Besides, GalCer can be produced by bacteroides (a member of the human gut microbiome),23 which is known to downregulate ACE2 expression in murine gut, and bacteroides showed significant inverse correlation with fecal SARS-CoV-2 viral load in patients with COVID-19.24 Therefore, the decreased expression of CerG1 might reflect the reduction of bacteroides, which was correlated with the severity of COVID-19. This evidence concerns the gene ACE2 and COVID-19.