Plasma α-synuclein is decreased in subjects with Parkinson's disease

α-Synuclein (αSN) is implicated in Parkinson's disease (PD) and is the major component of Lewy bodies (LBs). Although αSN is mainly expressed in neuronal cells and exists as a cytoplasmic protein, it has been found in body fluids including cerebrospinal fluid and blood. This study explored plasma αSN as a diagnostic marker for PD. Western blot analysis was used to characterize plasma αSN compared to brain αSN. Plasma αSN of 16 kDa migrates with the same mobility as its brain counterpart and recombinant αSN on denatured polyacrylamide gels and reacted with three different antibodies against the C-terminal and NAC regions of the αSN protein. The αSN levels in plasma from PD subjects are significantly lower than that in age-matched controls (p = 0.001), and the αSN levels in patients with early-onset PD are lower than that in both late-onset PD and controls. This initial study indicates that measurement of αSN in plasma can provide support for a clinical diagnosis of Parkinson's disease and warrants further study in a larger population.