Presenilin immunoreactivity in Alzheimer's disease.

The role of presenilin (PS) mutations in familial Alzheimer's disease (AD) may be as a toxic gain of function, but in sporadic disease their contribution is more difficult to understand. In this study, we investigated PS proteins in sporadic AD by comparing the immunocytochemical profiles in sporadic AD with control brains using a quantitative immunocytochemical approach to both the N- and C-terminals of PS1 and PS2. Ten patients with pathologically proven AD (using modified Consortium to Establish a Registry for Alzheimer's Disease [CERAD] criteria) and 10 controls were age- and sex-matched. The immunocytochemical primary antibodies were affinity-purified goat polyclonal antibodies and the secondary antibodies were biotinylated donkey anti-goat to the N- and C-terminal of both PS1 and PS2. The number of PS-containing neurones was quantified manually and without the knowledge of the diagnosis. We found no significant differences in the number of PS1- and PS2-containing neurones in three anatomical regions for both N- and C-terminals between AD and controls. Our findings argue in favour of functional changes in PS molecules contributing to the pathogenesis of AD and are consistent with the hypothesis of dysfunction of the entire gamma-secretase complex, of which PS proteins are a constituent.

Polymorphisms in the tau gene in sporadic frontotemporal dementia and other neurodegenerative disorders.

The tau gene on chromosome 17 is fundamental in the pathogenesis of a number of neurodegenerative disorders. Mutations in tau are found in familial frontotemporal dementia (FTD) and the A0/A0 genotype associated with progressive supranuclear palsy (PSP). This study investigates the hypothesis that polymorphisms in the tau gene are associated with sporadic FTD. Western Australian populations of patients with sporadic frontotemporal dementia, PSP, Alzheimer's disease (AD), Huntington's disease (HD) and normal controls were studied. A new method was developed using fluorescently labelled probes to determine polymorphisms in the GT repeat region of intron 9. The A0/A0 genotype was found in 95% of PSP patients (n=20), 58.3% of FTD patients (n=48), 60.8% of AD patients (n=52), 75% of HD patients (n=40), and 75% of normal controls (n=40). None of these differences in genotype frequency were found to be significant by the Fisher exact test (P > 0.05). There were no significant differences in the frequencies of A0/A3 and A0/A1 haplotypes. We have not observed a significant increase in the A0/A0 genotype frequency in sporadic frontotemporal dementia suggesting that this polymorphism is unlikely to be related to the development of this condition. Furthermore, we have observed an increase in the A0/A0 genotype in PSP which did not reach statistical significance, suggesting that there may be population differences in the role of genetic factors in conferring risks to neurodegenerative disorders. Our work does not exclude that tau may interact with other genetic factors.

The mRNA of the NR1 subtype of glutamate receptor in Alzheimer's disease.

Glutamate has been implicated in the pathogenesis of Alzheimer's disease (AD). Controversial data exists regarding changes in the N-methyl-D-aspartate (NMDA) receptor complex in AD. We wished to elucidate the hypothesis that the NMDA receptor system is involved in the pathogenesis of AD using a gene expression approach targeting the mRNA of the universal subtype of the NMDA receptor NR1. This was performed using in situ hybridization and antisense 35S-labelled oligonucleotides on brain tissue collected at post-mortem. Relative mRNA expression was measured in standardised optical density units (OD units) using videodensitometry without knowledge of the diagnosis. The study population consisted of AD (n = 6) and neurodegenerative non-Alzheimer controls (non-AD, n = 14). Gene expression was measured in the frontal lobe, superior temporal gyrus and three areas within the hippocampus. We have observed no significant differences in the relative mRNA expression of the NR1 subtype of glutamate receptor in the following regions: frontal lobe AD = 60.7 +/- 14.1 OD units mRNA (x +/- 1SE) vs 52.6 +/- 1 in non-AD (Mann-Whitney test, p = 0.477); the superior temporal gyrus: AD = 53.3 +/- 13.9 vs 38.2 +/- 7 (p = 0.37); the CA1 region: AD = 37.8 +/- 7.75 vs 81.5 +/- 25.7 (p = 0.66); subiculum AD = 46.7 +/- 11.0 vs 105 +/- 43.3 (p = 0.82); parahippocampal gyrus AD = 36.6 +/- 9.3 vs 81.7 +/- 40.6 (p = 0.90). There were trends to a reduction in NR1 mRNA in the hippocampus and increased NR1 within the frontal and superficial temporal gyrus which were not significant. There was variation within and between all patients with and without AD in the magnitude of NR1 expression in all anatomical regions studied. The findings suggest heterogeneity in the involvement of the post-synaptic glutamatergic system in AD.

A new PRNP mutation (G131V) associated with Gerstmann-Sträussler-Scheinker disease.

BACKGROUND: Gerstmann-Sträussler-Scheinker disease is a rare form of prion disease. OBJECTIVE: To determine the prion mutation in a 51-year-old man without a family history of neurologic disease who died from Gerstmann-Sträussler-Scheinker disease. PATIENT AND METHODS: The patient was a 51-year-old man who died after a 9-year illness characterized by dementia and eventually ataxia. Neuropathologic studies were performed, the results of which revealed abundant prion protein-immunopositive amyloid plaques in the cerebellum without spongiform degeneration. RESULTS: Genetic analysis of the prion protein gene showed a novel mutation at codon 131 that caused a valine-for-glycine substitution (G131V) and homozygosity at codon 129 (129M). Proteinase K-resistant prion protein was detected by Western blot analysis. CONCLUSIONS: This is the first mutation described in the short, antiparallel beta-sheet domain of the prion protein. This report highlights the importance of genetic analysis of patients with atypical dementia even in the absence of a family history.

Amyloid precursor protein gene isoforms in Alzheimer's disease and other neurodegenerative disorders.

Differential expression of the amyloid precursor protein gene (APP) may be important in the development of amyloidosis in Alzheimer's disease (AD) and experimentally in the brain's response to injury. Controversial data suggests that APP isoforms containing the Kunitz protease inhibitor isoform (APP KPI+) are over expressed in the brains of patients with AD when compared to the non-Kunitz protease inhibitor containing isoforms (APP KPI-). We have investigated this hypothesis using a quantitative analysis of gene expression on brain tissue collected at post-mortem. In situ hybridization has been used with synthetic oligonucleotide probes labelled with 35S to detect the two principal splice variants of APP: APP 695 (KPI-) and APP 751 (KPI+). A prospective brain bank of frozen brain specimens has been established and includes pathologically proven AD (n=15) and other neurodegenerative disorders as controls (n=18). The controls consist of frontal lobe atrophy (n=4), Huntington's disease (n=5), Parkinson's disease (n=4), motor neuron disease (n=2), multi-infarct dementia (n=1), multisystem atrophy (n=1), and subacute sclerosing panencephalitis (n=1). We have observed no significant differences in the expression of APP 695 KPI- mRNA in frontal lobe: 17.49+/-3.26 optical density (OD) units of mRNA expression in AD vs. 16.13+/-1.76 OD units mRNA in controls (P=0.80, linear regression); or temporal lobe: 14.73+/-2.96 in AD vs. 16.49+/-2.15 in controls (P=0.55). No significant differences have been found in APP 751 KPI+ in frontal lobe: 12.86+/-2.98 in AD vs. 13.70+/-2.88 in controls (P=0.97); and temporal lobe: 13.31+/-4.93 in AD vs. 11.07+/-1.99 in controls (P=0. 65). Analysis of the ratios of APP 751 KPI+ OD units of mRNA to APP 695 KPI- mRNA revealed a trend to an increased ratio which did not reach statistical significance: frontal lobe APP 751 KPI+/APP 695 KPI- 1.92+/-1.04 in AD vs. 0.86+/-0.17 in controls (P=0.54); temporal lobe 2.54+/-1.59 in AD vs. 0.96+/-0.11 controls (P=0.34). Our data has not revealed differential expression of APP mRNA isoforms in AD and supports the hypothesis that post-translational events in APP metabolism are important in amyloidogenesis and the pathogenesis of AD.