Turner was a star running back at the University of Alabama from 1988 to 1991
before being picked in the third round of the draft by the New England Patriots. He played for the Patriots for three seasons followed by five seasons with the Philadelphia Eagles. He was diagnosed with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, in 2010 and died in March of ALS.
It was believed that he had only ALS, but Thursday's announcement, made by Dr. Ann McKee of Boston University and the Concussion Legacy Foundation, changed that understanding.
In a statement, McKee said, "The severity of Mr. Turner's CTE was extraordinary and unprecedented for an athlete who died in his 40s.
"While he had typical cognitive symptoms and problems with impulse control associated with CTE, it also appears that CTE decimated the motor cortex of his brain at a young age, likely leading to his ALS symptoms," she added. McKee clarified that Turner's CTE brought on his ALS.
Hard hits linked to neurodegenerative diseases
In a 2013 interview with CNN affiliate WGCL
, Turner discussed how he believes playing football played a large part in his ALS diagnosis: "I really believe that had I not played all those years, that I wouldn't have this condition."
The eight-year NFL veteran was a lead plaintiff on the concussion-related lawsuit filed by more than 5,000 former players.
After his retirement, Turner dedicated his life to research and awareness of the health impacts of football and created the Kevin Turner Foundation
to raise awareness for ALS.
Professional football players are four times more likely to have ALS
and three times more likely to die from neurodegenerative diseases like ALS or Alzheimer's.
CTE has been diagnosed in 91 of 95 professional football players who donated their brains for CTE research at the VA-BU-CLF Brain Bank and the Concussion Legacy Foundation.
The disease has Alzheimer's-like symptoms including dementia, memory loss, mood swings, aggression and depression.
Scientists are working to find potential biomarkers so the disease can be diagnosed in people while they are still alive.
"After now completing the analysis of the brains of 228 former football players, we have seen a clear trend that length of career is associated with CTE severity," McKee added in a statement.
Turner played 25 seasons in his career, starting to play tackle football at the age of 5.
CTE and the NFL
While much of the talk surrounding head safety in football is around concussions, researchers believe that CTE is a result of repeated hits to the head, which then result in a buildup of the abnormal protein tau. Unlike Alzheimer's, the tau protein tangles of CTE appear in the brains of younger people and take over specific parts of the brain, regions typically not affected by Alzheimer's.
Some of the most famous names to have suffered from the disease include Hall of Famer and legendary sportscaster Frank Gifford
, who died at the age of 84 in summer 2015, as well as San Diego Chargers player and fellow Hall of Famer Junior Seau. Seau was just 43 years old when he took his own life in 2012.
Though the disease is most commonly associated with football players, it has also been diagnosed in hockey players and wrestlers.
"I was the one telling these parents that it's a safe game to play. 'Look at me. I've been playing since I was 5,' and turned out I was wrong," Turner said in the 2013 interview. "I was just so dead wrong about the hits to the head thing. I feel ignorant now."