GENE THERAPY FOR DMD WORKED IN DOGS, WITH IMMUNOSUPPRESSION

MDA-supported researchers John Howell of Murdoch University and the Australian Neuromuscular Research Institute in Western Australia and George Karpati of the Neuromuscular Research Group at Montreal Neurological Institute were members of a team that recently showed that gene therapy using a gene for the muscle protein dystrophin can be successful in dogs if their immune systems are suppressed with drugs. Dystrophin is the protein missing in boys with Duchenne muscular dystrophy (DMD).

The scientists, who published their work in the March 20 issue of Human Gene Therapy, transferred genes for dystrophin into a leg muscle in the dogs, using a modified adenovirus as a gene carrier (vector). The approach they used is similar to the one planned for human use in the near future. The size of dog muscles, compared to those in mice, allows researchers to better predict human response.

Dogs that received the immunosuppressive drug cyclosporine showed prolonged production of dystrophin in the injected leg muscle after two months, while the dogs that received no immunosuppression showed declining levels of dystrophin in the injected muscle over the same time.

The findings suggest that immunosuppression may be necessary for such gene transfers, the authors note in their paper. However, they also note that there are better gene vectors available now that may help transferred proteins evade the immune system.

Karpati added that dogs can't tolerate the immunosuppressant known as FK506 but that humans can. This drug, which may be superior to cyclosporine, is the one being considered for use in human gene therapy trials.

"I think that there is great potential in gene therapy for DMD in humans," Howell commented. "I believe that with the vectors currently in use, immunosuppression will be required, but results obtained by Dr. Karpati and others in mice and our recent studies in the dog indicate that it may not be necessary to continue immunosuppression for a great period of time. I think that this field is still in the early stages of development and that more breakthroughs will follow."

ENZYME CORRECTS METABOLIC MUSCLE DISORDER IN BIRDS

MDA grantee Yuan-Tsong Chen in the Department of Pediatrics at Duke University Medical Center in Durham, N.C., was part of a team that delivered a protein to muscle cells by intravenous injection and corrected a metabolic muscle disorder in birds. The experiments were done in quails with acid-maltase deficiency, or Pompe's disease. The disorder also affects humans and is part of MDA's program.

In quails and in humans with acid maltase deficiency, an energy-storing compound known as glycogen builds up in skeletal and cardiac muscles and in other tissues, such as the liver, because the enzyme acid maltase isn't available to break it down. Children with the most severe form of acid maltase deficiency generally die before the age of 2.

The researchers injected a modified form of the enzyme acid maltase into veins in the birds and significantly improved the muscle disorder.

"This is the first time that anyone has been able to show that you can inject a protein intravenously and have it end up in the muscle," Chen said of the experiments, noting that he's already laying the groundwork for anticipated trials of the acid maltase enzyme treatment in children.

The research team used a new approach to delivering a protein to muscle. In the past, acid maltase has been injected into the circulation in its "mature" form, Chen explained, but it didn't get into muscle cells. The new approach makes use of specialized docking sites on the cell surface known as mannose 6-phosphate receptors. An "immature" form of the enzyme can get into cells through these receptors, but the mature form can't.

The team genetically engineered an immature, or precursor, form of acid maltase that docked at the receptors and was taken into the cells.

Chen says the approach has potentially broad applications, although at present these are only theoretical.

The findings are published in the Feb. 15 issue of the Journal of Clinical Investigation.

STUDIES SUGGEST NEW DIRECTIONS IN SBMA

MDA grantee Diane Merry of the Department of Neurology of the University of Pennsylvania School of Medicine was on a team of researchers who recently built on several years of MDA-funded research to understand the molecular cause of spinal-bulbar muscular atrophy (SBMA), also known as Kennedy's disease.

Nerve cells from mice show abnormal clumbs (bright areas) formed from abnormal androgen receptor molecules.

The disorder results from a flaw in an X-chromosome gene that codes for the androgen receptor, a protein that carries androgen (male hormone) from the main cell compartment into the cell nucleus. SBMA affects men almost exclusively. They experience progressive muscle weakness from loss of muscle-controlling nerve cells (motor neurons) and sometimes show signs of androgen loss, such as breast development and decreased fertility.

Merry's team found that, when abnormal androgen receptor molecules were put into cells in lab dishes, they formed clumps (aggregates) and underwent unusual digestion by enzymes. The affected cells died.

Merry's group is now trying to determine whether the abnormal clumping is the cause of the cells' death and, if so, how it's happening. If the clumping is the cause, Merry says, then the finding "will have relevance for the eventual development of therapeutic strategies. Once we start to understand the structure of these aggregates, we can start to construct models and look for small molecules that might prevent aggregation."

The study is in the April issue of Human Molecular Genetics.

NEW STUDIES PROBE MYOTONIC DYSTROPHY

Myotonic dystrophy (MMD) is a disorder that affects several tissues. In its most severe form, the disorder causes weakness and wasting of skeletal muscles, as well as myotonia (inability to relax muscles), heart problems, subtle brain dysfunction, cataracts, gastrointestinal problems, hormonal abnormalities and diabetes.

In 1992, MDA-funded researchers identified an area of DNA on chromosome 19 that contains too many of the chemical sequences known as "CTG repeats" and linked this region of the chromosome to myotonic dystrophy. Most people with the disorder have these so-called expanded CTG repeats. But, until now, it hasn't been clear just how these repeats cause the disease.

A protein known as CUG-BP may play a key role in myotonic dystrophy, say Thomas Cooper of the Department of Pathology and Lubov Timchenko of the Department of Medicine at Baylor College of Medicine in Houston, both MDA grantees and research team leaders. The Baylor teams showed that a crucial effect of the genetic defect in myotonic dystrophy is that it interferes with the action of CUG-BP. The protein is needed for the processing of many genes, the researchers say, including one that produces a key heart-muscle protein. The finding helps explain how so many tissues can be affected by one genetic defect and could ultimately lead to treatment strategies. The study is published in the May 1 issue of Science.

The genetic defect in chromosome-19 myotonic dystrophy can be repaired in laboratory systems, say researchers at England's Oxford University. Using an enzyme-like chemical called a ribozyme, Leonidas Phylactou and colleagues successfully cut out genetic material from chromosome 19 and spliced the two ends together in cells in laboratory containers. This kind of strategy could possibly be used to treat myotonic dystrophy, the study says, if it could be safely and effectively delivered to human cells. The study is in the April issue of Nature Genetics.

Not all myotonic dystrophy results from a chromosome-19 defect, say researchers at the University of Minnesota. Laura Ranum and colleagues published a study in the June issue of Nature Genetics that shows some myotonic dystrophy can be attributed to an as-yet-unidentified defect on chromosome 3.

Affected members of the five-generation family studied by the Minnesota team "exhibit remarkable clinical similarity" to the much more common type of myotonic dystrophy, the study authors say.

Ranum has previously worked with MDA, and study co-author John Day is an MDA clinic co-director at the University of Minnesota Hospital in Minneapolis, from which study participants were recruited. The June findings could complicate genetic testing for myotonic dystrophy but are likely to shed light on the basic mechanisms underlying both forms of the disease.

Apathy and excessive sleeping probably result from specific abnormalities in brain function and not from generalized depression, muscle weakness or other factors, says a study in the April issue of the Journal of Neurology, Neurosurgery and Psychiatry. M.S. Rubinsztein and colleagues at England's University of Cambridge found that a generally apathetic attitude toward life and excessive sleeping in myotonic dystrophy are fairly common, are independent of each other, and are probably both linked to disturbances in brain function related to the genetic disorder itself. The proposed brain abnormalities deserve study, the investigators say, because they might be treatable.