MAPT and Alzheimer disease: Amyloid plaques consisting of the extracellular accumulation of abnormally folded Aβ with 40 or 42 amino acids (Aβ40 and Aβ42), and intracellular neurofibrillary tangles (NFT), mainly composed of paired helical filaments of hyperphosphorylated tau protein, represent the two main neuropathological hallmarks of AD.