A Hidden Clue in the Gut May Signal Parkinson’s Disease

Parkinson’s disease is a progressive condition that affects movement and can significantly impact quality of life. While both genetic and environmental factors play a role, scientists are still trying to understand why some people at higher risk develop the disease while others do not.

One of the strongest known genetic risk factors is a change in the GBA1 gene. People who carry certain variants of this gene can have up to a 30 times higher risk of developing Parkinson’s disease. However, only about one in five of these individuals actually goes on to develop symptoms — raising an important question: What protects the others?

A study published in Nature Medicine explored whether the answer lies in the gut microbiome, the collection of bacteria and other microorganisms living in the digestive system.

“Parkinson’s disease is a major cause of disability worldwide, and the fastest growing neurodegenerative disease in terms of prevalence and mortality,” said lead investigator Anthony Schapira, M.D., head of the Department of Clinical Neurosciences at UCL Queen Square Institute of Neurology. “There is an urgent need to develop treatments that can stop or slow the disease’s progression.”

Investigators analyzed stool samples and clinical data from three groups: people with Parkinson’s disease, individuals with GBA1 variants but no symptoms, and healthy individuals without the gene variant.

The findings revealed a striking pattern. About 25% of the gut microbiome in people who carry the GBA1 variant (but do not yet have Parkinson’s) looked “intermediate” between healthy individuals and those with the disease. In other words, their gut bacteria composition was somewhere in between.

Even more importantly, this “intermediate” microbiome pattern was strongly linked to early warning signs of Parkinson’s disease, such as subtle changes that can occur before clear symptoms appear. It was also associated with how the disease progresses in people who already have Parkinson’s.

“In recent years there has been a growing recognition of the links between Parkinson’s disease — a brain disorder — and gut health,” Schapira said. “Here we have strengthened that evidence and shown that microbes in the gut can reveal signs of Parkinson’s and may be an early warning signal of Parkinson’s risk years before symptom onset.”

Investigators also looked at additional patient groups in the United States, South Korea and Turkey. They found similar microbiome patterns across these diverse populations, suggesting the results may apply broadly.

“For the first time we identify bacteria in the gut of people with Parkinson’s that can also be found in those with a genetic risk for the disease, but before they develop symptoms,” Schapira noted. “Importantly, these same changes can be found in a small proportion of the general population that may put them at increased risk for Parkinson’s.”

This research suggests that changes in gut bacteria could serve as an early signal that someone is at risk of developing Parkinson’s disease — even before symptoms begin.

While this doesn’t yet translate into a test used in everyday care, it opens the door to earlier detection and possibly even prevention strategies in the future. It also reinforces the growing understanding of the gut-brain connection in neurological diseases.

“This discovery opens the way not only to see if the bacteria are a way to identify those at risk of Parkinson’s, but also to see if changing the bacterial population, through dietary changes or medication, can reduce a person’s risk for Parkinson’s,” Schapira concluded.