SICKLE CELL ANEMIA


DEFINITION

Sickle cell anemia is an inherited blood disorder in which the body produces c-shaped red blood cells. Because of their shape, these cells may stick to each other or to the sides of blood vessels, and cause serious health disorders.

DESCRIPTION

Blood is made up of many kinds of cells, including red blood cells (RBCs). An important function of RBCs is to carry oxygen from the lungs to cells throughout the body. Red blood cells contain a molecule known as hemoglobin (pronounced HEE-muh-GLOW-bihn) that collects oxygen from the lungs then releases it when the RBC reaches other cells in the body.

Normally, red blood cells have a plump doughnut shape. In some cases, however, a person's body makes red blood cells that are curved with sharp points at the end. They are called sickle cells because they look like a sickle (a long farm tool with a curved blade that is used to cut grain).

Hemoglobin Genes

Sickle cell anemia is caused by defective genes. Genes are chemical units found in all cells that tell cells what functions to perform. For example, RBCs contain genes that tell the cell how to make hemoglobin molecules.

When a gene becomes damaged, the message it carries to the cell is incorrect. A damaged gene for hemoglobin tells the cell to make the wrong kind of hemoglobin. This defective hemoglobin creates a sickle shaped RBC rather than the correct doughnut-shaped RBC.

Sickle Cell Anemia: Words to Know

Anemia:
A condition caused by a decrease in the number of red blood cells in the blood, characterized by fatigue, pale color of the skin, and shortness of breath.
Antibiotic:
A substance derived from bacteria or other organisms that fights the growth of other bacteria or organisms.
Bone marrow:
A spongy tissue in the center of bones where blood cells are produced.
Bone marrow transplantation:
A process by which marrow is removed from the bones of a healthy donor and transferred to the bones of a person's with some kind of blood disorder.
Gel electrophoresis:
A laboratory test that separates different types of molecules from each other.
Hemoglobin:
A molecule found in blood that gives blood its red color. Hemoglobin is responsible for transporting oxygen through the blood stream.
Hydroxyurea:
An experimental drug being tested for use with sickle cell anemia patients.
Red blood cell (RBC):
Blood cells that transport oxygen and carbon dioxide through the blood stream.
Sickle cell:
A red blood cell with an abnormal shape due to the presence of an abnormal form of hemoglobin.

Genes are passed from both parents to their children. A person who receives a damaged hemoglobin gene from just one parent will not get sickle cell anemia. People who have only one defective hemoglobin gene are called carriers. Being a carrier of this particular defective gene may actually increase a person's resistance to malaria (see malaria entry), a dangerous infectious disease. However, if a person receives a defective hemoglobin gene from both parents, he or she will develop sickle cell anemia.

Problems Associated with Sickle Cell Anemia

The presence of sickle cells in the blood can cause many health problems. For instance, sickle cells die more rapidly than normal cells. When this happens, the body often cannot produce new blood cells fast enough to replace the dying ones. Such a loss of RBCs can lead to anemia (pronounced uh-NEE-mee-uh; see anemia entry). Anemia is a disorder caused by an insufficient number of red blood cells.

Sickle cells can also cause health problems because of they tend to stick to each other and to the sides of blood vessels. As they clump or build up they can eventually block the flow of blood through a blood vessel. This blockage limits the flow of blood to cells, keeping them from getting the oxygen they need, and can eventually cause the cells to die.

Blockage can also lead to a stroke. If the clump of cells blocking a vessel breaks loose it may travel to the brain. If the clump blocks blood flow

Healthy blood cells have a round, doughnut shape. Sickle cells are longer and narrow with sharp points at the ends. (Photograph by Dr. Gopal Burti, National Audubon Society. Reproduced by permission of Photo Researchers Inc.)
Healthy blood cells have a round, doughnut shape. Sickle cells are longer and narrow with sharp points at the ends. (Photograph by
Dr. Gopal Burti, National Audubon Society
. Reproduced by permission of
Photo Researchers Inc.
)

to the brain it can cause damage to the brain known as a stroke (see stroke entry).

Sickle cell anemia occurs primarily among people with African, Mediterranean, Middle Eastern, and Indian ancestry. Worldwide, about 250,000 children are born each year with sickle cell anemia. About two million Americans are thought to have at least one damaged hemoglobin gene. Approximately 72,000 Americans have two damaged hemoglobin genes and therefore have sickle cell anemia.

In the United States, the condition is most common among African Americans. About 1 in 12 African Americans is a carrier for sickle cell anemia. Hispanic Americans are also heavily affected. About 1 in every 1,000 to 1,400 Hispanic American babies are born with sickle cell anemia.

CAUSES

Sickle cell anemia is caused when a person receives a defective hemoglobin gene from both parents, causing the body to make abnormal red blood cells, which may clump and tend not to live as long as normal red blood cells. A person with sickle cell anemia may become anemic or develop other health problems.

SYMPTOMS

The symptoms of sickle cell anemia usually appear during the first year or two of life. However, some individuals do not develop symptoms until they become adults, and may not be aware for many years that they have the disorder. Some typical symptoms of sickle cell anemia include:

  • Anemia. Anemia is caused by an inadequate number of red blood cells. It can result in fatigue, paleness, shortness of breath, headache, mild fever, and general ill health.
  • Painful crises. Pain can strike the patient in any part of the body without notice. These attacks can occur as rarely as once a year or as often as every few weeks. They can also last for a variable period of time, from a few hours to a few weeks. Pain in the hands and feet are sometimes the earliest symptoms of sickle cell anemia in a child.
  • Enlarged spleen and infections. Sickle-cell blockages can affect any of the body's organs. The organs do not receive the oxygen they need to grow normally. The spleen is especially at risk and may become enlarged or it may die completely. This can weaken the immune system and increase the chance that a patient will develop infections.
  • Delayed growth. Children with sickle cell anemia usually do not grow as fast as other children. They may also reach puberty (sexual maturity) at a later age.
  • Stroke. Blockages of blood vessels in the brain are especially dangerous. The brain may not get the oxygen it needs to function normally. When blockages occur, a person may become numb on one side of the body, may lose vision or the ability to speak, and may experience dizziness. Children between the ages of one and fifteen are at the highest risk for having a stroke due to sickle cell anemia.
  • Acute chest syndrome. Acute chest syndrome is caused by blockage of blood vessels in the lungs. Symptoms of the condition include fever, cough, chest pain, and shortness of breath. The condition can reoccur many times and may cause permanent lung damage.

Other problems caused by blood vessel blockage include kidney damage, enlarged liver, vision problems, and priapism (a condition in which a man experiences repeated and painful erections of the penis not related to sexual arousal; pronounced PREE-uh-piz-um).

DIAGNOSIS

Anemia is easily diagnosed from its symptoms. Once a patient is diagnosed with anemia, a doctor will then try to trace the cause of the disorder. If the person is of African American or other high-risk heritage, sickle cell anemia may be suspected. This diagnosis can be confirmed by at least two laboratory tests. In the first test, a sample of the patient's blood is examined under the microscope where the presence of sickle cells is easy to see.

A doctor can confirm that sickle cells are present with a second test, called gel electrophoresis (pronounced jel ih-LEK-tro-fuh-REE-siss). Gel electrophoresis is a method for distinguishing similar kinds of molecules from each other and will show whether abnormal forms of hemoglobin are present in the blood.

TREATMENT

Sickle cell anemia cannot be cured. However, many of its symptoms can be treated. Its most serious complications can also be prevented. The important factor is to diagnose the disorder as early as possible and begin treatment immediately. Methods used to treat symptoms include:

  • Pain management. Pain is a common problem with sickle cell anemia. Some patients get the relief they need from over-the-counter medication, such as aspirin and acetaminophen. Others need stronger painkillers. Care givers should be careful giving aspirin to children as it has been linked with development of Reye's syndrome (see Reye's syndrome entry).
  • Blood transfusions. Blood transfusions are generally used only in extreme situations, such as severe anemia or especially bad episodes of pain.

Dying tissue on a sickle cell patient's leg. (© 1995 Science Photo Library. Reproduced by permission of Custom Medical Stock Photo.)
Dying tissue on a sickle cell patient's leg. (© 1995
Science Photo Library
. Reproduced by permission of
Custom Medical Stock Photo
.)

  • Drugs. Infants are often treated with antibiotics to prevent infections. (Antibiotics are substances derived from bacteria or other organisms that fight the growth of other bacteria or organisms.) Such treatments may last to the age of six. Research is constantly being conducted to develop drugs for the cure of sickle cell anemia. One promising candidate is hydroxyurea, which seems to reduce pain and acute chest syndrome and can limit the need for blood transfusions in some cases.
  • Bone marrow transplantation. Bone marrow transplantation is used in only the most severe cases of sickle cell anemia. It is based on the fact that new blood cells are made in the marrow of bones. The marrow is soft tissue found in the center of bones. In a bone marrow transplant, marrow is removed from the bones of a healthy donor. It is then injected into the bones of a person with sickle cell anemia. If the procedure is successful, the donor marrow begins making normal, rather than sickle cell, RBCs. Bone marrow transplantation is a very risky procedure with only limited chances of success.

Alternative Treatment

Sickle cell anemia is best treated by conventional medical techniques. However, alternative treatments may help ease some symptoms of the condition. Relaxation techniques, application of warm compresses, and adequate hydration may increase a patient's comfort. Good nutrition, the avoidance of stress, and proper rest may also help prevent some complications of the disorder.

PROGNOSIS

The average life expectancy for men with sickle cell anemia in the United States is forty-two years. For women, it is forty-eight years. The prognosis for any one individual depends on many factors but in general, patients receiving proper medical care may learn to lead relatively normal lives with the disorder.

PREVENTION

Sickle cell anemia is a genetic disorder. There is no prevention for the disease other than genetic screening. Adults can have tests to find out if they carry the gene for sickle cell anemia. If they find they are carriers they can decide whether or not they want to have children. If they decide to have children, there is a known risk that the children may develop sickle cell anemia.

FOR MORE INFORMATION

Books

Bloom, Miriam. Understanding Sickle Cell Disease. Jackson, MS: University Press of Mississippi, 1995.

Beshore, George W., ed. Sickle Cell Anemia. New York: Franklin Watts, Inc., 1994.

Silverstein, Alvin, Virginia Silverstein, and Laura Silverstein Nunn. Sickle Cell Anemia. Hillside, NJ: Enslow Publishers, Inc., 1997.

Organizations

Sickle Cell Disease Association of America. 200 Corporate Point, Suite 495, Culver City, Ca 90230–7633. (310) 216–6363; (800) 421–8453. http://sicklecelldisease.org.

Sickle Cell Disease Program, Division of Blood Diseases and Resources. National Heart, Lung, and Blood Institute. 11 Rockledge Centre, 6701 Rockledge Dr., MSC 7950, Bethesda, MD 20892–7950. (301) 435–0055.