A potential breakthrough in the treatment of motor neurone disease has been announced by scientists in the US who have prolonged the survival of mice suffering from the same fatal disorder of the nervous system.

The researchers used a radical form of genetic treatment to protect vital nerve cells in the brain and spinal cord that would otherwise degenerate in motor neurone disease. As a result of the gene therapy, the average lifespan of the mice doubled and there was a delay in the onset of symptoms which, in humans, result in a gradual and total paralysis of the muscles.

The scientists claim that the results are the best that anyone has achieved with motor neurone disease, and say they expect to start clinical trials on humans next year - though it will still be many years before it is approved for wider use.

The study, published in the journal Science, was carried out by a team led by Fred Gage, professor of genetics at the Salk Institute in La Jolla, California, and Jeffrey Rothstein, professor of neurology and neuroscience at Johns Hopkins University in Baltimore, Maryland.

Using a type of common cold virus genetically engineered with a gene for insulin-like growth factor (IGF-1) - a protein that can protect nerve cells - the scientists gave the mice injections into their muscles.

The virus carried the gene into the nerves and to the brain and spinal cord, where it counteracted the effects of the disease, Professor Gage said.

Mice treated with the IGF-1 gene at 60 days of age developed symptoms 31 days later than untreated mice, and lived 40 days longer.