Sickle Cell Anemia
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Sickle cell anemia is a condition that causes damage to red blood cells and can lead to episodes of pain, organ damage, and other health problems. Although carriers of sickle cell anemia do not have the disease, their children might if the other parent is a carrier too. Carriers have a less serious condition called sickle cell trait.
More about sickle cell anemia
Healthy red blood cells are round and flexible. This allows them to travel smoothly through one’s blood vessels, taking life-giving oxygen to all the places it’s needed in the body. People with sickle cell anemia have abnormal, crescent-shaped blood cells which don’t deliver enough oxygen to all parts of their bodies. This lack of oxygen can cause attacks of severe pain and other serious problems such as infections, organ damage, stroke, and a shorter-than-average lifespan.
Sickle cell anemia leads to problems with oxygen delivery for a couple of reasons. First, sickle cells are fragile: They break apart more easily than normal blood cells. This can cause a shortage of red blood cells. And this shortage leads to less oxygen getting to vital organs.
A second reason is related to the shape of sickle cells. Because sickle cells are inflexible and sticky, they can get stuck in blood vessels and slow down—or block—the flow of blood. Since red blood cells are the ones that carry oxygen throughout the body, blocking the flow of blood also blocks the flow of oxygen.
Sickle cell anemia is just one form of sickle cell disease (SCD). But it’s the most common and typically most severe form. As many as 100,000 people in the U.S. may have SCD. It can be found in many populations, but SCD occurs more frequently among people from parts of the world where malaria was or is more common. For example, the chance of being a carrier for sickle cell anemia is about 1 in 13 for African Americans. And compared to the general U.S. population, people of Latin American descent are more likely to be carriers of sickle cell anemia. It’s believed that people who are carriers of the sickle cell trait may have some protection against malaria.
What are the symptoms of sickle cell anemia?
The symptoms of sickle cell anemia can vary from person to person, but typically they begin to show up during the first year of a newborn’s life. Early symptoms of sickle cell disease—of which sickle cell anemia is a type—can include:
- Yellowish coloration: A yellowish color of the skin (jaundice) or in the whites of the eyes (icterus) can occur when a lot of red blood cells break apart.
- Painful swelling of the hands and feet: Also known as dactylitis, it’s caused by the blocking of the blood flow to the hands and feet by sickle cells.
- Anemia: Sickle cells die more quickly than normal red blood cells, leading to a shortage of blood cells. Anemia is often associated with fatigue.
Other symptoms and signs of sickle cell anemia are numerous and can change over time. But some examples include:
- Pain crises: Sudden episodes of intense pain in a body part can last for hours or even weeks. Some people with sickle cell anemia have at least a dozen of these pain crises in a year.
- Vision loss: The part of the eye that processes light and images—the retina—can get damaged if sickle cells block the blood vessels in the eyes.
- Frequent infections: Sickle cell anemia can lead to organ damage, including damage to the spleen, the organ that fights off infection. If one’s spleen is damaged, one will be more vulnerable to infections, some of which could be life-threatening.
- Stroke: If sickle cells clump together in a blood vessel and block the flow of blood to the brain, sickle cell anemia can lead to a stroke.
People with all types of sickle cell diseases, including sickle cell anemia, have a shorter-than-average lifespan. They have a median life expectancy of 42-47 years, according to the American Society of Hematology.
What is sickle cell trait?
Sickle cell anemia is caused by a DNA difference in the HBB gene, which encodes a protein that helps make a component of your red blood cells. If someone has sickle cell anemia, they have this DNA difference in both copies of the HBB gene. But if they have this DNA difference in just one copy of their HBB gene, then they are a carrier of sickle cell anemia.
While carriers don’t have sickle cell anemia, their carrier status means they have sickle cell trait. People with sickle cell trait sometimes have some symptoms of sickle cell anemia, such as pain crises. This is rare, but it does happen.
Sickle cell trait cannot turn into sickle cell disease. But it is possible for individuals with sickle cell trait to pass the DNA difference in their HBB gene to their children. However, it is highly unlikely that a carrier of sickle cell anemia’s children will have sickle cell anemia unless the other biological parent is also a carrier of it—or of a related disease.
Why is it important to know about sickle cell anemia?
There is no widely available cure for SCDs like sickle cell anemia, but scientists may be making progress toward one. And the number of children who die from the disease at a young age has been decreasing in recent decades.
Sickle cell anemia has an impact not only on those affected with the condition but on carriers as well. They could have a child with sickle cell anemia if the other biological parent is also a carrier. Each child of two carriers has a 1 in 4 chance of having sickle cell anemia.
Being a carrier can affect what some couples think about when deciding to have children. Some may choose not to have children, and others may, after discussing their options with a healthcare provider, choose to use a variety of techniques to lower the chances that their child will have sickle cell anemia. Some people may choose to do nothing with the information.
How is sickle cell anemia passed down?
People who are carriers of sickle cell anemia most likely had it passed to them from one of their parents. This means that at least one of their parents is probably a carrier too. It also means each of their biological brothers and sisters has a 1 in 2 chance of also being a carrier.
If someone is a carrier of sickle cell anemia and the other biological parent is not a carrier, each child has a:
- 2 in 4 chance of being a carrier of sickle cell anemia
- 2 in 4 chance of not being a carrier of sickle cell anemia
If both biological parents are carriers, each child has a:
- 2 in 4 chance of being a carrier of sickle cell anemia
- 1 in 4 chance of not being a carrier of sickle cell anemia
- 1 in 4 chance of having sickle cell anemia
The fact that a child of two carriers of sickle cell anemia has a 1 in 4 chance of having the disease is what’s most concerning for many carriers.
Here is how the inheritance works in most cases: A person has two copies of most of their genes, one from each parent. To have sickle cell anemia, they would need two DNA differences linked to sickle cell anemia—one in each copy of the gene tied to the disease. If someone only had a DNA difference in one copy of this gene, they would be a carrier. This is called autosomal recessive inheritance.
What does the test offered through AncestryHealth® look at?
The test offered through AncestryHealth® looks at the one specific place in the HBB gene that can cause sickle cell anemia.
What does this gene do? The HBB gene has the instructions for making hemoglobin. Hemoglobin is in people’s red blood cells and transports oxygen to—and carbon dioxide away from—their tissues.
The DNA difference in the HBB gene affects hemoglobin and thus affects red blood cells. It makes the red blood cells fragile, which is why people with this condition suffer from anemia. This hemoglobin also forces the red blood cell into a sickle shape. These sickle-shaped blood cells can get stuck in small blood vessels, which causes the pain episodes associated with sickle cell anemia.
AncestryHealth® includes laboratory tests developed and performed by an independent CLIA-certified laboratory partner, and with oversight from an independent clinician network of board-certified physicians and genetic counselors. The test results are not diagnostic and do not determine your overall chance of developing a disease or health condition. The tests are not cleared or approved by the U.S. Food and Drug Administration. You should consult a healthcare provider before taking any action based on AncestryHealth® reports, including before making any treatment, dietary, or lifestyle changes. AncestryHealth® is not currently available in New York, New Jersey, or Rhode Island.
- American Society of Hematology. Accessed June, 2019. www.hematology.org/Patients/Anemia/Sickle-Cell-Trait.aspx
- Bender MA. Sickle Cell Disease. 2003 Sept 15 [Updated 2017 Aug 17]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2019. Available from: www.ncbi.nlm.nih.gov/books/NBK1377/
- Centers for Disease Control and Prevention. Data & Statistics on Sickle Cell Disease. Accessed August 29, 2019. www.cdc.gov/ncbddd/sicklecell/data.html
- Genetics Home Reference. Sickle Cell Disease. Accessed June, 2019. ghr.nlm.nih.gov/condition/sickle-cell-disease