ACE2 and Cowden disease: In SARS-CoV-2-infected or Chron’s disease (CD) patients, decreased expression of transmembrane ACE2 due to cleavage by a disintegrin and metallopeptidase domain 17 (ADAM17) or interaction with SARS-CoV-2 may interrupt the absorption of tryptophan, which potentially leads to dysregulation of the gut microbiota.