Researchers for more than a decade have furthered the understanding of what is now known as CTE, including the pioneering work of neuropathologist Bennet Omalu's study of the brain of former Pittsburgh Steelers great Mike Webster.
"Behavior, mood, and cognitive symptoms were common among those with mild and severe CTE pathology and signs of dementia were common among those with severe CTE pathology".
Dr. McKee, chief of neuropathology at the VA Boston Healthcare System and director of the CTE Center at Boston University, has amassed the largest C.T.E. brain bank in the world.
The players had an average of 15 years playing football, and the median age at death was 66. Physicians who study brain trauma say CTE might be caused by the accumulation of seemingly benign, non-violent blows, rather than head-jarring concussions alone.
This new study, published today in the journal JAMA, is the latest linking risky head injuries to football, though the authors note that the true risk may be lower than the results suggest.
Among those questions are "how common is this" among a general population and all football players, "how many years of football is too many, ' and 'what is the generic risk"?
The set of players posthumously tested by Dr. McKee is far from a random sample of N.F.L. retirees.
The disease can only be diagnosed by examining brain tissue after death, but identifying symptoms of survivors can still serve as a determination.
In addition to the NFL players, CTE was found in brain samples of 48 out of 53 college players, nine out of 14 brains of semi-professional players, seven out of eight brains of players in the Canadian Football League (CFL), and three out of 14 high school players. "It can be used by researchers to detect the disease, and to help find the disease during a person's life", McKee said. The disease has been linked with repeated head blows and the results confirm that it can happen even in young players.
Former Alabama quarterback Ken Stabler is amongst the deceased players that donated their brains as part of the study.
New ones include retired tight end Frank Wainright, whose 10-year National Football League career included stints with the Miami Dolphins, New Orleans Saints and Baltimore Ravens. She said he had struggled nearly eight years with frightening symptoms including confusion, memory loss and behavior changes. He feared CTE and was adamant about donating his brain, she said. "It's like a storm that you can't quite get out of", his wife said.
"I know I'm suffering through it, and it's been a struggle and I feel for all the guys out there that are going through this", said Wycheck, 45. The study found that the high school players had mild cases, while college and professional players showed more severe effects. He was not included in the current report. There were 18 suicides among the 177 diagnosed.