A pill that can correct a wide range of faulty genes which cause crippling illnesses should be available within three years, promising a revolution in the treatment of thousands of conditions.

The drug, known as PTC124, has already had encouraging results in patients with Duchenne muscular dystrophy and cystic fibrosis. The final phase of clinical trials is to begin this year, and it could be licensed as early as 2009.

As well as offering hope of a first effective treatment for two conditions that are at present incurable, the drug has excited scientists because research suggests it should also work against more than 1,800 other genetic illnesses.

PTC124 targets a particular type of mutation that can cause very different symptoms according to the gene that is disrupted. This makes it potentially useful against a range of inherited disorders.

The same drug could be given to patients with Duchenne muscular dystrophy, the most serious form of the muscle-wasting condition, cystic fibrosis, which mainly affects the lungs, and haemophilia, in which the blood does not clot. It can be taken orally, and safety trials have not revealed any major side effects.

“There are literally thousands of genetic diseases that could benefit from this approach,” Lee Sweeney, of the University of Pennsylvania, who is leading the research, said. “What’s unique about this drug is it doesn’t just target one mutation that causes disease, but a whole class of mutations.”

In most genetic conditions, between 5-15 per cent of cases are caused by a defect called a “nonsense mutation”. Genes are instruction manuals for cells to make proteins, but nonsense mutations in effect introduce a command halfway through that stops production. The kind of protein disrupted determines the nature of the disease.

In Duchenne muscular dystrophy, for example, the protein necessary for normal muscle development is not made, and the fatal wasting disease is the result. In haemophilia, it is the gene for the clotting agents factor VIII or factor IX that is disrupted.

PTC124 works by binding to a part of the cell called the ribosome, which translates genetic code into protein, and allows it to ignore nonsense mutations. The gene can be read straight through and a normal protein is produced.

The beauty of the drug is that it should be useful with any disease caused by a nonsense mutation, no matter what its outward effects. The error is not corrected, but ignored. Patients would have to take the pill throughout their lives.

PTC124, which is made by PTC Therapeutics, has been staggeringly successful in animal models. A study published today in Nature shows that in mice with a nonsense mutation that causes Duchenne muscular dystrophy, the drug starts dystrophin production and restores their muscles to health.

The drug has passed safety trials in humans, and the results of phase-two trials on cystic fibrosis and Duchenne muscular dystrophy will be published shortly.

About 13 per cent of patients with Duchenne muscular dystrophy have a nonsense mutation and should respond to the drug. It would not be suitable for treating different mutations in the dystrophin gene, or diseases not caused by nonsense mutations.

Other diseases that can be caused by nonsense mutations include beta thalassaemia, a blood disorder, and Hurler syndrome, in which children’s mental and physical development stops and most patients die by the age of 10.

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