Sickle cell anemia is and autosomal dominant anemia characterized by crescent- or sickle-shaped erythrocytes and by accelerated hemolysis, due to substitution of a single amino acid (valine for glutamic acid) in the sixth position of the beta chain of hemoglobin; affected homozygotes have 85–95% Hb S and severe anemia, while heterozygotes (said to have sickle cell trait) have 40–45% Hb S, the rest being normal Hb A; low oxygen tension causes polymerization of the abnormal beta chains, thus distorting the shape of the red blood cells to the sickle form. Homozygotes develop “crises”; episodes of severe pain due to micro vascular occlusions, bone infarcts, leg ulcers, and atrophy of the spleen associated with increased susceptibility to bacterial infections, especially streptococcal pneumonia. Occurs almost exclusively in blacks. Syn: crescent cell anemia, sickle cell disease, drepanocytic anemia.

click on the figure below to see how a smear of the a blood sample from a sickle cell patient looks like.

when a blood smear of a sickle cell patient is viewed under a microscope, as in the picture by the left, you would notice that most of the cells are elongated and sickled in shape.

This results to low oxygen tensions on the sickle cells themselves and this is what causes the anemia. click on this link t

see  an animation on how a normal red blood cell is turned into a sickle cell. sickle cell animation

CAUSE

The presence of two defective genes (SS) is needed for sickle cell anemia. If each parent carries one sickle hemoglobin gene (S) and one normal gene (A), with each pregnancy, there is a 25 percent chance of the child's inheriting two defective genes and having sickle cell anemia; a 25 percent chance of inheriting two normal genes and not having the disease; and a 5 0 percent chance of being an unaffected carrier like the parents. 

EPIDEMOLOGY 

Sickle cell anemia affects millions of people throughout the world. It is particularly common among people whose ancestors come from sub- Saharan Africa; Spanish speaking regions (South America, Cuba, Central America); Saudi Arabia; India; and Mediterranean countries, such as Turkey, Greece, and Italy.

In this country, it affects approximately 72,000 people, most of whose ancestors, come from Africa. The disease occurs in approximately 1 in every 500 African-American births and 1 in every 1,000-1,400 Hispanic American births. 

Approximately 2 million Americans, or 1 in 12 African Americans, carry the sickle cell trait. 

The clinical course of sickle cell anemia does not follow a single pattern; some patients have, mild symptoms, and some ha ve very severe symptoms. However, the basic problem is the same - the sickle-shaped red blood cells tend to get stuck in narrow blood vessels, blocking the flow of blood. 

CLINICAL SYMPTOMS 

This results in the following conditions: 

Hand-foot syndrome. When the small blood vessels in the hands or feet are blocked, pain and swelling can result, along with fever. This may be the first symptom of sickle cell anemia in infants. 

Fatigue, paleness, and shortness of breath are all symptoms of anemia, or a shortage of red blood cells. 

Pain that occurs unpredictably in any body organ or joint, wherever the sickled blood cells block oxygen flow to the tissues. The frequency and amount of pain varies. Some patients have painful episodes (also called crises) less than once a year, and some have as many as 15 or even more episodes in a year. Sometimes the pain lasts only a few hours; sometimes it lasts several weeks. For especially severe, ongoing pain, the patient may have to be hospitalized and treated with painkillers and intra-venous fluids. Pain is the principal symptom of sickle cell anemia in both children and adults. 

Eye problems. When the retina, the "film" at the back of the eye that receives and processes visual images, does not get enough nourishment from circulating red blood cells, it can deteriorate. Damage to the retina can be serious enough to cause blindness. 

Yellowing of the skin and eyes. These are signs of jaundice, resulting from the rapid breakdown of red blood cells. 

Delayed growth and puberty in children and often a slight build in adults. The slow rate of growth is caused by a shortage of red blood cells. 

Infections. In general, both children and adults with sickle cell anemia are more vulnerable to infections and have a harder time fighting them off once they start. This is the result of damage to the spleen from the sickled red cells which prevents the spleen from destroying bacteria in the blood. Infants and young children, especially, are susceptible to bacteria[ infections that can kill them in as little as 9 hours from onset of fever. Pneumococcal infections used to be the principal cause of death in young children with sickle cell anemia until physicians began routinely giving penicillin on a preventive basis to infants who are identified at birth or in early infancy as having sickle cell anemia. 

Stroke. The defective hemoglobin damages the walls of the red blood cells, causing them to stick to blood vessel walls. This can result in the development of narrowed, or blocked, small blood vessels in the brain, causing a serious, lifethreatening stroke. This type of stroke occurs primarily in children. 

Acute chest syndrome - a lifethreatening complication of sickle cell anemia, similar to pneumonia, that is caused by infection or trapped sickled cells in the lung. This is characterized by chest pain, fever, and an abnormal chest x-ray. 

MANAGEMENT

Although there is no cure for sickle cell anemia, doctors can do a great deal to help sickle cell patients, and treatment is constantly being improved.

Basic treatment of painful crises relies heavily on pain-killing drugs and oral and intravenous fluids to reduce pain and prevent complications.

Blood transfusions are used to treat and to prevent some of the complications of sickle cell ane- mia. Transfusions correct anemia by increasing the number of nor- mal red blood cells in circulation. Transfusions are used to treat spleen enlargement in children before the condition becomes life- threatening. Regular transfusion therapy also can help prevent recurring strokes in children at high risk of crippling nervous system complications.

Giving young children with sickle cell anemia oral penicillin twice a day, beginning when the child is about 2 months old and continuing until the child is at least 5 years old, can prevent pneumococcal infection and early death in these children. Recently, however, several new strains of pneumonia bacteria that are resistant to penicillin have been reported. Since the vaccines for these bacteria are ineffective in young children, studies are being planned to test new vaccines.

The first effective drug treatment for adults with severe sickle cell anemia was reported in early 1995, when a study conducted by the National Heart, Lung, and Blood Institute showed that daily doses of the anticancer drug hydroxyurea reduced the frequency of painful crises and of acute chest syndrome in these patients. Patients taking the drug also needed fewer blood transfusions.

The long-term side effects of hydroxyurea and its effects in children with sickle cell anemia are still being studied.

Sickle cell anemia patients with severe chest or back pain that prevents them from breathing deeply may be able to avoid potentially serious lung complications associated with acute chest syndrome by using an incentive spirometer. This is a small plastic device, shaped like a tube, with a ball inside. The patient must breathe into it hard enough to force the ball up the tube, so using it helps the patient breathe more deeply.

Most complications of sickle cell anemia are treated as they occur. For example, laser coagulation and other types of eye surgery may be used to prevent further vision loss in patients with eye problems. Surgery may be recommended for cert ain kinds of organ damage for example, to remove gallstones or replace a hip joint. Leg ulcers may be treated with cleansing solutions and zinc oxide, or with skin grafts if the condition persists.

Regular health maintenance is critical for people with sickle cell anemia. Proper nutrition, good hygiene, bed rest, protection against infections, and avoidance of other stresses all are important in maintaining good health and preventing complications. Regular visits to a physician or clinic that provides comprehensive care are necessary to identify early changes in the patient's health and ensure that the person receives immediate treatment.

Today, with good health care, many people with sickle cell anemia are in reasonably good health much of the time and living productive lives. In fact, in the past 30 years, the life expectancy of people with sickle cell anemia has increased. Many patients with sickle cell anemia now live into their mid-fortles and beyond. 

GENETIC COUNSELING

People who are planning to become parents should know whether they are carriers of the sickle cell gene, and, if they are, they may want to seek genetic counseling. The counselor can tell prospective parents what the chances are that their child will have sickle cell trait or sickle cell anemia. Accurate diagnostic tests and information are available from health departments, neighborhood health centers, medical centers and clinics that care for Individuals with sickle cell anemia.