PRKN and Parkinson disease: Unlike sporadic forms of PD which account for 95% of PD cases, familial forms of PD are mainly caused by mutations in synuclein alpha (SNCA), parkin, PTEN-induced putative kinase 1 (PINK1), DJ-1 and leucine-rich repeat kinase 2 (LRRK2) (Klein and Westenberger, 2012).