Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content + Print Section ++ For further information, see CMDT Part 40-20: Disorders of Homocysteine Metabolism + Key Features Print Section ++ ++ Caused by cystathionine β-synthase deficiency, which results in extreme elevations of plasma and urinary homocysteine levels Autosomal recessive inheritance + Clinical Findings Print Section ++ ++ 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 + Diagnosis Print Section ++ ++ 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 + Treatment Print Section ++ ++ 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