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At a glance

It is an extremely rare severe progressive neurodegenerative and neurometabolic disease, characterized by convulsions, severe mental and motor retardation resistant to the treatment. Other features include spastic tetraparesis, brain atrophy, abnormal muscle tone, myoclonic spasms, dislocated lenses, and xanthine urinary stones.

Synonyms

MOCOD; Sulfite oxidase deficiency.

Incidence

The exact incidence remains unknown. The prevalence is estimated between 1:100,000 and 200,000 live births in the general population. There are presently 100 cases reported in the medical literature. It is possible that most patients are not diagnosed and this would affect the true incidence.

Genetic inheritance

It is believed inherited as an autosomal recessive trait. Heterozygotes show no symptoms.

Pathophysiology

This cofactor is essential for function of the enzymes sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. Symptoms are the result of combined deficiencies of these enzymes. However, isolated deficiency in sulfite oxidase produces the same symptoms. The accumulation of toxic metabolites produces severe encephalopathy, demyelinization of white matter, gliosis, and diffuse spongiosis of the brain.

Diagnosis

Deficiency of sulfite oxidase in fibroblasts or of molybdenum cofactor in liver biopsy. The presence of high concentrations of sulfite, thiosulfate, taurine, xanthine, and hypoxanthine associated with very low levels of uric acid in the urine is diagnostic. Antenatal diagnosis is also possible.

Clinical aspects

Clinical manifestations are apparent within a few weeks of birth and were formerly called “infantile encephalopathy”: mainly severe convulsions unresponsive to therapy and caused by sulfite production from oral protein intake. The presence of poor feeding, vomiting, seizures, spastic quadriparesis, and severe developmental delay are characteristics. Bilateral dislocation of the ocular lens is a common finding. There is no effective treatment, and death usually occurs before age 2 years.

Precautions before anesthesia

Assess neurologic status until the day of surgery. It is recommended to optimize seizure therapy and ensure that medications are taken the day of the anesthesia.

Anesthetic considerations

Anesthetic management in this condition has not been described. The severity of neurologic defects determines anesthetic management. Patients may be at risk for pulmonary aspiration and recurrent infections. Poor feeding and vomiting may lead to electrolyte abnormalities, which should be corrected preoperatively.

Pharmacological implications

Succinylcholine should be avoided in presence of spastic tetraparesis. Seizure medications must be optimized intraoperatively and postoperatively.

References

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Alkan  M, Kip  G, Şahin  Ş, Atabek  D:.Choice of anesthesia in molybdenum cofactor deficiency: A case report. J Res Med Sci 19(11):1103–1105, 2014.  [PubMed: 25657759]
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Rezvani  I: Defects in metabolism of amino acids, in Behrman  RE, Kliegman  RM, Arvin  AM (eds): Nelson Textbook of Pediatrics, 16th ...

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