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PD in the Feces: Stool Samples Could Detect Early Parkinson’s

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New research finds a Parkinson’s-related biomarker in stool samples from individuals with a sleep disorder linked to later developing Parkinson’s.

Making an accurate Parkinson’s disease (PD) diagnosis is complicated because there is no single test. Doctors look at symptoms such as tremor, rigidity and difficulty walking to make a diagnosis. As a result, it can take years after the onset of early symptoms to get an accurate diagnosis. And while there are treatments available to alleviate symptoms, they can’t slow down or stop the disease.

A new study suggests that a stool sample could help detect Parkinson’s before movement symptoms start. Detecting Parkinson’s early can help researchers better understand how Parkinson’s works and ultimately, develop treatments that can slow disease progression.

What is alpha synuclein?

When it comes to Parkinson’s, the protein called alpha synuclein plays a critical role. This protein, believed to be important for normal neuronal function, begins to form sticky clumps in neurons (cells in the brain) in PD. Over time, the clumping kills neurons and impairs the brain’s ability to produce dopamine, leading to Parkinson’s symptoms and ultimately a diagnosis.

To develop a test for a disease, researchers often rely on a biological indicator (called a biomarker). A potential biomarker of Parkinson’s is a protein called alpha-synuclein, which is involved in normal brain cell function but accumulates abnormally in Parkinson's. The presence and increase in alpha-synuclein clumping levels in the cerebrospinal fluid (CSF) in Parkinson’s has been well documented; however, collecting the CSF is invasive and challenging. Alpha-synuclein aggregates have also been detected in the saliva, tears, urine, and blood of people with Parkinson’s. However, to this date, no method has been developed to reliably predict or diagnose Parkinson’s using these samples.

A recent study published in Nature Parkinson’s Disease and funded by the Parkinson’s Foundation, describes how alpha-synuclein levels detected in stool samples could predict Parkinson’s disease onset. Gültekin Tamgüney, PhD, a Parkinson’s Foundation Impact Award recipient, led the research team.

Doctor holding a stool sample container

The study is based on recent research that indicated that it might be possible for alpha-synuclein to be shed in the gut, and therefore found in feces. The amounts of alpha-synuclein shed by the body are too small for standard lab techniques to detect them. Thus, a team of researchers studied whether they could use a special technique called sFIDA (surface-based fluorescence intensity distribution analysis) to accurately detect alpha-synuclein in stool samples.

The researchers used sFIDA in stool samples from people with Parkinson’s, healthy people, and people who have a sleep disorder called isolated rapid eye movement sleep behavior disorder (iRBD). Past research indicates that 80% of individuals with iRBD — which can lead people to act out their dreams through movements such as kicking, punching, or getting out of bed and walking around — later develop Parkinson’s or dementia. Importantly, individuals with iRBD also display many of the non-movement symptoms observed in people with Parkinson’s and have high amounts of alpha-synuclein aggregates in their nervous system.

Study Results

  • The sFIDA technique was successful at detecting alpha-synuclein aggregates in stool samples. 
  • Stool from individuals with iRBD showed significantly higher levels of alpha-synuclein aggregates than healthy individuals — the researchers were able to distinguish 76% of people with iRBD from healthy individuals. 
  • Unexpectedly, alpha-synuclein aggregate levels were similar between healthy people and people with Parkinson’s. 

The researchers were surprised that alpha-synuclein aggregates are found in the stool of people with iRBD, but not in people with a Parkinson’s diagnosis. They speculated that the presence of alpha-synuclein in the stool may be related with disease progression — the more advanced the disease is, the less alpha synuclein aggregates are shed through stool. 

What does this mean?

With further improvement, this method of detecting alpha-synuclein in the stool could be a noninvasive way to detect Parkinson’s many years before the movement symptoms appear. Earlier detection would allow for earlier treatment once researchers identify a successful disease-modifying drug. 

Additionally, researchers could use this method to monitor the effectiveness of treatments in clinical studies. For example, if a drug treatment reduces alpha-synuclein aggregate levels in stool over time, it could indicate that the treatment is having an effect.

What do these findings mean to the people with PD right now? 

Currently, this method cannot be used to diagnose Parkinson’s. Studies like this one are an exciting step toward allowing the medical research field to find a biomarker that can help doctors diagnose and track disease progression.

Learn More

The Parkinson’s Foundation believes in empowering the Parkinson’s community through education. Learn more about PD and the topics in this article through our below resources, or by calling our free Helpline at 1-800-4PD-INFO (1-800-473-4636) for answers to your Parkinson’s questions.


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