SIT1 and COVID-19: Further, in a genomewide association study of severe COVID-19 a locus spanning six genes showing cross replicating associations with disease severity was identified and, interestingly, one of these genes codes the transporter SIT-1, a protein that interacts with angiotensin converting enzyme 2 (ACE), the SARS-CoV-2 cell receptor [83] and that is directly involved in the transport of proline, an amino acid associated to protein folding.