Although the cause of sporadic PD remains poorly understood, the identification of genetic factors associated with familial forms of the disease, such as multiplication of the SNCA gene, together with the presence of Lewy bodies containing α-synuclein (α-syn) fibrils, point to α-syn accumulation, misfolding and aggregation as a core mechanism in PD pathogenesis. Here, SNCA is linked to Parkinson disease.