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The tau gene has an important role in frontotemporal dementia (FTD) as pathogenic mutations have been found in hereditary forms of the disease. Furthermore, a certain extended tau haplotype has been shown to increase the risk for progressive supranuclear palsy, corticobasal degeneration, Parkinson's disease and, in interaction with the apolipoprotein E (apoE) epsilon4 allele, Alzheimer's disease. By microsatellite analysis we investigated an intronic tau polymorphism, in linkage disequilibrium with the extended tau haplotype, in FTD patients (n = 36) and healthy controls (n = 39). No association between any of the tau alleles/genotypes and FTD was seen, but certain tau alleles and apoE epsilon4 interactively increased the risk of FTD (p = 0.006). We thus propose that this extended tau haplotype in combination with apoE epsilon4 is a genetic risk factor for FTD.

To analyse the influence of apolipoprotein E (APOE) genotype on the extent of white matter lesions (WMLs) in Alzheimer’s disease (AD), we examined 60 AD patients with magnetic resonance imaging. The WMLs were rated visually in different brain regions. The patients with the APOE genotype σ4/4 had more extensive WMLs in the deep white matter than patients with genotypes σ3/3 and σ3/4. There was a correlation with age for WMLs in the deep white matter in patients with the APOE σ3/3 genotype. In patients carrying at least one σ4 allele, the WMLs showed no age correlation. The results could imply that in APOE allele σ4 carriers, the WMLs represent a pathological process related to the aetiology of the disease.

Tau proteins are central to the neuropathology of Alzheimer’s disease and tau levels in cerebrospinal fluid are elevated in affected individuals. In this study, we investigated the presence of tau in plasma from subjects with Alzheimer’s disease (n = 16), frontotemporal dementia (n = 10), vascular dementia (n = 16) and from healthy controls (n = 15). By using an ELISA with monoclonal tau antibodies, tau immunoreactivity was detected in approximately 20% of the subjects. However, no difference between the disease and control groups was seen. After gel filtration of tau immunopositive plasma, the peak reactivity was found in the 160-kD fraction, indicating the source to be tau-like molecules of high-molecular-weight or polymers of low-molecular-weight tau isoforms. We conclude that measurements of tau in plasma cannot be utilized diagnostically for Alzheimer’s disease or for the other dementias investigated.

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