Biochemical signatures of skin α-synuclein in synucleinopathies revealed by RT-QuIC assay end-product analysis.

Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), share pathological accumulation of misfolded α-synuclein (αSyn) in the brain and overlapping clinical features, complicating accurate diagnosis with current methods. In this study, we utilized a real-time quaking-induced conversion (RT-QuIC) assay to demonstrate that autopsied skin samples from PD, DLB, and MSA patients (but not non-synucleinopathy controls) seed aggregation of recombinant αSyn. While RT-QuIC generated similarly positive fluorescence kinetic curves across synucleinopathies, biochemical and morphological analyses of RT-QuIC end products revealed distinct properties in the resulting αSyn aggregates. Notably, αSyn aggregates from DLB samples exhibited the highest resistance to proteinase K digestion, whereas MSA-derived aggregates showed the least aggregated bands on Western blots. Transmission electron microscopy revealed significant differences in length, width, and volume of skin αSyn fibrils of RT-QuIC end products from different synucleinopathies. These findings provide critical insights into disease-specific αSyn structural characteristics and suggest new strategies to improve diagnostic discrimination.