Parents, brothers and sisters of diabetes patients are testing a novel treatment for the disease in a national study which scientists call "the first of its kind."

The National Institutes of Health announced last week the launching of a study that may lead to Type I diabetes prevention.

A select group aged three to 45 at high risk of developing Type I diabetes will be treated with small doses of insulin to prevent the disease. Currently, insulin is only used to treat those already afflicted with the disease.

"We're hoping that insulin treatment before the disease expresses itself will prevent the disease altogether," says Dr. R. Paul Robertson, professor of medicine at the University of Minnesota. "In the best of all possible worlds, this method would prevent or delay Type I diabetes," he says.

The University of Minnesota is one of ten participating centers for the national study, which is being conducted by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). At Boston's Joslin Diabetes Center, which is also participating, the study is being led by Associate Professor of Medicine Dr. Richard A. Jackson.

Type I or juvenile-onset diabetes occurs when a body's immune system attacks the cells that create insulin. Insulin is necessary for the body to break down sugars for energy. The disease progresses slowly with few symptoms.

Type I diabetes particularly afflicts children and teenagers, with 11,000 new cases reported every year. It often leads to serious complications, including heart, nerve, eye and kidney disease.

The study will span seven years, with an actual trail period of four years. High risk participants will be injected with insulin while lower risk subjects will take the insulin orally. The insulin injection trial is now underway, and the oral insulin trial will start next year.

The study will screen between 60,000 and 80,000 people within the next four years, hoping to find 830 people that will be classified as "high risk."

"Over the past decade, using a combination of tests, it has become possible to predict, with considerable confidence, who is at risk of developing diabetes over the next several years," says Dr. Jay Skyler, professor of internal medicine at the University of Miami.

The doctors will first look for people with antibodies that attack cells which produce insulin. They will then try to identify people who release little insulin when injected with glucose.

People who fit both of these criteria have a 50% greater risk of developing Type I diabetes within five years than the general population, Robertson says.

Parents, siblings or children of diabetics are prime candidates for the study, since they are most likely to have the antibodies that kill insulin-producing cells.

Two theories new exist to explain why giving potential diabetics low doses of insulin may slow, or even stop, the progress of the disease.

In high-risk patients, there are few insulinmaking cells. Injected insulin would allow the cells that do create insulin to "rest," says Dr. Darell M. Wilson, associate professor of pediatrics at Stanford University Medical School.