Corticospinal Tract Involvement in DM1

Published on Tue, 11/06/2018

Value of CNS Imaging in DM1

Brain imaging has shown potential to assess progression of DM1 and thus may prove to be an important biomarker or outcome measure to assess candidate therapeutics targeted to the CNS. Consistent with neuropathologic assessments, a recent systematic review of such studies (Okkersen et al., 2017) concluded that DM1 causes broad structural changes in both white and gray matter with little evidence of specific regional involvement or sparing. This imaging data also has been correlated with individual patient cognitive or neuropsychological findings. PET and SPECT imaging did identify patterns of specificity in cortical region involvement. However, data have not yet been available to evaluate links between brain pathology and motor function in DM1. Understanding such structural/functional associations is critical to the design, conduct, and interpretation of interventional clinical trials targeting the CNS in DM1 patients.

Identification of Pathway-Specific Involvement and Linkage to Motor Function

To determine the relationship between cerebral cortical changes and motor function, Dr. Yongmin Chang (Kyungpook National University) and colleagues studied a cohort of 18 adult DM1 patients (mean CTG repeat length of 360) and 20 age-matched healthy controls using voxel-based quantitative MRI (including DTI) in conjunction with motor functional assessments (hand grip, 6-minute walk test (6MWT), and MRC sum score (MRCSS)).

The team showed that reductions in volume of specific gray matter regions correlated with CTG length, hand grip score, and disease duration. The broadest range of cortical involvement was seen in the correlation of hand grip score with pathology in specific gyri and sulci in frontal, parietal, and occipital lobes, including both precentral and postcentral gyri. DTI data established correlations between genetic and clinical parameters (CTG repeat length, MRCSS, and 6MWT) and abnormalities in the posterior limb of the internal capsule and middle section of the corticospinal tract. These white matter changes were accompanied by reduction in volume in both precentral and postcentral gyri, as measured by DTI—the authors argue that these data support a strong association between gray and white matter changes in DM1.

Overall, the research team noted strong relationships between the motor functioning of DM1 patients and abnormalities in the corticospinal tract, and specifically linked the degree of gray matter and descending motor tract changes, as measured by DTI parameters, to severity of hand grip performance. They reaffirmed prior calls for longitudinal imaging/clinical studies to better characterize the natural history of CNS changes and improve clinical trial readiness in DM1.


Brain imaging in myotonic dystrophy type 1: A systematic review.
Okkersen K, Monckton DG, Le N, Tuladhar AM, Raaphorst J, van Engelen BGM.
Neurology. 2017 Aug 2. pii: 10.1212/WNL.0000000000004300. doi: 10.1212/WNL.0000000000004300. [Epub ahead of print] Review.

Diffusion tensor imaging and voxel-based morphometry reveal corticospinal tract involvement in the motor dysfunction of adult-onset myotonic dystrophy type 1.
Park JS, Song H, Jang KE, Cha H, Lee SH, Hwang SK, Park D, Lee HJ, Kim JY, Chang Y.
Sci Rep. 2018 Oct 22;8(1):15592. doi: 10.1038/s41598-018-34048-9.

Challenges in Assessing the CNS in DM1

Published on Tue, 11/06/2018

Towards CNS Endpoints for Clinical Trials in DM1

CNS deficits represent an important component of the DM1 phenotype and play a key role in overall burden of disease. Yet, complex brain functional assessments may be complicated by the interaction of peripheral and central contributors, so it is important to understand any limitations imposed by such interactions.

The MDF Research News previously highlighted an important series of DM-focused reviews in Frontiers of Neurology. A new original research article in the same journal, by Mark Hamilton (Queen Elizabeth University Hospital, Glasgow) and colleagues (Hamilton et al., 2018), offers an important new perspective on developing clinical outcome measures for assessing CNS function in clinical studies of and interventional trials in DM1.

Deficits of Patient Motor and Cognitive Insight May Confound CNS Outcome Measures

The Glasgow-based research team assessed 45 adult or late-onset DM1 subjects and 20 controls using a battery of neuropsychological and symptomatic instruments, as well as assessments of CNS structure (by MRI) and CTG repeat length. Neuropsychological tests followed OMMYD recommendations, including Stroop test (controlled for reading speed), Trail Making tests (controlled for speed), Delis-Kaplan Executive Function System, and Block Design test. Study subjects also completed the Edinburgh Cognitive and Behavioral ALS Screen and the FAS controlled oral word association test. Self-reported instruments used assessed fatigue, daytime sleepiness, depression, pain, dysexecutive symptoms, as well as MDHI and DM1-ActivC. The overall test battery appeared to be well-tolerated by DM1 subjects.

Neuropsychological testing assessing multiple domains identified impairment in function of DM1 patients versus controls, although correction for reading or motor speed mitigated the magnitude of some of these differences. The researchers highlighted the impact that dysarthria and upper limb weakness could have upon some neuropsychological measures.

Self-reported assessments of cognitive function obtained data consistent with prior reports—that DM1 patients reported greater fatigue, lower mood, greater levels of pain, and executive dysfunction. However, findings of lower mood (including depression) strongly correlated with increased self-reporting of cognitive deficits. MRI gray and white matter measures correlated with various neuropsychological findings.

Selecting CNS Outcome Measures for DM1

The researchers concluded that muscle weakness interacts with and can potentially compromise the interpretation of data from cognitive assessment tools commonly used in studies of DM1. Moreover, they show that patient-reported assessments are subject to influence of mood and insight. The potential for peripheral physical limitations, mood, and/or insight (i.e., disease awareness) to influence CNS assessments should be considered in the choice of instruments for natural history studies or interventional clinical trials in DM1. Instruments not subject to limitations, or with known limitations that can be controlled for, of mood, basic speed of information processing or manual dexterity or dysarthria may be of greatest value in assessing CNS function in this multi-system disorder.


Outcome Measures for Central Nervous System Evaluation in Myotonic Dystrophy Type 1 May Be Confounded by Deficits in Motor Function or Insight.
Hamilton MJ, McLean J, Cumming S, Ballantyne B, McGhie J, Jampana R, Longman C, Evans JJ, Monckton DG, Farrugia ME.
Front Neurol. 2018 Oct 2;9:780. doi: 10.3389/fneur.2018.00780. eCollection 2018.

Mechanism of Myogenic Defects in CDM

Published on Tue, 11/06/2018

Defective Myogenesis: Mechanisms Contributing to Severity of CDM

Prior reports have implicated developmental defects during myogenesis in the pathogenesis of congenital myotonic dystrophy (CDM). Moreover, a recent study has linked a disruption of developmentally regulated RNA alternative splicing in CDM to skeletal muscle pathology (Thomas et al., 2017). Mechanistically, CDM is not simply a more severe phenocopy of DM1 and an understanding of its molecular pathogenesis may provide new insights into CDM-targeted therapeutic strategies.

Mechanism of Myogenesis Inhibition in CDM

Dr. Marcella Simili (Institute of Biophysics, Pisa) and colleagues previously demonstrated alterations in key signal transduction pathways responsible for muscle differentiation in cell lines from DM1 embryos carrying long repeats (3200 CTG) and also provided evidence of autophagy that might be responsible for the severe skeletal muscle phenotype in CDM (Beffy et al., 2010). In a new report (Rizzo et al., 2018) this group examines whether autophagy causally links to abnormal myogenesis and severe muscle deficits in CDM.

The research team conducted electron microscopic and molecular studies of myogenesis in two fetal cell lines, CDM13 and CDM15, with 1800 and 3200 CTG repeats, respectively. They showed that, while both cell lines undergo autophagy, impaired myogenic differential occurred only in CDM15. This finding is interpreted as evidence that induction of autophagy is independent, and thus not a proximate cause, of impaired myogenesis.

Comparisons of myogenic regulatory factor (MYOD and MEF2A) activation and subsequent activation of miRNAs that control muscle differentiation showed their upregulation only in the lower repeat number CD13 line. These data provided additional evidence dissociating autophagy from impaired myogenesis.

Finally, the research team determined that markers of cellular stress and specific interferon (IFN) type 1 pathway induction (upregulation of IRF7, STAT1, OAS1, OAS2, and OAS3) was associated with the abnormal differentiation in CD15 cells, but not in CD13 or control myoblasts. IFN1 pathway induction was exacerbated when myogenic differentiation was induced in CD15. In turn, addition of IFN1 pathway inhibitors (targeted to IRF7 and TLR3) corrected the myogenic defect in CD15 myoblasts.

A Putative Target for a Muscle Therapeutic in CDM?

Taken together, Dr. Simili and colleagues concluded that inappropriate activation of the innate immune response, independent of autophagy, may underlie the impaired myogenesis and severe skeletal muscle pathology that characterizes CDM. They suggest that IFN1 pathway inhibitors might constitute a new therapeutic strategy for CDM.


Disrupted prenatal RNA processing and myogenesis in congenital myotonic dystrophy.
Thomas JD, Sznajder ŁJ, Bardhi O, Aslam FN, Anastasiadis ZP, Scotti MM, Nishino I, Nakamori M, Wang ET, Swanson MS.
Genes Dev. 2017 Jun 1;31(11):1122-1133. doi: 10.1101/gad.300590.117. Epub 2017 Jul 11.

Altered signal transduction pathways and induction of autophagy in human myotonic dystrophy type 1 myoblasts.
Beffy P, Del Carratore R, Masini M, Furling D, Puymirat J, Masiello P, Simili M.
Int J Biochem Cell Biol. 2010 Dec;42(12):1973-83. doi: 10.1016/j.biocel.2010.08.010. Epub 2010 Aug 24.

Activation of the interferon type I response rather than autophagy contributes to myogenesis inhibition in congenital DM1 myoblasts.
Rizzo M, Beffy P, Del Carratore R, Falleni A, Pretini V, D'Aurizio R, Botta A, Evangelista M, Stoccoro A, Coppedè F, Furling D, Simili M.
Cell Death Dis. 2018 Oct 19;9(11):1071. doi: 10.1038/s41419-018-1080-1.

What We Do (and Don’t) Know About Cognitive Function in DM1

Published on Thu, 11/01/2018

The Gap in Natural History Data

Cognitive impairment is a substantial unmet need in DM1. Increasingly, drug companies are aware that targeting therapies to the brain will be essential to addressing the overall burden of disease. Yet, therapy development efforts in other types of muscular dystrophy tell us that it is critical to understand disease natural history in order to facilitate efficient and effective clinical trials. Many of the studies to date that have characterized neuropsychological function in DM1 are both limited in scope and underpowered. As a consequence, it currently is unclear whether DM1 is characterized by a global pattern of cognitive deficits or whether specific functions are affected. The key question is—how do we best utilize available resources to construct a natural history of cognitive dysfunction in DM1 that is sufficient to support interventional trial outcome measure selection and to improve patient care?

A Path Forward Through Meta-Analysis

Kees Okkersen and colleagues at Radboud University Medical Center and the University of Amsterdam recently characterized the cognitive profile of DM1 patients through a meta-analysis of psychological data from 40 eligible studies identified in Embase, Medline, and PsychInfo (totaling 1122 patients and 952 controls). Eligible studies employed a large battery of neuropsychological tests. The analytic approach was to characterize the individual cognitive tests as informative of specific cognitive domains and then determine the level of effect from meta-data across each of 12 cognitive domains.

Although effect size varied, performance of DM1 subjects versus controls was impaired across all cognitive domains. Domains most heavily impacted by DM1 included global cognition, intelligence, visual memory, visuospatial perception, visuoconstruction, psychomotor speed, and social cognition. Analyses suggested that conclusions from the pooled data were not influenced by either publication bias or any inordinate impact of single studies.

Current Status of Understanding DM1 Cognitive Profiles

While the research team concluded, based on meta-analysis of a large cohort and the preponderance of evidence, that DM1 is characterized by significant deficits across all cognitive domains, they noted that heterogeneity is the hallmark of this patient group. Detection of a large effect size in any specific cognitive domain could either be due to consistent deficits across DM1 patients, substantial involvement of the specific domain among a subset of patients, or acute sensitivity of the neuropsychological tests that inform that domain. A recent meta-analysis of neuroimaging studies in DM1 validated a similar pattern of widespread and heterogeneous involvement in CNS.

While some of the neuropsychological tests assessed by the research team showed substantial levels of effect and consistency (e.g., Rey-Osterrieth Complex Figure, Wechsler Digit Symbol Coding, and Raven Progressive Matrices), these tests readout on multiple cognitive functions. The research team argued that future studies should include specific, rather than broad, cognitive assessments, and concluded that meta-analyses of the often small cohorts in individual DM1 studies can better elucidate CNS mechanisms as well as inform best practices for future patient assessment.


The cognitive profile of myotonic dystrophy type 1: A systematic review and meta-analysis.
Okkersen K, Buskes M, Groenewoud J, Kessels RPC, Knoop H, van Engelen B, Raaphorst J.
Cortex. 2017 Aug 16;95:143-155. doi: 10.1016/j.cortex.2017.08.008. [Epub ahead of print] Review.

Non-Invasive Biomarkers for DM1

Published on Tue, 10/16/2018

Pharmacodynamic Biomarkers and DM

There is now strong support for the concept that a panel of splicing events may serve as a pharmacodynamic biomarker for go/no go decisions in drug development for DM1. Data establishing splicing event sensitivity to free MBNL levels has converged with the natural history of alternative splicing patterns in DM patients to yield a subset of splicing events with the sensitivity and reproducibility to evaluate candidate therapeutics in early stage clinical trials. Quantitative pharmacodynamic biomarkers are invaluable in de-risking industry drug discovery and development, as they facilitate early stage assessment of molecular target engagement and modulation and may inform dose ranging studies. The only caveat is the dependence of these measures upon repeated muscle biopsies (a risk reduced, but not eliminated, by more tolerable needle biopsies). The identification and validation of a non-invasive assay of patient splicing status would be a valuable step forward for clinical trials in DM.

Early Support for a Non-Invasive Biomarker for DM1

Dr. Thurman Wheeler and colleagues at Massachusetts General, Harvard Medical, and Boston Children’s have explored the concept that a subset of extracellular RNAs (exRNAs) released into blood or urine may: (a) reflect alternative splicing status in DM-affected tissues and (b) thereby serve as an easily accessible pharmacodynamic biomarker platform for DM1 (Antoury et al., 2018). These studies were supported in part by a grant to facilitate “Development of Biomarkers for MDF Studies” from MDF.

The research team initially found that > 30 transcripts that are alternatively spliced in DM1 muscle biopsies were detectable in human blood and urine samples; follow-up studies confirmed the presence of RNAs in extracellular fluids/exosomal particles. Normalized DMPK expression levels in urine from DM1 patients, by droplet digital PCR, were ~50% of unaffected controls. Assessments of DM1-established alternative splicing events showed that a subset (10/33) also occurred in urine exRNA, including being conserved in longitudinal (6-26 month) studies of the same patients. Assessments of alternative splicing events in blood exRNA did not yield the same value.

Using principal component analysis of 10 alternative splicing events observed in urine exRNA, the research team then generated a putative composite biomarker panel for DM1. The ensuing predictive model of alternative splicing in DM1 proved to be 100% accurate in comparisons of training and independent validation data sets to distinguish DM1 from unaffected controls and in distinguishing disease status of subsequently enrolled subjects. The research team also linked alternative splicing patterns in urine exRNA to variation in DM1 clinical phenotypes, suggesting that modeling of urine exRNA alternative splicing may allow both the tracking of disease progression and the impact of candidate therapeutics.

Finally, to address questions as to the source of urine exRNA, the team assessed alternative splicing in urinary tract cells of DM1 mouse models (the ubiquitous Mbnl1 ko and the tissue-specific HSALR). While kidney and bladder cells of the Mbnl1 ko reflected patterns in skeletal muscle, assessments of the same tissues in the HSALR showed no differences from control mice. These data strongly suggested that the exRNAs assessed in urine reflect exosomes released from urinary tract cells. Some of the alternatively spliced transcripts in urine exRNA also were shown to be altered by antisense oligonucleotide drugs previously shown to correct splicing patterns in DM1 mouse models. The research team’s parallel studies of Duchenne muscular dystrophy also supported the concept that urine exRNA has utility as a pharmacodynamic biomarker in drug intervention studies.

Towards a Non-Invasive Biomarker for DM1

Taken together, these data provide compelling proof of concept that a panel of alternative splicing events assessed in urine may serve as a robust composite biomarker of DM1 progression and as a tool for assessment of candidate therapeutics. A non-invasive biomarker such as this would greatly extend the ability to perform repeated measurements in longitudinal natural history studies (as a disease progression biomarker) and in interventional clinical trials (as patient stratification and pharmacodynamic biomarkers), including making assessment of pediatric DM1 patient cohorts feasible. Although it is not essential to formally qualify a biomarker, existing regulatory agency guidance documents (see References below) provide a valuable evidentiary framework for moving non-invasive biomarker work towards an accepted clinical tool for DM1.


Analysis of extracellular mRNA in human urine reveals splice variant biomarkers of muscular dystrophies.
Antoury L, Hu N, Balaj L, Das S, Georghiou S, Darras B, Clark T, Breakefield XO, Wheeler TM.
Nat Commun. 2018 Sep 25;9(1):3906. doi: 10.1038/s41467-018-06206-0.

Framework for Defining Evidentiary Criteria for Biomarker Qualification. Evidentiary Criteria Writing Group.

Guidance for Industry and FDA Staff: Qualification Process for Drug Development Tools.

Review: What Have We Learned About RAN Translation?

Published on Tue, 10/16/2018

Avoiding the Pitfalls of Tunnel Vision

In a reward system driven by grant dollars in hand and publication numbers/journal impact factors, it is only too easy to put on the blinders and succumb to tunnel vision. Single-minded focus is a prized career trait in academia. Yet the puzzle that is myotonic dystrophy may only be solved by modelling that benefits from diseases not within the focus of your current R01 or the publication track record that you’re building. The role that Repeat-Associated Non-ATG (RAN) translation plays in DM1/DM2 is likely one of those cases where insights can be defeated by excessive focus on just ‘your disease.’

A Cross-Disease Framework for Understanding RAN Translation

Although studies in DM1 contributed toward the initial identification and characterization of a new molecular phenomenon, RAN translation, its role in the pathogenesis of DM remains elusive. Evidence on RAN translation acquired from ‘other diseases’ may advance understanding of basic and conserved molecular mechanisms, but also may inform what specific role RAN translation plays in DM and whether this mechanism needs to be targeted by therapeutic strategies. A new publication by Dr. Laura Ranum and colleagues at the University of Florida (including a former MDF Fellow as lead author, Dr. John Cleary) sought to review current knowledge of RAN translation across multiple microsatellite expansion disorders of the nervous system (Cleary et al., 2018).

The review article gives a nice synopsis of the discovery and initial characterization of RAN translation in neurological disorders. Initial discovery was in Spinocerebellar ataxia type 8, but the mechanism was also rapidly found in DM1 as appropriate control experiments were included to ensure that RAN proteins could not arise from another mechanism. Discovery and characterization in other diseases rapidly followed, often expanding the potential pathological mechanisms operative in a disease—FXTAS being a prominent example where the field had pushed a toxic RNA gain of function mechanism, but now toxic RAN proteins had to be considered as well. By contrast, toxic polyglutamine proteins have been a leading pathogenic mechanism in Huntington’s disease, but it was soon discovered that CAG repeats in canonical open reading frames yielded multiple RAN proteins. RAN translation was subsequently discovered in other diseases where MBNL sequestration had been linked to the disease mechanism—DM2 and Fuch’s Endothelial Corneal Dystrophy. Finally, the authors devote space to the extensive work in C9orf72 ALS/FTD, where the literature now implicates RAN translation in specific molecular roles that may contribute to disease.

The authors of this review also discuss targeting of the RAN translation mechanism in drug discovery and development efforts. They note that such strategies may facilitate the determination of the differential roles of RNA gain-of-function versus RAN translation proteins.

Lessons Learned

It’s encouraging that many DM researchers have ties to the broader microsatellite expansion disorder community and attend conferences with that distributed agenda. Thus, there’s already a strong inclination to avoid the blinders and seek understanding of how similarities and differences across this > 40 neurological disease class with repeat expansions (8 of which have now been reported to exhibit RAN proteins) can provide insights into the individual diseases. Finally, it’s important to remember that both laser-like focus on DM and attention to lessons from the broader neurological disease class that invokes similar mechanisms may represent the optimal path forward to help patients living with DM.


Repeat associated non-ATG (RAN) translation.
Cleary JD, Pattamatta A, Ranum LPW.
J Biol Chem. 2018 Sep 13. pii: jbc.R118.003237. doi: 10.1074/jbc.R118.003237. [Epub ahead of print]

MDF Releases DM1 Care Recommendations

Published on Tue, 09/25/2018

SAN FRANCISCO, CA (September 25, 2018): MDF is pleased to announce the publication of the first-ever Consensus-based Care Recommendations for Adults with Myotonic Dystrophy Type 1. The Quick Reference Guide to the full Consensus-based Care Recommendations was published in Neurology Clinical Practice online September 13. The article will be published in the NCP print version in October. MDF is working internationally to help ensure that the care recommendations are disseminated and adopted broadly.

Currently no evidence-based guideline exists to establish a standard of care for myotonic dystrophy, and a comprehensive care guideline will not be available until a number of studies are conducted to establish the rigorous evidence needed to create one. As a result, patients report difficulty accessing quality care and informed clinicians. Sixty-six clinicians highly experienced in the care of people living with myotonic dystrophy type 1 worked collaboratively for over a year to develop consensus regarding care strategies for over 20 different body systems. The resulting clinical care recommendations are intended to help standardize and elevate care for people living with myotonic dystrophy, improving quality of life for affected families and reducing variability in clinical trial and study environments.

Consensus-based Care Recommendations for Adults with Myotonic Dystrophy Type 1 Resources:

Update: DM1 Care Recommendations are now available in German, Italian, French, French-Canadian, Spanish, Swedish & Georgian! Download the recommendations here.

About Myotonic Dystrophy

Described as “the most variable of all diseases found in medicine”, myotonic dystrophy (DM) is an inherited disorder that can appear at any age and that manifests differently in each individual. The most common form of adult-onset muscular dystrophy, DM may affect as many as 1:2,550 people worldwide, and can cause muscle weakness, atrophy and myotonia, as well as problems in the heart, brain, GI tract, endocrine, skeletal and respiratory systems. There is currently no treatment or cure for DM.

About MDF

MDF is the world’s largest DM patient organization. Its mission is My Cause. My Cure: is to enhance the lives of people living with myotonic dystrophy, and advance research efforts focused on finding treatment and a cure for this disorder through education, advocacy and outreach.

For additional clinical resources offered by MDF, click here.

Status: Clinical Outcome Measures for DM2

Published on Tue, 09/25/2018

The Reality: Clinical Trial Readiness Determines Tractability and Pharma/Biotech Interest

Ensuring clinical trial readiness is critical for any rare disease. If the patients to participate in clinical trials can’t be identified (function of registries), disease progression is not well understood (function of natural history studies), measures of target engagement and modulation aren’t available (function of pharmacodynamic biomarkers), and clinically meaningful measures are not available and validated (function of validated clinical outcome measures), then it is difficult to convince drug developers that a disease is tractable. The myotonic dystrophy field and MDF have been working toward checking these boxes to de-risk the disease for development of drugs and biologics. Yet, the majority of the efforts and accomplishments in achieving clinical trial readiness have been for DM1. There is a clear need to further invest in trial readiness for DM2.

What is the Status of Clinical Outcome Measures for DM2?

A systemic review has just been published, assessing one aspect of clinical trial readiness for DM2—the status of functional tests and patient-reported outcome measures that have been used in clinical studies and trials of DM2 patients. Drs. Emanuele Rastelli and Benedikt Schoser, and their colleagues at University of Rome Tor Vergata and Ludwig-Maximilians University, report their assessment and the critical need to invest further effort and resources into identification and validation of clinical outcome measures for DM2.

In their meta-analysis, the research team identified outcome measures used in studies of genetically confirmed DM2 subjects that were published before April 2018 (identified via key word searches of PubMed, EMBASE, Cochrane Reviews, and Cochrane trials databases). A similar search was conducted for the broader neuromuscular disease literature in order to identify and evaluate other outcome measures that could potentially be used for DM2.

The systematic process of identifying, screening, and determining eligibility resulted in inclusion of 10 studies of DM2 and 48 studies of outcome measures used in other neuromuscular diseases.

The most significant conclusion from this study is that none of the measures considered (either clinical function or patient-reported) have yet been validated in DM2. Utilization and pros/cons of each of the outcome measures in the studies evaluated here are reported in tabular form in the  paper.

INQoL, SF-36, MPQ, and BPI were the most frequently used patient-reported measures. It appeared that none of these were particularly effective in assessing the mild myotonia that characterizes DM2. MPQ showed value in differentiating characteristics of a prominent DM2 symptom, pain, while BPIsf exhibited difficulty in distinguishing pain in DM1 vs. DM2. Data on assessment of pain with a pressure algometer showed its potential as an outcome measure. The research team also identified liabilities in the broader patient-reported indices, INQoL and SF-36.

For evaluation of muscle strength, the team noted the frequent use of both MMT and QMT in assessment of DM2 subjects. While QMT was regarded as having higher potential to evaluate changes in strength over time (e.g., in longitudinal natural history studies or clinical trials), they suggest that inter-rater reliability has not yet been established in DM2. No publications came through the selection and screening process for clinical evaluation of myotonia in DM2; the authors noted the low reported disease burden of myotonia in DM2, thus quantitative testing may have little value for clinical trials in this patient group. Finally, the research team list in tabular fashion a total of 21 other outcome measures gleaned from the literature on other neuromuscular diseases that they deem as “suitable” for use in DM2. Assessment and validation of these measures would have to be performed in a DM2 cohort.

Path Forward

Taken together, the take-away from this systemic review is that availability of reliable and validated outcome measures represents an important gap in trial readiness for DM2. That is not to say that some measures already identified in studies of DM2 and other neuromuscular diseases might ultimately prove to be very adequate for use in natural history studies and interventional clinical trials.


Towards clinical outcome measures in myotonic dystrophy type 2: a systematic review.
Rastelli E, Montagnese F, Massa R, Schoser B.
Curr Opin Neurol. 2018 Oct;31(5):599-609. doi: 10.1097/WCO.0000000000000591.

Human iPSC-Derived Neurons for DM2

Published on Tue, 09/25/2018

Human iPSCs as Disease Models and Drug Screening Tools

The ability to program human iPSCs derived from patients with genetic disorders into affected cell types has provided a better understanding of pathogenic mechanisms and a tool for early stage evaluation of putative drug development targets and therapeutic strategies. In conjunction with relevant animal models, iPSCs provide a platform to achieve preclinical proof of concept and the scientific rationale to move into clinical evaluation of candidate therapeutics. Given the involvement of the CNS in myotonic dystrophy, the availability of patient iPSC-derived neuronal cells would represent an important resource for therapy development.

Neuronal Differentiation of DM2 iPSCs

Establishment of patient-derived neural cell lines can provide an important tool for mechanistic studies and therapy development in neurodegenerative diseases, providing access to otherwise inaccessible brain tissues. For DM1, Dr. Tee Ashizawa and colleagues previously established DM1 iPSC lines and showed that iPSC-derived neural stem cells could be differentiated into neurons and glia with intranuclear RNA-MBNL foci (Xia et al., 2013).

In a recent report, Dr. Paola Spitalieri (University of Rome Tor Vergata) and colleagues have generated two DM2 and two wild type human iPSC lines from skin biopsies and differentiated these into cells expressing neuronal markers (Spitalieri et al., 2018). Established hallmarks of DM2 were conserved in differentiated neural cells—CNBP CCTG expansion length and number of CCUG-MBNL nuclear foci increased during neuronal differentiation. Assessment of various neuronal markers over the 25-30 days required to achieve neuronal conversion showed the differentiated population to contain an admixture of neurons, astrocytes, and oligodendrocytes.

Utility of DM2 iPSCs

The temporal pattern of expression of neuronal markers suggests that the time course of neurogenesis could be evaluated in vitro in DM2 versus wild type cells in an assessment of the suspected disease impact upon neurodifferentiation. Moreover, DM2 iPSCs may provide a renewable cell population for rapid screening of candidate therapeutics that address primary disease mechanisms in DM2. MDF has been working with RUDCR Infinite Biologics to establish DM iPSC cell lines that are available to all investigators without intellectual property constraints. RUDCR already has human iPSC lines established and quality controlled for DM1 and now available for distribution. We anticipate that human DM2 iPSC lines will be available soon.


Generation of neural cells from DM1 induced pluripotent stem cells as cellular model for the study of central nervous system neuropathogenesis.
Xia G, Santostefano KE, Goodwin M, Liu J, Subramony SH, Swanson MS, Terada N, Ashizawa T.
Cell Reprogram. 2013 Apr;15(2):166-77. doi: 10.1089/cell.2012.0086.

Generation and Neuronal Differentiation of hiPSCs From Patients With Myotonic Dystrophy Type 2.
Spitalieri P, Talarico RV, Murdocca M, Fontana L, Marcaurelio M, Campione E, Massa R, Meola G, Serafino A, Novelli G, Sangiuolo F, Botta A.
Front Physiol. 2018 Jul 27;9:967. doi: 10.3389/fphys.2018.00967. eCollection 2018.

Furamidine Mechanism of Action in DM1

Published on Tue, 09/25/2018

Small Molecule Approaches to DM1

A variety of small molecules have been evaluated in models of DM1 as putative therapeutics. Small molecules have the advantage of chemical optimization of drug-like traits, including blood-brain barrier permeability, and thus are attractive for multisystemic disorders like DM1.

Prior studies of the small molecule, pentamidine, and its analogs showed efficacy in restoring splicing defects in DM1 cells and animal models and suggested that the mechanism of action was binding to and inhibition of transcription of the expanded repeat transcript (Coonrod et al., 2013). Chemical modification/analysis of structure-activity relationships of the pentamidine backbone led to identification of the more efficacious and less toxic molecule, furamidine (Siboni et al., 2015).

In evaluation of compounds for marketing approval, FDA and other regulatory agencies regard understanding of the molecular target and mechanism of action as important factors in establishing confidence in the efficacy and safety of candidate therapeutics. Thus, mechanistic studies, using cell and animal models in preclinical studies and molecular markers in clinical trials, represent important steps in evaluation of candidate therapeutics for DM.

Mechanism of Action of Furamidine

Dr. Andy Berglund (University of Florida) and colleagues have built upon their prior work with pentamidine analogs to examine the mechanisms of action (MOA) of furamidine in DM1 models (Jenquin et al., 2018). Dr. Leslie Coonrod, a former MDF Postdoctoral Fellow, was a coauthor on the publication. Information on the structure, properties, vendors, publications, and patents around furamidine is available in the public chemical database, PubChem. Overall the research team reported promiscuous activity for furamidine, potentially impacting multiple pathways in restoring the splicopathy that characterizes DM1.

Furamidine was evaluated in HSALR mice for safety and impact upon gene expression and splicing and in DM1 myotubes for safety and impact on splicing. Head to head comparisons were made with another pentamidine analog, heptamidine.

In the HSALR model, furamidine (daily, over 7 days) reduced HSA transgene levels and rescued multiple splicing events, suggesting binding of CTG•CAG expanded repeats and transcription inhibition as an important MOA for the drug. In comparison to heptamidine, furamidine rescued more splicing events in the mouse model. Evaluation of furamidine in a patient myoblast line (~2900 repeats) also showed partial rescue of the characteristic mis-splicing pattern. Although dose-limiting toxicity was seen in the cell line studies, efficacy on splicing was obtain at 10x and greater multiples below toxic dose—this was confirmed in follow-up cell toxicity assays. However, in the cell-based assays and in contrast to the HSALR data, the impact of the drug on CUG RNA levels was modest.

In additional studies with the human DM1 cell lines, data suggest that furamidine reduces nuclear foci and disrupts the binding of MBNL1 to expanded CUG repeats. Yet, at higher concentrations, furamidine exacerbated mis-splicing while producing a significant reduction in nuclear foci—a finding that the research team first interpreted as drug-induced reduction of MBNL levels; this hypothesis was not confirmed as transcript and protein levels were increased by furamidine treatment.

Assessing a Complex MOA

Taken together, furamidine exhibited a complex MOA, with both similar and discordant findings in cell vs. animal models and across a 100-fold dosing range studied by the research team. They conclude that its primary MOA in the HSALR mouse appears to be inhibition of transcription of the expanded repeat, but cannot exclude disruption of MBNL from expanded CUG repeat binding. By contrast, the team posits that increased levels of MBNL proteins and furamidine-induced disruption of the MBNL–CUG complex represent the primary MOA for splicing rescue in patient cell lines. Differences in the pathways engaged by the effective drug concentrations at the target tissues (i.e., tissue bioavailability/exposure) may, at least in part, explain differences in MOA findings in the two models.


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