Beta-amyloid production results from cleavage in the extracellular domain of APP by the beta-secretase (BACE1) , which results in the production of the APP C-terminal fragment C99. This fragment is further cleaved by the gamma-secretase at residues 40-42 to produce beta-amyloid 40 and 42 peptides. Beta-amyloid aggregation and neuritic plaque formation are pathologic hallmarks of Alzheimer disease. This fragment is the amino terminus (1-42) of beta-amyloid.