APP and Alzheimer disease: These pathologies cause Aβ accumulation by disrupting the integrity of the BBB and preventing the clearance of neurotoxic molecules (such as Aβ) in the CNS.1Microtubule-associated tau proteins and the Aβ40, Aβ42, the most common form of Aβ produced by cleavage of APP, represent the molecular-level character of AD.