European scientists have identified genes that predispose children and adults to asthma.
Some of the genes tell the immune system when the lining of the airways has been damaged. Others may control healing of the airways after they have been injured, the researchers said.
"But the genes are different genes for children than for adults," said study coauthor Dr Erika von Mutius, a professor of paediatrics at University Children's Hospital in Munich, Germany.
"However, even if we have been able to identify a number of these genes, we cannot predict disease just based on these genes because other factors, including environmental factors, are important as well," she added. "The genes do not explain everything."
The report is published in the New England Journal of Medicine.
How the study was done
For the Gabriel study, von Mutius and colleagues from London, Paris, Munich and Oxford looked at genes from 10,365 asthmatics and compared them with the genes of 16,110 people without asthma.
After looking at all the genes in these individuals, the researchers found some new genes that predispose people to asthma. Among adults, the effect of genes in the development of asthma was weaker than in children.
Among children, the most important gene linked to asthma is called ORMDL3/GSDMB, and is not involved in adults who develop asthma, von Mutius and colleagues found.
These newly identified gene variants affected more than one-third of children with asthma. In addition, these genes had strong effects on severe asthma, the study authors noted.
However, despite these findings, genetic testing would be of no value in predicting early in life which children might eventually develop asthma, because environmental factors are also important for asthma to develop, von Mutius said.
Finding may lead to better treatments
These scientists are working to identify environmental causes that can trigger asthma, she added. However, the researchers suggested that the identification of these genes might one day lead to better treatments for asthma.
The researchers also looked at genes that control antibodies linked to allergies. However, these genes had little effect on the presence of asthma, and the asthma genes had little effect on the levels of antibodies, which means, they said, that the allergies that often accompany asthma are most likely a consequence of the asthma not its cause.
Dr Norman H. Edelman, chief medical officer at the American Lung Association, called the study "very well done." He added, "Its most critical attribute is the large number of subjects and genes studied, allowing for good confidence in conclusions about lack of association as well as association with candidate genes."
The study is also important, he said, because it found several aspects of asthma that have been suspected but not proven.
For example, "there are many key differences between adult- and childhood-onset asthma. They probably should be considered to be different diseases," Edelman said.
Also, allergy is not likely to be an important underlying cause of asthma, he added.
"There is no simple genetic basis for asthma; it seems to be the end result of many different genetic predispositions," Edelman said.
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