QUEST Volume 12, Number 3, MAY/JUNE 2005

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Mayo Researchers ID New Form of MD

Andrew Engel

Researchers at the Mayo Clinic in Rochester, Minn., have identified a previously unknown form of adult-onset muscular dystrophy.

The dystrophy arises from a mutation in a gene called ZASP, located on chromosome 10, and appears to be inherited in an autosomal dominant pattern, meaning a person need inherit only one flawed ZASP gene from either parent to show symptoms. The average age of symptom onset in this study was 54.

Fifty-four adults with symptoms of muscle disease, such as skeletal muscle weakness and cardiac abnormalities, certain biopsy findings, and a general diagnosis of myofibrillar myopathy (a general category of muscle disease), were tested to see whether their illness was linked to the ZASP gene.

ZASP gene mutations were found in 11 of the 54 people studied. Most had weakness in the muscles close to the center of the body (proximal) as well as those farthest away from the center (distal), but distal weakness was greater than proximal weakness in six people. Three people had cardiac abnormalities.

The ZASP protein, for which the ZASP gene carries instructions, is in a part of the muscle cell known as the Z-disk. Z-disks separate contracting units of muscle cells from each other deep inside muscle fibers. Many other forms of muscular dystrophy, in contrast, have to do with deficiencies or abnormalities in proteins in the membrane surrounding the fiber.

Neurologist and longtime MDA grantee Andrew Engel, with neurologist Duygu Selcen, announced the findings in the March issue of Annals of Neurology.

“This is another cause of muscular dystrophy,” Engel said, noting that ZASP MD is one of the few dystrophies linked to a protein in the muscle cells’ contracting parts.

Gene Therapy Aids Mice With Pompe’s Disease

A team including MDA grantees Andrea Amalfitano, Yuan-Tsong Chen and Dwight Koeberl at Duke University in Durham, N.C., has given mice with acid maltase deficiency (Pompe’s disease) a successful gene-based treatment to compensate for their missing acid maltase enzyme. The finding was announced in the January issue of Molecular Therapy.

Mice bred to develop the metabolic muscle disease received genes for acid maltase injected into the liver. The mice were also bred not to mount an immune response against the compound, including its viral delivery vector.

Male mice showed complete correction of the main Pompe’s characteristic, which is excess glycogen (starch) storage in the heart and skeletal muscles. In female mice with Pompe’s, glycogen storage decreased only in the heart. The reason for this difference appears to be that male hormones speed the conversion of the therapeutic DNA from an inactive to an active form.

The researchers believe the liver acted as a “depot” for the enzyme, which then entered the bloodstream.

Gene therapy is an alternative strategy to enzyme replacement therapy (see “Genzyme Forges Ahead.”) for Pompe’s disease.

Another Gene Linked to Charcot-Marie-Tooth Disease

Mutations in a chromosome 19 gene known as dynamin 2 have been added to the long list of genetic abnormalities that can lead to Charcot-Marie-Tooth (CMT) disease, a disorder of the nerve fibers that run between the spinal cord and the rest of the body.

Some 20 genes have, when flawed, been implicated as CMT causes. The dynamin 2 form of CMT appears to follow an autosomal dominant pattern, requiring a person to inherit the flawed gene from only one parent.

A multinational research team, which published its findings in the March issue of Nature Genetics, identified a North American, an Australian and a Belgian family, each of which has a different CMT-causing mutation in the dynamin 2 gene, leading to three flaws in the dynamin 2 protein.

The researchers say the dynamin 2 protein is normally involved in a broad variety of cellular mechanisms, any of which could be disrupted by various mutations.

Jeffery Vance	Margaret Pericak-Vance

Study team members Margaret Pericak-Vance, Jeffery Vance and Marcy Speer at Duke University in Durham, N.C.; Garth Nicholson at ANZAC Research Institute in New South Wales, Australia; and Vincent Timmerman at the University of Antwerp (Belgium) have all received MDA funding to identify neuromuscular disease genes.

New Approach to MG Targets Molecular Holder

Minako Oshima, an MDA grantee at Baylor College of Medicine in Houston, was on a team that recently performed laboratory experiments blocking the unwanted immune system response that occurs in myasthenia gravis (MG). This disorder is most often caused by a misguided immunologic attack on specialized areas of muscle cells called acetylcholine receptors. In people with MG, proteins of the acetylcholine receptor appear as antigens — targets flagged for destruction.

The researchers, who published their results in the March issue of Autoimmunity, created immune system proteins — antibodies — that thwarted the body’s ability to present receptor proteins as targets.

The antibodies blocked an antigen “holder” called an MHC molecule. This move obstructed the antigen presentation and interrupted the unwanted immune response.

The authors write that “the present findings suggest that blocking the function of disease-related MHC alleles [molecules] ... by selectively targeting the antigen-presenting region could make an effective and feasible strategy for immunointervention in MG.”

They say the strategy could have broad implications for autoimmune diseases as well as for allergic reactions and other conditions involving unwanted immune responses.

Cardiac Stem Cells Come Closer to Clinic

The laboratory of MDA grantee Kenneth Chien at the University of California-San Diego announced in the Feb. 10 issue of Nature that its researchers have discovered in the hearts of mice, rats and humans a new type of stem cell that can become a mature cardiac cell.

Chien says these are the actual cells that form the heart during fetal development and that his group has identified them by the presence of a protein called islet-1.

Muscle-specific stem cells (myoblasts or myogenic precursor cells) have long been known to populate skeletal muscle tissue throughout life and to move in when repairs are needed. But until recently, it was believed that the heart didn’t contain such cells after birth.

Although the number of islet-1-bearing cells, dubbed cardioblasts by the researchers, is small (500 to 600 in young rats), they can be coaxed to multiply into millions in the lab.

“The findings are significant both as a new model to study human heart disease and to develop potential treatments,” Chien says.

In a separate study, researchers at the University of Louisville (Ky.) and New York Medical College in Valhalla treated damaged rat hearts with cardiac stem cells (different cells from Chien’s) delivered into a major blood vessel. The rat hearts, damaged by a blockage in a major artery, showed significant benefit from the injected cells.

In the March 8 issue of Proceedings of the National Academy of Sciences, the researchers write, “This study demonstrates that CSCs [cardiac stem cells] are effective when delivered in a clinically relevant manner.”

Because people with genetic disorders would have cardiac stem cells with genetic abnormalities, their own cells would have to undergo genetic modification before being reinjected in any future treatment scenario. Or donor cells could be used.

Researchers Block Flawed Genetic Message in Myotonic MD Cells

An MDA-supported research group has found that a biological mechanism can destroy abnormal genetic information before it leaves the cell nucleus, the compartment in which it’s made.

The mechanism can likely be exploited for treatment of certain diseases, particularly myotonic muscular dystrophy (MMD), the researchers say.

Scientists had previously thought this phenomenon, called RNA interference, operated only outside the cell nucleus, making it useless for combating large, abnormal sections of the genetic material RNA, such as those seen in type 1 and type 2 MMD. In MMD, these don’t leave the nucleus but cause trouble there.

(RNA is derived from and is similar to DNA.)

MDA grantees Jack Puymirat at Laval University in Sainte-Foy, Quebec, and Nan Sook Lee at the Beckman Research Institute of the City of Hope in Duarte, Calif., were on the team, which introduced laboratory-engineered DNA into cells affected by type 1 MMD. The DNA led to production of short pieces of RNA, which in turn caused the destruction of the oversize, abnormal RNA in these cells. The researchers used viral vehicles to deliver the DNA.

Inside the cell nucleus, the short RNA pieces apparently marked the abnormal RNA and targeted it for destruction.

In their paper, the investigators say their findings have “important implications” for treatment of MMD or other nuclear (nucleus-involving) diseases.

Other techniques for eliminating abnormal RNA messages include the use of antisense, a strategy that can block or destroy abnormal RNA (see “Research Updates,” May-June 2003); and RNA “editing” using ribozymes, enzymes that can splice out unwanted RNA pieces (see “Research Updates,” February 2003).

CLINICAL TRIALS AND STUDIES

Early Drug Treatment May Prolong Heart Function in Duchenne MD

In a study of 51 boys with Duchenne muscular dystrophy (DMD), a French research group found that early treatment with 2 milligrams to 4 milligrams a day of the drug perindopril prevented the development of serious cardiac dysfunction when patients began taking it while their heart function was still normal.

Denis Duboc at Cochin Hospital in Paris, with colleagues at 10 institutions, randomly assigned the study participants to receive perindopril, an ACE (angiotensin-converting enzyme) inhibitor, or a placebo (inert substance). All participants were boys with DMD between 9.5 and 13 years old, and all had normal cardiac function at the start of the study.

After three years, there were no significant differences between the perindopril group and the placebo group. At that time, perindopril was given to all participants.

After two additional years, the researchers compared the boys who had received the drug for all five years with those who started the drug three years into the study. One boy who had taken perindopril for all five years showed significant cardiac function loss, but eight participants who had taken it for only two years showed this type of loss.

The investigators concluded that “studies of preventive treatment with perindopril at a younger age are warranted.”

Elizabeth McNally, a cardiologist and MDA research grantee at the University of Chicago, commented on the findings, which are published in the March 15 issue of the Journal of the American College of Cardiology.

“The key finding is that early treatment was associated with fewer patients developing a more severe decline in heart function (one out of 24 versus eight out of 24),” she said.

She noted that other ACE inhibitors will likely have the same effect as perindopril, and that additional medications, such as beta blockers, are also effective in cardiomyopathy.

“Those medications should be similarly tested,” she said.

Myostatin Blocker to Be Tested in 3 Forms of MD

Wyeth Pharmaceuticals of Collegeville, Pa., is conducting a clinical trial of MYO-029, a compound that blocks myostatin, a natural protein that ordinarily puts a brake on the growth of muscles. The study is open to 108 adults with facioscapulohumeral (FSHD), Becker (BMD) and limb-girdle muscular dystrophies (LGMD).

MDA will provide supplemental support to the sites where the trial will take place. As of March, two sites were open to recruitment. See www.clinicaltrials.gov.

Research by MDA and by Wyeth has suggested that blocking myostatin’s activities might improve muscle growth and survival and at least partially offset muscle degeneration. MYO-029 is a laboratory-engineered human antibody (immune-system protein) that sticks to myostatin and interferes with its functions.

Participants must be at least 18 years old and able to walk.

SomatoKine Trial in Myotonic MD Under Way

A clinical trial to test the experimental compound SomatoKine in people with myotonic muscular dystrophy (MMD) at the University of Rochester (N.Y.) Medical Center is under way, after some initial delays. The investigators will study 15 people and aren’t seeking more at this time.

Richard Moxley, director of the Neuromuscular Disease Center at URMC, one of three muscular dystrophy centers of excellence co-funded by MDA and the National Institutes of Health, has been working closely with Insmed of Glen Allen, Va., the company that developed SomatoKine. The drug combines insulin-like growth factor 1 (IGF1), a muscle-building protein, with another protein, resulting in a compound that may allow high doses of IGF1 to be given safely.

Genzyme Forges Ahead With Enzyme for Pompe’s

The multinational biotechnology company Genzyme, headquartered in Cambridge, Mass., is finalizing the study design for a new trial of Myozyme, a laboratory-modified enzyme designed to compensate for a lack of acid maltase in acid maltase deficiency, also known as Pompe’s disease.

MDA grantee Yuan-Tsong Chen at Duke University in Durham, N.C., is credited with laying much of the scientific foundation for Myozyme’s development during the 1990s.

The new, late-onset (after the first year of life) Pompe’s Myozyme treatment study will include some participants from an earlier observational study and others.

So far, Genzyme has conducted two clinical trials of Myozyme in infantile-onset Pompe’s and one observational study of late-onset Pompe’s. Results of all three closed studies are now being analyzed.

Infantile-onset Pompe’s patients who aren’t in a trial of Myozyme can receive the compound through an expanded access program. An access program for late-onset Pompe’s patients isn’t enrolling participants at this time but will field inquiries.

Information about these programs is posted at www.clinicaltrials.gov (search under “Myozyme”). Patients and physicians can contact Genzyme’s Medical Information Department at (800) 745-4447, (617) 768-9000 or medinfo@genzyme.com.

The company has applied to the European Medicines Agency for approval of Myozyme and anticipates filing an application with the U.S. Food and Drug Administration this year.

Women With CMT Risk Childbirth Complications

Charcot-Marie-Tooth (CMT) disease, a disorder of nerve fibers that connect the spinal cord with the rest of the body, is a factor for complications during pregnancy and delivery, says a large study conducted in Norway between 1967 and 2002 and published in the Feb. 8 issue of Neurology.

Jana Hoff and colleagues at the University of Bergen reviewed the records of 108 births by mothers with CMT and compared them to a reference group of 2.1 million births by women without CMT.

In the CMT-affected group, the rate of abnormal positioning of the baby was 9.3 percent, compared to 4.5 percent in the unaffected women. Bleeding after delivery occurred in 12 percent of the CMT-affected women, compared with 5.8 percent of the women without CMT.

Women with CMT delivered their babies by Caesarean or with the aid of forceps or a vacuum device 29.6 percent of the time, while women without CMT underwent these procedures 15.3 percent of the time. The majority of CMT Caesarean operations were emergencies, and forceps were used three times as often in the CMT group as in the non-CMT group.

The researchers speculate that these differences could be caused by CMT-related weakness in the baby and lack of muscle tone in the mother’s uterus.

“CMT has up till now been acknowledged as a disease mainly affecting distal [far from the body’s center] extremities with no significant effect on pregnancy, delivery and the newborn,” the authors write. “The results from our study question this view and show that maternal CMT should be considered a potential risk factor during delivery.”

Similar results were reported with respect to delivery complications in women with myasthenia gravis (see “Research Updates,” March-April 2004).

Topiramate Treats Obesity in Two With Duchenne MD

Greg Carter, a physical medicine and rehabilitation specialist who co-directs the MDA clinic at the University of Washington Medical Center in Seattle, recently reported that two boys with Duchenne muscular dystrophy (DMD) lost significant weight while being treated with topiramate, a drug used to treat epilepsy and migraine headaches and that often reduces appetite.

One boy is a 5-foot, 6-inch, 15-year-old whose weight was 196 pounds and in whom dietary management alone had failed. He began losing weight two weeks after starting topiramate, while maintaining a diet of 800 calories a day.

After 18 months of topiramate at a variety of dosages, ending at 50 milligrams a day four days a week, his weight was down to 145 pounds.

The second is a 5-foot, 3-inch, 13-year-old with DMD whose weight had reached 250 pounds. After dieting failed to reduce his weight, he started taking bupropion, an antidepressant known to suppress appetite. After four months of bupropion, which failed to reduce his weight or appetite, he started taking topiramate, stabilizing his medication dose at 50 milligrams twice a day and his diet at 800 calories a day. After about a year, his weight is down to 147 pounds.

“These cases provide anecdotal evidence that topiramate is well tolerated and may help patients with DMD to lose weight,” Carter writes in Muscle & Nerve, published online March 18.

Carter commented, “Although this is a very preliminary report, the findings are encouraging. Because obesity is a significant clinical problem for boys with DMD and caregivers as well, further study is clearly warranted.

“In the meantime, I would encourage parents of obese boys with DMD to ask their MDA physicians about a trial of topiramate. A dose of 50 milligrams a day should be well tolerated and be enough to induce a decrease in appetite. There should be some effect within several weeks.”

Exercise Shown Safe, Beneficial in FSH MD

Training on a stationary bicycle for 12 weeks improved oxygen uptake and workload capacity without causing apparent muscle damage in adults with facioscapulohumeral muscular dystrophy (FSHD), Danish researchers report in the March 22 issue of Neurology.

David Olsen at National University Hospital in Copenhagen and colleagues studied four men and four women with FSHD judged “not severe.” He compared the effects of the training program on these subjects with the effects of the same program on four men and three women without FSHD.

Training for 35 minutes five times a week increased measures of physical fitness in both groups. No muscle damage, assessed by biopsies and blood tests, occurred in either group.

In both groups, there was a slight increase in the number of capillaries in the muscles, a normal response to exercise.

Six people with FSHD reported an increase in strength, seven an increase in endurance, and five an increase in activity level after training. No one said walking ability had changed, and only one person reported a lessening of fatigue.

In an accompanying “patient page,” neurologist Robin Brey advises that people with FSHD talk with their doctors about exercise.