AbstractBackground and purposeThe insidious onset of Parkinson's disease (PD) makes early diagnosis difficult. Notably, idiopathic rapid eye movement sleep behavior disorder (iRBD) was reported as a prodrome of PD, which may represent a breakthrough for the early diagnosis of PD. However, currently there is no reliable biomarker for PD diagnosis. Considering that α‐synuclein (α‐Syn) and neuroinflammation are known to develop prior to the onset of clinical symptoms in PD, it was hypothesized that plasma total exosomal α‐Syn (t‐exo α‐Syn), neural‐derived exosomal α‐Syn (n‐exo α‐Syn) and exosomal apoptosis‐associated speck‐like protein containing a caspase activation and recruitment domain (ASC) may be potential biomarkers of PD.MethodsIn this study, 78 PD patients, 153 probable iRBD patients (pRBD) and 63 healthy controls (HCs) were recruited. α‐Syn concentrations were measured using a one‐step paramagnetic particle‐based chemiluminescence immunoassay, and ASC levels were measured using the Ella system.ResultsIt was found that t‐exo α‐Syn was significantly increased in the PD group compared to the pRBD and HC groups (p < 0.0001), whilst n‐exo α‐Syn levels were significantly increased in both the PD and pRBD groups compared to HCs (p < 0.0001). Furthermore, although no difference was found in ASC levels between the PD and pRBD groups, there was a positive correlation between ASC and α‐Syn in exosomes.ConclusionsOur results suggest that both t‐exo α‐Syn and n‐exo α‐Syn were elevated in the PD group, whilst only n‐exo α‐Syn was elevated in the pRBD group. Additionally, the adaptor protein of inflammasome ASC is correlated with α‐Syn and may facilitate synucleinopathy.