Multiple Sclerosis (MS)

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Genetics

In addition, increasing scientific evidence suggests that genetics may play a role in determining a person's susceptibility to Multiple Sclerosis (MS). Some populations, such as Gypsies, Eskimos, and Bantus, never get Multiple Sclerosis (MS). Native Indians of North and South America, the Japanese, and other Asian peoples have very low incidence rates. It is unclear whether this is due mostly to genetic or environmental factors.

In the population at large, the chance of developing Multiple Sclerosis (MS) is less than a tenth of one percent. However, if one person in a family has Multiple Sclerosis (MS), that person's first-degree relatives-parents, children, and siblings have a one to three percent chance of getting the disease.

For identical twins, the likelihood that the second twin may develop Multiple Sclerosis (MS) if the first twin does is about 30 percent. For fraternal twins (who do not inherit identical gene pools), the likelihood is closer to that for non-twin siblings, or about 4 percent. The fact that the rate for identical twins both developing Multiple Sclerosis (MS) is significantly less than 100 percent suggests that the disease is not entirely genetically controlled. Some (but definitely not all) of this effect may be due to shared exposure to something in the environment, or to the fact that some people with Multiple Sclerosis (MS) lesions remain essentially asymptomatic throughout their lives.

Further indications that more than one gene is involved in Multiple Sclerosis (MS) susceptibility comes from studies of families in which more than one member has Multiple Sclerosis (MS). Several research teams found that people with Multiple Sclerosis (MS) inherit certain regions on individual genes more frequently than people without Multiple Sclerosis (MS). Of particular interest is the human leukocyte antigen (HLA) or major histocompatibility complex region on chromosome 6. HLAs are genetically determined proteins that influence the immune system.

The HLA patterns of Multiple Sclerosis (MS) patients tend to be different from those of people without the disease. Investigations in northern Europe and America have detected three HLAs that are more prevalent in people with Multiple Sclerosis (MS) than in the general population. Studies of American Multiple Sclerosis (MS) patients have shown that people with Multiple Sclerosis (MS) also tend to exhibit these HLAs in combination, that is, they have more than one of the three HLAs, more frequently than the rest of the population. Furthermore, there is evidence that different combinations of the HLAs may correspond to variations in disease severity and progression.

Studies of families with multiple cases of Multiple Sclerosis (MS) and research comparing genetic regions of humans to those of mice with experimental allergic encephalomyelitis (EAE) suggest that another area related to Multiple Sclerosis (MS) susceptibility may be located on chromosome 5. Other regions on chromosomes 2, 3, 7, 11, 17, 19, and X have also been identified as possibly containing genes involved in the development of Multiple Sclerosis (MS).

These studies strengthen the theory that Multiple Sclerosis (MS) is the result of a number of factors rather than a single gene or other agent. Development of Multiple Sclerosis (MS) is likely to be influenced by the interactions of a number of genes, each of which (individually) has only a modest effect. Additional studies are needed to specifically pinpoint which genes are involved, determine their function, and learn how each gene's interactions with other genes and with the environment make an individual susceptible to Multiple Sclerosis (MS). In addition to leading to better ways to diagnose Multiple Sclerosis (MS), such studies should yield clues to the underlying causes of Multiple Sclerosis (MS) and, eventually, to better treatments or a way to prevent the disease.

References:
Office of Communications and Public Liaison
National Institute of Neurological Disorders and Stroke (NINDS)
National Institutes of Health
January 23, 2008
www.ninds.nih.gov/disorders/multiple_sclerosis/detail_multiple_sclerosis.htm

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