Apolipoprotein E genotype 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.

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.

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.

Lack of association of apolipoprotein E polymorphism in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) could be considered a neurodevelopmental disorder, from several lines of evidence. One of the most widely studied genes in these disorders is the apolipoprotein E gene, particularly allele 4. We analyzed for association among patients with OCD versus normal controls and cognitively impaired patients. There were no significant differences between OCD probands compared with population controls. However, the cognitively impaired group showed a higher frequency of allele apolipoprotein E gene compared with normal controls and patients with OCD.

Apolipoprotein E epsilon4 and tardive dyskinesia in a Japanese population

The findings that free radicals play a causative role in the occurrence of tardive dyskinesia (TD) and that apolipoprotein E (ApoE) 4 has decreased anti-oxidant activity suggest a potential link between TD and ApoE alleles. We, therefore, examined ApoE allelic frequencies in schizophrenic subjects with TD and non-TD. Serum samples were obtained from 333 DSM IV-diagnosed schizophrenic patients and 191 controls in Japan. The presence of TD was evaluated by research diagnostic criteria for TD. ApoE phenotypes of the serum samples were determined by polyacrylamide gel isoelectricfocusing. A total of 62 TD subjects (31 males, 31 females) were identified among all patients examined. No significant differences in ApoE allelic frequency were found between TD and non-TD groups. ApoE epsilon4 allele frequency, however, was significantly lower in the female TD group than in the male TD group. These findings do not clearly demonstrate a certain association between TD and the epsilon4 allele, but may preliminarily reveal a difference in influence of this allele on the development of TD between males and females.

Apolipoprotein E-varepsilon4 frequency in deficit schizophrenia

The apolipoprotein E (ApoE) genotype has been found to affect the expression of several neuropsychiatric disorders. We determined ApoE genotype frequencies and their relationship to primary negative symptoms in 61 non-deficit and 45 deficit schizophrenic patients, and compared them with 98 control subjects. No difference was observed when genotype or allele frequencies were compared between the three groups. Our data do not support a role for ApoE in the phenotypic expression of schizophrenia.

No association of apolipoprotein epsilon 4 allele with schizophrenia even in cognitively impaired patients

Given the strong association of the apolipoprotein E (apoE) allele epsilon 4 (epsilon 4) with Alzheimer's disease or cognitive decline in elderly, we tested whether cognitive performance in schizophrenic subjects is associated with an increase in the frequency of the ApoE epsilon 4 allele. Our data indicate that in our sample: (1) there is no association between schizophrenia and the ApoE epsilon 4 allele; and (2) the ApoE epsilon 4 allele is not of major importance with regard to the cognitive decline observed in schizophrenia.

Apolipoprotein E epsilon2 allele and early onset schizophrenia

To explore the role of apolipoprotein E (ApoE) in schizophrenia, we investigated ApoE phenotypes in a group of patients with schizophrenia. Serum samples were obtained from 122 schizophrenic patients and 126 controls in Japan and were examined using isoelectric focusing/immunoblotting. This experiment showed a trend toward a decreased frequency of ApoE epsilon4 in schizophrenia and no link between ApoE epsilon4 and familial schizophrenia or early onset schizophrenia. On the other hand, a decreased frequency of ApoE epsilon2 in early onset schizophrenia was detected. These results suggest that ApoE epsilon2 protects against early onset schizophrenia, and that ApoE epsilon4 is not involved in the development of schizophrenia in Japanese.