Several biomarkers of oxidative stress have been identified during the last few years in patients with MASLD and MASH as well as reduced liver concentration/activity of both enzymatic (e.g., catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase) and non-enzymatic antioxidants (e.g., ascorbic acid, glutathione, α-tocopherol, ubiquinone, thioredoxin, and bilirubin) has been found in clinical and experimental models of MASLD and MASH [32]. The gene discussed is CAT; the disease is metabolic dysfunction-associated steatohepatitis.