Sickle Cell Disease Causes and Risk Factors
Who can get sickle cell disease?
People with sickle cell disease two in hemoglobin – one from each parent – leading to a faulty protein called hemoglobin S. Sickle cell disease can also occur when a child inherits a hemoglobin S gene from one parent and a gene for a different type of faulty hemoglobin, such as beta (β) thalassemia or hemoglobin C, from the other parent.
Sickle cell disease is sometimes called sickle cell anemia.
People have sickle cell trait when they inherit a hemoglobin S gene from one parent and a normal hemoglobin gene, called hemoglobin A, from the other. In general, people who have sickle cell trait are healthy. They may be called of the hemoglobin S gene because they can pass it on when they have children.
How is sickle cell disease inherited?
In this image, both parents are
of sickle cell disease. Each has one normal hemoglobin A gene and one hemoglobin S gene. This means each of their children has:
- A 25%, or 1 in 4, chance of inheriting two normal hemoglobin A genes. This child does not have sickle cell trait or disease.
- A 50%, or 1 in 2, chance of inheriting one normal hemoglobin A gene and one hemoglobin S gene. This child has sickle cell trait and is a carrier of the hemoglobin S gene.
- A 25%, or 1 in 4, chance of inheriting two hemoglobin S genes. This child has sickle cell disease.
It is important to keep in mind that each time this couple has a child, the chances of that child having sickle cell disease remain the same. In other words, if the first child has sickle cell disease, there is still a 25% chance that the second child will also have the disease. Both boys and girls can inherit sickle cell trait, sickle cell disease, or normal hemoglobin.
If a person wants to know whether they carry a sickle hemoglobin gene, a healthcare provider can order a blood test to find out.
Do some groups have higher risk of sickle cell disease?
The disease is most common in people of African, Middle Eastern, Mediterranean, Central and South American, and South Asian origin or descent. Sickle cell disease now exists in most countries.
What should you do if you are a carrier or have the disease?
If you are planning to have children, you may want to meet with a genetic counselor. A genetic counselor can answer questions about the risk and explain the choices that are available.
What is a “sickled” cell?
Red blood cells with the normal type of are disc-shaped and flexible so that they can move easily through large and small blood vessels and deliver oxygen throughout the body.
Sickle hemoglobin is not like normal hemoglobin. Under low oxygen conditions, hemoglobin S transforms into stiff strands within red blood cells. These stiff strands change the shape of the cell, causing the “sickled,” or crescent-shaped, red blood cell that gives the disease its name. Sickled red blood cells are not flexible and can stick to vessel walls, which can block or slow blood flow.
Blockage of blood flow means that the sickled cells cannot deliver oxygen to the rest of the body. This can cause attacks of sudden severe pain, called pain crises. Pain crises can occur without warning, and a person who has them often needs to go to the hospital for treatment. A pain crisis can last several hours or several days.
Sickled cells are not only stiff but also very fragile, and they tend to burst apart in a process called . Normal red blood cells live about 90 to 120 days, but sickled cells last only 10 to 20 days.
The body is always making new red blood cells to replace the old cells. However, in sickle cell disease, the body has trouble keeping up with the rate that the cells are being destroyed. This can lead to a low number of red blood cells, called anemia. The resulting anemia can cause a person to be easily tired with less energy.
