This study aims to assess the levels of phosphorylated alpha-synuclein (P-SYN) in patients with Parkinson's disease and REM Behavior Disorder using a minimally invasive skin punch biopsy. It seeks to understand the natural progression of P-SYN deposition over time to explore the potential of P-SYN quantification as a biomarker for disease progression.

This is a prospective, longitudinal study involving 75 Parkinson's disease patients and 25 patients with REM Behavior Disorder. Each participant will undergo a baseline evaluation followed by follow-ups every six months over an 18-month period. The evaluations will include clinical assessments, neurologic exams, and skin biopsies from three locations. Data will be collected on disease progression and the amount of P-SYN in cutaneous nerve fibers.

Inclusion Criteria:

1. Male and female 50 to 85 years of age
2. Clinical confirmed diagnosis of Parkinson's disease or REM Sleep Behavior

Exclusion Criteria:

1. Clinical evidence of severe vascular disease (history of ulceration, poor wound healing or vascular claudication)
2. History of allergic reaction to Lidocaine for local anesthesia needed for skin biopsies
3. Use of blood thinners (Plavix or Aspirin used separately is allowed)
4. Significantly impaired wound healing or history of scarring or keloid formation

sex at birth

Subjects will be enrolled from 18 sites across the US from academic institutions and private clinics.