A defective gene has been identified as a root cause of allergies such as hayfever, scientists say.

The gene plays a key role in triggering unwelcome reactions, such as a blocked-up nose, sneezing and itchy eyes, by preventing the immune system from regulating itself properly, they suggest.

Allergic responses are caused when the immune system wrongly identifies allergens such as dust mites, pollen, peanuts or cat hair as being dangerous.

This triggers the release of histamine in the body, which causes minor symptoms such as itching, wheezing, and sneezing but can also prove fatal in the most serious cases.

Researchers hope that the latest findings, published today in the journal PLoS Biology, will allow therapies to be developed that prevent allergies reaching epidemic proportions, by stopping the immune system overreacting in this way.

The research shows that a gene known as GATA-3 can block the development of regulatory cells in the immune system by blocking the action of another gene.

This gene, FOXP3, is key to producing so-called “regulatory T cells”, which control the body’s own immune reactions to prevent healthy cells and tissue from being attacked.

The scientists, from Imperial College, London, and the Swiss Institute of Allergy and Asthma Research in Davos, Switzerland, hope that if they can develop therapies to stop FOXP3 being blocked, they can ensure that regulatory T cells are free to work normally. Regulatory T cells are believed to be vital for averting allergic reactions in healthy individuals because they keep the other cells in check, suppressing the cells that can enact allergic reactions and stopping the immune system from attacking the body needlessly.

The researchers reached their conclusions by analysing the genes related to regulatory T cells and analysing how they interacted. They confirmed their findings by using mouse models to show that mice that were genetically engineered to express the GATA-3 gene in all T cells showed dramatic defects in the production of regulatory T cells.

Carsten Schmidt-Weber, the lead investigator on the research from the National Heart and Lung Institute at Imperial College, said: “This finding will help us to understand how healthy individuals are able to tolerate allergens and what we need to do to reinduce tolerance in the immune systems of patients with allergies.

Dr Schmidt-Weber and his colleague Stephen Durham, also from Imperial College, hope that the new findings will eventually lead to new, more effective treatments for hayfever and other allergies, to be used in combination with existing immunotherapies.

Known risk factors for allergy can be divided into genetic and environmental factors, with heredity being by far the most important of the former.

Although children are more likely to have allergies if their parents also suffer from them, researchers suggest that this may be because of inherited irregularities of the GATA-3 gene or other influences on the immune system, rather than a specific allergen.

It is unlikely that recent increases in the incidence of allergic disorders can be explained by genetic factors alone, however.

The four main environmental factors thought to be causing a rise in allergies are the exposure to infectious diseases during early childhood, pollution, general levels of allergens and dietary changes.

The pressure group Allergy UK claims to speak for 18 million allergy sufferers, while about half that number are estimated to suffer from hayfever.

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