Sickle Cell Disease - Causes and Risk Factors

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Genetic counseling can help those at risk of having a child with sickle cell disease. Sickled red blood cells do not deliver enough oxygen to the body and do not survive in the blood as long as normal cells. 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<li class="section-menu-item subnav-link"> <a href="/health/sickle-cell-disease/health-effects" aria-label="How Sickle Cell Disease May Affect Your Health-Sickle Cell Disease" hreflang="en">How Sickle Cell Disease May Affect Your Health</a> </li> <li class="section-menu-item subnav-link"> <a href="/health/sickle-cell-disease/living-with" aria-label="Living With Sickle Cell Disease-Sickle Cell Disease" hreflang="en">Living With Sickle Cell Disease</a> </li> <li class="section-menu-item subnav-link"> <a href="/health/sickle-cell-disease/pregnancy" aria-label="Pregnancy, Reproduction, and Sickle Cell Disease-Sickle Cell Disease" hreflang="en">Pregnancy, Reproduction, and Sickle Cell Disease</a> </li> </ul> </div> </div> </div> </div> <div class="block block-nhlbi-health-topics block-nhlbi-health-topics-more-info"> <div class="field field--name-field-component-more-information field--type-entity-reference-revisions field--label-hidden field__item"> <div class="paragraph 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block-nhlbi-health-topics-book-name"> <div>Sickle Cell Disease</div> </div> <div class="block block-layout-builder block-field-blocknodehealth-topicstitle"> <h1 class="field field--name-title field--type-string field--label-hidden responsive-container responsive-container-constrained field__item"><span class="ht-kicker">Sickle Cell Disease </span>Causes and Risk Factors <hr> </h1> </div> <div class="block block-addtoany block-addtoany-block"> <div class="responsive-container responsive-container-constrained"> <span class="a2a_kit a2a_kit_size_24 addtoany_list" data-a2a-url="https://www.nhlbi.nih.gov/health/sickle-cell-disease/causes" data-a2a-title="Causes and Risk Factors "> <a class="a2a_dd addtoany_share" href="https://www.addtoany.com/share#url=https%3A%2F%2Fwww.nhlbi.nih.gov%2Fhealth%2Fsickle-cell-disease%2Fcauses&title=Causes%20and%20Risk%20Factors%20"> <img src="/themes/custom/nhlbi/images/share-alt-icon.svg" alt="Share"> </a> <a class="a2a_button_email"></a> <a class="a2a_button_print"></a> </span> </div> </div> <div class="language-switcher-language-url block block-language block-language-blocklanguage-content" role="navigation"> <div class="responsive-container responsive-container-constrained"><h2 class="visually-hidden" aria-label="Switch to Espanol">Language switcher</h2><ul class="links"><li hreflang="en" data-drupal-link-system-path="node/92851" class="is-active" aria-current="page"><a href="/health/sickle-cell-disease/causes" class="language-link is-active" hreflang="en" data-drupal-link-system-path="node/92851" aria-current="page">English</a></li><li hreflang="es" data-drupal-link-system-path="node/92851"><a href="/es/salud/enfermedad-de-celulas-falciformes/causas" class="language-link" hreflang="es" data-drupal-link-system-path="node/92851">Español</a></li></ul> </div> </div> <div class="block block-layout-builder block-field-blocknodehealth-topicsfield-component-page-links"> </div> <div class="block block-layout-builder block-field-blocknodehealth-topicsfield-component-sections"> <div class="field field--name-field-component-sections field--type-entity-reference-revisions field--label-hidden"> <div class='field__items'> <div class="paragraph component component-section component-theme-white component-section-theme-white component-section-node-theme- paragraph--type--component-section paragraph--view-mode--default"> <div class="responsive-container responsive-container-constrained"> <h2 class="field--name-field-component-section-titl component-section-section-title">Who can get sickle cell disease?</h2> <div class="field field--name-field-component-section-content field--type-text-long field--label-hidden clearfix field__item"> <figure class="align-right b-loaded caption caption-img "> <div class="embed-video-container embed-video-text-container-disabled align-"> <div class="field field--name-field-video-url field--type-video-embed-field field--label-hidden field__item"><div class="video-embed-field-provider-vimeo video-embed-field-responsive-video"><iframe width="854" height="480" frameborder="0" allowfullscreen="allowfullscreen" title="Causes of Sickle Cell Disease" src="https://player.vimeo.com/video/721514041?autoplay=0"></iframe> </div> </div> </div> <figcaption><em>Sickle cell disease is a genetic disorder caused by  mutations in hemoglobin genes, leading to a faulty hemoglobin protein, called hemoglobin S. Hemoglobin S changes flexible red blood cells into rigid, sickle-shaped cells. The sickled cells can block blood flow and cause pain and organ damage.</em> <a href="https://catalog.nucleusmedicalmedia.com/" target="_blank" rel="noopener noreferrer"><em>Medical Animation Copyright © 2024 Nucleus Medical Media, All rights reserved.</em></a> </figcaption> </figure> <p class="MsoNormal">People with <strong>sickle cell disease</strong>  <span data-entity-type="node" data-entity-uuid="e4c7fd67-5ed8-492e-ad85-62f82298d49b" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"none","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of inherited " alt="Definition of inherited" data-term="inherited" data-pronunciation="in-HAYR-ih-ted" data-definition="The passing of genetic information from a parent to a child through genes." role="link"> inherited </a> </span> two  <span data-entity-type="node" data-entity-uuid="8e4c3a7e-80e0-49e0-a9a9-3cb203559601" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"plural","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of mutation " alt="Definition of mutation" data-term="mutation" data-pronunciation="myoo-TAY-shun" data-definition="Any change in a nucleic acid sequence, such as DNA or RNA." role="link"> mutations </a> </span> in hemoglobin  <span data-entity-type="node" data-entity-uuid="3c4ce4aa-1e17-470f-9373-16716a87b874" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"plural","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of gene " alt="Definition of gene" data-term="gene" data-pronunciation="jeen" data-definition="The unit that passes heredity from parents to children. Genes are pieces of DNA and contain information for making a specific protein." role="link"> genes </a> </span>  – one from each parent –<span style="mso-spacerun:yes;">  </span>leading to a faulty  <span data-entity-type="node" data-entity-uuid="b7eca5a0-efb6-40fd-adb2-aa0b2711c89e" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"none","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of hemoglobin " alt="Definition of hemoglobin" data-term="hemoglobin" data-pronunciation="HEE-moh-GLOH-bin" data-definition="A protein in red blood cells that carries oxygen throughout the body." role="link"> hemoglobin </a> </span> protein called hemoglobin S. Sickle cell disease can also occur when a child inherits a hemoglobin S gene from one parent and a gene for a different type of faulty hemoglobin, such as beta (β) <a href="https://www.nhlbi.nih.gov/health/thalassemia" rel="noreferrer">thalassemia</a> or hemoglobin C, from the other parent.</p><p class="MsoNormal"><strong>Sickle cell disease </strong>is sometimes called sickle cell <a href="https://www.nhlbi.nih.gov/health/anemia" rel="noreferrer"><span style="mso-bidi-font-style:italic;">anemia</span></a>.<span style="color:#00B050;"> <o:p></o:p></span></p><p class="MsoNormal">People have <strong>sickle cell trait</strong> when they inherit a hemoglobin S gene from one parent and a normal hemoglobin gene, called hemoglobin A, from the other. In general, people who have sickle cell trait are healthy. They may be called  <span data-entity-type="node" data-entity-uuid="46af0d68-ae4c-480e-8a00-e3d654a955dd" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"plural","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of carrier " alt="Definition of carrier" data-term="carrier" data-pronunciation="KAYR-ee-er" data-definition="In genetics, a person who has one copy of a mutated (changed) disease-causing gene but has no symptoms or mild symptoms. Carriers can pass on the mutated gene to a biological child. " role="link"> carriers </a> </span> of the hemoglobin S gene because they can pass it on when they have children.</p></div> </div> </div> <div class="paragraph component component-section component-theme-white component-section-theme-white component-section-node-theme- paragraph--type--component-section paragraph--view-mode--default"> <div class="responsive-container responsive-container-constrained"> <h2 class="field--name-field-component-section-titl component-section-section-title">How is sickle cell disease inherited?</h2> <div class="field field--name-field-component-section-content field--type-text-long field--label-hidden clearfix field__item"><p><img data-entity-uuid="e1e44a56-c8a7-45eb-9aeb-ada99ba921d6" data-entity-type="file" alt="scd inherited trait chart" class="align-right b-lazy" width="1200" height="1117" data-src="/sites/default/files/inline-images/scd_inheritance_0_0_0.jpg" src="/modules/custom/nhlbi_blazy/images/clear.png">In this image, both parents are  <span data-entity-type="node" data-entity-uuid="46af0d68-ae4c-480e-8a00-e3d654a955dd" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"plural","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of carrier " alt="Definition of carrier" data-term="carrier" data-pronunciation="KAYR-ee-er" data-definition="In genetics, a person who has one copy of a mutated (changed) disease-causing gene but has no symptoms or mild symptoms. Carriers can pass on the mutated gene to a biological child. " role="link"> carriers </a> </span> of sickle cell disease. Each has one normal hemoglobin A gene and one hemoglobin S gene. This means each of their children has:</p><ul><li>A 25%, or 1 in 4, chance of inheriting two normal hemoglobin A genes. This child does not have sickle cell trait or disease.</li><li>A 50%, or 1 in 2, chance of inheriting one normal hemoglobin A gene and one hemoglobin S gene. This child has sickle cell trait and is a carrier of the hemoglobin S gene.</li><li>A 25%, or 1 in 4, chance of inheriting two hemoglobin S genes. This child has sickle cell disease.</li></ul><p>It is important to keep in mind that each time this couple has a child, the chances of that child having sickle cell disease remain the same. In other words, if the first child has sickle cell disease, there is still a 25% chance that the second child will also have the disease. Both boys and girls can inherit sickle cell trait, sickle cell disease, or normal hemoglobin.</p><p>If a person wants to know whether they carry a sickle hemoglobin gene, a healthcare provider can order a blood test to find out.</p></div> </div> </div> <div class="paragraph component component-section component-theme-white component-section-theme-white component-section-node-theme- paragraph--type--component-section paragraph--view-mode--default"> <div class="responsive-container responsive-container-constrained"> <h2 class="field--name-field-component-section-titl component-section-section-title">Do some groups have higher risk of sickle cell disease?</h2> <div class="field field--name-field-component-section-desc field--type-text-long field--label-hidden clearfix field__item"><p>The disease is most common in people of African, Middle Eastern, Mediterranean, Central and South American, and South Asian origin or descent. Sickle cell disease now exists in most countries.</p></div> </div> </div> <div class="paragraph component component-section component-theme-white component-section-theme-white component-section-node-theme- paragraph--type--component-section paragraph--view-mode--default"> <div class="responsive-container responsive-container-constrained"> <h2 class="field--name-field-component-section-titl component-section-section-title">What should you do if you are a carrier or have the disease?</h2> <div class="field field--name-field-component-section-desc field--type-text-long field--label-hidden clearfix field__item"><p>If you are planning to have children, you may want to meet with a genetic counselor. A genetic counselor can answer questions about the risk and explain the choices that are available.</p><h2>What is a “sickled” cell?</h2><p>Red blood cells with the normal type of  <span data-entity-type="node" data-entity-uuid="b7eca5a0-efb6-40fd-adb2-aa0b2711c89e" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"none","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of hemoglobin " alt="Definition of hemoglobin" data-term="hemoglobin" data-pronunciation="HEE-moh-GLOH-bin" data-definition="A protein in red blood cells that carries oxygen throughout the body." role="link"> hemoglobin </a> </span>  are disc-shaped and flexible so that they can move easily through large and small blood vessels and deliver oxygen throughout the body.</p><p> <div data-entity-type="node" data-entity-uuid="08bd5218-39ab-4edd-9283-2c2af13cb205" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-callout-width":"half"}" class="align-right callout-embed-width-half entity-embed-callout embedded-entity" data-langcode="en"> <article class="node node--type-callout node--promoted node--view-mode-callout-descriptive red"> <div class="node__content"> <div class="component-callout-container component-callout-container-descriptive component-callout-container-descriptive-red component-callout-container-descriptive-white callout-descriptive-no-image"> <div class="callout-descriptive"> <div class="callout-descriptive-text"> <div class="field field--name-field-callout-description field--type-text-long field--label-hidden field__item"> <h3>Can the sickle cell gene protect against malaria?</h3><p>Sickle cell disease and trait are common in parts of Africa and other areas where <a href="https://www.niaid.nih.gov/diseases-conditions/malaria" rel="noreferrer">malaria</a> affects many people. Studies show that having the hemoglobin S gene protects against serious malaria. The “malaria protection theory” explains why the gene mutation leading to hemoglobin S is found more often among people whose ancestry traces to areas where malaria is common. It is still important to prevent malaria in children with sickle cell disease. </p> </div> </div> </div> </div> </div> </article> </div> Sickle hemoglobin is not like normal hemoglobin. Under low oxygen conditions, hemoglobin S transforms into stiff strands within red blood cells. These stiff strands change the shape of the cell, causing the “sickled,” or crescent-shaped, red blood cell that gives the disease its name. Sickled red blood cells are not flexible and can stick to vessel walls, which can block or slow blood flow. </p><p>Blockage of blood flow means that the sickled cells cannot deliver oxygen to the rest of the body. This can cause attacks of sudden severe pain, called pain crises. Pain crises can occur without warning, and a person who has them often needs to go to the hospital for treatment. A pain crisis can last several hours or several days.</p><p>Sickled cells are not only stiff but also very fragile, and they tend to burst apart in a process called  <span data-entity-type="node" data-entity-uuid="e09dc064-e1b6-4213-a73a-8bb7c1cb76db" data-embed-button="node" data-entity-embed-display="entity_reference:entity_reference_entity_view" data-entity-embed-display-settings="{"view_mode":"default","data-glossary-capitalization":"none","data-glossary-plural":"none","data-glossary-style":"0|0|0"}" data-langcode="en" class="entity-embed-glossary_term embedded-entity"> <a class="glossary-term" href="#" title="Definition of hemolysis " alt="Definition of hemolysis" data-term="hemolysis" data-pronunciation="hee-MAH-lih-sis" data-definition="The breakdown of red blood cells. Red blood cells normally live for up to 120 days. After that, they naturally break down and are most often removed from the blood by the spleen." role="link"> hemolysis </a> </span> . Normal red blood cells live about 90 to 120 days, but sickled cells last only 10 to 20 days. </p><p>The body is always making new red blood cells to replace the old cells. However, in sickle cell disease, the body has trouble keeping up with the rate that the cells are being destroyed. This can lead to a low number of red blood cells, called anemia. The resulting anemia can cause a person to be easily tired with less energy.</p> <figure class="align-center b-loaded caption caption-img "> <img alt="sickle cell disease diagram" data-entity-type="file" data-entity-uuid="5b0465bd-7fdc-4013-a5b4-35b90a342451" width="375" height="600" data-src="/sites/default/files/inline-images/SCD%20%281%29_1.jpg" src="/modules/custom/nhlbi_blazy/images/clear.png" class="b-lazy"> <figcaption><em><strong>Normal red cells and sickled red cells. </strong>Figure A shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin. Figure B shows abnormal, sickled red blood cells blocking blood flow in a blood vessel. The inset image shows a cross-section of a sickled cell with abnormal (sickle) hemoglobin S forming abnormal stiff rods.</em></figcaption> </figure> </div> </div> </div> </div> </div> </div> <div class="block block-nhlbi-health-topics block-nhlbi-book-nav-block"> <nav id="book-navigation-92298" class="book-navigation responsive-container-constrained" role="navigation" aria-labelledby="book-label-92298"> <h3 class="visually-hidden" id="book-label-92298">Book traversal links for Causes and Risk Factors </h3> <ul class="book-pager"> <li class="book-pager__item book-pager__item--previous"> <h4 class="nav-label">Previous</h4> <a href="/health/sickle-cell-disease" rel="prev" title="Go to previous page"><i class="fas fa-angle-left"></i> What Is Sickle Cell Disease?</a> </li> <li class="book-pager__item book-pager__item--next"> <h4 class="nav-label">Next</h4> <a href="/health/sickle-cell-disease/symptoms" rel="next" title="Go to next page">Symptoms <i class="fas fa-angle-right"></i></a> </li> 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