Asthma not a single disease, study reveals

By Amy Middleton 6 December 2010
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The world’s largest genetic study of asthma has shown it has many forms, which should not be treated in the same way.

ASTHMA IS NOT ONE single disease, and should not be treated as such, according to the world’s largest genetic study of the illness.
Researchers from the University of Western Australia in Perth are among a group of scientists from 19 countries who were involved in the DNA analysis of a total 26,000 people, with and without asthma.

From this extensive study, findings suggest significant biological differences exist between variations of the illness, such as the childhood onset of asthma compared to its adult manifestation.

Researcher Dr Jennie Hui from the University of Western Australia says that prior to this study, asthma was often considered a single disease, with a single view of treatment. But the study has shown that “early onset [asthma] is possibly even a completely different disease than adult-onset asthma,” she says.

Flip flopping figures

The prevalence of asthma in Australia is currently about 10 per cent, according to the most recent (2008) figures from the Australian Centre for Asthma Monitoring. In children up to 14 years, asthma is more common in boys;  beyond 14 years, the statistics flip and adult women are more likely to suffer from the illness. Speculation continues as to what causes the different types of asthma in children and adults.

John Upham, professor of respiratory medicine from the University of Queensland, says that almost all western countries have seen a significant increase in asthma over the last two or three decades, and he doesn’t believe our genetic makeup is the whole story.

“The benefit of this research is that it helps to pick out those who have asthma from different mechanisms,” John told Australian Geographic. “These could include environmental effects, ways in which the immune system behaves and how the lungs have grown.”

Lung growth during formative years could be one explanation for the change in asthma levels between gender groups, John proposes. As males grow, he says, their lung capacity expands, allowing for easier respiratory function. Other factors, including hormones, and even a woman’s menstrual cycle, have also been identified as contributors.

The immunity factor

The ‘hygiene hypothesis’ is another common theory, in which it’s believed that children raised in a sterile environment can develop inappropriate immune system responses. “While gene and environment interactions play an important role,” Jennie says. “You also have to look at your early age immunity.”

John Upham also subscribes to this theory, particularly, he says, because children raised in an urban environment have a higher likelihood of asthma than those raised on farms where there is contact with farm animals and other potential allergens. He also cites changes in diet and high levels of obesity as possible contributors.

Hazards of the job can also increase the severity of asthma: “For some people, asthma is triggered by chemicals in their workplace such as spray paint, formaldehyde or dust and other fumes,” says John.

While asthma’s contributing factors remain largely hypothetical, scientists generally agree on how much the illness varies. “As with other diseases, including cancer, we are learning that you really need to tailor the treatment to the individual,” John Upham says.

Much of the data from the world’s largest study comes from the Busselton Health Study, a program based in Western Australia that has been collecting data on the topic since 1966. The research was published in The New England Journal of Medicine.