Biomarkers for Parkinson's disease. 
Biomarkers for detecting the early stages of Parkinson's disease (PD) could accelerate development of new treatments.  Such biomarkers could be used to identify individuals at risk for developing PD, to improve early diagnosis, to track disease progression with precision, and to test the efficacy of new treatments.  Although some progress has been made, there are many challenges associated with developing biomarkers for detecting PD in its earliest stages.