An impaired antioxidant system has been observed in PD, including decreased superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activity and heme oxygenase-1 (HO-1) expression (Khurana and Gajbhiye, 2013; Lu et al., 2015). The gene discussed is HMOX1; the disease is Parkinson disease.