An inherited blood disorder in which red blood cells become sickle-shaped
- Present from birth; first symptoms appear after about 6 months
- Due to an abnormal gene inherited from both parents; mainly affects black people
- Strenuous exercise and high altitudes may trigger symptoms
- Gender is not a significant factor
Sickle-cell disease is the result of an abnormality of haemoglobin, the pigment within red blood cells that binds to oxygen in the lungs and carries it to body tissues. When the amount of oxygen that is bound to the abnormal haemoglobin is reduced, the red blood cells become distorted into an elongated sickle shape. Because these sickle-shaped cells are rigid, they can become lodged in small blood vessels and obstruct the flow of blood, depriving the tissues of oxygen. Sickle-shaped red cells are fragile and may be destroyed prematurely, which can lead to anaemia.
Sickle-cell disease occurs most commonly in people of African descent, and the condition is less common among people from Mediterranean countries.
What are the causes?
Sickle-cell disease is a genetic disorder in which an abnormal gene is inherited from both parents in an autosomal recessive manner (see Gene disorders). If an abnormal gene is inherited from only one parent, a condition called sickle-cell trait results. Sickle-cell trait does not usually produce symptoms or require treatment. Having one abnormal gene (sickle cell trait) confers a small degree of protection against malaria but having two abnormal genes (sickle-cell disease) does not. In communities in which sickle-cell disease is particularly common, genetic testing may be recommended for couples planning to have children. If both partners are found to carry the sickle-cell gene, genetic counselling will be offered.
What are the symptoms?
The symptoms of sickle-cell disease are highly variable, even among affected individuals in the same family. In children, the symptoms first appear from about 6 months of age and may include intermittent painful swelling of the fingers and toes and delayed growth.
Distinct episodes of illness, known as sickle-cell crises, occur intermittently throughout childhood and into adult life. These crises may be precipitated by infections, but they can also occur after strenuous exercise, on exposure to cold, or at high altitude. Sickle-cell crises can produce different groups of symptoms, which may include:
Pallor, tiredness, and faintness due to severe anaemia.
Severe pain and swelling around a bone or joint.
Breathlessness and chest pain.
Blood in the urine.
Sickle-cell crises usually require urgent admission to hospital for treatment, and they can be life-threatening.
Are there complications?
People who have sickle-cell disease are more susceptible to serious infections, such as pneumococcal infection (see Pneumonia), and any infection can trigger a sickle-cell crisis. Gallstones may develop. The abnormal cells can cause problems by blocking and damaging small blood vessels throughout the body, which may lead to kidney damage (see Chronic kidney failure). The risk of transient ischaemic attacks and stroke is also increased. Women with sickle-cell disease may have decreased fertility, and those who become pregnant face an increased risk of miscarriage.
What might be done?
To confirm the diagnosis, your doctor may take a sample of blood to look for sickle-shaped cells under a microscope and to test for defective haemoglobin.
If sickle-cell disease is mild, folic acid (see Vitamins), which is necessary for the production of red blood cells, may be prescribed. If the disease is more severe, you may require long-term drug treatment with hydroxyurea, which reduces the proportion of abnormal red cells in the blood. You may also need to take a preventive antibiotic continually and to be vaccinated against pneumococcal infection.
Immediate hospital admission is usually necessary for sickle-cell crises. You may be given intravenous fluids to treat dehydration, antibiotics for underlying infections, and painkillers. People who have recurrent sickle-cell crises may be given exchange transfusions, in which some of their blood is replaced with blood from a healthy donor. In some cases, a stem cell transplant may be considered.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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