Possibly, the formation of superoxide radical (O2-•) and hydrogen peroxide (H2O2), which appear to be increased in individuals with OSA, is due to the conversion of xanthine dehydrogenase (type D) into its oxidase (type O) form in hypoxia, followed by the activation of the oxidase form during reoxygenation (normoxia) by the hypoxanthine formed during hypoxia. This evidence concerns the gene XDH and obstructive sleep apnea syndrome.