Multiple sclerosis (MS) damages the covering which surrounds the long nerve fibres. Damaged nerves cannot pass messages around the body efficiently.
Nerve damage can cause problems with vision and movement.
The first signs of MS usually appear between the ages of 20 and 40. You cannot catch MS and scientists are unsure why it suddenly appears.
MS affects 85 000 people in Britain.
The symptoms of MS generally develop slowly and depend on which nerves are affected. It may start with numbness or tingling in the hands and feet, arms or legs, pain at the back of the eyes or blurred vision.
Some people experience anxiety or depression and personality changes.
Although symptoms tend to come and go they generally get worse over the years.
MS is caused by damage to myelin – the fatty covering which insulates nerve fibres. When myelin is damaged nerve messages are sent more slowly. They may be muddled or not reach their destinations at all.
Myelin is destroyed, probably as the body's own immune defence system mistakenly attacks it.
Most often, MS causes problems with movement and vision.
There are no cures for MS, but there are some drugs which may help.
Beta-interferon may speed up the recovery from an attack, but its long-term effects are still being studied.
Steroids can help prevent damage to nerves from the eyes.
Drugs which stop the immune system attacking myelin are undergoing preliminary trials.
In the future, it might be possible to give drugs that prompt the myelin to repair itself, or to use stem cells to bring about remyelination of damaged neurons.
For advice and information, go to the MS society website.