Alzheimer's disease detectable through shape changes in three blood proteins, study finds

A new study has identified structural changes in three specific blood proteins that closely track with Alzheimer's disease progression, suggesting that a blood test built around these protein shape signatures could detect the disease before cognitive symptoms become apparent. The research used a technique called hydrogen-deuterium exchange mass spectrometry to measure how accessible different regions of each protein are to solvent molecules, which changes when a protein's three-dimensional shape is altered. The three proteins identified are complement component 3, fibrinogen alpha chain, and alpha-2-macroglobulin, all of which circulate in blood plasma and showed measurably different structural conformations in Alzheimer's patients compared to cognitively healthy controls.

The reason this approach is different from existing Alzheimer's blood tests is that it reads structural information rather than concentration. Current blood-based biomarkers for Alzheimer's, including plasma phosphorylated tau 217 and plasma amyloid beta 42/40 ratios, measure how much of a particular protein is present. Those markers require precise quantification and can be confounded by individual baseline variation. The protein shape approach in this study looks at how the protein is folded, which provides a different dimension of biological information about the disease state in the patient.

The three proteins and what their shape changes reveal

Complement component 3, or C3, is part of the immune system's complement cascade and plays a role in clearing cellular debris including amyloid beta plaques. In Alzheimer's patients, C3 showed a conformational change in a region of the protein associated with its cleavage activation site, suggesting that the chronic inflammatory environment of an Alzheimer's brain is producing sustained complement activation that alters C3's structural state even when the protein is circulating in blood outside the brain.

Fibrinogen alpha chain showed structural changes in its polymerization domain, the region that allows fibrinogen to assemble into blood clots. This is consistent with existing evidence that fibrinogen accumulates in the brains of Alzheimer's patients and contributes to vascular dysfunction. The shape change in blood-circulating fibrinogen suggests that the coagulation system is under altered stress in Alzheimer's disease in ways detectable peripherally, not just in brain tissue.

Alpha-2-macroglobulin, a large plasma protease inhibitor, showed structural alterations in its bait region, the domain that captures and inhibits proteases. Alpha-2-macroglobulin binds amyloid beta and transports it out of the brain, and its structural state in plasma appears to reflect the degree to which it has been engaged by the disease process. In the study, the magnitude of the alpha-2-macroglobulin structural shift correlated with Clinical Dementia Rating scores with a Spearman correlation coefficient of 0.71, indicating a moderately strong relationship between the protein's conformation and disease severity.

How the study was conducted and what samples were used

The research team analyzed blood plasma samples from 268 participants across four groups: cognitively healthy controls, individuals with mild cognitive impairment, patients with mild Alzheimer's dementia, and patients with moderate to severe Alzheimer's dementia. Samples were drawn from the Alzheimer's Disease Neuroimaging Initiative biobank, which provides well-characterized specimens with associated clinical, cognitive, and neuroimaging data. Each participant's amyloid status was confirmed through either PET imaging or cerebrospinal fluid biomarker testing, ensuring that Alzheimer's was distinguished from other causes of cognitive decline in the study population.

Hydrogen-deuterium exchange mass spectrometry works by replacing hydrogen atoms in a protein with deuterium atoms from heavy water. Regions of the protein that are more exposed to solvent exchange deuterium faster than regions that are buried or engaged in tight interactions. By measuring the exchange rate at different parts of each protein, the researchers could map which structural regions had changed their exposure pattern in Alzheimer's patients compared to healthy controls. The analysis was performed on all three proteins simultaneously from a single plasma sample, and the entire measurement procedure took approximately four hours per sample.

Diagnostic accuracy of the three-protein signature

When the structural data from all three proteins were combined into a composite score, the model distinguished Alzheimer's patients from cognitively healthy controls with an area under the receiver operating characteristic curve of 0.89, which corresponds to strong diagnostic performance. For comparison, plasma phosphorylated tau 217 alone achieves an AUC of approximately 0.86 to 0.91 in comparable cohorts, suggesting that the protein conformation approach performs at a similar level to the best currently available blood biomarkers.

The three-protein composite showed an AUC of 0.81 for distinguishing mild cognitive impairment cases confirmed to have underlying Alzheimer's pathology from healthy controls, which is the most clinically useful comparison for early detection purposes. The early detection window, before significant symptom onset, is when current disease-modifying treatments like lecanemab and donanemab have the most potential benefit, since both drugs work by clearing amyloid plaques that accumulate before cognitive symptoms appear.

How this differs from current Alzheimer's blood tests already in use

The FDA cleared two Alzheimer's blood tests for diagnostic use in 2024. Lumipulse plasma pTau217, from Fujirebio, and the Quanterix Simoa pTau217 assay both measure phosphorylated tau 217 concentration in plasma and achieved AUC values of 0.89 to 0.92 in validation studies. They are already being used by clinicians in the US to support Alzheimer's diagnosis without requiring a PET scan or lumbar puncture.

The protein conformation approach does not replace those tests. What it potentially adds is a complementary measurement dimension that captures different aspects of the disease process, since C3, fibrinogen, and alpha-2-macroglobulin reflect inflammatory, vascular, and protease clearance pathways that tau measurements do not capture. A combined panel using both concentration-based and conformation-based biomarkers might achieve higher diagnostic accuracy than either approach alone, which is what the research team is testing in their planned follow-up validation study.

What needs to happen before this reaches clinical practice

The hydrogen-deuterium exchange mass spectrometry technique used in this study is not currently a routine clinical laboratory procedure. It requires specialized instrumentation and analytical expertise that most hospital laboratories do not have. Before a test based on protein conformation could be deployed clinically, the measurement approach would need to be simplified into a format compatible with standard clinical laboratory equipment, such as an immunoassay that uses antibodies specific to the disease-associated conformational state of each protein.

The study was conducted by a team at the University of Washington's Department of Chemistry and the Memory and Brain Wellness Center at UW Medicine. The paper was published in Nature Aging in February 2026. The research team received a $2.1 million grant from the Alzheimer's Association to fund a 400-participant validation cohort study and parallel work on developing simplified immunoassay-based detection methods for the three protein conformational signatures, with results expected in 2028.