We and others previously found that PD risk mutant alleles (e.g., A53T alpha-synuclein, G2019S-LRRK2) causes more severe neurotoxicity in the presence of oxidative stress environment (Smith et al., 2005; West et al., 2007; Li et al., 2010; Liu et al., 2011b). Here, LRRK2 is linked to Parkinson disease.