For the first time, scientists have confirmed a diagnosis of chronic traumatic encephalopathy (CTE) — a neurological disease linked to head injuries from sports like football — in a living person. Until now, we’ve only been able to diagnose CTE in dead patients. Finding the disease while the patient is still alive could help scientists find a way to treat it.

CTE develops from repeated hits to the head and has been linked to severe memory loss, depression, and dementia. It’s been found in 99 percent of the donated brains of NFL players. In a study published in the journal Neurosurgery, researchers found a telltale sign of CTE, a specific protein, in the brains of 14 retired NFL players who underwent a brain scan. Now that one of the players has died and doctors have been able to take a closer look at his brain, they have confirmed the CTE diagnosis.

Many former National Football League players like Aaron Hernandez and Junior Seau have been found to have the progressive brain disease. Last year, the NFL reached a billion-dollar settlement, the largest in sports history, over a lawsuit from former players who suffered concussions and now have severe neurological diseases like amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease).

The subject of the paper was former NFL player Fred McNeill, according to CNN. McNeill played 12 seasons in the National Football League for the Minnesota Vikings, reporting one concussion. But by the time he was 59, McNeill was already experiencing serious problems with his motor skills, and so he sat for the brain scan. Scientists found increased levels of certain proteins in his brain, including the tau protein, which has been linked to Alzheimer’s. After McNeill died two years ago, at 63, detailed brain-tissue analysis confirmed that his brain had other physical signs of CTE, suggesting that the tau protein is linked to the disease. A study from September suggested that the levels of another protein, called CCL11, may also be used to diagnose CTE in living patients.

Right now, the data on CTE is skewed. Being limited to donated brains means scientists are studying the brains of people whose relatives probably already suspected that something was wrong. One study, for example, showed that playing high school football, was not linked to cognitive problems later in life. So being able to diagnose people while they’re still alive could tell us a lot about how common CTE really is, and it could be crucial for developing treatment for players while they’re alive.

More studies are needed to confirm this method, according to the researchers, and some scientists are skeptical. Lili-Naz Hazrati, a neuroscience researcher at Toronto’s Hospital for Sick Children, told the Chicago Tribune that tau can be found in healthy brains, too. Having a robust way of detecting CTE may still be far off, but we may be one step closer. And if this pans out, it could be a game-changer for athletes.