Sickle cell disease is the name of a group of inherited blood disorders that is characterized by chronic anemia, periodic episodes of pain and other complications.
The disease affects the red blood cells. Sickle cell disease results when red blood cells make mostly hemoglobin S instead of the normal hemoglobin A. Normal red blood cells are smooth, round and soft; their shape and softness enable them to move easily through the blood vessels to carry oxygen to all parts of the body.
In sickle cell disease, the abnormal hemoglobin S causes the red blood cells to become hard, pointed and sticky and shaped like crescents or sickles. When these hard and pointed red cells go through the small blood vessels, they often get stuck and block the vessels. They also stick to and damage the lining of larger blood vessels. The damaged vessels become scarred, narrowed and sometimes completely closed. The blockage of blood flow through blood vessels can lead to pain, stroke and damage to many organs.
Sickle cells also break up too easily and survive for only 10 to 20 days compared to 120 days for normal red blood cells. The rapid destruction of sickle cells leads to anemia — a shortage of red blood cells and hemoglobin. It becomes difficult for the body to make new red blood cells fast enough to keep up with the needed supply.
Sickle cell disease affects millions of people throughout the world. It is common in people whose origins are:
People with sickle cell conditions predominantly live in countries in Africa, the Americas (North, Central and South), the Caribbean region, Mediterranean region, the Middle East, India and Western Europe.
In the United States, sickle cell disease affects:
About 3 million Americans carry the sickle cell "trait" (which means they don't have the disease themselves but could potentially pass it on to their children). About 1 in 12 African-Americans has the sickle cell trait.
There are several tests suitable for determining what type of hemoglobin is made by a person's red blood cells. These include:
These tests can determine whether a person has a type of sickle cell disease or sickle cell trait.
DNA analysis is used to determine changes in the genes for making hemoglobin. This test indirectly predicts the type of hemoglobin made in the red cells.
Tests that are not suitable for determining sickle cell disease or sickle cell trait include:
A "positive" result from these tests simply indicates the presence of hemoglobin S in a person's blood; this occurs in both sickle cell trait and all types of sickle cell disease.
Other tests that are not useful by themselves for diagnosing sickle cell conditions include:
Sickle cell conditions are inherited. People who make hemoglobin S in their red blood cells have inherited the sickle cell gene from one or both parents. Children who inherit the sickle cell gene from both parents will have sickle cell disease (SS). The sickle cell gene tells the body to make a variant (different from normal) hemoglobin. Children who inherit the sickle cell gene (S) from one parent and another abnormal hemoglobin gene from the other parent may have different types of sickle cell disease.
There are four common types of sickle cell disease: SS, SC, S/beta-plus thalassemia, and S/beta-zero thalassemia. A person who is SS has inherited a double dose of the sickle cell gene (S), one from each parent. People with any other type of sickle cell disease have inherited the S gene from one parent and another abnormal hemoglobin gene from the other parent.
Children who inherit the sickle cell (S) gene from only one parent and the normal genes for hemoglobin A from the other parent will not have the disease, but will have the sickle cell trait (AS). People with AS generally have no symptoms of the disease and lead normal lives, but can pass the gene on to their children.
When two people with the sickle cell trait have a baby, they can have a child with normal hemoglobins (AA), sickle cell trait (AS), or the SS type of sickle cell disease. These possibilities exist with each pregnancy.
Anemia is the most common feature of sickle cell disease. Anemia may cause fatigue, paleness, yellowing of the skin and eyes (jaundice), or shortness of breath.
Pain is the most common symptom of sickle cell disease. Some people have few or no severe pain episodes a year while others have 15 or more. Pain may last a few hours to a few days, and, in some cases, it can last for weeks. Some people have chronic, almost daily pain.
The pain occurs in organs or joints and results from tissue damage caused when sickle cells block blood flow. Mild pain episodes may be treated with over-the-counter pain medications such as acetaminophen and ibuprofen. Pain that is severe may require treatment in the hospital with strong pain medicines given intravenously (into a vein).
Complications of sickle cell disease may be acute or or chronic. Acute complications include:
Sickle cell conditions can be accurately diagnosed at any age. However, the newborn period is the best time. Newborn diagnosis enables healthcare providers to start preventive treatment (penicillin prophylaxis) and family health education before the start of symptoms.
Forty-nine U.S. states, the District of Columbia, Puerto Rico and the Virgin Islands currently screen all newborns for sickle cell disease through blood tests. These tests use blood from the same samples taken for other routine newborn screening tests and can determine if the child has the disease itself or only the trait. It is also possible to identify sickle cell disease before birth by getting a sample of amniotic fluid or tissue taken from the placenta; this test can be done as early as the first few months of pregnancy.
The goals of treatment are to prevent infections, relieve pain, and prevent or control complications. Infections are the leading cause of death in sickle cell disease. Pain attacks are the leading cause of emergency room visits and hospitalizations.
Because infections may lead to death, special measures are taken to prevent or reduce the severity of infections. This includes twice-daily penicillin for children for at least the first five years of life, special vaccines, and aggressive evaluation and treatment when patients develop fever or other signs of infection.
Vaccinations against certain dangerous bacteria (pneumococcus, haemophilus influenza type B, and meningococcus) and viruses (hepatitis B and influenza) are especially important for people with sickle cell disease. For more information about what vaccinations your child needs, visit The Children's Hospital of Philadelphia Vaccine Education Center.
Blood transfusions are used to treat some acute complications and to prevent the occurrence or recurrence of other complications. Children who have had a stroke or are at high risk for initial stroke are given blood transfusions on a regular and long-term basis to prevent stroke.
Pain is most often treated with acetaminophen, nonsteroidal anti-inflammatory drugs (also known as NSAIDs) and opioids, which are the strongest pain medications and include substances such as morphine, oxycodone and hydrocodone.
Important health maintenance measures in sickle cell disease include:
Up to age 2, children with sickle cell disease should see a doctor every two or three months. After age 2, visits should be at least every six months.
Researchers are investigating new medications, bone marrow transplants and gene therapy to treat — and hopefully to one day cure — sickle cell disease. Fortunately, a child may live a full, productive life with the disease, as doctors know a great deal about the disease and how to manage it.
Reviewed by: Kwaku Ohene-Frempong, MD
Date: September 2006