Bulk and single-cell RNA sequencing in both humans and mouse revealed that ACE2 and coronavirus cell entry-related genes are expressed in respiratory epithelium and olfactory epithelium, but not in olfactory sensory neurons or olfactory bulb neurons, indicating that SARS-CoV-2 may infect nonneuronal cell types in the olfactory bulb and thus lead to anosmia in COVID-19 patients [128]. This evidence concerns the gene ACE2 and COVID-19.