the concern is that they will neglect the advanced pwp and use younger participants when developing treatments.

Here's an NIH study.
Biomarkers of Risk of Parkinson Disease

The point i noticed here is that they acknowledge pwp lack norepinephrine and of course dopamine. No mention of pwp needing acetylcholine. Or having too much.

https://pdrisk.ninds.nih.gov/AboutThisStudy.aspx
https://pdrisk.ninds.nih.gov/Welcome.aspx

here are some clinical trials on the subjects
http://www.clinicaltrial.gov/ct2/res...on%27s+disease

http://www.clinicaltrial.gov/ct2/res...on%27s+disease

http://www.clinicaltrial.gov/ct2/res...+parkinson%27s

here's one on RBD sleep disorder and chemical changes
http://clinicaltrials.gov/ct2/show/N...r=Open&rank=16