New Blood Test Could Revolutionize Alzheimer’s Disease Diagnosis
Alzheimer’s disease (AD) is the most common cause of dementia in the elderly, and given the aging of the population—and the fact no treatments are proven to reverse or cure AD—incidence of the disease seems likely to keep rising. One issue complicating the search for a cure is that there are as yet no tests that can accurately diagnose AD before symptoms set in. “There is evidence that the AD disease process begins years before its clinical manifestation, so by the time a person exhibits signs of AD, the damage is advanced,” says neurologist Sam Gandy, MD, PhD, associate director of the Mount Sinai Alzheimer’s Disease Research Center. “Many scientists believe that detecting the disease before it progresses is crucial for helping to pinpoint preventive strategies and early treatments.” Recent research points to a simple blood test that could prove to be a breakthrough.
Abnormal Protein Buildup AD is characterized by an abnormal buildup of two brain proteins: amyloid-beta (A-beta), which clumps into plaques between brain cells; and tau, which forms tangles inside brain cells. Together, these proteins disrupt communication between brain cells and between different regions of the brain.
Currently deposits of A-beta and tau can be measured only with positron-emission tomography (PET) scans and/or tests that look for protein fragments in samples of cerebrospinal fluid (CSF). These tests are costly, and CSF testing requires that you undergo a lumbar puncture. The latter involves having a needle inserted between two vertebrae in the lower back into the spinal canal. The procedure can result in a severe headache and back pain, though side effects are rare.
Accuracy and Early Detection The new blood test measures levels of a specific tau protein called phospho-tau217 (p-tau217). For a study published July 28 in the Journal of the American Medical Association, researchers evaluated the blood test in 1,402 cognitively impaired and unimpaired people. In one group of participants, the blood test discriminated between people with clinical diagnoses of AD and other neurodegenerative diseases with 96 percent accuracy, similar to tau PET scans and CSF biomarkers, and better than several other blood tests and magnetic resonance imaging (MRI) scans. The test also distinguished between people with and without an abnormal tau PET scan with 93 percent accuracy. “Overall, people in this group with AD had seven times more p-tau217 than people who did not have dementia or had another neurodegenerative disease, such as Parkinson’s disease,” Dr. Gandy notes. “Levels of p-tau 217 also seemed to correlate with a buildup of A-beta.”
In another group of study participants, the blood test discriminated between those with and without A-beta plaques and tau tangles at autopsy with up to 98 percent accuracy. And, in a third group, the test detected signs of AD in younger people with a genetic predisposition to the disease 20 years before they would be expected to notice memory and thinking problems.
Promising Advance Dr. Gandy emphasizes that the blood test needs more investigation in large-scale trials. “However, these early data suggest the test has more promise than imaging scans that rely more on measurements of A-beta, since many people with A-beta deposits don’t actually go on to develop AD,” he says. “The blood test appears to assess both A-beta and tau. Measuring the latter may be important for more than diagnosis because tau tends to increase as dementia progresses, meaning that it can help predict the speed at which a person’s cognition may decline.”
Dr. Gandy points to other potential advantages, too. “If further studies replicate these findings, we will have a test that is significantly less expensive than PET and avoids the anxiety associated with having a lumbar puncture,” he says. “Moreover, the test can be made available outside larger cities and medical centers.”
Would You Want to Know? We don’t yet know when—or if—the blood test will become available for clinical use. If it does, should you consider getting it? You may wonder if it’s worth confirming that any memory lapses you are experiencing do signal AD if there isn’t a cure for the disease. Another thing to consider is that memory problems don’t always signal AD. With these factors in mind, you might prefer to avoid the anxiety of waiting for test results, or living with the worry that every memory slip is the first sign of AD. You can still follow the lifestyle strategies that may help preserve your brain health. “These include controlling high blood pressure, eating a healthful diet, and getting plenty of exercise,” Dr. Gandy says. Whatever you feel about AD testing, Dr. Gandy also recommends you do consider planning ahead for a time when you may not be able to make decisions about your finances and medical care. It’s a good idea to establish an advance care plan that makes your wishes known to your family (see our May issue for more) even if you aren’t overly concerned about your cognition.
Others may see some advantages to being forewarned that their cognition is likely to deteriorate. “Knowing in advance means you can take AD medications early in the course of the disease,” Dr. Gandy notes. “While these drugs don’t stop or reverse AD, some people find that they help reduce the symptoms for a while, if they are started when the disease is fairly mild.” You also may be able to participate in clinical trials to test new therapies that could benefit you and others—see From the Editor, on page 3, for more on this.
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