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Systemic Lupus Erythematosus (SLE) is an autoimmune disease that can affect many parts of the body. It is most common in women between the ages of 15 and 44.
SLE is often mistaken for other diseases. For this reason, it has been called the "great imitator". The signs of SLE differ from person to person. Some people have just a few signs; others have more.
Common signs of SLE are:
Other signs are mouth sores, unexplained seizures (convulsions), hallucinations, repeated miscarriages, and unexplained kidney problems.
The onset of lupus may be acute, resembling an infectious process, or it may be a progression of vague symptoms over several years. As a result, diagnosing SLE is often a challenge. A consistent, thorough medical examination by a doctor familiar with lupus is essential to an accurate diagnosis.
No single test can determine whether a person has lupus, but several laboratory tests may help the doctor to make a diagnosis. The most useful tests identify certain autoantibodies often present in the blood of people with lupus. For example, the antinuclear antibody (ANA) test is commonly used to look for autoantibodies that react against components of the nucleus of the body’s cells. Most people with lupus test positive for ANA; however, there are a number of other causes of a positive ANA besides lupus, including infections, other autoimmune diseases, and occasionally as a finding in healthy people. The ANA test simply provides another clue for the doctor to consider in making a diagnosis. In addition, there are blood tests for individual types of autoantibodies that are more specific to people with lupus, although not all people with lupus test positive for these and not all people with these antibodies have lupus. These antibodies include anti-DNA, anti-Sm, anti-RNP, anti-Ro (SSA), and anti-La (SSB). The doctor may use these antibody tests to help make a diagnosis of lupus.
Some tests are used less frequently but may be helpful if the cause of a person's symptoms remains unclear. The doctor may order a biopsy of the skin or kidneys if those body systems are affected. Some doctors may order a test for anticardiolipin (or antiphospholipid) antibody. The presence of this antibody may indicate increased risk for blood clotting and increased risk for miscarriage in pregnant women with lupus.
Other laboratory tests are used to monitor the progress of the disease once it has been diagnosed. A complete blood count, urinalysis, blood chemistries, and the erythrocyte sedimentation rate (ESR) test can provide valuable information. Another common test measures the blood level of a group of substances called "complement". People with lupus often have increased ESRs and low complement levels, especially during flares of the disease. X rays and other imaging tests can help doctors see the organs affected by SLE.
In SLE, the body’s immune system does not work as it should. A healthy immune system produces proteins called antibodies and specific cells called lymphocytes that help fight and destroy viruses, bacteria, and other foreign substances that invade the body. In SLE, the immune system produces antibodies against the body’s healthy cells and tissues. These antibodies, called autoantibodies, contribute to the inflammation of various parts of the body and can cause damage to organs and tissues. The most common type of autoantibody that develops in people with SLE is called an antinuclear antibody (ANA) because it reacts with parts of the cell's nucleus.
Scientists do not yet understand all of the factors that cause the immune system disorder. It is likely that a combination of genetic, environmental, and possibly hormonal factors work together to cause the disease.
There is considerable evidence showing that genes play a role in the development of lupus. The extremely high occurrence of lupus in both members of a pair of identical twins and the increased prevalence of lupus among first- and second-degree relatives of people with lupus suggests a genetic component. In addition, when researchers look at autoantibodies typically found in an lupus patient and her or his siblings and compare them with clinical manifestations of the disease in the individuals, they find that the individuals have the autoantibodies in common more often than they have the clinical manifestations in common. This finding indicates a genetic basis for the formation of autoantibodies that play a role in lupus.
Studies to date suggest that many different genes contribute to lupus susceptibility and that no single genetic abnormality causes the disease. It also appears that genes may be influential in determining the type or severity of lupus. Genes that have been associated with lupus in humans include:
Researchers studying lupus in animals have discovered a single gene that causes a lupus-like illness in mice. In these mice, the fas gene, one of the genes that controls apoptosis (programmed cell death), is defective. When the defective fas gene is replaced with a normal gene, the mice no longer develop signs of the disease.
SLE is more prevalent in women during their reproductive years. In addition, disease activity sometimes flares during pregnancy or during the postpartum period. For these reasons, researchers have long considered that hormones may influence SLE.