Sickle Cell Disease

What is sickle cell disease?

Sickle cell disease is the name of an inherited group of blood disorders. If you have sickle cell disease, your body produces red blood cells that become stiff and C-shaped (or sickle-shaped) and stick together. This is caused by an abnormality in hemoglobin, the oxygen-carrying protein found in red blood cells.

This can prevent your red blood cells from delivering enough oxygen to your tissues and organs. This can lead to pain and life-threatening complications.

Sickle cell disease is an inherited condition which means it has been passed on from your parents. You develop sickle cell disease when you inherit a combination of genes that cause abnormal hemoglobin.

What are the symptoms of sickle cell disease?

The symptoms of sickle cell disease usually begin during infancy, although the age at which symptoms develop and their severity can vary from person to person. Symptoms of sickle cell disease may include:

• Fatigue
• Jaundice (yellowish skin and whites of the eyes)
• Paleness
• Severe pain
• Swollen joints
• Swollen, painful hands and feet
• Weakness

What are the complications of sickle cell disease?

The most common complication of sickle cell disease is pain. This is referred to as sickle cell crisis and occurs when sickled red blood cells block or slow blood flow to your tissues and organs. The pain may be temporary, or it may last for several hours or days. Some people may develop chronic pain. Other symptoms, such as fatigue, dizziness and weakness are also associated with sickle cell crisis. Other complications of sickle cell disease can include:

• Anemia
• Acute chest syndrome
• Blood clots
• Damage to the heart, liver or kidneys
• Infections
• Leg ulcers
• Pulmonary hypertension
• Sleep apnea
• Stroke
• Vision problems

What causes sickle cell disease?

Sickle cell disease is caused by a genetic variation in the gene which contains instructions for making part of hemoglobin, called the HBB gene. Variations in the HBB gene cause your body to make abnormal hemoglobin, called hemoglobin S.Red blood cells are normally disc-shaped and are flexible, so they can move freely around your blood vessels, carrying oxygen to your tissues and organs. If your red blood cells have hemoglobin S, they become C-shaped or sickle-shaped and stick together. They don’t live as long as normal red blood cells and can become stuck in your blood vessels. As a result, your tissues and organs don’t receive enough oxygen to function properly.

Are there different types of sickle cell disease?

There are several different types of sickle cell disease:

• Hemoglobin SS (HbSS): This is the most common form of sickle cell disease and is generally one of the most severe forms. It happens when you inherit a copy of the HBB gene that causes hemoglobin S from each parent. It is also called sickle cell anemia.
• Hemoglobin SC (HbSC): This type of sickle cell disease is often less severe than HbSS, although serious complications can still occur. It happens when you inherit one copy of the HBB gene that causes hemoglobin S and one copy that causes hemoglobin C, another abnormal type of hemoglobin.
• Sickle cell beta thalassemia (HbS/beta-thalassemia): This happens when you inherit one HBB gene that causes hemoglobin S and a beta-thalassemia variant in the other HBB gene. The severity of the condition depends on the type of beta-thalassemia variant.
• Rare types of sickle cell disease: Other combinations of hemoglobin S and other abnormal hemoglobins can cause rare forms of sickle cell disease.

What is sickle cell anemia?

Sickle cell anemia is a type of sickle cell disease. It is the most common and one of the most severe forms of the condition. It occurs when you inherit a copy of the HBB gene from each parent. Sickle cell anemia can cause serious complications which can become life-threatening.The complications of sickle cell anemia may include:

• Acute chest syndrome (ACS): This may happen when sickled cells block blood vessels in your lungs, restricting blood flow. It can cause chest pain, fever an difficulty breathing.
• Vaso-occlusive crisis (VOC): Also called sickle cells crisis, this can cause severe pain in your arms, legs, abdomen, and lower back.
• Kidney, liver and lung damage: These complications can occur when sickled cells block blood flow and reduce the amount of oxygen reaching these organs.
• Detached retinas: This can happen if sickled cells clog the blood vessels in your retina.
• Splenic sequestration: This can happen if sickled cells become stuck in your spleen, causing it to enlarge and potentially causing severe anemia.
• Stroke: The risk of stroke is increased because sickled cells can block blood flow to the brain.

What are the risk factors for sickle cell disease?

You are more likely to carry a gene that causes sickle cell disease if your parents or other relatives are of African, Central or Southern American, Mediterranean, Middle Eastern, or South Asian descent.

How is sickle cell disease diagnosed?

In countries with newborn screening programs, sickle cell disease can be diagnosed via a heel prick test at birth. It can also be diagnosed before birth via prenatal screening.To be diagnosed with sickle cell disease, you need to have a combination of hemoglobin genes that cause the disease. This may include inheriting two copies of the gene that causes hemoglobin S or inheriting one hemoglobin S gene and another gene that causes an abnormal form of hemoglobin, such as hemoglobin C or beta thalassemia. If you inherit only one copy of the gene that causes hemoglobin S and one normal hemoglobin gene, you have sickle cell trait. Sickle cell trait does not usually cause symptoms of sickle cell disease, but you can pass the hemoglobin S gene on to your children.

How is sickle cell disease treated?

Treatments can help to manage sickle cell disease and may include:

• Antibiotics: To help prevent infections.
• Blood transfusions: To provide you with healthy red blood cells.
• Disease-modifying medications: These include medications that can reduce damage to red blood cells and to make them less sticky.

A bone marrow transplant is the only potential cure for sickle cell disease, which replaces your bone marrow, which makes red blood cells, which bone marrow from a healthy donor.

Gene therapy can also potentially cure sickle cell disease. Some gene therapies involve modifying your blood-forming stem cells in a laboratory before infusing the modified cells back into your body.

Can sickle cell disease be prevented?

Sickle cell disease is an inherited condition that you are born with. If you have sickle cell disease or the sickle cell trait, genetic counseling can help you to understand the risk of passing it onto your children. This may involve carrier screening and advice on family planning choices.