This study is looking at a protein called phosphorylated alpha-synuclein or P-SYN, which may help doctors understand Parkinson's disease better. This protein is found in the skin, so they will use a skin punch biopsy, a small procedure to take a bit of skin. The study will last 18 months with check-ups every six months. They want to see if the amount of P-SYN changes over time in people with Parkinson's disease or REM Behavior Disorder. This might help in tracking the disease's progress.

• Participants need to be between 50 and 100 years old and have Parkinson's disease or REM Sleep Behavior Disorder.
• The study includes regular medical exams and skin biopsies every six months.
• People with certain health issues like severe vascular disease or allergies to Lidocaine cannot join.