SNCA and Parkinson disease: Only one study has previously measured plasma SNCA and pS129 SNCA levels in the same sample set (Foulds et al., 2013), reporting values of 1222 ± 2233 ng/ml and 143 ± 531 ng/ml, respectively, and suggesting increased plasma pS129 SNCA levels as a potentially useful diagnostic biomarker in PD.