Asthma Emerging as Genetic Disorder
If both parents have it, child's odds of getting the disease approach 70 percent
SATURDAY, June 26, 2004 (HealthDayNews) -- Asthma rates have risen sharply in the United States in recent decades. The chronic condition, in which the airways become inflamed and stifle breathing, now affects more than 20 million Americans, including more than five million children.
Asthma kills nearly 5,000 people a year, according to the American Academy of Allergy, Asthma and Immunology. Asthma attacks lead to 1.8 million emergency room visits and 14 million missed days of school annually, the group says.
Dr. Deborah Gentile, an asthma specialist at Allegheny General Hospital, in Pittsburgh, said immunologists are increasingly coming to understand asthma as a genetic disorder -- at least, in its beginnings. "We're thinking that there are different types of asthma driven by different genes."
A child with one parent who has asthma has a 30 percent chance of developing the airway condition herself. If both parents have it, her odds of getting it approach 70 percent -- not a given but a stacked deck.
Gentile said there are three factors that contribute to a person's risk of asthma. The first is the genetic legacy from parents; the second is exposure to infections and irritants that "program" the immune system and make it sensitive. The third is timing: It seems that the immune system is particularly sensitive during the first two years of life, Gentile said, so children with the right combination of genes and the right mix of exposures early in life are at the greatest risk of developing asthma.
Once a person's susceptibility to asthma has been established, he or she can suffer breathing attacks when they experience onset symptoms known as triggers. Well-known triggers of asthma include respiratory infections, breathing cold air and cigarette smoke, and even vigorous laughter or sobs. Various irritants, such as pet dander, dust mites, cockroaches, pollen and mold, also can worsen the symptoms of asthma, according to the National Institutes of Health.
Some evidence suggests that women who take estrogen replacement therapy during menopause may be more likely to develop asthma as they age. However, the extent of the connection isn't fully understood, experts say.
Aspirin and other painkillers are also known to exacerbate asthma in about 10 percent of people with the condition. Dr. Carlos Camargo, an asthma expert at Harvard Medical School, in Boston, said some recent evidence suggests that acetaminophen, the active ingredient in Tylenol, may both cause and trigger asthma attacks in rare cases.
"It's important to distinguish exposures that cause asthma versus those that exacerbate existing asthma," Camargo said. "Although these are, at times, the same, there are also factors that worsen existing asthma but are unlikely to cause disease," such as strong odors like perfumes, he said.
Because asthma is so widespread throughout the American population, there are always research initiatives in progress. The federal government's National Institute of Environmental Health Sciences lists some of the research under way.