Headlines last week touted the promise of a new blood test for Alzheimer’s disease — a simple, non-invasive way to detect the condition before symptoms occur. It measures levels of 10 lipids or fats circulating in the blood, and a study of 525 healthy seniors published in Nature Medicine found that it could predict within 90 percent accuracy whether the subjects would go on to develop memory loss or other symptoms five years later.
The test could be a potentially huge development given that half a million Americans are estimated to die from Alzheimer’s disease every year, according to a recent study published in the journal Neurology.
But “potential” is the operative word here. “We are certainly getting closer to having a blood test for Alzheimer’s, which I thought was impossible five years ago,” said Dr. Robert Stern, director of clinical research of the Boston University Alzheimer’s Disease Center. “But I predict it will take another five or 10 years for one to become available.”
Likely, he said, the lipid measurement will be just one marker assessed in a blood test to measure various markers for the disease — similar to the way doctors measure various components of cholesterol and an inflammatory marker to screen for heart disease. It could, for example, be combined with another blood test developed by Australian researchers last year that also appears to predict Alzheimer’s by measuring different biomarkers.
(These are distinct from genetic tests already available to screen for mutations that predict hereditary Alzheimer’s disease.)
The drive to develop a cheap, easy way to screen for Alzheimer’s has been getting more urgent as evidence builds to suggest that patients likely benefit most from treatments at the first subtle sign of memory loss or even years before they develop symptoms.
“Drugs need to be used very early in the disease before there’s too much destruction of brain tissue,” Stern said. “By the time symptoms develop, the destruction is usually irreversible.”
Research suggests more than half of brain cells crucial to memory retention and cognitive processing are lost by the time one begins to develop personality changes and impaired memory.
Three clinical trials are getting underway to test experimental drugs designed to clear or prevent the formation of amyloid plaques thought to be involved in the destruction of brain cells in Alzheimer’s patients. For example, researchers at Brigham and Women’s Hospital and elsewhere are enrolling 3,000 healthy volunteers ages 65 to 85 in a trial to test an amyloid-clearing drug called solanezumab.
“We’re looking for older people with no symptoms or perhaps subtle memory concerns who aren’t at the stage where they would go to the doctor for an evaluation,” said study investigator Dr. Reisa Sperling, director of the Brigham’s Center for Alzheimer Research and Treatment. Potential participants in the study, called A4, will first take a cognitive test, and those who fall in the “normal” range for their age will be given a brain imaging scan using positron emission tomography (PET) to check for the presence of amyloid plaques.
Those who have amyloid plaques will then be randomly assigned to take solanezumab, an antibody that targets amyloid plaque, or a placebo to see if the drug works better than a sugar pill to prevent the onset of memory loss and other cognitive symptoms.
PET brain scans tend to be used only in the research setting because the $3,000 to $5,000 cost per scan isn’t covered by the federal government’s Medicare insurance plan.
Sperling and Stern agree that the new experimental blood test is promising and likely one step of many that will need to be taken before a blood test will be available for clinical use.
“It’s important that this test can predict memory loss, but can it also detect amyloid formation before the development of any symptoms?” Sperling said. She and her research team plan to make blood samples and PET scans collected during the study available to outside researchers working on screening blood tests to help speed development.
“We’re in a Catch-22 at the moment,” Stern said. “In order for us to develop really good modifying treatments for Alzheimer’s, we need to identify people very early on in the course of the disease. But we still don’t have a cheap and easy way to do that.”