Fourth, since BCAAs compete with neurotransmitter precursors (i.e., aromatic amino acids such as tyrosine, phenylalanine, tryptophan) to enter the brain via the same large amino acid transporter (LAT) [106], it is hypothesized that by gaining access to the brain, high plasma BCAAs interfere with the entry of precursors that would dramatically reduce neurotransmitter synthesis as observed in AD. This evidence concerns the gene SLC38A7 and Alzheimer disease.