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Release: March 4, 1999

UI study reveals important information about molecular defect in muscular dystrophy

IOWA CITY, Iowa -- For the first time ever, University of Iowa researchers have confirmed how a protein complex, when defective, causes limb girdle muscular dystrophy.

This information could help scientists to develop new ways to treat limb girdle forms of muscular dystrophy. Limb girdle varieties affect between one in 20,000 and one in 50,000 individuals.

"We have established a cell culture system that we can use to mimic the defect in limb girdle muscular dystrophy," said Kevin Campbell, Ph.D., UI professor of physiology and biophysics, and neurology, and a Howard Hughes Medical Institute Investigator.

The UI findings appeared in a recent issue of the Journal of Biological Chemistry.

Campbell, along with Kate Holt, Ph.D., a postdoctoral fellow in Campbell's lab, used the cell culture system to find out how the protein complex, called the sarcoglycan complex, forms. The sarcoglycan complex, composed of four distinct transmembrane glycoproteins, is part of the dystrophin-glycoprotein complex, a group of proteins located in muscle cell membranes. The dystrophin-glycoprotein complex is thought to stabilize the membrane against contraction-induced damage. Past studies have shown that mutations to the sarcoglycan complex cause various types of limb girdle muscular dystrophy.

Muscular dystrophy is a group of diseases characterized by hereditary progressive muscle weakness and degeneration. The unifying theme among limb girdle varieties of the disease is the initial involvement of the shoulder and pelvic girdle muscles, with relative sparing of most other muscle groups.

Despite rapid advances regarding the genetic defects that cause limb girdle muscular dystrophy, researchers know little about the molecular defects underlying the disease. Through their cell culture model, Campbell and Holt were able to show that complete assembly of the sarcoglycan complex is dependent on the simultaneous synthesis of all four sarcoglycans. Any mutant sarcoglycan blocks the complex formation and its insertion into the plasma membrane. Campbell and Holt's confirmation of how the sarcoglycan complex develops is a step toward learning more about the basic molecular underpinnings of the disease.

"If we can determine where the defect or blockage of the biosynthesis occurs, then that might give us a clue as to a way that we could potentially treat the disease," Holt said.

One potential treatment could involve developing pharmacological reagents that would allow proteins with mutations to be properly expressed, Campbell added.

"We're going to use the model to further study the sarcoglycan complex," Campbell said. "Now that we can synthesize the complex in the laboratory, it will be easier to study the function of these proteins and the molecular pathogenesis of limb girdle muscular dystrophy."