Timeline of key discoveries in myotonic dystrophy research since DM was first described in 1909. Click on the corresponding timeline entry for links to research abstracts or reviews.
Abstracts not available for: Greenfield and Fleischer, 1911/1918; Bell, 1947; Vanier, 1960.
Nicholas Johnson, MD, and researchers at the University of Rochester recently published an article in The Journal of Child Neurology that describes the impact of childhood and congenital myotonic dystrophy on quality of life. The authors interviewed 21 children with childhood and congenital myotonic dystrophy and 13 parents. After recording these interviews, the authors reviewed transcripts to identify the most important symptoms to parents and children. Overall, participants reported 189 different symptoms.
Dr. Johnson and his colleagues found that many of the parents and children identified trouble speaking (dysarthria) as the primary symptom that impacted the children’s lives. Other participants identified learning difficulties and problems concentrating as life altering symptoms. Although many of the study participants did not identify a diagnosis of autism specifically, autistic traits, such as a narrow scope of interest, repetitive speech, inappropriate social responses, and inflexibility were reported.
As expected, many of the symptoms affecting those with congenital and childhood myotonic dystrophy are different from the symptoms of adult-onset myotonic dystrophy type-1. Prior work by Chad Heatwole, MD, MS-CI, the senior author on this study, identified fatigue, hand and finger weakness, and difficulty walking as significantly impacting the quality of life of those with adult-onset myotonic dystrophy type-1. While these symptoms were also reported in children with myotonic dystrophy, their presentation and significance were different.
Importantly, many symptoms of congenital and childhood myotonic dystrophy, such as communication difficulties, already have available treatments. The authors hope that by identifying the wide range of symptoms affecting children with myotonic dystrophy, doctors will be able to identify critical symptoms earlier and initiate timely treatment strategies.
Dr. Johnson and University of Rochester researchers, with the support of MDF, have used information from this study to develop a survey, which was distributed to US, Canadian and Swedish patients with congenital and childhood myotonic dystrophy. Results from this international group of patients will be used to further define and prioritize the most important symptoms to patients with congenital and childhood myotonic dystrophy. Ultimately this data will be used to help guide researchers in designing future therapeutic trials for these populations.
06/25/2013
Maurice Swanson, Ph.D., Professor of Molecular Genetics and Microbiology at University of Florida, Gainesville, and a team of researchers have found that the muscleblind-like 2 (MBNL2) protein in the central nervous system (CNS) may be responsible for the neurological impacts of myotonic dystrophy (DM), providing hope for new treatments. Muscleblind is a type of protein that plays an important role in switching proteins typically found only in babies to proteins found in adults. If this switch isn’t made, an imbalance exists that leads to myotonic dystrophy.
Dr. Swanson states that the team’s work seeks to understand what causes myotonic dystrophy beyond the mutations in the DM1 and DM2 genes.
Dr. Swanson examined which genes were affected by loss of MBNL2 in the brain and found more than 800 affected genes. Many of them had one thing in common: the encoded protein could be made in both fetal and adult forms and MBNL2 appeared to regulate which version was created, according to an article in Neurology Today. One persistent concern that people living with DM1 and DM2 have is the effects of this disease on the brain. “People who don’t have DM usually feel refreshed after a night’s sleep. Myotonic dystrophy patients do not routinely achieve a normal sleep pattern; instead, they have an interrupted series of sleep-wake patterns that do not allow for deep, restful sleep cycles”.
Dr. Swanson created a mouse that lacks the MBNL2 protein as an animal model for DM effects on the CNS. These mice showed normal skeletal muscle structure and function. However, the mice did have DM-related sleep issues, such as a higher number of REM sleep episodes and more REM sleep in general, leading to less restful sleep. In mice lacking MBNL1, another member of the MBNL protein family, the skeletal muscle effects were similar to what is seen in DM. But the central nervous system was not affected, according to Dr. Swanson.
“What we would like to do now is identify the specific cellular events that are abnormal in the DM brain and see if there is something we can do to treat these disease manifestations with focused therapy development. We would also like to understand the heart and muscle problems in DM. We have developed mice with DM-associated problems and we want to use these mouse models to develop effective drug treatments. Also, we want to understand what is so different about the congenital form of DM. Why does it manifest in babies and children? If we can develop animal models for congenital DM, then we can begin to address the important question of what goes wrong during fetal life,” explains Dr. Swanson.
Recently, therapy development for DM has accelerated and treatments based on anti-sense oligonucleotides will hopefully enter clinical trials in the near future. These new studies focused on the roles of MBNL proteins in CNS function should lead to alternative therapeutic strategies designed to reverse effects caused by expression of the mutant DM1 and DM2 genes.
04/16/2013
Methylphenidate, a psycho-stimulant drug, also known by its 1948 trademarked name of Ritalin, could be useful in the treatment of excessive daytime sleepiness (EDS) for DM1 patients, according to a recent study conducted by The Department of Human Genetics at the Centre Hospitalier Universitaire de Quebec in Quebec City, Canada.
A total of 24 French-Canadian patients who had DM1 and an Epworth Sleepiness Scale score of more than 10 (0-9: normal, 10-24: sleepy and medical advice should be sought) were invited to participate in the 3-week crossover trial of 20-mg/d of methylphenidate versus a placebo. There were two groups in the study; one group took the drug for 3 weeks, followed by a 2-week washout period, followed by 3 weeks of placebo, and the other group took placebo for 3 weeks, followed by a 2-week washout period, followed by 3 weeks of drug. Of the 24 patients (12 men; 12 women; median age 46 years), 17 completed the study.
Patients’ Daytime Sleepiness Scale and the Epworth Sleepiness Scale, measured at the end of each 3-week period, were used to measure the effectiveness of methylphenidate as a treatment for EDS. The drug’s effectiveness was also determined by a mean sleep latency test, patients’ energy and vitality after the study, and patients’ moods. Tolerability to treatment was monitored by blood pressure, the results of an echocardiogram, and other lab tests. Adverse reactions to the treatment were based on patients’ reporting and were recorded at each visit to the clinic.
The study concluded that a single 20-mg/d dose of methylphenidate significantly reduced daytime sleepiness in this small group of patients with DM1. The median scores on the Epworth Sleepiness Scale and the Daytime Sleepiness Scale showed a significant change. However, measurements of patients’ moods, energy, and vitality showed no changes, and the mean sleep latency test showed no significant changes. The most common adverse effects included nausea, loss of appetite, and palpitations, as reported by more patients who were treated with methylphenidate than by those receiving the placebo. Three patients stopped taking methylphenidate due to adverse effects that arose during treatment, which included diarrhea, nervousness and irritability. One patient died during the trial, but the autopsy results eliminated methylphenidate as the cause of death.
01/23/2013
MENLO PARK, CA (January 2013): MDF is pleased to announce its most recent round of Fund-A-Fellow postdoctoral fellowship research grant awards. In January 2013, MDF awarded two $100,000 grants to postdoctoral Fellows working in universities and research facilities to encourage basic research in the management, treatment and cure of myotonic dystrophy (DM) for a commitment of $200,000.
This award cycle brings the total research funding awarded by MDF to over $1.5M since its founding in 2006, and builds on MDF’s commitment to increasing the number of investigators focused on myotonic dystrophy research. To date, MDF Fellows have attracted additional research funding from larger organizations such as the National Institutes of Health, have helped influence interest in DM research at major pharmaceutical companies, and have risen to senior positions at academic and clinical settings across the United States. MDF Fund-a-Fellows have collaboratively deepened understanding of and commitment to myotonic dystrophy research significantly since the program’s founding in 2009.
Each of the two 2013-2014 FAF recipients will receive $50,000 a year for two years. The applicant pool for this year’s grant awards was extremely competitive and totaled 15, the largest ever for MDF fellowship funding. Applications were reviewed by a panel of distinguished international researchers and clinicians in the field of myotonic dystrophy. Final selections were determined by the MDF Board of Directors.
The two 2013-2014 $100,000 postdoctoral fellowship grants have been awarded to: Dr. Suzanne Rzuczek, Ph.D., The Scripps Research Institute – Florida; and Dr. Ayal Hendel, Ph.D., Stanford School of Medicine.
CTG/CAG repeat tracts represent the genetic basis for more than a dozen inherited dominant neurological disorders including Myotonic Dystrophy type 1 (DM1) and Huntington’s disease that currently have no cure. Despite the multitude pathologies underlying these devastating disorders, they all share common etiology: the expansion of CTG/CAG repeats. Interestingly, expanded CTG/CAG repeats have been shown to be prone to double-strand breaks (DSBs). Moreover, it was shown that the repair of the DSBs leads mainly to repeat contractions. These findings suggest that controlled DSBs might provide a way to induce repeat contractions that will correct disease-causing mutation and reduce disease risk. Dr. Hendel’s research will harness a unique genome editing technology in combination with induced pluripotent stem cells to examine the contribution of DSB repair to the stimulation of repeat contractions in DM1 cells, ultimately exploring new cellular and molecular DM1 pathological mechanisms involved in myotonic dystrophy.
Dr. Rzuzcek, in conjunction with the Disney Lab of The Scripps Institute, plans on using small molecules to disrupt the interaction between repeating CUG RNA and MBNL1 (muscleblind-like 1 protein), freeing it to function normally. The Disney Lab, of which Dr. Rzuczek is a member, has designed and synthesized several compounds that specifically bind the expanded CUG RNA and disrupt the interaction with MBNL1 in vitro. These compounds contain CUG-binding small molecules tethered together by a spacer. This approach is called modular assembly. Recently the spacer has been optimized to increase bioactivity and cell uptake. Dr. Rzuczek and her colleagues will improve the activity of the modularly assembled compounds using two approaches. The first will use the repeating DM1 RNA as a template to assemble small compounds with their optimized spacer into large modularly assembled structures within cells. This process is known as in situ click chemistry. The second approach will screen many small molecules that are similar to the known binders of DM1 RNA. Hit compounds will be screened in cells using a method that detects low levels of bioactivity. Compounds that are active in cells will be modularly assembled on the Disney-optimized spacer to enhance the interaction with DM1 RNA and improve bioactivity. If successful, these compounds could become a treatment for myotonic dystrophy.
01/23/2013
A generic cardiovascular drug called mexiletine, initially developed to treat heart rhythm abnormalities, appears to hold some potential for treating muscle stiffness and other symptoms of non-dystrophic myotonias (NDMs), a rare group of disorders without progressive muscle wasting and weakness, that have abnormalities in the function of ion channels in the muscle cells (chloride or sodium channels). The abnormal ion channel function leads to stiffness and delayed relaxation of muscle following grip or tight closing of the eyes (myotonia). Myotonic dystrophy (DM) has as one of its alterations abnormal function of the chloride channel. This causes myotonia and stiffness, and, like the patients with non-dystrophic myotonia, DM patients show a beneficial response to treatment with mexiletine.
Cells contain a striking diversity of RNA types, many of which have been implicated in the pathogenesis of neuromuscular disease. Unlike most RNAs, circular RNAs (circRNAs) are single-stranded, covalently closed loops. CircRNAs arise via one of three mechanisms: (a) direct ligation of 5′ and 3′ ends of linear RNAs, (b) as intermediates in RNA processing reactions, or (c) via “back splicing,” when a downstream 5′ splice site (donor) is joined to an upstream 3′ splice site (acceptor). A variety of biologic roles for circRNAs have been identified.
While aberrant RNA splicing represents a central disease mechanism in DM1, virtually nothing is known regarding the potential for dysregulation of circRNAs. Dr. Fabio Martelli (IRCCS Policlinico San Donato) and colleagues have recently published an analysis of dysregulation of circRNAs in DM1 patient skeletal muscle biopsies (Voellenkle et al., 2019). The authors show that specific myogenesis-associated circRNAs are altered in DM1 biopsies and in DM1 patient myogenic cell cultures.
The research team identified specific circRNAs through review of 30 published DM1 RNAseq databases—relative abundance of a circRNA to its linear counterpart was used as an initial filter, followed by comparison to a list of circRNAs that were previously identified in human or murine myoblasts. Thus, the analysis was not comprehensive, but geared toward identification of transcripts most likely to be dysregulated in skeletal muscle tissue. Candidate circRNAs meeting the investigators’ criteria then were validated using qPCR of skeletal muscles from DM1 subjects and age-/sex-matched controls. Primer specificity was confirmed and the possibility that results were due to a general increase in transcription in DM1 was excluded, and results were confirmed in independent muscle biopsies.
Taken together, four circRNAs—circCDYL, circHIPK3, circRTN4_03, and circZNF609—exhibited significantly increased circular-to-linear RNA ratio in DM1 muscles versus controls. The research team subsequently used receiver operating characteristic curve analysis and confirmed that a transcript’s circular-to-linear ratio could discriminate between DM1 and healthy controls. Finally, the increase in circular fraction for the four circRNAs correlated with a variety of clinical and molecular characteristics of study subjects. Circular fraction ratios correlated with both skeletal muscle strength and splicing biomarkers of disease severity. Moreover, circular fraction was higher in the more severely affected DM1 patients. Induction of two of the dysregulated circRNAs (circCDYL and circRTN4) was also detected in plasma. Finally, analyses of DM1 myogenic cell lines identified a pattern of circRNA dysregulation that was, in part, similar to data obtained in patient muscle biopsies.
The research team self-identified caveats and described these findings as pilot data. Any putative contributing role that dysregulated circRNAs may have in the pathogenesis of DM1 is currently unknown. Yet the discovery of specific, dysregulated circRNAs in DM1 skeletal muscle, if confirmed, may offer advantages for drug development efforts—circRNAs are exceptionally stable in that they are resistant to exonuclease degradation and their dysregulation was detectable in plasma and myogenic cell lines from DM1 patients. These traits make them amenable to use as pharmacodynamic biomarkers for clinical studies and trials in DM1.
Reference:
Dysregulation of Circular RNAs in Myotonic Dystrophy Type 1.
Voellenkle C, Perfetti A, Carrara M, Fuschi P, Renna LV, Longo M, Sain SB, Cardani R, Valaperta R, Silvestri G, Legnini I, Bozzoni I, Furling D, Gaetano C, Falcone G, Meola G, Martelli F.
Int J Mol Sci. 2019 Apr 19;20(8). pii: E1938. doi: 10.3390/ijms20081938.
In a disease that exhibits somatic mosaicism, somatic cell instability, and the consequent tissue-to-tissue variability in expanded repeat length, assigning an “actual progenitor repeat length” value to individual DM1 patients has been problematic. The connotations here are obvious—how do we use repeat length for essential drug development functions from molecular biomarkers to genotype-phenotype analyses to stratification of patients in interventional clinical trials, if the parameter is hard to pin down? A recent paper from a multi-site team (Universidad de Costa Rica, University of Texas MD Anderson Cancer Center, and University of Glasgow) attempts to determine the optimal body fluid/tissue to sample and thereby yield insight into the best path forward for clinical studies and interventional clinical trials (Corrales et al., 2019).
Dr. Fernando Morales and colleagues sought to build on their prior findings (Morales et al., 2012 & 2016) that used small pool-PCR (SP-PCR) to control for somatic instability in estimations of progenitor allele length measured in blood. The goal was to improve upon allele length correlations with age of DM1 onset. In their latest work, the research team reports out on comparison of saliva vs. blood as the analyte source for progenitor allele length determinations.
This report was based upon analysis of progenitor allele length in saliva and blood from 40 DM1 patients that had been characterized for age of onset; screening also assessed for presence of variant repeats and methylation of CTCF binding sites adjacent to the DMPK locus, as these may be modifiers of somatic instability. Modal allele length was slightly larger in saliva (529 repeats) than concurrently collected blood samples (486 repeats). Progenitor allele length then was estimated as the lower boundary of allele distribution from SP-PCR—values from the two sample sources were highly correlated and, again, were higher in saliva than blood (414 vs. 310).
Analyses showed that progenitor allele length estimated from blood samples explained 75% of the variation in DM1 age of onset, while that from saliva explained 66% of the variation. The authors suggest that the “true progenitor allele length” needed for genotype-phenotype studies and other preclinical and clinical development purposes is more likely reflected by the values obtained from blood samples.
Additional single molecule SP-PCR studies, excluding two CDM cases, revealed greater somatic instability in blood than in saliva. The research team also showed that the lower boundary of allele distribution was slightly higher in saliva than in blood, while the overall degree of somatic variation was typically lower in saliva than in blood. Finally, analyses of repeat variants and methylation levels as putative modifiers of somatic instability showed that neither were significant factors.
The authors of this paper summarize the compelling literature case against use of skeletal muscle samples (essentially the confounding effect of tissue-specific rate of somatic expansion) to estimate progenitor allele size, bringing the choice down to blood or saliva. These data show that somatic mosaicism is comparable in blood and saliva DNA from DM1 patients, while saliva is obtained by considerably less invasive means—a feature that is potentially vital for interventional clinical trials in CDM or repeated sampling to assess efficacy of a candidate therapeutic in either CDM or DM1.
References:
Analysis of mutational dynamics at the DMPK (CTG)n locus identifies saliva as a suitable DNA sample source for genetic analysis in myotonic dystrophy type 1.
Corrales E, Vásquez M, Zhang B, Santamaría-Ulloa C, Cuenca P, Krahe R, Monckton DG, Morales F.
PLoS One. 2019 May 2;14(5):e0216407. doi: 10.1371/journal.pone.0216407. eCollection 2019.
Somatic instability of the expanded CTG triplet repeat in myotonic dystrophy type 1 is a heritable quantitative trait and modifier of disease severity.
Morales F, Couto JM, Higham CF, Hogg G, Cuenca P, Braida C, Wilson RH, Adam B, del Valle G, Brian R, Sittenfeld M, Ashizawa T, Wilcox A, Wilcox DE, Monckton DG.
Hum Mol Genet. 2012 Aug 15;21(16):3558-67. doi: 10.1093/hmg/dds185. Epub 2012 May 16.
A polymorphism in the MSH3 mismatch repair gene is associated with the levels of somatic instability of the expanded CTG repeat in the blood DNA of myotonic dystrophy type 1 patients.
Morales F, Vásquez M, Santamaría C, Cuenca P, Corrales E, Monckton DG.
DNA Repair (Amst). 2016 Apr;40:57-66. doi: 10.1016/j.dnarep.2016.01.001. Epub 2016 Mar 8.
Given the novel disease mechanisms that are operative for myotonic dystrophy (DM), “drugging the RNA World” is a very popular theme in drug discovery and development for this disease. Small and large molecule approaches based on this strategy are in preclinical development for DM. Companies such as Expansion Therapeutics are moving toward interventional clinical trials to test the strategy. Dr. Steven Zimmerman (University of Illinois at Urbana–Champaign) and colleagues have recently published data in a model organism in support of a multivalent candidate therapeutic targeting both expanded repeat DNA and RNA in addressing the RNA gain-of-function in DM1 (Lee et al., 2019).
Dr. Zimmerman and his colleagues have exploited their expertise in bioorganic, synthetic organic, and physical organic chemistry to design and evaluate multivalent ligands targeted to expanded CTG DNA and expanded CUG RNA in a preclinical discovery and development effort for DM1 therapeutics. The Zimmerman team describes the approach as exploiting “smart molecules designed to enter the cell nucleus, bind the target DNA or RNA specifically and operate to reverse the deleterious effects of the expanded repeats.” The efficacy of this strategy lies in the use of a single ligand that targets both transcription of expanded CTG repeat DNA and interactions of expanded CUG repeat RNA with Muscleblind to mitigate the consequences of DM1.
The research team first focused on rational optimization of their existing small molecule inhibitor that targets DM1 expanded repeat RNA. Dimerization of the inhibitor markedly improved its efficacy, but vastly reduced cell permeability—thus necessitating a strategy change to ensure drug-like properties of the candidate therapeutic. Utilization of a linker sequence improved cell permeability and allowed oligomerization of the original monomer to further enhance binding to CUG expansions. Moreover, optimization of their synthetic and purification procedures provided a means to move forward with further testing of the molecule.
Studies in HeLa cells transfected with 960 CTG-repeat DMPK showed the ability of the multivalent compound to disrupt the nuclear foci and rescue the mis-splicing characteristic of DM1 in a dose-dependent manner. Activity in suppressing nuclear foci in the HeLa cell model was 1000-fold greater than with the original monomeric compound. The oligomer also showed promising activity in DM1 patient-derived myoblasts.
A surprising finding with the oligomeric compound tested here was that it also targeted expanded CTG DNA—this dual mechanism capability in targeting both transcription of the expanded repeat DMPK gene and its toxic transcript could potentiate the activity of the compound. Finally, in initial model organism efficacy testing, the oligomer showed activity in a DM1 Drosophila climbing assay and in a liver-specific DM1 mouse model—supporting both the bioavailability and activity of the compound. Preliminary toxicity studies showed no liabilities.
Taken together, a multivalent, cell-penetrating compound with potential to knock down both production of toxic DMPK RNA transcript and its interactions with MBNL represents an attractive opportunity for therapy development in DM1. The model organisms that this compound has been tested in thus far, a DM1 fly and liver-specific DM1 mouse, are not ‘traditional’ models for therapy development in the disease, but establish an initial level of proof of concept. The strength of the Zimmerman group lies in bioorganic chemistry expertise and partnership with groups with strengths in DM1 disease mechanisms and preclinical models should help ascertain the value in moving forward with the novel compounds developed here.
Reference:
Intrinsically cell-penetrating multivalent and multitargeting ligands for myotonic dystrophy type 1.
Lee J, Bai Y, Chembazhi UV, Peng S, Yum K, Luu LM, Hagler LD, Serrano JF, Chan HYE, Kalsotra A, Zimmerman SC.
Proc Natl Acad Sci U S A. 2019 Apr 11. pii: 201820827. doi: 10.1073/pnas.1820827116. [Epub ahead of print]
Antisense oligonucleotides – short segments of genetic material designed to target specific areas of a gene or chromosome – that activate an enzyme to “chew up” toxic RNA (ribonucleic acid) could point the way to a treatment for a degenerative muscle disease called myotonic dystrophy, said researchers from Baylor College of Medicine and Isis Pharmaceuticals, Inc., in a report in the journal Proceedings of the National Academy of Sciences (www.pnas.org) .
“This is a proof-of-principle therapy that is very effective in cell culture and mice,” said Dr. Thomas A. Cooper, professor of pathology and immunology and molecular and cellular biology at BCM and the report’s corresponding author. “The treatment will have to be refined to deliver systemically in people with myotonic dystrophy.”
Myotonic dystrophy is the most common muscular disease in adults, affecting mainly the skeletal muscles, heart and central nervous system. It occurs because of a mutation that causes numerous repeats of three letters of the genetic code (CTG) in a gene called DMPK. RNA is made as a step in the cell’s production of the protein associated with the gene. The messenger RNA (the chemical blueprint for making a protein) that is produced from the mutated gene also contains the abnormal long repeats that cause the RNA to accumulate in the cell’s nucleus. There it sequesters and blocks the function of a protein called Muscleblind-like 1 and activates another protein called CELF1. These proteins antagonize one another and the result is abnormal expression of proteins from many other genes in adult tissues, resulting in disease.
To counteract this, Cooper and his colleagues created antisense oligonucleotides called gapmers, which are simply strands of genetic material that seek out portions of the abnormal RNA repeats and target an enzyme called RNase H to the toxic RNA causing its degradation. They also showed that combining the gapmers with other antisense oligonucleotides that help released the sequestered Muscleblind-like1 can enhance the effect.
“It worked in cultures of cells with the expanded repeats and in mice that model myotonic dystrophy,” said Cooper. “We did it in skeletal muscle first because we can inject the material directly into the muscle.”
Later, he plans to determine if the material also works in the animals’ hearts.
Using the treatment in people will require more fine-tuning, said Cooper. He would like to be able to give the therapy systemically rather than directly into the muscle. They saw some muscle damage and inflammation in the animals they treated.
Antisense oligonucleotide treatments are being tested in Duchenne muscular dystrophy and another disease called spinal muscular atrophy, said Cooper.
Others who took part in this research include Johanna E. Lee of BCM and C. Frank Bennett of Isis.
Funding for this work came from the National Institutes of Health, the Muscular Dystrophy Association and the Shanna and Andrew Linbeck Family Charitable Fund.
Reposted with permission from Baylor College of Medicine
05/16/2012