APP and early-onset autosomal dominant Alzheimer disease: In addition to the proteolytic processing of NRG1, BACE1 is one of the β-secretase enzymes required for the endoproteolysis of the amyloid precursor protein (APP), and hence the production of the 42-amino acid long β-amyloid peptide (amyloid-β42), widely considered to be neurotoxic and crucial during the early onset of Alzheimer’s disease (Vassar, 2004).