APP and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease is the most frequent cause of adult dementia (Nichols et al. 2019) and two major histopathological hallmarks have previously been described for this disorder: (i) Extracellular aggregation of amyloid-beta (Aß) peptides derived from the amyloid precursor protein (APP), which leads to the formation of characteristic Aß plaques.