New US-led research has brought closer the day when a genetic test can predict whether children with asthma are likely to grow out of it by the time they become adults.

The study, led by researchers from Duke University in North Carolina, is published in the 28 June online issue of The Lancet Respiratory Medicine.

About half of children with asthma grow out of it by the time they reach their teen or adult years. But at present there are no tests that can predict which children will never grow out of the disease and which will.

For this latest study, the researchers looked at the results of a huge genetic study of asthma, drafted a profile of asthma risk genes and tested it against a leading asthma research database of individuals that have been followed from birth to their 30s.

They looked at the asthma-specific health information (such as allergies and lung function) and made comparisons among those individuals who developed asthma (and when they developed it), and those who did not, and among the former, who still had the disease in adulthood.

The huge study from which they constructed the genetic profile of asthma risk was from the GABRIEL Consortium, the largest-ever genome-wide association study of asthma, which included more than 26,000 participants.

And the large database of individuals who were followed for their first 40 years of life, was New Zealand's Dunedin Multidisciplinary Health and Development Study, a unique sample of 1,000 individuals who underwent extensive measurement of asthma and related traits during the study period.

For their analysis the researchers included 880 individuals from the New Zealand cohort.

The results showed that individuals who had the highest genetic risk scores were the ones most likely to develop asthma, and also developed it earlier.

Among people who started with asthma while they were children, the ones who still had it when they became adults were mostly ones with a higher genetic risk score.

The study also showed that genetic risk was specifically linked with allergic asthma that led to chronic symptoms of impaired lung function.

People who had a higher genetic risk score also tended to have more severe asthma. Compared to counterparts with a lower risk profile, they missed more school and work days because of asthma, and they were also more frequently admitted to hospital due to asthma.

Another important result from the study was that the genetic risk profile was able to give more information about asthma risk than you could get from looking at family history of the disease.

However, although the study shows it is possible to use a genetic risk profile to predict which children with asthma will grow out of and which will have the persistent form of the disease, more work needs to be done before it can be used with patients.

The predictions made in the study "are not sufficiently sensitive or specific to support their immediate use in routine clinical practice," lead author Daniel Belsky, a National Institute on Aging Postdoctoral Fellow at Duke University Center for the Study of Aging and Human Development, says in a statement.

"As additional risk genes are discovered, the value of genetic assessments is likely to improve," says Belsky.

Belsky has published a comprehensive web-based Fact Sheet of the study.

Little is known about why asthma develops, how it constricts the airways, or why patients respond differently to the same treatment. But another team in the US recently reported discovering that a common type of childhood asthma is unconnected to allergens or inflammation, and is quite different from other asthma cases.

Written by Catharine Paddock PhD