High levels of tau（牛磺酸） protein in fluid bathing the brain are linked to poor recovery after head trauma, according to a study from Washington University School of Medicine in St. Louis and the Fondazione IRCCS Ca Granda-Ospedale Maggiore Policlinico in Milan, Italy. "We are particularly interested in finding ways to predict prognosis after traumatic brain injury," says senior author David L. Brody, MD, PhD, assistant professor of neurology（神经病学） at Washington University. "Right now, it's very hard to tell who is going to live, who is going to die, who is going to have severe disability and who is going to recover well."

The results, reported online Nov. 23 in the journal Brain, show that initial tau levels in all injured patients are high and drop off over time. Those who had the highest tau levels in the first 12 hours of monitoring had worse outcomes six to 12 months later. Recovery was measured using the eight-category Extended Glasgow Outcome Scale (GOS-E): 1 indicates death, 2 is vegetative state, 3-4 is severe disability, 5-6 is moderate disability, and 7-8 is good recovery.

"If we can identify early who is likely to have a poor outcome, we can design better clinical trials that don't include those patients who are going to do fine," he says.

Brody says the correlation between high tau levels and worse outcome is not perfect, at 0.6 (with a perfect correlation being 1 and no correlation being 0), but they found it to be a better predictor of recovery than markers currently used, including measures of glucose（葡萄糖） , glutamate（谷氨酸盐） and the ratio of lactate（乳酸盐） to pyruvate（丙酮酸盐） in the brain.

Tau is part of the cellular scaffolding that supports and protects the brain's nerve cells, especially the cells' long, thin "wires" known as axons that connect different parts of the brain. Abnormal tau protein that forms clumps called "tangles" is also a marker of some forms of dementia, including Alzheimer's disease.