In light of the importance of ACE2 protein in the current pandemic as the SARS-CoV-2 receptor, further investigations on the issue of ACE2 in brains with Alzheimer’s disease are warranted, considering the possibility that the high level of ACE2 in patients with Alzheimer’s may affect their responses to COVID-19. Here, ACE2 is linked to early-onset autosomal dominant Alzheimer disease.