Implications of the neuropathology of HIV encephalitis for the pathogenesis of Alzheimer disease.

The strong familial association of Alzheimer disease (AD), the difficulty in transmitting the disease to animals, the mapping of the amyloid gene to human chromosome 21, and the non-inflammatory neuropathology have all been considered evidence against a viral etiology for this disease. However, unconventional slow viral infections share some of these traits with AD and yet they are caused by retroviruses or suspected viruses. The recent discovery of 2 human retroviruses causing central nervous system pathology similar to spongiform encephalopathies should prompt renewed search for retroviral causes of human neurodegenerative diseases.