Causes of Sickle Cell Disease

Sickle cell anemia is a disorder affecting red blood cells, the cells that carry oxygen from the lungs to tissues throughout the body.

Normally, red blood cells are flexible discs that glide smoothly through the blood vessels. In people with sickle cell anemia, these blood cells are stiff and sickle- or crescent-shaped. Because of their stiffness, these abnormal red blood cells may get stuck inside small blood vessels. This can cause episodes of pain, known as pain crises. The sickle cells can also cause other symptoms, such as swelling of the hands or feet, and they can damage organs.

Red blood cells in sickle cell anemia die more quickly than their normal counterparts. The normal lifespan of healthy red blood cells is around 120 days, while the red blood cells of sickle cell anemia patients typically live for about 10 to 20 days. This results in a red blood cell deficiency known as anemia. People with anemia may get tired easily because they have fewer red blood cells delivering oxygen throughout the body. 

A genetic disease

Sickle cell anemia results from a mutation in a gene called HBB, which contains the blueprint for cells to make part of a protein called hemoglobinThe hemoglobin protein is made up of two alpha chains and two beta chains. Each chain includes an iron-containing “heme” portion. The iron gives red blood cells their color. It also allows the hemoglobin molecule to bind to and then release oxygen molecules.

The mutation in the HBB gene in sickle cell anemia changes one of the amino acids, the building blocks of proteins, in the beta chain of hemoglobin. This defect causes the hemoglobin protein to stick together and form stiff fibers. These fibers distort the shape of the red blood cells and make them more fragile.

The hemoglobin in sickle cell anemia patients is called hemoglobin S, whereas those unaffected by the disease have the hemoglobin A form of the molecule.


Sickle cell anemia is inherited in an autosomal recessive manner. This means that the disease develops when someone receives two copies of the mutated HBB gene: one from the mother and one from the father. A person with just one copy of the mutated gene is said to have the sickle cell trait. Although they are a carrier of the disease, these people generally do not display any symptoms but can pass the disease to their children.

Sickle cell anemia is more common among people of certain ancestries, including those of African, Caribbean, Middle Eastern, Eastern Mediterranean, and Asian descent.


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