A blood test that tracks the toxic protein clumps behind Alzheimer’s disease can also point to advanced chronic traumatic encephalopathy (CTE), researchers have found, raising hopes of diagnosing the brain disease in living patients for the first time.
CTE is a degenerative brain disease linked to repeated blows to the head, affecting former contact-sport athletes, boxers and combat veterans. At present it can only be confirmed by examining brain tissue after death, which has made it impossible to diagnose patients while they are alive — and has hampered efforts to develop treatments, since trials have no reliable way to identify participants or measure whether a drug is working.
The study, published on 13 November in the Journal of the American Medical Association (JAMA) and led by researchers at Washington University School of Medicine in St Louis, examined a fragment of the tau protein known as eMTBR-tau243. Tau normally helps support the internal structure of nerve cells, but in Alzheimer’s disease and CTE it clumps into toxic tangles in the brain. The fragment’s levels in blood had already been shown to reflect tau build-up in Alzheimer’s patients.
Testing blood samples from more than 80 people whose brain diseases had been confirmed at autopsy, the team found the marker unexpectedly high in one patient with no sign of Alzheimer’s. Checking that person’s records, they discovered the brain showed advanced CTE.
They then tested blood from 11 people whose CTE had been confirmed at autopsy. Levels of eMTBR-tau243 were higher than in healthy people and rose with the severity of the disease. The test distinguished people with advanced CTE from healthy volunteers with high accuracy.
But the researchers are careful about the limits. The finding rests on a small number of cases, and the test could not reliably identify early-stage CTE — the point at which treatment would matter most. Levels in CTE were also much lower than in Alzheimer’s disease, and because the protein is elevated in Alzheimer’s too, which often occurs alongside CTE, the marker alone cannot separate the two conditions.
“This is not going to be a standalone biomarker,” said co-senior author Chihiro Sato, an assistant professor of neurology at WashU Medicine. “But if someone has a history of repeated head injury, tests negative for Alzheimer’s, and this biomarker comes up, it might be CTE.”
Washington University has licensed the technology to measure eMTBR-tau243 in blood to C2N Diagnostics, a university spin-out that also developed an FDA-cleared blood test to help diagnose Alzheimer’s disease. The test has not been validated for diagnosing CTE, and larger studies are needed before it could be used in clinics.
If the results are confirmed, clinicians could one day use such a blood test to monitor people at risk of CTE, and drug trials could use it to see whether treatments targeting tau are working. “We are potentially opening a new door for diagnosing and treating CTE in living patients,” said co-senior author Kanta Horie.
Sources: Washington University School of Medicine in St Louis (https://medicine.washu.edu/news/progress-toward-a-blood-test-for-disease-caused-by-brain-injury/); Horie et al., “Fluid eMTBR-tau243 as a Biomarker of Mixed 3-Repeat and 4-Repeat Tau Pathology”, JAMA, 13 November 2026 (DOI: 10.1001/jama.2026.24689).
