Abstract
Alpha-synuclein (αSyn) aggregates are pathognomonic of Parkinson's disease (PD) and play a critical role in its pathogenesis. However, existing diagnostic approaches rely on invasive cerebrospinal fluid (CSF) sampling or tissue biopsies, limiting their accessibility and scalability in clinical practice. Here, we present the Constant Shake-Induced Conversion (CSIC) assay, a novel plasma-based technique for the detection of αSyn aggregates. A total of 102 participants, comprising 42 PD patients and 60 healthy controls (HCs), were enrolled. Plasma samples were subjected to CSIC and validated via αSyn depletion, enzyme-linked immunosorbent assay (ELISA), and Western blotting. Diagnostic performance was assessed using receiver operating characteristic (ROC) analysis, and clinical associations were examined using Spearman's correlation. The CSIC assay achieved an area under the curve (AUC) of 0.91, with 81% sensitivity and 85% specificity in distinguishing PD from HCs. Assay specificity was confirmed through αSyn depletion, and reproducibility assessments yielded intra- and inter-assay coefficients of variation below 10% and ~20%, respectively. Notably, plasma αSyn aggregate levels correlated with Hoehn and Yahr (H&Y) stage (r = 0.69), Unified Parkinson's Disease Rating Scale (UPDRS) (r = 0.68), and Montreal Cognitive Assessment scores (r = -0.47). These findings establish CSIC as a robust, non-invasive diagnostic method with strong potential for clinical implementation in PD.