eMedicine Specialties > Pediatrics: Genetics and Metabolic Disease > Metabolic Diseases

Sulfite Oxidase Deficiency: Differential Diagnoses & Workup

Author: Georgianne L Arnold, MD, Director of Inherited Metabolic Disorders Clinic, Department of Pediatrics and Genetics, Associate Professor, University of Rochester School of Medicine and Dentistry
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Updated: Feb 18, 2009

Differential Diagnoses

Vitamin B-6 Dependency Syndromes

Other Problems to Be Considered

Glutaric aciduria types 1 and 2
Nonketotic hyperglycinemia
Other causes of primary lactic acidosis

Workup

Laboratory Studies

A positive sulfite dipstick finding of very fresh urine is highly suggestive of sulfite oxidase deficiency; however, a negative dipstick finding should not eliminate suspicion.

For quantitative plasma and urine amino acids, alert the laboratory to look for characteristic cysteine metabolite s-sulfocysteine, which may not be detected or reported unless specifically requested. S-sulfocysteine elutes in the early part of the chromatogram, before the main amino acids of interest do. Special techniques may be required to differentiate the peak from other more common substances.

Urine organic acids may reveal lactate (a nonspecific finding) but should rule out common organic acidemias. Urinary urothion (a degradation product of molybdopterin) can be measured by a few laboratories. A low level is virtually diagnostic for molybdenum cofactor deficiency (except in cases of profound molybdenum deficiency). Urinary thiosulfate (a metabolite of cysteine) can also be measured in a few selected laboratories.

An elevated urinary thiosulfate level is essentially diagnostic of sulfite oxidase deficiency or molybdenum cofactor deficiency. The plasma uric acid level is typically low or low-normal in individuals with molybdenum cofactor deficiency; however, it is normal in those with isolated sulfite oxidase deficiency. Plasma lactate and pyruvate levels may be highly elevated, although this finding is nonspecific. Urinary xanthine and hypoxanthine levels can be measured in selected laboratories. These levels are elevated in individuals with molybdenum cofactor deficiency but are normal in those with sulfite oxidase deficiency.

Mutations in the SUOX gene (sulfite oxidase) and in the component of the molybendum cofactor (MOCS1, MOCS2, or GEPH) have been described, with no single predominate mutation.

Imaging Studies

Cranial CT or MRI may reveal the following:

• Abnormal gyration
• Cerebral atrophy
• Decreased density of white matter
• Dilated ventricles
• Neuronal loss
• Cystic lesions (in basal ganglia and/or cerebellum)
• Calcifications
• Cerebral edema

Magnetic resonance spectroscopy (MRS) findings in 3 cases revealed a reduced peak area N -acetylaspartate–to–total creatine ratio, an increased peak choline–to–total creatine ratio, increased lactate and lipid levels, and pronounced elevation of glutamate and glutamine levels.²

Other Tests

Prenatal diagnosis has been achieved by measurement of sulfite oxidase activity in chorionic villi or by DNA analysis in families in whom the mutation is known in the index case.

Histologic Findings

Neuropathological findings include cerebral atrophy or edema; microgyri and abnormal sulci; multicystic subcortical and juxtacortical focal lesions in white matter; microscopic lesions in frontal, temporal, and occipital cortex; demyelination; spongiosis; and microcavitation.

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