SIT1 and COVID-19: A significantly higher frequency of the risk allele for severe COVID-19 was found on chromosome 3, which codes for the SIT1 amino acid transporter as well as receptors for inflammatory cytokines, CC-motif chemokine receptor 9 (CCR9) and the C-X-C motif chemokine receptor 6 (CXCR6) among other genes [137].