Multiple sclerosis-Definition, Causes & Risk factors-By Mayo Clinic staff


Multiple sclerosis (MS) is a potentially debilitating disease in which your body's immune system eats away at the protective sheath that covers your nerves. This interferes with the communication between your brain and the rest of your body. Ultimately, this may result in deterioration of the nerves themselves, a process that's not reversible.
Symptoms vary widely, depending on the amount of damage and which nerves are affected. People with severe cases of multiple sclerosis may lose the ability to walk or speak. Multiple sclerosis can be difficult to diagnose early in the course of the disease because symptoms often come and go sometimes disappearing for months.
There's no cure for multiple sclerosis. However treatments can help treat attacks, modify the course of the disease and treat symptoms


The cause of multiple sclerosis is unknown. It's believed to be an autoimmune disease, in which the body's immune system attacks its own tissues. In multiple sclerosis, this process destroys myelin - the fatty substance that coats and protects nerve fibers in the brain and spinal cord.
Myelin can be compared to the insulation on electrical wires. When myelin is damaged, the messages that travel along that nerve may be slowed or blocked.
Doctors and researchers don't understand why multiple sclerosis develops in some people and not others. A combination of factors, ranging from genetics to childhood infections, may play a role

Risk factors

These factors may increase your risk of developing multiple sclerosis:

■Being between the ages of 20 and 40. Multiple sclerosis can occur at any age, but most commonly affects people between these ages.

■Being female. Women are about twice as likely as men are to develop multiple sclerosis.
■Having a family history. If one of your parents or siblings has had multiple sclerosis, you have a 1 to 3 percent chance of developing the disease — as compared with the risk in the general population, which is just a tenth of 1 percent. But the experiences of identical twins show that heredity can't be the only factor involved. If multiple sclerosis was determined solely by genetics, identical twins would have identical risks. However, an identical twin has only a 30 percent chance of developing multiple sclerosis if his or her twin already has the disease.
■Having certain infections. A variety of viruses have been linked to multiple sclerosis. Currently the greatest interest is in the association of multiple sclerosis with Epstein-Barr virus, the virus that causes infectious mononucleosis. How Epstein-Barr virus might result in a higher rate of MS remains to be clarified.
■Being white. White people, particularly those whose families originated in northern Europe, are at highest risk of developing multiple sclerosis. People of Asian, African or Native American descent have the lowest risk.
■Living in countries with temperate climes. Multiple sclerosis is far more common in Europe,
southern Canada, northern United States, New Zealand and southeastern Australia. The risk seems to increase with latitude.
A child who moves from a high-risk area to a low-risk area, or vice versa, tends to have the risk level associated with his or her new home area. But if the move occurs after puberty, the young adult usually retains the risk level associated with his or her first home.
■Having certain other autoimmune diseases. You're very slightly more likely to develop multiple sclerosis if you have thyroid disease, type 1 diabetes or inflammatory bowel disease

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