APP and Alzheimer disease: Experimental proof of the amyloid hypothesis is based on the following facts: (1) amyloidplaques are accumulated in the brains of AD patients; (2) the heritable formof AD (HAD) is caused by nonsense–mutations in theβ–amyloid Aβ precursor protein (АРР); and (3)HAD is also caused by nonsense mutations in presenilins, which form thecatalytic subunit of γ–secretase, an enzyme that cleaves APP.