Researchers Discover Gene Connected To Rare Muscle Disease

While the researchers studied mice, they are now looking for patientswho have mutations in this newly discovered muscle gene, Srpk3. Micethat lack the gene have a condition much like the human disease,centronuclear myopathy.

"It's easy to imagine that human patients could have symptoms similarto those we saw in mice," said Dr. Osamu Nakagawa, assistant professorof internal medicine and the paper's lead author. "The human researchis just starting, but already we found patients who may have mutationsin the gene."

The researchers' work appears in the Sept.1 issue of Genes and Development.

There are several forms of centronuclear myopathy, including one thatis apparent at birth. Children with the condition have trouble movingor breathing and often must depend on ventilators. Other forms show uplater in life.

"Treatment may be in the far distant future, but I think diagnosis isvery important," Dr. Nakagawa said. Knowing the form of the conditioncould guide treatment, for instance.

Dr. Eric Olson, senior author and chairman of molecular biology, said,"The discovery of this new muscle gene is very exciting because itsheds light on a biochemical process involved in the muscle-wastingdisorder centronuclear myopathy. This information represents a firststep toward potential therapies to improve muscle function duringdisease." Dr. Olson directs the Nancy B. and Jake L. Hamon Center forBasic Research in Cancer and the Nearburg Family Center for BasicResearch in Pediatric Oncology.

The first stage of the UT Southwestern study involved searching forimportant muscle genes downstream of muscle-specific gene regulation.Scientists have known that one protein, called MEF2, is essential tothe formation of skeletal muscles and heart, but didn't know its exactmechanism.

The researchers found that one of MEF2's jobs is to activate the genethey discovered, Srpk3. Dr. Nakagawa compared Srpk3 to a light bulb andMEF2 to the switch: MEF2 binds to DNA, and that action turns on thegene that creates the Srpk3 protein.

You need both genes for normal function, he said. "If you have a switch but no light bulb, the room would remain dark."

The second part of their study was to see what happened in two groupsof mice: one without the Srpk3 protein, and one with too much.

In both cases, the muscles were defective. Most of the group withoutSrpk3 showed the same defect as people with centronuclear myopathy --the nuclei of their muscle cells were in the center of the cellsinstead of at the edges where they are normally.

The mice with too much Srpk3 also showed marked muscle damage. Theirmuscles degenerated, and they showed deformities. They died at about 2months of age or earlier.

"Srpk3 could be an additional disease gene," Dr. Nakagawa said. "It'sstill a hypothesis. We are trying to be very careful and conservativein discussing possible human mutations, but we are actively analyzingthe functions of mutations in Srpk3."

The next step is to find what Srpk3 does -- for instance, does it acton a particular protein that the researchers can identify, Dr. Nakagawasaid. They know Srpk3 is a molecule that regulates functions of otherproteins in the cells, but they have to find which proteins are itstargets. By studying what the Srpk3 protein does, they will try to findout if it directly causes disease in humans.

Other UT Southwestern researchers involved in the study were Dr. MasayoNakagawa, senior research associate in internal medicine; Dr. HideakiHamada, former postdoctoral fellow in molecular biology; John Shelton,senior research scientist in internal medicine; Dr. James Richardson,professor of pathology and molecular biology; and Michael Arnold, afellow in the Medical Scientist Training Program. Researchers at theUniversity of Iowa Roy J. and Lucille A. Carver College of Medicine,the Albert Einstein College of Medicine of Yeshiva University, and theNational Center of Neurology and Psychiatry in Tokyo also contributed.

The work was supported in part by the Muscular Dystrophy Association,the National Institutes of Health and the Robert A. Welch Foundation.