The idea that Parkinson’s starts in the gut might be wrong—it looks like brain-only cases are actually 16 times more common.
It has become widely accepted that Parkinson's starts in the gut and spreads to the brain, but this exhaustive autopsy study found that pathology restricted to the brain is actually the norm. The findings suggest that the spread of the disease from the gut is a rare exception rather than the primary cause.
Brain-Only Versus GI-Only Synucleinopathy: A Comprehensive Autopsy Study With Both IHC and SAA
medRxiv · 10.64898/2026.03.18.26348355
Braak and others have proposed that Lewy body pathology LBP in Parkinson disease PD may arise not only in the brain but alternatively from an initial site in the gastrointestinal GI tract with subsequent passage to the central nervous system CNS through the vagus nerve or other routes. We tested this hypothesis by using both immunohistochemistry IHC and RT QuIC a form of alpha synuclein seed amplification assay SAA to detect alpha synuclein LBP in samples from selected brain regions and 10 GI tr