Apolipoprotein E genotype and schizophrenia: further negative evidence

The genetic basis of onset age in schizophrenia: evidence and models

Schizophrenia is a heritable neurocognitive disorder affecting about 1% of the population, and usually has an onset age at around 21-25 in males and 25-30 in females. Recent advances in genetics have helped to identify many common and rare variants for the liability to schizophrenia. Earlier evidence appeared to suggest that younger onset age is associated with higher genetic liability to schizophrenia. Clinical longitudinal research also found that early and very-early onset schizophrenia are associated with poor clinical, neurocognitive, and functional profiles. A recent study reported a heritability of 0.33 for schizophrenia onset age, but the genetic basis of this trait in schizophrenia remains elusive. In the pre-Genome-Wide Association Study (GWAS) era, genetic loci found to be associated with onset age were seldom replicated. In the post-Genome-Wide Association Study era, new conceptual frameworks are needed to clarify the role of onset age in genetic research in schizophrenia, and to identify its genetic basis. In this review, we first discussed the potential of onset age as a characterizing/subtyping feature for psychosis, and as an important phenotypic dimension of schizophrenia. Second, we reviewed the methods, samples, findings and limitations of previous genetic research on onset age in schizophrenia. Third, we discussed a potential conceptual framework for studying the genetic basis of onset age, as well as the concepts of susceptibility, modifier, and "mixed" genes. Fourth, we discussed the limitations of this review. Lastly, we discussed the potential clinical implications for genetic research of onset age of schizophrenia, and how future research can unveil the potential mechanisms for this trait.

N6-methyladenine-modified DNA was decreased in Alzheimer’s disease patients

BACKGROUND

In recent years, the prevalence of Alzheimer’s disease (AD) has increased, which places a great burden on society and families and creates considerable challenges for medical services. N6-methyladenine (m6A) deoxyribonucleic acid (DNA) adenine methylation is a novel biomarker and is abundant in the brain, but less common in AD. We support to analyze the relationship between DNA m6A and cognition in patients with AD and normal controls (NCs) in China.

AIM

To analyze the relationship between the novel m6A DNA and cognition in patients with AD and NCs in China.

METHODS

A total of 179 AD patients (mean age 71.60 ± 9.89 years; males: 91; females: 88) and 147 NCs (mean age 69.59 ± 11.22 years; males: 77; females: 70) who were age- and sex-matched were included in our study. All subjects underwent neuropsychological scale assessment and magnetic resonance imaging examination. Apolipoprotein E (APOE) genotypes were measured through agarose gel electrophoresis. Global m6A levels were evaluated by a MethylFlash m6A DNA Methylation ELISA Kit (colorimetric). Global m6A levels in total DNA from ten AD patients with 18F-AV-45 (florbetapir) positron emission tomography (PET) positivity and ten NCs with PET negativity were analyzed by dot blotting to determine the results.

RESULTS

Our ELISA results showed that the global m6A DNA levels in peripheral blood were different between patients with AD and NCs (P = 0.002; < 0.05). And ten AD patients who were PET positive and ten NCs who were PET negative also showed the same results through dot blotting. There were significant differences between the two groups, which indicated that the leukocyte m6A DNA levels were different (P = 0.005; < 0.05). The m6A level was approximately 8.33% lower in AD patients than in NCs (mean 0.011 ± 0.006 vs 0.012 ± 0.005). A significant correlation was found between the Montreal Cognitive Assessment score and the peripheral blood m6A level in the tested population (r = 0.143, P = 0.01; < 0.05). However, no relationship was found with APOE ε4 (P = 0.633, > 0.05). Further studies should be performed to validate these findings.

CONCLUSION

Our results show that reduced global m6A DNA methylation levels are significantly lower in AD patients than in NCs by approximately 8.33% in China.

Verbal memory improvement in first-episode psychosis APOE-ε4 carriers: a pleiotropic effect?

BACKGROUND

Verbal memory impairment is a core feature in schizophrenia even at early stages of the disease, but its etiopathogenesis is not fully understood. The APOE-ε4 is the main genetic risk factor for late-onset Alzheimer's disease. Our primary goal was to ascertain whether APOE-ε4 status had a pleiotropic effect in early stages of the illness.

PARTICIPANTS AND METHODS

A total of 86 first-episode psychosis (FEP) outpatients and 39 healthy volunteers were recruited. Demographic and clinical data, APOE genotyping, and a neuropsychological test battery including the California Verbal Learning Test - second edition (CVLT-II) were administered and assessed at study entry and at 1-year follow-up. Data were analyzed using mixed-model repeated measures, where the dependent variable was verbal memory indexed by California Verbal Learning Test (CVLT) Trials 1-5 total recall score.

RESULTS

FEP-APOE-ε4 carriers and FEP-APOE-ε4 noncarriers had similar symptom severity, clinical outcomes, premorbid and current intelligence quotient, and exposure to antipsychotics. There was a main effect of group on CVLT 1-5 (FEP =43.30 vs control =58.25; F[1, 119.7]=42.97; P<0.001) as well as an APOE-ε4 by group by time (F[4, 116.2]=2.73, P=0.033) interaction with only FEP-APOE-ε4 carriers showing improved verbal memory at follow-up.

CONCLUSION

Our study is the first to report improvement in verbal memory in persons afflicted by FEP who are APOE-ε4 carriers and replicates the prominent verbal memory deficits present in FEP. Our work provides further evidence pointing to an antagonistic pleiotropic effect of APOE-ε4 in neuropsychiatric disorders. Our results merit further research into antagonistic pleiotropic effects in schizophrenia.

No association between ApoE and schizophrenia: Evidence of systematic review and updated meta-analysis

INTRODUCTION

Schizophrenia affects between 0.3% and 2% of the worldwide population. A genetic contribution has been postulated in the development of this disorder. Genes such as ApoE have been implicated in the neurodevelopment associated with schizophrenia in case-control and meta-analysis studies, but the results remain inconclusive. Due to this, the aim of the present study was to explore the association between ApoE and schizophrenia through a meta-analysis.

MATERIAL AND METHODS

We collected all relevant studies by searching PubMed and EBSCO databases. The pooled odds ratios with 95% confidence intervals were calculated to estimate the association. The following models were evaluated: A) ε4 vs ε3, B) ε4 vs ε2, C) ε4 vs ε3+ε2, D) Caucasian population and E) Asian population. Statistical analyses were performed using EPIDAT 3.1 software.

RESULTS

The meta-analyses comprised 28 association studies, which included 4703 controls and 3452 subjects with schizophrenia. A significant protective effect was found for allele ε3 in the Asian population (OR=0.73, 95% CI=0.54-0.98). No significant associations were observed in the other models and populations analyzed.

CONCLUSIONS

Our meta-analysis suggests a protective association between ApoE allele ε3 and schizophrenia in the Asian population.

Apolipoprotein E polymorphism is associated with susceptibility to schizophrenia among Saudis

INTRODUCTION

Apolipoprotein E (APOE) genotypes influence the phenotype of several neurodegenerative disorders including Alzheimer's and Parkinson disease and may affect schizophrenia pathogenesis. This study was undertaken to determine the association between APOE gene polymorphisms and schizophrenia in the Saudi population.

MATERIAL AND METHODS

APOE allele and genotype frequencies were studied in 380 Saudi subjects including schizophrenia patients and matched controls using polymerase chain reaction (PCR) and reverse-hybridization techniques.

RESULTS

The frequencies of the APOE allele ε2 and genotypes ε2/ε3 and ε2/ε4 were significantly higher in the schizophrenia patients as compared to controls, suggesting that the ε2 allele and its heterozygous genotypes may increase the susceptibility to schizophrenia. In contrast, the frequencies of the ε3 allele and ε3/ε3 genotype were lower in patients as compared to controls, suggesting a protective effect of APOE ε3 for schizophrenia. This study indicated that APOE ε4 was differentially associated with schizophrenia depending on the symptoms as the frequency of the ε4 allele was significantly higher in schizophrenia patients with positive symptoms. By contrast, no significant association between APOE ε4 and schizophrenia patients with negative symptoms was observed. Genotypes ε2/ε2 and ε4/ε4 were absent in patients and controls. Moreover, the age of onset was significantly lower in patients with the APOE ε2/ε3 genotype. There was no significant difference in the frequencies of APOE alleles and genotypes between male and female schizophrenia patients.

CONCLUSIONS

The results of this study clearly show that APOE alleles and genotypes are associated with risk of developing schizophrenia and early age of onset in Saudis.

Apolipoprotein E and central nervous system disorders: reviews of clinical findings

Dementia is a major health problem in developed countries with over 25 million people affected worldwide and probably over 75 million people at risk during the next 20 years. Alzheimer's disease (AD) is the most frequent cause of dementia (50-70%), followed by vascular dementia (30-40%), and mixed dementia (15-20%). AD pathogenesis is still to be elucidated but it is believed to be the complex interaction between genetic and environmental factors in later life. Three causative genes for familial AD have been identified: amyloid precursor protein, presenilin-1, and presenilin-2. There are 150 genes involved with increased neuronal vulnerability to premature death in the AD brain. Among these susceptibility genes, the apolipoprotein E (ApoE) gene is the most prevalent as a risk for AD pathogenic process in which complex interactions between genetic and environmental factors are involved, leading to a cascade of pathogenic events converging in final pathways to premature neuronal death. Some of these mechanisms are common to several neurodegenerative disorders that differ depending upon the genes affected and the involvement of environmental conditions. ApoE is a key lipoprotein in lipid and cholesterol metabolism and it is also the major risk gene for AD and many other central nervous system disorders. The pathogenic role of ApoE-4 is still to be clarified; however, diverse evidence suggests that ApoE may play pleiotropic functions in dementia and central nervous system disorders.

Different apolipoprotein E, apolipoprotein A1 and prostaglandin-H2 D-isomerase levels in cerebrospinal fluid of schizophrenia patients and healthy controls

OBJECTIVES

To identify proteins differentially expressed in schizophrenia patients, we collected 50 microl cerebrospinal fluid from 17 first-episode schizophrenia patients and 10 healthy controls.

METHODS

Their proteins were separated by two-dimensional gel electrophoresis without using any depletion method and identified by mass spectrometry.

RESULTS

Approximately 550 spots were detected, six of which had significantly different intensities in schizophrenia compared to control specimens. We were able to validate in individual samples the upregulation of apolipoprotein E, apolipoprotein A1 and prostaglandin-H2 D-isomerase by Western blot analyses and detect the downregulation of transthyretin, TGF-beta receptor type-1 and coiled-coil domain-containing protein 3 precursor.

CONCLUSIONS

These findings may help to elucidate the disease mechanisms and confirm the hypothesis of disturbed cholesterol and phospholipid metabolism in schizophrenia, and thus reveal the final role players. Moreover, a grouped protein expression analysis of apolipoprotein E, apolipoprotein A-I, and prostaglandin-H2 D-isomerase in cerebrospinal fluid from patients might be a potential diagnostic tool for schizophrenia.

Meta-analysis of association between ApoE epsilon4 allele and schizophrenia

Several case-control studies have reported an association between schizophrenia and the epsilon4 allele of Apolipoprotein E gene. The results have been equivocal. This meta-analysis has evaluated the collective evidence for an association between the epsilon4 allele of Apolipoprotein E gene and schizophrenia. We analyzed published data sequentially first considering epsilon4 allele itself, and then epsilon4 carrier status as risk factors for schizophrenia using a sample of 17 population-based case-control studies, of which 6 were from Asian and 11 from Caucasian populations. The pooled odds ratios from the Caucasian populations showed a modest association with risk of schizophrenia for epsilon4 allele and epsilon4 carrier genotype. No other alleles or genotypes were significant in either Asian or Caucasian populations when analysed separately or combined, although the sample size had over 80% power to detect a significant odds ratio of 1.9 in Asian-population studies and 1.6 in Caucasian-population studies. After allowing for sensitivity analysis of the studies and assessment of publication bias, we conclude that the epsilon4 allele of Apolipoprotein E does not play a major role in risk of schizophrenia in Caucasian populations. Since significant heterogeneity was present among the 6 Asian populations reported to date, further studies using larger sample sizes are required.

Negative evidences in association between apolipoprotein E polymorphism and panic disorder

The aim is to investigate the association between apolipoprotein E (ApoE) and panic disorder (PD). Genotyping 92 PD patients [Diagnostic Statistic Manual IV (DSM IV) criteria] and 174 controls no differences were found between both groups. Variation in the ApoE-gene was not associated with the development of PD.

Apolipoprotein E polymorphism is associated with age of onset in schizophrenia

The aims of the study were to investigate the relationship between Apolipoprotein E (APOE) polymorphism, risk of schizophrenia, treatment response to conventional anti-psychotics, and age of onset in schizophrenia. The sample comprised 94 Finnish patients with a DSM-IV diagnosis of schizophrenia. Forty-three of the patients were good responders to conventional anti-psychotics and 51 were classified as non-responders. The control group consisted of 98 healthy blood donors. The APOE allele frequencies (epsilon 2, epsilon 3, and epsilon 4) were 4.8, 72.3, and 22.9% in patients and 7.1, 75.0, and 17.9 in controls. None of the differences between groups were statistically significant. No association between treatment response and APOE genotype was found. Patients with APOE epsilon 4/epsilon 4 genotype had a markedly lower age of onset compared with rest of the sample (p=0.0015), which remained significant when controlling for gender (p=0.02). There was an increasing linear trend between the number of epsilon 3 alleles (0, 1, or 2) and age of onset in schizophrenia (p=0.08). An inverse trend was found between the number of epsilon 4 alleles and age of onset (p=0.07). No relationship between APOE polymorphism and risk for schizophrenia was found. APOE epsilon 4/epsilon 4 genotype may be associated with early onset schizophrenia. APOE epsilon 3 allele may function protectively in later onset in this disease.

Apolipoprotein E in schizophrenia: a French association study and meta-analysis

Schizophrenic disorders are complex genetic disorders that may involve multiple genes of small effect. Apolipoprotein E (ApoE) gene variants are associated with alterations in brain function and an increased risk of Alzheimer's disease (AD). However, conflicting results have been reported in schizophrenia. We compared the ApoE genotypes of 114 French Caucasian schizophrenic patients and 91 normal controls. No differences in ApoE allele or genotype frequencies were observed between the two groups. However, we observed a possible association between male schizophrenic patients and the ApoE epsilon 2 epsilon 3 genotype. In addition, a meta-analysis of all published case-control studies on ApoE and schizophrenia did not support a major role for ApoE gene variants in schizophrenia as a whole. However, ApoE may be associated with particular forms of schizophrenia.