The β‐secretase BACE1 (β‐site amyloid precursor (APP) cleaving enzyme 1) is a major drug target for Alzheimer's disease (AD), as it catalyzes the first step in amyloid β (Aβ) generation, but has additional substrates and functions, in particular in the brain. The gene discussed is BACE1; the disease is early-onset autosomal dominant Alzheimer disease.