The identification of several causative genes for rare monogenic forms of PD, such as SNCA (α-synuclein) [75], Leucine-rich repeat kinase 2 (LRRK2) [76], Parkin [77], PTEN-induced putative kinase 1 (PINK1) [78] and DJ-1 [79], overturned the traditional view that PD is not hereditary and unequivocally demonstrated the major role of genetics in PD etiology [80]. Here, LRRK2 is linked to Parkinson disease.