1. Subjects with MoCA \< 19, Hoehn and Yahr score \>/=1, contraindications to skin biopsy

2. Diagnosis of Parkinson's disease

3. Diagnosis of dementia of any type

4. Diagnosis of multiple system atrophy

5. REM sleep behaviors/disturbances secondary to another cause (e.g., narcolepsy, dementia, and Parkinson's disease)

6. Contra-indications to skin biopsy:

1. Clinical evidence of severe vascular disease (history of ulceration, poor wound healing, and vascular claudication)

2. History of allergic reaction to local anesthesia for skin biopsies

3. Use of blood thinners (aspirin of Plavix alone is allowed)

4. Significantly impaired wound healing or history of scarring or keloid formation

The Syn-Sleep Study