Who Gets MS?

For decades, the number of people living in the United States with MS has been estimated at 400,000. However, no system or database exists to provide an exact figure, and some sources are now estimating that the population of individuals with MS in the United States may be much higher than this earlier number. Estimates for the global MS population typically range between 2.3 and 2.5 million. As more information becomes available, MSAA will provide updates on these estimates.

Most people with MS experience their first symptoms and are diagnosed between the ages of 15 and 50, although individuals of any age may be diagnosed with MS. MS in childhood and adolescence is now being diagnosed more frequently, due in part to an increased awareness that children can get MS. Known as pediatric MS, diagnosis in children is still extremely involved, as experts have identified more than 40 common diseases that may initially behave similarly to early MS. In the United States, previous estimates ranged from 7,000 to 10,000 children and teens with MS. Similar to other population figures, MSAA will provide updates as more information becomes available.

The distribution of this disease is not totally random. On average, with relapsing forms of MS, women are three times more likely than men to develop this disorder. However, with the primary-progressive form, genders are more equally divided.

Geographically, people who live farther from the equator (in more temperate climates) have a higher risk of developing MS than people living in hotter areas near the equator, or in very cold areas near the north or south poles. Individuals living beyond the 40-degree mark north or south of the equator are far more likely to develop MS, and this is especially true for people in North America, Europe, and southern Australia. The degree of risk associated with where someone lives as a child will remain throughout his or her life.

MS is very rare in Inuit populations living in the far north. Asia continues to have a lower incidence of MS. More prevalent among those of northern European or Scandinavian ancestry, Caucasians have a higher incidence than those of African heritage to develop MS. One study, however, indicated that African Americans are at a higher risk of MS than originally thought, but more research is needed to confirm this finding.

African Americans and Asians tend to have more symptoms at the time of diagnosis, which are usually limited to the optic nerves and spinal cord, and this is termed “opticospinal MS.” This means that African Americans and Asians may experience more problems with vision and mobility, versus other common MS symptoms.

African Americans may be older at disease onset, and the disease course tends to be more aggressive, with more frequent relapses and higher lesion volume. Additionally, African Americans are thought to respond less to disease-modifying therapies, although studies are being conducted to see which medications are the most effective for this ethnic group.

Hispanic Americans are often diagnosed at an earlier age than Caucasian Americans, and a larger percentage are diagnosed with RRMS versus PPMS. They are more likely to present with opticospinal MS, optic neuritis (inflammation along the optic nerve), and/or transverse myelitis (causing inflammation in one location across both sides of the spinal cord).

Hispanic Americans have a much lower risk of MS compared to Caucasian Americans and African Americans. However, clinical observation reveals greater spinal-cord involvement, which more significantly affects ambulation, but more studies are needed to confirm this observation.

While MS is not contagious or hereditary, MS susceptibility is increased if a family member (blood relative) has MS. The average risk of developing MS in the United States is one in 1,000, or one-tenth of one percent. For first-degree relatives (such as a child or sibling), the risk increases to three or four percent. This is not true for adopted children or half siblings (who do not share the same parent who has MS), whose risk is the same as unrelated individuals.

In situations where one identical twin has been diagnosed with MS, the other twin has a 31-percent risk of developing the disease. If MS was strictly hereditary, when one identical twin has MS, the other identical twin would have a 100-percent risk of getting MS. The risk for twins who are not identical is five percent – similar to that of other siblings. Other groups of individuals who appear to have an increased risk of developing MS include those who smoke cigarettes, individuals with less exposure to sunlight and with lower amounts of Vitamin D, as well as people living in cleaner environments with fewer parasites. These findings are explained later on page 8, under “Possible Causes of MS.”

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