Harvard Scientists Describe New Mechanism in Myotonic MD

The DNA flaw (mutation) that underlies most cases of myotonic muscular dystrophy (MMD) was identified, with MDA support, in 1992, but new discoveries about this flaw an expanded section of DNA on chromosome 19 are still coming to light.

Now, MDA grantee Richard Junghans at Harvard Medical School and Beth Israel Deaconess Medical Center in Boston, with Alexander Ebralidze and others, have uncovered yet another of MMDs secrets. Their findings are published in the Dec. 4 issue of Science Express, an online edition of the
journal Science.

The elongated sections of genetic material produced in MMD, they say, stick to and interfere with the actions of proteins called transcription factors, which are needed for cells to "read" DNA and make proteins.

With these factors trapped by overly long genetic material (long RNA, made from long DNA), many proteins probably cant be made in sufficient quantities.

The investigators also showed that adding back a transcription factor to MMD cells "cured" one protein-manufacturing problem.

Other MDA-supported discoveries in MMD have included findings that the expanded chromosome 19 DNA may directly affect neighboring genes; and that expanded RNA may interfere with proteins called muscleblind, needed for muscle fiber maturation.

When transcription factors stick to the extra genetic material (RNA) in MMD-affected cells, its likely that many cellular proteins cant be manufactured. Increasing levels of these factors might be a way to treat MMD.

Expanded DNA on chromosome 3 causes a very similar disease type 2 MMD leading the authors to suggest that one mechanism might operate in both forms of MMD.

"Most genetic diseases are defined by a defect in a particular protein," Junghans said. "In MMD, however, its been very hard to track down the protein defects that cause the multitude of abnormalities.

"Because most transcription factors appear to be susceptible to being blocked in MMD, any cell carrying the mutant RNA could be deficient in many proteins, with a different pattern for different organs."

He added that, once the critical transcription factors have been identified in MMD, increasing their levels in cells might be a treatment possibility.

Drugs May Help DMD-Affected Cells Read Through Genetic Errors

The biopharmaceutical company PTC Therapeutics of Plainfield, N.J., is moving ahead with plans to develop PTC124, a compound that may allow cells to bypass certain types of genetic errors.

The new drug may function with less toxicity than that sometimes found with other drugs, such as gentamicin, that have shown similar effects.

While the new, experimental agent isnt a panacea, as it only targets one type of genetic flaw (mutation), studies in mice with Duchenne muscular dystrophy (DMD) have shown low toxicity and restored expression of dystrophin, the missing protein in DMD, when the animals were treated with PTC124.

Still under development and testing, the compound is slated for a research publication next year and clinical trials as early as 2005. MDA funding to the company was under consideration as of the fall.

"This compound has the potential to treat patients whose genetic disorder results from a premature stop codon," said Stuart Peltz, CEO of PTC Therapeutics. A premature stop codon tells the cell to stop processing the gene before the full genetic recipe has been read. For updated information, see the companys Web site at www.ptcbio.com.

A trial of gentamicin in boys with DMD (see "Research Updates," June 2002), co-funded by MDA and the National Institutes of Health, is temporarily stalled because of regulatory concerns, according to principal investigator and MDA grantee Jerry Mendell at Ohio State University in Columbus.

However, an Italian study published in the May issue of Acta Myologica found that dystrophin production was increased in three out of four boys with DMD who received gentamicin for two six-day cycles, seven weeks apart.

Blocking Progesterone Improves Rats With CMT1A

Male rats with the 1A type of Charcot-Marie-Tooth (CMT) disease given the compound onapristone, which interferes with the hormone progesterone, showed better motor function and less nerve damage than did untreated rats with this condition.

A report in the December issue of Nature Medicine from the laboratory of Klaus-Armin Nave at the Max Planck Institute in Gottingen, Germany, suggests that the progesterone-blocking drug reduced production of molecules that give rise to the protein PMP22, a component of the myelin sheath that surrounds nerve fibers. Overproduction of PMP22 is the underlying cause of CMT1A.

Female rats werent in the experiments because of the fluctuating levels of progesterone found in females.

The investigators say that clinical trials of antiprogesterone strategies for CMT "will have to await the comparison of available antiprogestins, long-term applications in males and females, and safety studies that address possible side effects." They suggest that such studies should be undertaken.

Mice With SMA Respond to Riluzole

The drug riluzole (brand name Rilutek), used for nearly a decade in the treatment of amyotrophic lateral sclerosis (ALS), has now been tested in mice with spinal muscular atrophy (SMA), another disease of the motor neurons, nerve cells that control muscle action.

According to a report in the October issue of Muscle & Nerve, 21-day-old mice with SMA that started treatment with riluzole lived longer than untreated mice, and their motor nerve fibers looked more normal at the place where these fibers interact with muscle cells.

Riluzoles mechanism isnt clear, but its known to decrease release of the nervous system chemical glutamate, which may be toxic in ALS and SMA, and it seems to have generally positive effects on nerve cell growth and maintenance.

However, the riluzole-treated animals didnt show any improvement in function. When the drug was administered to newborns, it actually reduced their survival time.

The investigators say that riluzole "may be regarded as a candidate molecule for therapeutic trials in human SMA," with the caveat that the drug could be toxic in infants.

NIH Creates Centers on Ion Channel Diseases

Periodic paralysis and genetic forms of myotonia (delayed muscle relaxation), neuromuscular diseases covered by MDA, are among the rare diseases to be studied through the newly established Rare Diseases Clinical Research Network, under the National Institutes of Health (NIH).

The network aims to increase collaboration and data sharing between scientists and nonprofit organizations in order to shed more light on rare or "orphan" diseases, defined as conditions that affect fewer than 200,000 people in the United States.

Over five years, $51 million in federal funding will advance research on the diagnosis and treatment of rare diseases at seven clinical research centers.

Periodic paralysis and myotonias, both of which result from abnormalities in the ion channels, or microscopic pores in cells, will be studied at the University of Rochester (N.Y.), at a center devoted to "nervous system channelopathies pathogenesis and treatment." MDA grantee Robert C. Griggs will head the center.

MDA Grantee Receives Prestigious Award

MDA grantee Michael Ehlers accepted the Eppendorf & Science Prize for Neurobiology at the annual Society for Neuroscience meeting in New Orleans in November.

Duke University Medical Center neuroscientist Michael Ehlers recently received the prestigious Eppendorf & Science Prize for Neurobiology, which recognizes the best of the worlds neurobiological research by young scientists.

The international prize, established in 2002, encourages the work of promising young neurobiologists by providing support in the early stages of their careers. It came with $25,000 and publication of his winning essay in the Oct. 31 issue of Science.

Ehlers is researching how activity levels can affect synapses (connections) in the brain. Hes also conducting MDA-funded research on why motor neurons (the nerve cells that determine muscle movement) may be hypersensitive to the natural brain chemical glutamate and thus selectively degenerate in ALS.

Review Suggests Heart Checks in MG

People with myasthenia gravis (MG), a disease in which the immune system attacks the part of each muscle fiber that receives nerve signals, arent usually told theyre at risk for heart disease.

But researchers at the Cooper Hospital/University Medical Center of the Robert Wood Johnson Medical School in Camden, N.J., say they recommend that physicians set a "low threshold for pursuing cardiac investigations in patients with MG with unexplained fatigue or exercise intolerance, especially if disproportionate to other signs of MG."

In a comprehensive review of some 60 studies of MG and heart abnormalities conducted since the early 20th century, the authors found that various types of abnormalities are probably more common in this disease than they are in the general population.

Maya Guglin and colleagues say that inflammatory heart disease (myocarditis), rhythm disturbances, blocks of conduction signals through the heart, contraction abnormalities, and cardiac disease secondary to respiratory dysfunction have all been noted in people with MG over the years.

They caution that many of the studies were conducted without taking into account the patients ages and other factors besides their MG that may have contributed to their heart problems. And the diagnostic criteria for MG have changed, meaning some patients may have been included in MG studies in past decades who wouldnt have MG by todays criteria.

Nevertheless, the article, published in the June 2003 issue of the Journal of Clinical Neuromuscular Disease, sounds a cautionary note and suggests a need for further investigations to determine the scope and possible causes of heart disease in MG.

 

CLINICAL TRIALS AND STUDIES

Supplement Test Results in Duchenne MD Are Slightly Encouraging

A six-month, MDA-supported study that tested the effects of the dietary supplements creatine and glutamine separately in boys with Duchenne muscular dystrophy (DMD), has found reasons for encouragement but not for clear recommendations.

Diana Escolar

The trial was conducted at centers belonging to the Cooperative International Neuromuscular Research Group (CINRG).

Both supplements failed to meet the criteria for statistical significance on the main outcome measure, manually tested muscle strength (MMT). MMT measurements are made by having the patient push against an examiners resistance.

In boys 7 or older, however, muscle strength measured by quantitative muscle testing (QMT) a sophisticated system using a force transducer attached to a computer showed a trend toward less deterioration with creatine use. QMT can measure more subtle changes in muscle strength than can MMT.

In addition, in boys 5 to 7 years old, the investigators saw statistically significant differences in two timed function tests for those taking either creatine or glutamine when compared to those taking a placebo. (Since the timed tests werent the main outcome measure, they cant be taken as seriously as the MMT evaluations, the investigators say.)

The boys taking a supplement were able to climb four steps without a handrail and get up from the floor significantly faster.

"The study was negative because we failed to demonstrate statistically significant changes in both groups according to the primary outcome measure, which was manual muscle testing," said Diana Escolar, principal investigator at Childrens National Medical Center in Washington.

Escolar emphasized that two unanticipated factors made the study results difficult to evaluate.

The first, she said, was the observation that the age of the participants mattered, even though previous studies had suggested it wouldnt. Boys under 7 responded differently from the older boys, she said, forcing the researchers to divide the participants into age groups and making it much harder for any result to reach mathematical significance.

Second, the placebo group didnt deteriorate as expected. Even though previous studies had suggested a certain deterioration in strength and function would occur over six months in boys between 5 and 10 years old with DMD, it didnt occur, again making it hard to compare the supplements with the placebo.

The researchers dont know why the placebo group didnt deteriorate.

QMTs ability to detect more subtle muscle strength changes than MMT was confirmed in this study, Escolar noted. That finding will influence future trial designs, she said.

Because the study ended up "underpowered" to detect changes in the main factor being measured, Escolar says she "cannot recommend the use of these supplements, based on the results of this trial."

She noted, however, that a future trial designed with QMT as the main measurement and two age groups might show significant differences between supplements and a placebo.

High-Dose Prednisone Trial in DMD Revised, Now Open

Erik Henricson

An MDA-supported, one-year trial of high-dose, weekend-only treatment with the corticosteroid drug prednisone compared to daily, moderate-dose prednisone in Duchenne muscular dystrophy (DMD) is now open at centers belonging to the Cooperative International Neuromuscular Research Group (CINRG).

The trials opening was delayed because of new findings about the natural history of DMD in boys at different ages (see "Supplement Test").

The investigators are seeking 60 boys between 4 and 10 years old who have a confirmed diagnosis of DMD and have never taken corticosteroid medications. Participants must meet several other study criteria.

U.S. sites are in Washington; Rochester, Minn.; St. Louis; Pittsburgh; San Juan, Puerto Rico; Memphis, Tenn.; Dallas; and Richmond, Va.

For information, contact Erik Henricson, study coordinator, at Childrens National Medical Center in Washington, at (202) 884-3813 or at ehenricson@cnmcresearch.org.

Spinal Muscular Atrophy Trials Aimed at Boosting Vital SMN Protein

Two new trials of drugs that appear in preliminary tests to increase the production of full-length survival of motor neuron protein (SMN) in cells affected by spinal muscular atrophy (SMA) are under way in Salt Lake City under the direction of Kathryn Swoboda.

One drug is valproic acid, already on the market for treatment of seizures, and the other is sodium phenylbutyrate, a compound approved to treat high levels of ammonia in the blood.

Swoboda, a physician-investigator in the Department of Neurology at the University of Utah, has MDA funding to develop "motor unit number estimation" (MUNE) techniques. MUNE is a method for evaluating the existing number of spinal cord cells and the muscle fibers to which they send signals.

Swoboda and colleagues are testing the reliability of MUNE as a measurement of change in clinical trials in SMA and related disorders.

The valproic acid study involves 30 children with SMA who are at least 2 years old and can travel safely to Salt Lake City several times. The study is full.

The phenylbutyrate study seeks 20 babies with SMA who are less than 2 years old and can safely travel to Salt Lake City for periodic testing.

For more information on each of these trials, contact Swoboda at (801) 585-9717 or Mark Wride, study coordinator, at mwride@genetics.utah.edu.

TAKING ADVANTAGE OF NATURE'S BACKUP GENE TO TREAT SMA
1. Most people have SMN1 and SMN2 genes. Full length SMN protein is the main product of the SMN1 gene, while short SMN protein is the main product of the SMN2 gene, but both types of protein can be made from either gene. 2. In SMA, the SMN1 gene is missing or nonfunctional, vastly decreasing the amount of full-length SMN protein. However, the remaining SMN2 genes still produce some full-length protein. 3. The goal of drug treatment is to increase the amount of full-length SMN protein produced from the SMN2 gene's instructions.

 

Tacrolimus May Be Useful in Myasthenia Gravis

A Japanese trial of the relatively new immune-system suppressant tacro-limus (Prograf, FK506) in myasthenia gravis (MG) suggests the drug may have promise in this disorder.

In most cases of MG, the immune system attacks the acetylcholine receptor, a docking site on muscle cells that receives signals from the nervous system. The result is fluctuating weakness that can be highly disabling.

Patients are commonly treated with drugs that increase acetylcholine signaling and with corticosteroids and other medications that dampen the immune response. All these medications have complex and potentially serious side effects when given for long periods.

In this 16-week study of 19 people with MG (16 of whom finished the study), seven showed considerable improvement on a scale of disease activity, and eight improved on measures related to activities of daily living. There were no serious side effects.

The study was open-label, meaning there was no comparison group taking a placebo (inert substance).

The investigators say the results suggest that tacrolimus "could safely serve as an adjunct to steroid therapy for MG at low dosage."