APP and Alzheimer disease: To further elucidate the potential contributions of APP to the Aβ diurnal pattern and the balance of the α- and β- pathways in APP processing, we measured APP proteolytic products sAPPβ, sAPPα, Aβ40, and Aβ42 over 36 hours in CSF from cognitively normal young and elderly participants, as well as in CSF from participants with AD.