Sickle Cell – Definition, Causes and Treatment
Sickle cells are abnormally shaped red blood cells that occur in sickle cell disease and can obstruct blood flow throughout the body.
Things worth knowing about "Sickle Cell"
Sickle cells are abnormally shaped red blood cells that occur in sickle cell disease and can obstruct blood flow throughout the body.
What Is a Sickle Cell?
A sickle cell (medically known as a sickle erythrocyte) is an abnormally shaped red blood cell that, instead of its normal round, disc-like form, takes on a characteristic crescent or sickle shape. This deformation is caused by a genetic mutation in hemoglobin, the oxygen-carrying protein found in red blood cells. Sickle cells are the hallmark of sickle cell disease (SCD), also known as sickle cell anemia, one of the most common inherited blood disorders in the world.
Causes
The formation of sickle cells is caused by a point mutation in the HBB gene, which encodes the beta chain of hemoglobin. This mutation results in the production of hemoglobin S (HbS) instead of normal hemoglobin A. Under low-oxygen conditions, HbS polymerizes into long, rigid fibers that distort the red blood cell into the characteristic sickle shape.
- The condition is inherited in an autosomal recessive pattern.
- Individuals who carry only one copy of the mutated gene have the sickle cell trait and are usually symptom-free, but can pass the mutation on to their children.
- Those who inherit two copies of the mutated gene develop sickle cell disease with clinical symptoms.
- The mutation is especially common in regions with high malaria prevalence (sub-Saharan Africa, parts of the Mediterranean, India), as the sickle cell trait provides some protection against malaria.
Properties and Effects of Sickle Cells
Compared to normal red blood cells, sickle cells have several problematic characteristics:
- Reduced flexibility: Normal red blood cells are pliable and can squeeze through narrow capillaries. Sickle cells are rigid and become stuck in small blood vessels.
- Shortened lifespan: Normal red blood cells live approximately 120 days, while sickle cells survive only 10 to 20 days, leading to chronic hemolytic anemia.
- Vascular blockages: Sickle cells can block blood vessels, interrupting blood supply to organs and tissues, causing painful crises and organ damage.
- Increased stickiness: Sickle cells adhere more readily to vessel walls, raising the risk of clot formation.
Symptoms of Sickle Cell Disease
The symptoms caused by sickle cells are wide-ranging and vary in severity:
- Pain crises (vaso-occlusive crises): Sudden, severe pain often in the bones, joints, chest, or abdomen, triggered by vascular blockages.
- Chronic anemia: Pallor, fatigue, weakness, and shortness of breath due to increased breakdown of red blood cells.
- Susceptibility to infections: Impaired spleen function makes patients more vulnerable to certain bacterial infections.
- Organ damage: Repeated disruptions in blood flow can permanently damage the kidneys, lungs, liver, eyes, and brain.
- Acute chest syndrome: A life-threatening complication involving chest pain, fever, and breathing difficulties.
- Stroke: Vascular blockages in the brain can occur, especially in children.
Diagnosis
Sickle cells and sickle cell disease are diagnosed through several tests:
- Blood smear: Microscopic examination of blood reveals sickle-shaped red blood cells.
- Hemoglobin electrophoresis or HPLC: Used to detect hemoglobin S in the blood.
- Newborn screening: In many countries, a blood test shortly after birth allows for early detection of the disease.
- Genetic testing: Used to confirm the diagnosis and provide guidance for family planning.
Treatment
A complete cure for sickle cell disease is currently only possible through a stem cell transplant or through newer gene therapies. Otherwise, treatment focuses on relieving symptoms and preventing complications:
- Hydroxyurea (hydroxycarbamide): A medication that stimulates the production of fetal hemoglobin (HbF), which inhibits sickle cell formation.
- Pain management: Analgesics, including opioids for severe crises.
- Blood transfusions: Used to treat severe anemia or to prevent strokes.
- Antibiotics and vaccinations: To prevent and treat infections.
- Voxelotor and crizanlizumab: Newer medications specifically approved for sickle cell disease.
References
- World Health Organization (WHO): Sickle-cell disease and other haemoglobin disorders. Fact Sheet. Geneva, 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/sickle-cell-disease
- Rees D.C., Williams T.N., Gladwin M.T.: Sickle-cell disease. In: The Lancet, 376(9757), pp. 2018-2031, 2010. DOI: 10.1016/S0140-6736(10)61029-X
- National Heart, Lung, and Blood Institute (NHLBI): Evidence-Based Management of Sickle Cell Disease. Expert Panel Report, U.S. Department of Health and Human Services, 2014.
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