Pathogenesis of Parkinson disease--the gut-brain axis and environmental factors.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing clinical, pathological, and animal model evidence without systematic review methodology.
PubMed 26503923 · doi:10.1038/nrneurol.2015.197
What was done
The authors conducted a narrative review of clinical, pathological, and epidemiological evidence along with animal models evaluating the hypothesis that Parkinson disease pathogenesis originates in peripheral sites (the enteric nervous system or olfactory bulb) via environmental exposures and spreads trans-synaptically to the substantia nigra and central nervous system.
What was found
The abstract reports no quantitative data or numerical effect estimates. It notes that early nonmotor symptoms (olfactory deficit and constipation) align with the presence of α-synuclein pathology in peripheral gateway tissues according to Braak staging, and highlights that intragastric administration of the pesticide rotenone in mice recapitulates typical Parkinsonian pathological and clinical features.
Why it matters
Synthesizing evidence for a gut-to-brain trans-synaptic propagation model highlights early peripheral phases of Parkinson disease as potential windows for early biomarker discovery and therapeutic intervention.
Limits
The abstract describes a narrative review rather than a systematic review or meta-analysis, omitting search criteria and study counts. Much of the mechanistic evidence relies on animal models (such as mouse rotenone toxicity) and observational clinicopathological correlations that do not definitively establish causality in human disease.
Cited by
- partial For most individuals, the pathology of Parkinson's and Alzheimer's disease begins in the nose with misfolded protein and spreads backwards into the brain.