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NIH MedlinePlus the Magazine, Trusted Health Information from the National Institutes of Health

Special Section:
Sickle Cell Disease

Sickle Cell Research: Yesterday, Today, and Tomorrow

A diagram showing normal and sickled red blood cells

Figure A shows normal red blood cells flowing freely through a blood vessel.
The inset image shows a cross-section of a normal red blood cell with normal

Figure B shows abnormal, sickled red blood cells blocking blood flow in a
blood vessel. (Other cells also may play a role in this process.) The inset image
shows a cross-section of a sickle-cell with abnormal hemoglobin.
Illustration courtesy of National Heart, Lung, and Blood Institute

For an estimated 70,000 to 100,000 people in the United States, sickle cell disease is a painful, lifelong battle. But advances in sickle cell research are allowing many sickle cell patients to live productively. Sickle cell disease (also known as sickle cell anemia) is a serious disease in which the body makes sickle-shaped red blood cells."Sickle-shaped" means that the cells look like crescents instead of the normal disc shape.

Under a microscope, normal red blood cells look like doughnuts without holes in the center. They move easily through blood vessels. Red blood cells contain the iron-rich protein hemoglobin. This gives blood its red color and carries oxygen from the lungs to the rest of the body.

Sickle cells contain abnormal hemoglobin that causes the cells to become sticky and crescent shaped, when the hemoglobin releases its oxygen. The stiff, sickle-shaped cells can stick to the lining of the blood vessels. This can damage the lining, creating"danger" signals that attract defensive cells. This response may enhance the"stickiness" and lead to more slowing of normal blood flow through the vessel. This reduces oxygen delivery to the tissues supplied by this partly blocked vessel.

People with sickle cell disease have a lower-than-normal number of red blood cells because sickle cells don't live as long as normal cells after they leave the bone marrow. Sickle cells usually die after about 10 to 20 days, compared to normal red blood cells, which live an average of 120 days. The bone marrow can't make new red blood cells fast enough to replace all the dying ones. This causes anemia, low blood count that results in fatigue, shortness of breath, and related symptoms. Because the cells are made normally, but die too rapidly, this is termed a"hemolytic" (destruction of red cells) anemia.

What Causes Sickle Cell Disease?

Sickle cell disease is inherited. Hemoglobin, the oxygen-carrying protein that is responsible for the red color of blood, is made of iron-containing heme and proteins called globins. People who have the disease inherit two copies of the globin gene that causes sickle cell disease. Those who live with the condition inherit a copy of the gene from each parent.

These genes, known as sickle globin genes, cause the body to make abnormal hemoglobin. In sickle cell disease, the abnormal hemoglobin chains may stick together after oxygen is delivered to the body's tissues.

Those who inherit only one copy of the sickle globin gene (from one parent) and one copy of the normal globin gene, will not have sickle cell disease. Instead, they will have sickle cell trait. People who have sickle cell trait usually have few, if any, symptoms and lead normal lives. However, they can pass on the sickle globin gene to their children.

Who Is at Risk?

Sickle cell disease is most common in people whose families come from, or have ancestors from, sub-Saharan Africa, South or Central America (especially Panama), Caribbean islands, Mediterranean countries (such as Turkey, Greece, and Italy), India, and Saudi Arabia.

Ask Your Health Professional

If you, your child, or another loved one has been diagnosed with sickle cell disease, here are a few questions to ask.

  1. How can you tell that this is sickle cell disease?
  2. Will my other children have the disease or sickle cell trait?
  3. What other tests should be carried out?
  4. What medications do you recommend, and why?
  5. Will there be side effects?
  6. Are there other treatments you can suggest that would also be helpful?
  7. What is the long-term outlook for this disease?
  8. Are there any restrictions on diet or exercise?

Winter 2011 Issue: Volume 5 Number 4 Page 17