An inherited, autosomal recessive disease that affects approximately 1 out of 400 African Americans. Caused by a mutation in amino acid #6 of the Hemoglobin beta chain from Glutamic acid to Valine. It is surmised that this mutation persisted in the population because the heterozygote state (no symptoms) confers a resistance to malaria. The actual cause of the disease was first discovered by Linus Pauling, a discovery for which he won the Nobel Prizes: Chemistry in 1954. This mutation causes the red blood cells to "sickle" into a crescent shape in conditions of low oxygen or dehydration. These misshapen blood cells can block blood vessels, causing extreme pain, swelling, jaundice, and organ/central nervous system damage. It can also lead to hemolytic crisis, where red blood cells are destroyed, and aplastic crises, where the bone marrow ceases to produce blood cells. There is currently no cure, prenatal screening is recommended for couples at risk.

This disease hasn't dissapeared because the recessive allele that causes it makes carriers more resistant to malaria. Hence, this increases the chance of a carrier surviving even though some of their children will die young from the disease.

If two carriers have children, there is a 1/4 chance the child will be a sufferer, a 1/2 chance they will be a carrier, and a 1/4 chance they will be normal.

Within the red blood cell is a substance called hemoglobin, whose function is to carry oxygen. Hemoglobin has a certain chemical structure known as hemoglobin A. In about 0.3 percent of U.S. African Americans, there is an inherited disease in which an abnormality occurs in the structure of the hemoglobin. This abnormally configured hemoglobin is called hemoglobin S, or sickle hemoglobin.

Two forms of inheritance occur. The abnormal hemoglobin may be present in only one of the parents and the child can only inherit a single gene and its cells will contain only a small proportion of the abnormal pigment, In such cases little harm will result. If both parents carry the gene, however, the child may be homozygous, causing the red blood cells to contain a large amount of the abnormal pigment. Serious illness may then follow.

The presence of large amounts of hemoglobin S in the red blood cells results in a tendency for the red blood cells to become distorted in a crescent shape ("sickle cells") if the level of oxygen in the arterial blood falls. This sickling can be identified by microscopic examination of the blood.

Sickle-cell disease refers to the inheritance of hemoglobin S from both parents with large amounts of sickle hemoglobin in the cells. Even slight degrees of oxygen lack will result in a marked "sickling" change in the blood and consequent obstruction to the circulation in various parts of the body by masses of sickled cells ("sickle-cell crisis"). During a sickle-cell crisis (and, to a lesser extent, at other times as well), the sickle cells are destroyed and liberate hemoglobin into the blood plasma in great quantity---sometimes enough to produce jaundice and to lower the red cell count seriously. Severe pain, dangerous organ damage, and even death may result.

Inheritance of a single dose of hemoglobin S from one parent results in a condition called "sickle-cell trait." Although abnormalities can be noted on careful examination of the blood, usually sickle-cell trait rarely results in symptoms.

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