PGP and Alzheimer disease: In addition, Cirrito et al. [19] reported that P-gp deficiency at the BBB increased amyloid-β deposition in a murine model of Alzheimer’s disease, suggesting that P-gp normally discharges Aβ out of the brain or periarterial interstitial fluid, and that perturbation of Aβ efflux directly affects Aβ accumulation within the brain or perivascular areas.