Amyloid plaques in Guam amyotrophic lateral sclerosis/ parkinsonism-dementia complex contain species of Aβ similar to those found in the amyloid plaques of Alzheimer's disease and pathological aging

The Guamanian amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is characterized by abundant neurofibrillary pathology and neuron loss. In contrast to Alzheimer's disease (AD), where extensive neurofibrillary lesions always occur with deposits of Aβ in numerous amyloid plaques, Aβ-rich amyloid plaques are absent or rare in most ALS/PDC patients. To characterize the amyloid plaques in the latter patients, we probed plaque-rich sections of their brains by immunohistochemistry using well-characterized antibodies to specific epitopes in the N and C termini of Aβ as well as to defined epitopes in hyperphosphorylated tau (PHF-tau). The results indicate that the species of Aβ in the amyloid plaques of ALS/PDC patients resemble those detected in the amyloid plaques of cognitively intact subjects with pathological aging as well as patients with AD. However, the paucity of PHFtau-positive neurites in the ALS/PDC plaques suggests that they reflect pathological aging rather than AD.