SLC38A7 and autism spectrum disorder: Since LAT1 is the primary amino acid transporter in the blood–brain barrier [32] and its deficiency is associated with decreased levels of specific amino acids (branched-chain amino acids, including leucine) in the brain in the pathogenesis of autism spectrum disorder [33,34], we raised the question as to whether HMB has the ability to enhance the expression of LAT1 in hCMEC/D3 cells.