A common treatment for asthma may be having little effect on a large number of young people who have the condition.
Salmeterol is prescribed by the health service to treat asthma
A gene variation present in some of the population means sufferers could be getting no benefit from the use of the medicine salmeterol.
The claims come from Dundee University researchers, who are looking into the development of "personalised medicine".
Experts hope that improvements in genetic information will lead to the more effective use of drugs.
The researchers found that a specific genetic variant, known as the Arg/Arg-16, caused salmeterol to be ineffective.
They found that 13% of young asthma sufferers in Tayside possessed the variant.
Those with the variant have almost double the number of asthma attacks compared to those with the other forms of the gene, it was claimed.
Dr Somnath Mukhopadhyay, who led the Dundee team, said: "It was apparent that some patients with asthma could be failing to respond to inhaled salmeterol, but we have identified a likely cause for this that is linked to this genetic status.
"Where this discovery takes us is towards more personalised asthma treatment, where we can identify which medicines can be used or avoided depending on an individual's genetic profile and we can ensure the best possible treatment."
Salmeterol is prescribed by the NHS asthma patients who fail to respond well to inhaled steroids.
There are 5.2 million people in the UK currently receiving various forms of asthma treatment, with an estimated 675,000 carrying the Arg/Arg-16 variation.
The results of the Dundee project have been published in the chest medical journal Thorax.