TMPRSS2 and viral load: Triplication of TMPRSS2, located on chromosome 21, may enhance viral entry in DS and thus increase the likelihood of infection with SARS-CoV-2 as it interacts with the viral S protein to allow SARS-CoV-2 entry into the host cells.7 Viral diseases that use ACE-2-receptor/TMPRSS2 for cell binding/cell entry include influenza, SARS-CoV-1, metapneumovirus and MERS.