Sickle cell disease (SCD) is a disease of the hemoglobin. In SCD, defective hemoglobin causes the red blood cells to become stiff instead of flexible and to form a sickle or a crescent. SCD is an inherited disease that is present at birth. The child inherits two defective hemoglobin genes (called hemoglobin S), one from each parent, which causes the body to make faulty hemoglobin. If a child inherits just one defective hemoglobin S gene and the other hemoglobin gene is normal (hemoglobin A), the child will have sickle cell trait and will not have any SCD symptoms.
Crescent or sickle-shaped red blood cells can get stuck in small blood vessels, blocking them. This keeps red blood cells and the oxygen they carry from getting to all parts of the body. Blocked blood flow can cause severe pain and organ damage. Complications from SCD can range from mild tiredness to more severe symptoms such as strokes, heart attacks, infections and repeated episodes of severe pain. SCD is a serious, life-threatening hematologic disorder that significantly reduces the quality of life for most individuals and is associated with a decrement in life span.
It is estimated that between 55,000 and 80,000 persons in the United States are affected by SCD and that 2000 new births occur annually. It is most common among African Americans and Hispanics, but is also found in other ethnic and racial groups.
Allogeneic transplant for SCD is currently reserved for patients with clinical features that indicate a poor outcome or significant sickle-related morbidity. Most of the experience has been with use of HLA matched sibling donors although there has been some experience with use of umbilical cord blood unit and unrelated donors. While transplant is the only curative therapy for SCD, other treatments such as hydroxyurea and regular RBC transfusions may pose fewer short term risks and should be considered.