Sickle cell anemia
Introduction
Sickle cell anemia is an inherited form of anemia — a condition in which there aren't enough healthy red blood cells to carry oxygen throughout your body.
Under normal circumstances, your red blood cells are flexible and round, and they move easily through your blood vessels to carry oxygen to all parts of your body. In people with sickle cell anemia, the red blood cells become rigid and sticky and are shaped like sickles or crescent moons. These irregular-shaped blood cells die prematurely, resulting in a chronic shortage of red blood cells. Plus, they can get stuck when traveling through small blood vessels, which can slow or block blood flow and oxygen to certain parts of the body. This produces pain and can lead to serious complications.
There's no cure for most people with sickle cell anemia. However, treatments can relieve pain and prevent further problems.
Signs and symptoms
People with sickle cell trait have one gene for the disease. They don't develop the disease and usually have no signs and symptoms. Approximately one in 12 black Americans has sickle cell trait.
People with sickle cell anemia have two genes for the disease — one from each parent. They usually show some signs and symptoms after four months of age. Some people with sickle cell anemia have mild symptoms. Others have severe symptoms and need frequent hospitalization.
Signs and symptoms of the disease include:
- Anemia. Sickle cells are fragile. They break apart easily and die, leaving you chronically short on red blood cells to carry oxygen to your tissues — a condition known as anemia. Without enough red blood cells in circulation, your body can't get the oxygen it needs to feel energized. That's why anemia causes fatigue.
- Episodes of pain. Periodic episodes of pain, called crises, are a major symptom of sickle cell anemia. Pain develops when sickle-shaped red blood cells block blood flow through tiny blood vessels to your chest, abdomen and joints. Pain can also occur in your bones. The pain may vary in intensity and can last for a few hours to a few weeks. Some people experience only a few episodes of pain. Others experience a dozen or more crises a year. If a crisis is severe enough, you may need hospitalization for painkillers to be injected into your veins (intravenously).
- Hand-foot syndrome. Swollen hands and feet are often the first signs of sickle cell anemia in babies. The swelling is caused by sickle-shaped red blood cells blocking blood flow out of the hands and feet. Hand-foot syndrome is often accompanied by pain and fever.
- Jaundice. Jaundice is a yellowing of the skin and eyes that occurs because of liver damage or dysfunction. Occasionally, people who have sickle cell anemia have some degree of jaundice because the liver, which filters harmful substances from the blood, is overwhelmed by the rapid breakdown of red blood cells. In people with dark skin, jaundice is visible mostly as yellowing of the whites of their eyes.
- Frequent infections. Sickle cells can damage your spleen, an organ that fights infection. This may make you more vulnerable to infections. Doctors commonly give infants and children with sickle cell anemia antibiotics to prevent potentially life-threatening infections, such as pneumonia.
- Stunted growth. Red blood cells provide your body with the oxygen and nutrients you need for growth. A shortage of healthy red blood cells can slow growth in infants and children and delay puberty in teenagers.
- Vision problems. Some people with sickle cell anemia experience vision problems. Tiny blood vessels that feed your eyes may become plugged with sickle cells. This can damage the retina — the portion of each eye that processes visual images.
Causes
Sickle cell anemia is caused by a mistake in the gene that tells your body to make hemoglobin — the red, iron-rich protein that gives blood its red color. Hemoglobin is a component of every red blood cell in your body. It allows red blood cells to carry oxygen from your lungs to all parts of your body, and to carry carbon dioxide waste from other parts of your body to your lungs so that it can be exhaled.
Under normal circumstances, the body makes healthy hemoglobin known as hemoglobin A. People with sickle cell anemia make hemoglobin S — the S stands for sickle.
The sickle cell gene is passed from generation to generation in a pattern of inheritance called autosomal recessive inheritance. This means that both the mother and father must pass on the defective form of the gene for a child to be affected. Most often, sickle cell disease is passed down the family tree by parents who have sickle cell trait.
People with sickle cell trait have one normal hemoglobin gene and one defective form of the gene. So their bodies make both normal hemoglobin and sickle cell hemoglobin. Their blood may contain some sickle cells, but they usually don't experience symptoms unless they're in an area with low oxygen — such as at high altitudes on an airplane or on a mountain. However, they are carriers of the disease, which means they can pass the defective gene on to their children.
Two carriers have a 25 percent chance of having an unaffected child with normal hemoglobin, a 50 percent chance of having a child who also is a carrier, and a 25 percent chance of having a child with sickle cell anemia. These chances are the same in each pregnancy.
Evolution of a defective gene
Researchers believe the defective hemoglobin gene that causes sickle cell anemia evolved many years ago, among people living in parts of Africa, the Mediterranean, the Middle East and India. At that time, malaria epidemics killed many people in those regions.
But some people in those regions had a genetic mutation that caused some of their red blood cells to change shape — a condition now known as sickle cell trait. The sickle cells actually interfered with the growth of the parasite that causes malaria. So people with sickle cell trait often survived malaria outbreaks.
Over time, these survivors migrated and continued on with their lives. In some cases, two people with the sickle cell trait had children. And some of their children inherited two copies of the mutated gene, which results in sickle cell anemia. Today, millions of people all over the world have sickle cell anemia.
How defective hemoglobin causes anemia
Red blood cells with normal hemoglobin are smooth and round and glide through blood vessels. Red blood cells with defective hemoglobin may become hard, sticky and shaped like a sickle used to cut wheat. These crescent-shaped cells can get stuck in small blood vessels, blocking blood flow and causing episodes of pain and damage to organs.
Your bone marrow — the red, spongy material found within the cavity of many of your large bones — regularly produces red blood cells. Bone marrow also produces white blood cells to fight infections and platelets to help blood clot. These two types of blood cells aren't directly involved in sickle cell anemia.
Once red blood cells leave your bone marrow, they normally live for about three to four months before they die and need to be replaced. However, sickle cells die after only 10 to 20 days. So, it's difficult for your body to produce enough replacements. The result is a chronic shortage of red blood cells, known as anemia.
Treatment
Bone marrow transplant offers the only potential cure for sickle cell anemia. But very few people have a suitable donor for transplant.
As a result, treatment is usually aimed at avoiding crises, relieving symptoms and preventing complications. If you or your child has sickle cell anemia, you'll need to make regular visits to your doctor to check your red blood count and monitor your health. You may also require treatment from specialists at a hospital or sickle cell anemia clinic. Treatments may include medications to reduce pain and prevent complications, blood transfusions and supplemental oxygen, as well as bone marrow transplant.
Treating complications
Doctors treat most complications of sickle cell anemia as they occur. Treatment may include antibiotics, blood transfusions, pain-relieving medicines, other medications and possibly surgery, such as to correct vision problems or to remove a damaged spleen.
Prevention
If you carry the sickle cell trait, you may wish to see a genetic counselor before trying to conceive a child. A genetic counselor can help you understand your risk of having a child with sickle cell anemia. He or she can also explain possible treatments, preventive measures and reproductive options.
There is an in vitro fertilization procedure that improves the chances that parents who both carry the sickle cell gene will have a child with normal hemoglobin. This procedure is known as preimplantation genetic diagnosis. First, eggs are taken from the mother. Then, sperm is taken from the father. In a laboratory, the eggs are fertilized with the sperm. The fertilized eggs are then tested for the presence of the sickle cell gene. Fertilized eggs free of the sickle cell gene can be implanted into the mother for normal development. However, this procedure is expensive and not always successful.
Informations obtained from National Institute of Health.