Researchers say developed countries with better sanitation seem to have more cases of multiple sclerosis than other places.

It turns out immigration may increase the risk of developing multiple sclerosis.

That's what a research team led by Queen Mary University of London and Barts Health NHS Trust concluded.

Environmental factors may be more involved in increasing the chances of developing multiple sclerosis (MS) than previously thought, according to the team led by Dr. Klaus Schmierer, Ph.D., FRCP.

Schmierer is a reader in clinical neurology at Blizard Institute, Queen Mary University of London, as well as a consultant neurologist at the Royal London Hospital (Barts Health NHS Trust).

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Schmierer's study focused on east London, where he found that black residents and those from South Asia had a higher prevalence of MS compared with the same groups living in their ancestral countries.

Researchers say these findings suggest an environmental influence on developing the disease, which is yet undetermined.

"My team recognized we work in one of the ethnically most diverse parts of the U.K. With its small catchment/high population density, east London lends itself to investigate the impact of migration from territories of very low MS prevalence to the U.K., where MS prevalence is very high," Schmierer said in an interview with Healthline.

Both genetic and environmental factors are thought to contribute to developing MS, but the cause is still unknown.

MS is a neurodegenerative disease of the central nervous system, and the most common chronic, nontraumatic cause of disability in young adults.

There is no cure, although there are treatments that may reduce the frequency and seriousness of attacks.

According to Dr. Nicholas LaRocca, vice president of healthcare delivery and policy research for the National Multiple Sclerosis Society, the east London study is one of a number that examine population groups and the rates of diagnosis of MS.

"This is an exciting time in MS research," he said.

LaRocca noted that earlier in his career, before the introduction of treatment with interferon in the 1990s, options for MS patients were limited.

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Schmierer found in his study that the number of occurrences of MS based on geography is significant.

For example, in Ghana the incidence of MS was 0.24 per 100,000 people, the highest in sub-Saharan Africa. The prevalence of MS in the east London population was 74 per 100,000 people.

"The magnitude of this effect in our dataset is stunning," he said. "Whilst Mendelian genetics may influence the disease course once MS is established, the risk of actually getting the disease seems only weakly influenced by genetics. Note, however, X/Y chromosomes do play an important role in MS risk, with women being two to three times more frequently affected than men."

LaRocca told Healthline that gender is also being studied, citing the fact that women with MS rarely have serious outbreaks during the last trimester of pregnancy.

"Is there a hormonal component here?" he asked.

"If you look at a map of the world," he added, "you'll see that the risk increases as you move farther away from the Equator."

In other words, developed countries," and ones with better sanitation," LaRocca added, have a higher prevalence of MS. That raises the question of whether we are too rigorous in killing microorganisms, both good and bad.

"We know that as sanitation improves, so does the risk of contracting MS," LaRocca said.

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The Schmierer study, published in the Multiple Sclerosis Journal, used electronic records from general practices in four east London boroughs.

Local doctors were asked for the number of their patients diagnosed with MS, grouped by ethnicity.

A total of 907,151 patients were registered with doctors in east London. Of that number, 776 had a diagnosis of MS. The overall prevalence of the disease in east London was 111 per 100,000 (152 for women and 70 for men). The prevalence per 100,000 was 180 for whites, 74 for blacks, and 29 for people from South Asian.

The research team plans further investigation to determine what environmental agents might provide an explanation for the higher figures found in the development of MS in the United Kingdom.

In the meantime, Schmierer cautions against reading too much into his study, noting the findings apply only in east London and must be replicated in other areas.

"Replicating our results in other parts of the country where a significant number of immigrants from low prevalence countries/territories have settled would bolster our case further that the focus must be on the definition, and potential to alter, the environmental factors leading to such a step-change in the risk of getting MS," he said.

But he does suggest that the results, however preliminary, need to be noted by general practitioners as well as specialists, who frequently do not include MS in their diagnoses. That assumption is based on the low risk of MS in blacks and South Asians when living in their ancestral territories.