APP and amyloidosis: Amyloid plaques are extracellular aggregates made of amyloid-β (Aβ) peptide, which derives from the alternative amyloidogenic processing of the amyloid precursor protein (APP), by the β-secretase [encoded by beta amyloid cleaving enzyme 1 (BACE1)], and the γ-secretase [whose catalytic subunit is encoded by presenilin 1 (PSEN1)].