BBB dysfunction could lead to a chain of events in neurodegenerative disorders, including increased BBB permeability, microbleeds, impaired glucose transport, impaired P-glycoprotein function, perivascular deposits, and the accumulation of amyloid-β (Aβ), especially in AD pathology, because the BBB is what removes Aβ across the barrier. This evidence concerns the gene ABCB1 and Alzheimer disease.