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Caused by cystathionine β-synthase deficiency, which results in extreme elevations of plasma and urinary homocysteine levels
Autosomal recessive inheritance
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Similar to Marfan syndrome in body habitus
Ectopia lentis almost always present
Mental retardation 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
Myocardial infarction, stroke, and pulmonary embolism are most common causes of death
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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 helpful diagnostic test: elevated plasma methionine and homocysteine levels
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In ∼50% of cases, β-synthase deficiency improves biochemically and clinically with pharmacologic doses of pyridoxine (50–500 mg/day) and folate (5–10 mg/day)
Treatment from infancy can prevent retardation 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 documented venous thrombosis
Prophylactic use of warfarin or antiplatelet agents not recommended