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People with Down syndrome face one of the highest known risks of developing Alzheimer's disease, yet they have largely been left out of the recent boom in blood tests designed to detect the condition.
A new study suggests that may be starting to change.
Researchers found that two blood tests already used to detect biological signs of Alzheimer's disease were able to identify Alzheimer's-related changes in people with Down syndrome with nearly the same accuracy reported in the general population.
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The findings, published in Communications Medicine, could mark an important step toward making Alzheimer's screening easier and more accessible for a group that currently relies on more invasive forms of testing.
Blood Tests Show Promise for Down Syndrome Patients
The research focused on two tests—Lumipulse G p-tau217/β-Amyloid 1-42 and PrecivityAD2—which look for signs of amyloid buildup and abnormal tau proteins in the brain. Both substances are closely linked to Alzheimer's disease and begin changing years before symptoms become severe.
While blood tests have attracted growing attention because they are simpler than brain scans or spinal taps, people with Down syndrome have not typically been included in studies evaluating how well these tests work.
"These blood tests are revolutionizing the field," said Michael Rafii, professor of clinical neurology at the Keck School of Medicine of USC and the study's corresponding author.
That exclusion is notable because people with Down syndrome are at exceptionally high risk of Alzheimer's disease. According to the researchers, almost all people with Down syndrome have amyloid plaques in their brains by age 40. Although not everyone develops Alzheimer's dementia, the lifetime risk of the disease exceeds 90 percent.
Scientists believe the connection stems from the genetic changes that cause Down syndrome. The same duplicated genetic material that defines the condition also leads to increased amyloid accumulation, one of the hallmarks of Alzheimer's disease.
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Why Alzheimer's Can Be Harder to Diagnose in People With Down Syndrome
Dr. Yıldız Değirmenci, professor of neurology at Medicana Health Group, who was not involved in the study, told Newsweek that diagnosing Alzheimer's disease in people with Down syndrome is particularly challenging because clinicians must distinguish new cognitive decline from lifelong intellectual disability.
She said the disease also often presents differently in this group, with early changes in executive functioning, personality or behavior rather than the memory loss more commonly seen in late-onset Alzheimer's disease.
For the study, researchers enrolled 39 people with Down syndrome. Participants underwent both blood testing and positron-emission tomography (PET) scans, a form of brain imaging widely considered the gold standard for detecting Alzheimer's-related changes.
When investigators compared the results, they found that both blood tests successfully identified individuals with abnormal amyloid levels in the brain.
The team also developed preliminary thresholds that could help distinguish between people with and without Alzheimer's-related brain pathology in the Down syndrome population.
In practical terms, the findings suggest a future in which a simple blood draw could help determine whether Alzheimer's disease is likely to be present before patients undergo more complicated testing.
That could be particularly important because the current diagnostic options are not always easy to access.
Amyloid PET scans are generally available only at larger or specialized medical centers, while another diagnostic approach requires collecting fluid from around the brain and spinal cord through a lumbar puncture.
"The blood test is much more accessible as a screening test," said Zinayida Schlachetzki, the study's first author. "It is easier to perform, less expensive and readily scalable, and it places substantially less burden on patients."
Değirmenci said blood-based biomarkers could make diagnosis more accessible because PET imaging and cerebrospinal fluid testing are often impractical for many people with Down syndrome. However, she emphasized that blood biomarkers should be interpreted alongside clinical history and cognitive assessments rather than in isolation.
What's Next for Blood Testing
Researchers said the tests may also provide benefits beyond identifying Alzheimer's disease.
Symptoms such as memory problems or changes in behavior can have several possible causes. According to the study authors, a reliable way to rule out Alzheimer's could help doctors look for other explanations.
"There's a huge value to families in ruling out Alzheimer's disease," Rafii said. "Doctors can then search after some other cause for the symptoms, such as untreated depression or undiagnosed sleep apnea."
The study's authors stressed that more work is needed before the findings can be broadly applied. They plan to evaluate the tests and their proposed diagnostic thresholds in a larger group of people with Down syndrome.
Michael S. Rafii, MD, PhD, professor of clinical neurology at the Keck School of Medicine of USC and medical director of the USC Epstein Family Alzheimer's Therapeutic Research Institute, told Newsweek that the biggest hurdle to bringing these blood tests into routine care for people with Down syndrome is validation.
“Our recent findings are very encouraging, but the tests need to be studied in larger, more diverse, and longitudinal cohorts of people with Down syndrome. We need to confirm the appropriate thresholds and determine how results should be interpreted alongside changes in cognition, behavior, and everyday functioning,” Rafii said.
“Other barriers include regulatory review, insurance coverage, laboratory availability, clinician education, and equitable access to specialists and treatment. Testing must also be accompanied by appropriate counseling, since Alzheimer’s-related biological changes can be detected years before dementia symptoms become apparent.”
Still, the results are already expected to influence future research. Investigators said blood-based screening will be used to identify eligible participants in an upcoming clinical trial testing the Alzheimer's treatment donanemab in people with Down syndrome.
For researchers, the study is also about inclusion. Despite having helped scientists understand key aspects of Alzheimer's biology, people with Down syndrome have often been absent from clinical trials and testing studies.
"Being inclusive of this group is not only a scientific imperative, but also an ethical one," Rafii said. "This population taught us so much about the biology of Alzheimer's. It's sad, and wrong, to see them excluded from clinical trials."
Reference:
Other study co-authors are Oliver Langford, Michael Donohue, Xiaoyu Zhou, Sonal Sukreet, Sara Abdel-Latif and Robert Rissman, all of USC; Matthew Zammit of the University of Wisconsin–Madison; and Joel Braunstein of C2N Diagnostics. The study was supported by the National Institutes of Health [R61AG066543]. DOI: 10.1038/s43856-026-01709-0
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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