APP and Alzheimer disease: While Aβ40 is the principal component of CAA in AD [9], the presence of Aβ42 in the leptomeningeal blood vessels of Aβ-inoculated AppNL−F mice likely reflects the presence of the Iberian/Beyreuther APP mutation, which results in a large increase in the Aβ42:Aβ40 ratio [22, 51].