APP and Alzheimer disease: In reference to neurodegenerative diseases, the pathology of AD is characterized by the accumulation of senile plaques in the brain, which result in the abnormal amyloid-β (Aβ) peptide processing of the amyloid precursor protein (APP), neurofibrillary tangles as a consequence of tau hyperphosphorylation, synaptic disruption, and selective neuronal loss in brain areas associated with memory and cognition.