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.

Potential biomarkers in psychiatry: focus on the cholesterol system

Measuring biomarkers to identify and assess illness is a strategy growing in popularity and relevance. Although already in clinical use for treating and predicting cancer, no biological measurement is used clinically for any psychiatric disorder. Biomarkers could predict the course of a medical problem, and aid in determining how and when to treat. Several studies have indicated that of candidate psychiatric biomarkers detected using proteomic techniques, cholesterol and associated proteins, specifically apolipoproteins (Apos), may be of interest. Cholesterol is necessary for brain development and its synthesis continues at a lower rate in the adult brain. Apos are the protein component of lipoproteins responsible for lipid transport. There is extensive evidence that the levels of cholesterol and Apos may be disturbed in psychiatric disorders, including autistic spectrum disorders (ASD). Here, we describe putative serum biomarkers for psychiatric disorders, and the role of cholesterol and Apos in central nervous system (CNS) disorders.

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.

Increased levels of apolipoprotein E in the frontal cortex of subjects with schizophrenia

BACKGROUND

It is unclear whether altered expression of a specific isoform of apolipoprotein E (apoE) is associated with the pathology of schizophrenia.

METHODS

To address whether apoE may be involved in the pathology of schizophrenia, we measured the genotypic and allelic frequency of polymorphisms in its gene and transcriptional regulatory region in DNA from Brodmann's area (BA) 9 obtained postmortem from schizophrenic and control subjects as well as its levels in the same tissue using Western blot analysis.

RESULTS

The genotypic or allelic frequencies of any polymorphism studied did not vary between diagnostic cohorts. There was a significant increase in the levels of apoE protein in BA 9 from the schizophrenic subjects (Mean +/- SEM: 270 +/- 8.3 vs. 238 +/- 7.1 ng apoE/mg protein, p =.008) and a decrease in tissue from an analogous cortical region from rats treated with haloperidol compared with vehicle-treated animals (50 +/- 6.4 vs. 116 +/- 9.2 ng apoE/mg protein; p =.0002).

CONCLUSIONS

These data support the hypothesis that increased levels of apoE may be associated with the pathology of schizophrenia and that antipsychotic drugs decrease apoE levels as part of their therapeutic actions.

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.

Apolipoprotein E genotype and schizophrenia: further negative evidence

OBJECTIVE

To investigate the association between apolipoprotein E (ApoE) genotype and schizophrenia.

METHOD

We genotyped 106 schizophrenic out-patients [Diagnostic Statistic Manual IV (DSM-IV) criteria] and 250 healthy volunteers (hospital staff and blood donors) from Asturias (Northern Spain). The ApoE genotypes (epsilon2, epsilon3, epsilon4-alleles) were determined after polymerase chain reaction (PCR) amplification, followed by digestion with the restriction enzyme Cfol and electrophoresis on a 4% agarose gel.

RESULTS

No significant differences in ApoE-allele frequencies between patients and controls was found, although an increased 64-frequency was recorded in patients compared with controls [9.0% vs. 6.2%, P = 0.124; odds ratio (OR) = 1.49; 95% confidence interval (CI) = 0.82-2.70]. ApoE-genotype frequencies did not differ between both groups. The mean age of onset for schizophrenic patients that carried the epsilon4-allele was not significantly different from that of patients without this allele.

CONCLUSION

Variation in the ApoE gene was not associated with the development of schizophrenia in our population. ApoE-genotypes did not modify the age of onset of the disease.

Apolipoprotein E epsilon3 allele is not a risk factor of schizophrenia: a study of 314 Japanese patients

The association between apolipoprotein E (ApoE) alleles and schizophrenia has remained controversial. A recent report claiming that ApoE epsilon3 Taiwan Chinese carriers have an increased risk of schizophrenia prompted us to investigate the allele frequency in a large group of Japanese schizophrenic patients. Serum samples were obtained from 314 schizophrenic patients and 188 controls in Japan and examined using isoelectric focusing/immunoblotting. There were no significant differences in ApoE allele frequencies between schizophrenic patients and controls and in the odds ratios for schizophrenia among the epsilon2, epsilon3 and epsilon4 carriers. In contrast to the report from Taiwan, our findings and results of the majority of previous studies suggest no effects of ApoE alleles on the development of schizophrenia.

Apolipoprotein E genotype and schizophrenia

Schizophrenic disorders are complex genetic disorders and may involve multiple genes of small effect. The presence of apolipoprotein E (apoE) is associated with several neuropsychiatric disorders. Previous studies on apoE genotype distribution in schizophrenia have reported conflicting findings. We studied the genotype frequencies in a large group of schizophrenic patients. The genotype distribution was significantly different between the schizophrenic patients and the control subjects. Persons who were sigma3 carriers have an increased risk of schizophrenia. This result suggests that apoE isoforms may play a functional role in the pathogenesis of schizophrenic disorders. Some possible mechanisms regarding the effect of apoE on the development of schizophrenia are discussed.