MAPT and Alzheimer disease: Positive amyloid-β biomarkers substantially increase the likelihood that AD is the primary causative mechanism, but given their limited specificity, the possibility of amyloid-β as comorbid pathology cannot be ruled out, especially in older individuals and those who carry APOEε4.38,101 The addition of biomarker evidence for tau pathology further increases the certainty for a bvAD diagnosis (ie, probable bvAD).