British researchers are to trial a new gene therapy for cystic fibrosis in which sufferers simply inhale a spray laden with DNA.

The announcement comes just days after Gordon Brown, the chancellor, and his wife Sarah announced that their four-month-old son Fraser had been diagnosed with the inherited condition.

If it works, the £20m programme could lead to a treatment that will improve and extend the lives of thousands of cystic fibrosis sufferers around the world.

“I’m optimistic. We’ve harnessed the best scientific talent in the UK and they’re very focused,” said Rosie Barnes, chief executive of the Cystic Fibrosis Trust, the charity that is funding most of the cost of the trial. “If anybody’s able to do it, they are.”

The disease is caused by a defective gene that causes the lungs and airways to fill with sticky mucus, which acts as a breeding ground for bacteria.

About one in 25 people unwittingly carry a copy of the defective gene. but it proves harmful only if a child is unlucky enough to inherit two copies, one from each parent.

About 10,000 people in Britain have cystic fibrosis. Most can expect to live no more than 31 years and much of their life will be spent struggling to control the symptoms, which can include liver failure and diabetes.

Researchers emphasise that such trials must be treated and publicised with caution for fear of raising false hopes among sufferers. It will also take at least three years for the early results to emerge.

However, the large-scale medical trials follow studies in animals and smaller trials in humans that have already hinted at powerful benefits.

Professor Eric Alton, a specialist in gene therapy at the Brompton hospital and Imperial College London, who is leading the study, said it would involve 200 patients at the Brompton in London and at the Western general hospital in Edinburgh.

Half of these would be given the genuine therapy and half a “dummy” treatment. Then their conditions would be compared to see if the therapy had made a significant difference.

If the results are promising, the scientists expect to team up with one or more private partners willing to stand the cost of a worldwide trial involving a great many more patients.

The costs of this could run into hundreds of millions of pounds, but early discussions are already under way with a number of candidate companies.

The technique being tested involves the use of a nebuliser that injects a fine spray into the airways. Within the spray are tiny soap-like bubbles called liposomes containing DNA without the cystic fibrosis defect.

The liposomes fuse with the outer surfaces of cells lining the lungs and the DNA passes by natural processes into their nuclei.

Once installed, it is hoped the DNA will prompt the cells to make the essential protein lacking in cystic fibrosis sufferers.

Because of the constant replacement of cells in the body, the treatment would have to be taken repeatedly to sustain its effect.

The scientists do not expect to provide a full cure, but Alton said: “What makes this trial very novel is that we will for the first time be trying to achieve clinical improvement rather than just alleviating symptoms.”

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