APP and Alzheimer disease: The risk for developing AD increases with age and neuropathologically it is identified with certain types of protein accumulation such as amyloid plaques and neurofibrillary tangles.2,3 Amyloid precursor protein (APP), a transmembrane protein, is the source of beta-amyloid peptide; the proteases known as alpha, beta, and gamma-secretases separate beta-amyloid peptide from APP.