Signal pathway analysis of COVID-19 brains showed that elements of nervous system development, retrograde neurotrophin signaling, neuroprotection and brain-derived neurotrophic factor signaling pathways were downregulated (Fig. 4e).38,39 Multiple molecules and pathways as well as protein–protein interactions were involved in COVID-19 neuropathology (Fig. 4f). The gene discussed is BDNF; the disease is COVID-19.