Central nervous system (CNS) barriers, consisting of the blood–brain barrier (BBB) and blood–cerebrospinal fluid barrier, are responsible for the protection of the microenvironment, which is vital in the regulation of neuronal functions.1There is increasing evidence that abnormal expression of efflux transporters (ATP-binding cassette [ABC]) in the BBB, a semipermeable barrier composed of endothelial cells, causes CNS-related diseases such as Parkinson's disease and Alzheimer's disease (AD). This evidence concerns the gene ABCB6 and Alzheimer disease.