Case-control study of presenilin-1 intronic polymorphism in sporadic early and late onset Alzheimer's disease

No association between an intronic polymorphism in the presenilin-1 gene and Alzheimer disease in a Tunisian population

We examined the potential involvement of the polymorphism in intron 8 of the presenilin-1 (PSEN1) gene as a risk factor for Alzheimer disease (AD), both through independent effect and interaction with the apolipoprotein E (APOE) ε4 allele risk, in 85 patients and 90 controls. We found no significant differences in the distribution of PSEN1 genotype and allele frequency between both groups; and post stratification distribution with APOE ε4 allele. Age of onset suggests that this polymorphism influences AD progression.

Presenilin-1 gene intronic polymorphism and late-onset Alzheimer's disease

Presenilin-1 is known to contribute to the pathogenesis of Alzheimer's disease. The association of an intronic polymorphism (rs165932) of the presenilin-1 gene with late-onset Alzheimer's disease has been documented. However, contradicting results have been shown in different populations. The aim of the current study is to determine whether there is an association between the intronic polymorphism of the presenilin-1 gene and late-onset Alzheimer's disease in a cohort of Turkish patients. One hundred and seven participants with dementia of the Alzheimer type and 106 age-matched controls were genotyped according to BamH I restriction site in intron 8 of the presenilin-1 gene. The distribution of genotypes and alleles did not significantly differ according to chi-square test (P = .52, P = .32, respectively), when the control and patients were compared. Consequently, our results showed that the 1/1 genotype does not increase the risk of developing late-onset Alzheimer's disease in the Turkish population.

Cholesterol retention in Alzheimer's brain is responsible for high beta- and gamma-secretase activities and Abeta production

Alzheimer's disease (AD) is characterized by overproduction of A beta derived from APP cleavage via beta- and gamma-secretase pathway. Recent evidence has linked altered cholesterol metabolism to AD pathogenesis. In this study, we show that AD brain had significant cholesterol retention and high beta- and gamma-secretase activities as compared to age-matched non-demented controls (ND). Over one-half of AD patients had an apoE4 allele but none of the ND. beta- and gamma-secretase activities were significantly stimulated in vitro by 40 and 80 microM cholesterol in AD and ND brains, respectively. Both secretase activities in AD brain were more sensitive to cholesterol (40 microM) than those of ND (80 microM). Filipin-stained cholesterol overlapped with BACE and A beta in AD brain sections. Cholesterol (10-80 microM) added to N2a cultures significantly increased cellular cholesterol, beta- and gamma-secretase activities and A beta secretion. Similarly, addition of cholesterol (20-80 microM) to cell lysates stimulated both in vitro secretase activities. Ergosterol slightly decreased beta-secretase activity at 20-80 microM, but strongly inhibited gamma-secretase activity at 40 microM. Cholesterol depletion reduced cellular cholesterol, beta-secretase activity and A beta secretion. Transcription factor profiling shows that several key nuclear receptors involving cholesterol metabolism were significantly altered in AD brain, including decreased LXR-beta, PPAR and TR, and increased RXR. Treatment of N2a cells with LXR, RXR or PPAR agonists strongly stimulated cellular cholesterol efflux to HDL and reduced cellular cholesterol and beta-/gamma-secretase activities. This study provides direct evidence that cholesterol homeostasis is impaired in AD brain and suggests that altered levels or activities of nuclear receptors may contribute to cholesterol retention which likely enhances beta- and gamma-secretase activities and A beta production in human brain.

Presenilin gene predisposes to late-onset degenerative but not vascular dementia: a comparative study of PS1 and ApoE genes in a North Indian Cohort

BACKGROUND

Variation in the presenilin gene shifts the cleavage site of amyloid precursor protein producing an insoluble peptide Abeta(42) (instead of Abeta(40), which is soluble when produced in restricted amount), which is prone to aggregation in the brain in the form of amyloid plaques not only in Alzheimer's disease (AD) but also in other degenerative dementias. The role of presenilin 1 (PS1) and apolipoprotein E (ApoE) genes has not been explored in degenerative dementias other than AD.

OBJECTIVE

To study the association of PS1 intron 8 and ApoE epsilon4 gene polymorphism in degenerative and vascular dementia patients in the North Indian population.

DESIGN

A hospital-based association study on degenerative and vascular dementia patients proven on the basis of clinical profile and MRI.

PARTICIPANTS

A group of 107 dementia patients and 162 age- and sex-matched controls from a North Indian cohort participated in the study. All patients had Mini Mental State Examination scores less than 24 and met the DSM-IV criteria for dementia.

RESULTS

The frequency of genotype 1/1 and allele 1 in degenerative dementias (73.12 and 83.70%, respectively) was higher than what had been reported so far in AD. A significant association of PS1 intron 8 polymorphism was found with degenerative dementias but not with vascular dementias (OR 2.50, 95% CI 1.27-5.00). On the other hand, ApoE epsilon4 allele was found to significantly increase the risk for both vascular and degenerative dementias (p = 0.0001, OR 3.45, 95% CI 1.74-6.86).

CONCLUSION

While ApoE epsilon4 allele increases the susceptibility to both degenerative and vascular dementia, PS1 allele 1 increases the susceptibility to degenerative dementias only.

Association study and meta-analysis of Alzheimer's disease risk and presenilin-1 intronic polymorphism

Numerous studies have tested for associations between an intronic polymorphism (rs165932) of presenilin-1 (PS-1) gene and the risk of Alzheimer's disease (AD), but results have been conflicting. To throw light on this issue, we investigate the possible involvement of PS-1 genotype in a case-control study based on a relatively stable population in Spain and a meta-analysis of published studies. An examination was conducted of 85 patients with probable or possible AD, along with controls from the same community, by using an chi(2) test for homogeneity and a binary logistic regression model. For comparison purposes, a meta-analysis of data from all available published studies was assessed. In our patients, homozygosity of the allele 2 in the PS-1 gene increased for late-onset AD (OR 2.38, 95% CI 1.07-5.29, P<0.05). The presence of at least one allele of apoE was also associated with AD (OR 4.01, 95% CI 1.93-8.34, p<0.05). The regression model showed that, overall, the presence of the apoE epsilon 4 allele and the PS-1 2/2 genotype were independent factors for the development of AD in our sample. In our genotype-based meta-analysis, the PS-1 2/2 genotype was probably related with AD for the European sub-group (fixed effects model, OR 1.19, 95% CI 1.02-1.37, p<0.05), but there are many confusing factors between different studies. Presenilin-1 2/2 genotype is a risk factor for late onset Alzheimer disease in the Spanish population, and probably, for Europeans.

Systematic meta-analyses of Alzheimer disease genetic association studies: the AlzGene database

The past decade has witnessed hundreds of reports declaring or refuting genetic association with putative Alzheimer disease susceptibility genes. This wealth of information has become increasingly difficult to follow, much less interpret. We have created a publicly available, continuously updated database that comprehensively catalogs all genetic association studies in the field of Alzheimer disease (http://www.alzgene.org). We performed systematic meta-analyses for each polymorphism with available genotype data in at least three case-control samples. In addition to identifying the epsilon4 allele of APOE and related effects, we pinpointed over a dozen potential Alzheimer disease susceptibility genes (ACE, CHRNB2, CST3, ESR1, GAPDHS, IDE, MTHFR, NCSTN, PRNP, PSEN1, TF, TFAM and TNF) with statistically significant allelic summary odds ratios (ranging from 1.11-1.38 for risk alleles and 0.92-0.67 for protective alleles). Our database provides a powerful tool for deciphering the genetics of Alzheimer disease, and it serves as a potential model for tracking the most viable gene candidates in other genetically complex diseases.

Association between presenilin 1 intronic polymorphism and late onset Alzheimer's disease in the North Chinese population

The association between presenilin 1 intronic polymorphism (rs165932) and late onset Alzheimer's disease (LOAD) has been a matter of controversy. Within China, varied results have been reported. Therefore, we collected a large sample from the North Chinese population to test the association of the PS1 polymorphism with LOAD. AD patients (467 total, mean age=75.3+/-7.3, age at onset=70.2+/-5.1) and age-matched normal elderly controls (480 total) were recruited. Genotypes of PS1 and apolipoprotein E (APOE) were determined by PCR and RFLP. The results showed that there were significant differences in the distributions of both alleles (chi(2)=45.305, P<10(-5)) and genotypes (chi(2)=53.055, P<10(-5)) of PS1 gene between the AD and control groups. The APOE epsilon4 allele was more prevalent in patients than in controls (chi(2)=46.389, P<10(-5)). It was significantly different when PS1 alleles and genotypes were compared between AD and controls with APOE epsilon4 negative. However, no significance was found when PS1 alleles or genotypes were compared between AD and controls with APOE epsilon4 positive. Furthermore, with PS1 2/2 genotype as a reference, the odds ratios (ORs) of LOAD with PS1 1/2, 1/1+1/2 and 1/1 genotypes gradually increased allele 1 copy number, suggesting that allele 1 is a crucial risk for LOAD. In summary, we found an association between presenilin 1 intronic polymorphism and LOAD, but no influence of APOE epsilon4 on the distribution of the PS1 intronic polymorphism. In addition, the larger sample size raises the possibility that ethnic and regional differences in China may explain the differences in reported results.

Real time PCR assay with fluorescent hybridization probes for genotyping intronic polymorphism in presenilin-1 gene

BACKGROUND

Identification of all susceptibility loci for Alzheimer's disease has been a major goal in resolving the pathogenesis of this disease.

METHODS

A PCR assay with fluorescently labeled oligonucleotide hybrinization probes with subsequent fluorescent probe melting point analysis was developed.

RESULTS

Allelic discrimination of intronic polymorphism of presenilin-1 gene and the restriction fragment length polymorphism method yielded identical results, proving its usefulness for genotyping PS1 gene.

CONCLUSIONS

This method provides excellent robustness, speed, and accuracy, and is well suited for determination of the polymorphism in both small and large numbers of samples. This assay could help to overcome the controversy regarding the association between the PS1 s165932 intronic polymorphism and Alzheimer's disease.

Polymorphism of the regulatory region of the presenilin-2 gene in sporadic Alzheimer's disease: a case-control study

OBJECTIVE

presenilin-2 is one of the causative genes for familial Alzheimer's disease, and the apolipoprotein E epsilon4 allele is a major genetic risk factor for late-onset and sporadic early-onset Alzheimer's disease. Polymorphism of the regulatory region of presenilin-2 has recently been reported to be associated with sporadic Alzheimer's disease in a Russian population. The purpose of this study was to determine whether Alzheimer's disease is associated with the presenilin-2 gene polymorphism and the apolipoprotein E genotype in an extended case-control study.

METHODS

We examined 230 patients with Alzheimer's disease, along with an equal number of age- and sex-matched controls from the same community, in a Japanese population by using a Chi-square test for homogeneity and a logistic regression analysis.

RESULTS

The presenilin-2 polymorphism frequencies were similar in early-onset Alzheimer's disease patients (0.17) and younger controls (0.15), and in late-onset Alzheimer's disease (0.20) and elderly controls (0.20). We found no evidence for an association between the presenilin-2 polymorphism and the apolipoprotein E epsilon4 allele.

CONCLUSIONS

Our results fail to support an association of presenilin-2 gene polymorphism with Alzheimer's disease. The discrepancy between our results and the results of the Russian study appear to be due to racial differences.

Pharmacogenomics of neurodegenerative diseases

Current knowledge of sporadic degenerative disorders suggests that, despite their multifactorial etiopathogenesis, genetics plays a primary role in orchestrating the pathological events, and even dramatically changes the disease phenotype from patient to patient. Genes may act as susceptibility factors, increasing the risk of disease development, or may operate as regulatory factors, modulating the magnitude and severity of pathogenic processes or the response to drug treatment. The goal of pharmacogenomics is the application of this knowledge to elaborate more specific and effective treatments and to tailor therapies to individual patients according to their genetic profile. Here, we outline the leading theories on the etiopathogenesis of neurodegenerative diseases, including amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer disease, and we review the potential role of genetic variations, such as gene mutations and polymorphisms, in each context. We also suggest potential targets for new therapeutic approaches and variability factors for current treatments based on genotype features. Finally, we propose a few options of preventive therapeutic interventions in patients with a high genetic risk of disease.

Polymorphisms of the human apolipoprotein E promoter and bleomycin hydrolase gene: risk factors for Alzheimer's dementia?

In addition to the apolipoprotein E (ApoE) tri-allele polymorphism, genetic variants of the apolipoprotein E promoter (-491A/T) and the bleomycin hydrolase (BH-PEN) gene have also been proposed as genetic risk factors for Alzheimer's dementia (AD). Since reports about the relevance of these polymorphisms for the pathogenesis of AD have been contradictory, we performed an association study with some modifications. First, the control group in this study was made up of non-demented psychiatric inpatients, rather than healthy subjects. This procedure allows the specificity of the relationship between a given genotype and AD (as opposed to other psychiatric disorders) to be determined. Second, as an alternative to preexisting relatively time consuming techniques, BH-PEN polymorphism was determined using a simplified method based on PCR genotyping. We found a significant linkage disequilibrium between the -491A/T and ApoE polymorphisms. However, no direct association was observed between the -491A/T or BH-PEN polymorphism and AD.