MDA clinic directors and researchers gather for three days of talks
Nearly 600 conferees gathered at the South Point Hotel in Las Vegas Jan. 26-28, 2009, for the MDA National Clinic Directors’ Conference, where a number of speakers presented research and care updates on Duchenne muscular dystrophy, myotonic dystrophy, facioscapulohumeral muscular dystrophy, limb-girdle muscular dystrophy, congenital muscular dystrophy, Friedreich’s ataxia, spinal muscular atrophy, acid maltase deficiency and ALS.
Carsten Bonnemann, an MDA research grantee who co-directs the MDA clinic at Children’s Hospital of Philadelphia, talked about the similarities and differences among various types of congenital muscular dystrophy.
Susan Iannaccone, who directs the MDA clinic at Children’s Medical Center of Dallas, emphasized the need for multidisciplinary care for children with spinal muscular atrophy.
Katherine Mathews, who directs the MDA clinic at University of Iowa Hospitals & Clinics in Iowa City, reported early data from the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet), a project of the Centers for Disease Contol and Prevention.
John Day, an MDA research grantee who directs the MDA clinic at the University Medical Center-Fairview in Minneapolis, discussed the need for doctors to “recognize the multiple faces of myotonic dystrophy.” |
Lamin defects may disrupt nerve-muscle signals in Emery-Dreifuss MD
Mutations in the lamin A/C gene on chromosome 1 and the emerin gene on the X chromosome both can cause Emery-Dreifuss muscular dystrophy (EDMD), but the precise mechanisms by which they do so are still being identified.
Now, a multinational team has found that, in mice with an EDMD-like disease, lamin protein defects interfere with the way cell nuclei normally localize in skeletal-muscle fibers at the point where each fiber receives signals from a nerve cell.
The researchers say their results “strongly indicate” that defects at the neuromuscular junction (where nerve and muscle connect) contribute to the lamin A/C type of human EDMD, and provide insights into at least one cellular and molecular mechanism operating in this disease.
The team, coordinated by Tom Misteli at the National Cancer Institute of the National Institutes of Health in Bethesda, Md., published its findings Jan. 5, 2009, in the Journal of Cell Biology. Investigators found that the neuromuscular junctions are abnormally organized in these mice and that nerve-to-muscle signals are altered. They say humans with lamin A/C-related EDMD show similar molecular defects in their muscles.
MDA grantee Howard Worman at Columbia University, who has conducted several studies of the molecular consequences of EDMD, cautions that heart-muscle cells, which are severely affected in lamin-related EDMD, do not have neuromuscular junctions, demonstrating that a different disease mechanism exists in these cells.
In October 2008, Worman’s group identified a signaling pathway in the heart called ERK as a mechanism of cardiac damage in lamin A/C-related EDMD. (See Research Updates, January 2009.)
Freeing MBNL1 from RNA trap seen as step toward MMD1 treatment
The identification of small molecules that can block the genetic defect that causes type 1 myotonic dystrophy (MMD1, DM1) may be the first step toward developing a new drug treatment for the disease, say researchers at the University of Rochester (N.Y.) Medical Center (URMC).
The abnormality that underlies MMD1 is a stretch of genetic material derived from DNA on chromosome 19 that contains more than the usual number of a repeating chemical sequence known as a CUG (cytosine, uracil, guanine) triplet repeat.
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| Newly identified molecules prevent the MBNL1 protein from becoming ensnared in an RNA “trap” in MMD1-affected cells. |
A major effect of the CUG triplet repeats in RNA (genetic instructions derived from DNA) is the entrapment and disabling of a protein called MBNL1, also known as muscleblind 1. Normally, MBNL1 helps build cellular channels for chloride ions, which are essential for muscle function. But when it’s stuck to CUG triplet repeats, it can’t play this role.
The newly identified small molecules prevent MBNL1 from becoming ensnared in the CUG triplet repeat trap, freeing it to do its usual job helping muscle function.
The molecules potentially could be developed into a therapy that would prevent the toxic interaction between MBNL1 and CUG triplet repeats and treat the disease.
A research team led by chemist Benjamin Miller published its findings online Nov. 7, 2008, in the Journal of the American Chemical Society. The team included neurologist Charles Thornton, who co-directs the MDA-supported clinic at URMC and who has received MDA funding for MMD1 research.
“This is an important first step toward developing a drug treatment for myotonic dystrophy,” Thornton said. “The message from our patients is loud and clear — push this forward as fast as possible.”
Researchers identify new modifier of SMA severity
Molecular silencing of so-called SMN2 genes, known to be beneficial in patients with spinal muscular atrophy (SMA), all of whom lack functional SMN1 genes, has recently been found to play a role in how beneficial SMN2 genes are in this disease.
The severity of SMA correlates in general with the number of SMN2 genes a person has; the more SMN2 genes, the milder the disease usually is. (See “In Focus: SMA.”)
However, researchers have noted many exceptions to the “more SMN2 genes, milder disease” principle in this disorder of motor neurons (muscle-controlling nerve cells) in the spinal cord.
Now, German and Australian researchers coordinated by Eric Hahnen at the University of Cologne (Germany) have found that some SMN2 genes are inactive because they’re tagged with a chemical grouping of a carbon and three hydrogen molecules (“methyl” group) that keeps them “silent.” Drugs known as histone deacetylase (HDAC) inhibitors, which are already being tested in SMA, can help remove these methyl groups.
In laboratory experiments, Hahnen’s team found two HDAC inhibitors, vorinostat and romidepsin, were particularly good at bypassing silencing of the SMN2 gene. They suggest these compounds be tried in SMA.
SMA cell ‘reprogramming’ may aid search for treatment
In a development that could lead to better screening of drugs for spinal muscular atrophy (SMA), skin cells from a child with type 1 SMA have been “reprogrammed” back to a stem-like state and then coaxed to develop into SMA-affected motor neurons, the nerve cells that normally control muscle movement but malfunction and die in this disease.
Allison Ebert, assistant scientist in the laboratory of Clive Svendsen at the University of Wisconsin-Madison, and colleagues, who published their findings online Dec. 21, 2008, in the journal Nature, say the results will allow the study of SMA in motor neurons in the lab and probably will allow drugs for SMA to be screened more effectively than is currently possible.
Although they note that further testing is necessary, so far they believe the child’s SMA-affected cells faithfully reproduce the SMA disease process and haven’t been altered by the reprogramming procedure — a critical feature for accurate research.
The investigators also took skin cells from the child’s unaffected mother and treated them the same way as the child’s cells. In contrast to the child’s cells, the mother’s unaffected motor neurons are developing normally, they say.
The research team included Christian Lorson, associate professor at the University of Missouri-Columbia, who has MDA funding for SMA work. Lorson, with graduate students Virginia Mattis and Frankie Rose, analyzed cellular levels of the SMN protein, a deficiency of which is the root cause of SMA.
Although motor neurons have been created from the skin cells of patients with other neurologic diseases, including amyotrophic lateral sclerosis (ALS), (see Research Roundup, ALS Newsmagazine, October 2008), those reprogrammed motor neurons so far have not demonstrated disease-specific effects, the researchers note.
The SMA-affected motor neurons in the current study have also responded positively to compounds known to increase SMN protein levels. Raising SMN levels to save motor neurons is a major goal of current SMA drug development.
The researchers note that “this new model should provide a unique platform for studies aimed at both understanding SMA disease mechanisms that lead to motor neuron dysfunction and death, and the potential discovery of new compounds to treat this devastating disorder.”
Boosting defense mechanism helps SBMA-affected cells
A defense mechanism called “autophagy” that neurons (nerve cells) use to protect themselves from dangerous misfolded proteins may hold promise for developing treatments for spinal-bulbar muscular atrophy (SBMA, Kennedy disease) and perhaps similar neurodegenerative diseases, new research shows.
Autophagy, which means “self-digestion,” is used by cells to degrade protein molecules that have folded into dangerous shapes that can cause cell death. (SBMA-affected cells attempt to utilize this mechanism, but it’s insufficient in these cells.) Many neurological and neuromuscular diseases involve overproduction of and damage from misfolded protein molecules, because neurons are exquisitely vulnerable to misfolded protein stress.
Until now, studying autophagy with the aim of exploiting its possible therapeutic effects has been technically difficult, and attempts to induce it in the laboratory have destroyed cells.
But MDA grantee Albert La Spada and co-workers at the University of Washington Medical Center in Seattle recently found a new and convenient way to study autophagy. They published their findings online Nov. 18, 2008, in the Journal of Biological Chemistry.
La Spada and colleagues found that depriving neurons of certain nutrients while they’re being maintained in the lab can induce autophagy without killing the cells, giving the researchers a valuable window on the process.
They found that, in the laboratory, neurons producing misfolded androgen receptor protein molecules, which cause cell death in SBMA, were protected by enhanced autophagy after they were deprived of selected nutrients.
Knowing more about this neuroprotective pathway and how it might be enhanced in disease-affected neurons “will better guide strategies for therapy development,” the researchers say.
Longtime MDA grantee was innovative researcher, compassionate physician
Neurologist and neuroscientist George Karpati, a longtime MDA grantee at the Montreal Neurological Institute, passed away suddenly on Feb. 6, 2009. The Institute is part of McGill University.
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Longtime MDA research grantee George Karpati |
Karpati held the I.W. Killam Chair and was a professor of neurology and neurosurgery at McGill. He made significant contributions to the field of neuromuscular disorders in general, focusing specifically on gene therapy and the augmentation of the utrophin protein as potential treatments for Duchenne muscular dystrophy (DMD) since the 1990s.
In addition to his substantial research contributions, he was known for his clinical acumen and compassion for patients and families. |
Two research teams treat CMD mice
Recently published findings from two independent groups have suggested possible treatment pathways for the merosin-deficient and integrin-deficient forms of congenital muscular dystrophy (CMD).
Doxycycline fights cell death and lessens disease severity in merosin-deficient mice The first finding, published online Dec. 11, 2008, in Annals of Neurology, shows doxycycline, normally used as an infection-fighting antibiotic but known to have other properties, increased survival time, improved growth and delayed the onset of paralysis of the back legs in merosin-deficient mice with a CMD-like disease.
MDA grantee Jeffrey Boone Miller of Harvard Medical School in Boston and Boston Biomedical Research Institute in Watertown, Mass., coordinated the merosin-deficient CMD research team, which also included Mahasweta Girgenrath, lead author on the report and an MDA grantee at Boston University.
This type of CMD is caused by mutations in the gene for laminin alpha 2, a protein strand in a larger protein called merosin (also known as laminin 2), which connects muscle fibers to their surrounding tissue. Without the laminin alpha 2 strand, the normally three-stranded merosin protein can’t perform this connective function or carry out other roles, and severe neuromuscular dysfunction results.
Earlier research has shown that at least one mechanism by which merosin-deficient CMD leads to weakness, paralysis and premature death is the inappropriate induction of a “cell death program” (apoptosis) in skeletal muscles and the nerve cells controlling them.
Because doxycycline and related antibiotics have been reported to interfere with apoptosis, Girgenrath and colleagues decided to see how it might affect disease progression in merosin-deficient CMD mice.
They randomly assigned some of the CMD mice to receive doxycycline in their drinking water starting one to three days after birth and others to receive water without doxycycline.
In the doxycycline-treated group, half the mice were still alive at about 70 days after birth, while in the untreated group, half had died at about 32 days.
And at 3.5 weeks after birth, doxycycline-treated mice weighed 30 percent to 40 percent more than untreated mice.
In marked contrast to the back leg paralysis seen in all the untreated mice four to six weeks after birth, the majority of the treated mice didn’t have this paralysis at age 10 to 12 weeks. At age 6 weeks, doxycyclinetreated merosin-deficient mice stood on their hind legs about as often as mice with normal merosin levels, while untreated merosin-deficient mice did this less than one-third as often.
In addition, the muscles of the treated mice showed less inflammation and fewer indicators of apoptotic cell death than those in the untreated mice.
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| Congenital muscular dystrophies result from the loss of laminin 2, alpha 7 integrin or other muscle proteins. |
“Our study demonstrated that disease due to loss of laminin alpha 2 was indeed significantly ameliorated by oral administration of doxycycline,” the researchers write.
However, they note two warnings: It’s not known if doxycycline or similar therapies would still be effective if started later in life than they were in these experiments; or if other drugs in the same family as doxycycline might be more effective than this medication. They also caution that extensive repair of injured skeletal muscles requires formation of new blood vessels and that doxycycline appears to interfere with this repair mechanism.
The researchers say a pharmacological therapy to slow disease progression in human merosin-deficient CMD would be of considerable benefit and that additional inhibitors of apoptosis should be tested.
Laminin 111 restores muscle repair process in integrin-deficient mice
A research team coordinated by Dean Burkin at the University of Nevada School of Medicine in Reno has found a way to improve muscle repair in a mouse model of integrin-deficient CMD. The team’s findings were published in the January 2009 issue of the American Journal of Pathology.
Like merosin, integrins are part of the apparatus that helps anchor muscle fibers to their surroundings. Evidence also shows that some integrin proteins, such as alpha 7 integrin, are needed to maintain normal levels of laminin alpha 2 and merosin and apparently activate the muscle repair and regeneration process.
Children with mutations in the gene for alpha 7 integrin have a deficiency of this protein, with muscle abnormalities, delayed developmental milestones and impaired mobility. Mice lacking alpha 7 integrin develop a CMD-like disease with muscle and blood-vessel defects.
To see whether alpha 7 integrin is important for skeletal muscle regeneration and repair, Burkin, with colleagues at the University of Nevada and the University of Washington-Seattle, purposely damaged muscle tissue in alpha-7-integrin-deficient mice and found that regeneration in response to injury was defective.
They say the regenerative capacity of skeletal muscle depends on an “intricate interplay” between cells that carry out muscle repair and their normally laminin-rich environment, leading them to test the hypothesis that injecting a laminin protein might improve muscle repair.
Prior to injury, they injected integrin-deficient mouse muscle with laminin 111, normally produced in muscle during embryonic development. After the mice were injured, their muscle repair was restored to normal.
“One possible explanation for the improved muscle regneration ... is that injection of laminin 111 may [reactivate] an embryonic myogenic program in adult skeletal muscle,” the researchers write, which may in turn result in improved muscle repair.
They also note that, because loss of regenerative capacity has been implicated in a variety of muscular dystrophies, including merosin-deficient CMD and Duchenne muscular dystrophy, they’re now investigating whether laminin 111 protein therapy might also be beneficial in other forms of MD.
MDA developing CMT research network
In January, MDA began funding development of the North American CMT Network to provide an infrastructure for clinical research in Charcot-Marie-Tooth disease (CMT) to aid researchers in locating potential participants for clinical studies. An early goal is to establish scoring systems for functional evaluations in children with CMT.
The network builds on the CMT North American Database (www.med.wayne.edu/neurology/clin_programs/Labs/CMT/index.htm), which has been collecting information from CMT-affected families since 2001 and also has received MDA support.
As the network gets under way, patients will have the opportunity to be evaluated at one of six CMT centers of excellence and have DNA samples obtained and banked.
Participation in the database and network is voluntary, and information that can be traced to an individual will not be released without that person’s written consent.
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Exon-skipping trial allowed dystrophin production in 10 boys with DMD
On Jan. 21, 2009, AVI BioPharma of Portland, Ore., announced that its experimental compound AVI4658 for the treatment of Duchenne muscular dystrophy (DMD) yielded promising results in a phase 1 clinical trial in the United Kingdom.
AVI4658 is a laboratory-engineered molecule that coaxes muscle cells to ignore, or “skip over,” a section (exon) of genetic instructions for the dystrophin protein, which is missing in DMD patients. The strategy, known as “exon skipping,” is designed to cause cells to make nearly normal dystrophin molecules.The AVI4658 construct, which specifically targets exon 51 of the dystrophin gene, was developed by an international team of investigators that included MDA-supported Stephen Wilton at the University of Western Australia in Perth and Judith van Deutekom, then at Leiden University in the Netherlands, working in collaboration with AVI BioPharma.
The study, which involved fewer than 10 DMD-affected boys between 12 and 17 years old, was conducted at Hammersmith Hospital in London and at the Institute of Human Genetics of the University of Newcastle Upon Tyne (U.K.).
Each boy received an injection of either 0.09 or 0.9 milligrams of AVI4658 into a foot muscle, and a salt solution into the corresponding muscle on the other foot. Three to four weeks later, each injected muscle was examined for evidence of dystrophin production.
Results showed the AVI4658-injected foot muscles produced dystrophin in all participants, and that the amount produced correlated with the injected dose. All participants tolerated the compound well, and there were no significant adverse events related to its administration.
The trial was funded by the U.K. Department of Health and led by Francesco Muntoni at Imperial College London, who has MDA support to study another muscle disease.
“As a clinician and scientist, I am very pleased by these findings and the prospects they offer for the potential treatment of this serious, lifethreatening condition,” Muntoni said in a Jan. 21 company press release. “Biopsies from muscles injected with the higher dose of test drug showed an unequivocal, widespread and robust response in terms of number of dystrophin positive muscle fibers. We will publish these exciting data in a peerreviewed journal in due course.”
The company says it will now study the effects of systemic (intravenous) delivery of AVI4658. It’s also developing four related exon-skipping compounds that target different dystrophin exons.
In December 2007, the Dutch biotechnology company Prosensa announced positive results for its exon-skipping compound, PRO051. In that study, conducted in the Netherlands and reported in the Dec. 27, 2007, issue of the New England Journal of Medicine, four boys with DMD between ages 10 and 13 began producing dystrophin after receiving injections into a leg muscle.
MDA is funding studies to develop exon skipping and related strategies to treat DMD and other diseases.
Enrollment complete for phase 2b study of DMD drug
PTC Therapeutics of South Plainfield, N.J., developers of the experimental compound PTC124 for a subset of patients with Duchenne muscular dystrophy (DMD), announced in February that enrollment for its current clinical trial of this drug is complete. MDA has funded a portion of the drug’s development.
PTC124, recently given the generic name ataluren, is designed to coax muscle cells to ignore an erroneous molecular stop signal that keeps them from synthesizing dystrophin, the muscle protein needed but missing in DMD.
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| SMA is a major focus for MDA’s research program. See the special In Focus center pullout section of this issue. |
If it leads to production of functional dystrophin, as early trials have suggested it does in some patients, it’s expected to be developed as a treatment for the 13 percent of boys with DMD estimated to have a stop-signal genetic flaw (mutation), known as a “premature stop codon” or “nonsense” mutation.
The one-year, multicenter trial of 174 boys will compare ataluren with a placebo (inert substance) on measures of safety and effectiveness. Results will likely be available in late 2010 or early 2011.
PTC has called this “phase 2b” trial (earlier phases were smaller, had no placebo group, and weren’t designed to detect efficacy) its “pivotal” study of ataluren.
Valproic acid to be tested in walking adults with SMA3
A study at Ohio State University Medical Center in Columbus is seeking 36 adults with type 3 spinal muscular atrophy (SMA3) who can walk 30 feet independently and meet other study criteria to participate in a study of valproic acid. Laboratory studies have indicated that valproic acid increases levels of full-length SMN, the protein deficient in SMA, in patients’ cells. Contact Sharon Chelnick, clinical research manager, at (614) 293-4973 or chelnick.1@osu.edu
In January, researchers announced that a trial of valproic acid and carnitine showed the drugs were not beneficial in children with SMA ages 2 to 8 who were not walking. Results for children 3 to 17 years old who were able to stand or walk and who also were part of that study were not yet available.
Researchers to determine SMA ‘biomarkers’
A study to compare functional, genetic and biochemical information in 120 children 2-12 years old with and without spinal muscular atrophy (SMA) is under way at some 20 institutions throughout North America. The goal of the study is to generate SMA-specific biochemical indicators (biomarkers) that can be used to track responses to experimental treatments in clinical trials. For information, go to www.clinicaltrials.gov and enter “pilot study of biomarkers for spinal muscular atrophy” in the search box.
MDA grantee studying children with SMA not linked to chromosome 5
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| Lisa Baumbach-Reardon has MDA support to study SMA not linked to chromosome 5. |
Lisa Baumbach-Reardon at the University of Miami has MDA support to extend studies of non-chromosome-5 spinal muscular atrophy (SMA). Mutations in the SMN1 gene on chromosome 5 are by far the most common form of SMA. Baumbach-Reardon is interested in hearing from families with children who initially appeared to have infantile-onset, chromosome-5 SMA but whose DNA did not reveal any SMN1 gene abnormalities. She can be reached at (305) 243-3997, or lbaumbac@med.miami.edu. |
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