One of these challenges is the observation of negative tau PET scans in individuals suspected of having symptomatic AD [4–7] or, conversely, positive tau PET scans in individuals suspected for a non-AD neurodegenerative disorder like frontotemporal lobar degeneration (behavioral or language phenotype) or Parkinsonian disorders [5, 6, 8, 9]. The gene discussed is MAPT; the disease is frontotemporal dementia.