Abstract
In recent years evidence has emerged that neurodegenerative diseases (NDs) are strongly associated with the microbiome composition in the gut. Parkinson’s disease (PD) is the most intensively studied neurodegenerative disease in this context. In this review, we performed a systematic evaluation of the published literature comparing changes in colonic microbiome in PD to the ones observed in other NDs including Alzheimer’s disease (AD), multiple system atrophy (MSA), multiple sclerosis (MS), neuromyelitis optica (NMO) and amyotrophic lateral sclerosis (ALS). To enhance the comparability of different studies, only human case-control studies were included. Several studies showed an increase of Lactobacillus, Bifidobacterium, Verrucomicrobiaceae and Akkermansia in PD. A decrease of Faecalibacterium spp., Coprococcus spp., Blautia spp., Prevotella spp. and Prevotellaceae was observed in PD. On a low taxonomic resolution, like the phylum level, the changes are not disease-specific and are inconsistent. However, on a higher taxonomic resolution like genus or species level, a minor overlap was observed between PD and MSA, both alpha synucleinopathies. We show that standardization of sample collection and analysis is necessary for ensuring the reproducibility and comparability of data. We also provide evidence that assessing the microbiota composition at high taxonomic resolution reveals changes in relative abundance that may be specific to or characteristic of one disease or disease group, and might evolve discriminative power. The interactions between bacterial species and strains and the co-abundances must be investigated before assumptions about the effects of specific bacteria on the host can be made with certainty.
Highlights
The causes of the heterogenic group of neurodegenerative diseases (NDs) are still unknown but several contributing factors including genetic and lifestyle factors and age-related aberration of health are likely to play a role
We show that analysis of colonic bacterial composition at the highest possible resolution may be predictive for Parkinson’s disease (PD) and discriminate PD from other neurodegenerative diseases [19,28,29,30,31,32]
Changes in the composition of colonic microbiota are found in PD and several other NDs [26,27]
Summary
The causes of the heterogenic group of neurodegenerative diseases (NDs) are still unknown but several contributing factors including genetic and lifestyle factors and age-related aberration of health are likely to play a role. While some researchers question whether PD begins in the gut, a potential role of the gut microbiome in PD pathology is undisputed [4]. In the intestinal tracts of PD patients, a pro-inflammatory microbiota composition was discovered, which might lead to increased gut permeability. This high permeability of the intestinal mucosa is known as leaky gut, since bacterial products and inflammatory mediators could pass through the gut’s mucosa and invade the blood [5].
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