Parkinson’s disease could originate in the appendix, according to one of the largest studies of the neurodegenerative illness.

The analysis of health records of more than 1 million individuals in Sweden found that having the appendix removed early in life is linked to a 19% reduced risk of developing Parkinson’s disease. The findings are the latest to implicate the gut and immune system in the genesis of the disease, in which the loss of neurons in a brain area that controls movement lead to a tremor and slurred speech.

Viviane Labrie, an assistant professor at Van Andel Research Institute in Michigan and senior author of the study, said: “Despite having a reputation as largely unnecessary, the appendix actually plays a major part in our immune systems, in regulating the makeup of our gut bacteria and now, as shown by our work, in Parkinson’s disease.”

Labrie said that the discovery could provide a path towards new treatment strategies that target the gastrointestinal tract’s apparent role in the development of the disease.

The study also revealed that the appendix acts as a major reservoir for abnormally folded proteins, called alpha-synuclein, which are closely linked to Parkinson’s onset and progression, providing a potential biological explanation for the link.

Unexpectedly, clumps of the abnormal proteins were found in healthy people too, showing that their presence alone is not enough to cause the disease. One possibility is that Parkinson’s is triggered in the rare events when the protein escapes the appendix and travels up the vagus nerve, which links the gut to the brain stem.

“There has to be some other mechanism or confluence of events that allows the appendix to affect Parkinson’s risk,” said Labrie. “That’s what we plan to look at next – which factor or factors tip the scale in favour of Parkinson’s.”

The study, published in the journal Science Translational Medicine, found further corroborative evidence of a link in a US database of 849 Parkinson’s patients, where they found that those who had undergone an appendectomy developed the disease on average 3.6 years later.

Labrie said the fact that removal of the appendix was linked to a decreased risk and not complete protection suggested that there may be multiple sites of origin in the body for the disease.

By 2020 it is predicted that 162,000 individuals in the UK will be living with the condition. While existing drugs help to control its symptoms, there are currently none available that slow or halt its progression.

Claire Bale, head of research at Parkinson’s UK, said: “There is much still to learn about how surgical approaches, such as removing the appendix, may stop the progression of toxic proteins that cause Parkinson’s.

“However, these approaches are unlikely to eliminate the condition, as Parkinson’s may also start in other areas of the body or brain. In most cases, the causes of Parkinson’s are a mystery. But understanding how the condition starts and progresses is the first step to stopping it.”

Prof Tom Foltynie of the Institute of Neurology at UCL said: “This is strong, highly valuable, long-term epidemiological evidence providing further links between gut pathology and the subsequent risk of developing Parkinson’s disease.

“The question that remains is why Parkinson’s develops in only some people with abnormal alpha synuclein aggregation in the gut, and why others are seemingly resistant. An answer to this will help us intervene to prevent those processes linking gut pathology to brain disease.”