APOE and Alzheimer disease: MRI and [18F]FDGPET provide only modest diagnostic accuracy1 3 and amyloid-β positivity on PET or CSF also occurs frequently in bvFTD patients, especially with advancing age and in the presence of an APOE ε4 allele.42 Tau PET, however, shows very high specificity for tau neurofibrillary tangles in AD dementia,43 as tau PET signal is low in non-AD neurodegenerative disorders (including sporadic forms of bvFTD44).