Multiple sclerosis is a chronic, unpredictable disease of the central nervous system (CNS), which is made up of the brain, spinal cord and optic nerves. It is thought to be an immune-mediated disorder, in which the immune system incorrectly attacks healthy tissue in the CNS.

MS can cause many symptoms, including blurred vision, loss of balance, poor coordination, slurred speech, tremors, numbness, extreme fatigue, problems with memory and concentration, paralysis, and blindness and more. These problems may come and go or persist and worsen over time. Most people are diagnosed between the ages of 20 and 50, although individuals as young as 2 and as old as 75 have developed it.

Anyone may develop MS but there are some patterns. More than two to three times as many women as men develop MS and this gender difference has been increasing over the past 50 years. Studies suggest that genetic risk factors increase the risk of developing MS, but there is no evidence that MS is directly inherited. Environmental factors, such as low Vitamin D and cigarette smoking have also been shown to increase the risk of MS. MS occurs in most ethnic groups, including African-Americans, Asians and Hispanics/Latinos, but is most common in Caucasians of northern European ancestry.

• Read more about who gets MS

More than 2.3 million people are affected by MS worldwide. Because the Centers for Disease Control and Prevention (CDC) does not require U.S. physicians to report new cases, and because symptomscan be completely invisible, the prevalence of MS in the U.S. can only be estimated. The Society continues to advocate for the establishment of a national registry that will track the number of people living with MS and has made a commitment to re-evaluate the current prevalence estimate and investigate the process by which an updated estimate can be identified.

Because MS causes damage in the CNS, nearly any function can be adversely affected. However, the most common symptoms are overwhelming fatigue, visual disturbances, altered sensation and difficulties with mobility.

Symptoms of MS are unpredictable, and vary in type and severity from one person to another and in the same person over time. Symptoms may disappear or remit completely or they may persist and may worsen over time.

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MS symptoms occur when the immune-system produces inflammation within the CNS.  The inflammatory attack damages myelin, (the protective insulation surrounding nerve fibers), oligodendrocytes (cells that make CNS myelin) and sometimes the underlying nerve fiber. The damage caused by inflammation can produce symptoms that resolve over weeks to months or symptoms that are permanent.

No. Moreover, the majority of people with MS do not become severely disabled. Two-thirds of people who have MS remain able to walk, though many will need an aid, such as a cane or crutches, and some will use a scooter or wheelchair because of fatigue, weakness, balance problems, or to assist with conserving energy.