The HBB gene encodes the β-globin chain of hemoglobin, a protein found in red blood cells. Mutations in the this gene result in the production of abnormal hemoglobin and can lead to sickle cell disorders. Hemoglobin S, C and E are abnormal forms of hemoglobin that contribute to the characteristic sickle shape of red blood cells in people suffering from a sickle cell disorder. This test will determine if you have the genetic changes in the HBB gene that result in the production of hemoglobin S, C or E. Sickle cell disease is an autosomal recessive disorder, which means two defective copies of HBB are necessary to inherit the disease. There are different forms and severity of the sickle cell disorder, depending on which HBB mutations have been inherited:
- Hemoglobin SS disease or sickle cell anemia (HbSS) – This is the most common type of sickle cell disease and patients have sickle-shaped red blood cells. These individuals have inherited two defective copies of HBB that each encode for the abnormal hemoglobin S.
- Hemoglobin SC disease (HbSC) – Affected individuals have two defective copies of HBB, where one copy encodes hemoglobin S and the other encodes hemoglobin C. This is the second most common form of sickle cell disease. Symptoms are often (but not always) milder than those experienced by individuals with sickle cell anemia.
- Hemoglobin SE disease (HbSE) – Affected individuals have two defective copies of HBB, where one copy encodes hemoglobin S and the other encodes hemoglobin E. Symptoms are milder than those experienced by individuals with sickle cell anemia.
- Sickle cell trait (HbAS) – A condition where individuals have only one affected copy of HBB that encodes hemoglobin S. The other copy of HBB is normal and encodes for the normal hemoglobin A. These individuals generally do not show symptoms of the disorder.
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