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Sickle beta thalassemia


Other Names for this Disease

  • Hb S beta-thalassemia
  • Hemoglobin sickle-beta thalassemia
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Overview

What is sickle beta thalassemia?

What are the signs and symptoms of sickle beta thalassemia?

What causes sickle beta thalassemia?

Is sickle beta thalassemia inherited?

Is genetic testing available for sickle beta thalassemia?

How is sickle beta thalassemia diagnosed?

What is sickle beta thalassemia?

Sickle beta thalassemia is an inherited condition that affects hemoglobin, the protein in red blood cells that carries oxygen to different parts of the body. It is a type of sickle cell disease. Affected people have a different change (mutation) in each copy of their HBB gene: one that causes red blood cells to form a "sickle" or crescent shape and a second that is associated with beta thalassemia, a blood disorder that reduces the production of hemoglobin. Depending on the beta thalassemia mutation, people may have no normal hemoglobin (called sickle beta zero thalassemia) or make a mix of normal and sickle hemoglobin (called sickle beta plus thalassemia). The presence of sickle-shaped red blood cells, which often breakdown prematurely and can get stuck in blood vessels, combined with reduced or absent mature red blood cells leads to the many signs and symptoms of sickle beta thalassemia. Features, which may include anemia (low levels of red blood cells), repeated infections, and frequent episodes of pain, generally develop in early childhood and vary in severity depending on the amount of normal hemoglobin made. Sickle beta thalassemia is inherited in an autosomal recessive manner. Treatment is supportive and depends on the signs and symptoms present in each person.[1][2][3]
Last updated: 12/21/2014

What are the signs and symptoms of sickle beta thalassemia?

Signs and symptoms of sickle beta thalassemia may include:[4][3]
  • Anemia (low levels of red blood cells)
  • Repeated infections
  • Frequent episodes of pain
  • Pulmonary hypertension
  • Acute chest syndrome (pneumonia-like condition due to entrapment of infection or sickle cells in the lungs)
  • Stroke
  • Enlarged spleen and/or liver
  • Heart murmurs
  • Delayed puberty
  • Slowed growth
  • Jaundice

The symptoms of sickle beta thalassemia vary in severity based on the amount of normal hemoglobin made. Affected people may have no normal hemoglobin (called sickle beta zero thalassemia) or make a mix of normal and sickle hemoglobin (called sickle beta plus thalassemia). Although these two forms share many of the same features, people with sickle beta zero thalassemia are generally more severely affected than those with sickle beta plus thalassemia. For example, people with sickle beta plus thalassemia generally experience less frequent episodes of pain and are less likely to develop stroke, pulmonary hypertension and acute chest syndrome.[4]
Last updated: 12/21/2014

What causes sickle beta thalassemia?

Sickle beta thalassemia is caused by changes (mutations) in the HBB gene, which encodes a component of hemoglobin called "beta globin". Different mutations in HBB impact the production of hemoglobin in various ways. Some mutations lead to sickle hemoglobin, an abnormal form of hemoglobin that causes red blood cells to form a "sickle" or crescent shape. Other mutations reduce the production of beta globin, which leads to low levels of functional hemoglobin and a low number or mature red blood cells (beta thalassemia).[2]

People affected by sickle beta thalassemia have a different mutation in each copy of the HBB gene: one that produces sickle hemoglobin and a second that is associated with beta thalassemia. Depending on the beta thalassemia mutation, people may have no normal hemoglobin (called sickle beta zero thalassemia) or make a mix of normal and sickle hemoglobin (called sickle beta plus thalassemia). The presence of sickle-shaped red blood cells, which often breakdown prematurely and can get stuck in blood vessels, combined with reduced or absent mature red blood cells leads to the many signs and symptoms of sickle beta thalassemia.[2]
Last updated: 12/21/2014

Is sickle beta thalassemia inherited?

Sickle beta thalassemia is inherited in an autosomal recessive manner. This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. People affected by sickle beta thalassemia inherit a different mutation in the HBB gene from each parent: one that produces sickle hemoglobin (called sickle trait) and a second that results in reduced levels of functional hemoglobin (called beta thalassemia).[1] The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition. When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier.
Last updated: 12/21/2014

Is genetic testing available for sickle beta thalassemia?

Yes, genetic testing is available for HBB, the gene known to cause sickle beta thalassemia.[1] Carrier testing for at-risk relatives and prenatal testing are possible if both disease-causing mutations in the family are known.

The Genetic Testing Registry (GTR) is a centralized online resource for information about genetic tests. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
Last updated: 12/21/2014

How is sickle beta thalassemia diagnosed?

In the United States, babies affected by sickle beta thalassemia are often diagnosed at birth through newborn screening. In the absence of newborn screening, a diagnosis is usually suspected in infants or young children with signs and symptoms associated with the condition. Specialized laboratory tests that measure the amounts of abnormal hemoglobin in the blood and/or genetic testing to identify changes (mutations) in the HBB gene can be used to confirm a diagnosis.[1]
Last updated: 12/21/2014

References
  1. MA Bender, MD, PhD and Gabrielle Douthitt Seibel, MN, MPH, ARNP. Sickle Cell Disease. GeneReviews. October 2014; http://www.ncbi.nlm.nih.gov/books/NBK1377/.
  2. Sickle Cell Disease. Genetics Home Reference. August 2012; http://www.ghr.nlm.nih.gov/condition/sickle-cell-disease.
  3. Sickle Cell Disease. NORD. April 2008; https://www.rarediseases.org/rare-disease-information/rare-diseases/byID/25/viewAbstract.
  4. Elliott P Vichinsky, MD. Variant sickle cell syndromes. UpToDate. March 2014;
  5. Joseph E Maakaron, MD. Sickle Cell Anemia. Medscape Reference. September 2014; http://emedicine.medscape.com/article/205926-overview.


Other Names for this Disease
  • Hb S beta-thalassemia
  • Hemoglobin sickle-beta thalassemia
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.