Why the CTE Playbook is Incomplete
Extraordinary numbers of NFL football players are likely to have Chronic Traumatic Encephalopathy (CTE), the brain disease that develops from ongoing hits to the head – it could be as high as 97% of all players. A study published last week in The BMJ found CTE in at least 25% of former NFL players who died between 2016 and 2021. The research team at Mass General Brigham reported that number as the conservative end of a range that could run as high as 97%, depending on how the data is modeled. Understanding the dynamics behind this wide range is key.
Most of what researchers know about CTE has come from brains donated by families who had noticed symptoms like memory loss or mood changes. This, in turn, created a selection bias, meaning that scientists don’t actually know what CTE looks like in someone who played the same sport but never showed any symptoms.
This new study tried to correct for that by comparing a group of 1,712 former NFL players who died during a six-year window — most with no documented neurodegenerative disease — against a smaller set of donated brains that researchers have access to. That comparison produced the 25% floor and the 97% ceiling. But where that number actually falls remains unknown. That broad range in the middle is the scary part.
Finding the actual number is possible only if the donor pool broadens. That’s exactly why brain donation is so consequential to all neurological research, not just CTE. A player who retired without a diagnosis, without memory problems, without any reason to suspect CTE, is arguably just as valuable as one who already showed symptoms. Comparing affected tissue to unaffected tissue at the cellular level is one of the only ways researchers can ascertain how CTE impacts brain function.
None of this is unique to football. The same selection bias applies to hockey, soccer, boxing, and to the far larger number of people who experience repeated head impacts in lines of work other than sports. It also applies to survivors of intimate partner violence, who are predominantly women and rarely part of the CTE conversation.
For clinicians, athletic trainers, and anyone advising a family on what to consider after a career in contact sports, or after a history of repeated head injury, this study is a good prompt to raise the conversation early. Remember: brain donation is separate from organ donation, requires its own registration, and must be arranged in advance.
CTE is one thread in the much larger pattern. The same issue comes up whether it’s research into Parkinson’s Disease, multiple sclerosis, treatment-resistant depression, or dozens of other conditions science doesn’t have all the answers to yet.
This study exists because enough families said yes to brain donation. The next breakthrough in neuroscience depends on the same thing: generous brain donors willing to make a lasting contribution to science. They don’t need to be athletes; they don’t even need to have a neurological diagnosis. They just need to be forward-thinking and make plans to help when the time comes.
💡 For more information on how brain donors help advance CTE research, visit braindonorproject.org/cte/
