The earliest evidence that the gut might be involved in Parkinson’s emerged more than 200 years ago. In 1817, the English surgeon James Parkinson reported that some patients with a condition he termed “shaking palsy” experienced constipation.
https://www.scientificamerican.com/article/does-parkinsons-begin-in-the-gut/
https://www.scientificamerican.com/article/does-parkinsons-begin-in-the-gut/