Increased Fetal Hemoglobin in Patients Receiving Sodium 4-Phenylbutyrate

To the Editor: Increases in the production of fetal hemoglobin can ameliorate the severity of both sickle cell disease and β-thalassemia. Three groups of agents are known to increase the production of fetal hemoglobin in humans: cytotoxic drugs,^{1 , 2} growth factors,³ and agents that induce differentiation, such as butyrate.⁴ The clinical application of these drugs has been hindered by dose-limiting myelotoxicity or the requirement for continuous intravenous infusion. These difficulties may now be overcome through the exploitation of the recent discovery of sodium phenylacetate as a nontoxic inducer of differentiation affecting fetal hemoglobin production.⁵ Sodium phenylacetate and its pro-drug, sodium 4-phenylbutyrate,…