CTE cannot be diagnosed until the patient has died and their brain examined. But doctors said there are symptoms such as changes in cognition, mood and behavior. The American Brain Foundation said they can include difficulty thinking, short- and/or long-term memory loss, depression, anxiety, paranoia, headaches and suicidal thoughts or behavior.

The gunman in the deadly Midtown Manhattan shooting, Shane Tamura, wrote about the brain disease CTE in a note obtained by investigators.

CTE is defined as a progressive neurodegenerative disease that causes brain damage similar to what’s seen in patients with Alzheimer’s disease, per the National Institutes of Health (NIH). There is a known link between repeated head trauma, contact sports, and the development of CTE.