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Researchers have found a gene that, when flawed, causes a rare but life-threatening form of muscular dystrophy known as Emery-Dreifuss, Italian researchers said Wednesday.

The gene carries instructions for a protein, dubbed emerin, that appears to play a role in healthy muscle cells, the researchers reported in the journal Nature Genetics.Scientists, led by Silvia Bione of the Institute of Biochemical Genetics and Evolution in Pavia, Italy, noted the gene's remarkably small size may be an advantage in developing gene therapy approaches to treat the disorder.

"The implications of this work are far-reaching," said Dr. Arnold Gale, a neurologist in Santa Clara, California, and the medical information officer for the Muscular Dystrophy Association, who supported the project.

"The finding is not only important in this disease but in understanding what goes wrong in other muscular dystrophies."

Emery-Dreifuss muscular dystrophy affects males, usually in young adulthood or middle age, causing progressive weakness of skeletal muscles, joint contractures and heart problems.

The heart problem common in Emery-Dreifuss is known as cardiac conduction block and is the most serious aspect of the disease. A cardiac pacemaker can prevent death from conduction block, but patients must be identified and treated early for this condition.

"This disease has a prominent feature that is dangerous - the heart problem, which is what usually results in death," Gale said.

"The heart problem can be treated, but early diagnosis is essential. We've got to know who those people are; now we will know earlier."

The findings released in the Nature Genetics report, by speeding accurate diagnosis, will help prevent cardiac deaths, Gale said. They also may increase understanding of the causes of conduction blocks in people with heart disease.

Bione and her colleagues studied eight genes in a small region of the X chromosome and found that the people they studied with Emery-Dreifuss dystrophy have a mutation in one of these genes.

The mutations were found only in males with the disorder and female carriers of the disorder.

A genetic test that can identify the carriers or potential sufferers should be available within a year, Gale said.

Investigators think the emerin protein may play a role in transporting substances inside vesicles, or packets, in muscle cells.

Other researchers have found more than 20 genes for neuromuscular diseases since 1986, when they found the gene for the more common Duchenne and Becker muscular dystrophies.