Nearly half a million Americans experience symptoms including numbness or weakness on one side of the body, vision loss on one side of the body, dizziness and slurred speech, tingling and electric shock-like sensations, and bowel and bladder difficulties. These are symptoms of multiple sclerosis which occurs when the protective covering over the spinal chord is damaged or destroyed. The symptoms usually start to appear in the person’s late teens to late 50s, but scientists recently found that there are antibodies in blood that can be found some time before any symptoms start to appear.
The antibodies appear to be what is attacking the protective layer, called the myelin sheath, but it is unclear what cases them to form. Risk of developing multiple sclerosis goes up further from the equator, though with prominent exceptions including high-risk Sardinians in the tropics, low-risk American Indians and Māori closer to the poles. This geographical factor is unusual except in parasitic illnesses, but there is no evidence multiple sclerosis is caused by a parasite. It has been suggested the the condition is triggered by bacteria; a recent study found that food poisoning, in particular a toxin produces by a species of the foodborne bacteria Clostridium, can damage myelin, but this may not be the sole cause.
While multiple sclerosis does not appear to be hereditary, it does often appear with autoimmune diseases, most of which are, and there is a genetic component to risk. Another thing that increases the risk is use of hormonal birth control. Women who in a study, took pills the combined estrogen and progestin were more than one third more likely to develop multiple sclerosis than women who weren’t on the pill. It was not clear whether different combinations of hormones, or hormonal birth control not taken orally, had the same effect.
A link has also been found between sleep disorder and multiple sclerosis. This, researchers say, may be the fatigue that is often part of the disease. An earlier study found that many people with multiple sclerosis also suffer sleep apnea, but one reason for that may be that obesity is a risk factor for both. The more recent study found that around a third of multiple sclerosis patients experience moderate to severe insomnia, though most are undiagnosed.