What Causes Sickle Cell Anemia?

Sickle cell anemia is an inherited disease. People who have the disease inherit two copies of the sickle cell gene—one from each parent.

The sickle cell gene causes the body to make abnormal hemoglobin. Hemoglobin is the iron-rich protein that gives blood its red color and carries oxygen from the lungs to the rest of the body.

In sickle cell anemia, the hemoglobin sticks together when it delivers oxygen to the body’s tissues. These clumps of hemoglobin are like liquid fibers. They cause the red blood cells to become stiff and shaped like a sickle, or “C.” The sickled red blood cells tend to stick together and get caught in the blood vessels. (Other cells also may play a role in this process.)

Two copies of the sickle cell gene are needed for the body to make the abnormal hemoglobin found in sickle cell anemia.

Sickle Cell Trait

If you inherit only one copy of the sickle cell gene (from one parent), you will not have sickle cell anemia. Instead, you will have sickle cell trait.

People who have sickle cell trait usually have no symptoms and lead normal lives. However, they can pass the sickle cell gene to their children.

The following image shows how two parents who have sickle cell trait can pass the sickle cell gene to their children.

Example of an Inheritance Pattern for Sickle Cell Trait

The image shows how sickle cell genes are inherited. A person inherits two copies of the hemoglobin gene—one from each parent. A normal gene will make normal hemoglobin (A). An abnormal (sickle cell) gene will make abnormal hemoglobin (S).

When each parent has a normal gene and an abnormal gene, each child has: a 25 percent chance of inheriting two normal genes; a 50 percent chance of inheriting one normal gene and one abnormal gene; and a 25 percent chance of inheriting two abnormal genes.