MAPT and early-onset autosomal dominant Alzheimer disease: In carriers of autosomal dominant mutations linked to Alzheimer’s disease, cerebrospinal fluid (CSF) Aβ42 decline can occur 25 years before expected symptom onset, positron emission tomography (PET)-detected Aβ deposition is found 15 years before expected symptom onset, and CSF tau elevation can be found 15 years before expected symptom onset [11].