What Is Sickle Cell Disease?
Sickle cell disease (SCD) is the most common inherited blood disorder. That means it’s passed down through families. You’re born with SCD. It’s not something you catch or develop later in life.
Sickle cell disease is also known as:
- HbS disease
- Hemoglobin S Disease
- SCD
- Sickle cell disorders
- Sickling disorder due to hemoglobin S
The disease gets its name because when you have SCD, your red blood cells look like a sickle, which is a C-shaped farm tool.
Red blood cells contain a molecule called hemoglobin, which carries oxygen throughout the body. In a healthy person, hemoglobin is smooth, round, and flexible. That allows red blood cells to glide easily through your bloodstream. But if you have SCD, the hemoglobin’s shape is abnormal, causing red blood cells to become rigid and curved. The odd-shaped cells block blood flow. It’s dangerous and can cause extreme pain, anemia, and other symptoms.
About 100,000 people in the U.S. have sickle cell disease. Most of them are African American.
Sickle Cell Disease Symptoms
Babies born with SCD usually show symptoms at around 5 months of age. Symptoms vary from person to person and change over time. Symptoms can include:
Anemia. Sickle cells are more fragile than normal red blood cells and tend to die in 10-20 days. Normal cells live for about 120 days. This causes a shortage of red blood cells, known as anemia. There aren’t enough red blood cells to carry oxygen around the body, so it brings on fatigue.
Pain crises. These bouts of pain are a major symptom of sickle cell disease. Sickle-shaped red blood cells block blood flow through tiny blood vessels, causing pain in your chest, abdomen, joints, and bones. The pain can vary in intensity and frequency, and sometimes you might need to go to the hospital.
Swelling of hands and feet. When sickle-shaped red blood cells block blood flow to the hands and feet, this causes swelling.
Frequent infections. Sickle cells sometimes damage your tissues, leading to ulcers. If they damage your spleen, you could get infections. Doctors sometimes give SCD patients vaccinations and antibiotics to prevent dangerous infections.
Yellowing of the skin and eyes. This can result from damaged sickle red blood cells.
Vision problems. Sickle cells can get stuck in the blood vessels that supply your eyes, causing damage to your retina as well as vision problems.
Developmental delays. Children with SCD may grow at a slower rate than other children. Teenagers may reach puberty later than their friends.
Sickle Cell Disease Causes and Risk Factors
Sickle cell disease is caused by a problem in the hemoglobin-beta gene found on chromosome 11. The defect forms abnormal hemoglobin.
Both your parents need to pass the abnormal hemoglobin gene on to you for you to develop the disease. If both your parents carry the defective gene, you have a 1 in 4 chance of inheriting the disease and becoming sick with it.
If a child is born with one defective hemoglobin-beta gene, they may become a carrier of the disease. Carriers usually don’t develop SCD symptoms. But they can pass the disease on to their children if their partner also carries the sickle cell trait.
People of some ethnicities are more at risk for sickle cell disease than others.
In the U.S., SCD affects African American people more than other races. One in 13 African American babies are born with sickle cell trait, and 1 in 365 Black children are born with sickle cell disease.
SCD also affects people from Hispanic, southern European, Middle Eastern, and Asian Indian backgrounds.
Types of Sickle Cell Disease
There are several forms of sickle cell disease. The type you or your child inherits depends on many things, including the specific type of abnormal hemoglobin you have.
Hemoglobin SS, also called sickle cell anemia, is usually the most severe type of this disorder.
Other common forms include:
- Hemoglobin SC (usually mild)
- Hemoglobin sickle beta thalassemia
Rare types are:
- Hemoglobin SD
- Hemoglobin SE
- Hemoglobin SO
Sickle Cell Disease Diagnosis
A blood test can check for the defective form of hemoglobin found in people with sickle cell disease. This test is available for newborns, older children, and adults. In the U.S., this test is a routine part of screening for newborn babies.
If you or your child has sickle cell disease, your doctor might suggest some extra tests, such as a special ultrasound to find out your risk for stroke. They may also refer you and your child to a genetic counselor (since you both carry the gene).
If you or your partner has sickle cell disease or sickle cell trait, a check of amniotic fluid can let you know if your unborn baby may have the disease. Talk to your doctor to find out more.
Sickle Cell Disease Treatments
Treatment for people with sickle cell disease usually involves:
- Avoiding pain crises
- Relieving symptoms of the disease
- Preventing complications
Treatments include:
- Medications
- Daily hydroxyurea (Droxia, Hydrea, Siklos) can lower the frequency of your pain crises and might curb other complications such as infections and anemia. This medication shouldn’t be taken if you're pregnant.
- Pain relievers can help when you are having a pain crisis.
- Other drugs can reduce the frequency of pain crises, such as crizanlizumab (Adakveo) and L-glutamine oral powder (Endari). The former is given by injection.
- Voxelotor (Oxbryta) can help with anemia.
- Blood transfusions
- Stem cell transplants might cure the disease for some children and teenagers.
CRISPR gene editing for sickle cell disease
In December 2023, the FDA approved two gene therapy treatments for sickle cell disease. The two therapies, Casgevy and Lyfgenia, both work by modifying stem cells taken from bone marrow, the spongy inside of bones. These stem cells are then modified into normally shaped red blood cells. The first therapy restores normal cell function, and the second modifies a gene to create normally functioning hemoglobin A cells.
Casgevy uses CRISPR, an immune feature used by microbes to help ward off viruses or other invaders. CRISPR is turned into a drug delivery system that helps recreate fetal hemoglobin, which then changes into red blood cells. Because the gene mutation for sickle cell disease is not found in fetal hemoglobin cells, these CRISPR-modified cells go on to produce healthy red blood cells.
Lyfgenia does not use CRISPR technology, but it uses a benign virus to insert genetic material that modifies the mutated gene, turning the malfunctioning hemoglobin A cells in sickle cell disease into new, regularly formed hemoglobin A cells.
Sickle Cell Disease Life Expectancy
It's estimated that people with sickle cell disease have a life expectancy that's 20 years shorter than average. With optimal treatment, people with sickle cell disease can live six decades or more. With improved treatments, survival rates and quality of life for people with the disease are getting better. However, many people with the disease report challenges in getting quality care and often experience stigma when they seek it.
Sickle Cell Disease Prevention
Sickle cell disease is a genetic condition that people are born with, so there isn't a way to prevent it. By law, all babies born in the U.S. are screened for sickle cell at birth. A child must inherit a sickle cell gene from both parents to develop the disease. Genetic testing allows doctors to diagnose sickle cell disease in as few as 10 weeks of pregnancy. Early diagnosis is important for managing the disease because children can develop symptoms early in life.
Sickle Cell Disease and Malaria
Malaria is a serious and sometimes fatal disease that is common in tropical climates. Malaria is spread to people by mosquitoes. Scientists believe that sickle cell trait evolved thousands of years ago to help people survive malaria. If a person with sickle cell trait is bitten by a mosquito, their illness is less severe than in people without the trait. That's because the sickle-shaped red blood cells interfere with the malaria germ's ability to grow.
Takeaways
Sickle cell disease is caused by a genetic mutation in the hemoglobin within red blood cells. This abnormal hemoglobin sticks together, changing the shape of a person's red blood cells. These misshapen cells can disrupt blood flow, leading to pain, anemia, infection, and other complications. People with sickle cell disease have a lower-than-average life expectancy, but new treatments are making it easier to live with the disease and survive it longer.
Sickle Cell Disease FAQs
Why is sickle cell common in Black people?
Sickle cell disease occurs in around 1 of every 365 births of Black children, and about 100,000 Americans live with the disease. The National Heart, Lung, and Blood Institute estimates that 9 in 10 people in the U.S. with sickle cell disease have African ancestry or identify as Black. It's believed that people with ancestry in tropical regions such as Africa carry this genetic mutation that evolved thousands of years ago as a protection against malaria. About 8%-10% of African Americans carry a single gene for sickle cell disease (sickle cell trait), but more than 100 million people worldwide have the trait, including people of African, Central and South American, southern European (Mediterranean), South Asian, and Middle Eastern ancestry.
How does sickle cell affect a person's life?
The sickle-shaped cells characteristic of sickle cell disease can interrupt blood flow and cause intense pain, which patients describe as sharp, stabbing, or throbbing. Chronic pain is common too. Sickle cell disease can lead to organ damage including the heart and kidneys. Additional complications include:
- Slow growth and delayed onset of puberty
- Vitamin deficiencies, particularly vitamins C and D and the nutrients omega 3 and zinc
- Infection due to spleen damage
- Joint damage
- Blood clots
- Issues in pregnancy
Can sickle cell disease be cured?
Blood and bone marrow transplants offer a possible cure for some people with sickle cell disease. However, these transplants need a donor who is well-matched to the recipient, usually someone closely related by blood. Most of these transplants are now performed on children with a history of severe complications from their disease. The procedure holds more risk for adult patients, but scientists are looking at ways to provide this treatment to more people.
What is the difference between sickle cell disease and thalassemia?
Both sickle cell and thalassemia are inherited genetic disorders caused by a mutation in hemoglobin genes, the substance that carries oxygen in red blood cells. Both conditions cause symptoms such as jaundice, fatigue, and pain. In thalassemia, also called Mediterranean anemia, the body reacts to mutated hemoglobin by killing red blood cells, thereby resulting in anemia. To make up for the loss, the body tries to quickly make additional red blood cells, which in turn causes more complications. In contrast, the abnormal hemoglobin in sickle cell disease causes elongated red blood cells that can block small blood vessels and cause the characteristic symptoms of the disease.