A preliminary study at the University of California-San Diego has found promising signs that using gene therapy to introduce nerve growth factor into the brain may be able to retard the progression of Alzheimer's disease.

The team, led by Dr. Mark Tuszynski, studied five women and three men, with an average age of about 70, who were in the early stages of Alzheimer's disease.

The study was focused on determining the safety of the procedure and not its effectiveness. But in the process, the researchers found that the treatment delayed progression of the disease by 40 percent to 50 percent for at least two years, Tuszynski said.

By contrast, the Alzheimer's drugs now available delay progression only about 5 percent, and the effects persist for only about six months, he said.

"If the magnitude of these effects is borne out in larger, controlled trials, this could be a significant advance over existing therapies for Alzheimer's disease," said Tuszynski, who presented the results yesterday at a San Francisco meeting of the American Academy of Neurology.

The team is already planning a larger follow-up study whose results should be available in about a year and a half, Tuszynski said.

If everything goes well, the treatment could be widely available in about four years, he added.

The San Diego researchers collected skin cells from each patient, genetically engineered them to produce nerve growth factor, then implanted them through needles inserted into the center of the frontal lobe, which is important in memory and cognitive function.

The patients underwent standard cognitive testing before and after the surgery and the rate of their decline was estimated by physicians.

The patients also underwent Positron Emission Tomography imaging, which showed a sharply increased metabolic rate in the region of the brain where the cells were implanted.

The new clinical trial will use a somewhat simpler procedure that has proved equally effective in animal studies. Instead of using skin cells, surgeons will simply inject the vector -- the virus used to modify the skin cells in the earlier studies -- directly into the affected area of the brain, where it will insert the nerve growth factor gene directly into brain cells.