Detection of Alpha-Synuclein Seeding Activity in Tear Fluid as a Non-Invasive Biomarker for Parkinson’s Disease

Introduction: Parkinson’s disease (PD) is marked by the misfolding and aggregation of alpha-synuclein (aSyn). Non-invasive biomarkers detecting this pathology could greatly improve early diagnosis and disease monitoring.

Objectives: To assess the feasibility of using tear fluid (TF) to detect misfolded aSyn via the synuclein seed amplification assay (synSAA).

Methods: SynSAA was applied to TF samples from a discovery cohort (11 PD patients, 13 healthy controls) and a validation cohort (9 PD patients, 11 non-synucleinopathy controls, including prion disease patients). A subset of post-reaction TF samples was analyzed by electron microscopy (EM) to visualize aSyn fibrils. Matched cerebrospinal fluid (CSF) and TF samples were analyzed from selected individuals.

Results and Discussion: aSyn seeding activity was detected in over 55% of PD patients across both cohorts. One control sample tested positive, which may suggest possible subclinical pathology or an incidental finding, while all prion disease samples were negative. PD patients consistently exhibited the highest seeding activity. Results were concordant between TF and matched CSF samples, supporting TF’s reliability in reflecting central synuclein pathology.

Conclusion: This study is the first to demonstrate the detection of Lewy body-type aSyn aggregation in tear fluid using synSAA, further supported by EM visualization of fibrils. TF emerges as a promising, non-invasive biofluid for PD diagnosis and monitoring.