The highly conserved non-amyloid-β component (NAC) domain of α-synuclein is alone sufficient to form pathological fibrils24,61 and has been shown to be shielded by the C-terminus region to prevent spontaneous aggregation.62 However, circumstances that expose the NAC domain have been found to promote fibril formation, leading to cytotoxicity and pathology.61,63 Whatever the pathogenic species of α-synuclein may be, it is clear that misfolding and aggregation, followed by spread in a prion-like manner, is in some way involved in the development of PD. Here, SNCA is linked to Parkinson disease.