This study looks at using a medicine called adalimumab to see if it can help people with a sleep problem called REM Sleep Behavior Disorder (RBD). RBD is when people act out their dreams because they lack muscle relaxation during sleep. The study will compare adalimumab with a placebo (a fake treatment) to check if it can slow down brain changes related to synucleinopathy, which can lead to diseases like Parkinson's Disease. Researchers will use a special brain scan called FDG-PET to see changes in brain activity.

Key Points:

• The study lasts about 2 years, with visits every 4 to 24 weeks.
• Participants will need to wear a sensor at home for 7 days every 6 months to track sleep.
• Some participants will have a cerebrospinal fluid test to study brain changes.

To join, participants must have RBD, have a study partner, and be able to inject the study drug. Women must not be pregnant or breastfeeding. People with certain health issues, or those taking specific medications, cannot participate. Participants will be monitored for safety and changes in their condition throughout the study.