Finding the ‘When’ of Alzheimer’s Through a Simple Blood Test Can Streamline Treatment

Chris Hemsworth might not remember being Thor in the MCU.

As crazy as it sounds, on one episode of Limitless, a National Geographic show on ways to live better for longer and prevent age-related diseases, he was revealed to be prone to Alzheimer’s. He underwent a series of genetic tests to figure out what his genes hold for his future. He has two copies of the APOE4 gene, which is linked to a greater risk of Alzheimer’s, often with an early onset (before 65 years).

“Predicting if and when patients are likely to develop Alzheimer’s symptoms could be useful in designing trials of interventions to prevent or delay symptom onset,” says Howard Fink, a physician at the Minneapolis Veterans Affairs Health Care System in Minnesota. A simple blood test can serve this exact purpose, working as a molecular ‘clock’ that not only predicts whether a person will get Alzheimer’s, but when. 

The test is based on an abnormal form of a protein called tau, which circulates in the blood and begins accumulating in the brain long before the memory loss symptoms of Alzheimer’s appear. If the test results hold up in larger studies, it can provide a way to step in earlier, when treatment might be more effective. It can also introduce a new, measurable biomarker, making clinical trials for this neurodegenerative disease easier and less expensive.

Although in-home blood tests are available for the form of tau the researchers have focused on, Suzanne Schindler, a neurologist at Washington University School of Medicine in St. Louis, Missouri, and lead author of the study, recommends against having an Alzheimer’s biomarker test for a person without impaired cognition.

Abnormal tau proteins form a tangled mass in the brain, which can disrupt communication among the neurons. Brain-imaging tests can reveal these tangled tau fibers, and apart from diagnosis, preliminary studies suggest that such tests can also predict when symptoms of Alzheimer’s will start to show. But imaging techniques are cumbersome and expensive, and so researchers have been looking for simpler blood-based tests to track tau.

To mark the molecular ‘clock’, Schindler and her team collected data from blood tests and cognitive assays of 600 adults put in two large Alzheimer’s disease studies. They set their sights on a particular form of abnormal tau protein, p-tau217. Researchers noted that the ratio of p-tau217 to normal tau began to rise well before the onset of Alzheimer’s symptoms. The rate of increase in p-tau217 levels was also consistent across participants. The scientists fused p-tau217 data and age to devise a model that can estimate when Alzheimer’s will start appearing, with an error margin of three to four years.