The expression level of DPP9 in COVID-19 male patients was higher than that in female patients (Sharif-Zak et al., 2022), and the expression of DPP9 was correlated with gonadal steroids (Mayneris-Perxachs et al., 2021), suggesting that gender might be an important influencing factor. The gene discussed is DPP9; the disease is COVID-19.