[α-Synuclein as Diagnostic Biomarker].

Although α-synuclein protein (αS) undergoes aggregation from a monomer to assemblies, such as oligomers, protofibrils, and mature fibrils, the early intermediate aggregates, that is, oligomers, are considered to be the most toxic species in the pathogenesis of α-synucleinopathies, including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). While it has been reported that the αS concentration in cerebrospinal fluid (CSF) is decreased significantly in patients with PD and DLB, there have been reports of the αS oligomer concentration being elevated in the CSF of patients with PD. Moreover, it is supposed that the αS oligomer concentration is also elevated in the blood of patients with PD. Recently, it has been reported that lower cerebrospinal β-amyloid (Aβ)1-40, Aβ1-42, and αS levels are associated with cognitive decline in PD. Further combination studies of the CSF and blood may lead to the establishment of the candidate αS as a biomarker for α-synucleinopathies, including PD and DLB.