Doctors confirmed that former NFL wide receiver Demaryius Thomas, who was found died in his home in December, had been suffering from stage 2 CTE.
Chronic Traumatic Encephalopathy, or CTE, is associated with symptoms including paranoia and depression. Doctors are Boston University's CTE Centre diagnosed Mr Thomas's condition posthumously.
The cause and manner of Mr Thomas's death have not been released by the county's medical examiner.
He was 33 years old when he died.
Mr Thomas's mother, Katina Smith, said in a statement that she suspected he may have been suffering from CTE in the final months of his life.
"Once I became aware of CTE and began to familiarize myself with the symptoms, I noticed that Demaryius was isolating himself and I saw other changes in him," she said. "He was just so young, and it was horrible to see him struggle. His father and I hope all families learn the risks of playing football. We don’t want other parents to have to lose their children like we did."
Mr Thomas's cousin, LaTonya Bonseigneur, told the Associated Press shortly after his death that he had been suffering from seizures. She said he had been weathering the seizures for more than a year, and that ultimately he died during a convulsive episode.
USA Today reported that BU doctors do not believe the seizures were associated with CTE. Family members reportedly told them his seizures began after he was involved in a serious car crash in Denver in 2019.
"He had two different conditions in parallel," Ann McKee, the director of the BU CTE Center, told The New York Times.
CTE has become a serious concern in professional football and other high-contact sports like boxing. The condition can result from repeated impacts to to the head, something common for athletes in both sports.
BU researchers found CTE present in 99 per cent of the brains of former NFL players that they were able to obtain and study. They found 91 per cent of college football players’ brains that they studied were impacted by CTE.
