AD progresses toward three stages: An early preclinical stage where no symptoms are observed (although the process of Aβ and tau misfolding, spreading, and aggregation are already in progress); a middle stage characterized by the presence of mild cognitive impairment (MCI) where memory and thinking functions are impaired (without significant interferences with the normal life of the patient); and a late-stage marked by the presence of many symptoms of dementia (memory loss, visual/spatial problems, the patient is no longer independent). Here, MAPT is linked to Alzheimer disease.