A new study from scientists at the Washington University School of Medicine in St. Louis is suggesting a novel blood test can identify subjects at an early stage of Alzheimer's disease, years before any symptoms appear. The blood test may even be more accurate than PET brain scans, and is hoped to accelerate screening of patients for participation in clinical trials.
A blood test to diagnose Alzheimer's disease is not a new idea. For years we have seen study after study present a range of different biomarkers attempting to detect the devastating disease at its very earliest, pre-symptomatic stages. Despite a growing volume of alternative hypotheses, measuring levels of amyloid beta protein deposits in the brain is still the best diagnostic tool for tracking the progression of the disease.
Two years ago researchers from Washington University School of Medicine in St. Louis revealed amyloid deposits in the brain could be effectively tracked by measuring levels of two amyloid subtypes in the bloodstream. That study found that as levels of amyloid beta 40 and amyloid beta 42 go down in the bloodstream, amyloid beta deposits increase in the brain.
At the time the researchers found the blood test could determine amyloid brain deposits with an accuracy rate of 88 percent compared to PET scans. In a newly published follow-up study, that accuracy rate has been raised to an impressive 94 percent by incorporating two additional well-known Alzheimer's risk factors: age and a genetic variant called APOE4.
The new study examined 158 adults over the age of 50, the vast majority of whom were cognitively healthy. Perhaps most interesting was the finding that some of the false positives seen in initial blood tests were ultimately found to be predictive of subsequent amyloid build-ups, identified years later in brain scans. This suggests the blood test could identify the potential of amyloid deposits in the brain several years before any deposits can be identified by PET scans. This exciting result points to the blood test being extremely valuable for researchers screening patients for clinical trials.
"Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years," explains senior author on the study, Randall Bateman. "But with a blood test, we could potentially screen thousands of people a month. That means we can more efficiently enroll participants in clinical trials, which will help us find treatments faster, and could have an enormous impact on the cost of the disease as well as the human suffering that goes with it."
It is important to note the researchers make no correlation at this stage between symptomatic signs of dementia and these blood test results. Further work is inevitably needed to clarify this connection as amyloid deposits can be found in cognitively healthy older subjects. However, in the short term, it's hoped this study will assist researchers in conducting human clinical trials working to develop anti-Alzheimer's drugs.
"If you want to screen an asymptomatic population for a prevention trial, you would have to screen, say, 10,000 people just to get 1,500 or 2,000 that would qualify," says Bateman. "Reducing the number of PET scans could enable us to conduct twice as many clinical trials for the same amount of time and money. It's not the US$4,000 per PET scan that we're worried about. It's the millions of patients that are suffering while we don't have a treatment. If we can run these trials faster, that will get us closer to ending this disease."
The new research was published in the journal Neurology.
Source: Washington University School of Medicine in St. Louis
