Alzheimer’s disease (AD) is characterized by amyloid plaques composed of the β-amyloid (Aβ) peptide surrounded by swollen presynaptic dystrophic neurites consisting of dysfunctional axons and terminals that accumulate the β-site amyloid precursor protein (APP) cleaving enzyme (BACE1) required for Aβ generation. The gene discussed is BACE1; the disease is early-onset autosomal dominant Alzheimer disease.