Apolipoprotein E Pittsburgh variant is not associated with the risk of late-onset Alzheimer's disease in a Spanish population

The objective of this study was to assess whether the APOE(Pittsburgh) variant (APOE*4P) is associated to Alzheimer's disease (AD) in a population from Madrid (Spain). APOE*4P variant is caused by an exonic mutation which results in the substitution of proline-28 for leucine-28, only present in APOE*4 alleles. A study in a US population associated this APOE variant with an increased risk for AD, about five times higher than the risk attributed to APOE*4 carriers overall. One hundred and seventeen cases of late-onset AD and 121 matched control subjects from Madrid (Spain) were included. We studied the APOE polymorphism and the APOE*4P occurrence, by PCR and restriction analysis, and plasma lipids levels using standard protocols. As expected, APOE*4 was significantly overrepresented in AD cases. The APOE*4P mutation was observed in heterozygous state in four subjects, two AD (1.71%) and two controls (1.65%). APOE*4P did not confer higher risk for AD, globally (odds ratio 0.14; 95% confidence interval (CI) 0.02-1.12) or respect to APOE*4 carriers (odds ratio 0.14; 95% CI 0.02-1.24). There were no differences in plasma lipids levels among genotype groups. The mutation frequency in controls was higher in our sample than in the US one (1.65 and 0.18%, respectively; Fisher test P = 0.049). Our results suggest that this variant is not so uncommon in our population and is not directly related to AD, contrary to what has been proposed for other populations.

Identification and characterization of a novel human brain-specific gene, homologous to S. scrofa tmp83.5, in the chromosome 10q24 critical region for temporal lobe epilepsy and spastic paraplegia

We describe the structure, genomic organization, and some transcription features of a human brain-specific gene previously localized to the genomic region involved in temporal lobe epilepsy and spastic paraplegia on chromosome 10q24. The gene, which consists of six exons disseminated over 16 kb of genomic DNA, is highly homologous to the porcine tmp83.5 gene and encodes a putative transmembrane protein of 141 amino acids. Unlike its porcine homolog, from which two mRNAs with different 5'-sequences are transcribed, the human gene apparently encodes three mRNA species with 3'-untranslated regions of different sizes. Mutation analysis of its coding sequence in families affected with temporal lobe epilepsy or spastic paraplegia linked to 10q24 do not support the involvement of this gene in either diseases.

A clinical and pathological study of motor neurone disease on Guam

Despite over 40 years of intensive study, the cause of the high incidence of motor neurone disease (MND) on Guam, and the relationship between this disease and MND seen in the rest of the world are still uncertain. We present a series of 45 cases of Guamanian MND, which reaffirm the clinical similarity between this disease and MND seen in other countries. However, the occurrence of MND among the indigenous Chamorros of Guam is distinguished by four factors: (i) high prevalence; (ii) frequent familial occurrence; (iii) co-occurrence with the parkinsonism-dementia complex (PDC); and (iv) association with an unusual and distinctive linear retinopathy termed Guam retinal pigment epitheliopathy (GRPE). These distinguishing factors were not present in four non-Chamorros who resided on Guam when their MND symptoms occurred. Pathologically, the classical features of MND were seen in Guamanian Chamorro cases including ubiquitin inclusions. Neurofibrillary tangles were frequently seen. The neurofibrillary tangles appeared in the same distribution as described in the PDC but, unlike classical PDC, they were not usually associated with cell loss and occurred less frequently. While neurofibrillary tangle formation and the clinicopathological syndrome of MND may occur in parallel, observations from this series suggest that pathologically classical MND on Guam may occur independently of neurofibrillary degeneration and the clinical features of PDC.

The genetic and pathological classification of familial frontotemporal dementia

BACKGROUND

Frontotemporal dementia (FTD) is an important cause of neurodegenerative dementia, particularly in younger patients. TAU has been identified as the gene responsible for FTD linked to chromosome 17, but it is likely that there is pathological and genetic heterogeneity among families with FTD.

OBJECTIVE

To explore the genetic and pathological basis of familial FTD.

DESIGN

Clinical case series with genetic analysis of each family, and pathological confirmation of diagnosis where possible.

SETTING

Specialist dementia research group, particularly recruiting patients with young-onset dementia.

PATIENTS

Twenty-two families with an index member with FTD, meeting Lund-Manchester criteria, and a family history of other affected members with dementia were ascertained.

RESULTS

Half of the families had mutations in the TAU gene (TAU exon 10 +14, +16, and P301S), and pathological diagnoses were available in 17 of 22 families. Three main pathological diagnoses were made: FTD with neuronal and glial tau deposition, FTD with ubiquitin inclusions, and FTD with neuronal loss and spongiosis but without intracellular inclusions. No cases of familial Pick disease were identified. With the use of the pathological diagnoses, each family with FTD with neuronal and glial tau deposition had a TAU mutation, whereas TAU mutations were not identified in families in the other 2 diagnostic groups.

CONCLUSIONS

This study illustrates the value of TAU sequencing in FTD and suggests that around one half of individuals with familial FTD have TAU mutations and dementia with tau pathological findings. Furthermore, these data suggest that there are at least 2 additional genes to be identified among families with autosomal dominant FTD.

Susceptibility locus for Alzheimer's disease on chromosome 10

The apolipoprotein E (APOE) gene is the only genetic risk factor that has so far been linked to risk for late-onset Alzheimer's disease (LOAD). However, 50 percent of Alzheimer's disease cases do not carry an APOE4 allele, suggesting that other risk factors must exist. We performed a two-stage genome-wide screen in sibling pairs with LOAD to detect other susceptibility loci. Here we report evidence for an Alzheimer's disease locus on chromosome 10. Our stage one multipoint lod score (logarithm of the odds ratio for linkage/no linkage) of 2.48 (266 sibling pairs) increased to 3.83 in stage 2 (429 sibling pairs) close to D10S1225 (79 centimorgans). This locus modifies risk for Alzheimer's disease independent of APOE genotype.

The presenilin 1 C92S mutation increases abeta 42 production

Although wild-type human presenilin 1 (PS1) rescues the C. elegans egg-laying (egl) phenotype that is caused by a loss of function mutation in the C. elegans presenilin homologue sel12, most familial Alzheimer's disease (FAD)-linked PS1 mutants only partially rescue this phenotype. To investigate the effects of the loss of function sel12 mutation on Abeta production in mammalian cells, we analyzed Abeta production in transfected H4 neuroglioma cells expressing the PS1 homologue of the sel12 C60S mutant, PS1 C92S. This analysis revealed that PS1 C92S increased Abeta42 levels in a similar fashion to other pathogenic Alzheimer's disease (AD) PS1 mutations. Significantly, the PS1 C92S mutation has recently been identified as the pathogenic mutation in an Italian family with FAD. Thus, placing a mutation that results in loss of function in C. elegans into a context whereby its effect on mammalian cells can be evaluated suggests that all FAD-linked PS1 mutants result in increased Abeta42 production through a partial loss of function mechanism.

No association between TAU haplotype and Alzheimer's disease in population or clinic based series or in familial disease

We and others have previously identified two distinct haplotypes of the TAU gene in Caucasian populations. In this study, we have assessed whether these haplotypes show an association with Alzheimer's disease in a variety of populations. They do not. These data are consistent with the view that the involvement of TAU in Alzheimer's disease is a downstream event.

Alzheimer's disease presenilin-1 exon 9 deletion and L250S mutations sensitize SH-SY5Y neuroblastoma cells to hyperosmotic stress-induced apoptosis

Mutations in the presenilin-1 (PS1) and presenilin-2 (PS2) genes account for the majority of early-onset familial Alzheimer's disease cases. Recent studies suggest that presenilin gene mutations predispose cells to apoptosis by mechanisms involving altered calcium homeostasis and oxidative damage. In the present study, we determined whether PS1 mutations also sensitize cells to hyperosmotic stress-induced apoptosis. For this, we established SH-SY5Y neuroblastoma cell lines stably transfected with wild-type PS1 or either the PS1 exon 9 deletion (deltaE9) or PS1 L250S mutants. Cultured cells were exposed to an overnight (17 h) serum deprivation, followed by a 30 min treatment with either 20 mM glucose, 10 nM insulin-like growth factor-1 or 20 mM glucose + 10 nM insulin-like growth factor-1. Cells were then cultured for a further 3, 6 or 24 h and stained for apoptotic condensed nuclei using propidium iodide. Confirmation that cells were undergoing an active apoptotic process was achieved by labelling of DNA strand breaks using the terminal dUTP nick end labelling (TUNEL) technique. We also determined cell viability using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Propidium iodide staining revealed that all cell lines and controls showed an increased number of apoptotic cells appearing with condensed nuclei at 24 h compared with 6 h and 3 h. High glucose-induced hyperosmotic stress resulted in significantly more apoptotic cells in the PS1 deltaE9 and PS1 L250S mutation cell lines at 24 h, compared with the wild-type PS1 lines (P < 0.001, ANOVA for both comparisons). Mean values (+/-S.D.) for the percentage number of apoptotic cells at 24 h following high glucose treatment were 16.1 +/- 3.5%, 26.7 +/- 5.5% and 31.0 +/- 5.7% for the wild-type PS1, PS1 deltaE9 and PS1 L250S lines, respectively. The pro-apoptotic effects of high glucose treatment were reversed by 10 nM insulin-like growth factor-1, although to a lesser extent in the mutation cell lines (5.8 +/- 2.4%, 15.2 +/- 7.3% and 13.2 +/- 2.0% for the wild-type PS1, PS1 deltaE9 (P < 0.01 for comparison with wild-type PS1) and PS1 L250S (P < 0.01 for comparison with wild-type PS1) transfected lines, respectively. TUNEL labelling of cells at 24 h following treatment gave essentially the same results pattern as obtained using propidium iodide. The percentage number of apoptotic cells with DNA strand breaks (means +/- S.D.) following high glucose treatment was 15.4 +/- 2.6% for the wild-type PS1, 26.8 +/- 3.2% for the PS1 deltaE9 (P < 0.001 for comparison with wild-type PS1) and 29.7 +/- 6.1% for the PS1 L250S transfected lines (P < 0.001 for comparison with wild-type PS1). The PS1 deltaE9 and PS1 L250S transfected lines also showed a higher number of apoptotic cells with DNA strand breaks at 24 h following high glucose plus insulin-like growth factor-1 treatment (11.4 +/- 2.0% and 14.3 +/- 2.8%, respectively), compared with values for the wild-type PS1 lines (8.5 +/- 2.4%). These differences were significant (P < 0.01) for the comparison of wild-type PS1 and PS1 L250S, but not PS1 deltaE9 lines. The mutation-related increases in number of apoptotic cells at 24 h following high glucose treatment were not accompanied by significant differences in cell viability at this time-point. Our results indicate that PS1 mutations predispose to hyperosmotic stress-induced apoptosis and that the anti-apoptotic effects of insulin-like growth factor-1 are compromised by these mutations. Perturbations of insulin-like growth factor-1 signalling may be involved in PS1 mutation-related apoptotic neuronal cell death in Alzheimer's disease.

Association of an extended haplotype in the tau gene with progressive supranuclear palsy

We describe two extended haplotypes that cover the human tau gene. In a total of approximately 200 unrelated caucasian individuals there is complete disequilibrium between polymorphisms which span the gene (which covers approximately 100 kb of DNA). This suggests that the establishment of the two haplotypes was an ancient event and either that recombination is suppressed in this region, or that recombinant genes are selected against. Furthermore, we show that the more common haplotype (H1) is significantly over-represented in patients with progressive supranuclear palsy (PSP), extending earlier reports of an association between an intronic dinucleotide polymorphism and PSP.

A novel mutation in the apolipoprotein E gene (APOE*4 Pittsburgh) is associated with the risk of late-onset Alzheimer's disease

Using a combination of polymerase chain reaction (PCR), single-strand conformation polymorphism (SSCP) and DNA sequencing techniques, we identified a unique missense mutation (T-->C) in exon 3 of the APOE gene which resulted in the substitution of pro-28 for leu-28. We screened 1118 White cases of late-onset (>60 years) Alzheimer's disease (AD) from three independent centers (Pittsburgh = 489, Indiana = 319, Mayo Clinic Rochester = 310) and 1123 controls (607 clinically assessed and 516 individuals randomly ascertained from the general population). Two of the 1123 control subjects had the pro-28 mutation (0.18%). However, this mutation was observed in heterozygous state in 2.66, 2.51 and 1.94% of the AD cases from Pittsburgh, Indiana and Mayo Clinic Rochester, respectively, with an overall frequency of 2.42%. All individuals with this mutation were carriers of the APOE*4 allele and hence the mutation was denoted as APOE*4 Pittsburgh (APOE*4P). Compared with the non-E*4P carriers, the E*4P carriers were associated with an increased risk of AD (odds ratio (OR) 13.2) and this risk remained significant even after adjusting for the known effect of APOE*4 (OR 5.4). The risk associated with the E*4P/E*4 combination was about five times (OR 29.1) the risk attributed to APOE*4 carriers alone (OR 5.7). Our data indicates that the new mutation most likely exists in cis-orientation with APOE*4 and is associated with increased risk of developing AD.

Apolipoprotein E genotype does not affect the age of onset of dementia in families with defined tau mutations

We have assessed whether apolipoprotein E (ApoE) genotype influences the age of onset of dementia in a series of families with frontal temporal dementia with defined mutations in the tau gene. In contrast to the situation in Alzheimer's disease (AD), we could find no evidence that the age of onset of disease was influenced by the ApoE genotype.

A full genome scan for late onset Alzheimer's disease

We have genotyped 292 affected sibling pairs (ASPs) with Alzheimer's disease (AD) according to NINCDS-ADRDA diagnostic criteria and with onset ages of >/=65 years using 237 microsatellite markers separated by an average distance of 16.3 cM. Data were analysed by SPLINK and MAPMAKER/SIBS on the whole sample of 292 ASPs and subsets of 162 ASPs where both members possessed an apolipoprotein E (APOE)straightepsilon4 allele and 63 pairs where neither possessed anstraightepsilon4 allele. Sixteen peaks with a multipoint lod score (MLS) >1 either in the whole sample, the straightepsilon4-positive or -negative subgroups were observed on chromosomes 1 (two peaks), 2, 5, 6, 9 (two peaks), 10 (two peaks), 12, 13, 14, 19, 21 and X (two peaks). Simulation studies revealed that these findings exceeded those expected by chance, although many are likely to be false positives. The highest lod scores on chromosomes 1 (MLS 2.67), 9 (MLS 2.38), 10 (MLS 2.27) and 19 (MLS 1.79) fulfilLander and Kruglyak's definition of 'suggestive' in that they would be expected to occur by chance once or less per genome scan. Several other peaks were only marginally less significant than this, in particular those on chromosomes 14 (MLS 2.16), 5 (MLS 2.00), 12, close to alpha2-macroglobulin (MLS 1.91), and 21, close to amyloid precursor protein (MLS 1.77). This is the largest genome scan to date in AD and shows for the first time that this is a genetically complex disorder involving several, perhaps many, genes in addition to APOE. Moreover, our data will be of interest to those hoping to identify positional candidate genes using information emerging from neurobiological studies of AD.

A chromosome 4p haplotype segregating with Parkinson's disease and postural tremor

We investigated a large family with levodopa-responsive, Lewy body parkinsonism in which the disease segregates as an apparent autosomal dominant trait. After performing a genome screen, we identified a chromosome 4p haplotype that segregates with the disease. However, this haplotype also occurs in individuals in the pedigree who do not have clinical Lewy body parkinsonism but rather suffer from postural tremor, consistent with essential tremor. These data demonstrate a new locus for Lewy body parkinsonism and suggest that in some circumstances postural tremor can be an alternative phenotype of the samepathogenic mutation as Lewy body parkinsonism.

Genetic dissection of Alzheimer's disease and related dementias: amyloid and its relationship to tau

Molecular genetic analysis is revealing the etiologies of Alzheimer's disease (AD) and related dementias. Here we review genetic and molecular biological evidence suggesting that the peptide A beta 42 is central to the etiology of AD. Recent data also suggests that dysfunction in the cytoskeletal protein tau is on the pathway that leads to neurodegeneration and dementia. Tau is produced either indirectly, by A beta 42, or directly, in some forms of frontotemporal dementia by mutations in tau itself. These data support are refine the amyloid cascade hypothesis for AD and suggest that understanding the causes and consequences of tau dysfunction is an important priority for dementia research.

Cloning and characterization of the presenilin-2 gene promoter

Mutations in the presenilin-2 (PS-2) have been shown to cause early onset Alzheimer's disease (AD) in a series of families known as the Volga Germans and in an unrelated Italian kindred. Expression of the PS-2 gene is regulated during AD, aging, development and brain injury. Although expressed primarily in neurons, enhanced levels of PS-2 have been reported in astrocytes activated by neuronal damage. Understanding the regulation of the PS-2 gene may thus provide an insight into its role in AD. We have isolated a 3635 bp DNA fragment that contains 2934 bp of DNA sequence upstream from the PS-2 gene. Primer extension analysis was used to map three major transcriptional start sites within the PS-2 gene. The promoter sequence, upstream of each transcriptional start site, does not contain TATA or CAAT boxes but does contain several GC rich sites (Sp-1 and AP-2). A reporter gene construct containing the PS-2 promoter (PS2P, -2934 to +702) transfected into M17 cells drives basal transcription to 20% of the levels of the SV-40 viral promoter. Addition of NGF to PC-12 cells was found to upregulate the PS2P promoter and an NGF-responsive element was localized by deletional analysis between -403 and +13 within the promoter. Since the PS-2 gene has multiple start sites and the upstream sequence is GC rich with no TATA box, the PS-2 promoter is consistent with the GC class of 'housekeeping' genes.

A variant of Alzheimer's disease with spastic paraparesis and unusual plaques due to deletion of exon 9 of presenilin 1

We describe a novel variant of Alzheimer's disease (AD) in a Finnish pedigree with 17 affected individuals of both sexes in three generations. The disease is characterized by progressive dementia which is, in most cases, preceded by spastic paraparesis. Neuropathological investigations revealed numerous, distinct, large, round and eosinophilic plaques as well as neurofibrillary tangles and amyloid angiopathy throughout the cerebral cortex. The predominant plaques resembled cotton wool balls and were immunoreactive for Abeta but lacked a congophilic dense core or marked plaque-related neuritic pathology. Molecular genetic analysis revealed that the disease was caused by a deletion of exon 9 (delta9) of the presenilin 1 (PS1) gene from the mRNA: unlike previous examples of the delta9 variant, the deletion was not caused by a splice acceptor site mutation.

Low frequency of alpha-synuclein mutations in familial Parkinson's disease

A mutation in exon 4 of the alpha-synuclein (NACP) gene has been reported to explain the chromosome 4 linkage to autosomal dominant Parkinson's disease. We developed primers and methods for exonic sequencing of this gene and sequenced the entire coding region of the gene in 6 families with autosomal dominant disease and in 2 cases of lytico and bodig from Guam. In addition, we have sequenced exon 4 of this gene in 5 cases of familial disease and have screened for the specific mutation (A53T) in a 40 cases of idiopathic Parkinson's disease, 3 cases of multisystem atrophy, and 15 cases of Lewy body dementia. We have found no genetic variation in the gene. We discuss these findings with respect to both the epidemiology of Parkinson's disease and the possibility that NACP is not the chromosome 4 locus for disease.

Increased Abeta42(43) from cell lines expressing presenilin 1 mutations

Mutations in the presenilin 1 (PS1) gene on chromosome 14 are a major cause of autosomal dominant, early-onset Alzheimer's disease. Here, we show that transfecting cells with several mutant, but not wild-type, PS1 cDNAs alters the processing of the amyloid precursor protein (APP) such that more Abeta42(43) is produced, confirming and extending several recent reports. The most effective mutation in this regard was the exon 9 splice-out mutation (delta9). The correlation between the size of the effect on APP processing and the age of onset of disease assessed in families with the mutations was not informative, and the possible reasons for this are discussed.

Early-onset Alzheimer's disease with a presenilin-1 mutation at the site corresponding to the Volga German presenilin-2 mutation

We describe a new mutation causing Alzheimer's disease (AD) in presenilin-1 (N135D) that is at the homologous site to the presenilin 2 mutation (N141I) in Volga German kindreds. The phenotype of PS1 N135D is an early-onset (34-38 years) disease. The mutation forms part of, and extends, the alpha-helical array of mutations in transmembrane 2 of the presenilins and leads to the suggestion that disruption of this helical face is the molecular insult that leads to disease.

A further presenilin 1 mutation in the exon 8 cluster in familial Alzheimer's disease

Recent studies suggest that mutations in the presenilin 1 gene, which encodes a polypeptide predicted to be a multispanning membrane protein, are responsible for the majority of cases of early onset, autosomal dominant Alzheimer's disease. Here we describe a further mutation in the presenilin 1 gene (R269G) in a family with early onset Alzheimer's disease. This mutation is in exon 8 which appears to be a favoured region for pathogenic mutations. In the presenilin protein the region coded for by this exon is likely to comprise a domain located on the membrane surface. We discuss the likely effects of the exon 8 mutations on the structure of the exon and in the pathogenesis of the disease.

Structure and alternative splicing of the presenilin-2 gene

Missense mutations in the presenilin-1 (PS-1) and presenilin-2 (PS-2) genes have been shown to be causes of autosomal dominant Alzheimer's disease (the AD3 and AD4 loci, respectively). Alternative splicing has previously been reported in the PS-1 gene. In this study, elucidation of intron/exon boundary sequences revealed that PS-2 is encoded by 10 coding exons. In addition, PS-2 cDNA cloning and RT-PCR using RNA from a variety of normal tissues revealed the presence of alternatively spliced products. These products included species with in frame omissions of exon 8 and simultaneous omissions of exons 3 and 4.

Complete analysis of the presenilin 1 gene in early onset Alzheimer's disease

The presenilin 1 gene has recently been identified as the locus on chromosome 14 which is responsible for a large proportion of early onset, autosomal dominantly inherited Alzheimer's disease (AD). We have elucidated the intron/exon structure of the gene and designed intronic primers to enable direct sequencing of the entire coding region (10 exons) of the presenilin gene in a large number of families. This strategy has enabled us to find a further two novel mutations in the gene. We discuss the distribution of mutations and the proportions of autosomal dominant AD with a mean age of onset below 60 years caused by mutations in this gene.

The role of presenilin 1 in the genetics of Alzheimer's disease

Approximately 75% of AD patients have an onset of the disease after the age of 60 years, and 60% of AD patients have no family history of the disease. Some cases of EOAD are clearly inherited in an autosomal-dominant manner. The beta APP gene on chromosome 21, the PS-1 gene on chromosome 14, and the PS-2 gene on chromosome 1 have all been characterized as genes in which mutations lead to familial EOAD. For LOAD, the work on ApoE indicates that the epsilon 4 allele is a risk factor for developing AD. However, 35-50% of all AD patients do not have an epsilon 4 allele. Other loci contributing to LOAD remain to be mapped and characterized. As in other complex disorders, these additional loci may involve genetic interactions with the known AD loci. Identification of all susceptibility loci for AD is a major goal in resolving the pathogenesis of AD.

A mutation in Alzheimer's disease destroying a splice acceptor site in the presenilin-1 gene

A series of mutations has been reported in the presenilin-1 (PS-1) gene which cause early onset Alzheimer's disease (AD). The mutations reported to date have encoded missense mutations which alter residues conserved between PS-1 and the presenilin-2 (PS-2) gene. We have recently determined the intron/exon structure of the PS-1 gene and this information has been used to identify a mutation in the splice acceptor site for exon 9 in a family with early onset AD. Amplification of cDNA from lymphoblasts of affected individuals revealed that the effect of the mutation was to cause splicing out of exon 9, however it does not change the open reading frame of the mRNA. The importance of this observation is discussed.