GWAS of COVID-19 susceptibility have, however, consistently reported a signal in the ABO locus (Bhattacharjee et al., 2020; Shelton, 2020), despite prior observations that controls used in the first published GWAS of COVID-19 (Ellinghaus et al., 2020) may be over-represented for blood group O (the most common blood group) and can result in associations due to selection bias. The gene discussed is ABO; the disease is COVID-19.