Could the Appendix Be Key to Parkinson's Disease?
Long belittled as inconsequential, the appendix is hardly the rock star of body organs. But its reputation may get a boost from new research that suggests that removing it may lower the risk for Parkinson's disease.
The finding follows an analysis that examined how appendix removal surgery (appendectomy) affected Parkinson's risk among 1.6 million Swedish residents.
The study couldn't prove cause and effect, but it found that appendectomy lowered Parkinson's risk by roughly 20 percent.
"This is a tissue that most people consider to be a useless organ. It's attached to the large intestine, and it's removed as a very common surgical practice," said study author Viviane Labrie. She's a neuroscientist with the Center for Neurodegenerative Science at the Van Andel Research Institute in Grand Rapids, Mich.
The new findings suggest, "that the appendix may be a tissue site that plays a role in the initiation of Parkinson's disease," she said.
Why? "The hallmark pathology of Parkinson's disease in the brain is Lewy bodies, which is characterized by a clumped form of a protein called alpha-synuclein," Labrie explained.
What's more, clumps of this protein are found in the intestinal tract and are "present in the appendixes of all of us," sometimes years before Parkinson's symptoms arise, she said.
So, "we think that if in rare events [such protein clumps] were to escape the appendix and enter the brain, this could lead to Parkinson's disease." How? Simply by traveling up the nerve that connects the intestinal tract directly to the brain, Labrie said.
Parkinson's attacks the nervous system and results in a progressive loss of both motor function and many non-motor functions.
Common among the complications of Parkinson's is the onset of gastrointestinal dysfunction -- including constipation -- which can actually precede mobility loss by as much as 20 years. This signaled a potential link between Parkinson's onset and the appendix, the researchers explained.
To investigate, researchers pored over data previously collected by the Swedish National Patient Registry. The registry is unique because since 1964 it has maintained a full record of diagnoses and surgeries for a huge swath of the Swedish patient pool.
Of the 1.6 million covered patients, more than 550,000 had undergone an appendectomy.
After following Parkinson's incidence for up to 52 years post-surgery, investigators found that Parkinson's was ultimately diagnosed in 1.2 out of every 1,000 appendectomy patients, compared to a risk of 1.4 out of every 1,000 people in the general Swedish population.
That meant that Parkinson's risk had dropped by 19.3 percent among those who had had their appendix removed.
What's more, after honing in on the specific experiences of about 850 Parkinson's patients, the researchers determined that appendix removal was also associated with a 3.6-year delay in the onset of Parkinson's among those who had the surgery and still developed the disease.
Still, Labrie stressed that "we are not saying that having an appendix causes Parkinson's disease, and that all people should go out and remove their appendix."
Rather, "we think that what actually distinguishes a person that goes on to develop Parkinson's from one that does not is not the presence of this pathology, but rather the factors that trigger departure from the appendix." That raises the prospect for developing new therapies designed to prevent such protein clumps from escaping the appendix.
The findings were published in the Oct. 31 issue of Science Translational Medicine.
Dr. Rachel Dolhun is vice president of medical communications for the Michael J. Fox Foundation for Parkinson's Research. She described the link between Parkinson's and the appendix as "particularly interesting."
"But it's important to stress these are associations and do not establish causation," she said. "In other words, having an appendectomy will not definitely decrease [the] risk of Parkinson's."
Dolhun added, "Investigating the association between the gut and brain further could potentially lead to deeper understandings of the causes of Parkinson's, as well as how Parkinson's starts and progresses, and how to intervene to stop it. But much work remains to be done."
There's more on Parkinson's disease at The Michael J. Fox Foundation for Parkinson's Research.
SOURCES: Viviane Labrie, Ph.D., neuroscientist and assistant professor, Center for Neurodegenerative Science, Van Andel Research Institute, Grand Rapids, Mich.; Rachel Dolhun, M.D., vice president, medical communications, Michael J. Fox Foundation for Parkinson's Research, NYC; Oct. 31, 2018, Science Translational Medicine
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