SNCA and Platelet storage pool disease: As monomers and tetramers of α-synuclein are well-characterized physiological species, we focused on the investigation of physiological, disordered, aggregation-prone monomeric α-synuclein and physiological, cytosolic, helically-folded, tetrameric α-synuclein in human blood and analyzed changes of the α-synuclein protein in well-characterized genetic, familial PD (fPD) forms i.e., G51D mutation in the α-synuclein gene (SNCA) and sporadic PD (sPD) from two independent cohorts.