Whilst biomarker levels of oxidative damage such as 8-hydroxydeoxyguanosine (8-OHdG), lipid peroxidation products [19], and protein carbonyl [20] levels are found to be increased in patients with periodontitis, serum enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxide (GSHPx), and non-enzymatic antioxidants (GSH, vitamins E and C) are found to be significantly lower [19] than healthy control subjects. The gene discussed is CAT; the disease is periodontitis.