Asthma researchers have identified seven genetic variants that greatly increase the risk of developing the condition, and their findings could lead to better treatments. The results of the largest genetic study of asthma could improve the lives of sufferers through new therapies and drug treatments.

The findings of the GABRIEL consortium, which includes St George’s, University of London, suggest that asthma is not caused by allergies, as had been thought, but that allergies are a consequence of the disease. They also show that adult-onset asthma and childhood asthma are different diseases. And they suggest that genetic testing would not help predict who is likely to develop asthma.

The study was led by Imperial College London, and was co-authored by David Strachan, professor of epidemiology ay St George’s, in partnership with scientists from 19 European countries as part of the GABRIEL consortium.

The team conducted half a million genetic tests on the DNA of 26,000 people – 10,000 with asthma and 16,000 without – covering all the genes in the human genome. They pinpointed seven locations on the genome where differences in the genetic code were associated with asthma.

“Asthma is a complex disease in which many different parts of the immune system can become activated," said Professor William Cookson, director of respiratory sciences at Imperial College London, who coordinated the study. "One of the problems with asthma research has been choosing where to intervene in the disease pathways. Our study now highlights targets for effective asthma therapies, and suggests that therapies against these targets will be of use to large numbers of asthmatics in the population. "

One in seven children in the UK suffers from asthma. When the airway is irritated in a person with asthma, the airway narrows and the lining becomes inflamed, causing difficulty breathing. The causes of the disease are poorly understood, but genetic and environmental factors are thought to play roughly equal roles.

The new variants linked to asthma were found in more than a third of children with asthma in the study. The gene with the strongest effect on children did not affect adults, and adult-onset asthma was more weakly linked to other genetic differences, suggesting that it may differ biologically from childhood-onset asthma.

Prof Strachan said: "Asthma has often been considered a single disease, but our genetic findings suggest that childhood-onset asthma may differ biologically from asthma that is acquired in adult life. The GABRIEL consortium is now investigating whether the causes of asthma differ between people with and without these newly discovered genetic variants."

Childhood asthma, which affects boys more than girls and can persist throughout life, is often linked to allergies, and it has been assumed that these can trigger the condition. However, the study found that genes controlling the levels of antibodies that cause allergies had little effect on the presence of asthma, suggesting that allergies are more likely to be a consequence of asthma than a cause.

Professor Miriam Moffatt, professor of human genetics at Imperial College London and one of the study's leaders, said: "As a result of genetic studies we now know that allergies may develop as a result of defects of the lining of the airways in asthma. This does not mean that allergies are not important, but it does mean that concentrating therapies only on allergy will not effectively treat the whole disease."

Some of the genes identified are involved in signalling pathways that tell the immune system when the lining of the airways has been damaged. Other genes appear to control how quickly the airways heal after they have been injured. Identifying these genes should help direct research into new treatments for asthma, the researchers suggest.

The study also found that the genes associated with asthma did not have strong enough effects to be useful for predicting early in life which children might eventually develop the disease. This indicates that environmental factors are also very important in causing asthma to develop. The GABRIEL consortium is working to identify environmental exposures that could protect against the illness.

Professor Erika von Mutius at the University of Munich and cocoordinator of GABRIEL said: "The puzzle now is to work out what is causing the damage to the airway lining in asthma. The GABRIEL study has also been busy looking for clues as to the environmental causes of asthma, particularly by dissecting the strong protective effects of living on a farm. In the next year we will be combining the results from the genetic and environmental wings of the GABRIEL study, and we are greatly looking forward to what we may find."

The study was primarily funded by the European Commission, the French Ministry for Higher Education and Research, the charity Asthma UK and the Wellcome Trust.