Combined deficiency of sulfite oxidase and xanthine oxidase as a result of defective synthesis of molybdenum-cofactor: 77

Abstract

Combined deficiency of sulfite oxidase and xanthine oxidase as a result of defective synthesis of molybdenum-cofactor. A girl is presented with congenital abnormalities including asymmetry of the skull and slight mediofacial dysplasia. The eye lenses were dislocated. Severe neurological abnormalities and deep mental retardation were observed. On routine screening a low serum urate (0.01-0.07 mmol/1) was observed. Chromatography of urinary purines revealed xanthinuria. In addition the sulfite test in the urine was repeatedly positive. Sulfite oxidase deficiency was suggested by high excretions of S-sulfocysteine, taurine and thiosulfate and low levels of urinary sulfate. Deficiencies of both xanthine oxidase and sulfite oxidase were demonstrated in a liver biopsy specimen. Because sulfite oxidase and xanthine oxidase are known to require an activated form of molybdenum (Mo-cofactor), investigations of Mo metabolism were carried out. A complete absence of hepatic Mo-cofactor activity was demonstrated and analysis by atomic absorption revealed a severe depletion of hepatic Mo as well. A near normal amount of inactive xanthine oxidase protein was present, but several immunological techniques failed to detect any sulfite oxidase apo-enzyme. It is suggested that a defective synthesis of Mo-cofactor causes the biochemical abnormalities. Treatment with oral supplements of molybdenum did not result in biochemical or clinical improvement.