymorphism is associated with the risk and severity of schizophrenia in a sexually dimorphic way and contributes more to the clinical symptoms and cognitive impairment in male patients with schizophrenia.

Investigation of inflammation related gene polymorphism of the mannose-binding lectin 2 in schizophrenia and bipolar disorder

OBJECTIVES

To investigate the association between mannose-binding lectin 2 (MBL2) codon 54 polymorphism and clinical features of patients diagnosed with schizophrenia (SCZ) or bipolar disorder (BD).

METHODS

One hundred and eighteen patients with SCZ, 100 patients with BD, and 100 healthy volunteers were included in the case-control study. The patients consecutively admitted to the outpatient clinic in December 2017-May 2018 and were evaluated with some scales for clinical parameters. Polymerase chain reaction and RFLP were used to determine MBL2 polymorphism in DNA material.

RESULTS

The MBL2 gene polymorphism distributions in SCZ or BD patients were significantly different from the control group. The heterozygous genotype percentages were significantly higher in the control group than in the SCZ or BD patients (OR: 0.450; 95% Cl: 0.243-0.830; p=0.010; OR: 0.532; 95%Cl: 0.284-0.995; p=0.047, respectively), and there were statistically significant differences in the MBL2 polymorphism distributions between treatment-responsive SCZ or BD patients and treatment-resistant patients diagnosed with SCZ or BD. The heterozygous genotype percentages were also significantly higher in the treatment-responsive group than in the treatment-resistant group in SCZ or BD patients (OR: 7.857; 95% Cl: 1.006-61.363; p=0.023; OR: 8.782; 95% Cl: 1.114-69.197; p=0.016, respectively).

CONCLUSION

The presence of a heterozygous MBL2 genotype seems to be favorable both in terms of the absence of SCZ and BD in the healthy population and treatment response for Turkish patients.

The Associations between COMT and MAO-B Genetic Variants with Negative Symptoms in Patients with Schizophrenia

Negative symptoms of schizophrenia, including anhedonia, represent a heavy burden on patients and their relatives. These symptoms are associated with cortical hypodopamynergia and impaired striatal dopamine release in response to reward stimuli. Catechol-O-methyltransferase (COMT) and monoamine oxidase type B (MAO-B) degrade dopamine and affect its neurotransmission. The study determined the association between COMT rs4680 and rs4818, MAO-B rs1799836 and rs6651806 polymorphisms, the severity of negative symptoms, and physical and social anhedonia in schizophrenia. Sex-dependent associations were detected in a research sample of 302 patients with schizophrenia. In female patients with schizophrenia, the presence of the G allele or GG genotype of COMT rs4680 and rs4818, as well as GG haplotype rs4818-rs4680, which were all related to higher COMT activity, was associated with an increase in several dimensions of negative symptoms and anhedonia. In male patients with schizophrenia, carriers of the MAO-B rs1799836 A allele, presumably associated with higher MAO-B activity, had a higher severity of alogia, while carriers of the A allele of the MAO-B rs6651806 had a higher severity of negative symptoms. These findings suggest that higher dopamine degradation, associated with COMT and MAO-B genetic variants, is associated with a sex-specific increase in the severity of negative symptoms in schizophrenia patients.

Effectiveness of a social problem solving training in youth in detention or on probation: An RCT and pre-post community implementation

The effectiveness of a 10-session social problem-solving training (SPST) was evaluated in two independent studies in a juvenile justice (JJ) setting. In both studies, we aimed to examine main intervention effects on social problem-solving skills and recidivism, as well as differential effects as modulated by anger, anger regulation, and single nucleotide polymorphisms in the COMT gene. In Study 1, a randomized controlled trial (RCT), 289 male detainees (M_age= 14.95 years) were randomly assigned to SPST or treatment-as-usual (TAU). In Study 2, a pre-post community implementation, 187 youth (M_age = 16.03 years) on probation were assessed before and after SPST. No significant main effects of SPST on social problem solving or recidivism were shown in either study. With regard to differential effects, among youth in detention,COMT haplotypes predicted intervention effects on state anger. Moreover, independent of SPST, inward anger expression was associated with an increase in state anger from pre- to post and an increase in state anger with a decrease in social problem solving. Among youth on probation, COMT haplotypes predicted social problem-solving skills, and, in turn, an increase in social problem-solving skills decreased the odds of recidivism after SPST. The lack of main effects of SPST may be due to low program integrity in JJ settings. Juveniles' emotional and genetic characteristics might modulate the effectiveness of interventions in JJ settings. We recommend studying large samples to substantiate this observation.

Prevalence, Sociodemographic, and Clinical Correlates of Older Chinese Patients With Deficit Schizophrenia

OBJECTIVE

No study has investigated the frequency and risk factors for deficit schizophrenia (DS) in Chinese Han population. We investigated the prevalence of DS among community-dwelling older Chinese patients with schizophrenia and examined the sociodemographic and clinical correlates of DS in this population.

METHODS

A total of 326 community-dwelling older patients with schizophrenia were recruited in this cross-sectional study. Deficit schizophrenia was confirmed using the Chinese version of the Schedule for the Deficit Syndrome. Data pertaining to sociodemographic and clinical characteristics were collected. Psychopathology was assessed using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

The prevalence of DS in the study population was 26.7% (31.2% among male patients and 21.6% among female patients with schizophrenia). Patients with DS had significantly higher current smoking rate, hospitalizations, PANSS negative score, PANSS total score, and had earlier age at onset than patients with non-deficit schizophrenia (N-DS). The N-DS patients had higher PANSS positive scores and a greater proportion of married patients. Multiple logistic regression analysis indicated that negative PANSS score (odds ratio [OR] = 1.10, 95% confidence interval [CI] = 1.04-1.16, P < .001), male sex (OR = 1.71, 95% CI = 1.53-1.91, P = .037), age at onset (OR = 0.88, 95% CI = 0.82-0.94, P = .035), and current smoking (OR = 1.37, 95% CI = 1.15-1.63, P = .041) were independently associated with DS.

CONCLUSION

Deficit schizophrenia is relatively common among older community-dwelling Chinese patients with schizophrenia. High negative symptom scores, male sex, early onset, and smoking were independent correlates for DS.

Negative symptoms of psychosis: A life course approach and implications for prevention and treatment

AIM

Negative symptoms are a cause of enduring disability in serious mental illness. In spite of this, the development of effective treatments for negative symptoms has remained slow. The challenge of improving negative symptom outcomes is compounded by our limited understanding of their aetiology and longitudinal development.

METHODS

A literature search was conducted for life course approach of negative symptoms using PubMed. Further articles were included following manual checking of reference lists and other search strategies. The paper contains a theoretical synthesis of the literature, summarized using conceptual models.

RESULTS

Negative symptom definitions are compared and considered within a context of the life course. Previous studies suggest that several illness phases may contribute to negative symptoms, highlighting our uncertainty in relation to the origin of negative symptoms.

CONCLUSIONS

Similar to other aspects of schizophrenia, negative symptoms likely involve a complex interplay of several risk and protective factors at different life phases. Concepts suggested in this article, such as "negative symptom reserve" theory, require further research, which may inform future prevention and treatment strategies.

Haplotypic and Genotypic Association of Catechol-O-Methyltransferase rs4680 and rs4818 Polymorphisms and Treatment Resistance in Schizophrenia

Treatment-resistant schizophrenia (TRS) continues to be a challenge. It was related to different factors, including alterations in the activity of brain dopaminergic system, which could be influenced by the dopamine-degrading enzyme, catechol-O-methyltransferase (COMT). Variants of the COMT gene have been extensively studied as risk factors for schizophrenia; however, their association with TRS has been poorly investigated. The aim of the present study was to determine the haplotypic and genotypic association of COMT rs4680 and rs4818 polymorphisms with the presence of TRS. Overall, 931 Caucasian patients diagnosed with schizophrenia (386 females and 545 males) were included, while 270 participants met the criteria for TRS. In males, no significant haplotypic and genotypic associations between COMT rs4680 and rs4818 polymorphisms and TRS were detected. However, genotypic analyses demonstrated higher frequency of COMT rs4680 AA genotype carriers compared to G-allele carriers (p = 0.033) and higher frequency of COMT rs4818 CC genotype carriers than G-allele carriers (p = 0.014) in females with TRS. Haplotype analyses confirmed that the presence of the G allele in females was associated with lower risk of TRS. In women with TRS, the high activity G-G/G-G haplotype was rare, while carriers of other haplotypes were overrepresented (p = 0.009). Such associations of COMT rs4680 and rs4818 high-activity (G variants), as well as G-G/G-G haplotype, with the lower risk of TRS in females, but not in males, suggest significant, but sex-specific influence of COMT variants on the development of treatment-resistance in patients with schizophrenia. However, due to relatively low number of females, those findings require replication in a larger sample.

DNA methylation of membrane-bound catechol-O-methyltransferase in Malaysian schizophrenia patients

AIM

This study examined catechol-O-methyltransferase (COMT) DNA methylation in the peripheral blood of schizophrenia patients and also in healthy controls to investigate its potential use as a peripheral biomarker of schizophrenia and its relations with the clinical variables of schizophrenia patients.

METHODS

We examined the DNA methylation levels of COMT using genomic DNA from the peripheral blood of schizophrenia patients (n = 138) and healthy control participants (n = 132); all were Malaysian Malays. The extracted DNA was bisulfite converted, and the percentage methylation ratio value was calculated based on the results following a MethyLight protocol analysis.

RESULTS

The percentage methylation ratio of COMT was lower in schizophrenia than it was in the healthy controls (P < 0.001) and was different between the body mass index (P = 0.003) and antipsychotic (P = 0.004) groups. The COMT DNA methylation rate was lower in patients receiving atypical antipsychotics (P = 0.004) and risperidone (P = 0.049) as compared to typical antipsychotics. The Excitement and Depressed subdomains of the Positive and Negative Syndrome Scale were inversely related (P < 0.001) and therefore predictors (Excitement: b = -11.396, t = -4.760, P < 0.001; Depressed: b = -7.789, t = -3.487, P = 0.001) of COMT DNA methylation.

CONCLUSION

Our results suggested that the methylation level was affected by the severity of the clinical symptoms of schizophrenia and might also be influenced by pharmacological treatment. The epigenetic alteration of COMT in the peripheral blood could be a potential peripheral biomarker of schizophrenia.

Genetic Basis of Positive and Negative Symptom Domains in Schizophrenia

Schizophrenia is a highly heritable disorder, the genetic etiology of which has been well established. Yet despite significant advances in genetics research, the pathophysiological mechanisms of this disorder largely remain unknown. This gap has been attributed to the complexity of the polygenic disorder, which has a heterogeneous clinical profile. Examining the genetic basis of schizophrenia subphenotypes, such as those based on particular symptoms, is thus a useful strategy for decoding the underlying mechanisms. This review of literature examines the recent advances (from 2011) in genetic exploration of positive and negative symptoms in schizophrenia. We searched electronic databases PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature using key words schizophrenia, symptoms, positive symptoms, negative symptoms, cognition, genetics, genes, genetic predisposition, and genotype in various combinations. We identified 115 articles, which are included in the review. Evidence from these studies, most of which are genetic association studies, identifies shared and unique gene associations for the symptom domains. Genes associated with neurotransmitter systems and neuronal development/maintenance primarily constitute the shared associations. Needed are studies that examine the genetic basis of specific symptoms within the broader domains in addition to functional mechanisms. Such investigations are critical to developing precision treatment and care for individuals afflicted with schizophrenia.

Association of EPHB1 rs11918092 and EFNB2 rs9520087 with psychopathological symptoms of schizophrenia in Chinese Zhuang and Han populations

Two single-nucleotide polymorphisms (SNPs) (rs11918092 and rs9520087) were genotyped in Chinese Zhuang and Han populations. Symptoms of schizophrenic patients were assessed by the Positive and Negative Syndrome Scale. No association of any SNP with schizophrenic susceptibility was found. However, associations of rs9520087 with the total scale score (P = 0.014), positive scale score (P = 0.013), negative scale score (P = 0.032), and general psychopathology scale score (P = 0.031) were found in Zhuang patients. Additionally, rs11918092 was associated with positive scale score (P = 0.035) in Han patients. The two SNPs might influence symptoms of schizophrenia.

Characterization of premorbid functioning during childhood in patients with deficit vs. non-deficit schizophrenia and in their healthy siblings

Impaired premorbid adjustment has been reported in patients with schizophrenia, generally in association with unfavorable aspects of the illness (e.g., poor outcome and severe negative symptoms). Several studies attempted to define the domains of premorbid dysfunction associated with negative symptoms and poor outcome; however, most of them assessed broadly defined negative symptoms. The present study was aimed to characterize premorbid functioning in a group of patients with deficit schizophrenia (DS), characterized by the presence of at least two primary and persistent negative symptoms (PPNS), and one of patients with a diagnosis of schizophrenia who did not meet criteria for DS (NDS). The presence of emotional/behavioral problems during childhood was investigated using the Childhood Behavior Checklist (CBCL) in both patient groups and in their respective healthy siblings. The Premorbid Adjustment Scale (PAS) was also used to assess premorbid functioning during childhood in the two patient groups. PPNS were also treated as a continuous variable and correlated with the indices of premorbid functioning regardless the DS/NDS categorization. DS patients, as compared to NDS, showed higher scores on the CBCL subscale "Withdrawn". Both DS and NDS patients showed, as compared to their healthy siblings, a greater impairment on almost all CBCL subscales. PAS findings revealed that DS patients had poorer premorbid adjustment than NDS. No significant correlation between premorbid functioning and PPNS was observed. These findings support the hypothesis that DS has a different developmental trajectory with respect to NDS, and that premorbid adjustment is one of the essential aspects of its characterization.

Neurobiological background of negative symptoms

Studies investigating neurobiological bases of negative symptoms of schizophrenia failed to provide consistent findings, possibly due to the heterogeneity of this psychopathological construct. We tried to review the findings published to date investigating neurobiological abnormalities after reducing the heterogeneity of the negative symptoms construct. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, genetics and neurobiology of schizophrenia. We searched PubMed with the keywords "negative symptoms," "deficit schizophrenia," "persistent negative symptoms," "neurotransmissions," "neuroimaging" and "genetic." Additional articles were identified by manually checking the reference lists of the relevant publications. Publications in English were considered, and unpublished studies, conference abstracts and poster presentations were not included. Structural and functional imaging studies addressed the issue of neurobiological background of negative symptoms from several perspectives (considering them as a unitary construct, focusing on primary and/or persistent negative symptoms and, more recently, clustering them into factors), but produced discrepant findings. The examined studies provided evidence suggesting that even primary and persistent negative symptoms include different psychopathological constructs, probably reflecting the dysfunction of different neurobiological substrates. Furthermore, they suggest that complex alterations in multiple neurotransmitter systems and genetic variants might influence the expression of negative symptoms in schizophrenia. On the whole, the reviewed findings, representing the distillation of a large body of disparate data, suggest that further deconstruction of negative symptomatology into more elementary components is needed to gain insight into underlying neurobiological mechanisms.

Association of microRNA137 gene polymorphisms with age at onset and positive symptoms of schizophrenia in a Han Chinese population

OBJECTIVES

MicroRNA137 (miRNA137) regulates several gene expressions involved in brain development, and a recent large genome wide association study (GWAS) revealed a possible association between miRNA137 and schizophrenia.

METHODS

The allelic variants of rs66642155, a variable number tandem repeat polymorphism, and the single nucleotide polymorphism rs1625579 A/C in the miRNA137 host gene fragment were compared between 300 schizophrenic patients and 300 healthy controls from the Han Chinese population. The association of these polymorphisms with clinical characteristics of schizophrenia was also tested.

RESULTS

Genotype and allele frequencies of these polymorphisms were not significantly different between patient and control populations. In patients, however, age at onset was much later in wild type rs66642155 carriers than in mutation carriers. Total positive score on the Positive and Negative Symptom Scale (PANSS), total five-factor model positive score, and the delusions symptom score were all significantly higher in wild type rs66642155 carriers with schizophrenia, while the disturbance of volition symptom score was significantly higher in the mutation carriers with schizophrenia.

CONCLUSIONS

MiRNA137 may not be a significant susceptibility gene for schizophrenia, but in patients, rs66642155 allelic variant of miRNA137 appears to influence age at onset and the severity of positive symptoms.

BDNF rs 6265 polymorphism and COMT rs 4680 polymorphism in deficit schizophrenia in Polish sample

BACKGROUND

Deficit schizophrenia (DS) is distinguished from the group of schizophrenic psychoses based on the presence of primary negative symptoms. It differs from nondeficit (NDS) forms of schizophrenia in dimensions such as risk factors, family history, course of illness and neurobiological differences. The aim of the study was assessment of a potential association of the investigated polymorphisms of the brain-derived neurotrophic factor (BDNF) and catechol-O-methyltransferase (COMT) genes with the deficit syndrome in schizophrenia.

METHODS

A cohort of 200 patients with schizophrenia (81 DS and 119 NDS subjects) and a group of 100 control subjects matched for ethnicity, sex and age were recruited. Somatic and psychometric assessment were conducted as well as structured interview about the influence of adverse biological, family and social factors. Genetic analysis of the BDNF (Val66Met) rs6265 and the COMT (Val158Met) rs4680 polymorphisms was performed.

RESULTS

We found significant differences between DS and NDS in rs4680 COMT genotype distribution: more homozygous Val/Val were found (31 vs. 17%) in the NDS compared to the DS subgroup. No associations were found between the investigated polymorphisms of the BDNF gene and the presence of schizophrenia either in DS and NDS subgroups.

CONCLUSION

The analysis of the COMT rs4680 polymorphism in the present DS and NDS study shows that some genetic factors may be relevant in analyzing the reasons for the differentiation of schizophrenic subtypes.

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

Association of estrogen receptor alpha gene polymorphism with age at onset, general psychopathology symptoms, and therapeutic effect of schizophrenia

BACKGROUND

Estrogen is believed to play an important role in the central nervous system (CNS) and exert a protective role against schizophrenia. Estrogen receptor alpha (ESRα) mediates the biological action of estrogen. Rs2234693 and rs9340799, single nucleotide polymorphisms of ESRα, may be related to many psychiatric disorders, while their association with schizophrenia has not been clarified.

METHODS

Genotypes rs2234693 and rs9340799 were detected in 303 schizophrenic patients and 292 healthy controls in a Chinese population. The positive and negative syndrome scale (PANSS) was used to estimate symptoms and therapeutic effects. The association of these polymorphisms with schizophrenia and clinical characteristics was analyzed by the chi-square test, analysis of variance, and others.

RESULTS

The distribution of genotypes and allele frequencies of rs2234693 and rs9340799 exhibited no significant differences between patients and controls, while haplotypes consisting of these polymorphisms had significant differences. For 2234693, T-allele carriers had an earlier age at onset. CC-homozygote carriers had a higher general psychopathology score and its percentage reduction in male and paranoid patients, respectively. CC-homozygote carriers had a higher tension (G4) and poor impulse control (G14) score, mainly in paranoid patients. Furthermore, patients with the CC homozygote had higher reductions of G4 and G14 scores when treated by aripirazole and risperidone, respectively.

CONCLUSIONS

Haplotypes consisting of these two polymorphisms in ESRα may be strongly associated with schizophrenia. The rs2234693 was related to age at onset, general psychopathology, G4 and G14 symptoms, even the therapeutic effect in different groups.

ANK3 as a risk gene for schizophrenia: new data in Han Chinese and meta analysis

Histological and neuroimaging evidence supports the hypothesis that neuronal disconnectivity may be involved in the pathogenesis of schizophrenia. A genome-wide association study (GWAS) showed a single nucleotide polymorphism (SNP), rs10761482 in ankyrin 3 (ANK3), a major neuron-enriched gene, was associated with schizophrenia although inconsistent results had been reported. Two meta analyses reported another SNP rs10994336 in ANK3 gene confers risk to bipolar disorder (BD). Due to evidence of genetic overlap between schizophrenia and BD, we investigated common findings by analyzing the association of ANK3 polymorphisms (rs10761482, rs10994336, and two missenses, rs3808942 and rs3808943) with schizophrenia, using the Han Chinese population. A total of 516 schizophrenia cases, 400 controls, and 81 trios of early onset schizophrenia were recruited for association studies. Furthermore, the published datasets were combined with our results to determine the effect of the loci on schizophrenia. Our association study showed the frequencies of C allele of rs10761482 and T allele of rs10994336 were higher in patients than in controls. Furthermore, allele condition analyses indicated the association signal observed at rs10761482 and rs10994336 was independent. A haplotype analysis revealed the rs10761482-rs3808942-rs3808943 haplotype was associated with schizophrenia. The frequency of the T-T-T haplotype was higher in patients than in controls. In the transmission disequilibrium test analysis, the C allele of rs10761482 and the rs10761482-rs3808942-rs3808943 haplotype were preferentially transmitted in the trios. Meta analysis incorporating previous and current studies also showed rs10761482 and rs10994336 were associated with schizophrenia. We conclude that ANK3 gene has a major influence on susceptibility to schizophrenia across populations.

No association between catechol-o-methyltransferase Val108/158Met polymorphism and schizophrenia or its clinical symptomatology in a Mexican population

The gene coding for catecol-o-methyltransferase (COMT), participant in the metabolism of catecholamines, has long been implicated as a candidate gene for schizophrenia. We determined the relation of the COMT Val108/158Met polymorphism with schizophrenia or its symptomatology (negative, disorganized and psychotic dimension). We conducted a case–control study comprising 186 patients with schizophrenia and 247 controls. The diagnosis of schizophrenia was established using the DSM-IV criteria for this illness. The clinical symptomatology was assessed through the Scale for the Assessment of Negative Symptoms and the Scale for the Assessment of Positive Symptoms. No significant differences were found in the distribution of alleles (χ2 = 0.01, df = 1, p = 0.90) or genotypes (χ2 = 1.66, df = 2, p = 0.43) between schizophrenic patients and the control group. Multivariate analysis showed that the COMT Val108/158Met polymorphism has no influence in the clinical symptomatology of schizophrenia. Our results showed no association between COMT Val108/158Met and schizophrenia or evidence for an association between COMT and the clinical symptomatology of this illness. This suggests that the COMT gene may not contribute to the risk for schizophrenia among the Mexican population.

Association of MB-COMT polymorphisms with schizophrenia-susceptibility and symptom severity in an African cohort

The catechol-O-methyltransferase (COMT) gene is an attractive schizophrenia candidate gene, encoding a catabolic dopamine enzyme. The enzyme exists as two distinct isoforms, with the membrane bound enzyme (i.e. MB-COMT) being predominantly expressed in the brain. Since African populations remain underrepresented in genetic/genomic research, we performed an association study to determine whether MB-COMT genetic variants are associated with schizophrenia-susceptibility and symptom severity in the South African Xhosa population. Fourteen candidate polymorphisms were selected by means of a literature search and in silico analyses and were subsequently genotyped in a cohort of 238 Xhosa schizophrenia patients and 240 healthy Xhosa controls. Genetic association was tested with schizophrenia-susceptibility as well as symptom severity within the patient group. Polymorphisms of interest were also analysed using functional assays. Two SNPs, rs2020917 (OR=0.54, 95% CI 0.37-0.79; P=0.0011) and rs737865 (OR=0.52, 95% CI 0.36-0.74; P=0.0002), in the P2 promoter region were significantly associated with schizophrenia as well as an increase (increase=11.2%, 95% CI 3.7%-19.2%; P=0.0031) in reporter gene expression. The minor alleles of these SNPs were underrepresented in the schizophrenia cohort, indicating a possible protective effect. The P2 region also formed part of a haplotype found to be associated with the severity of the negative symptoms of the disorder. The data generated by this study indicate that genetic variation of MB-COMT could be associated with schizophrenia and negative symptom severity in the Xhosa population and may therefore be one of the genomic loci contributing towards the disorder in the South African community. Future large-scale studies in other African schizophrenia populations are required to further elucidate the significance of these findings.