Multiple sclerosis (MS) affects the nerve fibres of the central nervous system: the brain and spinal cord. These nerves gradually lose their ability to transmit electric signals between the brain and body. However, most patients have long periods of remission, when the disease does not get any worse and may even improve. Symptoms often include blurred vision, loss of balance, muscle weakness, fatigue and slurred speech. MS usually occurs in people aged 22-40, and affects more women than men.