Definition
What is sickle cell disease?
Sickle cell disease covers a group of inherited disorders of hemoglobin, the oxygen-carrying protein in red blood cells. It is caused by a variant of the HBB gene, which codes for beta-globin: a single DNA letter change swaps glutamic acid for valine at position six, giving hemoglobin S. Inheritance is autosomal recessive, so a person must receive hemoglobin S from one parent and hemoglobin S or another faulty beta-globin from the other. The most common form, sickle cell anemia, means two copies of hemoglobin S.
When hemoglobin S gives up its oxygen, the molecules stick together into rigid fibers that bend the cell into a sickle shape. These stiff cells break down early, causing anemia and jaundice, and jam in small vessels. The result is sudden pain crises and damage to the spleen, lungs, kidneys and brain, with a higher risk of infection and stroke. Carriers with one copy, said to have sickle cell trait, are usually healthy and partly protected from severe malaria, which is why the variant is common in people with roots in Africa, the Mediterranean, the Middle East and India.
Most cases are found by newborn screening. Care includes preventing infection, pain relief, hydroxyurea, which raises fetal hemoglobin, and blood transfusions, while stem cell transplants and new gene therapies can cure some patients.
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- HemoglobinHemoglobin is the iron-containing protein in red blood cells that picks up oxygen in the lungs and releases it to the body's tissues.
- Red blood cellA red blood cell, or erythrocyte, is a disc-shaped blood cell without a nucleus that is packed with hemoglobin and carries oxygen around the body.
- AnemiaAnemia is a condition in which the blood has fewer healthy red blood cells or less hemoglobin than normal, so less oxygen reaches the tissues.
- Recessive alleleA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- MalariaMalaria is a life-threatening infection caused by Plasmodium parasites, which infected female Anopheles mosquitoes pass to people when they bite.
- Gene therapyGene therapy is a treatment that changes the genes inside a patient's cells, by adding, replacing, silencing or editing DNA, to treat or prevent disease.
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Written for biofideX in plain words, after checking these references:
- MedlinePlus Genetics: Sickle cell disease
- NHLBI: What Is Sickle Cell Disease?
- NHGRI Talking Glossary: Sickle Cell Disease
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