Altered chromatin conformation in Alzheimer's disease.

Chromatin samples were prepared from forty human brains. Chromatin was separated into a heavy heterochromatin fraction and two euchromatin fractions: intermediate euchromatin and light euchromatin. Employing a bacterial RNA polymerase as probe, only the euchromatin fractions were capable of RNA synthesis. In Control human brains, in brains of patients with dialysis dementia and in brains of elderly individuals without or with dementia of a type other than Alzheimer's disease, the euchromatin fractions accounted for about 75 per cent of the total DNA. In contrast, in brains of patients with advanced senile dementia or presenile dementia of the Alzheimer type, a wide range of euchromatin content was encountered with an average value of 55 per cent. Heterochromatization occurred in both neuron and glia enriched fractions suggesting that a major alteration in protein metabolism occurs in Alzheimer's disease.