Sleep Issues May Indicate Parkinson’s or Dementia Years in Advance

September 27, 2025

Brain Biomarkers Predict Neurodegenerative Disease Risk

Recent research indicates that certain brain biomarkers can forecast whether individuals with REM sleep behavior disorder (iRBD) may later develop Parkinson’s disease or dementia with Lewy bodies (DLB). By analyzing MRI scans, scientists found that diminished function in the glymphatic system is linked to a higher risk for Parkinson’s, while increased levels of free water in the basal nucleus of Meynert suggest a greater chance of progressing to DLB.

This research represents the most extensive imaging studies ever conducted on patients diagnosed with iRBD. The outcomes could lead to earlier diagnoses, focused monitoring, and even preventive interventions before significant brain damage takes hold.

Key Points

Parkinson’s Indicator: Lower glymphatic fluid circulation significantly raises the risk of Parkinson’s.
DLB Indicator: Increased free water in the basal nucleus of Meynert elevates DLB risk substantially.
Clinical Relevance: Provides new methods to distinguish disease outcomes well before any symptoms appear.

An international team led by a medical professor at Université de Montréal has achieved a significant breakthrough in predicting neurodegenerative diseases through two complementary studies. They can now identify, years ahead of time, which individuals exhibiting a specific sleep disorder may develop Parkinson’s or DLB.

These studies specifically target isolated REM sleep behavior disorder (iRBD)—a condition where individuals may shout, flail, or act out their dreams, sometimes risking injury to a partner.

As Rahayel, a neuropsychologist involved in the research, stated, “This isn’t merely restless sleep; it serves as a neurological red flag.” Roughly 90% of those diagnosed with this disorder will eventually develop Parkinson’s or DLB, yet previously, it was tough to predict the specific disease or its onset.

First Biomarker: Parkinson’s Prediction

The initial study, executed by a doctoral student from UdeM and published in Neurology, included 428 participants from five different countries: Canada, the U.S., France, the U.K., and Czechia. It focused on the brain’s glymphatic system, integral in clearing metabolic waste during sleep, including proteins associated with neurodegeneration. Impaired function of this system can lead to disease accumulation, such as Parkinson’s.

Utilizing a sophisticated MRI technique called DTI-ALPS, the research team evaluated fluid circulation in targeted brain regions among 250 iRBD patients and 178 healthy participants over an average follow-up of six years. The main takeaway? Participants showing lower DTI-ALPS indices in the left hemisphere were 2.4 times more likely to develop Parkinson’s in the ensuing years, though no correlation was observed with DLB.

“This asymmetry reflects what’s clinically observed in early stages of Parkinson’s, where symptoms commonly begin on one side—perhaps marking the initial phase of the disease,” Ayral noted. This research not only highlights the link between glymphatic function and Parkinson’s but also stands as the largest international study of this kind concerning patients with polysomnography-verified REM sleep disorder.

Second Biomarker: DLB Prediction

The follow-up study, conducted by another doctoral student and published in Alzheimer’s & Dementia, also involved 438 participants from the same five nations. It aimed to identify early symptoms of DLB, a condition combining traits of both Parkinson’s (like tremors) and Alzheimer’s (cognitive issues, confusion, hallucinations). DLB is the second most common form of degenerative dementia following Alzheimer’s.

Researchers assessed the volume of “free water” in the basal nucleus of Meynert, a critical area for thought and reasoning. Higher levels of this free water, indicative of microscopic changes such as inflammation or cell loss, served as a potential marker for neuronal degeneration. Remarkably, individuals who eventually developed DLB exhibited significantly elevated free water levels in this region, making them eight times more likely to transition to DLB. This approach proved to be more sensitive than traditional methods focused on brain shrinkage.

“It’s compelling that this marker can detect early changes, even before the onset of symptoms,” Haddad mentioned.

Steps Toward Precision Medicine

The studies mark a pivotal point in international imaging research concerning patients with confirmed iRBD, laying the groundwork for personalized screening methods that can predict which disease may arise before any symptoms manifest. Researchers suggest that healthcare providers could adapt their monitoring strategies to match individual patient pathways and more effectively direct clinical trials aimed at preventive therapies. Their model for early intervention could be revolutionary in addressing neurodegenerative conditions before irreversible issues occur.

“We’ve known that isolated REM sleep behavior disorder signals potential for these diseases,” Rahayel explained. “What we didn’t entirely grasp was the specifics of who might develop what. These allied studies have equipped us with tools to better predict and customize treatment.”