Levels of a protein called tau in spinal fluid may help predict which former pro athletes with multiple concussions will end up with long lasting effects from their history of jolts to the brain, a new study suggests.
Elevated tau levels found in some concussed former athletes were associated with signs of damage to brain-cell connection bundles on brain scans and with poorer performance on cognitive tests, the study team reports in Neurology.
Past research suggests that elevated levels of certain versions of the tau protein are a marker of brain cell damage and degeneration, the authors note.
“We’re moving closer to being able to tell at a single-person level, what they might be in danger of developing,” said study coauthor, Dr. Carmela Tartaglia, the Marion and Gerald Soloway Chair in Brain Injury and Concussion Research at the University of Toronto.
The elevated levels of tau found in some of the athletes in the study “make us concerned that there is neurodegeneration going on,” Tartaglia said. “But we don’t know if they have CTE. That can be determined only after death.”
CTE, chronic traumatic encephalopathy, is a neurodegenerative disease that other studies have linked to repeated jolts to the brain. Currently it can only be diagnosed on autopsy.
One important finding from the new study, Tartaglia said, is that not all people who experience multiple concussions end up with long-lasting brain damage. And that falls in line with what has been observed in the past.
“Lots of people are exposed to repetitive head injury,” Tartaglia said. “But it definitely looks like not everybody gets this. We’re going to have to start looking very hard at what the difference is between the two groups.”
For the new study, Tartaglia and her colleagues recruited 22 male former pro athletes - most of them former Canadian Football League players or pro hockey players, and one snowboarder. For comparison, they also recruited five healthy volunteers and 12 volunteers who had been diagnosed with Alzheimer’s disease, both groups a mixture of men and women.
All 39 participants agreed to undergo lumbar punctures so that the researchers could examine their cerebrospinal fluid for levels of tau. They also agreed to take cognitive tests and to undergo a type of brain scan, diffusion tensor imaging, that can provide information on the integrity of the white matter that sheathes long brain-cell connections known as axons.
Tau levels were highest among the volunteers with Alzheimer’s and lowest in the healthy control group. Among the former athletes, 12 out of 22 had higher levels of tau compared to the healthy controls, but lower than the volunteers with Alzheimer’s. The other athletes had tau levels comparable to those of the healthy controls.
When the researchers analyzed just these two groups of athletes, they found that the number of concussions an individual experienced or the number of years he played were not related to his levels of tau.
They also noted that higher tau levels did correlate well with poor performance on the cognitive tests and with brain scan findings. In the brain scans of athletes with higher levels of tau, there were signs of white matter damage.
The small study does show that axonal degeneration related to brain injuries can persist for months and years, said Dr. Douglas Smith, director of the Center for Brain Injury and Repair at the Perelman School of Medicine in Philadelphia, who wasn’t involved in the research.
Smith’s group has found that “in severe traumatic brain injury there is ongoing axonal degeneration and white matter loss,” he said. “This study tends to support the idea that this may also be the case in some individuals with repeat concussion exposure.”
While the findings show that elevated tau levels appear to indicate some type of injury process is going on in the brain, they can’t tell you whether this is going to develop into CTE, said Michael Alosco, associate director of the Alzheimer’s Disease Center Clinical Core at Boston University, who wasn’t involved in the study.
Nevertheless, Alosco said, “it does suggest a pathway through which repeated head trauma leads to white matter injury and also that elevations in total tau could be used to detect that injury.”