Sickle cell FAQs

Sickle cell disease is the name for an inherited group of  blood disorders, characterized primarily by chronic anemia and periodic episodes of pain. The underlying problem involves hemoglobin, a component of red blood cells. The hemoglobin molecules in red blood cells carry oxygen from the lungs to the body organs and tissues. Unlike normal red blood cells, which last about 120 days in the bloodstream, sickled red cells die after only 10 to 20 days. Because they cannot be replaced fast enough, the blood is chronically short of red blood cells, a condition called anemia. The sickled red cells also can block the blood flow to parts of the body ("vaso-occlusion"), and this causes pain and damage to organs.

What causes sickle cell anemia?

In sickle cell anemia, the most common form of sickle cell disease, both hemoglobin genes are defective. The defective genes tell the body to make the abnormal hemoglobin, called sickle hemoglobin (or hemoglobin S). After the hemoglobin molecules give up their oxygen in the tissues and organs of the body, some of them may cluster together and form long, rod-like structures. These structures cause the red blood cells to become stiff and to assume a sickled shape. Unlike normal red cells, which are usually smooth and donut-shaped, the sickled red cells cannot squeeze through small blood vessels. Instead, they stack up and cause blockages that deprive the organs and tissue of oxygen-carrying blood. This process produces the periodic episodes of pain and ultimately can damage the tissues and vital organs and lead to other serious medical problems.

Children who inherit copies of the defective sickle hemoglobin gene from both parents will have sickle cell anemia. Children who inherit the defective sickle hemoglobin gene from only one parent will not have the disease, but will carry the sickle cell trait. Individuals with sickle cell trait generally have no symptoms, but they can pass the sickle hemoglobin gene on to their children.

What is the origin of sickle cell disease?

The error in the hemoglobin gene results from a genetic mutation that occurred many thousands of years ago in people in parts of Africa, the Mediterranean basin, the Middle East and India. Malaria was very common at that time and the epidemic caused the death of great numbers of people. Studies show that in areas where malaria was a problem, children who inherited one sickle hemoglobin gene and carried the sickle cell trait (but not sickle cell disease) were more likely to survive infection with malaria. So, unlike the children who had normal hemoglobin genes, children with the trait better survived the malaria epidemics, grew up, had their own children, and passed on the gene for sickle hemoglobin. As a result of migration, the slave trade and new mutations, the sickle cell mutation spread to other Mediterranean areas, the Middle East and the Western Hemisphere. In the United States and other countries where malaria is not a problem, the sickle hemoglobin gene no longer provides a survival advantage. Instead, it is a threat to the children of people who carry the trait. Children who inherit two abnormal sickle hemoglobin genes (one from the mother and one from the father) have sickle cell anemia.

When was sickle cell disease discovered?

Sickle cell disease has probably been recognized for centuries in African tribal medicine. However, sickle cell disease was first recognized in Western medicine in 1910 by Dr. B. Herrick when he wrote a report about a patient who suffered from a "strange disease" that included such symptoms as pain, asthmatic conditions, and blood flow problems including body ulcers. This observation eventually led to the identification of the sickle cell hemoglobin (HbS) in the 1940s by Linus Pauling. In 1952, Pauling hypothesized on the nature of HbS and its role in sickle cell anemia by saying that the HbS proteins may act differently from regular hemoglobin (HbA) and stack together. Pauling also stated that sickling of the cells in sickle cell anemia might be due to the formation of "rods" by the hemoglobin and thus "sickle" the cell. From these hypotheses and experiments a physical understanding of sickle cell disease was formed. The physical mapping of the hemoglobin gene and protein allowed it to be one of the first human diseases to be characterized genetically. Even with these physical and genetic clues that have been known for decades, treatments (and cures) for sickle cell anemia have advanced slowly.

How common is sickle cell disease?

Sickle cell disease 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 70,000 to 100,000 people, most with ancestors from Africa. The disease occurs in 1 in every 500 African-American births and 1 in every 1,000 to 1,400 Hispanic-American births. Approximately 2 million Americans carry the sickle cell trait.

What are the signs and symptoms of sickle cell disease?

The clinical course of sickle cell disease does not follow a single pattern. Some patients have mild symptoms, and some have very severe problems. However the basic problem is the same: the sickle-shaped red blood cells don’t live very long, causing anemia, and they tend to get stuck in narrow blood vessels, blocking the flow of blood and causing pain.

Most individuals with sickle cell disease are generally well from day-to-day. But complications of the disease can develop, often unpredictable. Some of the problems and conditions caused by sickle cell anemia include:

  • Fatigue, pallor ("paleness"), and decreased endurance, which are 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.
  • Yellowing of the skin and eyes (jaundice), which results from the rapid breakdown of red blood cells.
  • Bacterial infections ---- in general, both children and adults with sickle cell anemia are more vulnerable to infections and have a harder time fighting off infection once it starts. This is a result of damage to the spleen from the sickled red cells.  The spleen which normally filters the blood, when clogged with sickled cells, is prevented from destroying bacteria in the blood. Infants and young children especially are susceptible to bacterial infections that can be fatal.
  • The spleen can enlarge suddenly due to the entrapment of blood. This is called acute splenic sequestration, and it can cause severe and sometimes life-threatening anemia.
  • Acute chest syndrome is a life-threatening 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.
  • Delayed growth and puberty in children and often a slight build in adults.
  • A stroke may occur when sickled red blood cells get trapped in the blood vessels of the brain. This causes a part of the brain to die (a stroke). This type of stroke occurs primarily in children.
  • Sickle cell can damage to the retina (a part of the eye), especially in older children and adult, that can be serious enough to cause blindness.

How is sickle cell disease diagnosed?

A simple blood test can determine if an individual carries at least one defective hemoglobin (S) gene. Early diagnosis of sickle cell anemia is critical so children who have the disease can receive proper treatment. Currently all 50 states have newborn screening programs. Texas initiated newborn screening in 1983, and sickle cell disease is one of the diseases that infants are screened for prior to leaving the hospital. However, most newborn screening programs are not funded to notify individuals who have sickle cell trait. If you were born in Texas prior to 1983, you should be tested for sickle cell trait. If both parents know they are carriers, they can seek genetic counseling to help them better understand sickle cell disease and how it may impact children they conceive.

How is sickle cell disease inherited?

If both parents have sickle cell trait (AS), then each of their children has a 25% chance of having normal hemoglobin (AA), a 50% chance of having trait (AS), and a 25% chance of having have sickle cell anemia (SS). Other forms of sickle cell disease can occur in children if only one of their parents has sickle trait and the other has thalassemia trait of hemoglobin C trait.

How is sickle cell disease treated?

Most individuals with sickle cell disease are generally well from day-to-day. However, babies and young children with sickle cell disease should take oral penicillin twice a day, beginning as soon as sickle cell anemia is diagnosed and continuing until at least 5 years of age. This penicillin can prevent fatal pneumococcal infection. If complications of the sickle cell disease occur, patients are treated and supported until they get better. For example, painful episodes are treated with pain medications and fluids. Blood transfusions are used to treat some of the complications of sickle cell disease. Transfusions correct anemia by increasing the number of normal red blood cells in circulation.

Problems from sickle cell disease can also be prevented.  For example, regular (monthly) blood transfusions can prevent strokes in children as well as prevent pain and other complications of the disease.. The medicine hydroxyurea can also lower the frequency of painful episodes and of acute chest syndrome. Patients taking this drug also needed fewer blood transfusions.

Stem cell (bone marrow) transplantation can cure children with sickle cell disease. However, this procedure is not without risk, and the transplant is safest when, the bone marrow comes from a healthy sibling donor (a brother or sister with the same mother and father) with the same tissue or bone marrow type. Only about 18 percent of children with sickle cell anemia are likely to have a matched sibling donor.

Need more information?

For more information, contact the Southwestern Comprehensive Sickle Cell Center at 214-456-5878 or email us at sicklecell@utsouthwestern.edu.

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