How is the gut linked to Parkinson’s disease?

[P]hysicians have noted that constipation is one of the most common symptoms of Parkinson’s, appearing in around half the individuals diagnosed with the condition and often preceding the onset of movement-related impairments. Still, for many decades, the research into the disease has focused on the brain.

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More recently, they have also focused on the aggregation of alpha synuclein, a protein that twists into an aberrant shape in Parkinson’s patients. A shift came in 2003, when Heiko Braak, a neuroanatomist at the University of Ulm in Germany, and his colleagues proposed that Parkinson’s may actually originate in the gut.

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The vagus nerve, a bundle of fibers that originates in the brain stem and innervates major organs, including the gut, may be the primary route through which pathological triggers of Parkinson’s travel from the gastrointestinal tract to the brain.

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If alpha-synuclein does travel from the intestines to the brain, the question still arises: why does the protein accumulate in the gut in the first place. One possibility is that alpha-synuclein produced in the gastrointestinal nervous system helps fight off pathogens.

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“I think there’s likely multiple sites of origin for Parkinson’s disease,” says Viviane Labrie, a neuroscientist at the Van Andel Research Institute in Michigan. “For some individuals, it might be the gut, for others it might be the olfactory system—or it might just be something that occurs in the brain.”

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