Multiple sclerosis (MS) is a disease caused by damage to the nerve fibres in the central nervous system. This damage disrupts the signals sent to and from the brain. MS is a progressive disease that worsens over time, eventually leading to death.
The central nervous system comprises the brain, spinal cord and a network of nerves that conduct messages across the body for controlling movements and actions. These nerve fibres are covered by an insulating substance called myelin that protects the nerve and aids the transport of impulses to and from the brain. In MS, this myelin becomes damaged, which interferes with conduction of the nerve signals, which may be slowed or not transported at all.
Causes of multiple sclerosis
MS is an autoimmune disease. Usually, the immune system protects the body against invading microbes or foreign bodies but in autoimmune diseases, the immune system mistakes healthy body tissue for foreign or damaged tissue that needs to be attacked.
In MS, the immune system mistakes the protective myelin sheath for a foreign body and mounts an attack against it. This destroys the myelin, which becomes inflamed in small areas called plaques or lesions of demyelination. As the inflammation subsides, the myelin left behind may be scarred (sclerosis) and the nerve fibre underneath may be damaged.
The exact cause of MS is not clearly understood but both genetic factors and environmental factors seem to play a role in causing the condition.
MS is not classed as a genetic condition because no one gene has yet been identified as causing the condition. However, researchers have shown that individuals with a relative who has had MS are more likely to develop it. Studies have also shown that if a twin develops the condition, the risk of the other twin developing MS is one in four. Research into the contribution of certain gene combinations to the risk of developing MS is ongoing.
Worldwide studies into MS suggest that individuals from countries that lie further north of the equator may be at a greater risk for the condition, which is more common in countries such as the UK and Scandinavia than in Ecuador or Malaysia, for example. Some studies have shown that lack of sunlight and a subsequent lack of Vitamin D may be linked to the incidence of MS.
Some researchers also believe MS may result from viral infection of the nervous system and/or the immune system and the Epstein-Barr virus (EBV) has commonly been implicated as a cause of MS.
Reviewed by Sally Robertson, BSc