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This is SCIENCE IN THE NEWS in VOA Special English. I'm Faith Lapidus.VOICE TWO:

And I'm Bob Doughty. This week, we tell about the disease multiple sclerosis.

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Joan Molenaar helps her husband Larry, a victim of multiple sclerosis, in a 2007 photo at their home in MinnesotaMultiple sclerosis is not very easy to say. Those who suffer from the disease may also have difficulty naming it. One sign of multiple sclerosis is losing the ability to speak clearly. It is estimated that more than two million five hundred thousand people worldwide suffer from multiple sclerosis, which also is called MS.

MS is a disease of the brain and spinal cord. The cause of the disease is not known. In patients with MS, the covering of the nerves is destroyed. This temporarily blocks signals that pass through the nerves to the muscles of the body and back to the brain.

The disease especially affects the ability to see, the sense of touch and the use of the arms and legs. Most forms of MS are described as progressive. This means that the disease gets worse as time passes.

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The central nervous system of the body includes the brain and the spinal cord. The system contains millions of nerve cells joined together by long thin fibers, like wires. Electric signals start in nerve cells and travel along these fibers to and from the brain. A fatty substance called myelin covers and protects the fibers. Myelin works in the same way that protective coverings work on electric wires.

In patients with MS, the myelin becomes infected. It swells, or grows larger, and loses its connection with the nerve fibers. As time passes, the unconnected myelin is destroyed. Hardened, scar tissue then forms over the nerve fibers. The process of hardening is called sclerosis. The word is from Latin and means scar. The many areas of hardened or scar tissue give the disease its name.

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In people with MS, when nerve signals reach a damaged area, some of the signals are blocked or delayed from traveling to or from the brain. This results in problems in different parts of the body. These problems may appear and then disappear, sometimes resulting in long periods when there are no problems at all. Or, they may happen more and more often and become worse. Doctors do not know what causes this process.

Experts say the disease affects women at least two times as often as men. And the experts say the average age of people found to have the disease is between twenty and fifty years old.

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For years, doctors believed that the cause of multiple sclerosis was environmental. They believed this because most of those suffering from the disease lived in northern Europe and the northern half of the United States.

In recent years, however, they have changed their beliefs about the causes of MS. Studies support the theory that there are several causes, instead of a single environmental cause or genetic problem. The studies appear to show that genetic problems are involved in making people likely to get the disease.

The studies also appear to show that environmental causes such as viruses or bacteria may be involved. However, researchers have not identified just what those causes might be. Another likely cause is a problem within the body's defenses against disease, when the defenses misunderstand signals and attack the body.

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Multiple sclerosis is different from many other diseases. The signs or symptoms of MS are not always the same. Sometimes, symptoms of the disease appear and then disappear for a long time. For example, one of the symptoms is a lack of feeling in one part of the body or another.

Two other symptoms of the disease are muscle weakness and tiredness. However, these also could be caused by other health problems that are not MS. Other symptoms include a loss of the ability to move normally or a loss of balance. A person suffering from MS also may have difficulty seeing well or speaking clearly.

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Doctors who suspect a patient has MS must carry out a number of tests and study the patient's history of health problems. MS symptoms can depend on where the nerve scars are in the body's central nervous system. And some of these signs are not always easy to see.

Magnetic Resonance Imaging is one way to tell if a patient has multiple sclerosis. The test, also known as MRI, involves studying the magnetic signals from all the cells in the body. An MRI can show if there are scars from MS along a patient's nerves. A doctor can use this test to tell if a patient might have the disease, as well as by studying the patient's medical history.

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There are four main kinds of multiple sclerosis. The first kind is called Relapsing-Remitting. About eighty-five percent of MS patients begin with this form of the disease. More than half of the patients have this form at any one time. These patients have one or two major MS-related problems every one to three years. Then they have periods with no signs of the disease.

The symptoms appear suddenly and last a few weeks or months before slowly disappearing. However, the symptoms may also become worse each time they appear.

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The second kind of MS is called Primary Progressive. In this form, the signs of the disease appear and begin to grow worse, with no periods of disappearance. About ten percent of patients begin their struggle with the disease this way.

The third kind of MS is called Secondary Progressive. This form of the disease affects about fifty percent of those with the Relapse-Remitting form of MS. It begins to affect them several years after they have had Relapse-Remitting MS. When the disease changes to Secondary Progressive, the disease begins to grow worse.

The fourth kind of MS is called Progressive Relapsing. It is the worst form of multiple sclerosis. New signs of MS appear while existing ones grow worse. This form of the disease is rare. It affects only five percent of MS cases.

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Scientists say multiple sclerosis does not appear to be passed from parents to children. However, it does appear to be found in families. The National Multiple Sclerosis Society says one in every seven hundred fifty Americans is at a risk of developing MS. But the risk rises to one in every forty people among those who have a close family member with the disease.

It does not appear that one gene is responsible for MS. Instead, several genes may increase the possibility that a person will develop MS. Common viruses or bacteria may also increase the chances that some people will develop the disease.

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There is no cure for multiple sclerosis. MS does not always result in severe disability. Many patients with the disease are able to live normal lives. The National Institute of Neurological Disorders and Stroke says many patients do well with no treatment at all. The agency notes that many medicines to treat the disease have serious side effects while some carry risks.

Several kinds of medicine are used to treat the symptoms. Some drugs reduce the swelling in nerve tissue. Drugs known as beta interferons also are used to treat MS. Interferons are genetically engineered copies of proteins found naturally in the body. These proteins help fight viral infections and help the body's defenses against disease.

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The United States Food and Drug Administration has approved three forms of beta interferon for treatment of Relapsing-Remitting MS. The FDA also has approved a man-made form of myelin basic protein to treat this kind of MS. And, a treatment to suppress the body's defenses against disease was approved to treat severe cases of MS.

The FDA has approved sales of the drug natalizumab to treat people with relapsing forms of MS. But the drug can be given only in centers where specially-trained doctors can observe patients.

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Scientists are working to develop new treatments for MS. The National Multiple Sclerosis Society says more than one hundred studies are continuing around the world. Doctors are hopeful that new treatments will help patients with multiple sclerosis in the future.

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This SCIENCE IN THE NEWS program was written by George Grow. Our producer was Brianna Blake. I'm Faith Lapidus.

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And I'm Bob Doughty. Read and listen to our programs at 51voa.com. Join us again next week for more news about science in Special English on the Voice of America.