This study looks at how the bacteria in our stomach, called gut microbiota, affects the progression of diseases like Parkinson's. **Alpha-synucleinopathies** is a big word for diseases where a protein in the brain, called alpha-synuclein, builds up and causes problems. One of the early signs of these diseases can be a sleep disorder called **idiopathic REM sleep behavior disorder (iRBD)**. People with iRBD might act out their dreams while sleeping, and this can be an early sign of diseases like Parkinson's.

The study will follow patients for 3 years, checking their gut microbiota and how their disease progresses. Only people who were part of a previous study can join, and they shouldn't have taken probiotics or antibiotics recently or have certain stomach problems.

• **Length**: 3-year follow-up with multiple visits.
• **Eligibility**: Must have been in a prior study and no recent probiotics/antibiotics.
• **Purpose**: Understand gut bacteria's role in Parkinson's progression.