APP and Alzheimer disease: It is well established that the increased amyloidogenic processing of amyloid precursor protein (APP), resulting in augmented production of either total amyloid‐β (Aβ) or a shift in the Aβ1–40:Aβ1–42 ratio toward formation of the more toxic Aβ1–42, are key features underlying the pathogenesis of AD 2, 3.