The Michael J. Fox Foundation for Parkinson's Research (MJFF), confirms the most significant breakthrough yet in the search for a Parkinson's biomarker: a biological test for Parkinson's disease that demonstrates high diagnostic accuracy, differentiates molecular subtypes and detects disease in individuals before cardinal movement symptoms arise. The new test, known as the alpha-synuclein seed amplification assay (?Syn-SAA), heralds the revolutionary ability for research to define Parkinson's disease biologically, offering a critical tool for clinical trial design and assessment of treatment effects, and for early detection of disease pathology.