Amyloid-β (Aβ), a peptide derived from the amyloid precursor protein (APP) and known to assemble into extracellular amyloid plaques, is hypothesized to initiate AD pathogenesis by stimulating the formation of neurofibrillary tangles and contributing to the development of a cytotoxic environment prone to neurodegeneration (2). The gene discussed is APP; the disease is Alzheimer disease.