XDH and neurodevelopmental disorder: In particular, many oxidative stress markers have been reported [8–11], including nitric oxide synthase (NOS), xanthine oxidase (XO), glutathione S-transferase (GST), paraoxonase-1 (PON-1), glutathione, methionine and cysteine, which have been suggested to be associated with neurodevelopmental disorders and oxidative stress [9, 10].