Research Updates

• Study of Gentamicin Expands in Duchenne MD
• Muscles Overcome by 'Junk' in Duchenne and Becker MDs?
• Better DNA Test Finds Virtually All Duchenne, Becker MD Mutations
• Aerobic Exercise Could Worsen mtDNA Disease
• Defective Gene Located for Rare Form of IBM
• Flawed Gene Found for Rare Type of SMA
• New Drugs in Pipeline for Dermatomyositis and IBM
• MDA Launches Initiative for CMT Therapy
• New Trials and Biotech Merger May Speed Pompe's Treatment Program

Study of Gentamicin Expands in Duchenne MD

An MDA-supported study of the antibiotic gentamicin (Garamycin) to treat Duchenne muscular dystrophy (DMD) is being expanded. The 36 boys selected for the study will be given intravenous gentamicin every three days for six months.

Participants must have a type of genetic mutation called a premature stop codon in the gene for the protein dystrophin, rather than a deletion, the more common type of gene flaw in Duchenne dystrophy.

Study candidates are directed to a center where they can obtain specialized testing for this mutation.

Two recent studies in people with DMD, as well as with Becker and limb-girdle muscular dystrophies, yielded confusing results (see "Research Updates," Quest, vol. 8, no. 3). While participants apparently failed to make increased amounts of needed muscle proteins, many displayed a possible indicator of better muscle preservation, namely, lower levels of creatine kinase (CK) in the blood.

For further information, contact Cheryl Wall, trials coordinator at Ohio State University in Columbus, at (614) 293-9016 or at wall.49@osu.edu.

Muscles Overcome by 'Junk' in Duchenne and Becker MDs?

A new MDA-funded study suggests that a normally harmless protein plays an active role in the muscle wasting that occurs in Duchenne and Becker muscular dystrophies (DMD/BMD). Blocking the protein's wayward activity might be a way to treat the disorder, the authors say.

Researchers discovered in 1986 that DMD and BMD are caused by genetic defects in the dystrophin protein, which sits just inside the muscle membrane (surface), and provides a link between the inside and outside of muscle cells. The new study provides support for the theory that losing dystrophin might trigger destructive changes in the activity of other muscle cell proteins.

In normal muscle cells, dystrophin appears to keep JNK1 turned off, leading to the expression of growth genes. In muscles affected by DMD, loss of dystrophin alows JNK1 to turn on, leading to the expression of "suicide" genes.

MDA grantee Lynn Megeney of the Ottawa Hospital Research Institute in Canada and his team found evidence that excess activity of a protein called JNK1 (pronounced junk-1) contributes to muscular dystrophy in mice that are deficient for dystrophin and another muscle protein called MyoD.

Megeney's group showed that JNK1 is overactive in degenerating muscle cells in the diseased mice. Overactive JNK1 seems to repress the expression (switching on) of genes that promote cell growth and division, and to enhance the expression of genes that promote cell suicide (apoptosis).

Most impressively, when leg muscles of the dystrophin-deficient, MyoD-deficient mice were injected with a naturally occurring protein inhibitor of JNK1 — called JIP1 — the treated muscle cells largely resisted degeneration. This implies that JNK1 inhibitors might be used to treat DMD and BMD, Megeney said.

He's begun a screening effort to identify chemicals that might block JNK1 activity, he said, adding, "we're also beginning to develop peptide [small protein] inhibitors of JNK1 as a 'small' drug approach."

Megeney and his team — which included MDA grantees Michael Rud-nicki of the Ottawa Hospital Research Institute and Jeffrey Chamberlain of the University of Washington in Seattle — published their study in the August issue of Current Biology.

Better DNA Test Finds Virtually All Duchenne, Becker MD Mutations

With support from MDA, a vastly improved test for mutations in the dystrophin gene, which underlie Duchenne and Becker muscular dystrophies (DMD/BMD), has been developed by investigators at Ohio State University in Columbus and the City of Hope National Medical Center in Duarte, Calif.

The test, called DOVAM for "detection of virtually all mutations," is said to detect some 90 percent of disease-causing mutations in DMD, compared to about 60 percent to 65 percent for the standard tests.

A report on the new test is in the Aug. 28 issue of the journal Neurology.

Standard tests identify only missing pieces (deletions) in the gene, which account for about 65 percent of DMD cases and 80 percent of BMD cases.

Knowing the specific mutation underlying a disease like DMD allows families to determine carrier status of relatives with accuracy, have prenatal testing performed and enter studies that require specific identification of mutations ("Study of Gentamicin,").

The new DOVAM test will probably result in fewer muscle biopsies being performed for diagnosis of DMD and BMD.

The $1,350 cost of the DOVAM test may be covered by some insurance plans.

Those interested in DOVAM testing can have a doctor or genetic counselor contact the Clinical Molecular Diagnostic Laboratory at City of Hope National Medical Center and request information or a blood sample collection kit, at (888) 826-4362 or cmdl@coh.org.

Aerobic Exercise Could Worsen mtDNA Disease

A new MDA-funded study shows that regular aerobic exercise has short-term benefits — but possibly long-term risks — for people with certain types of mitochondrial myopathy.

In muscles affected by mtDNA disease, aerobic exercise tends to increase the amount of mutant mtDNA (red) relative to normal mtDNA (green), which could be detrimental to muscle function in the long term.

Mitochondrial myopathies are caused by genetic defects in the mitochondria, microscopic factories that use the oxygen we breathe to produce energy for our cells. In these diseases, the mitochondria in muscle cells break down, leading to weakness and exercise intolerance, a feeling of extreme fatigue brought about by exercise.

Some mitochondrial myopathies are caused by mutations in the most abundant type of genetic material, called nuclear DNA (or nDNA), while others are caused by mutations in genetic material found inside mitochondria, called mitochondrial DNA (or mtDNA). People with these diseases tend to have a mixture of normal mtDNA and mutant mtDNA in their cells.

Scientists have reasoned that aerobic exercise should improve strength and exercise capacity in people with mitochondrial myopathy, just as it does in most people. In the new study, published in the August issue of Annals of Neurology, a research team led by MDA grantee Ronald Haller of the University of Texas Southwestern Medical Center in Dallas, put that idea to the test.

Ronald G. Haller

Haller's group examined the effects of aerobic exercise on 10 people with mtDNA diseases. At the end of the 14-week session, the participants showed overall improvements in exercise capacity (lower heart rates and faster pedaling on a stationary bike), and in their muscles' ability to use oxygen and produce energy. However, six participants showed an increase of mutant mtDNA relative to normal mtDNA in their muscles. (Three participants showed no change, and one wasn't examined.)

Both of those effects, Haller and his team say, might be explained by the fact that exercise stimulates mitochondria to proliferate (divide). As mitochondria proliferate, they copy their DNA, causing increases in normal mtDNA and in the muscle's capacity for work. But since mitochondria with mutant mtDNA are most likely to "feel" the strain of exercise, they might proliferate more than those containing normal mtDNA.

The increase in mtDNA didn't aggravate any symptoms in the study participants, but Haller notes that the study was only short-term. "These results encourage caution about recommending exercise training as therapy for mtDNA diseases," Haller says. "At the same time, lack of exercise would be expected to worsen the metabolic limitation in mitochondrial myopathy. Recognizing that considerable uncertainty remains, we advise that patients with mtDNA mutations maintain their current level of physical activities, avoiding extremes of exertion or inactivity."

By extreme exertion, Haller means sustained exercise at greater than 60 percent of maximal heart rate.

Defective Gene Located for Rare Form of IBM

The discovery of the defective gene underlying hereditary inclusion-body myopathy (hIBM) may offer hope for people with that disease and for those with sporadic inclusion-body myositis (sIBM).

Sporadic IBM is the most common muscle disease in people over 50, but its cause — likely a mixture of genetic and environmental factors — has eluded researchers. Hereditary IBM is a rare, but similar disorder with clear genetic origins. One version of hIBM, found mostly in families of Jewish descent, was recently attributed to a flawed gene somewhere on chromosome 9 (see "Advances in Inclusion-Body Myositis" in Quest, vol. 8, no. 2).

In the September issue of Nature Genetics, a team of researchers reported that the flawed gene is GNE, whose full name is a mouthful (UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase). The protein encoded by GNE manufactures sialic acid, a carbohydrate (sugar molecule) that gets incorporated into various proteins and facilitates signaling between cells in the body.

The research team, which included MDA grantees George Karpati of the Montreal Neurological Institute and Walter G. Bradley and Lisa Baumbach of the University of Miami, found GNE mutations in hIBM families from the Middle East, India, the Bahamas and the United States. The researchers say the finding will improve genetic testing and counseling for other hIBM families, and could shed light on sIBM.

Flawed Gene Found for Rare Type of SMA

Scientists have identified the defective gene that causes a rare form of spinal muscular atrophy (SMA) — a discovery that's expected to improve diagnosis and yield further insight into the disease.

SMA refers to a group of diseases that attack the muscle-controlling nerve cells (motor neurons) in the spinal cord, leading to muscle wasting. The most common form of the disease is linked to defects in the SMN1 gene, which encodes the survival motor neuron (SMN) protein. SMN deficiency tends to cause weakness that begins in the trunk muscles and progresses to include the respiratory (breathing) muscles.

A rare form of the disease called SMA with respiratory distress type 1 (SMARD1) causes pronounced weakness in the extremities and early respiratory problems.

In the August issue of Nature Genetics, a research team based at Humboldt University in Berlin reported linking SMARD1 to the gene encoding immunoglobulin mu-binding protein 2 (IGHMBP2). Interestingly, IGHMBP2 appears to have a similar function to that of SMN, which regulates the processing of RNA (the chemical step between genes and proteins). Thus, the researchers suggest that further studies of IGHMBP2 will help sort out the disease process in SMARD1 and the more common form of SMA.

MDA Launches Initiative for CMT Therapy

As knowledge about the genetic causes of Charcot-Marie-Tooth disease (CMT) grows, MDA is encouraging researchers to translate that knowledge into treatment strategies.

MDA-funded researchers have been sorting through a maze of CMT types, each one caused by a distinct genetic defect. To date, they've uncovered clues to nearly 20 CMT-linked genes, and identified nine of them (see "Researchers Probe the Origins of CMT," Quest, vol. 8, no. 1).

All types of CMT cause breakdown of the peripheral nerves, leading to weakness and sensory loss in the extremities. The nine discovered genes — essential to axons (the "wires" inside the nerves), or myelin (the insulation around the wires) — have helped unravel steps in that disease process.

"MDA funds are available for projects that have the clear goal of developing a therapy for any form of CMT," MDA Director of Research Development Sharon Hesterlee announced in a recent briefing to past and present MDA grantees. "Such projects may involve gene transfer, stem cells or drug interventions, and will be given high-priority status during the evaluation process."

New Trials and Biotech Merger May Speed Pompe's Treatment Program

The results of two new clinical trials of a potential therapy for Pompe's disease, also known as acid maltase deficiency and glycogen storage disease type 2, will soon reveal which of two types of "designer enzymes" should be brought before the U.S. Food and Drug Administration, say spokesmen for two biotech companies that have recently merged.

A laboratory-engineered version of the acid maltase enzyme, Pompase, was developed by the Genzyme Corp. of Cambridge, Mass. Its structure is based on research conducted in the 1990s at Duke University by MDA-supported Yuan-Tsong Chen. The other enzyme, known as NZ-1001, was developed by Novazyme Pharmaceuticals of Princeton, N.J.

Each designer enzyme mimics the actions of natural acid maltase, a lack of which is the underlying problem in Pompe's disease. Without acid maltase, glycogen (the storage form of sugar) builds up in muscle cells, including those involved in heart function and breathing. Death in early childhood is the result if the enzyme deficiency is severe.

In August, Genzyme announced it would purchase Novazyme and that the companies would join forces to produce a treatment for Pompe's.

Genzyme began this year a one-year clinical trial of Pompase; results are expected in late 2002. The study builds on encouraging results in three babies treated with Pompase, all of whom are still alive past age 2 (see "Research Updates," Quest, vol. 8, no. 3, and vol. 7, no. 6).

Novazyme will begin testing its NZ-1001 enzyme by the end of the year. The trial is likely to involve fewer than 20 patients. After just two injections of NZ-1001 over two weeks, a Novazyme spokesman said, normal enzyme activity in mice lacking acid maltase was restored; significant amounts of glycogen were cleared; and — most important — the Pompe's-affected mice quickly acquired normal muscle strength.

Genzyme also announced it would cover the expenses of a failing Dutch company, Pharming, that had been producing yet another form of the acid maltase enzyme.

For more information about the NZ-1001 trial, call the Genzyme medical information line at (617) 252-7832, or visit Genzyme (www.genzyme.com) or Novazyme (www.novazyme.com). 

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