By Michelle Roberts
Health reporter, BBC News
Blue inhalers contain "reliever" drugs
More than one in 10 children with asthma are taking inhalers that may do nothing for them, UK researchers say.
In Britain alone, 100,000 children - 13% of all children with asthma - carry two copies of a gene that renders the blue inhaler drug salbutamol redundant.
If these children need to use their "reliever" inhaler daily they are 30% more likely to suffer an asthma attack than others, their study shows.
Experts said children should continue to take medication as prescribed.
Co-author Professor Somnath Mukhopadhyay, of the Brighton and Sussex Medical School, said: "Do not stop using your inhaler or change the way you use the inhalers.
"Salbutamol via the blue inhaler is effective reliever treatment in most children but it is common experience among doctors that a proportion of children do not seem to respond to this medicine as well as others."
The reason for this appears to be a genetic variant called Arg16.
Although this gene does not increase an individual's chance of getting asthma in the first place or make their asthma worse, it does seem to alter how well certain asthma medicines will work.
This includes the beta-agonist drug salbutamol which is used for immediate relief of asthma symptoms, and a closely related drug called salmeterol.
Professor Mukhopadhyay, working with Professor Colin Palmer of Dundee University, found children with the genetic variant were less sensitive to salbutamol the more frequently it was used.
During the six months of the study, 70% of the children with the gene and who needed to use their blue inhaler daily experienced asthma attacks compared to 45% of those without the gene, even with the use of other drugs to control asthma, like steroids.
For these children, the researchers believe it may be better to try a different treatment approach, switching to another type of blue inhaler drug that will work rather than stepping up to use more add-on drugs.
Relievers like ipratropium work on different pathways in the body so are unlikely to be affected by Arg16.
It is possible to test for the gene change using a simple mouthwash.
However, the researchers say more studies are needed to see if screening would be beneficial and cost-effective for the NHS.
Poorly controlled asthma is a major problem in young sufferers, leading to in-patient hospital stays, frequent visits to a GP and school absences.
Dr Elaine Vickers, of Asthma UK, said: "It is well-established that over-use of some reliever inhalers can increase a person's risk of having an asthma attack, although the precise reasons for this are still unclear.
"This study adds to the evidence that children with a specific genetic makeup are more likely to be at risk of increased asthma attacks if they use their relievers too frequently.
"We would urge parents to keep track of how often their child uses their reliever inhalers and, if they use them more than three times a week, to take them to see their doctor or nurse to have their symptoms reviewed."
The research on more than 1,000 children is published in the Journal of Allergy and Clinical Immunology.