Mutations or multiplications of the α-synuclein encoding gene, SNCA, cause familial forms of PD (Polymeropoulos et al., 1997; Krüger et al., 1998; Singleton et al., 2003; Ibáñez et al., 2004; Zarranz et al., 2004), thereby suggesting a causal role of α-synuclein in PD. Here, SNCA is linked to Parkinson disease.