An experimental cell therapy has shown early promise in treating muscular dystrophy (MD), a degenerative fatal muscle disorder that afflicts one in every 3,500 males born in the United States.

University of Tennessee researcher Peter Law reported that the first of eight children with muscular dystrophy given an experimental treatment known as myoblast transfer had shown improvements in muscle function and structure. The patient also had elevated levels of the protein critical to healthy muscle development known as dystrophin, which, due to an inherited genetic defect, MD patients normally cannot produce, Law told the annual meeting of the Muscular Dystrophy Association in Tucson.

"Myoblast transfer holds great promise as a potential therapy for muscular dystrophy and other devastating hereditary muscle diseases," said Leon Charash, chairman of the Muscular Dystrophy Association's medical advisory committee. "Many more questions must be answered and much remains to be done before the procedure becomes a treatment, but Dr. Law's finding is an exciting first sign of success."

Researchers also stressed that the therapy is not a cure for muscular dystrophy but could buy valuable time for MD sufferers while more complete therapies are developed.

The idea behind myoblast therapy dates to the breakthrough discovery in 1987 that the basic defect in the muscles of children afflicted with the Duchenne variant of MD -- the most common form of the disease -- was the absence of dystrophin. Dystrophin acts like a kind of scaffolding in muscle tissue, reinforcing and stabilizing the structure of muscle tissue, and without it MD patients are typically put in wheelchairs before they reach adolescence and die in their early twenties.

Myoblast therapy consists of taking muscle cells from healthy people -- who are capable of making dystrophin -- and injecting them into the muscle of MD patients. Because muscle cells are constantly regenerating, fusing with other "satellite" cells outside muscle fiber, the theory is that the injected cells will join with the abnormal MD cells and produce hybrids capable of producing dystrophin.

This procedure had been shown to work in mice. But the results presented yesterday by Law mark the first time that there has been any evidence the procedure could work in a human. Three weeks after the first injection, Law said he found new muscle fibers containing dystrophin in the big toe of his first patient, where the injection had been given.

"We also found significant improvement in muscle structure and modest improvement in muscle function," Law said.

Law has 10 other patients, three who are waiting for injections and seven who are in the middle of the treatment.

He said he expects a wider range of results soon. Three studies involving the same procedure are either underway or about to begin at other medical facilities in North America.

Muscular dystrophy researchers cautioned about making too mucb of the study. They stressed that the findings were preliminary and that only one child has completed the therapy.

They also said it is not clear that the myoblast therapy, even if it proves successful in the early experiments, will be effective on all muscles effected by MD. For example, many MD patients eventually die from heart failure because of a degeneration of coronary muscle. But injecting muscle cells into the heart would be difficult. And in any case it is highly likely that because of the different way heart muscle grows and functions, myoblast therapy will not work there in the same way it does with skeletal muscle.

"This hopefully will be a stopgap procedure that might stop, slow or even reverse the degeneration of skeletal muscle, until such time as more effective gene therapy could come into play," said Lawrence Stern, research director of the Muscular Dystrophy Assocation. "This is not potentially a cure."