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For further information, see CMDT Part 40-21: Disorders of Homocysteine Metabolism

Key Features

  • Caused by cystathionine β-synthase deficiency, which results in extreme elevations of plasma and urinary homocysteine levels

  • Autosomal recessive inheritance with a prevalence of 1 per 100,000

Clinical Findings

  • Similar to Marfan syndrome in body habitus

  • Ectopia lentis almost always present

  • Mental impairment often present

  • Cardiovascular events caused by repeated arterial or venous thromboses

  • Bone mineral density is reduced in untreated patients

  • Life expectancy is reduced, especially in untreated and pyridoxine-unresponsive patients

  • Elevated blood homocysteine increases the risk of Alzheimer dementia in the elderly

  • Myocardial infarction, stroke, and pulmonary embolism are most common causes of death


  • Diagnosis suspected in patients in the second and third decades of life who have repeated arterial or venous thromboses and no other risk factors

  • DNA analysis can detect mutations in the cystathionine β-synthase gene

  • Amino acid analysis of plasma is most appropriate diagnostic test: elevated plasma methionine and homocysteine levels


  • In ~50% of cases, β-synthase deficiency improves biochemically and clinically with pharmacologic doses of pyridoxine (50–500 mg orally daily) and folate (5–10 mg orally daily)

  • Treatment from infancy can prevent neurologic impairment and the other clinical problems

  • Pyridoxine nonresponders must be treated with dietary reduction in methionine and supplementation of cysteine

  • Vitamin betaine useful in reducing plasma methionine levels

  • Anticoagulation for patients with documented venous thrombosis

  • Prophylactic use of warfarin or antiplatelet agents not recommended

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