Subsequently, further missense mutations (Kruger et al., 1998; Kiely et al., 2013; Zarranz et al., 2014) as well as duplications and triplications of the SNCA gene have been identified indicating that gene dosage is important for the pathogenesis of PD (Singleton et al., 2003; Ibanez et al., 2004). This evidence concerns the gene SNCA and Parkinson disease.