SNCA and Parkinson disease: Misfolded species of α-synuclein including oligomeric and phosphorylated α-synuclein seem to be increased in the CSF of PD patients, but their application as biomarkers is hampered by some limitations mainly dealing with their lower concentrations as compared to monomeric α-synuclein and the lack of selective antibodies with high affinity and avidity to these species [52,53].