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K. Ikeda1), H. Akiyama1), T. Arai1), H. Mori2), N. Sahara2), M. Sakata3), T. Mizutani3) Department of Neuropathology1) and Molecular biology2), Tokyo Institute of Psychiatry, 2-1-8 Kamikitazawa, setagaya-ku, Tokyo 156, Japan Department of Neuropathology, Tokyo Metropolitan Institute of Gerontology3), 35-2 Sakaecho, Itabashi-ku, Tokyo 173, Japan

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Neuropathological survey of the patients clinically diagnosed as senile dementia of Alzheimer's type (SDAT) or probable SDAT has revealed that a group of patients characterized with numerous neurofibrillary tangles (NFTs) and no or rare senile plaques in the cerebral cortex can be separated from a typical SDAT population. The onset of dementia in such patients is in their eighties or even later. The initial symptom is gradually progressive forgetfulness which is often accompanied by a delirious state or other psychiatric manifestations. In contrast to their profound memory disturbances, the cognitive functions, affective contiguity and personality of these patients are relatively spared. Neuropathologically, senile plaques are entirely absent or, if present, extremely rare. NFTs are abundant and are distribute in their preferential sites such as the hippocampal region. The ultrastructure and immunohistochemical profiles of NFTs in these patients are similar to those of typical SDAT. Approximately 5% of clinically diagnosed SDAT or probable SDAT patients belong to this group.

Whether this patient group is a subtype of SDAT or not remains unclear. The search for the allele of apolipoprotein E is now in progress. So far, the data from 7 patients are available. The genotype of these 7 patients is e2/4, 2/4, 2/2, 3/3, 2/2, 2/3, and 2/3 respectively. Though the current evidence is based on a very limited number of cases, such a high incidence of e2 allele together with the absence of amyloid b protein deposits suggests that this is a separate disease entity from SDAT. An alternative interpretation would be that some unknown factor(s) might suppers the deposition of amyloid b protein and modulate the clinical picture of SDAT in these patients.