SNCA and Parkinson disease: Further interest in extracellular Snca is due to data showing that extracellular Snca in an aggregated form may have a potential role in the spreading of the PD pathology, as suggested by the finding of Lewy bodies in fetal neurons transplanted to PD patients (Kordower et al., 2008; Li et al., 2008; Mendez et al., 2008) and the spreading of aggregation of neuronal endogenous Snca in response to the addition (cells) or injection (animals) of aggregated fibrillar Snca (Luk et al., 2009, 2012a,b; Volpicelli-Daley et al., 2011).