APP and early-onset autosomal dominant Alzheimer disease: Since several studies have implicated β-amyloid (Aβ) peptides in the etiology of Alzheimer's disease (AD) [46-48] and because Aβ is produced by the proteolytic cleavage of the amyloid precursor protein by β- and γ-secretase, γ-secretase inhibition is thought to have a therapeutic benefit for AD.