Localized proton MR spectroscopy in infants with urea cycle defect.

Urea cycle defect is an inborn error of ammonium metabolism caused by a deficient activity of the enzymes involved in urea synthesis. Localized short-TE proton MR spectroscopy, performed in two infants who had citrullinemia and ornithine transcarbamylase deficiency, respectively, showed a prominent increase of glutamine/glutamate and lipid/lactate complex in both cases. N-acetylaspartate, total creatine, and myo-inositol were decreased in the infant with citrullinemia. Proton MR spectroscopy provided useful information for the diagnosis and understanding of the pathophysiology of urea cycle enzyme defect.