APP and Alzheimer disease: One of the main pathological changes caused by AD is senile plaque deposition in the brain, which mainly consists of Aβ that comes from amyloid precursor protein (APP) after being sequentially cleaved by γ-secretase and β-site amyloid precursor protein cleaving enzyme 1 (BACE1), also called β-secretase 1, a key gene for Aβ accumulation in the brain of AD patients [12, 13].