As most of the vascular resistance within the brain parenchyma is located in capillaries.50–52 This could significantly reduce cerebral blood flow (as occurs following pericyte-mediated constriction after stroke and in Alzheimer’s disease).14,15 In addition, constriction of some capillaries but not others can lead to tissue hypoxia even without a large reduction of blood flow.55,56 Presumably the same mechanisms could evoke a similar reduction of blood flow and oxygen delivery in other organs where pericytes (or other nearby cells) express ACE2 and AT1 receptors. The gene discussed is ACE2; the disease is Alzheimer disease.