Aβ is a polypeptide consisting of about 42 amino acids, and it is formed by the sequential cleavage of Aβ precursor protein (APP) by β-secretase (β-amyloid cleaving enzyme 1, BACE1) and γ-secretase, which is also found to be the main cleavage pathway of APP in individuals with AD [19,20]. The gene discussed is APP; the disease is Alzheimer disease.