Therapies to slow or stop Parkinson's are advancing through development, but they all face a similar challenge: there's no objective measure of their impact on the underlying disease.

What's inside this guide?

• How lack of those measures, called biomarkers, slows testing of new treatments
• How biomarkers can help diagnose Parkinson's
• Where in the body researchers are looking for biomarkers
• How people with and without Parkinson's disease can help identify a biomarker to speed better treatments