APP and Alzheimer disease: Presenilin (PSEN), the catalytic subunit of γ-secretase [63,64,65,66], may also be modified via mutations in PSEN1 and PSEN2 genes (PSEN1 and PSEN2, respectively) [67], resulting in the destabilization of the γ-secretase–APP interactions [68], causing the generation of longer and more hydrophobic Aβ peptides that contribute to the pathogenesis of AD [41,68,69,70].