We would like to treat patients using bone marrow transplantation, a treatment that has been used for people with SCD. The transplant uses healthy "matched" bone marrow. This comes from a brother or sister who does not have sickle cell disease or severe thalassemia. If the treatment works, the sickle cell disease or thalassemia may be cured. This treatment has been used to treat patients with sickle cell disease or thalassemia. It has worked in most cases. We hope, but cannot promise, that the transplanted marrow will make healthy cells, and patients will not have sickle cell disease or severe thalassemia anymore.