APP and Alzheimer disease: Post-mortem examination of AD brains reveals neurodegeneration is highly correlated with accumulation of extracellular Amyloid-β (Aβ) plaques that are produced by the amyloidogenic cleavage of APP by secretases generating aggregating Aβ peptides such as the 42 amino acid (aa) peptide (Aβ42) (Selkoe and Hardy, 2016).