Parkinson's disease (PD) is a brain disorder that leads to shaking, stiffness, and difficulty with walking and balance. This study looks at changes in the brain over time in people with PD. The focus is on a protein called SV2A, which helps with communication between brain cells. Researchers want to see if SV2A loss spreads from the brainstem to the outer part of the brain (cerebral cortex) as PD progresses.

Participants who were part of a previous study about 7 years ago will be invited back. They will undergo tests, including a PET-CT scan, which uses a small amount of radiation to look at brain activity, and an MRI, which uses magnets to create pictures of the brain. These tests help us see changes in the brain over time.

• Participants must have been in the previous study (S61477).
• People with other brain disorders or certain health issues cannot join.
• Participants must not have had too much exposure to certain types of radiation in the past year.

This study helps us understand how PD affects the brain over time, which might help improve future treatments.