Yet, the serum levels of the neutral amino acids, including TYR and the essential amino acid tryptophan (TRP), were reduced in ACE2-deficient mice due to the lack of intestinal B0AT1, and indeed, a protein free-diet was reported to worsen DSS-induced colitis in WT mice to levels seen in ACE2 knockouts. Here, SLC6A19 is linked to colitis.