A Disrupted-in-Schizophrenia 1 Gene Variant is Associated with Clinical Symptomatology in Patients with First-Episode Psychosis

Markers of Schizophrenia—A Critical Narrative Update

Schizophrenia is a long-term mental disease, associated with functional impairment. Therefore, it is important to make an accurate diagnosis and implement the proper treatment. Biomarkers may be a potential tool for these purposes. Regarding advances in biomarker studies in psychosis, the current symptom-based criteria seem to be no longer sufficient in clinical settings. This narrative review describes biomarkers of psychosis focusing on the biochemical (peripheral and central), neurophysiological, neuropsychological and neuroimaging findings as well as the multimodal approach related with them. Endophenotype markers (especially neuropsychological and occulomotor disturbances) can be currently used in a clinical settings, whereas neuroimaging glutamate/glutamine and D2/D3 receptor density changes, as well as immunological Th2 and PRL levels, seem to be potential biomarkers that need further accuracy tests. When searching for biochemical/immunological markers in the diagnosis of psychosis, the appropriate time of body fluid collection needs to be considered to minimize the influence of the stress axis on their concentrations. In schizophrenia diagnostics, a multimodal approach seems to be highly recommended.

Distinctively lower DISC1 mRNA levels in patients with schizophrenia, especially in those with higher positive, negative, and depressive symptoms

BACKGROUND

The issue of genetic influence on schizophrenia has received considerable attention. The DISC1 gene has been shown in several studies to play a role in the pathophysiology of schizophrenia. However, the relationship between DISC1 mRNA expression vs. schizophrenia and its clinical symptoms is uncertain.

METHODS

Fifty-six subjects (32 patients with schizophrenia and 24 healthy controls) were enrolled. Peripheral blood was obtained from all subjects to exam the DISC1 mRNA expression. Schizophrenia patients were evaluated with Hamilton Rating Scale for Depression (HAMD), Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS) and Scale for the Assessment of Negative Symptoms (SANS) scales. Healthy subjects were assessed with HAMD scale.

RESULTS

Patients with schizophrenia had significantly lower levels of the DISC1 mRNA expression than the healthy control (P = 0.002). We also found that lower DISC1 mRNA levels in schizophrenia patients were associated with higher degree of depression in HAMD (P = 0.037), severer positive symptoms in PANSS (P = 0.032) and more negative symptoms in SANS (P = 0.038).

CONCLUSION

The results showed that schizophrenia patients had lower levels of DISC1 mRNA than healthy individuals, and that the schizophrenia patients with lower DISC1 mRNA levels were more likely to manifest more marked symptoms, including positive, negative, and depressive symptoms. The findings suggest that lower DISC1 expression may be related with the pathogenesis and phenotypes of schizophrenia. Future studies are needed to replicate the results and to further establish its potential role in clinical application of early diagnosis and outcome follow-up.

Crossroad between current knowledge and new perspective of diagnostic and therapy of late-onset schizophrenia and very late-onset schizophrenia-like psychosis: An update

Schizophrenia is a chronic, highly individualized disease with many symptoms that can occur with varying severity in different patients. Schizophrenia affects 1% of the population, but occurs in almost 20% of patients after 40 years of age. It should be noted that the next peak in the incidence of schizophrenia occurs at the age of 60 years, affects mostly females, and is closely associated with a high risk of developing memory disorders. Therefore, postadolescent schizophrenia includes two distinct groups of patients: those whose symptoms onset at the age of 45 or 60. The purposes of this literature review were as follows: (1) synthetically characterize the clinical manifestations of schizophrenia; (2) discuss difficulties in the diagnosis of schizophrenia, especially in patients over 40 years of age; (3) discuss the clinical utility of different classes of marker in diagnostic and differentiating schizophrenia from neurodegenerative diseases in elderly people; (4) discuss therapeutic options for schizophrenia, pharmacotherapy, and psychotherapy, emphasizing the role of caregivers of people with psychosis in therapy, in preadolescence and postadolescence schizophrenia. We have tried to primarily discuss the findings of original articles from the last 10 years with an indication of their clinical implications with the issues discussed in the various subsections. Moreover, despite many years of research, no specific, precise algorithm has been developed that can be used in clinical practice during the diagnosis of schizophrenia. For this reason, the diagnosis of schizophrenia is primarily based on an interview with the patient and his family, as well as on the experience of a psychiatrist. It also seems that schizophrenia treatment should be carried out holistically, including pharmacotherapy, psychotherapy, and the support of caregivers of patients who have this psychosis, which increases the achievement of therapeutic success. Finally, we must be aware of the difficulties in diagnosing schizophrenia in the elderly and the need to modify pharmacological treatment. Currently, no guidelines have been developed for the differentiation of negative symptoms in elderly patients with schizophrenia from amotivation/avolition/apathy symptoms in elderly patients with neurodegenerative disorders.

Disrupted-in-schizophrenia 1 functional polymorphisms and D2 /D3 receptor availability: A [11 C]-(+)-PHNO imaging study

The disrupted-in-schizophrenia 1 (DISC1) protein has been implicated in a range of biological mechanisms underlying chronic mental disorders such as schizophrenia. Schizophrenia is associated with abnormal striatal dopamine signalling, and all antipsychotic drugs block striatal dopamine 2/3 receptors (D_2/3 Rs). Importantly, the DISC1 protein directly interacts and forms a protein complex with the dopamine D₂ receptor (D₂ R) that inhibits agonist-induced D₂ R internalisation. Moreover, animal studies have found large striatal increases in the proportion of D₂ R receptors in a high affinity state (D₂ ^high R) in DISC1 rodent models. Here, we investigated the relationship between the three most common polymorphisms altering the amino-acid sequence of the DISC1 protein (Ser704Cys (rs821616), Leu607Phe (rs6675281) and Arg264Gln (rs3738401)) and striatal D_2/3 R availability in 41 healthy human volunteers, using [¹¹ C]-(+)-PHNO positron emission tomography. We found no association between DISC1 polymorphisms and D_2/3 R availability in the striatum and D₂ R availability in the caudate and putamen. Therefore, despite a direct interaction between DISC1 and the D₂ R, none of its main functional polymorphisms impact striatal D_2/3 R binding potential, suggesting DISC1 variants act through other mechanisms.

Association on DISC1 SNPs with schizophrenia risk: A meta-analysis

Schizophrenia is a major psychiatric disorder with complex genetic, environmental, and psychological etiologies. Although DISC1 gene has been shown as a risk factor for schizophrenia in some reports, there is a lack of a consensus. We therefore performed separate meta-analyses aiming to assess the associations between DISC1 SNPs and schizophrenia risk. We found that SNP rs821597 is significantly associated with schizophrenia risk in terms of both allelic and genotypic distribution, while SNP rs821616 is associated with schizophrenia in terms of genotypic distribution, especially in cases above 40 years old.

The effect of the DISC1 Ser704Cys polymorphism on striatal dopamine synthesis capacity: an [18F]-DOPA PET study

Whilst the role of the Disrupted-in-Schizophrenia 1 (DISC1) gene in the aetiology of major mental illnesses is debated, the characterization of its function lends it credibility as a candidate. A key aspect of this functional characterization is the determination of the role of common non-synonymous polymorphisms on normal variation within these functions. The common allele (A) of the DISC1 single-nucleotide polymorphism (SNP) rs821616 encodes a serine (ser) at the Ser704Cys polymorphism, and has been shown to increase the phosphorylation of extracellular signal-regulated protein Kinases 1 and 2 (ERK1/2) that stimulate the phosphorylation of tyrosine hydroxylase, the rate-limiting enzyme for dopamine biosynthesis. We therefore set out to test the hypothesis that human ser (A) homozygotes would show elevated dopamine synthesis capacity compared with cysteine (cys) homozygotes and heterozygotes (TT and AT) for rs821616. [18F]-DOPA positron emission tomography (PET) was used to index striatal dopamine synthesis capacity as the influx rate constant Kicer in healthy volunteers DISC1 rs821616 ser homozygotes (N = 46) and healthy volunteers DISC1 rs821616 cys homozygotes and heterozygotes (N = 56), matched for age, gender, ethnicity and using three scanners. We found DISC1 rs821616 ser homozygotes exhibited a significantly higher striatal Kicer compared with cys homozygotes and heterozygotes (P = 0.012) explaining 6.4% of the variance (partial η2 = 0.064). Our finding is consistent with its previous association with heightened activation of ERK1/2, which stimulates tyrosine hydroxylase activity for dopamine synthesis. This could be a potential mechanism mediating risk for psychosis, lending further credibility to the fact that DISC1 is of functional interest in the aetiology of major mental illness.

[Disturbance of oligodendrocyte differentiation in schizophrenia in relation to main hypothesis of the disease]

Increasing evidence coming from neuroimaging, molecular genetic and post-mortem studies have implicated oligodendrocyte abnormalities and compromised myelin integrity in schizophrenia. Activity-dependent myelination in adult brain is considered to be an important mechanism of neural circuit's plasticity due to the presence of a large population of oligodendrocyte progenitor cells (OPC) in the adult CNS. Growing evidence for impairment of oligodendrocyte differentiation has been reported in the brain of schizophrenia subjects. OPC are very vulnerable inflammation, oxidative stress, and elevated glutamate levels leading to excitotoxicity. The mechanisms of prolonged suppression of oligodendrocyte differentiation caused by prenatal maternal infection or preterm birth are discussed in view of increased risk of schizophrenia, neurodevelopmental and inflammation hypotheses of the disease. The data that some neuroleptics stimulate OPC differentiation and ameliorate myelin alterations support the notion that impairment in the differentiation of OPCs contributes to oligodendrocyte abnormalities and to the pathophysiology of schizophrenia.

Gene polymorphisms of DISC1 is associated with schizophrenia: Evidence from a meta-analysis

BACKGROUND

Previous studies suggest an association between Disrupted in schizophrenia 1 (DISC1) polymorphisms and schizophrenia (SCZ). However, the available data are often inconsistent, regarding the difference in sample size, ethnicity, genotyping method, etc. Thus, we carried out a meta-analysis to determine whether DISC1 polymorphisms contributed susceptibility to SCZ.

METHODS

A methodical literature review was operated using the English and Chinese core electronic databases. Odds ratios (ORs) with 95% confidence intervals (CIs) were applied to determine the correlation between DISC1 gene polymorphisms and SCZ susceptibility. Subgroup analyses were carried out by stratification of ethnicity. P values were Bonferroni adjusted to account for multiple testing. Publication bias was evaluated by funnel plots, Egger's test and the trim and fill method.

RESULTS

Meta-analyses results suggested that DISC1 polymorphisms (rs821616 and rs821597) increased SCZ risk in overall populations. In subgroups of ethnicity, DISC1 polymorphisms (rs821616 and rs821597) was associated with susceptibility to SCZ among the Chinese population (for rs821616: TT+AT vs. AA: OR=1.338, 95% CI=1.124-1.592, P=0.001; T vs. A: OR=1.300, 95% CI=1.124-1.504, P<0.000; for rs821597: AA+AG vs. GG: OR=1.508, 95% CI=1.268-1.794, P<0.001; A vs. G: OR=1.345, 95% CI=1.184-1.527, P<0.001). A positive correlation was also observed between the single marker rs821616 and SCZ among the Japanese population in the recessive model (TT vs. AT+AA: OR=1.524, 95% CI=1.185-1.959, P=0.001). There was no significant relationship between other DISC1 polymorphisms (rs3738401, rs2273890, rs3738398, rs3738402, rs2492367, rs843979, rs3737597, rs4658971, rs1538979, rs1000731 and rs3738399) and SCZ.

CONCLUSIONS

DISC1 polymorphisms increased a risk of SCZ, especially in the Chinese population. In order to further corroborate our findings, large well-designed epidemiological studies are needed.

The interaction of NOS1AP, DISC1, DAOA, and GSK3B confers susceptibility of early-onset schizophrenia in Chinese Han population

Although many major breakthrough had identificated potential susceptibility genes for schizophrenia, the aetiology of schizophrenia is still unknown. In the present study, we focused on the N-methyl-Daspartate receptors related genes nitric oxide synthase 1 adaptor gene (NOS1AP), disrupted in schizophrenia 1 gene (DISC1), d-amino acid oxidase activator gene (DAOA), and glycogen synthase kinase 3-beta gene (GSK3B). A family-based genetic association study (459 Han Chinese subjects in 153 nuclear families) using 3 single nucleotide polymorphisms in NOS1AP, 2 in DISC1, 1 in DAOA and 1 in GSK3B was conducted. We found rs12742393 have just positive trend with schizophrenia (SCZ) (p=0.07) after FDR correction. NOS1AP mRNA and serum levels were significantly elevated in SCZ patients (p<0.001; p<0.001) compared with healthy control. However, expression Quantitative Trait Loci (eQTL) analysis have demonstrated that rs12742393 genotype were not significantly associated with the NOS1AP mRNA expression. GMDR identified a significant seven-locus interaction model involving (NOS1AP-rs348624, rs12742393, rs1415263, DISC1-rs821633, rs1000731, DAOA-rs2391191and GSK3B- rs6438552) with a good testing accuracy (0.72). Our finding suggested statistically significant role of interaction of NOS1AP, DISC1, DAOA, and GSK3B polymorphisms (NOS1AP-rs348624, rs12742393, rs1415263, DISC1-rs821633, rs1000731, DAOA-rs2391191and GSK3B-rs6438552) in EOS susceptibility.

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.

Interaction of multiple gene variants and their effects on schizophrenia phenotypes

BACKGROUND

Schizophrenia is a clinically heterogeneous disorder and may be explained by its complex genetic architecture. Many schizophrenia susceptibility genes were identified but the picture remains unclear due to inconsistent or contradictory genetic association studies. This confusion may, in part, be because symptoms result from the combined interaction of many genes and these interacting genes are associated with specific sub-phenotypes of schizophrenia rather than schizophrenia as a whole. This study investigates the relationship between schizophrenia susceptibility genes and schizophrenia sub-phenotypes by identifying multiple gene variant interactions.

MATERIALS AND METHODS

Fifty SNPs from 21 genes were genotyped in 235 Australian participants with schizophrenia screened for various phenotypes. Schizophrenia participants were grouped into relevant phenotype clusters using cluster analysis and normalized phenotype cluster scores were calculated for each patient. The relationship between genotypes and normalized phenotype cluster scores were analyzed by linear regression analysis.

RESULTS

Three phenotype clusters were identified. There was some overlap in symptoms between phenotype clusters, particularly for depression. However, cluster 1 appears to be characterized by speech disorder and affective behavior symptoms, cluster 2 has predominantly hallucination symptoms and cluster 3 has mainly delusion symptoms. Interaction of five SNPs was found to have an effect on cluster 1 symptoms; ten SNPs on cluster 2 symptoms; and eight SNPs on cluster 3 symptoms.

CONCLUSION

The interaction of specific susceptibility genes is likely to lead to specific clinical sub-phenotypes of schizophrenia. Larger patient cohorts with more extensive clinical data will improve the detection of gene interactions and the resultant schizophrenia clinical phenotypes.

Increased density of DISC1-immunoreactive oligodendroglial cells in fronto-parietal white matter of patients with paranoid schizophrenia

Profound white matter abnormalities have repeatedly been described in schizophrenia, which involve the altered expression of numerous oligodendrocyte-associated genes. Transcripts of the disrupted-in-schizophrenia 1 (DISC1) gene, a key susceptibility factor in schizophrenia, have recently been shown to be expressed by oligodendroglial cells and to negatively regulate oligodendrocyte differentiation and maturation. To learn more about the putative role(s) of oligodendroglia-associated DISC1 in schizophrenia, we analyzed the density of DISC1-immunoreactive oligodendrocytes in the fronto-parietal white matter in postmortem brains of patients with schizophrenia. Compared with controls (N = 12) and cases with undifferentiated/residual schizophrenia (N = 6), there was a significantly increased density of DISC1-expressing glial cells in paranoid schizophrenia (N = 12), which unlikely resulted from neuroleptic treatment. Pathophysiologically, over-expression of DISC1 protein(s) in white matter oligodendrocytes might add to the reduced levels of two myelin markers, 2',3'-cyclic-nucleotide 3'-phosphodiesterase and myelin basic protein in schizophrenia. Moreover, it might significantly contribute to cell cycle abnormalities as well as to deficits in oligodendroglial cell differentiation and maturation found in schizophrenia.

Missense mutation in DISC1 C-terminal coiled-coil has GSK3β signaling and sex-dependent behavioral effects in mice

Disrupted-in-Schizophrenia 1 (DISC1) is a risk factor for schizophrenia and affective disorders. The full-length DISC1 protein consists of an N-terminal 'head' domain and a C-terminal tail domain that contains several predicted coiled-coils, structural motifs involved in protein-protein interactions. To probe the in vivo effects of missense mutation of DISC1's C-terminal tail, we tested mice carrying mutation D453G within a predicted α-helical coiled-coil region. We report that, relative to wild-type littermates, female DISC1(D453G) mice exhibited novelty-induced hyperlocomotion, an anxiogenic profile in the elevated plus-maze and open field tests, and reduced social exploration of unfamiliar mice. Male DISC1(D453G) mice displayed a deficit in passive avoidance, while neither males nor females exhibited any impairment in startle reactivity or prepulse inhibition. Whole brain homogenates showed normal levels of DISC1 protein, but decreased binding of DISC1 to GSK3β, decreased phospho-inhibition of GSK3β at serine 9, and decreased levels of β-catenin in DISC1(D453G) mice of either sex. Interrupted GSK3β signaling may thus be part of the mechanism underlying the behavioral phenotype associated with D453G, in common with the previously described N-terminal domain mutations Q31L and L100P in mice, and the schizophrenia risk-conferring variant R264Q in humans.