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  • Sickle Cell Conditions
Sickle Cell Disease Association of America, Inc. Research and Screening
Research & Screening / Overview / About SCD

About Sickle Cell Disease (SCD)

What is Sickle Cell Disease (SCD)?

Sickle cell disease is an inherited blood disorder that affects red blood cells. People with sickle cell disease have red blood cells that contain mostly hemoglobin* S, an abnormal type of hemoglobin. Sometimes these red blood cells become sickle-shaped (crescent shaped) and have difficulty passing through small blood vessels.

When sickle-shaped cells block small blood vessels, less blood can each that part of the body. Tissue that does not receive a normal blood flow eventually becomes damaged. This is what causes the complications of sickle cell disease. There is currently no universal cure for sickle cell disease.

Hemoglobin is the main substance of the red blood cell. It helps red blood cells carry oxygen from the air in our lungs to all parts of the body. Normal red blood cells contain hemoglobin A. Hemoglobin S and hemoglobin C are abnormal types of hemoglobin. Normal red blood cells are soft and round and can squeeze through tiny blood tubes (vessels). Normally, red blood cells live for about 120 days before new ones replace them.

People with sickle cell conditions make a different form of hemoglobin A called hemoglobin S (S stands for sickle). Red blood cells containing mostly hemoglobin S do not live as long as normal red blood cells (normally about 16 days). They also become stiff, distorted in shape and have difficulty passing through the body's small blood vessels. When sickle-shaped cells block small blood vessels, less blood can reach that part of the body. Tissue that does not receive a normal blood flow eventually becomes damaged. This is what causes the complications of sickle cell disease.

Types of Sickle Cell Disease

There are several types of sickle cell disease. The most common are: Sickle Cell Anemia (SS), Sickle-Hemoglobin C Disease (SC)

Sickle Beta-Plus Thalassemia and Sickle Beta-Zero Thalassemia.

What is Sickle Cell Trait?

Sickle Cell trait (AS) is an inherited condition in which both hemoglobin A and S are produced in the red blood cells, always more A than S. Sickle cell trait is not a type of sickle cell disease. People with sickle cell trait are generally healthy.

Inheritance

Sickle cell conditions are inherited from parents in much the same way as blood type, hair color and texture, eye color and other physical traits. The types of hemoglobin a person makes in the red blood cells depend upon what hemoglobin genes the person inherits from his or her parents. Like most genes, hemoglobin genes are inherited in two sets…one from each parent.

Examples:

  • If one parent has Sickle Cell Anemia and the other is Normal, all of the children will have sickle cell trait.
  • If one parent has Sickle Cell Anemia and the other has Sickle Cell Trait, there is a 50% chance (or 1 out of 2) of having a baby with either sickle cell disease or sickle cell trait with each pregnancy.
  • When both parents have Sickle Cell Trait, they have a 25% chance (1 of 4) of having a baby with sickle cell disease with each pregnancy.

How will I know if I have the Trait?

A SIMPLE BLOOD TEST followed by a laboratory technique called Hemoglobin Electrophoresis will determine the type of hemoglobin you have. When you pass an electric charge through a solution of hemoglobin, distinct hemoglobins move different distances, depending on their composition. This technique differentiates between normal hemoglobin (A), Sickle hemoglobin (S), and other different kinds of hemoglobin (such as C, D, E, etc.).

Medical Problems

Sickle cells are destroyed rapidly in the body of people with the disease causing anemia, jaundice and the formation of gallstones.

The sickle cells also block the flow of blood through vessels resulting in lung tissue damage (acute chest syndrome), pain episodes (arms, legs, chest and abdomen), stroke and priapism (painful prolonged erection). It also causes damage to most organs including the spleen, kidneys and liver. Damage to the spleen makes sickle cell disease patients, especially young children, easily overwhelmed by certain bacterial infections.

Treatment

Health maintenance for patients with sickle cell disease starts with early diagnosis, preferably in the newborn period and includes penicillin prophylaxis, vaccination against pneumococcus bacteria and folic acid supplementation.
Treatment of complications often includes antibiotics, pain management, intravenous fluids, blood transfusion and surgery all backed by psychosocial support. Like all patients with chronic disease patients are best managed in a comprehensive multi-disciplinary program of care.

Blood transfusions help benefit sickle cell disease patients by reducing recurrent pain crises, risk of stroke and other complications. Because red blood cells contain iron, and there is no natural way for the body to eliminate it, patients who receive repeated blood transfusions can accumulate iron in the body until it reaches toxic levels. It is important to remove excess iron from the body, because it can gather in the heart, liver, and other organs and may lead to organ damage. Treatments are available to eliminate iron overload.

Hydroxyurea for treating Sickle Cell Disease

A single randomized trial (MSH) of 299 patients with follow up of 21 months demonstrated that compared to placebo, Hydroxyurea was associated with lower annual rates of pain crises, longer time to first and second pain episodes and need for transfusions and reduce frequency of acute chest syndrome. Droxia, the prescription form of hydroxyurea, was approved by the FDA in 1998 and is now available for adult patients with sickle cell anemia. Hydroxyurea is also used in children.

A complication of blood transfusions is transfusional iron overload. The body does not have a way to get rid of iron received from blood transfusions. An agent that chelates iron is therefore needed to get rid of excess iron in the body. There are two agents. One agent is given intravenously and the other is by mouth. Iron build up is

Transfusional iron overload

Patients with sickle-cell disease (SCD) receiving chronic transfusions of red blood cells are at risk of developing transfusional iron overload over time. Transfusional iron overload is characterized by an increase of labile plasma iron (i.e., non-transferrin bound iron) in the body, which can lead to functional impairment in vital organs. The organs that are at risk of damage due to transfusional iron overload include the liver, heart, pancreas, thyroid, pituitary gland, and other endocrine organs. Buildup of labile plasma iron in these organs can lead to hepatic cirrhosis, cardiomyopathy, diabetes mellitus, hypoparathyroidism, impaired growth, infertility and hypogonadism.

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