ABO and respiratory failure: In addition to ABO blood type, receptors, and immune genes, GWAS studies on COVID-19 have revealed the association of SLC6A20 (rs2271616), LZTFL1 (rs10490770, rs11385942, rs73064425), and DPP9 (rs2109069) genes with respiratory failure caused by COVID-19 infection and critical illness [5,6,36].