SNCA and Parkinson disease: Several missense mutations in the SNCA gene, which encodes for aSyn, are linked to rare forms of familial PD (Polymeropoulos et al. 1997; Krüger et al. 1998; Zarranz et al. 2004; Singleton et al. 2003; Chartier-Harlin et al. 2004; Fujioka et al. 2014; Conway et al. 1998), suggesting aSyn may gain a toxic function that possibly contributes to disease.