APP and Alzheimer disease: AD is neuropathologically characterized by extracellular accumulation offibrillar amyloid beta peptide (Aβ in senile plaques, intraneuronalneurofibrillary tangles consisting of abnormally hyperphosphorylated tauprotein, oxidative neuronal damage, synaptic degeneration and, more recently, bythe build-up of soluble Aβ oligomers.17-19 Aggregationof Aβ appears to initiate a cascade of events that leads to neuronaldysfunction (likely explaining the early cognitive decline characteristic of AD)and, ultimately, to nerve cell death.