What Is It?

Multiple sclerosis, sometimes called just MS, is a disabling, neurological illness that affects the brain and spinal cord. The disease also is progressive, meaning it continues to get worse over time.

Nerve cells normally are surrounded by an insulating sheath made of a fatty substance called myelin that helps to transmit nerve impulses. In MS, this myelin sheath is inflamed or damaged, which disrupts or slows nerve impulses and leaves areas of scarring called sclerosis. These areas of myelin damage and scarring are called MS plaques.

The disruption of nerve signals causes a variety of symptoms that can affect vision, sensation and body movements. These symptoms usually come and go through a series of episodes when symptoms suddenly get worse (called relapses) alternating with periods of recovery when symptoms improve (called remissions). Many patients have a long history of multiple sclerosis attacks over several decades. In these cases, the disease may worsen in steps, when the attacks occur. For others, the disease worsens steadily. In a minority of patients, multiple sclerosis causes relatively few problems.

Although the exact cause of multiple sclerosis has been debated for decades, scientists now believe it is an autoimmune disease, which means the immune system mistakenly attacks its own body, in this case the myelin sheaths of the nerves. In some cases, the trigger for an attack seems to be a viral infection, but at other times, other physical or emotional stress is blamed. As a rule, the timing, duration and damage of attacks is unpredictable.

Multiple sclerosis is the most common neurological disease in young people, and it affects more than 1 million young adults worldwide. It is five times more common in temperate climates than in the tropics and affects women twice as often as men. Close relatives of a person with multiple sclerosis are 8 times more likely than the average person to develop the disease themselves, and children of a person with multiple sclerosis have 30 to 50 times the average risk. However, even though genetic (inherited) factors seem to play a large role in the development of this disease, no single multiple sclerosis gene has been identified. Instead, scientists suspect that the disease develops because of the influence of several genes acting together.