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A recurring headline in American sports news is the shocking frequency of a condition called chronic traumatic encephalopathy, or CTE. CTE is the result of years of repeated, small, traumatic brain injuries. These are not injuries that are severe enough to be diagnosed as a concussion. Each injury seems to cause the brain to protect itself by producing a substance called tau-protein. In small amounts, this tangled, filamentatious protein is not necessarily harmful to the brain, but in large amounts it can "strangle" neurons so that they can no longer send messages to each other.
In time, changes in the structure of the brain produce visible symptoms. At first there is something similar to attention deficit disorder, plus memory problems and headaches. Later there can be erratic behavior, difficulties in social interaction, and episodes of poor judgment. In its end stages, the face can take on a mask-like appearance (hypomimia), movement can become difficult, speech can become slurred, and there can be profound depression. Players who have just enough CTE to still be mobile are at high risk of suicide.
CTE Has Become a Major Concern in American-Style Football
American-style football offers many examples. Between 2008 and 2010, Dr. Ann McKee announced that she had found evidence of a condition called chronic traumatic encephalopathy (or CTE) in the brains of 12 deceased American football players. In 2011, Dr. Bennet Omalu, a forensic pathologist, announced that he had found evidence of a condition called chronic traumatic encephalopathy in the brains of football players Andre Waters, Terry Long, Justin Strzelczyk, Mike Webster, and Tom McHale, two of whom had died from suicide. The next year Kansas City Chiefs lineback Jovan Belcher killed his girlfriend and then drove to the stadium and killed himself in front of the team's general manager and head coach. His family demanded an autopsy, and it was later announced that he also had CTE. As this article is being written in November of 2016, 90 out of 94 deceased National Football League Players autopsied by Dr. McKee have been diagnosed with CTE.
CTE Isn't Just a Problem in American Football
CTE has been identified in star athletes in Australian rules football, Major League Baseball, pro wrestling, ice hockey, bull riding, rugby, mixed martial arts, and extreme sports. Major League Baseball outfielder Ryan Freel was found to have had CTE after he killed himself in 2012. Australian rugby union player Barry "Tizza" Taylor died of CTE in 2013. CTE was found in the brain of mixed martial arts star Jordan Parsons after he was killed by a drunk driver in 2016. Now researchers are looking at the possibility of brain damage from heading the ball in soccer, the game people outside North America usually call football. (For the rest of this article, I'll refer to the game as soccer.)