THOP1 and Alzheimer disease: Prior to the discovery of the transmembrane, aspartic acid protease, BACE, EP24.15 was thought to be the β-secretase activity initiating the processing of the APP into Aβ upon purification from human AD brains (Papastoitsis et al., 1994) or from platelets and megakaryocytes (Abraham et al., 1999).