SLC6A20 and COVID-19: The first GWAS analysis with 1980 patients with COVID-19 identified two loci associated with the most severe forms of COVID-19: one locus was 3p21.31, which includes the genes SLC6A20, LZTFL1, CCR9, FYCO1, CXCR6, and XCR1, while the other was 9q34.21, including the ABO blood group.