DPP9 and respiratory system disorder: Variants identified in these COVID-19 GWAS are linked to viral entry into host cells (SLC6A20, SFTPD, and TMPRSS2), the type I interferon pathway (IFNAR2, TYK2, JAK1, IRF1, IFNA10, TLR7, and DOCK2), the inflammatory pathway (OAS gene cluster, DPP9 and TYK2), as well as lung function and respiratory diseases (such as MUC5B, DPP9, and FOXP4).