APP and Alzheimer disease: In the 1990s, the pathogenic relationship between amyloid precursor protein (APP), presenilin1 (PSEN1) and AD was proven by genetic methodology, in which PSEN1, as the active site of the secretase, can influence the function of neuron γ secretase in AD patients, increase the level of plasma Aβ42 and accelerate the development of AD (Borchelt et al., 1996).