The neuropathology of AD is first characterized by the extracellular accumulation of amyloid plaques consisting of Aβ1–40 and Aβ1–42 peptides generated by amyloid precursor protein (APP) cleavage by β-site APP-cleaving enzyme 1 (BACE1) and the γ-secretase complex. The gene discussed is BACE1; the disease is Alzheimer disease.