DPP9 and COVID-19: Studies implicated the DPP9 gene was involved in Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Pairo-Castineira et al., 2021; Wang et al., 2021; Horowitz et al., 2022; Sharif-Zak et al., 2022).