α-
synuclein is thought to play a key role in
Parkinson's disease (PD) because it is the major
protein in Lewy bodies, and because its gene mutations, duplication, and triplication are associated with early-onset PD. There are conflicting reports as to whether serum and plasma concentrations of α-
synuclein and anti-α-
synuclein antibodies differ between PD and control subjects. The objectives of this study were to compare the levels of α-
synuclein and its
antibodies between individuals with typical PD (n=14), atypical Parkinson syndromes (n=11), idiopathic
rapid eye movement sleep behavior disorder (n=10), and healthy controls (n=9), to assess the strength of association between these
serum proteins, and to determine group sizes needed for a high probability (80% power) of detecting statistical significance for 25% or 50% differences between typical PD and control subjects for these measurements. Analysis of log-transformed data found no statistically significant differences between groups for either α-
synuclein or its
antibodies. The concentrations of these
proteins were weakly correlated (Spearman rho=0.16). In subjects with typical PD and atypical Parkinson syndromes, anti-α-
synuclein antibody levels above 1.5 µg/ml were detected only in subjects with no more than four years of clinical disease. Power analysis indicated that 236 and 73 samples per group would be required for an 80% probability that 25% and 50% differences, respectively, in mean α-
synuclein levels between typical PD and control subjects would be statistically significant; for anti-α-
synuclein antibodies, 283 and 87 samples per group would be required. Our findings are consistent with those previous studies which suggested that serum concentrations of α-
synuclein and its
antibodies are not significantly altered in PD.