The tauopathies are a class of diseases caused by misfolding of the tau protein. Tau prions begin replicating spontaneously in the frontal lobes.

Tau prions are observed in frontotemporal dementia (FTD), posttraumatic stress disorders (PTSD), dementia pugilistica, and chronic traumatic encephalopathy (CTE), which has been seen in boxers, football and hockey players, and soldiers after episodes of traumatic brain injury (TBI).

Many symptoms of PTSD resemble those of the FTDs: changes in personality, behavior, sleep patterns, and executive function dominate these illnesses. Behavioral alterations range from lethargy to disinhibition; apathetic patients may become socially withdrawn. Insomnia and nightmares are common, as are drug addiction and alcoholism. Violent mood swings from euphoria to depression can precede suicide.