Dementia is one of the biggest health challenges facing aging populations around the world. Millions of people develop memory loss and thinking problems as they grow older, and Alzheimer’s disease is the most common cause.
One of the biggest difficulties doctors face is that the disease often begins silently in the brain many years before symptoms such as memory loss become noticeable. By the time dementia is diagnosed, significant damage has usually already occurred in the brain.
A new study from researchers at the University of California San Diego suggests that a simple blood test might one day help identify people at risk for dementia decades before symptoms appear. The findings were published in the journal JAMA Network Open and focus on a protein in the blood called phosphorylated tau 217, or p-tau217.
Tau proteins are naturally present in the brain and help stabilize the structure of nerve cells. However, in Alzheimer’s disease, abnormal forms of tau accumulate and form tangled clumps inside brain cells. These tangles interfere with normal brain function and contribute to the loss of memory and thinking ability that characterizes dementia.
The specific form studied by the researchers, p-tau217, has been linked to the early biological changes associated with Alzheimer’s disease. Scientists have been investigating whether measuring this protein in blood could provide an early signal that these brain changes are beginning.
In the new study, researchers found that higher levels of p-tau217 in the blood were strongly associated with a greater risk of developing dementia years later. Remarkably, the protein could predict risk up to 25 years before symptoms appeared.
The research was led by Dr. Aladdin H. Shadyab, an associate professor of public health and medicine at the UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science and the School of Medicine. According to Shadyab, the results suggest that doctors may eventually be able to identify people at higher risk for dementia long before memory problems begin.
Such early detection could be extremely valuable. Instead of waiting until cognitive decline becomes obvious, doctors could monitor patients more closely and potentially use preventive strategies to reduce risk.
The findings come from the Women’s Health Initiative Memory Study, a large long-term study designed to understand factors that influence brain health in older women. The study originally enrolled thousands of women between the ages of 65 and 79 in the late 1990s and followed them for decades.
For the current analysis, the researchers examined data from 2,766 women who had no signs of cognitive problems when they first joined the study. At the start of the study, blood samples were collected from the participants and stored.
Years later, scientists analyzed these samples to measure levels of the p-tau217 protein. They then compared these levels with the participants’ cognitive outcomes during up to 25 years of follow-up.
Over time, some women developed memory problems, mild cognitive impairment, or dementia. The researchers found a clear pattern: women who had higher levels of p-tau217 in their blood at the beginning of the study were much more likely to develop dementia later in life.
The relationship was dose-dependent, meaning that as levels of the protein increased, the likelihood of future dementia also increased. Women with the highest levels of p-tau217 had the greatest risk.
However, the study also showed that the relationship between the biomarker and dementia risk varied among different groups of women.
For example, the association between higher p-tau217 levels and cognitive decline was stronger among women who were older than 70 at the beginning of the study compared with those who were younger. The protein was also more predictive among women who carried a genetic variant known as APOE ε4, which is known to increase the risk of Alzheimer’s disease.
Another interesting finding involved hormone therapy. The researchers observed that p-tau217 levels were more strongly associated with dementia among women who had been assigned to receive estrogen plus progestin hormone therapy during the original clinical trial compared with those who received a placebo.
The study also explored possible differences across racial groups. The strength of the association between p-tau217 and dementia differed somewhat between white and Black women. However, when the researchers combined p-tau217 measurements with information about age, the accuracy of dementia prediction improved similarly in both groups.
Experts say blood-based biomarkers like p-tau217 are particularly promising because they are much easier to obtain than other diagnostic tools currently used in Alzheimer’s research.
Traditional methods of detecting Alzheimer’s-related brain changes often involve expensive brain imaging scans or spinal fluid tests, which require a lumbar puncture procedure. In contrast, a blood test is far less invasive and could potentially be used more widely.
Dr. Linda K. McEvoy, the senior author of the study and a senior investigator at the Kaiser Permanente Washington Health Research Institute, explained that blood biomarkers could help accelerate research on dementia risk factors and prevention strategies.
If researchers can identify people who are likely to develop dementia years in advance, they may be able to test interventions aimed at slowing or preventing the disease before symptoms begin.
Despite these promising findings, the researchers caution that blood tests for p-tau217 are not yet ready for routine use in clinical practice. At present, they are mainly used in research settings. More studies are needed to determine how these tests should be used in medical care and whether early identification of risk can actually improve long-term outcomes.
Future research will also examine how p-tau217 interacts with other factors over time. Scientists are particularly interested in understanding how genetics, hormone therapy, lifestyle, and age-related health conditions influence the relationship between this biomarker and dementia risk.
Ultimately, the goal is not only to predict dementia but to prevent it. As Shadyab explained, identifying risk decades in advance could open the door to strategies that delay or even stop the disease from developing.
If successful, such approaches could dramatically change how doctors manage one of the most challenging diseases associated with aging.
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