Blood Tau Fragment Offers a Clue to Diagnosing CTE in Life

CTE can only be confirmed after death, and that's the problem this study circles. Doctors evaluate symptoms such as mood swings and memory loss to judge whether a patient may have chronic traumatic encephalopathy, the disease linked to concussions and repeated blows to the head. Other diseases cause the same symptoms, so a living diagnosis stays a guess until an autopsy settles it.

The clue came from a protein called tau. Tau normally supports neurons, but in Alzheimer's disease it turns abnormal and tangles inside nerve cells. Researchers at Washington University in St. Louis were using autopsy samples to study a tau fragment called eMTBR-tau243, which may help track those tangles, when they found a patient with high levels of the marker whose records showed no Alzheimer's — but advanced CTE instead.

The team then widened the search. Working through a larger collection of autopsied brain and other samples, they eventually tested blood stored from 11 people who had been classified as having CTE. Compared with healthy people, levels of eMTBR-tau243 were higher in those with advanced CTE, said study co-author Chihiro Sato, a WashU assistant professor of neurology.

The limits are plain in the result itself. The biomarker couldn't reliably identify early-stage CTE, the stage where a test would help most, and the blood sample behind the finding is 11 people. Sato, who studies tau diseases, stressed that much more research is needed before the marker means anything in a clinic.

An outside read landed in the same place. Dr. Rudolph Castellani, a neuropathologist at Northwestern University who wasn't involved in the research, called it an interesting but very preliminary finding that requires far larger studies to show whether there's a real connection. Abnormal tau shows up in several brain diseases, and those diseases often overlap in older adults, which makes any one marker hard to read on its own.

The findings were published in the medical journal JAMA and presented at a scientific meeting in Japan. The paper, by Kanta Horie and colleagues, frames eMTBR-tau243 as a biomarker of mixed 3-repeat and 4-repeat tau pathology. For now that's the honest size of it: a measurable signal in advanced cases, found by accident in Alzheimer's research, waiting on the larger studies that decide whether it becomes a diagnostic tool.

The path from here is enrollment, not headlines. A marker that separates advanced CTE from healthy controls in stored samples has to be tested in living patients whose symptoms are still ambiguous, followed over time, and read against the other tau diseases that crowd the same age group. Until a study of that size runs, eMTBR-tau243 stays where the JAMA paper leaves it: a named molecule, a plausible signal, and a research direction that didn't exist in this form before November.