Does Parkinson's disease start in the gut?

Current understanding of the pathophysiology of Parkinson's disease suggests a key role of the accumulation of alpha-synuclein in the pathogenesis. This critical review highlights major landmarks, hypotheses and controversies about the origin and progression of synucleinopathy in Parkinson's disease, leading to an updated review of evidence suggesting the enteric nervous system might be the starting point for the whole process. Although accumulating and compelling evidence favors this theory, the remaining knowledge gaps are important points for future studies.