Furthermore, several anti-oxidant and pro-oxidant enzymes have been associated with PD susceptibility in terms of genetic variability and activity, such as glutathione peroxidase (GPX1) (Power and Blumbergs, 2009), catalase (CAT) (de Farias et al., 2016), superoxide dismutase (SOD2) (Santiago et al., 2014), and nitric oxide synthase (NOS1) (Rife et al., 2009). The gene discussed is NOS1; the disease is Parkinson disease.