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Sickle Cell Disease

What is 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).

Sickle cell disease involves the red blood cells, or hemoglobin, and their ability to carry oxygen. 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 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 risk being 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 include the following:

Sickle cell trait

The person is carrying the defective gene, HbS, but also has some normal hemoglobin, HbA. This is referred to as HbAS. Persons with sickle cell trait are usually without symptoms of the disease. Mild anemia may occur. Under intense, stressful conditions, exhaustion, hypoxia (low oxygen), and/or severe infection, the sickling of the defective hemoglobin may occur and result in some complications associated with the sickle cell disease.

The person has most or all of the normal hemoglobin (HbA) replaced with the sickle hemoglobin (HbS). This is referred to as HbSS. It is the most common and most severe form of the sickle cell variations. These persons suffer from a variety of complications due to the shape and thickness of the sickled cells. Severe and chronic anemia is also a common characteristic for children with HbSS.

Sickle cell – hemoglobin C disease

The person has both HbS and HbC. This is often referred to as HbSC. Hemoglobin C causes red blood cells, called target cells, to develop. Having just some hemoglobin C and normal hemoglobin, a person will not have any symptoms of anemia. However, if the sickle hemoglobin S is combined with the target cell, some mild to moderate anemia may occur. These persons often suffer some of the complications associated with HbSS, sickle cell disease, but to a milder degree. Vasoocclusive crises (the flow of blood is blocked because the sickled cells have become stuck in the blood vessels), organ damage from repeated sickling and anemia, and high risk for infection are all similar traits for HbSS and HbSC.

Sickle cell – hemoglobin E disease

This variation is similar to sickle cell-C disease except that an element has been replaced in the hemoglobin molecule. This variation is often also seen in Southeast Asia populations. Some persons 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.

emoglobin 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 may also produce exacerbations as severe as those of sickle cell disease.

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

What causes 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 do not get 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 may also 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.

Children with sickle cell disease = S S (one in four, or 25 percent)

Children who are carriers of the gene like their parents = A S S A

(two in four, or 50 percent have sickle cell trait)

Children who do not get the gene from either parent: A A (one in four, or 25 percent)

Once parents have had a child with sickle cell disease, there is a one in four, or 25 percent chance with each subsequent pregnancy, for another child to be born with sickle cell disease. This means that there is a three out of four, or 75 percent chance, for another child to not have sickle cell disease. There is a 50 percent chance that a child will be born with sickle cell trait, like the parents.

Treatment for sickle cell disease:

Specific treatment for

sickle cell disease will be determined by your physician based on:

  • your age, overall health, and medical history
  • extent of the disease
  • your tolerance for specific medications, procedures, or therapies
  • expectations for the course of the disease
  • your opinion or preference