The appendix, which has long been considered to be a largely useless organ, is getting a major promotion thanks to the results of a study published on Oct. 31, 2018 in the journal Science Translational Medicine. Unfortunately, a pretty big chunk of the findings point to the appendix as an accomplice in the development of Parkinson's disease.
A neurodegenerative disorder, Parkinson's is hallmarked by the slow progression of life-inhibiting symptoms, such as tremor, limb rigidity and balance problems. Although the exact cause is unknown, abnormally folded alpha-synuclein proteins are linked to Parkinson's. The study found that the appendix functions as a "reservoir" for these proteins, indicating that it is far more involved in Parkinson's than originally thought.
"Our results point to the appendix as a site of origin for Parkinson's and provide a path forward for devising new treatment strategies that leverage the gastrointestinal tract's role in the development of the disease," said Viviane Labrie, Ph.D., senior author of the study in a press release. "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."
The team used data from two large health-record databases of nearly 1.7 million people (the Swedish National Patient Registry and Statistics Sweden) and followed the patient progression over 52 years in some cases. The scientists also culled information from the Parkinson's Progression Marker Initiative (an ongoing worldwide study), including the age of onset, genetic components and demographics.
The researchers found that people who'd had their appendixes removed early in life showed a 19 percent reduction in Parkinson's risk. For people in rural areas, the risk reduction was 25 percent (rural residents are generally at higher risk of the disease because it has been linked to pesticide exposure). These findings suggest that the appendix plays a role in developing the disease at some point in life. (Removing the appendix after Parkinson's had started didn't have any effect on disease progression.)
Interestingly, the presence of the alpha-synuclein proteins doesn't necessarily spell disaster, as the team found clumps of them in healthy people's appendixes, as well. Until now, they were only thought to be found in the appendixes of people with Parkinson's.
"We were surprised that pathogenic forms of alpha-synuclein were so pervasive in the appendixes of people both with and without Parkinson's. It appears that these aggregates — although toxic when in the brain — are quite normal when in the appendix. This clearly suggests their presence alone cannot be the cause of the disease," said Labrie, an assistant professor at Van Andel Research Institute in Grand Rapids, Michigan.
"Parkinson's is relatively rare — less than 1 percent of the population — so there has to be some other mechanism or confluence of events that allows the appendix to affect Parkinson's risk," she said. "That's what we plan to look at next; which factor or factors tip the scale in favor of Parkinson's?"