Advances in Early Detection of Alzheimer's Disease
Over time, Alzheimer’s disease robs people of memory, reasoning and eventually, identity. Currently, there is no definitive test to determine if someone has Alzheimer’s while they are alive. Recent advances in diagnosing early Alzheimer’s hold promise, however, and new tests may be on the horizon in the next several years. Early detection could help researchers develop treatments that target the disease before it destroys the brain and save countless older individuals from the ravages of Alzheimer’s.
Experts believe Alzheimer’s is the result of disrupted communication between nerve cells caused by abnormal structures in the brain known as plaques and tangles. Researchers are pursuing several avenues to develop reliable tests that detect these changes early on, or even before the plaques and tangles form. The Alzheimer’s tests include looking for ‘biomarkers,’ molecules that can be measured for signs (or ‘markers’) of Alzheimer’s. Also known as molecular or genetic testing, the molecules can be obtained from blood, body fluids, or body tissue. Another area of investigation is imaging techniques that show early changes in the brain.
The potential tests for early detection of Alzheimer’s include:
- Amyloid-beta blood test: Measures blood levels of the protein that causes plaque in the brain. Researchers have concluded the amyloid-beta test, when combined with a person’s age and the presence of a gene associated with Alzheimer’s, is up to 94% accurate, but the claim has not been verified by the FDA. The test could be done during a typical office visit and may be available within a few years.
- Tau blood test: Measures levels of a uniquely phosphorylated (p) form of tau protein (ptau), which forms long filaments, or ‘tangles’ in neurons of people with Alzheimer’s disease. Ptau tangles disrupt the brain cell's ability to communicate with other cells. Doctors currently test cerebrospinal fluid for ptau to distinguish Alzheimer’s from other neurological conditions; a ptau blood test would be a simpler and faster way to screen people for Alzheimer’s. In people with an Alzheimer’s gene mutation, the test detected changes in ptau up to 20 years before symptoms developed.
- RNA blood test: The presence of high levels of RNA produced by the PHGDH gene could lead to a blood test that would identify people who will probably develop Alzheimer’s, years before symptoms appear. The study was e-published March 26, 2020; more work is necessary to validate PHGDH as a biomarker for Alzheimer’s and for its use in a clinical setting.
- Spinal fluid test: Alzheimer's disease may affect the amount of the two proteins linked to it, tau and beta-amyloid, in spinal fluid. The cerebrospinal fluid test for Alzheimer’s involves a minimally invasive spinal tap to withdraw a sample of the fluid and measure tau and beta-amyloid protein levels. The test is still in the research and development phase.
- Molecular imaging: This avenue of research includes a technique based on MRI that measures the glucose level in the brain’s lymphatic system, which may be linked to Alzheimer’s. Another area of imaging research uses FDA-approved compounds to detect plaques in the brain. The compounds act as “radiotracers,” and are given by injection before the imaging test. However, the presence of beta-amyloid plaques does not always indicate Alzheimer’s disease.
Currently, doctors base a diagnosis of Alzheimer’s by assessing cognitive function and ruling out other causes of impairment (such as stroke) through a variety of tests and imaging. If a diagnosis of Alzheimer’s is given, there are medicines that may slow memory loss. There is also support to help both the patient and caregivers as the disease progresses. With encouraging indications that tests for earlier diagnosis may be available in the next few years, the possibility of effective treatments may also be closer.