Desferal is known to retard growth but I don't know if this has any relation to the nucleic acid inhibition. With hydroxyurea, the inhibition of the DNA is part of the reason it works. It slows down the excess bone marrow activity in addition to turning the fetal hemoglobin gene back on. The effect on excess blood production has an added effect in many intermedias by inhibiting the growth of extramedullary hematopoiesis. This is very significant as these growths can often become problematic, as is currently the case with Courtenay, as the mass is pressing on her lungs, causing a reduction in lung capacity.
From
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=12224008&dopt=AbstractPlusTreatment with hydroxyurea in thalassemia intermedia with paravertebral pseudotumors of extramedullary hematopoiesis.
Cario H, Wegener M, Debatin KM, Kohne E.
Department of Pediatrics, University of Ulm, University Children's Hospital, Prittwitzstr. 43, 89070 Ulm, Germany. holger.cario@medizin.uni-ulm.de
Excessive ineffective erythropoiesis in thalassemia intermedia may cause paravertebral pseudotumors of extramedullary hematopoiesis. Due to the proximity to the spinal canal, these paravertebral masses carry the risk of severe neurological damage. Treatment strategies include hypertransfusion, radiotherapy, and laminectomy. Hydroxyurea, stimulating fetal hemoglobin synthesis, may represent an alternative therapeutic approach. We report on a 26-year-old patient suffering from thalassemia intermedia with progressive anemia symptoms and presenting multiple intrathoracic paravertebral pseudotumors of extramedullary hematopoiesis. Hypertransfusion therapy and splenectomy were followed by regular transfusion (baseline hemoglobin 10 g/dl) and chelation with desferrioxamine. With this treatment, clinical symptoms disappeared, paravertebral hematopoietic masses did not progress, but severe hemosiderosis developed within a few years. Hydroxyurea therapy was initiated to increase the efficacy of erythropoiesis, thereby reducing the required transfusion volume but suppressing concomitantly further expansion of extramedullary hematopoiesis, and finally leading to a reduction of transfusional iron load. Treatment was started with 4 mg/kg per day and stepwise increased to 12.5 mg/kg per day. The fetal hemoglobin concentration increased from 4.5 to 5.5 g/dl after 1 year and to 9.9 g/dl after 2 years of treatment. The yearly transfusion volume was halved during the 1st year of treatment. At present, after 26 months of treatment, the patient has been transfusion-independent for 10 months. Serum ferritin levels decreased from 2844 to 1335 ng/ml. Size and shape of paravertebral hematopoietic pseudotumors remained stable. No side effects of hydroxyurea have been observed. In thalassemia intermedia patients with extramedullary hematopoiesis, hydroxyurea may lead to independence from regular transfusion therapy without further expansion of ectopic hematopoietic tissue.
PMID: 12224008 [PubMed - indexed for MEDLINE]
As with desferal, the benefits of hydroxyurea may far outweigh the risks. However, there is no argument that the search for safer fetal hemoglobin inducers must continue.