Sickle cell disease (SCD) is a group of conditions that cause red blood cells to malfunction. Sickle cell anemia is a type of SCD.
Healthy red blood cells are disc-shaped and flexible, which helps them move through blood vessels and deliver oxygen to the body’s cells.
In sickle cell anemia, these red blood cells are crescent- or sickle-shaped, inflexible, and sticky. These traits make them clump together, blocking blood vessels and impairing blood flow. The sickle cells also die early, resulting in a shortage of red blood cells.
This article outlines the different types of SCD. We also describe the symptoms, causes, and treatment options of sickle cell anemia.
Red blood cells contain a protein called hemoglobin, which delivers oxygen to the body’s cells. In all forms of SCD, the red blood cells have an abnormal type of hemoglobin. Doctors refer to this as sickle hemoglobin or hemoglobin S.
Besides hemoglobin S, there are other abnormal variants of hemoglobin. The type of SCD a person has depends on which abnormal hemoglobin genes they inherit from their parents.
Below are the three most common types of SCD.
Sickle cell anemia
Sickle cell anemia is the most common and severe type of SCD. It develops when a person inherits two hemoglobin S genes — one from each parent.
People with sickle cell anemia become anemic. This means that their body does not produce enough red blood cells to supply sufficient oxygen to their cells.
Sickle-hemoglobin C is a milder form of SCD. It occurs when a person inherits two different types of abnormal hemoglobin genes: one for hemoglobin S, and one for hemoglobin C.
Hemoglobin C causes milder symptoms than sickle cell anemia. As a result, a person with sickle-hemoglobin C usually has a higher red blood cell count and a reduced risk of developing anemia than someone with sickle cell anemia.
Sickle beta-plus thalassemia
Sickle beta-plus thalassemia occurs when a person inherits one gene for hemoglobin S and one gene for beta thalassemia.
Beta thalassemia is a different type of anemia, and the gene comes in two forms: 0 and +. Those with the 0 variant usually have a more severe illness than those with the + variant.
Less common types
Below are the rarer types of SCD.
Sickle-hemoglobin D occurs when a person inherits one gene for hemoglobin S and one gene for hemoglobin D. The two genes interact in a way that usually results in mild to moderate anemia. People with one of each gene may also experience bouts of pain.
Sickle-hemoglobin O occurs when a person inherits one gene for hemoglobin S, and one gene for hemoglobin O. The two genes interact to trigger various symptoms ranging from mild to severe.
People with sickle cell trait (SCT) inherit one sickle cell gene from one parent and one normal gene from the other. A person with SCT can pass the trait on to their offspring. If both parents have SCT, there is a