This study investigates whether signs of Parkinson's disease or REM Sleep Behavior Disorder (RBD) can be detected through tissue samples taken from the colon during routine colonoscopy. The purpose of this observational study is to find out if a protein called alpha-synuclein, which builds up in people with Parkinson's disease or RBD, can be identified in these samples. Participants will be in the study for the duration of their routine colonoscopy procedure, which is not extended by the study.

During the study, participants will undergo a standard colonoscopy procedure. During this procedure, doctors will take four additional small tissue samples, two from each side of the colon. These samples will be tested for the presence of the alpha-synuclein protein. The procedure itself will not require additional visits or change the normal course of a colonoscopy.

• Who can participate: Adults aged 40 to 99 diagnosed with Parkinson's disease or REM Sleep Behavior Disorder and scheduled for a routine colonoscopy can participate. Key eligibility factors include not using certain anticoagulants, not being under active treatment for colon cancer, and not having significant cognitive impairments.
• Study details: Participants will undergo a routine colonoscopy during which additional tissue samples will be collected. These samples will be analyzed for the alpha-synuclein protein. Participants will not receive individual results from this testing.