Health
Doctors believe it's caused by a combination of genetic and environmental factors. Although MS isn't primarily regarded as an inherited disorder, twin studies strongly suggest the presence of certain genes can make an individual susceptible to it. But other factors, possibly a viral infection, also play a part. There are no prenatal tests available.
MS appears to develop because of an autoimmune response - for some unknown reason the body attacks itself.
People with the condition experience recurrent episodes of inflammation and destruction of the sheaths that surround and protect nerves (known as dymyelination). Small plaques form throughout the central nervous system.
MS has a wide range of symptoms, is unpredictable and affects everyone differently. There are several different types, with different patterns of disease. One in five people affected has a benign form with mild attacks and no permanent disability, while another 15 per cent have a progressive disease that steadily worsens.
Symptoms vary depending on the type of MS, but typically come and go. The condition can affect any part of the body but usually starts with a single episode of nerve dysfunction, classically inflammation of the optic nerve in one eye.
Later there can be loss of coordination and speech difficulties. Depression often develops.
MS is the most common neurological disorder among young adults, affecting 85,000 people in the UK with 2,500 newly diagnosed each year. It's more common in temperate rather than tropical climates. Scotland has the highest incidence in the world. Onset is usually between 20 and 40 years of age.
It's more common in women, with a ratio of two men to three women affected.
As its precise cause remains unclear, it's not possible to prevent the condition and there's no cure. Treatments include medication to relieve pain and spasms, physiotherapy, occupational therapy, steroids and beta-interferon. Complementary therapies used include acupuncture, massage and yoga.
Cannabis is being researched as a possible treatment for pain and muscle spasticity in MS. Disease-modifying drugs may slow its progression.