This study looks at a new treatment called **XS411** for Early-onset Parkinson's Disease (EOPD). Parkinson's Disease is a condition that affects movement, causing symptoms like shaking and stiffness. This study is in two parts - Phase I and Phase II. Phase I tests the safety and how well people handle XS411. Up to 12 people will get a single shot of XS411 and be watched for 28 days. If all goes well, Phase II begins, testing if XS411 works better than a fake treatment (placebo). In Phase II, 81 people will receive either XS411 or the placebo. Key Points:
- Phases: Phase I focuses on safety, and Phase II on effectiveness.
- Duration: Participants can't join other studies or surgeries for 24 months.
- Eligibility: Ages 18-70 with EOPD, no recent brain surgeries, and stable anti-PD drug doses.