Our observation that both the mRNA and protein levels of RNF5 are higher in young adults than those in older populations, and its mRNA in mild COVID-19 patients is also more abundant than that of patients with severe disease symptoms (Fig. 7), suggests that the abundancy of RNF5 may be used as a biomarker for COVID-19 prognosis. The gene discussed is RNF5; the disease is COVID-19.