BACE1 and early-onset autosomal dominant Alzheimer disease: Aβ is a proteolytic fragment of the amyloid precursor protein (APP), known for its involvement in Alzheimer's disease.142 APP is produced in neurons, platelets, cardiomyocytes, and all vascular cells.141,142 β-secretase (BACE1) is involved in APP cleavage, and further cleavage by γ-secretases generates peptides of length 40 (Aβ40), which is found in vascular lesions, and 42 (Aβ42), which is associated with brain lesions in Alzheimer’s disease.