MAPT and Alzheimer disease: Alternatively, in a proportion of participants, their Aβ positivity may be comorbid to a primary non-AD neurodegenerative disorder [40, 41], which would explain the negative tau PET scan because [18F]flortaucipir and [18F]RO948 seem to primarily bind to “AD-like” tau pathology and less to the tau aggregates formed in other tauopathies [42, 43].