APP and neurodegenerative disease: AD is a neurodegenerative disease characterized by intracellular aggregates of neurofibrillary tangles (NFTs) made of hyperphosphorylated and truncated tau proteins, and the extracellular deposition of amyloid beta (Aβ) peptides generated through the proteolytic cleavage of the amyloid precursor protein (APP) [135,136].