Pharmacological therapy

Collectively sickle cell disease and beta-thalassaemia are the most commonly inherited single-gene defects world-wide and were the first group of diseases for which DNA-based detection strategies were utilized. Although genotypically distinct, these two groups of diseases exhibit several common clinical features: moderate-to-severe haemolytic anaemia, acute and progressive tissue damage, disease- or treatment-related organ failure and premature death. Within the last two decades, a striking improvement in life expectancy in the two patient populations has been observed, by dint of primary and secondary prevention strategies. However, apart from bone marrow transplantation, a generally applicable, specific and non-toxic form of treatment remains unavailable for these disorders. Nonetheless, a greater appreciation of the developmental control of human globin gene expression coupled with observations of the effects of certain classes of agents to 'reverse' erythroid cellular phenotype in in vitro and animal models have led to pharmacological trials to obtain meaningful increases in haemoglobin F production in patients affected by these two severe beta-globin disorders. Contemporary understanding of the quantitative relationship between the abnormal molecules in the red cells (aggregates of sickle haemoglobin) in the sickle cell syndromes and aggregated alpha-globin polypeptides in the beta-thalassemia syndromes, and the extent of the red cell and/or organ involvement, has now enabled investigators to predict how much inhibition of these intracellular pathogenic processes might be necessary to achieve partial or total abrogation of disease manifestations. The results of the Multicenter Study of Hydroxyurea and other controlled trials now bear out these predictions.