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For Urban Allergy Sufferers, Genes Make Matters Worse

By Robert Taylor

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People with certain genes are at risk for severe allergy symptoms in smoggy areas like Mexico City.
During ragweed season, allergy sufferers in urban areas often experience worse symptoms than their rural or suburban counterparts. Now new research links allergens, pollutants, and the severity of allergy responses to specific variations in one group of genes.

The findings also support the notion that allergy sufferers who carry these particular genes may experience lighter symptoms if they take antioxidant vitamins that help the body cope with the pollutants.

California researchers focused on genes for proteins that deactivate toxic oxygen compounds that form when water meets inhaled pollutants in the airways of the lungs and nose. According to lead researcher Frank Gilliland, about half the population carries at least one gene variant from this group.

People with these variants who also suffer from allergies are likely to sneeze, wheeze, and cough the most when pollution levels are high.

Gilliland and colleagues at the Keck School of Medicine at the University of Southern California in Los Angeles and at the Geffen School of Medicine at UCLA exposed 19 volunteers with moderate-to-severe ragweed allergies to ragweed pollen and to a mixture of ragweed pollen and diesel exhaust particles.

The results were unambiguous, says Gilliland. Allergic responses to ragweed in subjects with fully active genes were scarcely affected by the diesel exhaust particles. But subjects who carry less than fully active genes reacted far more severely to the ragweed pollen in the presence of diesel particles.

Gilliland emphasizes that the subjects were not allergic to the diesel particles alone. Instead, the pollutant particles seem to act by producing reactive oxygen molecules that interfere with immune system signals, heightening allergy symptoms.

The recent findings mesh with those of another recent study in which asthmatic children in Mexico City with variations in the same genes experienced worse symptoms when exposed to ozone—another reactive oxygen molecule. Their symptoms abated significantly when they took vitamins C and E.

There is no easily available test for the gene, but if you suffer from allergies, Gilliland suggests a low-tech approach: Take antioxidant vitamins such as vitamin C and observe whether they alleviate some allergy symptoms. Antioxidants may make up for the defective genes and help people with the gene variation to rid the body of toxic oxygen molecules.

“Nature is complicated,” says Gilliland. “This involves three factors—an allergen, a pollutant, and specific genes—and looking at each one individually does not provide the complete picture.” Gilliland adds that in follow-up studies, he and his colleagues will look for other genes that may contribute to allergic responses to pollution.
Gilliland, F. et al. Effect of glutathione-S-transferase M1 and P1 genotypes on xenobiotic enhancement of allergic responses: randomized, placebo-controlled crossover study. Lancet 363, 119-125 (January 10, 2004).
Romieu, I. et al.Genetic polymorphism of GSTM1 and antioxidant supplementation influence lung function in relation to ozone exposure in asthmatic children in Mexico City. Thorax 59, 3-4 (January 2004).

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