SNCA and Parkinson disease: The presence of different forms of α-synuclein in cerebrospinal fluid (CSF), blood plasma [56–58], and saliva [59] coupled to the discovery of α-synuclein pathology in embryonic nigral transplants of PD patients [10, 11, 60] suggested that α-synuclein can move from cell to cell and can initiate pathology in recipient neurons.