We searched PubMed from March 1, 2020, to Octuber 1, 2022, and references from relevant articles available in English, using the search terms “SARS-CoV-2”, “Alzheimer Disease”, “brain”, “Major Cognitive Disease”,”COVID-19”, “vascular dementia”, “ACE2”, “APOE 4ε”, “neuroinflammation”, “oxidative stress”, “amyloid beta”, “tau”, “grey matter volume”, “lifestyle”, “exercise”, and “therapeutic”. The gene discussed is ACE2; the disease is Alzheimer disease.