THURSDAY, Nov. 15 (HealthDay News) -- When injected into mice, a novel compound eliminated the severe muscle stiffness and weakness that is a disabling symptom of one form of muscular dystrophy.

But the research, though promising, is still in its infancy, the investigators and other experts stressed.

"It's an important step forward that should be encouraging for people with the condition and their families and it shows that doctors and scientists are really now beginning to fix their attention on fixing this disease, rather than trying to understand what goes wrong," said study senior author Dr. Charles Thornton, a professor of neurology at the University of Rochester School of Medicine and Dentistry.

Thornton cautioned that he would not use the term "breakthrough" to describe the results, however.

"It's an important first step and these results are encouraging that effective therapies for myotonic [muscle-stiffening] dystrophy can be developed that can actually ameliorate some of the clinical symptoms," added Dr. Valerie Cwik, medical director and vice president of research at the Muscular Dystrophy Association (MDA). "But this is a study in mice, and we know from lots of other disorders and studies in mice that what works in mice doesn't always translate into effective therapy in humans."

According to the MDA, myotonic dystrophy is one of nine forms of muscular dystrophy, a group of genetic, degenerative and potentially disabling diseases which primarily affect voluntary muscles.

Myotonic dystrophy type 1 is the most common form of muscular dystrophy affecting adults. It is caused when a section of DNA is repeated on either chromosome 19 or chromosome 3.

"Myotonic dystrophy affects multiple systems in the body, so it causes central nervous system problems with altered cognition in some people, sleep disturbances, cataracts, droopy eyelids, not only myotonia," Cwik explained. Myotonia involves a "difficulty relaxing muscles but also muscle weakness, which is actually more disabling for many people," she said. It also involves "intestinal problems and, importantly, it can affect the heart, with potentially life-threatening arrhythmias," Cwik explained. "It's a multi-system disorder."

"Presently there is no cure. There are some treatments that help manage symptoms. They're not highly effective," Thornton added. "The disease has been known for 100 years but, until about six years ago, hardly anything was understood about what causes muscle problems. Now there are detailed theories about what's going wrong. This was an attempt to test one of those to see if symptoms could be fixed."

Five years ago, Thornton's team showed that a genetic flaw leads to the overproduction of a certain type of messenger RNA (mRNA) in cells, which affects muscle control and other cellular functions.

The current study, published online Nov. 15 in the Journal of Clinical Investigation, focuses on myotonia.

The researchers postulated that myotonia was caused by a problem with the pathway that electrical charges use to move in and out of muscle cells.

When researchers injected a synthetic molecule directly into the muscles of mice with myotonic dystrophy and then corrected the electrical control problem, the symptoms were eliminated.

"When a particular chemical imbalance in the muscle tissue was restored, it eliminated stiffness," Thornton said. "This would be a partial solution to the person's symptoms with myotonic dystrophy, but it's also proof of principle that once we identify the cause that it can be corrected."

Considerably more work is needed, however.

For one thing, scientists need to find a way to inject the compound into a person's bloodstream so a systemic effect would take place. Injecting into muscles spurs only a local effect. "That's one obstacle that must be overcome in getting wide distribution," Thornton said.

Safety issues also have to be considered before human trials begin, Cwik added.

"They are only looking at one symptom of myotonic dystrophy," she noted. "Would this therapy or kind of therapy, which can reverse or eliminate myotonia, have any effect on some of the other potentially more disabling symptoms? While it's encouraging, there are a lot of cautions and caveats."

More information

There's more on myotonic dystrophy at the Muscular Dystrophy Association.