Homocystinuria: Metabolic studies on 3 patients

Homocystinuria is an inborn error of amino acid metabolism discovered in mentally deficient children. Homocystine is present in blood and urine and is derived from homocysteine. Homocysteine, like cystathionine, is an intermediate on the pathway from methionine to cysteine. Methionine loads have been administered to three children with homocystinuria and the results confirm that this amino acid is metabolized more slowly than in control subjects. Since the transport of methionine was normal in the children studied, the results support the view that the inborn error is a failure to convert homocysteine to the next intermediate cystathionine.