Neurologic injury in isolated sulfite oxidase deficiency.

Background: We review clinical, neuroimaging, and genetic information on six individuals with isolated sulfite oxidase deficiency (ISOD). Methods: All patients were examined, and clinical records, biochemistry, neuroimaging, and sulfite oxidase gene (SUOX) sequencing were reviewed. Results: Data was available on six individuals from four nuclear families affected by ISOD. Each individual began to seize within the first week of life. Neurologic development was arrested at brainstem reflexes, and severe microcephaly developed rapidly. Neuroimaging within days of birth revealed hypoplasia of the cerebellum and corpus callosum and damage to the supratentorial brain looking like severe hypoxic-ischemic injury that evolved into cystic hemispheric white matter changes. Affected individuals all had elevated urinary S-sulfocysteine and normal urinary xanthine and hypoxanthine levels diagnostic of ISOD. Genetic studies confirmed SUOX mutations in four patients. Conclusions: ISOD impairs systemic sulfite metabolism, and yet this genetic disease affects only the brain with damage that is commonly confused with the clinical and radiologic features of severe hypoxic-ischemic encephalopathy.