Blood Test May Predict Alzheimer’s Risk
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Long before people are diagnosed with Alzheimer’s disease, they have problems with memory and being confused. Studies show their brains are already being invaded with plaques made from a sticky protein called amyloid beta that are believed to contribute to the disease and grow more prevalent as the disease progresses.
Currently, there are only two ways to detect amyloid plaque in the brains of living victims. One is PET scanning, which is expensive and not widely available. The second is an invasive spinal tap.
Now, a study at Washington University School of Medicine in St. Louis found that amyloid beta can be detected in the blood. It suggests that measuring the amount has the potential to help identify people with abnormal levels in their brain’s cerebrospinal fluid.
If the researchers are correct, it could be a significant step in being able to predict who will develop the disease long before they could otherwise be diagnosed.
“Our results demonstrate that this amyloid beta blood test can detect if amyloid has begun accumulating in the brain,” said Randall J. Bateman, M.D., the study’s senior author. “This is exciting because it could be the basis for a rapid and inexpensive blood screening test to identify people at high risk of developing Alzheimer’s disease.”
As the brain performs its daily tasks, it continually produces and clears away amyloid beta. Some is released into the blood, and some floats in the cerebrospinal fluid, for example. If amyloid starts building up, though, it can collect into plaques that stick to neurons, triggering neurological damage.
The researchers measured blood levels of three amyloid subtypes — amyloid beta 38, amyloid beta 40 and amyloid beta 42 — using highly precise measurement by mass spectrometry to see if any correlated with levels of amyloid in the brain.
They studied 41 people aged 60 and older. Twenty-three were amyloid-positive, meaning they had signs of cognitive impairment. PET scans or spinal taps in these patients also had detected the presence of amyloid plaques in the brain or amyloid alterations in the cerebrospinal fluid.
The researchers also measured amyloid subtypes in 18 people who had no buildup of amyloid in the brain.
They measured amyloid levels by drawing 20 blood samples from each person over 24 hours. They found that levels of amyloid beta 42 relative to amyloid beta 40 were consistently 10 to 15 percent lower in the people with amyloid plaques.
“The differences are not big, but they are highly consistent,” Bateman explained. “Our method is very sensitive, and particularly when you have many repeated samples as in this study — more than 500 samples overall — we can be highly confident that the difference is real. Even a single sample can distinguish who has amyloid plaques.”
The test accurately classified patients as amyloid-positive or -negative 89 percent of the time, and a single blood sample was accurate in 86 percent of patients.
Amyloid plaques are one of the two characteristic signs of Alzheimer’s disease; the other sign is the presence of tangles of a brain protein known as tau. Another researcher at Washington University School of Medicine, David Holtzman, M.D., is developing a blood-based test for tau that could complement the amyloid test.
“If we had a blood test for tau as well, we could combine them to get an even better idea of who is most at risk of developing Alzheimer’s disease,” Bateman said. “That would be a huge step forward in our ability to predict, and maybe even prevent, Alzheimer’s disease.”
A study from Seton Hall University suggested that a voice test could detect early Alzheimer’s — even over the phone by analyzing the way patients talk. Researcher Sona Patel is developing ways to detect vocal differences between the voices of normal aging adults and those with Alzheimer’s disease.
“What I would envision is to put this software on an app that can be used by the patient directly or in a medical facility,” she told the Express.
“A patient or doctor could do a quick test with a vocal recording, and the score would indicate the likelihood of a neurological problem.
“If patients can be diagnosed in an early stage of disease, treatment and drug therapies can start at that time, possibly slowing the disease progression.”