They found the technique was successful, but caution that their experiments on lab mice are still in the early stages and it will be some time before human clinical trials could even be considered.

The findings will be presented Oct. 21 at the American Neurological Association's annual meeting in San Francisco.

"There are viable approaches to gene therapies that don't use viruses," says study author Dr. Thomas Rando, an associate professor of neurology at Stanford's School of Medicine and Medical Center and the Palo Alto VA Medical Center. "Simple plasmid DNA is easy to make, easy to purify and inexpensive."

Muscular dystrophy is an inherited disease caused by a missing or mutated gene. There are many different types of the disorder, such as Duchenne or Becker muscular dystrophy, but all are characterized by muscle weakness and wasting. Some forms of the disease are fatal.

The missing or mutated gene in muscular dystrophy expresses a protein called dystrophin. Any successful gene therapy would have to deliver the dystrophin gene to all of the muscle cells affected by muscular dystrophy.

Rather than try to test the dystrophin gene, Rando and his colleagues used a gene called luciferase. The advantage to this gene is that it emits a light that can be detected using a special camera. This way, the researchers could actually see if the gene was integrating into the cells.

Using lab mice, the researchers injected plasmids containing the luciferase gene into one hind leg and the luciferase gene plus integrase into the other leg.

Soon after the injection, both legs showed signs of the luciferase gene. Over time, however, the leg without integrase lost the luciferase gene. The leg with integrase continued to show signs of the luciferase gene, proving the gene had integrated into the cells' DNA.

Rando says the next step is to see if this technique works with the dystrophin gene.

One of the biggest challenges the researchers face, Rando says, is how to deliver the genes to all of the muscle cells. Currently, they can only deliver the gene locally, by injecting it directly into the muscle.

Another concern is adverse effects, though Rando says he and his team haven't yet seen any using this technique. One of the problems with standard gene therapy is that it uses viruses to deliver the gene. While viruses are quite effective at getting into cells, the body is also primed to mount an immune response against viruses to eliminate them. Also, viruses are small in size and often can't hold larger, therapeutic genes, Rando explains.

Sharon Hesterlee, director of research development for the Muscular Dystrophy Association, says, "This study is significant because they're not using a virus to deliver the gene."

"It's an interesting study and an incremental step in using the plasmid technique, but it's still in the very early stages," she notes.

More information

To learn more about the different types of muscular dystrophy, visit the Muscular Dystrophy Association. For more information on gene therapy, check with the American Society of Gene Therapy.