Sickle cell anemia, or sickle cell disease (SCD), is a genetic disease of the red blood cells (RBCs). Normally, RBCs are shaped like discs, which gives them the flexibility to travel through even the smallest blood vessels. However, with this disease, the RBCs have an abnormal crescent shape resembling a sickle. This makes them sticky and rigid and prone to getting trapped in small vessels, which blocks blood from reaching different parts of the body. This can cause pain and tissue damage.
SCD is an autosomal recessive condition. You need two copies of the gene to have the disease. If you have only one copy of the gene, you are said to have sickle cell trait.
Hemoglobin is the protein in red blood cells that carries oxygen. It normally has two alpha chains and two beta chains. The four main types of sickle cell anemia are caused by different mutations in these genes.
Hemoglobin SS disease: Hemoglobin SS disease is the most common type of sickle cell disease. It occurs when you inherit copies of the hemoglobin S gene from both parents. This forms hemoglobin known as Hb SS. As the most severe form of SCD, individuals with this form also experience the worst symptoms at a higher rate.
Hemoglobin SC disease: Hemoglobin SC disease is the second most common type of sickle cell disease. It occurs when you inherit the Hb C gene from one parent and the Hb S gene from the other. Individuals with Hb SC have similar symptoms to individuals with Hb SS. However, the anemia is less severe.
Hemoglobin SB+ (beta) thalassemia: Hemoglobin SB+ (beta) thalassemia affects beta globin gene production. The size of the red blood cell is reduced because less beta protein is made. If inherited with the Hb S gene, you will have hemoglobin S beta thalassemia. Symptoms are not as severe.
Hemoglobin SB 0 (Beta-zero) thalassemia: Sickle beta-zero thalassemia is the fourth type of sickle cell disease. It also involves the beta globin gene. It has similar symptoms to Hb SS anemia. However, sometimes the symptoms of beta zero thalassemia are more severe. It is associated with a poorer prognosis.
Hemoglobin SD, hemoglobin SE, and hemoglobin SO: These types of sickle cell disease are more rare and usually don’t have severe symptoms.
Sickle cell trait: People who only inherit a mutated gene (hemoglobin S) from one parent are said to have sickle cell trait. They may have no symptoms or reduced symptoms.
Symptoms of sickle cell anemia usually show up at a young age. They may appear in babies as early as 4 months old, but generally occur around the 6-month mark.
Signs and symptoms of sickle cell anemia, which vary from person to person and change over time, include:
Anemia: Sickle cells break apart easily and die, leaving you without enough red blood cells. Red blood cells usually live for about 120 days before they need to be replaced. But sickle cells usually die in 10 to 20 days, leaving a shortage of red blood cells (anemia).
Without enough red blood cells, your body can't get the oxygen it needs to feel energized, causing 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 varies in intensity and can last for a few hours to a few weeks. Some people have only a few pain episodes. Others have a dozen or more crises a year. If a crisis is severe enough, you might need to be hospitalized.
Some adolescents and adults with sickle cell anemia also have chronic pain, which can result from bone and joint damage, ulcers and other causes.
Painful swelling of hands and feet: The swelling is caused by sickle-shaped red blood cells blocking blood flow to the hands and feet.
Frequent infections: Sickle cells can damage an organ that fights infection (spleen), leaving you more vulnerable to infections. Doctors commonly give infants and children with sickle cell anemia vaccinations and antibiotics to prevent potentially life-threatening infections, such as pneumonia.
Delayed 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. Tiny blood vessels that supply your eyes may become plugged with sickle cells. This can damage the retina — the portion of the eye that processes visual images, leading to vision problems.
Sickle cell anemia is caused by a mutation in the gene that tells your body to make the red, iron-rich compound that gives blood its red color (hemoglobin). Hemoglobin allows red blood cells to carry oxygen from your lungs to all parts of your body. In sickle cell anemia, the abnormal hemoglobin causes red blood cells to become rigid, sticky and misshapen.
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 the father must pass on the defective form of the gene for a child to be affected.
If only one parent passes the sickle cell gene to the child, that child will have the sickle cell trait. With one normal hemoglobin gene and one defective form of the gene, people with the sickle cell trait make both normal hemoglobin and sickle cell hemoglobin. Their blood might contain some sickle cells, but they generally don't have symptoms. But they are carriers of the disease, which means they can pass the gene to their children.
Having a family history of sickle cell disease increases your risk for the disease. SCD mainly affects people whose families came from Africa, and Hispanics whose families are from the Caribbean. But the gene has also been found in people whose families are from the Middle East, India, Latin America, and Mediterranean countries. It has also been found in Native American Indians.
Complications of Sickle Cell Anemia
Sickle cell anemia can lead to a host of complications, including:
Stroke: A stroke can occur if sickle cells block blood flow to an area of your brain. Signs of stroke include seizures, weakness or numbness of your arms and legs, sudden speech difficulties, and loss of consciousness. If your baby or child has any of these signs and symptoms, seek medical treatment immediately. A stroke can be fatal.
Acute chest syndrome. This life-threatening complication causes chest pain, fever and difficulty breathing. Acute chest syndrome can be caused by a lung infection or by sickle cells blocking blood vessels in your lungs. It might require emergency medical treatment with antibiotics and other treatments.
Pulmonary hypertension. People with sickle cell anemia can develop high blood pressure in their lungs (pulmonary hypertension). This complication usually affects adults rather than children. Shortness of breath and fatigue are common symptoms of this condition, which can be fatal.
Organ damage. Sickle cells that block blood flow through blood vessels immediately deprive the affected organ of blood and oxygen. In sickle cell anemia, blood is also chronically low on oxygen. Chronic deprivation of oxygen-rich blood can damage nerves and organs in your body, including your kidneys, liver and spleen. Organ damage can be fatal.
Blindness. Sickle cells can block tiny blood vessels that supply your eyes. Over time, this can damage the portion of the eye that processes visual images (retina) and lead to blindness.
Leg ulcers. Sickle cell anemia can cause open sores, called ulcers, on your legs.
Gallstones. The breakdown of red blood cells produces a substance called bilirubin. A high level of bilirubin in your body can lead to gallstones.
Priapism. Men with sickle cell anemia can have painful, long-lasting erections, a condition called priapism. As occurs in other parts of the body, sickle cells can block the blood vessels in the penis. This can damage the penis and lead to impotence.
When to see a doctor
Although sickle cell anemia is usually diagnosed in infancy, if you or your child develops any of the following problems, see your doctor right away or seek emergency medical care:
A doctor may suspect sickle cell anemia based on symptoms an on routine blood test results. Early diagnosis of sickle cell anemia in children is extremely important. A simple, inexpensive blood test called hemoglobin electrophoresis is used to confirm the diagnosis, and can be used on newborn infants to screen for the condition.
This test is done at the same time and from the same blood samples as other routine newborn screening tests. It shows if hemoglobin S is present. If the hemoglobin electrophoresis test is positive, the test is repeated to confirm that the child carries the sickle cell trait.
If you or your child has sickle cell anemia, a blood test to check for a low red blood cell count (anemia) will be done. Your doctor might suggest additional tests to check for possible complications of the disease.
If you or your child carries the sickle cell gene, you'll likely be referred to a genetic counselor.
Bone marrow transplant, also known as stem cell transplant, offers the only potential cure for sickle cell anemia. It's usually reserved for people younger than age 16 because the risks increase for people older than 16. Finding a donor is difficult, and the procedure has serious risks associated with it, including death.
As a result, treatment for sickle cell anemia is usually aimed at avoiding crises, relieving symptoms and preventing complications. Babies and children age 2 and younger with sickle cell anemia should make frequent visits to a doctor. Children older than 2 and adults with sickle cell anemia should see a doctor at least once a year, according to the Centers for Disease Control and Prevention.
Treatments might include medications to reduce pain and prevent complications, and blood transfusions, as well as a bone marrow transplant.
Medications used to treat sickle cell anemia include:
Antibiotics: Children with sickle cell anemia may begin taking the antibiotic penicillin when they're about 2 months old and continue taking it until they're at least 5 years old. Doing so helps prevent infections, such as pneumonia, which can be life-threatening to an infant or child with sickle cell anemia.
As an adult, if you've had your spleen removed or had pneumonia, you might need to take penicillin throughout your life.
Pain-relieving medications: To relieve pain during a sickle cell crisis, your doctor might prescribe pain medications.
Hydroxyurea (Droxia, Hydrea): When taken daily, hydroxyurea reduces the frequency of painful crises and might reduce the need for blood transfusions and hospitalizations. Hydroxyurea seems to work by stimulating production of fetal hemoglobin – a type of hemoglobin found in newborns that helps prevent the formation of sickle cells.
Hydroxyurea increases your risk of infections, and there is some concern that long-term use of this drug might cause problems later in life for people who take it for many years. More study is needed.
Assessing stroke risk
Using a special ultrasound machine (transcranial), doctors can learn which children have a higher risk of stroke. This painless test, which uses sound waves to measure blood flow, can be used on children as young as 2 years. Regular blood transfusions can decrease stroke risk.
Vaccinations to prevent infections
Childhood vaccinations are important for preventing disease in all children. They're even more important for children with sickle cell anemia because their infections can be severe.
Your doctor will make sure your child receives all of the recommended childhood vaccinations. Vaccinations, such as the pneumococcal vaccine and the annual flu shot, are also important for adults with sickle cell anemia.
In a red blood cell transfusion, red blood cells are removed from a supply of donated blood, then given intravenously to a person with sickle cell anemia.
Blood transfusions increase the number of normal red blood cells in circulation, helping to relieve anemia. In children with sickle cell anemia at high risk of stroke, regular blood transfusions can decrease the risk. Transfusions can also be used to treat other complications of sickle cell anemia, or they can be given to prevent complications.
Blood transfusions carry some risk, including infection and excess iron buildup in your body. Because excess iron can damage your heart, liver and other organs, people who undergo regular transfusions might need treatment to reduce iron levels.
A bone marrow transplant, also called a stem cell transplant, involves replacing bone marrow affected by sickle cell anemia with healthy bone marrow from a donor. The procedure usually uses a matched donor, such as a sibling, who doesn't have sickle cell anemia. For many, donors aren't available. But stem cells from umbilical cord blood might be an option.
Because of the risks associated with a bone marrow transplant, the procedure is recommended only for people, usually children, who have significant symptoms and problems from sickle cell anemia.
If a donor is found, the person with sickle cell anemia receives radiation or chemotherapy to destroy or reduce his or her bone marrow stem cells. Healthy stem cells from the donor are injected intravenously into the bloodstream of the person with sickle cell anemia, where they migrate to the bone marrow and begin generating new blood cells.
The procedure requires a lengthy hospital stay. After the transplant, you'll receive drugs to help prevent rejection of the donated stem cells. Even so, your body might reject the transplant, leading to life-threatening complications.
Treating sickle cell complications
Doctors treat most complications of sickle cell anemia as they occur. Treatment might include antibiotics, vitamins, blood transfusions, pain-relieving medicines, other medications and possibly surgery, such as to correct vision problems or to remove a damaged spleen.
Scientists are studying new treatments for sickle cell anemia, including: