SNCA and Parkinson disease: Altered α-synuclein levels (soluble, aggregated and post-translationally modified forms) in cerebrospinal fluid (CSF), blood and saliva have been reported, with general consensus describing reduced total α-synuclein, higher oligomeric α-synuclein and higher oligomeric-to-total-α-synuclein ratios in PD patients compared to controls [10,11,12,13,14,15,16,17,18].