Finally, the up-regulation of the steady-state expression level of ACE2 occurring in several human tissues with an increasing age, mainly in the nasal neuroepithelium, which is one of the most accessible routes of SARS-CoV-2 invasion in the CNS, also accounts for the elevated risk of contracting COVID-19 in the elderly population in connection with poor clinical outcomes [135]. Here, ACE2 is linked to COVID-19.