A colonoscopy or similar test could one day diagnose Parkinson's disease years before symptoms occur. That's because signs of Parkinson's that appear in the brain also show up in the colon, a new study says.
Researchers examined tissue samples obtained during colon exams of people who later developed Parkinson's disease. The samples were taken several years before the patients showed symptoms of the neurological disorder.
The cells in the patients' intestinal walls were found to contain clumps of alpha-synuclein — a hallmark protein of Parkinson's.
In a previous study, these researchers found these aggregates were apparently unique to the gut of Parkinson's disease patients — they were not seen in people with certain gut disorders or in healthy people.
The findings suggest that tissue obtained during a colonoscopy or other colon cancer screening test could one day be used to predict who will develop Parkinson's, said study researcher Dr. Kathleen Shannon, a neurologist at Rush University Medical Center in Chicago.
However, first the findings will need to be replicated in studies that include more people, including people with other types of brain diseases, the researchers said.
Currently doctors cannot diagnose Parkinson's until patients show symptoms, such as shaking, slowed movements and stiff muscles. By then, however, the patients' brains have deteriorated significantly. Finding early markers of the disease could lead to a way to slow or stop the progression, the researchers said.
Parkinson's disease is caused by loss of brain cells that produce dopamine, a brain chemical needed to control muscle movement. One change that occurs in the brains of Parkinson's patients is the formation of clumps called Lewy bodies. The protein alpha-synuclein is found in all Lewy bodies, according to the Mayo Clinic.
Recent research suggests the Parkinson's disease process begins in nerve cells in the gut and spreads to nerves in the brain, Shannon said.
In a 2011 study, Shannon and colleagues examined intestinal tissue samples taken from nine Parkinson's patients, 23 healthy people and 23 people with Crohn’s disease or ulcerative colitis (both types of inflammatory bowel disease). The people in the study ranged in age from early 20s to late 70s.
All nine Parkinson's disease patients had clumps of alpha-synuclein in the nerves of their gut tissue, while none of the healthy people or people with gut disorders did. Two healthy people and three colitis patients had a small amount of alpha-synuclein in their cells, but it was distinct from the amount seen in the Parkinson's patients.
In a study published today (May 15) in the journal Movement Disorders, the researchers reported they examined tissue samples from three patients taken during colonoscopies two to five years before the patients developed Parkinson's disease symptoms. All the patients had the characteristic aggregates of alpha-synuclein in their gut.
"It's really interesting and provocative," Dr. William Weiner, a neurologist at the University of Maryland School of Medicine and member of the American Academy of Neurology, said of the study findings. The hypothesis that Parkinson's disease starts in the gut has not had much tangible evidence until now, Weiner said.
However, the new study does not demonstrate that clumps of alpha-synuclein in the gut develop before the protein begins to show up in the brain, Weiner said.
"The same changes might be going on in the brain at the same time," he said.
The idea that alpha-synuclein forms deposits in tissues other than the brain in Parkinson's patients is pretty well established, said Dr. Kenneth Marek, president and senior scientist at the Institute for Neurodegenerative Disorders, a research company in New Haven, Conn. However, "to what extent these findings suggest where the disease might begin or how it might begin is a much murkily question," Marek said.
But Marek agreed the findings suggest tissue samples taken during a colonoscopy "could be helpful in understanding whether you are at high risk to develop Parkinson's," Marek said.
Because the new study looked at only three people, much larger studies are needed to confirm the findings, Weiner said.
Pass it on: A colonoscopy someday may be able to identify Parkinson's disease, but much more work is needed first.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.