Sickle Cell Disease

Sickle cell disease is an inherited blood disorder characterized by defective hemoglobin (a protein in red blood cells that carries oxygen to the tissues of the body).

Normal hemoglobin cells are smooth, round and flexible, like the letter "O," so they can move through the vessels in our bodies easily. Sickle cell hemoglobin cells are stiff and sticky, and form into the shape of a sickle, or the letter "C," when they lose their oxygen. These sickle cells tend to cluster together and cannot easily move through the blood vessels. The cluster causes a blockage in small arteries or capillaries and stops the movement of healthy, normal oxygen-carrying blood. This blockage is what causes the painful and damaging complications of sickle cell disease.

Sickle cells only live for about 10 to 20 days, while normal hemoglobin can live up to 120 days. Also, sickle cells are destroyed by the spleen because of their shape and stiffness. The spleen is an organ that helps filter the blood of infections, and sickled cells get stuck in this filter and die. Due to the decreased number of hemoglobin cells circulating in the body, a person with sickle cell disease is chronically anemic. The spleen also suffers damage from the sickled cells blocking healthy oxygen carrying cells. Without a normal functioning spleen, these individuals are more at risk for infections. Infants and young children are at risk for life-threatening infections.

The most common variations of the sickle cell gene are:

Sickle cell trait

The child is carrying a single defective gene. Children with sickle cell trait usually are without symptoms of the disease. People with sickle trait are not normally anemic. Under intense stressful conditions, heat exhaustion, hypoxia (low oxygen), sickling of red cells can occur. Most children with the sickle cell trait lead normal lives.

Sickle cell anemia

The child has most or all of the normal hemoglobin replaced with the sickle hemoglobin. It is the most common and most severe form of the sickle cell variations. These children suffer from a variety of complications due to the shape and thickness of the sickled cells. Severe and chronic anemia also is a common characteristic for children with sickle cell anemia.

Sickle cell-hemoglobin SC disease

The child has one copy of both HbS and HbC – the sickle cell (S) with hemoglobin C, another abnormal cell. Hemoglobin C causes red blood cells, called target cells, to develop. A person having just some hemoglobin C and normal hemoglobin will not be anemic. However, if the sickle hemoglobin S is combined with hemoglobin C, mild to moderate anemia occurs. These children often suffer some of the complications associated with sickle cell disease, but to a milder degree.

Sickle cell-hemoglobin E disease

This variation is similar to sickle cell-hemoglobin SC disease except that an element has been replaced in the hemoglobin molecule. This variation is most often also seen in Southeast Asia populations. Some children with hemoglobin E disease are without symptoms. However, under certain conditions, such as exhaustion, hypoxia, severe infection and/or iron deficiency, some mild to moderate anemia may occur.

Hemoglobin S-beta-thalassemia

This involves an inheritance of both the thalassemia and sickle cell genes. The disorder produces symptoms of moderate anemia and many of the same conditions associated with sickle cell disease. While this disorder more often has milder symptoms than sickle cell disease, it also may produce exacerbations as severe as those of sickle cell disease.

All forms of sickle cell disease can exhibit the complications associated with the disease.

Sickle cell disease primarily affects those of African descent and Hispanics of Caribbean ancestry, but the trait also has been found in those with Middle Eastern, Indian, Latin American, American Indian and Mediterranean heritage.

It has been estimated that more than 70,000 people in the U.S. are affected by sickle cell anemia and that 2 million people, and 10 percent of African-Americans, have sickle cell trait. Millions worldwide suffer complications from sickle cell disease.

Sickle cell is an inherited disease caused by a genetic mutation. Genes are found on structures in the cells of our body called chromosomes. There are normally 46 total, or 23 pairs, of chromosomes in each cell of our body. The 11th pair of chromosomes contains a gene responsible for normal hemoglobin production.

A mutation or error in this gene is what causes sickle cell disease. This mutation is thought to have originated in areas of the world where malaria was common, since people with sickle trait tolerate malaria better and have a reproductive advantage in areas with malaria. The sickle trait actually protects them from the parasite that causes malaria, which is carried by mosquitoes. Malaria is most often seen in Africa and in the Mediterranean area of Europe.

Sickle cell (HbSS) is a genetic disease. A person will be born with sickle cell disease only if two HbS genes are inherited – one from the mother and one from the father. A person who has only one HbS gene is healthy and said to be a "carrier" of the disease. They also may be described as having "sickle cell trait." A carrier has an increased chance to have a child with sickle cell disease. This type of inheritance is called autosomal recessive.

Autosomal means that the gene is on one of the first 22 pairs of chromosomes that do not determine gender, so that males and females are equally affected by the disease.

Recessive means that two copies of the gene, one inherited from each parent, are necessary to have the condition.