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). The gene discussed is BACE1; the disease is Alzheimer disease.