Gastrointestinal problems in Parkinson’s disease patients could be due to changes in the gut microbiome leading to increased inflammation, suggest findings from a study carried out at the Quadram Institute in the U.K.
People with the common neurodegenerative disorder Parkinson’s disease often develop gastric symptoms that can sometimes start years before they develop any movement problems.
This and recent research linking the gut microbiome to a number of different neurological disorders has led researchers to investigate whether there are notable changes in the gut microbiome of patients with Parkinson’s.
Individual studies have suggested some microbiome differences between patients and healthy controls, but results have been inconclusive and difficult to compare, possibly because of variation in methods or between individuals and populations.
To try and overcome some of these difficulties, Stefano Romano, Ph.D., and colleagues from the Quadram carried out a meta-analysis including results from 10 studies including just over 1200 people (50% Parkinson’s, 50% controls) correcting for potential biases in the data.
The results, published in the journal npj Parkinson’s Disease, show distinct differences between the gut microbiome of people with Parkinson’s and controls.
The most noticeable difference in those with the neurodegenerative condition was an increase in bacteria from the Lactobacillus, Akkermansia, and Bifidobacterium genera and a decrease in Lachnospiraceae family and Faecalibacterium genus bacteria—both of which produce important fatty acids such as butyrate.
“The variability across studies is very big. However, we can still detect differences between the gut microbiome of patients and controls. This means that microbiome alterations in Parkinson’s disease are consistent across sampling cohorts,” says Romano.
“There is a clear need to further research gut microbial changes linked to diseases in diagnostic or prognostic applications.”
Butyrate and similar fatty acids are used by intestinal cells to help maintain the gut barrier. They also help regulate interactions between the gut, nervous system and the brain.
Previous studies have shown that butyrate is low in Parkinson’s disease patients, who also commonly have increased inflammation in the gut and permeability of the gut lining. This is something they have in common with inflammatory bowel disease patients who have a 20% to 30% increased risk of developing Parkinson’s compared with the overall population.
The bacteria found in increased amounts in the gut of Parkinson’s patients are involved in methane production and degradation of mucus, which may also contribute to the gastrointestinal symptoms seen in these individuals.
Because of the variability they observed and the meta-analysis nature of the study, the researchers write that “it is important to stress that using the available data it is impossible to determine whether the associations reported are causally linked to Parkinson’s disease.”
They suggest that future studies should “concentrate on standardizing the recruitment criteria and preferentially focus on early-stage drug-naive patients” to more accurately evaluate whether microbiome alterations could actually increase the risk of someone developing Parkinson’s.