Review summarizing how α-synuclein seed-amplification assays (SAAs) and their biophysical/procedural variables can be tuned to generate reproducible kinetic signatures that differentiate PD, DLB, and MSA strains.

By enabling standardized, strain-sensitive biochemical diagnosis and robust patient stratification, optimized α-syn SAAs can directly improve clinical trial design, target engagement assessment, and development of α-synuclein–directed therapies.

INTRODUCTION: Synucleinopathies are characterized by the misfolding and aggregation of α-synuclein (α-Syn) into pathogenic strains that seed Lewy-body pathology in neurons and/or glial cytoplasmic inclusions in oligodendrocytes. α-syn seed-amplification assays (α-Syn SAAs) detect as little as 20 femtogram of synthetic α-Syn pre-formed fibrils (PFFs) or analogous synthetic aggregates in biospecimens, offering high sensitivity and specificity for synucleinopathies. AREAS COVERED: We review how distinct α-Syn strains propagate in Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), and we summarize the biophysical and procedural variables that govern SAA kinetics. We aim to identify an optimal means of modulating α-Syn SAA parameters so that each synucleinopathy subtype consistently yields distinct and stable kinetic signatures, thereby facilitating accurate biochemical diagnosis. EXPERT OPINION: α-Syn SAA holds the potential to become a routine assay for discriminating among synucleinopathy subtypes. Future research should focus on standardizing α-Syn SAA protocols, exploring the detailed mechanisms of distinct α-Syn strains propagation, and developing novel therapeutic strategies based on these insights.