Alpha-synuclein misfolding as a fluid biomarker for Parkinson's disease and synucleinopathies measured with the iRS platform

Abstract Misfolding and aggregation of alpha-synuclein (αSyn) plays a key role in the pathophysiology of Parkinson’s disease (PD). It induces cellular and axonal damage already in the early stages of the disease. Despite considerable advances in PD diagnostics by αSyn seed-amplification assays (SAAs), an early and differential diagnosis of PD still represents a major challenge. Here, we extended the immuno-infrared sensor (iRS) platform technology from Alzheimer’s disease (AD), in which β-amyloid misfolding was monitored as a fluid biomarker towards αSyn misfolding in PD. Using the iRS platform technology, we analyzed cerebrospinal fluid (CSF) from two independent cohorts, a discovery and a validation cohort comprising clinically diagnosed PD (n=57), atypical Parkinsonian disorders with αSyn pathology (multiple system atrophy (MSA), n= 5) or Tau pathology (corticobasal degeneration (CBD), n=5, progressive supranuclear palsy (PSP) n=9), and further disease controls (frontotemporal dementia (FTD) n=7 and other, n=51). In the discovery cohort, an AUC of 0.90, 95 %-CL 0.85 – 0.96 is obtained for the differentiation of PD/MSA vs. all controls, and in the validation cohort, an AUC of 0.86, 95 %-CL 0.80 - 0.93, respectively. In the combined dataset, the αSyn misfolding classifies PD/MSA from controls with an AUC of 0.90 (n=134, 95 %-CL 0.85 - 0.96). Using two threshold values instead of one identified people in the continuum between clearly unaffected (low misfolding group) and affected by PD/MSA (high misfolding group) with an intermediate area in between. The controls versus PD/MSA in the low vs. high misfolding group were classified with 97% sensitivity and 92% specificity. The spectral data showed misfolding in CSF from an α-helical/random-coil secondary structure of αSyn in controls to β-sheet enriched secondary structures in PD and MSA patients. In subgroups, the iRS platform implied a potential for stratifying patients with overlapping clinical symptoms. With high accuracy, the iRS αSyn misfolding platform provides a novel diagnostic tool using body fluids for differential, biological classification of the αSyn associated disorders PD and MSA. The iRS platform, indicating directly and fast all αSyn conformers, is complementary to the αSyn SAAs, which also uses αSyn misfolding as a fluid biomarker. However, monomers amplify competent misfolded conformers in SAA over time. The iRS platform opens new avenues for the stratification of PD by a body-fluid analysis and follow-ups in the continuum of healthy to clinically impaired individuals.