Plasma α-synuclein domain profiles across α-synucleinopathies.

The differential diagnosis of α-synucleinopathies, including Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), remains challenging due to overlapping clinical features and the absence of reliable biomarkers. We developed a targeted mass spectrometry assay to profile α-synuclein peptides in plasma from Parkinson's disease (n = 82), DLB (n = 32), MSA (n = 8) and controls (n = 21). We hypothesized that disease-specific truncations or post-translational modifications would alter levels of non-modified α-synuclein peptides across α-synucleinopathies. The assay quantified non-modified peptides derived from the N-terminus and non-amyloid component (NAC) domain, regions implicated in aggregate formation. Although peptide levels were consistent across disease groups, a distinct NAC domain pattern observed in MSA may reflect unique pathological processes. This study presents the first blood-based profiling of α-synuclein peptides in these disorders, offering a basis for further investigation into disease mechanisms. Refinement of the assay to include post-translational modifications could enhance understanding of α-synucleinopathies and support future biomarker development.