Sickle cell trait occurs when a person inherits a sickle cell disease gene. People with sickle cell trait rarely have symptoms of sickle cell anemia or sickle cell disease. But they can pass the sickle cell gene to their children.

Sickle cell disease is a blood disorder. It causes the body to produce an abnormal type of hemoglobin. Hemoglobin is the protein in the red blood cells that carries oxygen. Normal hemoglobin is called hemoglobin A. People with sickle cell disease have only hemoglobin S. This turns normal, round red blood cells into abnormally curved (sickle) shapes. These curved blood cells aren't able to carry oxygen like normal red blood cells. And they are rigid and don't flow easily through blood vessels.

Normally, a person inherits two genes (one from each parent) that produce beta globin, a protein needed to produce normal hemoglobin (hemoglobin A). A person with sickle cell trait inherits one normal beta-globin gene (hemoglobin A) and one abnormal gene (hemoglobin S).

A person in whom both beta-globin genes are abnormal (they produce hemoglobin S) has sickle cell disease, which can cause serious problems. Both parents must have either the sickle cell trait or the disease itself for a child to have sickle cell disease.