Relationship between neuronal loss and 'inflammatory plaques' in early onset Alzheimer's disease.

We have previously described a novel 'inflammatory plaque' in the cortex of early onset Alzheimer's disease (EOAD) cases with presenilin 1 mutations (PS1). These plaques are associated with a significant inflammatory infiltrate consisting of reactive microglia and astrocytes. We speculated that these inflammatory plaques might be responsible for the more severe disease process seen in EOAD. In the present study using the superior frontal cortex, 63 EOAD cases with mutations in PS1, presenilin 2 (PS2) and amyloid precursor protein (APP) were categorized as either having inflammatory plaques (13 cases, two APP and 11 PS1) or not. To determine the impact on cell loss, seven EOAD cases with inflammatory plaques (EOIP) and seven EOAD cases without (EONIP) were selected and neuronal cell counts performed. These were compared with neuronal counts taken from the same cortical region of seven control and six sporadic AD cases. Cases with EOAD had significantly less neurones per field compared with sporadic AD and control cases (EOAD = 19.5 +/- 0.8 neurones/field, spAD = 23.7 +/- 1.2 neurones/field, controls = 30.37 +/- 1.2 neurones/field). However, no significant difference in the number of neurones per field was seen in EOAD cases with or without inflammatory plaque pathology (EOIP = 19.2 +/- 1.4, EONIP = 19.7 +/- 0.8). These data demonstrate that EOAD cases exhibit greater neuronal cell loss in the superior frontal cortex than sporadic AD and that this effect is independent of the presence or absence of inflammatory plaque pathology.