Sickle cell disease (SCD) is a global disease affecting up to 3,000,000 world-wide. In the United States, SCD is the most common inherited blood disorder. We don’t have a national registry but we believe there are at least 100,000 people living with SCD in the United States. In South Carolina, we think as many as 4,500 may be affected.
Despite improvements in childhood care, it remains a life-limiting disease with multi-organ complications that reduces the quality of life. The majority of affected patients in the United States are of African descent but there are also many individuals of all races and ethnicities affected SCD is a genetic condition–it cannot be “caught” or transmitted like a virus. SCD can only be inherited from an individual’s mother and father.
SCD is caused by an abnormal hemoglobin. Hemoglobin is a protein that lives in the red blood cell. The hemoglobin in the body is responsible for delivering oxygen to all tissue throughout the body. All parts of the body need oxygen to survive and the hemoglobin is responsible for delivering oxygen from the lungs to the organs, tissues, muscles and bones.
When babies are developing inside the uterus, their bodies make fetal hemoglobin (called hemoglobin F). This hemoglobin is especially for babies to help them get the oxygen they need to grow and develop in the uterus. After birth, the hemoglobin in the body slowly converts from hemoglobin F (fetal hemoglobin) to hemoglobin A (normal, adult hemoglobin). This conversion is usually completed by the end of the first year of life. However, individuals with sickle cell disease inherit two abnormal hemoglobins (one from each parent). At least one of the abnormal hemoglobins, is the sickle hemoglobin called Hb S. If a person has one normal hemoglobin (Hb A) and hemoglobin S, they will not have sickle cell disease. This person is a carrier or someone with sickle cell trait. If the other hemoglobin is HgbS or another abnormal Hb such as C, D, or E or a gene for beta-thalassemia, they will have sickle cell disease.
In SCD, the hemoglobin causes multiple problems. It has trouble holding on to the oxygen molecule and delivering the oxygen around the body. It also polymerizes (groups together) to form tight cords inside the red blood cell when it loses its oxygen making the cell rigid and change shape into the classic sickle cell. This shape change is part of the reason the cells get stuck in the blood vessels leading to pain and organ injury. Finally, even when it is not sickled, the Hb S is very fragile and can easily break down within the body causing low red blood cells (or anemia) as well as inflammation within the blood vessels. Over time there are many complications that can develop from the injury to blood vessels. However, there are also many drugs in development to fight these problems.