Multiple sclerosis (MS) usually affects woman more than men. The disorder most commonly begins between ages 20 and 40, but can strike at any age. The exact cause is not known, but MS is believed to result from damage to the myelin sheath, the protective material which surrounds nerve cells. It is a progressive disease, meaning the damage gets worse over time. Inflammation destroys the myelin, leaving multiple areas of scar tissue (sclerosis). The inflammation occurs when the body's own immune cells attack the nervous system. The inflammation causes nerve impulses to slow down or become blocked, leading to the symptoms of MS. Repeated episodes, or flare ups, of inflammation can occur along any area of the brain and spinal cord. Symptoms vary because the location and extent of each attack varies. Usually episodes that last days, weeks, or months alternate with times of reduced or no symptoms (remission). Recurrence (relapse) is common although non-stop progression without periods of remission may also occur. Researchers are not sure what triggers an attack. Patients with MS typically have a higher number of immune cells than a healthy person, which suggests that an immune response might play a role. The most common theories point to a virus or genetic defect, or a combination of both. There also appears to be a genetic link to the disease. MS is more likely to occur in northern Europe, the northern United States, southern Australia, and New Zealand than in other areas. Geographic studies indicate there may be an environmental factor involved. People with a family history of MS and those who live in a geographical area with a higher incidence rate for MS have a higher risk of the disease.
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