The oral microbiome of early stage Parkinson’s disease and its relationship with functional measures of motor and non-motor function Original paper

What was studied?

The focus keyphrase oral microbiome in early Parkinson’s disease centers this investigation into whether early Parkinson’s disease produces measurable shifts in the oral microbiome. According to the document from June 27, 2019, the study applied shotgun metatranscriptomic sequencing to saliva to determine how microbial taxa and their functional transcripts differ between early-stage Parkinson’s disease (PD) and neurologically healthy controls. This method captured both the microbial composition and the active gene expression profiles, allowing the researchers to evaluate functional pathways—including neurotransmitter-relevant ones—more directly than 16S approaches. The study sought to map microbial changes that could serve as clinically relevant biomarkers or mechanistic clues linking oral microbial activity to neurological features.

Who was studied?

As detailed in the document, subjects were recruited from the Syracuse and Upstate New York region and provided informed consent. The PD group included individuals previously diagnosed with late-onset PD who met diagnostic criteria, including bradykinesia and rigidity or resting tremor, while excluding those with advanced disease (Hoehn & Yahr ≥4) or secondary Parkinsonism causes. Controls were free of major medical conditions, PD medications, movement disorders, and first-degree relatives with PD. All participants lacked active oral disease and recent antibiotic exposure. Clinical assessments included MDS-UPDRS, autonomic questionnaires, quality-of-life measures, sensory and balance tests, and comprehensive motor evaluations.

Most important findings

Microbiome profiling revealed clear taxonomic and functional differences between PD and controls. Table 4 (page 11) shows significantly altered taxa, including increased Lactobacillus, Bifidobacterium, Acidaminococcus, Gardnerella, Parascardovia, Rhodococcus, and several Candida species, while decreases occurred in Buchnera, Campylobacter ureolyticus, Chryseobacterium, and others. Many shifts carried mechanistic relevance. Lactobacillus and Bifidobacterium produce GABA and acetylcholine, while Enterobacteriaceae and Bacillus species influence norepinephrine, serotonin, and dopamine synthesis. A particularly striking finding was increased Nocardiaceae, including Rhodococcus, which has been shown experimentally to induce movement disorders responsive to L-DOPA, suggesting a provocative link to PD-related neuroinflammatory pathways.

Key implications

The study demonstrates that early PD is associated with distinct oral microbial signatures involving neurotransmitter-associated taxa and inflammation-linked organisms. These findings hint at a potential oral–brain axis paralleling the more established gut–brain pathway. The work suggests value in oral microbiome profiling as a non-invasive biomarker and highlights microbial taxa with plausible mechanistic contributions to PD symptoms. Further validation in differential-diagnosis cohorts and longitudinal designs remains necessary.

Citation

Mihaila D, Donegan J, Barns S, LaRocca D, Zheng D, Vidal M, et al. The oral microbiome of early stage Parkinson’s disease: Functional correlates.PLOS ONE. 2019;14(6):e0218252. doi:10.1371/journal.pone.0218252