Diagnostic accuracy of alpha-synuclein detection assays in neurodegenerative diseases: towards precision biomarkers for early diagnosis, disease monitoring and neuropathological confirmation.

Background: The proposed clinical phenotype associated with Parkinson’s disease pathogenic process is widely known. However, the complexity of identification of early stage Parkinson’s disease (PD) is demonstrated by the long diagnostic delay (on average 10 years) to which patients are frequently submitted to. PD differential diagnosis, especially with other alpha-synucleinopathies, can also be challenging, impinging on a similar spectrum of motor and non-motor symptomatology. While current clinical diagnostic approaches are failing to detect the disease in a timely fashion, novel predictive markers are urgently needed for pathological characterization and progression. Purpose of the study: This research thesis is focused on assessing alpha-synuclein detection assays (histopathology and seeding amplification assays) in peripheral tissues and in the central nervous system as a possible predictive tool for the early differential diagnosis, disease monitoring and neuropathological confirmation of alpha-synucleinopathies. By detecting and classifying different patterns of protein aggregates, differential diagnosis of Parkinsonian syndromes could be more specific and non-invasive, transforming the clinical landscape for the affected patients. Methods: Pathological alpha-synuclein (phosphorylated, aggregated) and its seeding activity was evaluated via histopathology and seeding amplification assay in peripheral tissues and in the central nervous system of a cohort of patients with clinical diagnosis of Parkinson’s Disease (PD), Multiple System Atrophy (MSA), Progressive Supranuclear Palsy (PSP), Cortico-basal syndrome (CBS), Alzheimer’s Disease (AD), and in neurologically healthy subjects (HC). Disease phenotypes and alpha-synuclein distribution patterns were characterized, and their diagnostic accuracy was assessed. Results: Alpha-synuclein detection assays revealed high overall accuracy, sensitivity, and specificity for the detection of alpha-synuclein pathology across all analyzed tissues, as well as overall reliable concordance with clinical diagnosis. Ex-vivo neuropathological detection of alpha-synuclein pathology further confirmed the reliability of alpha-synuclein immunohistochemistry in peripheral tissues. Conclusion: Findings suggest that employed alpha-synuclein detection assays represent effective diagnostic tools for Parkinson’s disease and other neurodegenerative diseases, offering trustworthy and accurate identification of alpha-synuclein pathology. Moreover, the emerging role of multiple proteinopathies further stresses the need for protein-specific assays for accurate disease characterization.