A genetic mutation that protects people from the disease schistosomiasis, caused by parasitic worms, may increase their risk for asthma, according to new research.
The results may explain why people in the United States whose ancestors lived in Africa or Latin America — parts of the world where the worms are more common — are at greater risk for asthma, the researcher said.
However, it's likely many other genes play a role in a person's asthma risk, the researchers said. Figuring out what these genes are — and how they interact with an individual's environment — would allow physicians to better determine a person's risk for asthma.
“The goal would be to ultimately, someday, be able to characterize the individuals at risk by their genetic signature or blueprint,” said study researcher Kathleen Barnes, an allergy and asthma researcher at John Hopkins School of Medicine in Baltimore.
The study was presented at the annual meeting of the American Association for the Advancement of Science in Washington, D.C. on Feb. 19.
Barnes and her colleagues found that people living in a region of Bahia, Brazil had a genetic mutation that protects against the worms because it allows the immune system to produce abundant amounts of a protein called IgE. This would be helpful in fighting schistosomiasis, because IgE binds to the worm, labeling it for expulsion from the body, Barnes said.
“The theory is, the more IgE that you produce, the more protected you'll be against the disease,” Barnes said.
But IgE also sets off the swelling of the airways that occurs in people in asthma. An allergen or irritant, such as dust or pollen, triggers the release of IgE.
Asthma affects approximately 300 million people worldwide, according to the World Health Organization.
The findings also fit with what researchers call the hygiene hypothesis, which is the idea that extreme cleanliness in developed countries has made people's immune systems more sensitive, and has increased the prevalence of allergies and asthma.
In this case, the theory goes, individuals would be predisposed to develop asthma if they were not exposed to schistosomiasis — a likely scenario in the U.S. If IgE proteins aren't busy fighting parasites they might start to attack less nocuous substances, and elicit an asthmatic response.
The findings may explain why asthma is more prevalent among African-Americans than among Caucasians in the United States. About 3 million African-Americans have asthma, according to the National Women's Health Information Center (NWHIC). African-Americans are also three times more likely to die from asthma than Caucasians, the NWHIC says.
Pass it on: A genetic mutation that protects against the parasitic disease schistosomiasis might make individuals more prone to asthma, particularly in developed countries.
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