Chronic traumatic encephalopathy (CTE), a degenerative brain disease believed to be caused by repeated impacts to the head, was discovered in 99 percent of the brains of deceased NFL players in a recent study.

The findings were published in the medical journal JAMA.

The brains of 202 former football players (including high school, college, semi-pro, CFL, and NFL) were donated for the study.

CTE was diagnosed in 177 of the 202 brains, including 110 of the 111 former NFL players.

The study found CTE to be less severe in the brains of former high school players who did not continue to play football in college or the pros.

CTE can only be diagnosed with an autopsy.

The study does note a possible bias in that symptoms of CTE, including cognitive, mood and behavioral changes, may have motivated families of the deceased players to donate their brains for study.

Therefore, the study notes that it cannot be assumed that CTE is prevalent at the same rates among the entire football-playing population.

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