The E280A presenilin 1 Alzheimer mutation produces increased A beta 42 deposition and severe cerebellar pathology.

Missense mutations in the presenilin 1 (PS1) gene cause the most common form of dominant early-onset familial Alzheimer's disease (FAD) and are associated with increased levels of amyloid beta-peptides (A beta) ending at residue 42 (A beta 42) in plasma and skin fibroblast media of gene carriers. A beta 42 aggregates readily and appears to provide a nidus for the subsequent aggregation of A beta 40 (ref. 4), resulting in the formation of innumerable neuritic plaques. To obtain in vivo information about how PS1 mutations cause AD pathology at such early ages, we characterized the neuropathological phenotype of four PS1-FAD patients from a large Colombian kindred bearing the codon 280 Glu to Ala substitution (Glu280Ala) PS1 mutation. Using antibodies specific to the alternative carboxy-termini of A beta, we detected massive deposition of A beta 42, the earliest and predominant form of plaque A beta to occur in AD (ref. 6-8), in many brain regions. Computer-assisted quantification revealed a significant increase in A beta 42, but not A beta 40, burden in the brains from 4 PS1-FAD patients compared with those from 12 sporadic AD patients. Severe cerebellar pathology included numerous A beta 42-reactive plaques, many bearing dystrophic neurites and reactive glia. Our results in brain tissue are consistent with recent biochemical evidence of increased A beta 42 levels in PS1-FAD patients and strongly suggest that mutant PS1 proteins alter the proteolytic processing of the beta-amyloid precursor protein at the C-terminus of A beta to favor deposition of A beta 42.

The effect of the apolipoprotein E gene polymorphisms and haplotypes on behavioural and psychological symptoms in probable Alzheimer's disease.

BACKGROUND: Patients with Alzheimer's disease and dementia commonly suffer from behavioural and psychological symptoms of dementia (BPSD). A genetic component to BPSD development in Alzheimer's disease has been demonstrated. Several studies have investigated whether the exon 4 epsilon2/epsilon3/epsilon4 haplotype of the apolipoprotein E (APOE) gene is associated with BPSD, with variable results. OBJECTIVE: We investigated the exon 4 polymorphisms and extended this study to include promoter polymorphisms and the resultant haplotypes across the gene. METHODS: Our large independent cohort of 388 patients with longitudinal measures of BPSD assessed by the Neuropsychiatric Inventory was used to analyse whether any of these variants were associated with the presence of BPSD. RESULTS: We revealed several significant relationships before correction for multiple testing. The exon 4 haplotype was associated with hallucinations and anxiety, A-491T with irritability, T-427C with agitation/aggression and appetite disturbances, and T-219C with depression. Haplotype analyses of all variants did not reveal any statistically significant findings. CONCLUSIONS: Our data and a review of previous studies showed a diversity of relationships, suggesting that these findings might be due to chance and so collectively do not support a role for the APOE gene in BPSD.

Are interleukin-1 gene polymorphisms risk factors or disease modifiers in AD?

Polymorphisms in the interleukin-1 genes, IL-1A and IL-1B, have been associated with AD, but not in all studies. The authors genotyped the IL-1A(-889) and IL-1B(-511) polymorphisms in large independent cohorts of 503 control individuals and 395 patients with AD, and a further 100 with brain Abeta load. No evidence was found of risk for AD with these variants, nor of an effect on age at onset. However, an impact of IL-1B(-511) on Abeta(40) load (p < 0.05) was detected.

Hereditary dysphasic disinhibition dementia: a frontotemporal dementia linked to 17q21-22.

OBJECTIVE: The clinical and pathologic features of hereditary dysphasic disinhibition dementia (HDDD) are described to determine whether it is a variant of known dementias. BACKGROUND: Several dementing disorders have clinical and pathologic similarities with AD, Pick's disease, and the "nonspecific" dementias. A detailed description of clinical and pathologic presentation will aid classification, but ultimately the discovery of causative gene(s) will define these disorders. METHODS: The authors performed a clinical assessment: gross and microscopic pathologic evaluation of brain tissue, genetic linkage studies, and sequence analyses. RESULTS: HDDD is an autosomal-dominant frontotemporal dementia with many similarities to Pick's disease. Salient clinical features are global dementia with disproportionate dysphasia and "frontotemporal" symptoms. A linkage between HDDD and 17q21-22 was shown, with a maximum lod score of 3.68 at zero recombination. CONCLUSIONS: Several dementias have been linked to the same region and have been termed frontotemporal dementia with parkinsonism linked to chromosome 17. These disorders may represent phenotypic variants arising from mutations within a common gene.

Contribution of APOE promoter polymorphisms to Alzheimer's disease risk.

OBJECTIVE: To determine whether the effects of APOE promoter polymorphisms on AD are independent of the APOE-epsilon4 allele. BACKGROUND: Recently, the -491 A-->T and -219 G-->T polymorphisms located in the APOE promoter have been suggested to be risk factors for AD. However, the effects of these polymorphisms have not always been reproduced in case-control studies, possibly because of the strong linkage disequilibrium existing at this locus or the characteristics of the populations studied. METHODS: Data collection was performed from six independent samples (1,732 patients with AD and 1,926 control subjects) genotyped for APOE exon 4 and the two APOE promoter polymorphisms. The risks associated with the APOE polymorphisms for developing AD were estimated using logistic regression procedures and calculation of odds ratios with 95% CI adjusted by age, sex, and collection center. Independence of the APOE promoter polymorphisms was tested by stratification for APOE-epsilon4 and tertile design was used for age stratification. RESULTS: The independence of the -491 AA genotype was observed in the whole sample whereas the independence of the -219 TT genotype was observed only in the oldest population. CONCLUSION: The -491 and -219 APOE promoter polymorphisms incur risk for AD in addition to risk associated with the APOE-epsilon4 allele, with age accentuating the effect of the -219 TT genotype. Because these polymorphisms appear to influence apoE levels, these results suggest that APOE expression is an important determinant of AD pathogenesis.

Atherosclerotic plaque caps are locally weakened when macrophages density is increased.

The density of macrophages, identified by the antibody EBMII, in human aortic plaque caps was counted. A contiguous strip of cap tissue was tested mechanically. Aortic plaque caps which had undergone rupture (ulceration) at one end (n = 18) were compared with caps of intact plaques (n = 22). The caps of ruptured plaques showed a significant increase in macrophage density, an increased extensibility and decreased maximum stress (force per unit area) at fracture when compared with caps from intact plaques.

Collagen types I and III, collagen content, GAGs and mechanical strength of human atherosclerotic plaque caps: span-wise variations.

Measurements of total collagen, of the ratio of collagen types III/(I+III) and of sulphated glycosaminoglycans (GAGs) were compared with mechanical strength for individual ulcerated and non-ulcerated human aortic plaque caps and with intima adjacent to the plaques. The distributions of the collagen type ratio were similar for both ulcerated and non-ulcerated plaque caps but different from that of the adjacent intima. The proportions of different collagen types were not related to fracture stress and are thus unlikely to affect the potential to ulcerate. The distributions of the sulphated GAGs showed lower amounts for the plaque caps compared with the nearby intima, with the centres of ulcerated plaque caps having the lowest values. Total collagen had higher values in the peripheries of plaque caps compared with the nearby intima, but was distinctly lower in the centres of ulcerated plaque caps. Plaque caps appeared to require a higher collagen content than adjacent intima to support a given level of mechanical strength, suggesting that while collagen production had occurred in the plaque caps it was not as efficiently organized to resist fracture as a similar amount of collagen in the adjacent intima. Ulcerated plaque caps are notable for much larger transverse (centre vs. periphery) gradients of connective tissue constituents than for non-ulcerated plaque caps. The development of these transverse gradients may be a critical aspect in determining the propensity of a plaque to ulcerate.

17 Beta-oestradiol attenuates dexamethasone-induced lethal and sublethal neuronal damage in the striatum and hippocampus.

Abnormal corticosteroid release is extensively associated with mood disorders. This association may result from the toxic actions of endogenous corticosteroids which can induce apoptosis of hippocampal neurons. Similarly, dexamethasone, a synthetic corticosteroid, can induce lethal and sublethal damage to rat hippocampal and striatal neurons and can result in steroid-induced psychoses in humans. The experiments reported here tested the hypothesis that pre-treatment with oestrogen would also attenuate dexamethasone-induced neuronal damage as oestrogens have neuroprotective actions against a variety of insults and falling levels of oestrogen are associated with increased vulnerability to mood disorders. Male Sprague-Dawley rats received three systemic injections which were a combination of vehicle, 17-beta-oestradiol (0.2 mg/kg, s.c.), the oestrogen receptor antagonist tamoxifen (10 mg/kg, s.c.) and dexamethasone (0.7 mg/kg, i.p.) and were killed 24 h after the final injection. Injections of dexamethasone (when preceded by vehicle injections) resulted in elevated levels of apoptosis and sub-lethal damage, as demonstrated by reduced levels of microtubule-associated protein-2-immunopositive neurons, in the striatum and hippocampus. This damage was regional with the dorsomedial caudate putamen and the dentate gyrus and CA1 and CA3 hippocampal sub-fields being particularly affected. Pretreatment with oestrogen substantially attenuated the dexamethasone-induced neuronal damage. This oestrogen-induced neuronal protection was in turn virtually eliminated by giving an initial injection of tamoxifen. These results suggest, therefore, that oestrogens can protect from corticosteroid-induced neuronal damage via an oestrogen receptor-mediated process.

Human leucocyte antigen-A2 increases risk of Alzheimer's disease but does not affect age of onset in a Scottish population.

The use of non-steroidal anti-inflammatory drugs has been associated with a reduced incidence of Alzheimer's disease (AD), suggesting that attenuation of the inflammatory response may be beneficial. Several, but not all, genetic association studies have shown human leucocyte antigen (HLA)-A2, a major histocompatibility complex class I antigen-binding transmembrane protein has an increased frequency in AD compared to controls, and in some reports is associated with a lowered age of onset. We further investigated the role of HLA-A2 in an independent sample of AD cases, including a large early onset cohort. The results of this current study and meta analysis of all studies available to date support previous evidence of an excess of HLA-A2 in AD, but found no evidence of a relationship with age of onset.

No association found between Alzheimer's disease and a mitochondrial tRNA glutamine gene variant.

We have screened a large sample of patients with sporadic late-onset dementia of the Alzheimer type (DAT) and age-matched controls for a mitochondrial tRNA(Gln) variant previously reported to be associated with increased risk of developing Alzheimer's disease (AD). The frequency of an Ava II site gain was determined by restriction analysis of a PCR-amplified mitochondrial DNA product. One of 155 DAT cases and four of 105 age-matched controls carried the variant. Both the affected and control frequencies are statistically different from those previously reported. The mitochondrial lineage of those individuals harboring the variant was determined by sequencing a short region of the hypervariable mitochondrial D-loop. The affected individual and three of the four controls carrying the Ava II variant belong to the same mitochondrial lineage previously reported to be associated with AD.

A polymorphism in the presenilin 1 gene does not modify risk for Alzheimer's disease in a cohort with sporadic early onset.

Mutations in the presenilin 1 gene account for many cases of early onset familial Alzheimer's disease. Homozygosity for the 'T' allele of a polymorphism in the presenilin 1 gene has previously been reported to double the risk for Alzheimer's disease in a late onset Caucasian sample. Here we report that this polymorphism does not incur risk in a case control sample of early onset Alzheimer's disease, possibly suggesting a different disease etiology between the early and late onset forms.

Genetic association studies between dementia of the Alzheimer's type and three receptors for apolipoprotein E in a Caucasian population.

The epsilon 4 allele of the apolipoprotein E gene (ApoE) is associated with an increased risk for sporadic and some familial forms of Alzheimer's disease (AD) but the precise mechanism of pathogenesis is unknown. ApoE is a ligand for at least three receptors in the central nervous system, low density lipoprotein receptor (LDL-R), very low density lipoprotein receptor VLDL-R and low density lipoprotein-like receptor (LRP). We have tested for association between these receptors and dementia of the Alzheimer's type (DAT) in a clinically based sample of Caucasian cases and age-matched controls. In contrast to findings in a Japanese cohort we detected no association between DAT and a polymorphism in the VLDL-R gene. No association was detected with the LDL-R gene. We observed a possible association between the 87 allele of a polymorphism within the LRP gene and DAT which remained significant after correction for multiple testing. When the effects of known risk factors for AD such as ApoE epsilon 4 were applied, the effect of LRP no longer reached conventional levels of statistical significance. Nevertheless, LRP is a plausible candidate gene and we may be observing a minor risk factor that will require further examination in other large independent samples to assess whether it truly modifies susceptibility to DAT.

A polymorphism within intron 11 of the tau gene is not increased in frequency in patients with sporadic Alzheimer's disease, nor does it influence the extent of tau pathology in the brain.

There are numerous polymorphisms within the tau gene but these are in complete linkage disequilibrium and exist as two common extended haplotypes H1 and H2. We have investigated the frequency of these haplotypes in 83 cases of sporadic Alzheimer's disease (AD) using the +34 polymorphism in intron 11 of the tau gene as a marker of H1 and H2 haplotypes. The total amount of hyperphosphorylated tau protein (tau load), present as neurofibrillary tangles, neuropil threads or plaque neurites, was quantified in the frontal cortex of these patients and related to tau haplotype. We found no increase in H1H1 haplotype in this autopsy population of cases with AD compared to published control data. Stratification of cases for apolipoprotein E (APO E) genotype showed a slight, but not statistically significant, overrepresentation of epsilon 4 allele amongst bearers of H2 haplotype. There were no overall differences in tau load between haplotype groups though cases within each haplotype group bearing APO E epsilon 4 allele had a significantly higher tau load than those without epsilon 4 allele. Neither age at onset or duration of illness differed according to tau haplotype. We conclude that the frequency of tau gene H1 haplotype is not elevated in AD and possession of this has no impact upon the amount of tau pathology in AD.

A polymorphism in the angiotensin 1-converting enzyme gene is associated with damage to cerebral cortical white matter in Alzheimer's disease.

The impact of the insertion (I)/deletion (D) (I/D) polymorphism in the angiotensin 1-converting enzyme (ACE) gene on the extent of white matter myelin loss (ML) was investigated in four regions of the cerebral cortex in an autopsy-confirmed series of 93 patients with Alzheimer's disease (AD). The possible influence of APO E epsilon4 allele acting in concert with ACE D allele was assessed. The extent of ML did not differ between D/D, I/D and I/I genotype groups when data from all four brain regions were combined. However, separate analysis showed that the frontal and temporal cortex tended to be affected more severely by ML in patients with D/D genotype compared to those with I/D and I/I genotypes. Stratification according to APO E epsilon4 allele revealed a greater overall ML in patients bearing at least one copy of ACE D allele and one APO E epsilon4 allele, especially in individuals homozygous for both. The APO E epsilon4 allele may therefore act synergistically in patients with AD (and other subjects) bearing ACE D/D genotype to increase the risk of ML, perhaps through transient ischaemic episodes consequent upon poor cardiac output associated with coronary atherosclerosis in patients with the APO E epsilon4 allele.

The angiotensin 1-converting enzyme insertion (I)/deletion (D) polymorphism does not influence the extent of amyloid or tau pathology in patients with sporadic Alzheimer's disease.

An insertion (I)/deletion (D) polymorphism in the angiotensin 1-converting enzyme (ACE) gene has, in some studies, been associated with increased risk for Alzheimer's disease (AD), and functionally the enzyme has been implicated in the degradation of amyloid beta protein (Abeta). We have investigated the frequency of the I/D polymorphism in a clinic-based and autopsy-confirmed series of cases of AD, and investigated what impact the I/D polymorphism in ACE gene might have on the extent of Abeta and tau pathology in the frontal cortex in the autopsy-confirmed series. We found no differences in I/D allele or genotype frequencies between the clinic-based and autopsy-confirmed AD cases, or between the pooled clinic-based and autopsy-confirmed AD cases and a series of normal control subjects. Moreover, Abeta (Abeta(40) and Abeta(42)) load, tau load or extent of amyloid angiopathy did not differ between D/D, I/D and I/I genotype groups, though Abeta(42) load tended to be higher in bearers of I/I genotype (compared to D/D genotype). Neither age at onset nor duration of illness differed according to genotype. We conclude therefore that the frequency of ACE I-allele is not increased in AD and, in autopsy-confirmed AD cases, possession of the ACE I allele has no impact upon the pathology of AD, at least in terms of the amount of Abeta or tau deposited in the brain.

A SNP in the ACT gene associated with astrocytosis and rapid cognitive decline in AD.

There is biochemical and animal model evidence supporting a pathological role of the ACT gene in AD. However, direct genetic evidence remains controversial and has been mostly limited to individual single nucleotide polymorphism (SNP) analysis. To resolve this apparent conflict we have used a high-density ACT SNP map, constructed haplotypes and explored correlations with phenotype. SNPs were identified by sequencing and used to construct haplotypes in 668 AD patients and 419 controls and a case-control association study was performed. Five SNPs, comprising five common haplotypes, represented 93% of ACT gene variation. Although no single SNP or haplotype was associated with AD status, a SNP in intron 2 was associated with later onset and more rapid cognitive decline (P=0.04). This SNP was both individually associated with severe astrocytosis (P=0.004) in AD patients and when combined with the signal sequence SNP (P=0.002). This suggests that astrocytosis may have a protective function for a limited period in some patients. These SNP associations either support a direct role for the ACT gene, in AD pathology or alternatively reflect linkage with polymorphisms in other genes nearby.

Genetic associations between cathepsin D exon 2 C-->T polymorphism and Alzheimer's disease, and pathological correlations with genotype.

Genetic variations represent major risk factors for Alzheimer's disease (AD). While familial early onset AD is associated with mutations in the amyloid precursor protein and presenilin genes, only the e4 allele of the apolipoprotein E (APOE) gene has so far been established as a genetic risk factor for late onset familial and sporadic AD. It has been suggested that the C-->T (224Ala-->Val) transition within exon 2 of the cathepsin D gene (CTSD) might represent a risk factor for late onset AD. The objective of this study was to investigate whether possession of the CTSD exon 2 T allele increases the risk of developing AD, and to determine whether this modulates the amyloid pathology of the disease in conjunction with, or independent of, the APOE e4 allele. Blood samples were obtained from 412 patients with possible or probable AD and brain tissues from a further 148 patients with AD confirmed by postmortem examination. CTSD and APOE genotyping were performed by PCR on DNA extracted from blood, or from frontal cortex or cerebellum in the postmortem cases. Pathological measures of amyloid beta protein (Abeta), as plaque Abeta40 and Abeta42(3) load and degree of cerebral amyloid angiopathy were made by image analysis or semiquantitative rating, respectively. CTSD genotype frequencies in AD were not significantly different from those in control subjects, nor did these differ between cases of early or late onset AD or between younger and older controls. There was no gene interaction between the CTSD T and APOE e4 alleles. The amount of plaque Abeta40 was greater in patients carrying the CTSD T allele than in non-carriers, and in patients bearing APOE e4 allele compared with non-carriers. Possession of both these alleles acted synergistically to increase levels of plaque Abeta40, especially in those individuals who were homozygous for the APOE e4 allele. Possession of the CTSD T allele had no effect on plaque Abeta42(3) load or degree of CAA. Possession of the CTSD T allele does not increase the risk of developing AD per se, but has a modulating effect on the pathogenesis of the disorder by increasing, in concert with the APOE e4 allele, the amount of Abeta deposited as senile plaques in the brain in the form of Abeta40.

Exploring the etiology of Alzheimer disease using molecular genetics.

Alzheimer disease (AD), the most common cause of dementia in the elderly, exists in both familial and sporadic forms. Genetic studies have led to the identification of 3 genes, beta-amyloid precursor protein (APP), presenilin-1 (PS1), and presenilin-2 (PS2), which, when mutated, can cause familial forms of AD. Mutations in each of these genes result in elevated levels of A beta42/43, a proteolytic processing fragment of APP that is deposited in brains of AD patients. Transgenic mice carrying AD-causing mutations in APP develop spontaneous age-related beta-amyloid (A beta) deposition and memory impairment. Genetic linkage and association studies have also shown that the epsilon4 allele of the apolipoprotein E (APOE) gene increases risk for AD in a dose-dependent manner in both familial and sporadic forms of AD and may account for as much as 50% of the attributable risk. APOE genotyping may be useful both as an adjunct to diagnosis and in identifying patient groups for therapeutic intervention. While the biological basis for the association of APOE epsilon4 with AD is not known, age of onset and A beta deposition are positively correlated with epsilon4 allele dosage in some cases, suggesting that this risk may also be mediated directly or indirectly through A beta. Because 50% of AD cases have no APOE epsilon4 alleles and families showing mendelian inheritance of AD exist in whom there are no mutations in any of the APP, PS1, or PS2 genes, it is likely that there are additional AD risk factors, both genetic and environmental, still to be identified.

Testing of small connective tissue specimens for the determination of the mechanical behaviour of atherosclerotic plaques.

The tearing of the cap of atheromatous plaques is the commonest cause of thrombosis in human coronary arteries. It has been proposed that tearing arises because of structural weakening of the cap's connective tissue around the tear. To test this hypothesis we compared the mechanical properties of the intact edges of torn plaque caps and unbroken caps. Owing to limitations in plaque size, a purpose-built tensometer was developed to study stress-strain relationships of the small connective tissue specimens. The design of the tensometer is reported and was shown to detect accurately, minor differences in connective tissues and to generate complete stress-curves with computer-assisted image analysis.

Tau load is associated with apolipoprotein E genotype and the amount of amyloid beta protein, Abeta40, in sporadic and familial Alzheimer's disease.

The total amount of hyperphosphorylated tau protein (p-tau load), present as neurofibrillary tangles (NFTs), neuropil threads or plaque neurites, was quantified in the frontal cortex of 109 cases of sporadic Alzheimer's disease (AD) and 35 cases of familial AD due to missense mutations in the presenilin-1, presenilin-2 and amyloid precursor protein genes. p-tau load was inversely correlated with age at onset of illness in both sporadic and familial AD but not with duration of disease. There was no difference in p-tau load between cases of familial AD and others with sporadic AD, matching the familial cases for apolipoprotein E (APO E) genotype. However, p-tau was greater in cases of familial and sporadic AD in the presence of APO E epsilon4 allele and increased with gene dose. Conversely, p-tau load tended to be lower when epsilon2 allele was present. In sporadic AD, tau load was highly significantly correlated with amyloid beta40 (Abeta40), but not Abeta42(43), load. These data indicate that the burden of pathological tau deposited in the brain in both familial and sporadic AD is favoured in the presence of APO E epsilon4 allele and also related to the amount of Abeta40, this also being higher when epsilon4 allele is present. Abeta40 plaques are rich in microglial cells and it is possible that p-tau pathology in AD is triggered by reaction of microglial cells to the presence of Abeta40 and not this peptide directly.