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.
