TMPRSS2 and infection: The determinants of differing susceptibility to SARS-CoV-2 infection mostly appear to entail genes related to the initial stages of infection (i.e., cell entry components such as the cell receptor angiotensin-converting enzyme 2 (ACE2) and the transmembrane serine protease (TMPRSS2) that is utilized for the priming of the spike protein of the virus).