Furthermore, altered P-gp function at the BBB has been proposed as a possible etiology of neurodegenerative disease; for example, decreased P-gp function may decrease clearance of β-amyloid from interstitial fluid in the brain to the plasma, which would result in a predisposition for β-amyloid deposition in Alzheimer’s disease [14–20]. The gene discussed is PGP; the disease is early-onset autosomal dominant Alzheimer disease.