SNCA and Parkinson disease: Missense mutations and multiplication of the gene encoding alpha-synuclein SNCA (synuclein, alpha [non-A4 component of amyloid precursor]) were identified as genetic abnormalities associated with rare familial forms of PD (Polymeropoulos et al., 1997; Singleton et al., 2003; Chartier-Harlin et al., 2004; Ibanez et al., 2004).