PRKN and Parkinson disease: Independently to α-synuclein and 1 year later, gene mutations in parkin (Kitada et al. 1998) and ubiquitin c-terminal hydrolase-L1 (UCHL-1) (Leroy et al. 1998), which are capable of impairing the activity of the UPS, have been described in rare forms of hereditary PD.