Treatment neutralizes muscular dystrophy in mice

* Mice regained use of affected muscles

* Technology already being used in humans

CHICAGO, July 16 (Reuters) - U.S. researchers have found a way to block the genetic flaw that causes a common form of muscular dystrophy, the team reported on Thursday.

Mice injected with a compound that neutralizes faulty gene activity regained the use of muscles frozen by myotonic dystrophy, the researchers said.

“We haven’t corrected the underlying gene abnormality,” said Dr. Charles Thornton of the University of Rochester in New York, whose study appears in the journal Science.

“What we’ve done is made it behave in a more mannerly fashion,” Thornton said in a telephone interview.

The research relies on a technology called antisense, which uses synthetic molecules to block the activity of specific genes. Several companies, including Isis Pharmaceuticals ISIS.O, are developing drugs using this approach.

Thornton said unlike many inherited diseases in which faulty genes make faulty or missing proteins, myotonic dystrophy makes a toxic form of ribonucleic acid or RNA, which carries genetic instructions for making proteins.

In myotonic dystrophy, however, the RNA is toxic to cells, Thornton said.

“This RNA has proteins that get stuck on it,” he said.

Myotonic muscular dystrophy, which affects 40,000 people in the United States alone, is marked by the inability to relax muscles.

Thornton said people with myotonic dystrophy have all the ingredients for a healthy body. “It’s just that some proteins are in the wrong location,” he said in a telephone interview.

To fix that, Thornton’s team used antisense to create bits of genetic material that lock on to faulty RNA.

Usually, antisense drugs destroy the offending RNA, but Thornton’s lab designed a molecule to simply neutralize the toxic RNA.

“We didn’t want to destroy it. We simply wanted to get something that would bind to it, and release the stuck proteins so they can do their job,” Thornton said.

When they injected this compound into muscle tissue in mice with myotonic dystrophy, the stuck proteins were released and resumed normal function, allowing muscles to relax properly.

Thornton said the study shows promise for a new treatment for humans, but the team is looking for a better way of getting the treatment into the body than direct injection into affected muscles.

And they need to study whether muscles that have wasted away because of the disease can be restored to normal size and tone after treatment.

“There’s reason to be hopeful,” he said.

Editing by Maggie Fox and Eric Walsh