SLC7A5 and Alzheimer disease: Isoleucine and valine, branched chain amino acids (BCAA), whose disturbances were observed in AD (Gonzalez-Dominguez et al., 2015; Pan et al., 2016), could pass through the blood–brain barrier catalyzed by L-type amino acid transporter 1 in a competitive mode with long-chain neutral amino acids (LNAA) such as phenylalanine and tryptophan (Choi and Pardridge, 1986).