OTC deficiency, an X-linked disorder of urea synthesis, is associated with hyperammonemia and resultant neurodevelopmental disabilities. A mechanism for brain injury is postulated to involve excitotoxicity, associated with increases in brain glutamine (Gln), tryptophan (Trp), 5-hydroxyindoleacetic acid and quinolinic acid. We have previously shown correction of the peripheral biochemical abnormalities in OTC deficient spf/Y mice using vivo gene transfer with an adenoviral vector deleted in E1, with a temperature-sensitive mutation (ts 125) in E2a and containing the OTC cDNA. To determine if this approach also corrects the neurochemical abnormalities,spf/Y and control C3H mice were injected by tail vein with or OTC-expressing adenoviral vector (1×1011 particles). Plasma amino acids and urinary orotate were followed for 14 days and at day 16 brain tissue was harvested for analyses. As previously observed, plasma ammonium, Gln and urinary orotate were normalized in the spf/Y mice by the OTC construct. Cortical Gln levels were 5.9 ± 0.6 in C3H mice treated with the OTC construct and 5.4 ± 1 in C3H mice treated with theβ-galactosidase construct, compared to 4.8 ± 0.9 nmol/mg tissue in untreated C3H mice. Cortical Gln levels were 5.4 ± 0.9 in spf/Y mice treated with the OTC construct and 8.5 ± 3 in spf/Y mice treated with the construct, compared to 9.0 ± 2.9 nmol/mg tissue in untreated spf/Y mice. Cortical Trp levels were partially corrected in OTC-treated mice (31.8 ± 6.3 pmol/mg tissue) compared to C3H and spf/Y controls (21.8 ± 6.5 and 43.2± 8.3 pmol/mg tissue, respectively). Comparable correction was also observed in brainstem. These data suggests that gene therapy may have the potential to correct neurochemical as well as peripheral metabolic abnormalities. (HD32649)