In CSF, persons with CAA have reduced Aβ40 compared to both controls and AD; reduced Aβ42 compared to controls (though similar Aβ42 compared to AD); reduced Aβ42/40 compared to controls (though higher compared to AD); and elevated total‐tau and phosphorylated‐tau compared to controls, but lower than AD.21 This evidence concerns the gene MAPT and Alzheimer disease.