The reduction of several BBB efflux transporters, such as ABCB1 (P‐gp), ABCG2, OATP2B1, and ENT1 in AD patients is detected in Aβ‐accumulated brain districts like gray matter and hippocampus, while much abundant in cerebellum that are not affected by AD pathology [212]. The gene discussed is ABCG2; the disease is Alzheimer disease.