Presenilin‐1 protein expression in familial and sporadic Alzheimer's disease

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Abstract
Mutations of the presenilin PS1 and PS2 genes are closely linked to aggressive forms of early‐onset (PS1 complementary DNA, brain biopsy specimens from demented patients, and postmortem samples of frontal neocortex from early‐onset familial Alzheimer's disease cases (PS1 and PS2), lateonset sporadic Alzheimer's disease cases, and cases of other degenerative disorders. This truncated polypeptide contains the N‐terminus of PS1 and appeared unchaged across cases. In 2 early‐onset cases linked to missense mutations in the PS1 gene, a PS1 immunoreactive protein (∼49 kd) accumulated in the frontal cortex. This protein was similar in size to full‐length PS1 protein present in transfected cells overexpressing PS1 complementary DNA, and in lymphocytes from an affected individual with a deletion of exon 9 of the PS1 gene, suggesting that mutations of the PS1 gene perturb the endoproteolytic processing of the protein. Immunohistochemical studies of control brains revealed that PS1 is expressed primarily in neurons, with the protein localized in the soma and dendritic processes. In contrast, PS1 showed striking localization to the neuropathology in early‐onset familial Alzheimer's disease and sporadic Alzheimer's disease cases. PS1 immunoreactivity was present in the neuritic component of senile plaques as well as in neurofibrillary tangles. Localization of PS1 immunoreactivity in familial and sporadic Alzheimer's disease suggests that genetically heterogeneous forms of the disease share a common pathophysiology involving PS1 protein.