Patients with blood group A have a higher risk of requiring mechanical ventilation and extended ICU stay compared with patients with blood group O.15 These same variations at ABO had known associations with a spectrum of blood coagulation disorders identified in studies pre-dating COVID-19.16–18 The PheWAS of ABO variants identified associations with increased risk of deep vein thrombosis, pulmonary embolism, and other circulatory disorders, in line with prior studies, and recent studies among patients hospitalized with COVID-19.19–23. The gene discussed is ABO; the disease is deep vein thrombosis.