What Causes Sickle Cell Anemia?

Sickle cell anemia is an inherited condition. People with sickle cell anemia inherit two copies of the sickle cell gene, one from each parent.

The sickle cell gene makes abnormal hemoglobin. Hemoglobin is the protein inside red blood cells that carries oxygen to all parts of the body and gives blood its red color.

In sickle cell anemia, the abnormal hemoglobin sticks together when it gives up its oxygen to the tissues. These clumps are like liquid crystals that cause red blood cells to become stiff and shaped like a sickle, or “C.” It takes two copies of the sickle cell gene for the body to make the abnormal hemoglobin found in sickle cell anemia.

Sickle Cell Trait

People who inherit only one copy of the sickle cell gene (from one parent) will not have sickle cell anemia. They will have sickle cell trait.

People who have sickle cell trait generally have no symptoms and lead normal lives. Like people with sickle cell anemia, however, they can pass the sickle cell gene on to their children. The following image shows how two parents with sickle cell trait pass along the sickle cell gene.

Inheritance Pattern for Sickle Cell Trait

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