Boston University researchers may have found the key to CTE diagnosis in living patients. Until now, the disease could only be identified through examining brain tissue in deceased patients, so this development has the potential to shift how the disease is viewed and treated.

“The findings in this study are the early steps toward identifying CTE during life,” Dr. Ann McKee, the director of the CTE Center at Boston University, said in a statement released by the university. “Once we can successfully diagnose CTE in living individuals, we will be much closer to discovering treatments for those who suffer from it.”

What is CTE? Chronic traumatic encephalopathy is a disease caused by repeated brain trauma. Concussions can be a factor, but it can also be caused by continued lesser traumas that don’t cause concussions.

Symptoms include depression, memory loss, difficulty with impulse control, confusion, anxiety, sleeplessness, anger issues, suicidal thoughts and tendencies, and impaired judgment, among others. These symptoms are also associated with other conditions, which makes identifying CTE by symptoms alone an impossible task.

CTE can be diagnosed posthumously by examining brain tissue for the presence of abnormal tau proteins in the brain. Tau protein buildup is also associated with Alzheimer’s.

What’s the latest discovery in this study? McKee and her team discovered a specific biomarker in the brains of former football players. A biomarker is a measurable substance which is, in this case, found in the brain and identifies an abnormality.

This particular biomarker is called CCL11, and it’s a secreted protein the human body uses to help regulate the immune system and inflammation in the body.

They examined the brains of 23 former college and pro football players, 18 non-athletes, and 50 non-athletes who had been diagnosed with Alzheimer’s. Researchers found that the levels of CCL11 were higher for individuals who had played football longer.

This was a significantly smaller study than the one published in July 2017. In that one, researchers looked at the brains of 202 former football players from all levels of the game.

What did that study reveal about CTE? It was alarming. That study found that of the 202 brains from former players that were examined, 177 were diagnosed with CTE. It was even more troubling to isolate the results for former NFL players. There were 110 of 111 brains of former pro players that tested positive for CTE.

The study was flawed, primarily because this research can only be done on a deceased individual. Brains were donated to the study in part because the person had some of the symptoms of CTE before their death. But the prevalence of CTE in former players cannot, and should not, be brushed aside.

After that study, The New York Times published an interactive overview of the results. It noted that 1,300 former NFL players have died since Boston University began its research into CTE.

So even if every one of the other 1,200 players would have tested negative — which even the heartiest skeptics would agree could not possibly be the case — the minimum C.T.E. prevalence would be close to 9 percent, vastly higher than in the general population.

What happens next? This is a positive development, but there’s still a lot of work to be done. Once CTE can be identified in living patients, we’ll be able to develop a better idea of the dangers associated with playing football. If it’s as widespread as previous studies suggest, the league could be forced to take decisive action to better protect players.

One thing McKee and her team will work toward is learning whether elevated CCL11 levels indicate early or advanced stages of CTE, as well as whether the amount of CCL11 markers correlates to the severity of the disease.

Developing treatments is a whole other story and is a process that could take a long time. But being able to start moving in that direction is tremendous progress.