Parkinson’s disease is a neurodegenerative disorder. It primarily affects the neurons in the brain that produce dopamine, specifically in a part of the brain called substantia nigra. The symptoms include tremors, slow movement, rigid limbs, and gait and balance problems.

Although the cause of the disease is mostly unknown, the predominant thinking is it’s central nervous system-related.

But now, researchers from Van Andel Research Institute, based in Grand Rapids, Mich., found that people who had appendicitis resulting in the removal of the organ had a lower risk of developing Parkinson’s disease later in life. Their research was published in the journal Science Translational Medicine.

The appendix is considered a vestigial organ—useless, in other words, a leftover from our evolutionary past, but it does seem to store an abnormal protein. There is a theory that its function is to store “good” bacteria, which helps restore gut bacteria after diarrheal illnesses.

Part of the Van Andel group’s thinking is the appendix seems to store an abnormal protein. And if that protein finds itself in the brain, may cause or be involved with the development of Parkinson’s disease.

The study also suggested that the problematic protein is more common than expected, found in all ages, as well as in people with healthy brains and in Parkinson’s patients.

“We’re not saying to go out and get an appendectomy,” said Viviane Labrie, who led the research group, reported AP.

The connection between the gastrointestinal (GI) tract and the development of Parkinson’s has been noted before, with constipation and other GI problems common leading up to the tremors and movement issues.

The protein in question is a bad “alpha-synuclein” protein. It is known to travel from nerves in the GI tract up to the vagus nerve, which is a connecting point between the brain and the major organs in the body. Abnormal alpha-synuclein is toxic to the brain cells associated with movement.

An earlier study found that individuals whose vagus nerve was cut as part of therapy that is no longer performed had a lower risk of Parkinson’s. There were also some smaller suggestive studies related to appendectomies, but with inconsistent results.

Labrie’s team analyzed Sweden’s national health database, studying medical histories of nearly 1.7 million people followed since 1964. They found that in people who had appendectomies, there was a 19 percent lower risk of developing Parkinson’s later.

But the study isn’t without its puzzling details. For example, people who live in rural areas also seemed to have a lower risk. Labrie speculates that environmental factors may be in play.

Andrew Feigin, executive director of the Parkinson’s Institute at NYU Langone, who was not involved in the research, told AP that the study doesn’t prove that removing the appendix is what actually decreases the risk of Parkinson’s. The actual link, if there is one, is elusive.

Labrie’s team went further in their research and examined appendix tissue biopsied from 48 people with no Parkinson’s. They found the abnormal protein in 46 of those patients’ appendices. So did some of the patients with Parkinson’s. Appendix inflammation did not seem to matter.

Labrie indicates that this is a significant finding because says that harboring the protein in the GI tract isn’t enough to trigger Parkinson’s disease. There’s some other factor or another step that makes it high risk for some people. “The difference we think is how you manage this pathology,” she told AP.

There are other risk factors as well, including a traumatic brain injury. The disease is also more common in men and the risk increases with age. It is also more common in Caucasians than in Asians and people of African descent but has a higher incidence in Hispanics.