The abundances of various genera of gut bacteria found in individuals with PD differed significantly from those in the control group, found the team, led by researchers at the University of Luxembourg.
Patients in a third group, with idiopathic rapid eye movement sleep behaviour disorder (iRBD), revealed many similar trends to PD cases in gut microbiota differences versus healthy controls. People with iRBD carry a significantly increased risk of developing PD in later life.
"Parkinson's patients could be differentiated from healthy controls by their respective gut bacteria," explained first author Dr. Anna Heintz-Buschart.
The findings may enable monitoring of changes in the microbiome as a future prediction tool for PD risk.
"We hope that, by comparing the groups, we will learn to better understand the role of the microbiome in the process of the disease and to find out what changes occur and when," commented lead researcher Dr. Paul Wilmes. "This might deliver new starting points for early treatment of the disease. It would also be essential knowledge for one day being able to use the absence or presence of certain bacteria as a biomarker for early detection of the disease."
The study investigated the ‘two-hit’ hypothesis of PD development. This theoretical mechanism involves the entry of an unknown pathogen into the nose or gastrointestinal (GI) tract, which may initiate the misfolding of alpha-synuclein protein in the central nervous system. This process is thought to lead to the long-term development of Lewy bodies, a key characteristic of PD.
The bacterial composition of the gut and nasal microbiomes of 76 PD patients and 78 matched healthy individuals were analysed and compared with 21 subjects with iRBD.
No significant differences were found in nasal microbiome composition between PD and healthy controls, suggesting that nasal bacteria populations are not likely to be biomarkers for PD and that only gut microbiome composition differences might be relevant.
Species linked to specific PD symptoms
Higher abundance of Akkermansia sp. was found in PD patients, while two previously unknown types of bacteria were found to be depleted in those with the disease. The researchers speculated that the depleted species may provide a protective effect in healthy individuals, in whom they are present in greater numbers.
The team also found that relative abundance of certain types of bacteria were closely linked to particular symptoms of PD. Differences in numbers of Anaerotruncus spp., Clostridium XIVa, and Lachnospiraceae were significantly associated to motor symptoms in the PD group. Depression, commonly comorbid with PD, was significantly associated with differential abundance of Anaerotruncus spp.
The researchers also found an 80% overlap of differential bacterial abundances in PD and iRBD, strengthening the evidence for this sleep disorder as a prodrome for PD.
“In summary, our analysis revealed and confirmed differential abundances of gut, but not nasal, microbial taxa in PD patients and also revealed overlaps between PD and iRBD microbiota,” wrote the authors.
The mechanisms of microbial involvement in the development of PD would nevertheless need much further investigation, including full metagenomic analysis and metabolite detection, explained the researchers.
Source: Movement Disorders
Published online, doi: 10.1002/mds.27105
“The nasal and gut microbiome in Parkinson's disease and idiopathic rapid eye movement sleep behavior disorder”
Authors: Anna Heintz-Buschart, Paul Wilmes et al