α-Synuclein Real-Time Quaking-Induced Conversion Assay as a Biomarker for Parkinson’s Disease: Clinical Implications and Perspectives

Parkinson's disease (PD) has traditionally been diagnosed through clinical motor symptoms and the postmortem identification of pathological α-synuclein aggregates in Lewy bodies. The focus of diagnostic paradigms has recently moved from clinical approaches toward biological measures. The cerebrospinal-fluid-based real-time quaking-induced conversion (RT-QuIC) assay demonstrates high sensitivity and specificity, significantly enhancing its diagnostic accuracy. Although the RT-QuIC assay has not yet been fully integrated into clinical practice, rapid increases in its application have made it essential to diagnostic protocols. This review examines the development, current applications, and efficacy of the RT-QuIC assay in PD, dementia with Lewy bodies, multiple-system atrophy, prodromal conditions, and elucidating clinical-pathological discrepancies. The findings can provide clear guidance for clinicians and researchers, facilitate accurate interpretations of RT-QuIC results, support informed clinical decision-making, and ultimately improve diagnostic precision and personalized management strategies across the spectrum of synucleinopathies.