SULFITE OXIDASE DEFICIENCY
 
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SULFITE OXIDASE DEFICIENCY

 

DEFINITION:

An inborn error of cysteine metabolism characterized by an accumulation of sulfites resulting in ectopia lentis and progressive neurological deterioration.

EPIDEMIOLOGY:

  • incidence: extremely rare (about 3 cases worldwide)
  • age of onset:
    • newborn
  • risk factors:
    • familial - autosomal recessive
      • chrom.#: ?
      • gene: sulfite oxidase

PATHOGENESIS:

1. Background

  • in the final step of cysteine metabolism, sulfite is oxidized to sulfate by sulfite oxidase and a molybdenum cofactor
  • a deficiency of sulfite oxidase or the molybdenum cofactor can result in this disorder

2. Genetic Defect

  • genetic defect -> deficiency of sulfite oxidase activity -> accumulation of sulfite -> clinical manifestations

CLINICAL FEATURES:

1. Ocular Manifestations

  • lens - bilateral ectopia lentis, spherophakia
  • strabismus

2. Neurological Manifestations

  • refusal to feed and vomiting
  • seizures - tonic, clonic, and myoclonic
  • severe mental retardation
  • progressive cerebral palsy
  • movement disorders - chorea, ataxia

INVESTIGATIONS:

1. Urine

  • screening test:
    • positive cyanide-nitroprusside test on freshly-voided urine
  • chromatography
    • excessive amounts of sulfites, thiosulfates, taurine, and S-sulfocysteine
    • reduced level of sulfate

2. Diagnosis

  • deficiency of sulfite oxidase activity in cultured fibroblasts and from brain, liver, or kidney biopsies
  • prenatal:
    • deficiency of sulfite oxidase activity in cultured amniotic cells or chorionic villi sampling

MANAGEMENT:

1. Supportive

  • no treatment is available
  • fatal illness

 

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