Apolipoprotein E genotype in Spanish schizophrenic patients

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.

Association of APOE E2 and low-density lipoprotein with depressive symptoms in Chinese senile schizophrenia inpatients: A cross-sectional study

Background

Schizophrenia is considered to occur due to both environmental and genetic factors. Depressive symptoms and apolipoprotein E (APOE) gene polymorphisms are involved in the pathogenesis of schizophrenia. However, the effect of APOE gene polymorphism on depressive symptoms has never been investigated among Chinese elderly schizophrenia patients.

Objective

This cross-sectional study aimed to determine the effect of APOE gene polymorphism on blood lipid metabolism and depressive symptoms among elderly schizophrenia patients.

Method

A total of 301 elderly schizophrenia patients (161 males, age ranges from 60 to 92 years, with an average age of 67.31 ± 6.667) were included in the study. Depressive symptoms were assessed using the Geriatric Depression Scale (GDS). APOE gene polymorphisms were determined by polymerase chain reaction (PCR). Correlations between GDS and serum low-density lipoprotein (LDL) levels with APOE genotypes were assessed.

Results

The concentration of LDL in the APOE E2 group was significantly lower than those in the APOE E3 and APOE E4 groups, and the GDS scores in the APOE E2 and APOE E3 groups were higher than those in the APOE E4 group. Using partial correlation analysis and controlling the duration of disease and hyperlipidemia, we found that GDS scores were significantly correlated with LDL (r = −0.179, p = 0.025).

Conclusions

The APOE E2 genotype is associated with more depressive symptoms and lower serum LDL in elderly Chinese schizophrenia patients, and there is a negative correlation between depressive symptoms and LDL.

Apolipoprotein E-ε4 allele predicts escalation of psychotic symptoms in late adulthood

BACKGROUND

Research on a putative link between apolipoprotein-ε4 allele (APOE-ε4) and schizophrenia has been inconclusive. However, prior studies have not investigated the association between APOE-ε4 and symptom trajectories, nor has the existing literature taken into account the potentially moderating effect of age in genetic association studies.

METHODS

The association between APOE-ε4 and four symptom dimensions was investigated in a longitudinal study of 116 individuals with schizophrenia initially assessed during their first admission for psychosis and evaluated five times over the following 20years. A meta-analysis identified 29 case-control studies of APOE-ε4 allele frequency in schizophrenia, which were analyzed using random-effects meta-regression to test the potentially moderating effect of age.

RESULTS

Longitudinal models identified a specific association between APOE-ε4 and symptom trajectories, showing that APOE-ε4 portends worsening severity of hallucinations and delusions in late adulthood among people with schizophrenia, at a rate of a 0.46 standard deviation increase per decade. Meta-analysis showed a significant effect of age: the association between APOE-ε4 and schizophrenia was not detectable in younger people but became pronounced with age, such that APOE-ε4 increased the odds of diagnosis by 10% per decade.

CONCLUSIONS

Taken together, the meta-analysis and longitudinal analysis implicate APOE-ε4 as an age-related risk factor for worsening hallucinations and delusions, and suggest APOE-ε4 may play an age-mediated pathophysiological role in schizophrenia. The presence of an APOE-ε4 allele may also identify a subgroup of patients who require intensive monitoring and additional targeted interventions, especially in mid-to late-life.

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.

Low Density Lipoprotein Receptor-Related Protein and Apolipoprotein E Expression is Altered in Schizophrenia

Our recent microarray study reported altered mRNA expression of several low density lipoprotein receptor-related proteins (LRP) associated with the first 4 years following diagnosis with schizophrenia. Whilst this finding is novel, apolipoprotein E (APOE), which mediates its activity through LRPs, has been reported by several studies to be altered in brains of subjects with schizophrenia. We used qPCR to measure the expression of LRP2, LRP4, LRP6, LRP8, LRP10 and LRP12 mRNA in Brodmann's area (BA) 46 of the dorsolateral prefrontal cortex in 15 subjects with short duration of illness schizophrenia (SDS) and 15 pair matched controls. We also used Western blotting to measure APOE protein expression in BA46 from these subjects. Amongst the LRPs examined, LRP10 expression was significantly increased (P = 0.03) and LRP12 was significantly decreased (P < 0.01) in SDS. APOE protein expression was also increased in SDS (P = 0.01). No other marker examined in this study was altered with diagnosis. Our data supports a role for distinct members of the LRP family in the pathology of schizophrenia and adds weight to the hypothesis that aberrant apolipoprotein signaling is involved in the early stages of 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.

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.

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.