A team of researchers will soon try out an experimental drug that could prevent Alzheimer's disease in a group of people with a genetic mutation that makes it likely they will develop the debilitating condition.

Scientists will begin a clinical trial of crenezumab in about 300 Colombians whose genes predispose them to a rare form of Alzheimer's that hits very early - usually in the 40s or 50s - and can affect multiple members of the same family.  Funding for the study is provided by the National Institutes of Health, Genentech and the Banner Alzheimer's Initiative.  Genentech is the developer of the experimental drug.

There will also be a subjects with the same mutation recruited in the U.S., but those people still need to be identified.

"Clinical trials will be done at a time when a patient has no symptoms.  We're trying to stop or slow the onset of the disease in this group of patients," said Richard Scheller, executive vice president of research and development at Genentech.  "We know when they will contract the disease because of the numerous studies that have been done on the mutation.

Dr. Pierre N. Tariot, director of the Banner Alzheimer's Institute, said in a statement to ABC News that the implications for the trial are huge.

"If this approach to fighting Alzheimer's is successful, it has the potential to transform all future prevention and treatment research and to herald the beginning of the end of this devastating disease," Tariot said.

The drug acts on a substance known as ABeta.  Scheller explained that ABeta is a major component of the brain plaque that is a characteristic of Alzheimer's disease.

"The mutation causes a more rapid accumulation of ABeta in the brains of people who have it.  It activates the enzyme that produces the ABeta," he said.  The clinical trial, he added, will help answer the question of whether ABeta is definitely responsible for this rare form of the disease.

There are also separate clinical trials underway looking at the effects of crenezumab on mild to moderate Alzheimer's disease.

Experts not involved with the crenezumab research thus far say preventing Alzheimer's from ever happening is more promising than treating it once symptoms start appearing.  Drugs that are available now only target symptoms, not the mechanisms that cause the disease.

"In people who already have the disease, early data with this drug suggest the disease-modifying effect is not huge.  It may already be too late," said Dr. John Ringman, associate clinical professor of neurology at the Easton Center for Alzheimer's Disease Research at UCLA.  Ringman is involved in research that could help identify Alzheimer's patients before their symptoms appear, which could help identify potential American subjects for the crenezumab research.

"Plaque has been accumulating and many neurons are already damaged.  It may difficult to stop the course of the disease at that stage," said Scheller.

Dr. Gary Small, also at UCLA, said the research may help answer other questions as well.

"The positive thing about it is that they're going after the disease early and going after a reasonable target," he said.  "The risk is that it may not be enough to prevent the disease.  ABeta may not be the only thing going on in the brain."  Small is director of the UCLA Longevity Center and author of "The Alzheimer's Prevention Program."

If the results of the research do show promise in preventing the onset of Alzheimer's, Ringman and Scheller said that could eventually lead to studies of other genetically determined forms of the disease.

The clinical trial is expected to begin in 2013 and continue until 2018.