LAT and Alzheimer disease: 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.