Hemoglobinopathies are diseases caused by the production of abnormal hemoglobin or by a deficiency of hemoglobin synthesis. Hemoglobin is the protein in red blood cells (erythrocytes) that binds to oxygen, to distribute it throughout the body. The major hemoglobinopathies are sickle cell disease and several forms of thalassemia.
In the lungs, where oxygen concentration is high, each hemoglobin molecule can bind with one molecule of oxygen. The erythrocyte containing the hemoglobin then travels through the bloodstream to the body's cells, where oxygen concentration is low, and the hemoglobin releases the oxygen for use by local tissue. It also picks up carbon dioxide, and this waste product is transported back to th…
Hbs (sickling hemoglobin) causes red blood cells to take on a sickle shape under conditions of low oxygen. Each person possesses two copies of the beta globin gene, on separate homologous chromosomes. In most people, the two copies are identical. A person with two identical gene copies is said to be homozygous. In some people, the two beta copies are not identical. These people, who have tw…
Sickle cell disease is the most prevalent genetically based disease in the United States. Approximately 1 in 12 Americans of African descent are carriers, having one allele coding for HbS and one gene for HbA. About 1 in 375 Americans of African descent are homozygous for HbS and have the active disease. High occurrence of the HbS allele also occurs in people who live, or whose ancestors lived, in…
The thalassemias are a group of hemoglobinopathies that, like sickle cell disease, are caused by a genetic change. Unlike sickle cell disease, however, the genetic change does not result in the production of an abnormal form of the globin molecule. Instead, the bone marrow synthesizes insufficient amounts of a hemoglobin chain. This, in turn, reduces the production of red blood cells and causes a…
Being homozygous for either sickle cell disease or thalassemia can result in serious illness, but being heterozygous for either condition may actually be beneficial under certain circumstances. Both diseases occur primarily in people who live, or whose ancestors lived, in parts of the world where malaria occurs. Malaria is spread by a mosquito, but it is caused by plasmodia, single-celled organism…
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