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Neurofibrillary tangles (NFT) are found in several neurodegenerative disorders including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), amyotrophic lateral sclerosis/ parkinsonism-dementia complex of Guam (ALS/PDC) and to a lesser extent Pick's disease (PiD) . In AD, NFT result from the intraneuronal aggregation of pathological tau proteins, composed of a characteristic triplet made of tau 55, 64, and 69, also referred to as tau-PHF or A68 [2,3]. Pathological tau proteins are more extensively phosphorylated than tau proteins found in biopsy-derived materials and show a more acidic isoelectric point [4,5].
In Guamanian ALS/PDC, this tau triplet is also observed . However, PSP and CBD display a typical tau doublet made of tau 64 and 69 [7-11], whereas in PiD cases, a characteristic tau doublet composed only of tau 55 and 64 is observed [10,12].
NFT have also been described in cortical and subcortical regions in the brains of patients who survived the encephalitis lethargica pandemic in the years 1916-1926 and who later developed postencephalitic parkinsonism (PEP) [1,13]. However, the regional and laminar distribution of NFT in PEP differs from that observed in AD . In order to examine whether the pathological tau proteins are found in PEP and differ from those in other neurodegenerative disorders, we performed biochemical and immunohistochemical analyses in different brain regions from PEP cases using Western blotting and specific immunological probes directed against pathological tau proteins.