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Clusters of proteins found in the brains of people with Parkinson's disease are also found elsewhere in the body, inside the appendages of healthy people.
This discovery led researchers to study the link between the appendix and the risk of developing Parkinson's disease. For example, a study conducted in October 2018 revealed that withdrawal from the appendix was associated with a decreased risk of developing the disorder, reported Live Science.
But new findings suggest the opposite: removing the appendix is associated with an increased risk of developing Parkinson's disease. The study, which is yet to be published in a peer-reviewed journal, will be presented later this month at the Digestive Disease Week, a scientific meeting devoted to digestive tract diseases. [3 Myths About Parkinson’s Disease]
The new study examined data from more than 62 million patients, using a database of 26 major health care systems in the United States. The researchers identified patients with an appendectomy – a surgical procedure to remove the appendix – and identified those who developed Parkinson's disease. at least six months later.
Scientists have found that of the more than 488,000 patients whose appendixes were removed, 4,470 (0.9%) subsequently developed Parkinson's disease. Of the remaining 61.7 million patients who did not have appendectomy, approximately 177,000 (0.3%) later developed Parkinson's disease.
The results suggest that the risk of developing Parkinson's disease is about three times higher in people who have had an appendectomy than in those who do not, regardless of age, gender or race.
However, Dr. Gregory Cooper, senior author, professor of medicine at Case Western Reserve University in Cleveland, said that "at this point, it is still an association" and not from one cause to effect. In other words, the study does not prove that removing the appendix causes Parkinson's disease.
One possible explanation for the increased risk found in the study is that, during an appendectomy, a specific agent – called alpha-synuclein protein – is released into the body and travels up to the brain, a said Cooper. These proteins are known to form clusters called Lewy bodies – a telltale sign of Parkinson's disease.
Yet this explanation is "speculative," Cooper told Live Science.
Reverse causality?
Viviane Labrie, assistant professor of neuroscience at the Van Andel Research Institute in Michigan, who was not part of the new research, said that the study "does not have a long window of followed". This means that researchers could only link appendectomies to the onset of Parkinson's mobility problems, she said.
But these movement problems, or motor symptoms, do not really represent the onset of the disease, Labrie told Live Science. Parkinson's disease has a rather "prodromal period" of about 20 years before the onset of these telltale symptoms. During this time, other less obvious symptoms may occur.
For example, during the prodromal period, people with Parkinson's disease may experience symptoms such as constipation or other digestive issues, Labrie said. But, what complicates things further, these symptoms can increase the risk of appendicitis, the inflammatory condition leading to an appendectomy. Thus, it is possible that the prodromal symptoms of Parkinson's disease are at the origin of appendicitis and subsequent surgery, and not the removal of the appendix causing Parkinson's disease, she said.
Labrie was the lead author of a study published in October 2018 in Science Translational Medicine, which used data from a Swedish database of over 1.6 million people who had followed patients during a period of up to 52 years. This report revealed that people whose appendix had been removed when they were young had 19% to 25% less risk of developing Parkinson's disease later in life.
The "essential difference between [the Swedish] study and the [new] American study is [the] the patients were followed, "said Labrie.
Cooper agreed that one limitation of his study involved the limited data available during the follow-up period. This is because the patient information has been anonymized. The researchers were therefore unable to see how long it took for some patients to develop Parkinson's disease after an appendectomy. But since the database has been collecting data since 1997, at least some of the patients have been followed for almost 30 years, he said.
In addition, because researchers did not have access to patients' medical records, they could not examine other factors that may have influenced the results, such as specific symptoms or drugs, Cooper added.
The risk is still very low
In the end, there is still no consensus on whether appendicectomies are associated with a higher risk of Parkinson's disease.
A 2016 study published in the journal Movement Disorders revealed results similar to those of this new study, namely that an appendectomy was associated with an increased risk of Parkinson's disease 10 years or more after surgery. but this risk was much smaller than that noted in the recent study. Other research, such as a 2018 article published in Movement Disorders, has revealed a weak or no association between appendectomies and Parkinson's disease.
In any case, Cooper pointed out that, although the study found an association between an appendectomy and the risk of developing Parkinson's disease, the risk is very low: less than 1% of people developing Parkinson's disease had undergone an appendectomy, he said.
"I do not want people to come out of here and say," Well, I have appendicitis. I will not take out my appendix because I do not want to contract Parkinson's disease, "he said. "If you have appendicitis … you should get your appendix."
It was reminiscent of what Labrie told Live Science last fall, when her article was published: "One of the things we do not want people to understand is that [they] should have preventive appendectomies or simply because you have an appendix, you will contract Parkinson's disease. "
Originally published on Science live.
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