γ-Secretase cleavage of APP can produce different lengths of Aβ peptide, while AD-induced PSEN mutations continuously reduce γ-secretase activity, making the γ-secretase and APP complex unstable and easy to dissociate, resulting in longer and more Aβ amyloid peptide (Rajendran et al., 2006). The gene discussed is APP; the disease is Alzheimer disease.