Homocystinuria

Test

• Bacterial inhibition assay to determine the levels of serum methionine

Genetics

• Autosomal recessive
• 1:50,000 to 1:150,000

Pathology

• Excess methionine due to a disorder of the trans-sulfuration pathways that convert the sulfur atom of methionine into the sulfur atom of cystine.  Most commonly a deficiency of the enzyme cystathionine B-synthetase.

Diagnosis

• Marfanoid habitus, ectopia lentis (lens dislocation), glaucoma, cataracts, osteoporosis, high palatal arch, and muscle weakness with a shuffling gait.
• Consider in any child or young adult with thromboembolism affecting both the large and small arteries as well as the veins, particularly in association with developmental disabilities, mental retardation or skeletal findings.

Treatment

• 50% respond to large doses of vitamin B6.  Nonresponsive patients with cystathionine B-synthetase deficiency should be treated with a methionine-restricted cystine-supplemented diet.

Acknowledgment

Also see other Inborn Errors of Metabolism.
 

Genetics

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