CHICAGO -- Research on 202 former football players found evidence of a brain disease in nearly all of them, from athletes in the NFL down to high school.
It's the biggest update on chronic traumatic encephalopathy, or CTE.
The disease has been linked with repeated head blows and the results confirm that it can happen even in young players.
But the report only reflects high occurrence in samples at a Boston brain bank and many donors contributed because of troubling symptoms before death.
CTE was diagnosed in 177 former players or nearly 90 percent of brains studied.
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Researchers still don't know how common it is in football or the general population. Some players with repeated concussions never develop it.
The report is in Tuesday's Journal of the American Medical Association.