SENILE DEMENTIA OF LEWY BODY TYPE AND ALZHEIMER-TYPE ARE BIOCHEMICALLY DISTINCT IN TERMS OF PAIRED HELICAL FILAMENTS AND HYPERPHOSPHORYLATED TAN PROTEIN

We have used biochemical assays to examine cingulate and occipital cor tices from age-matched cases of Alzheimer's disease (AD; n = 12), seni le dementia of the Lewy body type (SDLT; n = 13), Parkinson's disease (PD; 5 nondemented cases and 7 cognitively impaired cases) and control s (n = 11) for paired helical filaments (PHFs), phosphorylated and nor mal tau protein and beta/A4-protein. Whereas cingulate cortex is chara cterised by relatively high densities of cortical Lewy bodies in the S DLT cases and lower numbers in PD, these inclusion bodies were absent in the cingulate cortex from AD and control cases. Protease-resistant PHFs and hyperphosphorylated tau protein were found in AD and, at low levels, in a minority of SDLT cases. Qualitatively, both of these prep arations were indistinguishable in SDLT from those found in AD but lev els of both parameters in SDLT were less than 5% of those in AD. SDLT, PD and control groups did not differ from each other in terms of the quantity of protease-resistant PHFs or the level of hyperphosphorylate d tau. Furthermore, PHF accumulation did not distinguish between PD ca ses with or without dementia. The levels of normal tau protein did not differ between the four groups. beta/A4 protein levels did not distin guish between PD and control groups, between AD and SDLT groups, or be tween SDLT and control groups for either cingulate or occipital cortic es. Thus extensive accumulation of PHFs in either neurofibrillary tang les or dystrophic neurites is not a feature of either SDLT or PD. Our findings provide molecular support for the neuropathological and clini cal separation of SDLT as a form of dementia that is distinct from AD.