Recent evidence also implicated key ABC family BBB transporters in Aβ trafficking between brain and circulatory compartments; luminal efflux transporter ABCG2 has been shown to prevent blood-borne Aβ from entry into the brain[8,15,16], whereas BBB P-glycoprotein/ABCB1's role in the brain clearance of Aβ has been demonstrated in both in vitro and transgenic AD models[16-20]. This evidence concerns the gene ABCG2 and Alzheimer disease.