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sickle cell trait
Sickle cell anaemia is an inherited blood disease. It causes serious health problems among African Americans or individuals of African descent and is not commonly seen in Australia. To develop sickle cell anaemia, a person must inherit two sickle cell genes. When only one gene is present, a person has another form of sickle cell disease known as sickle cell trait in which they will not get the full blown disease.
What is going on in the body?
Haemoglobin is the key molecule in the blood that carries oxygen to all parts of the body. A change in a certain gene causes a change in the structure of haemoglobin. Persons with normal haemoglobin have a genetic coding of AA. Persons with sickle cell trait have a genetic coding of AS. (The "S" refers to the sickle cell gene.)
Eight percent of African Americans are carriers of the sickle cell gene, and are said to have sickle cell trait. Most people with sickle cell trait are completely healthy and lead normal lives. Persons with the genetic coding SS have a double dose of the abnormal haemoglobin gene. They develop sickle cell anaemia. It affects approximately 15 out of every 1000 African Americans.
In sickle cell anaemia the red blood cells change shape from a rounded disc to a crescent or "sickle" shape. These abnormal red blood cells are more rigid and are more likely to clump together. They are also more likely to stick to the walls of blood vessels. They can even block the blood vessels themselves. These changes also mean that the haemoglobin molecule isn't able to carry oxygen as well as it should.
What are the signs and symptoms of the disease?
Persons with sickle cell anaemia have many symptoms. They often have problems in growth and development. Individuals may have pain in the joints and chest pain that is worse when they take a deep breath. Sickle cell anaemia causes repeated bouts of severe pain. These are called "painful crises" or "thrombotic crises." These attacks of pain are sudden, severe, and affect many areas of the body. The most common areas are the arms, legs, abdomen, chest, and back. The pain can last hours to several days or even weeks. During these painful crises there may be a high fever. The person may require hospitalisation. There is no specific cure for the episodes.
The signs of sickle cell anaemia can include:
What are the causes and risks of the disease?
- joint swelling
- enlargement of the spleen (early in the disease)
- a heart murmur, enlargement of the heart
- a decrease in vision
- leg ulcers
Sickle cell anaemia is caused by a change in a gene that changes the structure of the haemoglobin molecule.
Sickle cell anaemia is a long-term disease that causes a number of health risks. Individuals have a severe anaemia that puts extra strain on the heart, which can lead to heart enlargement. These individuals have a reduced life expectancy. They are at increased risk of the following:
Pregnant women with sickle cell anaemia are likely to have kidney infections, bleeding, premature infants, and foetal death.
- blood clots in the legs or lungs
- kidney failure
What can be done to prevent the disease?
For an individual with the SS genetic coding for haemoglobin, there is no effective prevention of sickle cell anaemia. However, individuals with sickle cell trait (AS coding) can benefit from genetic counselling. If two parents are both carriers of the sickle cell trait, they have a 25% chance of having a child with sickle cell anaemia.
How is the disease diagnosed?
The disease is diagnosed through a combination of medical history, physical examination, and laboratory testing. A vital laboratory test is the peripheral blood smear. This test will show the characteristic sickle shape of some red blood cells. There is usually a very low red blood cell count. This is due to the breakdown of the red blood cells. White blood cells counts are often higher than normal. Liver function tests may be abnormal. A specialised test called haemoglobin electrophoresis will confirm the diagnosis. X-rays may show abnormal changes in bone, especially of the spine and hip.
What are the long-term effects of the disease?
Many individuals with sickle cell anaemia develop serious, long-term medical problems. These include:
The repeated episodes of severe pain often reduce the quality of daily life. Narcotic pain relievers are often used to treat these painful crises. This can lead to a risk of becoming dependent on these drugs.
- severe anaemia , which is a shortage of red blood cells
- decrease in kidney function
- heart attacks
- brain haemorrhages
- leg ulcers that are difficult to heal
What are the risks to others?
Sickle cell anaemia is passed from parent to child. It is not contagious.
What are the treatments for the disease?
Sickle cell anaemia is a lifelong chronic disease. There is no cure. Because sickle cell anaemia causes so many health problems, persons with the disease need to establish a good relationship with a doctor.
Some treatments for sickle cell anaemia help to prevent other complications.
What are the side effects of the treatments?
- The pneumococcal vaccine helps prevent serious infections by the pneumococcus bacterium.
- Preventive antibiotics before a dental procedure are recommended.
- For persons who live where malaria is present, preventive medication is recommended.
- A daily folic acid supplement is recommended to prevent a deficiency of this nutrient.
- An annual eye examination by an eye doctor can detect eye problems early.
- Because of the increased risk of infection, it is necessary to have any fever, chills, or other signs of infection checked out by a doctor promptly. Infections are treated with antibiotics.
- Fluids are needed to prevent or correct dehydration.
- Individuals can develop blood in the urine, called haematuria, that lasts days to weeks. Plenty of fluid is essential to maintain urine flow and to prevent blood clots. If blood clots form in the legs or lungs, blood thinners, or anticoagulants, are used.
- Some men develop priapism, a painful and prolonged erection of the penis. Repeated episodes can lead to impotence, which can be helped with a penile prosthesis.
General supportive care, such as pain control and fluids, has no specific side effects.
What happens after treatment for the disease?
- Blood thinners used to treat blood clots can cause excessive bleeding.
- Antibiotics used to treat infection may also have side effects. These include rashes, gastrointestinal symptoms, and even anaphylaxis, a life-threatening allergic reaction.
- Chronic use of narcotics to relieve pain can sometimes lead to dependence and addiction.
After treatment of a specific problem, such as a painful crisis or an infection, the person may have periods of time with few symptoms.
How is the disease monitored?
There is no specific test for monitoring sickle cell anaemia. A person's symptoms and certain laboratory tests are the best ways to monitor the disease.
Author: Minot Cleveland, MD
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 21/09/2004
Potential conflict of interest information for reviewers available on request
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