APP and Alzheimer disease: Since the molecular cloning of APP more than 30 years ago (Goldgaber et al,1987; Kang et al,1987; Tanzi et al,1987) and the subsequent identification of autosomal dominant APP mutations linked to familial forms of AD (Goate et al,1991), the intensely studied role of APP and Aβ for AD etiology had occluded the analysis of its physiological functions (Müller et al,2017).