Moreover, histological analysis of post-mortem brain tissue has reported that the BBB’s breakdown in AD patients reduced cerebral blood flow, neural loss, and behavioral deficits independent of Aβ, and it was more noticeable among APOE4 carriers compared to those with APOE3 or APOE2 [94,95,96,97,98]. The gene discussed is APOE; the disease is Alzheimer disease.