But the effort paid off. Duan's team evaluated the mice after 10 months and found that the new gene had managed to spread through their hearts, producing dystrophin and keeping the heart muscle from deteriorating. Duan and Chamberlain's study, published in the journal Circulation, was the first to attempt virus-mediated gene therapy for DMD in heart muscle.

"When I started working on this disease I realized that most people were working on skeletal muscles," Duan said. "But one in five people with muscular dystrophy die of heart disease. If you want to cure muscular dystrophy, you have to work on the heart."

While the micro dystrophin gene significantly improved the condition of the mouse hearts, Duan wasn't convinced that it contained enough genetic information to serve as a cure for DMD.

So he developed a second way to pack more of the dystrophin gene into the virus. To do that, Duan has used a larger engineered dystrophin "minigene" that is about half the size of the actual gene. Even at this size, the gene is too big to fit into AAV. Duan solved this problem by cutting the gene in half, putting each part into separate viruses, and then injecting his mice with both vectors. If the gene was split just right, he reasoned, the two pieces would recombine once in the muscle cells and then start producing dystrophin.

Duan's team, which includes postdoctoral fellows Yi Lai, Mingju Liu and graduate students Arka Ghosh and Brian Bostick, injected the gene-loaded viruses into the leg muscles of DMD-affected mice. In areas where the virus had been injected, the researchers found minidystrophin molecules in 40 percent or more of the muscle fibers. The minidystrophin increased the fibers' strength and protected them from damage.

"After our paper was published [in Nature Biotechnology], researchers jumped at this, but they didn't realize you have to find the right place to split the gene," Duan says. "If you split it in the right place you can get nearly 100 percent [recombination]. If you split in the wrong place you may get zero percent."

Duan expects this two-vector strategy to prove useful in delivering other therapeutic genes that are too large to fit into AAV. These include cystic fibrosis, hemophilia A and a retinal disorder called Stargardt's disease. Duan and his team also have several other MD-related research projects in the works. Key to these projects, Duan says, is developing better lines of animal models.

He points, for instance, to his current crop of experimental mice. They lack dystrophin, as do people with MD, but don't become as ill. They grow weak but survive into old age. So Duan is working on a new strain of mice whose condition more closely mimics the human disorder. He says their first gene therapy attempt in this new model has shown promising results. It was published online in the journal Molecular Therapy on March 21.

Published by the Office of Research.

©2006 Curators of the University of Missouri. Click here to contact the editor.