Researchers in Sweden and Norway say they have found a signal in the blood that flags Parkinson's disease long before the first tremor.
The pattern shows up during the prodromal phase, which can stretch up to 20 years before motor symptoms appear.
The team, from Chalmers University of Technology and Oslo University Hospital, used RNA sequencing to read gene activity in blood samples.
They picked out a fingerprint tied to how cells repair damaged DNA. The study appeared in npj Parkinson's Disease in December 2025.
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The researchers drew on the Parkinson's Progression Markers Initiative, a long-running international patient cohort. They compared 188 healthy controls, 58 people in the prodromal phase and 393 with established Parkinson's, and followed them for 36 months.
The silent phase before the tremor
The prodromal phase is the early, quiet stretch of Parkinson's. The disease has begun in the brain, but has not yet caused the movement problems doctors use to diagnose it.
People in this stage may have subtle non-motor signs like sleep disturbances or a fading sense of smell, but nothing that usually sends them to a neurologist. That silent window matters because damage is already piling up.
"By the time the motor symptoms of Parkinson's disease appear, 50-80 per cent of the relevant brain cells are often already damaged or gone," said Danish Anwer, a doctoral student at Chalmers University of Technology.
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There is currently no confirmed early diagnostic blood test for Parkinson's. That means treatment usually starts only after substantial nerve loss has already happened.
What the blood picked up
The machine learning models built by the team pulled out a distinct pattern in the prodromal group, tied mainly to DNA repair and to a cellular stress response system.
Four genes stood out as the most predictive. They were ERCC6, PRIMPOL, NEIL2 and NTHL1.
Classifiers built on these signals separated prodromal patients from healthy people about 89 to 91 percent of the time. The same signature faded in patients with established disease, suggesting the body's early defensive response wears out as Parkinson's progresses.
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"In our study, we highlighted biomarkers that likely reflect some of the early biology of the disease and showed they can be measured in blood," said Annikka Polster, an assistant professor at Chalmers and one of the study's leads.
Overviews of the warning signs of Parkinson's that can appear years before diagnosis remain useful for anyone worried about a family history, though only a neurologist can make a diagnosis today.
A clinical test is still years away
The paper's own numbers set limits. Accuracy peaked in the later prodromal stage, not across every point on the disease timeline, and the signal did not cleanly separate established patients from healthy controls.
For now, no blood test for Parkinson's is available in clinics anywhere. The team estimates that a version built on this work could enter healthcare validation within about five years, once the signature is confirmed in larger and more diverse groups than the original cohort.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.