BackgroundThis study examines the relationship between oxidative stress, anti-oxidative markers, and the Ala16Val SOD2 polymorphism in children with autism spectrum disorder (ASD) to better understand ASD severity and susceptibility. Material and methodsThe study included 80 children (40 with ASD and 40 controls) from Erbil City, Iraq. ResultsSerum antioxidant markers, such as superoxide dismutase (SOD) and glutathione peroxidase (GPX), were significantly lower in ASD patients compared to controls (P = 0.036 and P < 0.001, respectively), while markers of oxidative damage, including malondialdehyde (MDA), nitric oxide (NO), and cytochrome C, were significantly elevated (P < 0.001). Regression analysis revealed reduced SOD and GPX activities were strongly associated with increased autism severity, as measured by the childhood autism rating scale (CARS), while elevated NO and cytochrome C levels also correlated positively with higher CARS scores. Although the Ala16Val SOD polymorphism was not significantly associated with ASD risk, logistic regression showed no connection between SOD genotypes and serum SOD levels. ConclusionThese findings suggest oxidative stress and impaired antioxidant defense play critical roles in ASD severity. PLAIN LANGUAGE SUMMARY This study explores the relationship between oxidative stress, antioxidant markers, and the Ala16Val SOD2 polymorphism in autism spectrum disorder (ASD). It involved 80 children (40 with ASD, 40 controls) from Erbil City, Iraq. Results showed significantly lower superoxide dismutase (SOD) and glutathione peroxidase (GPX) levels in ASD patients, with elevated oxidative damage markers, including malondialdehyde (MDA), nitric oxide (NO), and cytochrome C. Regression analysis linked reduced SOD and GPX levels and increased NO and cytochrome C levels with higher Childhood Autism Rating Scale (CARS) scores. While the SOD2 polymorphism was not associated with ASD risk, oxidative stress strongly influenced ASD severity. ARTICLE HIGHLIGHTS Reduced serum SOD and GPX activities were significantly linked to autism severity, with lower levels correlating with higher CARS scores. Elevated oxidative stress markers (MDA, NO, and cytochrome C) were significantly associated with increased autism severity. The Ala16Val SOD polymorphism was not associated with ASD risk or serum SOD levels. Regression analysis identified SOD, GPX, NO, and cytochrome C as predictors of autism severity, with SOD showing the strongest negative association. Oxidative stress and impaired antioxidant defense mechanisms play a critical role in the progression of ASD symptoms.