Gene therapy for HbSC disease and other compound heterozygous sickle hemoglobinopathies: a time for inclusion.

Two gene therapy products have been approved by the US Food and Drug Administration for sickle cell disease. Nearly all patients in the clinical trials that led to approval either were sickle hemoglobin (HbS) gene homozygotes (sickle cell anemia) or had HbS-β0 thalassemia. HbSC disease, caused by compound heterozygosity for HbS and hemoglobin C genes, is the second most common genotype of sickle cell disease. Gene therapy has not been tested in patients with HbSC disease who are severely symptomatic. We discuss the pathophysiology and clinical features of HbSC disease and how gene therapy is likely to provide a curative option for some individuals. We also discuss the mechanism through which fetal hemoglobin (HbF) and HbF-like HbA (HbAT87Q) might mitigate adverse clinical outcomes and end-organ damage in patients with HbSC disease and other compound heterozygous sickle hemoglobinopathies.