APP and Alzheimer disease: Moreover, we analysed gene expression levels of beta-secretase 1, also known as beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), the enzyme responsible for amyloid precursor protein (APP) cleavage and subsequent formation of Aβ peptides, including Aβ1-42, which aggregates into bioactive conformational species and likely initiates toxicity in AD.