ATLANTA (CNN) Chronic traumatic encephalopathy, known as CTE, was found in 99% of deceased NFL players’ brains that were donated to scientific research, according to a study published Tuesday in the medical journal JAMA.
The neurodegenerative brain disease can be found in individuals who have been exposed to repeated head trauma. The disease is pathologically marked by an buildup of abnormal tau protein in the brain that can disable neuropathways and lead to a variety of clinical symptoms. These include memory loss, confusion, impaired judgment, aggression, depression, anxiety, impulse control issues and sometimes suicidal behavior.
It can only be formally diagnosed with an autopsy, and most cases, although not all, have been seen in either veterans or people who played contact sports, particularly American football.
“There’s no question that there’s a problem in football. That people who play football are at risk for this disease,” said Dr. Ann McKee, director of Boston University’s CTE Center and coauthor of the new study. “And we urgently need to find answers for not just football players, but veterans and other individuals exposed to head trauma.”
The JAMA study is the largest of its kind and all of those studied were required to have football as their primary exposure to head trauma. The criteria for submitting a brain was based on exposure to repetitive head trauma, regardless of whether that individual exhibited symptoms during their lifetime.
The study points out potential bias because relatives of these players may have submitted their brains due to clinical symptoms they noticed while they were living. It also acknowledges the lack of a comparison group that represents all individuals exposed to college-level or professional football. Without that, the study lacks an overall estimate on the risk of participation in football and its effects on the brain.
Out of 202 deceased former football players total — a combination of high school, college and professional players — CTE was neuropathologically diagnosed in 177, the study said. The disease was identified in 110 out of 111 former NFL players. It was also found in three of the 14 high school players and 48 of the 53 college players. The study included brains of individuals who have been publicly confirmed to have had the disease, including Ken Stabler, Kevin Turner, Bubba Smith and Dave Duerson.
“The medical and scientific communities will benefit from this publication and the NFL will continue to work with a wide range of experts to improve the health of current and former NFL athletes,” the NFL told CNN in a statement, noting that “there are still many unanswered questions relating to the cause, incidence and prevalence of long-term effects of head trauma such as CTE.”
In 2016, the NFL publicly acknowledged for the first time a connection between football and CTE. In June 2015, a federal judge approved a class-action lawsuit settlement between the NFL and thousands of former players, providing up to $5 million per retired player for serious medical conditions associated with repeated head trauma.
“The NFL is committed to supporting scientific research into CTE and advancing progress in the prevention and treatment of head injuries,” the NFL statement on the study said. “In 2016, the NFL pledged $100 million in support for independent medical research and engineering advancements in neuroscience related topics. This is in addition to the $100 million that the NFL and its partners are already spending on medical and neuroscience research.”