Recent advances in the genetics of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is the most common cause of dementia in the elderly. It is a clinical-pathologic entity characterized by progressive dementia associated with the neuropathologic hallmarks of Abeta amyloid plaques, neurofibrillary tangles (NFTs), neuronal loss, and amyloid angiopathy. Three "causative" AD genes (i.e., genes in which a mutation is sufficient to result in clinical AD) for early-onset familial Alzheimer's disease (FAD) and one "susceptibility" gene that affects risk and age of onset of AD in familial and sporadic late-onset AD have been identified. The three causative genes are the amyloid precursor protein (APP gene) on chromosome 21, the presenilin-1 gene on chromosome 14, and the presenilin-2 gene on chromosome 1. The susceptibility gene is the apolipoprotein E (APOE) gene on chromosome 19. Investigations of the normal and aberrant function of these genes will provide insights into the mechanisms underlying AD and will suggest new strategies for therapeutic intervention.     

Molecular genetics of Alzheimer's disease--presenilin and other genes

We examined mutations of presenilin 1 (PS1), presenilin 2 (PS2) and amyloid precursor protein (APP) in 30 Japanese familial Alzheimer's disease (FAD) and 34 isolated cases of Alzheimer's disease (AD). We found mutations of PS1 in 17% of early onset FAD (H163R, H163R, R269H, E273A, G384A) and in a case (H163R) of isolated AD. The remaining cases were free from mutations in PS1, PS2 and APP. Since only a part of them could he explained by ApoE epsilon 4, we concluded that important genes are missing. We also examined association of apolipoprotein E (ApoE)epsilon 4, allele A of alpha 1-antichymotrypsin (ACT), 5 repeat allele of very low density lipoprotein receptor (VLDLR) and Alzheimer's disease. We confirmed that ApoE espilon 4 is significantly more frequent in both FAD and isolated AD cases than controls. We could not see any significant association in the ACT polymorphism. The 5 repeat allele of VLDLR was slightly but significantly more frequent in AD cases than controls. However, association with ApoE epsilon 4 was not seen in our study.     

Lipoproteins in clinical laboratory medicine]

The characteristics and metabolism of lipoproteins were reviewed. Apolipoproteins has been studied in the fields of neurological diseases as well as hyperlipidemia. A highly significant association between apolipoprotein E (ApoE) epsilone 4 allele and late-onset familial and sporadic Alzheimer's disease (AD) was reported. The recent studies also described the following: (1) late-onset familial AD linked to the proximal long arm of chromosome 19; (2) the presence in the CSF of several proteins, one of which was ApoE, what bound to immobilized amyloid beta-peptide (beta A4) with high avidity; and (3) staining by antisera to ApoE of senile plaques, neurofibrillary tangles, and cerebral vessel amyloid deposits in AD brains. Furthermore, (4) both purified ApoE isomers, ApoE3 and ApoE4, bound to beta A4 synthetic peptide, forming a complex that resisted dissociation by boiling in sodium dodecyl sulfate, but the isomers showed different kinetics in doing so: binding by ApoE4 was observed in minutes, while binding by ApoE3 required hours; and (5) ApoE4 did not bind to beta A4 peptide at pH less than 6.6, while ApoE3 bound to beta A4 peptide from pH7.6 to 4.6. We studied ApoE phenotype expression and the corresponding allele frequencies (epsilon 2, epsilon 3 and epsilon 4) in Japanese patients with late-onset sporadic AD. The frequency of the ApoE epsilon 4 allele was obviously high in AD patients compared with the controls, but it was not different between vascular dementia patients and the controls. These results suggest that ApoE isoforms may play a functional role in the pathophysiology of late-onset familial and sporadic AD and that the isoform-specific difference in beta A4 binding may be involved in forming the AD lesion.     

Comparison of calcium phosphate cement mixture and pure calcium hydroxide as direct pulp-capping agents

This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins.     

Presenilins and early-onset familial Alzheimer's disease

Thirty-seven missense mutations and a splice-site mutation in the presenilin gene PS1 on chromosome 14 and two missense mutations PS2 on chromosome 1 co-segregate with early-onset familial Alzheimer's disease (AD). The presenilins belong to a family of conserved integral membrane proteins which include Caenorhabditis elegans SPE4 and SEL12 and the rat apoptosis-linked gene, ALG3. This review summarizes the genetics of presenilins in AD and indicators of putative function based on cellular localization and the functions of non-human homologues. Findings to date suggest an important role of presenilins in beta-amyloid (A beta) production: in vitro and in vivo studies have shown that presenilin mutations are associated with relatively increased production of the longer, and highly fibrillogenic A beta 42(43) peptide, and a marked elevation in the number of A beta 42-immunoreactive plaques in the brains of individuals with familial AD who carry PS1 and PS2 mutations. There is growing evidence that the deposition of A beta 42(43) could in some cases be an early and key event in the AD pathogenic cascade. The genetic and molecular biological data discussed in this review describe mechanisms by which presenilin mutations could lead to the development of AD. Also, mutant presenilins may be more proapoptotic. It is argued that the understanding of the processes by which presenilin mutations lead to the development of AD will help in devising a coherent framework for therapeutic strategies.     

Catalytic properties of the purified rat hepatic cytosolic cholesteryl ester hydrolase

Alzheimer's disease (AD) is a heterogeneous entity presenting as sporadic and familial disease. In familial AD, there is evidence for genetic linkage to a yet undefined gene on chromosome 14 in early-onset pedigrees and on chromosome 19 in late-onset pedigrees. In a few early-onset kindreds, there were mutations in the amyloid precursor gene on chromosome 21. There is an increased frequency of apolipoprotein E (ApoE) epsilon4 allele in patients with late-onset AD. We studied the clinical presentation and profile of cognitive deficits in 58 AD patients at the early stage of the disease. We divided the AD patients into subgroups of sporadic late-onset (SLO) (> or = 65 years), familial late-onset (FLO) (> or = 65 years), sporadic early-onset (SEO) (<65 years), and familial early-onset (FEO) (<65 years) patients and into three subgroups according to their ApoE genotype zero epsilon4, one epsilon4, and two epsilon4 alleles. The AD subgroups did not differ in the global clinical severity of dementia or the duration of the disease. SLO, FLO, SEO, and FEO subgroups did not differ in clinical characteristics such as occurrence of rigidity, hypokinesia, tremor, myoclonus, hallucinations, delusions, or epileptic seizures nor in the profile of deficits on tests assessing memory, language, visuospatial, executive, and praxic functions. The epsilon4++ allele frequency was 0.43 for all AD patients and did not differ across subgroups divided according to the familial aggregation and age of onset. Patients with two epsilon4 alleles had earlier age at onset of dementia than those with no epsilon4 allele (63 +/- 9 versus 68 +/- 9 years), but otherwise the clinical symptoms and signs were not related to the ApoE genotype. However, the AD patients with two epsilon 4 alleles had lowest scores on memory tests and differed significantly from those with one or zero epsilon4 allele in the delayed list learning (p<0.05) and from those with zero epsilon4 allele in the immediate and delayed story recall. In contrast, verbal functions were better preserved in two epsilon4 patients than in those with other ApoE genotypes. This study failed to confirm the earlier reports of severe aphasia, agnosia, and apraxia in familial AD patients, but the clinical phenotype was similar irrespective to the familial aggregation. However, AD patients with two epsilon4 alleles are characterized by more severe memory loss and earlier age of onset than those without the epsilon4 allele.     

The Glu318Gly mutation of the presenilin-1 gene does not necessarily cause Alzheimer's disease

In early-onset familial Alzheimer's disease (AD) pathogenic mutations have been found in the amyloid precursor protein (APP) gene and in the presenilin (PS)-1 and PS-2 genes. We screened for mutations in these genes in 20 patients with familial AD from the Finnish population. In addition, we sampled 41 sporadic AD patients and 59 controls to test for mutations identified in our familial AD cases. We detected an A-to-G transition in the PS-1 gene, resulting in a glutamic acid (Glu)-to-glycine (Gly) substitution at codon 318 in 2 familial and 2 sporadic AD patients. The Glu318Gly mutation has previously been reported to cause AD. We also found the Glu318Gly mutation in 4 healthy aged controls (range, 74-87 years). We thus conclude that the mutation is most likely a rare polymorphism not related to AD.     

Modern views on etiopathogenesis of Alzheimer's disease

The aetiology of Alzheimer's disease (AD) remains, despite vast progress, not fully understood. Four genes involved in the development of the disease have been identified. Three fully penetrant ones (the amyloid beta-protein precursor on chromosome 21, presenilin 1 on chromosome 14, and presenilin 2 on chromosome 1) lead to the development of relatively rare familial form of AD. Together, they account for about half of this early-onset form of the disease. One genetic risk factor--polipoprotein E-4--is associated with late-onset Alzheimer's disease while at least two others are proposed. None of these genes can be by now adopted for use as a diagnostic or predictive test for Alzheimer's disease. Apart from the above, some environmental factors are also implicated in pathogenesis of the disease with the amyloid cascade hypothesis being the most commonly accepted as central. In the presented paper we have critically reviewed a literature on etiopatogenesis of Alzheimer's disease and discussed some practical consequences of the progress in understanding the mechanism of the disease.     

Abundance of the longer A beta 42 in neocortical and cerebrovascular amyloid beta deposits in Swedish familial Alzheimer's disease and Down's syndrome

Recent studies have demonstrated the deposition of amyloid beta (A beta) protein with carboxyl- and aminoterminal heterogeneity in cortical and cerebrovascular deposits of Alzheimer's disease (AD). Using carboxyl end-terminal specific antibodies to A beta peptides, we examined the immunocytochemical distribution of A beta 40 and A beta 42 species in brain tissue from a Swedish subject with familial AD (FAD) bearing the double mutation at codons 670/671 in the amyloid beta precursor protein (A beta PP), and from subjects with Down's syndrome and sporadic AD. In the Swedish subject, we found profound parenchymal A beta deposits and cerebral amyloid angiopathy in all four cortical lobes and cerebellum. A beta 42 was evident in almost all parenchymal deposits as well as many vascular deposits. Although A beta 40 was present in meningeal and intraparenchymal vessels, deposits containing this shorter peptide reactivity were sparse. Surprisingly, our observations in Swedish FAD showing a remarkable abundance of A beta 42 in both parenchymal and vascular deposits were qualitatively similar to the Down's syndrome and most sporadic AD cases, and to previously published A beta PP717 FAD. While previous transfection studies in different cell cultures indicate substantially increased soluble A beta production and A beta 40 species to be predominant, it would appear that the double A beta PP mutations in Swedish FAD largely result in the deposition of the longer A beta 42 in vivo.     

ApoE allele frequencies in Italian sporadic and familial Alzheimer's disease

Recent studies have provided evidence of association of apolipoprotein E (ApoE) epsilon 4 allele and late onset familial and sporadic Alzheimer's disease (AD). Epidemiological studies have established allelic variation at the ApoE locus. We have analyzed the ApoE gene polymorphism in a sample of 446 Italian subjects. Our data confirm a significant association between epsilon 4 allele and sporadic AD. The frequency of epsilon 4 allele in early onset familial AD patients was comparable to control values suggesting that epsilon 4 allele does not represent a risk factor for early onset familial AD (EOFAD). Moreover, we found a not previously reported association between ApoE epsilon 2 allele and sporadic AD and EOFAD.     

Presenilin 1 intronic polymorphism is not associated with Alzheimer type neuropathological changes or sporadic Alzheimer's disease

BACKGROUND: A genetic association between the presenilin 1 (PS-1) intronic polymorphism and sporadic Alzheimer's disease has been a matter of controversy. Recent findings have suggested that the PS-1 polymorphism is not associated with Alzheimer's disease or amyloid beta-protein (Abeta) deposition in brains from patients with Alzheimer's disease. OBJECTIVES: To elucidate the influence of the PS-1 polymorphism on Alzheimer type neuropathological changes and the development of Alzheimer's disease, the relation between the PS-1 polymorphism and quantitative severity of Alzheimer type neuropathological changes in the brains from patients with Alzheimer's disease and non-demented subjects was studied. METHODS: The PS-1 and apolipoprotein E (ApoE) genotypes, were examined, together with the densities of the senile plaques, senile plaques with dystrophic neurites, and neurofibrillary tangles in the brains from 36 postmortem confirmed patients with sporadic Alzheimer's disease and 86 non-demented subjects. Association of the PS-1 polymorphism with sporadic Alzheimer's disease and ages at onset and duration of illness in Alzheimer's disease was also examined. RESULTS: The PS-1 polymorphism was not associated with the senile plaques, senile plaques with dystrophic neurites, or neurofibrillary tangles in Alzheimer's disease or non-demented subjects. There was no association of the PS-1 intronic polymorphism with Alzheimer's disease, ages at onset, or durations of illness in Alzheimer's disease. The results remained nonsignificant even when the PS-1 genotype groups were divided into the subgroups with different ApoE epsilon4 status. CONCLUSIONS: The PS-1 intronic polymorphism does not itself have a direct causal role in the formation of Alzheimer type neuropathological changes or in the development of sporadic Alzheimer's disease.     

Chromosome 17 and hereditary dementia: linkage studies in three non-Alzheimer families and kindreds with late-onset FAD

Several previous families with differing clinical and pathologic characteristics have demonstrated linkage to the 17q21-22 region. We have performed a linkage analysis with chromosome 17 markers on three families showing autosomal dominant inheritance of non-Alzheimer dementia and 60 kindreds with late-onset familial Alzheimer's disease (FAD). Family A shows unequivocal evidence of linkage with a maximum lod score of 5.0 for marker D17S934 (theta = 0.001). This family has an unusual syndrome of a schizophrenia-like psychosis beginning in the fifth or sixth decade followed by severe dementia with an average disease duration of 13.8 years. Neuropathology from five autopsies in this family has shown marked neurofibrillary tangle formation (NFT), degeneration of the amygdala, and no amyloid plaques. This confirms the presence of a gene associated with dementia on 17q and extends the related phenotype to include schizophrenia-like symptoms and classic NFT pathology. A second family with early aphasia progressing to dementia and cortical-basal ganglion-like degeneration also has suggestive evidence for linkage to 17q. A third family with very early-onset dementia (mean, 31 years) and nonspecific pathology can be excluded from the 17q region and emphasizes additional genetic heterogeneity in non-Alzheimer hereditary dementia. Finally, we also present evidence against linkage to D17S579 in the set of 60 families with late-onset FAD, providing further evidence that the chromosome 17 gene is unlikely to be involved in the pathogenesis of typical AD.     

Atomic force microscopy examination of tobacco mosaic virus and virion RNA

The majority of early-onset familial Alzheimer's disease (FAD) is associated with mutations in the presenilin-1 (PS1) gene. We describe a novel Polish PS1 mutation of Pro117Leu, associated with the earliest average age of onset and death so far reported in a PS-linked, FAD kindred. Human kidney 293 and mouse neuroblastoma N2a cells were stably transfected with wild-type and PS1 P117L. There was a significant increase in the amyloid beta42/40 ratio in the N2a P117L PS1 transfected cells compared with N2a transfected with wild-type PS1. What role PS has in the pathogenesis of AD remains to be determined, however, the severity of the clinical picture associated with this PS1 mutation stresses the importance of presenilin.     

Increased amyloid-beta42(43) in brains of mice expressing mutant presenilin 1

Mutations in the genes encoding amyloid-beta precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2) are known to cause early-onset, autosomal dominant Alzheimer's disease. Studies of plasma and fibroblasts from subjects with these mutations have established that they all alter amyloid beta-protein (beta APP) processing, which normally leads to the secretion of amyloid-beta protein (relative molecular mass 4,000; M(r) 4K; approximately 90% A beta1-40, approximately 10% A beta1-42(43)), so that the extracellular concentration of A beta42(43) is increased. This increase in A beta42(43) is believed to be the critical change that initiates Alzheimer's disease pathogenesis because A beta42(43) is deposited early and selectively in the senile plaques that are observed in the brains of patients with all forms of the disease. To establish that the presenilin mutations increase the amount of A beta42(43) in the brain and to test whether presenilin mutations act as true (gain of function) dominants, we have now constructed mice expressing wild-type and mutant presenilin genes. Analysis of these mice showed that overexpression of mutant, but not wild-type, PS1 selectively increases brain A beta42(43). These results indicate that the presenilin mutations probably cause Alzheimer's disease through a gain of deleterious function that increases the amount of A beta42(43) in the brain.     

No association between the low density lipoprotein receptor-related protein (LRP) gene and late-onset Alzheimer's disease in a community-based sample

It is now commonly known that possession of the epsilon4 allele of the apolipoprotein E (APOE) gene confers an increased risk for both familial and sporadic Alzheimer's disease (AD), in a dose-dependent way. Other genes that may play a role in AD, either through independent association with the disease or through modification of the existing APOE risk, have been reported with conflicting results. One such gene, the low density lipoprotein receptor-related protein (LRP) gene, was recently reported by two groups to be associated with AD, although the groups identified different risk-conferring alleles. Both studies were based on clinic-derived AD populations (one American, one French), and both reported only marginally significant results. We have genotyped a community-based AD and control population at this LRP polymorphism and find no association between the variants at that polymorphism and the occurrence of AD. Further, despite the biochemical relationship between LRP and the ApoE protein, we find no significant statistical interaction between the alleles at these loci.     

The apolipoprotein E gene, attention, and brain function.

The ε4 allele of the apolipoprotein E (ApoE) gene is associated with alterations in brain function and is a risk factor for Alzheimer's disease (AD). Changes in components of visuospatial attention with ApoE-ε4, aging, and AD are described. Healthy middle-aged adults without dementia who have the ApoE-ε4 gene show deficits in spatial attention and working memory that are qualitatively similar to those seen in clinically diagnosed AD patients. The findings support an association between ApoE polymorphism and specific components of visuospatial attention. Molecular mechanisms that may mediate the ApoE-attention link by modulating cholinergic neurotransmission to the posterior parietal cortex are discussed. Studies of attention and brain function in ApoE-ε4 carriers without dementia can advance knowledge of the genetics of visual attention, may enhance understanding of the preclinical phase of AD, and may lead to better methods for early AD detection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of A beta 42 in Alzheimer's disease

Our recent studies of plasma, fibroblasts, transfected cells and transgenic mice show that a fundamental effect of the mutations linked to familial Alzheimer's disease (FAD) is to increase the extracellular concentration of A beta 42. This effect of the FAD-linked mutations is likely to be directly related to the pathogenesis of Alzheimer's disease (AD) because A beta 42 is deposited early and selectively in the senile plaques that are an invariant feature of all forms of AD. Thus our results provide strong evidence that the FAD-linked mutations all cause AD by increasing the extracellular concentration of A beta 42 (43), thereby fostering A beta deposition, and they support the hypothesis that cerebral A beta deposition is an essential early event in the pathogenesis of all forms of AD. Interactions between the basal forebrain cholinergic system and A beta that could influence AD pathogenesis are discussed.     

Two distinct populations of primary cytotoxic cells infiltrating into allografted tumor rejection sites: infiltration of macrophages cytotoxic against allografted tumor precedes that of multiple sets of cytotoxic T lymphocytes with distinct specificity to alloantigens

The majority of cases with familial Alzheimer's disease (FAD) are linked to mutations of the presenilin (PS) genes. These genes show considerable sequence similarity to the sel-12 gene of Caenorhabditis elegans, which has been postulated to function in the facilitated signalling by lin-12 and glp-1. In order to analyse the functional conservation of the presenilins, we introduced the human PS-1 cDNA, as well as clinical and deletion mutant proteins, into sel-12 mutant animals and tested their potential to rescue the egg-laying defect. Human PS-1 expressed from the sel-12 promoter fully rescued the sel-12 phenotype, whereas two missense mutations, C410Y and A246E, identified in pedigrees with FAD, exhibited a strongly decreased rescuing activity. The large hydrophilic loop and transmembrane domain 7 are required for the biological activity of PS-1. PS-1 protein was proteolytically cleaved in C. elegans as it is in human cells. A PS-1 splice variant (FAD mutation deltaexon9) that does not undergo proteolytic cleavage also substituted for sel-12. The conservation of function of human PS-1 and C. elegans sel-12 suggests that presenilin proteins are required, directly or indirectly, for the proper operation of the Notch signalling pathway. FAD-associated mutant proteins tested showed different rescuing activities, indicating that they might affect different functional or regulatory aspects of PS-1. Proteolytic processing is not a prerequisite for PS-1 function in C. elegans.     

Presenilin proteins undergo heterogeneous endoproteolysis between Thr291 and Ala299 and occur as stable N- and C-terminal fragments in normal and Alzheimer brain tissue

Humans inheriting missense mutations in the presenilin (PS)1 and -2 genes undergo progressive cerebral deposition of the amyloid beta-protein at an early age and develop a clinically and pathologically severe form of familial Alzheimer's disease (FAD). Because PS1 mutations cause the most aggressive known form of AD, it is important to elucidate the structure and function of this multitransmembrane protein in the brain. Using a panel of region-specific PS antibodies, we characterized the presenilin polypeptides in mammalian tissues, including brains of normal, AD, and PS1-linked FAD subjects, and in transfected and nontransfected cell lines. Very little full-length PS1 or -2 was detected in brain and untransfected cells; instead the protein occurred as a heterogeneous array of stable N- and C-terminal proteolytic fragments that differed subtly among cell types and mammalian tissues. Sequencing of the major C-terminal fragment from PS1-transfected human 293 cells showed that the principal endoproteolytic cleavage occurs at and near Met298 in the proximal portion of the large hydrophilic loop. Full-length PS1 in these cells is quickly turned over (T1/2 approximately 60 min), in part to the two major fragments. The sizes and amounts of the PS fragments were not significantly altered in four FAD brains with the Cys410Tyr PS1 missense mutation. Our results indicate that presenilins are rapidly processed to N- and C-terminal fragments in both neural and nonneural cells and that interference with this processing is not an obligatory feature of FAD-causing mutations.     

Co-expression of beta-amyloid precursor protein (betaAPP) and apolipoprotein E in cell culture: analysis of betaAPP processing

Apolipoprotein E (ApoE) is the major genetic risk factor for Alzheimer's disease (AD). The ApoE4 allele is associated with earlier disease onset and greater cerebral deposition of the amyloid beta peptide (Abeta), the major constituent of senile (amyloid) plaques. The molecular mechanism underlying these effects of ApoE4 remains unclear; ApoE alleles could have different influences on Abeta production, extracellular aggregation, or clearance. Because the missense mutations on chromosomes 14 and 21 that cause familial forms of AD appear to lead to increased secretion of Abeta, it is important to determine whether ApoE4 has a similar effect. Here, we have examined the effects of all three ApoE alleles on the processing of betaAPP and the secretion of Abeta in intact cells. We established neural (HS683 human glioma) and non-neural (Chinese hamster ovary) cell culture systems that constitutively secrete both ApoE and Abeta at concentrations like those in human cerebrospinal fluid. betaAPP metabolites, generated in the presence of each ApoE allele, were analysed and quantified by two methods: immunoprecipitation and phosphorimaging, and ELISA. We detected no consistent allele-specific effects of ApoE on betaAPP processing in either cell type. Our data suggest that the higher amyloid burden found in AD subjects expressing ApoE4 is not due to increased amyloidogenic processing of betaAPP, in contrast to findings in AD linked to chromosome 14 or 21. These co-expressing cell lines will be useful in the further search for the effects of ApoE on Abeta aggregation or clearance under physiologically relevant conditions.