Misfolding Of Alpha-Synuclein As Blood-Based Biomarker For Parkinson'S Disease

Parkinsons disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are characterized by pathological aggregation of misfolded alpha-synuclein (Syn) in the central and peripheral nervous systems. Seed amplification assays (SAAs) can detect misfolded Syn in cerebrospinal fluid (CSF), allowing a more precise biological classification of these diseases. Translating biomarker-based diagnostics to blood represents a crucial milestone to democratize access to molecular testing, as blood sampling is minimally invasive and widely scalable. However, current blood-based SAA approaches require extensive sample preprocessing, which introduces variability and has yielded inconsistent results. Here, we present the immuno-infrared-sensor (iRS) platform, which detects misfolded Syn directly in blood serum without sample preprocessing and without amplification. The iRS measures the secondary-structure distribution of Syn by distinguishing -helical/random-coil monomers from {beta}-sheet-rich oligomers and fibrils. This conformational distribution reflects disease-associated structural changes in blood and provides information beyond the binary readout of SAAs. In a combined cohort (n = 127) consisting of 74 individuals with synucleinopathies (PD, DLB, MSA and isolated rapid eye movement sleep behavior disorder (iRBD)) and 53 controls, the assay achieved a receiver operating characteristic area under the curve (ROC AUC) of 0.94 (95% confidence interval (CI), 0.88-0.99), with 88% sensitivity and 89% specificity in serum using a dual-threshold classification that categorized individuals as controls (no misfolding, green), at risk (low misfolding, yellow) or diseased (high misfolding, red). By extending the iRS platform from CSF to blood serum, this study demonstrates Syn misfolding as a promising blood-based structural biomarker for synucleinopathies. The iRS assay provides a broadly applicable platform technology for more precise biological classification, disease monitoring and assessment of drug response for PD in peripheral blood.