Chronic traumatic encephalopathy is a progressive degenerative disease found in the brains of people who have experienced repetitive brain trauma. It’s been found in the brains of former military personnel, hockey players, boxers, and, most controversially, players in the National Football League — all of whom experienced repeated hits to their head in their line of work. It was first identified in the 1920s, but doctors still don’t know how to treat it or diagnose it in the brains of living people.

But doctors are hopeful that a new study on CTE — the largest one conducted yet — will lead to those medical advancements. On Tuesday, in the Journal of the American Medical Association, a team of neuropathologists announced that in their analysis of the brains of 202 deceased American football players, CTE was present in 177 of them. Rates of CTE diagnosis were highest among the brains of people who had played in the National Football League, where 110 of 111 brains — over 99 percent — showed signs of the disease. These numbers, say the study’s authors, are evidence that CTE is an enormous public health concern that needs to be immediately addressed by both the NFL and the medical community.

“The main results were there was a shockingly high percentage of CTE amongst brain donors,” study lead Dr. Ann McKee, of the VA Boston Healthcare System and the Boston University CTE Center, said in a statement on Tuesday. “This says to us that CTE is a problem — it is a problem associated with football.”

Dr. Ann McKee examines a donated brain.

The brains that McKee and her team evaluated were all donated by individuals who had played American football in some form — whether pre-high school amateur athletes or professional players who had played in at least one regular-season NFL game. Family members provided information about whether there were pathological and clinical features associated with CTE when the player was alive, and then the team performed a neuropathological evaluation of the specimen’s brain volume and macroscopic features.

Of the brains they diagnosed with CTE, the researchers discovered that the prevalence of CTE increased with higher levels of play. For example, while three out of 14 brains of people who played just high school football had evidence of CTE, 48 out of 53 people who played college football had CTE. Brains of people who played in the NFL had the highest rate of occurrence, with CTE showing up in 110 of 111 brains.

McKee noted to The Washington Post that her team can’t pinpoint an average rate of CTE development because these brains were donated by families that had already suspected their loved one had CTE — in other words, representation in the study may have been skewed. But she is still convinced that this study is clear evidence that CTE is linked to football, and she hopes that now that these numbers are clear, the medical community can move on to solving the problem.

“What I would like to see going forward is comprehensive, collective determination to solve the CTE problem,” said McKee in a statement. “That is how we can diagnose it in young players, so that they can stop playing when they are already developing signs of it, and how we can treat it in players that are concerned that they already have it.”

In a statement provided to The Washington Post, the NFL congratulated the work of the scientists but noted that “there are still many unanswered questions relating to the cause, incidence, and prevalence of long-term effects of head trauma such as CTE.” The NFL, which has been ruled to (but has yet to actually) pay $5 million each to thousands of players diagnosed with head-injury caused neurological diseases, and only acknowledged in March 2016 a link between football-related head trauma and CTE, has historically been sketchy about the issue.

Meanwhile, doctors do know that CTE does tragically come with long-term symptoms that include depression, dementia, memory loss, confusion, and post-traumatic stress disorder.

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