DPP9 and COVID-19: When adding the naïve controls (n = 954; Methods section), the rs2109069 in DPP9 gene and rs657152 in ABO gene were significantly associated with COVID-19 severity (for rs2109069 A allele: P = 0.0042, OR = 1.33; for rs657152 A allele: P = 0.0017, OR = 1.27).