The protein acid protease active in intracellular protein breakdown and involved in the pathogenesis of several diseases such as breast cancer and possibly Alzheimer disease. It is specificity similar to, but narrower than, that of pepsin A and it does not cleave the 4-Gln-|-His-5 bond in B chain of insulin. It consists of a light chain and a heavy chain and expressed in the aorta extrcellular space. The Val-58 allele is significantly overrepresented in demented patients (11.8%) compared with non-demented controls (4.9%). Carriers of the Val-58 allele have a 3.1-fold increased risk for developing AD than non-carriers.It belongs to the peptidase A1 family