Biochemical and ultrastructural study of neurofibrillary tangles in amyotrophic lateral sclerosis/parkinsonism-dementia complex in the Kii peninsula of Japan.

Amyotrophic lateral sclerosis/parkinsonism-dementia complex of the Kii peninsula (Kii ALS/PDC) is a neurodegenerative disorder endemic to natives in the southern coast area of the Kii peninsula of Japan. The disorder closely resembles Guamanian ALS/PDC clinically and neuropathologically. The characteristic neuropathological finding is abundant neurofibrillary tangles (NFTs) without amyloid deposition. To elucidate the biochemical properties of hyperphosphorylated tau protein, the major component of the NFTs, we examined Kii ALS/PDC brains by immunoblotting and immunohistochemical analysis using well-characterized anti-tau antibodies specific to phosphorylation-dependent or -independent epitopes. Hyperphosphorylated tau in Kii ALS/PDC had phosphorylated epitopes common to tau of paired helical filaments (PHFs) in Alzheimer disease (AD): immunoblot showed triplet bands composed of 6 tau isoforms. Ultrastructurally, NFTs revealed a twisted filamentous shape similar to PHF of AD. The biochemical properties of its phosphorylated tau protein and the ultrastructural characteristics of the NFTs of Kii ALS/PDC are very similar, if not identical, to PHF tau in AD, although they are different taupopathies.