“CTE is linked to repetitive brain trauma and has a distinct pathology that can only be diagnosed at autopsy,” says Dr. Ross Zafonte, a principal investigator of the Football Players Health Study at Harvard University and executive vice dean at the University of Missouri School of Medicine.

The progressive brain disease can be caused by repeated trauma to the head and has caused serious health problems for athletes who participate in contact sports, such as football.

The man who killed four people in the New York City skyscraper that is home to NFL headquarters carried a note blaming the league for his mental health problems.