CAT and Schnyder corneal dystrophy: Similarly, in a clinical trial on children with SCD, blood levels of all three measured antioxidant enzymes, catalase, superoxide dismutase, and glutathione peroxidase, increased significantly following 6 weeks of addition of l‐arginine to their therapeutic regimen, and the level of malondialdehyde, an index of lipid peroxidation and presence of oxidative stress, decreased significantly.9