Among the monogenic forms of PD, mutations in LRRK2 (PARK8) coding for leucine-rich repeat kinase 2 protein and SNCA (PARK1/4) coding for α-synuclein cause autosomal dominant PD; LRRK2 mutations are responsible for a significant percentage of familial PD, but SNCA mutations are rare (Pankratz and Foroud, 2007; Lesage and Brice, 2009; Klein and Westenberger, 2012). Here, LRRK2 is linked to Parkinson disease.