Hence, oxidative stress might exert neurotoxicity also by impairing the ubiquitin-proteasome system, as found in Parkinson’s disease (PD) where a decreased protein clearance rate due to elevated ROS results in the accumulation of alpha-synuclein (Hashimoto et al., 1999; McNaught and Jenner, 2001). This evidence concerns the gene SNCA and Parkinson disease.