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Pedigree of Sickle Cell Disease

Sickle cell disease is an inherited disorder common amongst African-Americans. According to the National Center for Biotechnology Information, approximately 1 in 500 African-Americans have sickle cell anemia making it the most common blood disorder here in the United States.

  1. HBB Mutations

    • The cause of sickle cell anemia is mutations in the HBB gene which is responsible for the making of beta-globin. There are different types of HBB mutations that may occur. Mutations may produce hemoglobin S, hemoglobin C, and hemoglobin E. These are all abnormal versions of beta-globin and cause problems in its functioning. HBB mutations cause abnormal beta-globin, but they can also abnormal amounts of beta-globin. Beta thalassemia is a low level of beta-globin caused by HBB mutations.

    Sickle Cell Mutations

    • According to the Genetics Home Resource, sickle cell disease has root in the HBB mutation that causes at least one of the two beta-globin units to be a hemoglobin S. For sickle cell anemia, both beta-globin units are hemoglobin S instead of the normal beta-globin ones which produce normally shaped red blood cells. This difference is what gives the cells in people with sickle anemia their sickle shape. Red blood cells die early when they have the sickly-shape which leads to serious medical problems like the damage of organs.

    Inheritance

    • According to the Genetics Home Resource sickle cell anemia is an inherited autosomal recessive pattern. As such, for someone to develop sickle cell anemia, both parents must carry the gene for it. The parents do not need to have sickle cell anemia because they may only possess one of the genes for it. Remember that to have sickle cell anemia, you must have both genes and therefore get one from each parent. However, having both hemoglobin S genes does guarantee that sickle cell anemia will develop, only that there is potential for it to.

    HBB Mutations and Malaria

    • Areas with high levels of malaria generally have higher rates of HBB mutations because the mutation helps protect against malaria. Because African-Americans trace their origins to Africa, a continent with high levels of malaria; according to National Center for Biotechnology Information, approximately 8 percent of black Americans have the HBB mutation.

      Though all people can trace their genetic ancestry to Africa, mutations for malaria occurred more recently in the human genome. Therefore populations who left Africa before the mutations and do not have the HBB mutations.

    Gene Therapy

    • For those whose HBB mutations become the deadly sickle cell anemia, gene therapy may be an option for treatment. According to the National Human Genome Research Institute, researchers successfully fixed sickle cell disease in experiments with mice. Researchers implanted normal bone marrow into that of the mice. The normal bone marrow, producing normal blood cells, was able to offset the sickle shaped red blood cells in the mice. Once perfected, this method of treatment may be available to human patients.

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