Sickle Cell Disease - Symptoms

Risk Factors

The sickle cell gene for hemoglobin S (HbS) is the most common inherited blood condition in the United States. About 70,000 - 100,000 Americans -- mostly African-Americans -- have sickle cell disease. About 2 million Americans have sickle cell trait.

Sickle cell disease is inherited. People at risk for inheriting the gene for sickle cell descend from people who are or were originally from Africa or parts of India and the Mediterranean. The sickle cell gene also occurs in people from South and Central America, the Caribbean, and the Middle East. The high prevalence of the sickle cell gene in these regions of the world is due to the sickle cell's ability to make red blood cells resistant to the malaria parasite.

---

---

People inherit a pair of genes that regulate hemoglobin, with one gene coming from each parent:

• If one normal hemoglobin gene and one sickle cell gene are inherited, a person will have sickle cell trait. People who have sickle cell trait are protected from malaria and do not develop themselves sickle cell disease, but they are “carriers” who can pass the abnormal gene on to their children. In general, most people with sickle cell trait are healthy, although some individuals may face kidney complications and other health problems.
• If two sickle genes are inherited, a person will have sickle cell disease.

Risk of Inheritance

The risk of a child inheriting sickle cell disease or sickle cell trait is as follows:

• If both parents have sickle cell trait (each have one normal hemoglobin gene and one sickle cell gene), the child has a 50% chance of inheriting sickle cell trait (one normal gene, one sickle cell gene), 25% chance of inheriting sickle cell disease (two sickle cell genes), and 25% chance of not inheriting either the trait or the disease (two normal genes).
• If one parent has sickle cell trait (one normal gene and one sickle cell gene) and the other parent has two normal hemoglobin genes, the child has a 50% chance of inheriting sickle cell trait (one normal gene and one sickle cell gene) and a 50% of inheriting neither the trait nor the disease (two normal genes). The child is not at risk of inheriting sickle cell disease.
• If one parent has sickle cell disease (two sickle cell genes) and the other parent has sickle cell trait (one normal gene, one sickle cell gene), the child has a 50% chance of inheriting sickle cell trait and a 50% chance of inheriting sickle cell disease.
• If one parent has sickle cell disease and the other parent has two normal hemoglobin genes, the child has a 100% chance of inheriting sickle cell trait, but not the disease.
• If both parents have sickle cell disease, the child has a 100% chance of inheriting the disease.

Review Date: 01/13/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).