Scientists have been given the go-ahead to start trials to test whether gene therapy can slow the progress of the degenerative disorder Alzheimer's disease.

They believe the technique, if shown to be successful, could also be used to improve the brain function of people who are not suffering from dementia.

New Scientist magazine reports that the researchers, led by Mark Tuszynski, of the University of California, San Diego, believe a substance called nerve growth factor (NGF) can prevent the death of cells in the brain known as cholinergenic neurons, and stimulate new connections between the cells.

Experiments on rodents and primates have shown that NGF can reverse memory loss.

US authorities have given permission for the impact of NGF to be tested on eight people with early Alzheimer's disease who are able to understand and consent to the procedure.

The researchers will take cells called fibroblasts from the patients' skin and genetically engineer them to produce NGF. This will be done by adding extra copies of the gene using a mouse leukaemia virus modified to ensure it does not trigger cancer.

The cells will then be injected into the patients' brains.

The main aim of the trial is to assess the maximum dose of modified cells that can be safely injected.

However, the scientists will also monitor whether the progress of the Alzheimer's disease is slowed.

Cautious welcome

Dr Richard Harvey, director of research for the Alzheimer's Society, gave the trials a "cautious welcome" but warned the use of NGF as a treatment was a long way off.

He said previous research that had tried infusing NGF directly into the brain had produced very unpromising results.

However, he said the new technique could be an improvement as it would allow a steady supply of NGF to be produced in the brain.

Dr Harvey said: "You would need to demonstrate the treatment was very effective before it could be widely used in people with Alzheimer's."

NGF could never be a cure for Alzheimer's, he said, but it might be possible to slow down the progress of the disease to the point where sufferers would have a normal life expectancy.

Alzheimer's disease is a progressive, degenerative and irreversible brain disorder that causes intellectual impairment, disorientation and eventually death.

It is estimated that 2-5% of people over 65 years of age and up to 20% of those over 85 years of age suffer from the disease.