APP and Alzheimer disease: Most of AD forms are apparently sporadic (sAD) but dominantly inherited familial forms of AD (fAD) have been also reported; including those carrying mutation or duplication of amyloid-β precursor protein (APP) gene or mutations in the presenilin 1 and 2 genes (PS1 and PS2) which encode the major component of γ-secretase enzyme that cleaves APP into amyloid-β peptides and other cleavage fragments (Israel and Goldstein, 2011).