SNCA and Parkinson disease: By contrast, a toxic gain-of-function phenotype resulting in PD is caused by rare dominantly inherited mutations and multiplications in the genes SNCA (PARK1, PARK4) and LRRK2 (PARK8) (Lesage and Brice, 2009; Schapira and Tolosa, 2010; Klein and Westenberger, 2012).