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 at least four people in a N.Y.C. office building shooting claimed in his suicide note to have chronic traumatic encephalopathy (CTE). Here’s what to know about the degenerative brain disease.

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.