Apolipoprotein-E dependent role for the FAS receptor in early onset Alzheimer's disease: finding of a positive association for a polymorphism in the TNFRSF6 gene

The TNFRSF6 gene encodes FAS, a cell-surface receptor involved in apoptosis initiation. Elevated levels of FAS have been reported in the brains of Alzheimer's disease (AD) patients. We have tested a G/A polymorphism at position -670 in the TNFRSF6 gene for association with non-familial, early onset Alzheimer's disease (EOAD) by using dynamic allele-specific hybridization. In an initial set of Scottish EOAD cases (n=78) and controls (n=152), we found that, for individuals carrying one or two APOE4 alleles, the homozygous GG-genotype was enriched in the patients (26.7% versus 10.9% in controls). A second study was conducted on an independent set of Scottish individuals (87 EOAD, 358 controls). In this material, the TNFRSF6 GG-genotype frequency was elevated in patients regardless of APOE4 status (28.7% versus 15.1%) and was even more enriched in APOE4 carriers (35.9% versus 15.3%). A combination of the two sample sets (165 cases, 510 controls) gave a significant disease association for the TNFRSF6 GG-genotype that was irrespective of APOE4 (P=0.0020) and that was almost completely attributable to the enrichment present within the set of APOE4 carriers (P=0.0016). This represents an odds ratio of 8.71 for GG-homozygotes carrying at least one APOE4 allele compared with other TNFRSF6 genotypes in APOE4 non-carriers. The TNFRSF6 variation was further explored in Scottish late-onset Alzheimer's disease (n=159) but no associations were found. These results imply that TNFRSF6, in interaction with APOE4, is a genetic risk factor for sporadic EOAD. Hence, the AD risk contributed by APOE4 could be mechanistically related to a pathway in common with FAS-mediated apoptosis.     

Serum levels of pregnancy zone protein are elevated in presymptomatic Alzheimer's disease

We have sought for disease-related proteins that could predict the onset of Alzheimer's disease (AD) in a study population derived from the Rotterdam Scan Study, a population-based prospective cohort study designed to investigate the etiology and natural history of age-related brain changes in the elderly. The serum proteome of 43 persons who developed AD, after an average of 4.2 years (±2.6 years SD) after blood sampling, and 43 gender- and age-matched controls who remained dementia-free during follow-up was investigated by liquid chromatography mass spectrometry. We identified 61 differentially expressed peptides between presymptomatic AD and controls, 9 of which were derived from pregnancy zone protein (PZP). Quantitative measurements using a multiple reaction monitoring assay showed a significant increase in concentration of PZP in presymptomatic AD (34.3 ± 20.6 mg/L) compared with controls (23.6 ± 13.6 mg/L) (p = 0.006). The difference in PZP was significant in women. Immunohistochemical validation of the findings on brain tissue sections showed strong PZP expression in senile plaques and in microglial and glial cells in AD with only low expression in some scattered glial cells in controls.     

APP717, APP693, and PRIP gene mutations are rare in Alzheimer disease

The amyloid precursor protein (APP) gene codes for the precursor to the beta-protein found in the amyloid deposits of Alzheimer disease (AD). Recently Goate et al. identified in codon 717 of this gene a missense mutation which segregates with AD in a familial AD (FAD) kindred. The same mutation was also found in affected subjects from a second FAD family but not in other FAD families or in normal controls. The following work was undertaken to determine the frequency of the codon 717 mutation in FAD and nonfamilial AD cases and in normal controls. We tested 76 FAD families, 127 "sporadic" AD subjects, 16 Down syndrome cases, and 256 normal controls for this mutation, and none were positive. We also tested for the APP codon 693 mutation associated with hereditary cerebral hemorrhage with amyloidosis-Dutch type, for PRIP gene missense mutations at codons 102, 117, and 200, and for the PRIP insertion mutations which are associated with Creutzfeld-Jakob disease and Gerstmann-Straussler Scheinker syndrome. No examples of these mutations were found in our population. Thus these APP and PRIP mutations are rare in both FAD and nonfamilial AD.     

Amyloid beta-protein gene duplication is not common in Alzheimer's disease: analysis by polymorphic restriction fragments

The amyloid beta-protein(BP) is an important component of amyloid fibrils of both Alzheimer's disease(AD) and adult Down syndrome(DS). It has been hypothesized that sporadic AD may involve the duplication of a subregion of chromosome 21 containing the BP locus. However, an improved method for detection of the BP gene duplication using polymorphic Hind III fragments led us to a conclusion that BP gene duplication is rare, if any, in (Japanese) sporadic AD patients, indicating that the duplication of the BP gene itself is not the common underlying genetic defect in AD.     

Lack of association between α2-macroglobulin polymorphisms and Alzheimer's disease

This study was undertaken to investigate the role of two alpha2-macroglobulin (A2M) polymorphisms, an intronic 5-bp deletion and Ile1000Val, in the development of Alzheimer's disease (AD) and to evaluate the interaction between the apolipoprotein E (APOE) and A2M polymorphisms. The A2M polymorphisms were screened by using polymerase-chain-reaction-based assays in 555 white late-onset AD cases and 446 controls. The gentoype distributions of the 5-bp deletion and Ile1000Val polymorphisms were comparable between cases and controls (P = 0.158 and P = 0.148, respectively). Likewise, there was no significant difference in allele frequencies of each polymorphism among cases and controls (P = 0.361 and P = 0.062, respectively). The stratification of data by APOE*4 status also did not yield any significant association. In conclusion, we observed no association between either the intronic deletion polymorphism or the Ile1000Val polymorphism of A2M and AD in our case-control cohort.     

Alzheimer病患者APP及PS1基因表达量的研究

为了检测Alzheimer病（Alzheimer’s disease,AD）患者外周血中淀粉样前体蛋白（Amyloid Precursor Protein, APP）基因及早老素1（Presenilin 1, PS1）基因的表达情况,进而探讨APP及PS1基因的表达与AD的相关性,采用SYBRGreenⅠ的方法对45例AD患者、25例血管性痴呆（vascular dementia, VD）患者及60名正常对照组样本的mRNA进行绝对定量,检测得到APP基因及PS1基因在对照组中的表达水平分别为0.026±0.005 amol/μg cDNA和0.026±0.004 amol/μg cDNA;在AD患者组中的表达量分别为0.044±0.006 amol/μg cDNA和0.051±0.011 amol/μg cDNA;,在VD患者组中的表达水平分别为0.072±0.013 amol/μg cDNA和0.039±0.005 amol/μg cDNA 。经显著性检验,AD患者组APP基因的表达水平上调,t=2.639, P<0.01;PS1基因的表达水平同样呈上调趋势,t=2.173,P<0.05,差异均具有统计学意义。VD患者组APP基因的表达水平上调,t=3.028,P<0.01;PS1基因的表达水平也同样呈上调趋势,t=2.012,P<0.05,均有显著性差异。因此,APP及PS1基因的表达水平的增高并不一定与AD发生特异性关联,而可能与多种导致痴呆的脑部病变发生关联。     

In search of genes involved in neurodegenerative disorders

Dissecting the genetics of Alzheimer's disease (AD) and Parkinson's disease (PD) has contributed significantly to our understanding of the pathogenesis of neurodegeneration in these two complex disorders. For AD, three highly penetrant genes (amyloid precursor protein (APP, PSEN1 and PSEN2) and one susceptibility gene (APOE) have been identified. For PD, seven genes (SNCA, Parkin, UCHL1, NR4A2, DJ1, PINK1 and LRRK2) have been found. These genes explain only a small proportion of AD and PD patients and are mostly associated with an early onset presentation of the disease. APOE remains the only common gene, which increases the risk of both rare early and late onset AD. The ongoing challenge is to unravel the genetics of the most frequent forms of these complex disorders. In the present paper, we briefly review the state of the art in the genetics of AD and PD. We also discuss the prospects of finding new genes associated with common forms of these diseases in light of two hypotheses concerning the genetic variation of complex diseases: common disease/common variants and common disease/rare variants.     

Oxidative stress and reduced antioxidant defenses in peripheral cells from familial Alzheimer's patients

We have measured the levels of typical end products of the processes of lipid peroxidation, protein oxidation, and total antioxidant capacity (TAC) in skin fibroblasts and lymphoblasts taken from patients with familial Alzheimer's disease (FAD), sporadic Alzheimer's disease (AD), and age-matched healthy controls. Compared to controls, the fibroblasts and lymphoblasts carrying amyloid precursor protein (APP) and presenilin-1 (PS-1) gene mutations showed a clear increase in lipoperoxidation products, malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE). In contrast, the antioxidant defenses of cells from FAD patients were lower than those from normal subjects. Lipoperoxidation and antioxidant capacity in lymphoblasts from patients affected by sporadic AD were virtually indistinguishable from the basal values of normal controls. An oxidative attack on protein gave rise to greater protein carbonyl content in FAD patients than in age-matched controls. Furthermore, ADP ribosylation levels of poly(ADP-ribose) polymerase (PARP) nuclear substrates were significantly raised, whereas the PARP content did not differ significantly between fibroblasts carrying gene mutations and control cells. These results indicate that peripheral cells carrying APP and PS-1 gene mutations show altered levels of oxidative markers even though they are not directly involved in the neurodegenerative process of AD. These results support the hypothesis that oxidative damage to lipid, protein, and DNA is an important early event in the pathogenesis of AD.     

A gene expression profile of Alzheimer's disease.

Postmortem analysis of brains of patients with Alzheimer's disease (AD) has led to diverse theories about the causes of the pathology, suggesting that this complex disease involves multiple physiological changes. In an effort to better understand the variety and integration of these changes, we generated a gene expression profile for AD brain. Comparing affected and unaffected brain regions in nine controls and six AD cases, we showed that 118 of the 7050 sequences on a broadly representative cDNA microarray were differentially expressed in the amygdala and cingulate cortex, two regions affected early in the disease. The identity of these genes suggests the most prominent upregulated physiological correlates of pathology involve chronic inflammation, cell adhesion, cell proliferation, and protein synthesis (31 upregulated genes). Conversely, downregulated correlates of pathology involve signal transduction, energy metabolism, stress response, synaptic vesicle synthesis and function, calcium binding, and cytoskeleton (87 downregulated genes). The results support several separate theories of the causes of AD pathology, as well as add to the list of genes associated with AD. In addition, approximately 10 genes of unknown function were found to correlate with the pathology.     

New frontiers in Alzheimer's disease genetics.

Alzheimer's disease (AD) is a genetically complex disorder that accounts for the majority of dementia in the elderly population. Over 100 rare, highly penetrant mutations have been described in three genes (APP, PSEN1, PSEN2) for early-onset familial AD. In the more common late-onset form, a polymorphism in the apolipoprotein E gene has been associated with increased susceptibility. However, recent studies suggest that these four genes account for less than 30% of the genetic variance for AD and that more genetic factors remain to be identified. In this review, we present a brief history of AD genetics and preview some of the next frontiers in Alzheimer gene discovery primarily focusing on chromosomes 12, 10, and 9.     

Rare copy number variations in adults with tetralogy of fallot implicate novel risk gene pathways

Structural genetic changes, especially copy number variants (CNVs), represent a major source of genetic variation contributing to human disease. Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart disease, but to date little is known about the role of CNVs in the etiology of TOF. Using high-resolution genome-wide microarrays and stringent calling methods, we investigated rare CNVs in a prospectively recruited cohort of 433 unrelated adults with TOF and/or pulmonary atresia at a single centre. We excluded those with recognized syndromes, including 22q11.2 deletion syndrome. We identified candidate genes for TOF based on converging evidence between rare CNVs that overlapped the same gene in unrelated individuals and from pathway analyses comparing rare CNVs in TOF cases to those in epidemiologic controls. Even after excluding the 53 (10.7%) subjects with 22q11.2 deletions, we found that adults with TOF had a greater burden of large rare genic CNVs compared to controls (8.82% vs. 4.33%, p?=?0.0117). Six loci showed evidence for recurrence in TOF or related congenital heart disease, including typical 1q21.1 duplications in four (1.18%) of 340 Caucasian probands. The rare CNVs implicated novel candidate genes of interest for TOF, including PLXNA2, a gene involved in semaphorin signaling. Independent pathway analyses highlighted developmental processes as potential contributors to the pathogenesis of TOF. These results indicate that individually rare CNVs are collectively significant contributors to the genetic burden of TOF. Further, the data provide new evidence for dosage sensitive genes in PLXNA2-semaphorin signaling and related developmental processes in human cardiovascular development, consistent with previous animal models.     

Serum clusterin levels are not increased in presymptomatic Alzheimer's disease

Increased plasma levels of clusterin have recently been found to be associated with severity and progression in Alzheimer's disease (AD). We have investigated clusterin levels in serum of elderly people with presymptomatic AD from a population-based prospective cohort study. During 10 years follow-up, 43 participants were diagnosed with AD after on average 4.2 years (±2.6 years SD) after the initial blood sampling. At the time of blood sampling, these participants showed normal cognitive function. For each presymptomatic AD case, a control was matched on gender and age. Furthermore, the selected controls had to remain dementia-free and still be alive at the end of follow-up. Quantitative serum clusterin levels were measured with a newly developed multiple reaction monitoring (MRM) assay. Results of the assay showed no significant difference in clusterin levels between presymptomatic AD and controls (p-value 0.54). In conclusion, serum clusterin is not an early, presymptomatic biomarker for AD.     

Oxidative damage and protection by antioxidants in the frontal cortex of Alzheimer's disease is related to the apolipoprotein E genotype.

A great number of epidemiological studies have demonstrated that the frequency of the epsilon4 allele of the apolipoprotein E gene (APOE) is markedly higher in sporadic and in familial late onset Alzheimer disease (AD). In the frontal cortex of AD patients, oxidative damage is elevated. We address the hypothesis that the APOE genotype and reactive oxygen-mediated damage are linked in the frontal cortex of AD patients. We have related the APOE genotype to the levels of lipid oxidation (LPO) and to the antioxidant status, in frontal cortex tissues from age-matched control and AD cases with different APOE genotypes. LPO levels were significantly elevated in tissues from Alzheimer's cases which are homozygous for the epsilon4 allele of APOE, compared to AD epsilon3/epsilon3 cases and controls. Activities of enzymatic antioxidants, such as catalase and glutathione peroxidase (GSH-PX), were also higher in AD cases with at least one epsilon4 allele of APOE, while superoxide dismutase (SOD) activity was unchanged. In the frontal cortex, the concentration of apoE protein was not different between controls and AD cases, and was genotype independent. The Ginkgo biloba extract (EGb 761), the neurosteroid dehydroepiandrosterone (DHEA) and human recombinant apoE3 (hapoE3rec) were able to protect control, AD epsilon3/epsilon3 and epsilon3/epsilon4 cases against hydrogen peroxide/iron-induced LPO, while hapoE4rec was completely ineffective. Moreover, EGb 761 and DHEA had no effect in homozygous epsilon4 cases. These results demonstrate that oxidative stress-induced injury and protection by antioxidants in the frontal cortex of AD cases are related to the APOE genotype.     

Analysis of Copy Number Variation in Alzheimer’s Disease in a Cohort of Clinically Characterized and Neuropathologically Verified Individuals

Copy number variations (CNVs) are genomic regions that have added (duplications) or deleted (deletions) genetic material. They may overlap genes affecting their function and have been shown to be associated with disease. We previously investigated the role of CNVs in late-onset Alzheimer''s disease (AD) and mild cognitive impairment using Alzheimer’s Disease Neuroimaging Initiative (ADNI) and National Institute of Aging-Late Onset AD/National Cell Repository for AD (NIA-LOAD/NCRAD) Family Study participants, and identified a number of genes overlapped by CNV calls. To confirm the findings and identify other potential candidate regions, we analyzed array data from a unique cohort of 1617 Caucasian participants (1022 AD cases and 595 controls) who were clinically characterized and whose diagnosis was neuropathologically verified. All DNA samples were extracted from brain tissue. CNV calls were generated and subjected to quality control (QC). 728 cases and 438 controls who passed all QC measures were included in case/control association analyses including candidate gene and genome-wide approaches. Rates of deletions and duplications did not significantly differ between cases and controls. Case-control association identified a number of previously reported regions (CHRFAM7A, RELN and DOPEY2) as well as a new gene (HLA-DRA). Meta-analysis of CHRFAM7A indicated a significant association of the gene with AD and/or MCI risk (P = 0.006, odds ratio = 3.986 (95% confidence interval 1.490–10.667)). A novel APP gene duplication was observed in one case sample. Further investigation of the identified genes in independent and larger samples is warranted.     

Alzheimer's disease untangled.

The last year has seen major advances in the study of Alzheimer's disease (AD). Four mutations involving amino acid substitutions in exons 16 and 17 of the amyloid precursor protein (APP) gene, have been identified which co-segregate with the disease in some families multiply affected by early onset Alzheimer's disease. These mutations are strongly suggestive of a causative role for the amyloid precursor protein in Alzheimer's disease. Despite their rarity, these mutations are important because they represent the first known cause of Alzheimer's disease. Processing of APP must be central to the pathogenesis of the disease although the precise effects of these amino acid substitutions are not understood. Work is now being undertaken to characterise the processing pathways of APP and to identify other causes of AD. The development of models of AD using the APP mutations offers the possibility of identifying drug targets and developing more effective treatments than are presently available.