Pyridoxine-responsive Anemia: Influence of Tryptophan on Pyridoxine Responsiveness

This study presents evidence that the indolic amino acid, tryptophan, critically influences pyridoxine responsiveness in a patient with pyridoxine-responsive anemia. Continuing observations for 18 yr on this now 54-yr-old white man have shown responsiveness to oral crude liver extract and to pyridoxine. In addition, remissions of 8-mo duration followed oral administration of fractions of liver extract in doses of 2 mg daily. These nonprotein fractions contained acidic substances characterized as indoles. From 1959 to 1970, oral pyridoxine, in daily doses of 12.5 mg for 5 days, predictably produced prompt reticulocytosis, fall in serum iron content, and rise in hematocrit to nearly normal levels. Such responses to pyridoxine consistently lasted less than 2 mo. More recently, relative refractoriness to this dose of pyridoxine has developed. However, responsiveness has been restored by oral administration of I-tryptophan, 750 mg daily, an amount alone insufficient to maintain the hematocrit at optimal levels. These observations indicate relationships of tryptophan and pyridoxine in erythropoiesis that have not been recognized previously. Addition of I-tryptophan to the therapy of certain pyridoxine-responsive and other sideroblastic anemias might be considered.