ABSTRACT
Several decades ago, homocystinuria, a rare pediatric condition, was noted to be associated with musculoskeletal abnormalities and the development of venous thromboembolism and arterial disease in adolescence. The underlying metabolic defect for this condition was shown to be decreased enzymatic activity of cystathionine beta-synthase (1). This deficiency was associated with increased levels of methionine and homocysteine and a decrease in blood levels of cysteine. Later investigations of a patient with elevated homocysteine levels and similar clinical findings, but with a low concentration of methionine in the plasma and evidence of abnormal vitamin B 12 metabolism, led to the conclusion that another defect could account for elevated homocysteine levels and vascular disease (2,3).
