Amyloid-beta (Aβ), a peptide derived from APP, is a key component of plaque formation in neurodegenerative diseases such as AD.In AD, amyloid-beta 42 (Aβ42) accumulates in the brain while its blood levels decrease, whereas amyloid-beta 40 (Aβ40) remains relatively stable [8]. The gene discussed is APP; the disease is Alzheimer disease.