APP and Alzheimer disease: Alzheimer's Disease (AD) is associated with neurofibrillary tangles containing tau proteins, and with extracellular amyloid plaques containing fibrils formed by Aβ(1–40), Aβ(1–42) and Aβ(1–43), amyloid-β (Aβ) peptides generated by intracellular proteolytic cleavage of Amyloid Precursor Protein (APP), specifically the neuronal membrane APP homologue, APLP-1.