TMPRSS2 and viral infectious disease: In order to map host genetic variants, we focused on 496 genes implicated in SARS-CoV-2 infection (Additional file 2: Table S6): ACE2 and TMPRSS2, key genes for viral entry [28]; CTSL, CTSB, and BSG, which may have a role as alternative routes for viral entry [28, 32]; host genes with protein-protein interactions with viral proteins [29]; differentially expressed genes as a response to the infection in cultured airway epithelial cells [30]; genes involved in autophagy that might counteract viral infection [31]; and other high interest genes from the COVID-19 Cell Atlas.