Asthma may cause, rather than be caused by, allergies.

An international study by the GABRIEL consortium, a collaboration of 164 scientists from 19 countries in Europe, co-ordinated by researchers from Imperial College London, has analysed DNA samples from 10,000 children and adults with asthma and 16,000 non-asthmatics. Having performed more than half a million genetic tests on each subject, covering all the genes in the human genome, the study has pinpointed seven locations on the genome where differences in the genetic code are associated with asthma.

The causes of asthma (in which the airway is irritated, narrows and becomes in flamed thus causing difficulty breathing) are poorly understood but genetic and environmental factors had always been thought to play roughly equal roles. However, the study 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 – which suggests that environmental factors are very important in causing asthma to develop.

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.
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.

Childhood asthma (affecting more boys more than girls and often persisting 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. This does not mean that allergies are not important, but it does mean that concentrating therapies only on allergy will not effectively treat the asthma.

News release from Imperial College


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