Molecular basis of β thalassemia and potential therapeutic targets.

The remarkable phenotypic diversity of β thalassemia that range from severe anemia and transfusion-dependency, to a clinically asymptomatic state exemplifies how a spectrum of disease severity can be generated in single gene disorders. While the genetic basis for β thalassemia, and how severity of the anemia could be modified at different levels of its pathophysiology have been well documented, therapy remains largely supportive with bone marrow transplant being the only cure. Identification of the genetic variants modifying fetal hemoglobin (HbF) production in combination with α globin genotype provide some prediction of disease severity for β thalassemia but generation of a personalized genetic risk score to inform prognosis and guide management requires a larger panel of genetic modifiers yet to be discovered. Nonetheless, genetic studies have been successful in characterizing the key variants and pathways involved in HbF regulation, providing new therapeutic targets for HbF reactivation. BCL11A has been established as a quantitative repressor, and progress has been made in manipulating its expression using genomic and gene-editing approaches for therapeutic benefits. Recent discoveries and understanding in the mechanisms associated with ineffective and abnormal erythropoiesis have also provided additional therapeutic targets, a couple of which are currently being tested in clinical trials.