Isolated sulfite oxidase deficiency, a rare neurodegenerative disorder which mimics hypoxic-ischemic encephalopathy

Abstract

Isolated sulfite oxidase deficiency is a rare but devastating autosomal recessive neurometabolic disorder character- ized by neonatal-onset encephalopathy mimicking hypoxic-ischemic insult with intractable seizures and profound neurological dysfunction. Infants who survive characteristically manifest severe psychomotor retardation, progressive microcephaly, spastic quadriparesis, opisthotonus, movement disorders and lens dislocation. Sulfite oxidase is a mitochondrial enzyme encoded by the SUOX gene and is essential for the detoxification of sulfite, the terminal reaction in the degradation of sulfur-containing amino acids. Laboratory evidence of the disease includes a positive urinary sulfite dipstick test, abnormal amino acid profile with elevated plasma or urinary S-sulfocysteine level, high taurine and reduced cysteine concentration in plasma whilst serum uric acid and urinary excretion of uric acid, xanthine and hypoxanthine are normal. Brain magnetic resonance imaging demonstrates a pattern reminiscent of that observed in hypoxic-ischemic encephalopathy characterized by temporal alterations of initial cerebral edema and later severe white matter cavitary changes representing cystic encephalomalacia. In the absence of perinatal asphyxia, isolated sulfite oxidase deficiency should prompt appropriate biochemical evaluation. This report describes a male infant who presented with neonatal seizures and neuroimaging findings suggestive of ischemic encephalopathy.