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Around 100,000 people in the UK have MS. It's normally diagnosed in people between the ages of 20 and 40, and affects almost twice as many women than men.
Once diagnosed, MS stays with you for life, but treatments and specialists can help you to manage the symptoms.
A substance called myelin protects the nerve fibres in the central nervous system.
In MS, your immune system, which normally helps to fight off infections, mistakes myelin for a foreign body and attacks it.
This damages the myelin and strips it off the nerve fibres, either partially or completely, leaving scars known as lesions or plaques.
No one knows the exact cause of MS, but a mixture of genetic and environmental factors play a role.
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It's likely that a combination of genes make some people more susceptible to developing MS, but genes are only part of the story.
Find out more about causes
MS is complex and can cause many different symptoms, so it's not easy to diagnose.
It's hard to pinpoint exactly when MS begins, and the early signs and symptoms are different for everyone.
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Find out more about diagnosing MS
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