Sickle Cell Disease
What is sickle cell disease (SCD)?
Sickle cell disease is an inherited disorder that affects your red blood cells, producing a negative impact on your health. In SCD, your hemoglobin is not normal and cannot pass easily through your blood vessels. Hemoglobin is a protein that is part of your red blood cells. It is the substance that carries oxygen in the blood.
Normal red blood cells are round and can move through small blood vessels in the body to deliver oxygen. In SCD, a chemical change in hemoglobin causes the formation of long rods. These rigid rods change the shape of the red blood cell into a sickle (which looks like a crescent). The sickle-shaped cells do not pass easily through blood vessels. They can clog or break apart which also leads to decreased red blood cell life. Sickle cells do not live as long as normal red blood cells. This will lead to increased iron storage in the liver and the heart, which could potentially cause damage to these organs. The damage could result in conditions such as liver failure, cardiac arrhythmia (irregular heart rhythms), an enlarged heart (cardiomyopathy) and heart failure.
How common is sickle cell disease (SCD)?
SCD results from sickle cell trait (SCT). Sickle cell trait happens when people have one sickle cell gene and one normal gene. If you just have the SCT, you usually do not have symptoms and you don’t have SCD. However, you can pass SCT to your children. If both parents have the trait, the child may be more likely to have some type of sickle cell disease.
While there are an estimated 1 million to 3 million people in the U.S. who have SCT, there are only about 100,000 people with SCD.
Who is affected by sickle cell disease (SCD)?
Sickle cell trait, and therefore SCD, is found more often in certain ethnic groups, including African Americans, Hispanics, South Asians, Southern European Caucasians, and Middle Easterners. In the United States, about 1 in 350-400 African American babies have sickle cell disease. Worldwide, it is estimated that there are 300 million people with sickle cell trait. About one-third of this number are in sub-Saharan Africa.
What are some common types of sickle cell disease?
Sickle cell disease is a group of disorders that affect the hemoglobin including:
- Hemoglobin SS (HbSS) disease.
- Hemoglobin SB+ (beta) thalassemia.
- Hemoglobin SB0 (beta-zero) thalassemia.
- Hemoglobin SC disease.
- Hemoglobin SD disease.
- Hemoglobin SE disease.
- Hemoglobin SO disease.
Symptoms and Causes
What causes sickle cell disease (SCD)?
SCD is an inherited condition. It is caused by defective HBB gene. It is inherited in an autosomal recessive pattern, in which parents of an individual with SCD each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
What are the symptoms of sickle cell disease (SCD)?
SCD signs and symptoms begin to show when a child is around four to five months old. Before that, fetal hemoglobin stops the red blood cells from changing shape (sickling).
Signs and symptoms of SCD varies from person to person. Some people have mild symptoms, while others are frequently hospitalized for more serious complications
Signs and symptoms of SCD include:
- Anemia could present as fatigue and weakness.
- Swelling and inflammation of the joints.
- Blood blockage in the spleen or liver.
- Jaundice (yellowing of skin and eyes).
Diagnosis and Tests
How will your healthcare provider diagnose sickle cell disease (SCD)?
U.S. law requires all babies to be tested for sickle cell disease as part of a newborn screening program. At this point, the test will indicate if the baby has an abnormal hemoglobin trait.
Your doctor will order a blood test if you are not sure if you have sickle cell trait, disease or anemia.
Management and Treatment
What are the treatments for sickle cell disease (SCD)?
For most people with SCD today, medications are used to modify disease severity and to treat symptoms. These medications include:
- Disease modifying agent like hydroxyurea.
- Pain medication like nonsteroidal antiinflammatory drugs (NSAIDs) and opiate in an acute pain crisis.
- Antibiotics, such as penicillin.
- A new drug to inhibit hemolysis (Oxbryta®; voxelotor).
- A new drug to inhibit sickling (Adakveo®; crizanlizumab).
A blood or marrow transplant (also called a stem cell transplant) can cure SCD. The transplant requires a donor who is a good match, such as a sibling, and ongoing studies are looking to optimize the transplant from alternative donors such as mother, father or siblings who only half matched. There are risks involved with a transplant.
Currently, gene therapy is being tested to treat SCD. This calls for putting a normal hemoglobin gene into a person’s hematopoietic stem cells collected from marrow or peripheral blood and then putting those cells back into the body after receiving chemotherapy to create space for the new cells. There is promising early data and the hope is that gene therapy might one day be a routine treatment for SCD.
Transfusions and red blood cell exchange
Blood transfusions and red blood cell exchange do not cure sickle cell disease. However, they may be used to treat crisis situations, such as strokes, acute chest syndrome and organ failures.
What are the complications of sickle cell disease (SCD)?
Sickle cell disease can affect many parts of your body. Some of the effects are acute (they start suddenly) and some are chronic (they last for a long time). Sickle cell complications begin early and continue throughout life.
For instance, if you have SCD, you might have an acute pain crisis, which is also called a sickle cell crisis or vaso-occlusive crisis (VOC). When the deformed blood cells cause a blockage, you might experience pain anywhere in the body. Areas that are hit by VOCs more often include the abdomen, chest, back, legs and arms. You might also have chronic pain, or pain that lasts longer than three months.
Acute chest syndrome
This complication of SCD is serious because of the lung damage that can occur when the sickle cells form in the blood tissue of the lungs. This might happen a couple of days after a pain crisis. You might also have an infection. You should call your healthcare provider and you may be admitted to a hospital.
People with SCD are at risk for strokes. Sometimes the signs are obvious (clinical stroke). Sometimes the signs are not very obvious, and the stroke is said to be silent. (This is also called silent brain injury).
Neurological issues could lead to long-term problems in learning, making decisions, or being able to work and keep a job.
The deformed blood cells can cause damage to the retina of the eye. In turn, this could result in vision problems or in loss of vision. It is important to get regular eye exams and let your doctor know if you have any change in your vision.
SCD can cause growth to be slow. This includes a delay in sexual maturity.
Males can find themselves with priapism, a condition that happens when the deformed cells blocks blood flow out of an erect penis, and the penis stays erect for long periods of time. In addition to causing pain, priapism can harm the penis and result in impotence. Having an erection that lasts 4 hours or longer is a medical emergency.
Does sickle cell trait or sickle cell disease affect pregnancy?
Many women with sickle cell disease have healthy pregnancies, but the risks are higher. You should always have good prenatal care. If you have SCD, you might have problems like episodes of pain, infections, and vision problems. A woman with SCD has a higher risk of miscarrying, giving birth early, and having a baby who weighs less than 5 pounds and 8 ounces.
Most women with sickle cell trait have healthy pregnancies and, like all pregnant women, should have regular prenatal care.
How can you prevent sickle cell disease (SCD)?
You cannot prevent sickle cell disease. However, it is possible to be tested for sickle cell trait. If you are pregnant, you can have chorionic villus sampling (CVS) or amniocentesis (amnio) to test for SCT or SCD. You may want to consult a genetic counselor if you or your partner have SCT or SCD.
Who is at risk of developing sickle cell disease (SCD)?
Certain ethnic groups are more likely to develop SCD, including people of African, Hispanic and Mediterranean descent.
Outlook / Prognosis
What is the outlook for people with sickle cell disease (SCD)?
People who have sickle cell disease have a reduced life expectancy. Some people with the disease can remain without symptoms for years, while others do not survive beyond infancy or early childhood. New treatments for SCD are improving life expectancy and quality of life. People with sickle cell disease can survive beyond their 50s with optimal management of the disease.
When should you call your provider about sickle cell disease (SCD)?
Contact your healthcare provider or get to an emergency room when:
- You have a fever of 101°F (38°C).
- You have an erection that has lasted for four or more hours.
- You have pain that persists, especially chest pain or headache.
- You find it hard to breathe.
- You have problems with your vision.
What is the relationship between malaria and sickle cell disease?
Research shows that people with sickle cell trait are protected against malaria. Areas of the world that still struggle with malaria thus have high numbers of people with SCT.
Are there resources for people with sickle cell disease (SCD)?
If you or someone you care about has SCD, you might find helpful information and/or support from one of the following organizations. This list is not meant to be all-inclusive.