FAITH LAPIDUS:

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

BOB DOUGHTY:

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

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FAITH LAPIDUS:

Multiple sclerosis is not 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 2,500,000 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.

BOB DOUGHTY:

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.

FAITH LAPIDUS:

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, they say, the average age of people found to have the disease is between 20 and 50 years old.

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BOB DOUGHTY:

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, doctors 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 like 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.

Recently, an American study showed that women who get plenty of vitamin D during pregnancy may be protecting their babies from developing MS later in life. Vitamin D is found in fortified milk and fatty fish like salmon. Your body also produces the vitamin after contact between the skin and sunlight.

FAITH LAPIDUS:

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 symptom is a lack of feeling in one part of the body or another.

Two other symptoms are muscle weakness and low energy levels. 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.

BOB DOUGHTY:

Doctors who suspect a patient has MS must carry out tests and study the patient's history of health problems. MS symptoms can depend on where the nerve scars are in the 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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FAITH LAPIDUS:

There are four main kinds of multiple sclerosis. The first is called Relapsing-Remitting. About 85 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.

BOB DOUGHTY:

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 50 percent of those with the Relapsing-Remitting form of MS. It begins to affect them several years after they have had Relapsing-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.

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FAITH LAPIDUS:

Scientists say multiple sclerosis does not appear to be passed from parents to children. Yet it does appear to be found in families. The National Multiple Sclerosis Society says one in every 750 Americans is at risk of developing MS. But the risk rises to one in every 40 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.

BOB DOUGHTY:

There is no cure for multiple sclerosis. MS does not always result in severe disability. Many patients are able to live normal lives. The National Institute of Neurological Disorders and Stroke says some patients do well with no treatment at all. It 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.

FAITH LAPIDUS:

America's 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.

Last month, the FDA approved sales of dalfampridine extended release tablets to improve walking in MS patients. This is the first drug approved for this use.

Scientists are working to develop other treatments for MS. The National Multiple Sclerosis Society says more than 100 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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BOB DOUGHTY:

This SCIENCE IN THE NEWS program was written by Oliver Chanler and Brianna Blake, who was also our producer. I'm Bob Doughty.

FAITH LAPIDUS:

And I'm Faith Lapidus. Join us again next week for more news about science in Special English on the Voice of America.

multiple sclerosis: a disease of the nervous system that gets worse over a period of time with loss of feeling and loss of control of movement and speech 多发性硬化

myelin: a mixture of proteins and fats that surrounds many nerve cells, increasing the speed at which they send signals 髓磷脂，髓鞘（由脂质、蛋白质组成，包绕在神经纤维轴突上）

fortified milk: 强化乳

interferon: a substance produced by the body to prevent harmful viruses from causing disease 干扰素

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(来源：VOA 编辑：陈丹妮）