Gene fix for muscular dystrophy defect.

One out of every 3,500 boys born worldwide lacks a functional gene for the muscle protein dystrophin. The deficiency leads to muscular dystrophy, a progressive muscle wasting that begins in childhood. Boys with a complete lack of dystrophin -- who have a severe form of the disease, known as Duchenne's muscular dystrophy -- usually die in their early 20s from suffocation or heart failure.

Researchers seeking a genetic cure for muscular dystrophy have now successfully inserted normal copies of the human dystrophin gene into the muscles of mice born without the critical protein. Although they concede that "the efficiency of this gene-transfer technique needs to be increased before it can be used clinically," they say their achievement holds out hope for an eventual genetic fix for muscular dystrophy.

Using technology developed at Vical Inc. in San Diego, the researchers injected the thighs of the deficient mice with tiny circlets of DNA, called plasmids, containing the dystrophin gene. They report in the Aug. 29 NATURE that roughly 1 percent of the thigh-muscle cells in the mice took up the new genes and made dystrophin, which the researchers detected using labeled antibodies. Moreover, the dystrophin was located in its proper position on the cells' membranes.

"The dystrophin protein was in fact produced by the introduced genes, and was found in places where it's usually seen in normal muscle," says study director Jon A. Wolff of the University of Wisconsin-Madison.

However, when the team injected the same plasmids into the heart muscles of mice, dystrophin appeared in only a handful of isolated clumps. Wolff and his co-workers suggest that inserting new genes into the heart is more difficult because heart muscle cells, unlike those of skeletal muscle, do not fuse together to form large fibers that share proteins.

Last year, a team led by Peter K. Law of the University of Tennessee in Memphis pioneered a cell-transplant approach to treating muscular dystrophy (SN: 6/16/90, p.380). Law's group injected a patient's big toe with immature muscle cells taken from the arm of his father. These cells, called myoblasts, fused with the boy's big-toe muscle and produced dystrophin.

Terence A. Partridge, who first demonstrated the cell-transplant technique in a 1989 experiment with mice, calls Wolff's gene-transfer approach "superior." But myoblast transplants are "far more effective" for the time being, he asserts in an editorial accompanying the new report, because an injection of 100,000 cells can yield dystrophin production in 30 to 40 percent of muscle fibers, spread over a large area. Partridge is a histopathologist at Charing Cross and Westminster Medical School in London, England.