BACE1 and Alzheimer disease: BACE1 affects the buildup of Aβ in cells and synapses; it is a molecule that is directly related to synaptic functioning.27–29 The majority of BACE1 expression occurs in the brain, and neurons express it abundantly.30 In the brains of AD patients and mice models, accumulation of BACE1 is shown in both normal and dystrophic presynaptic terminals around amyloid plaques.