Induced pluripotential stem cell (iPSC) technology has provided opportunities to better understand disease mechanisms as well as to facilitate drug discovery and development programs. With the attendant molecular, cellular, and disease backgrounds of readily expandable, patient-derived cells, iPSC “disease-in-a-dish” models have supported the translation of candidate therapeutics from discovery into clinical testing.

As long as limitations are recognized, such as potential genetic and epigenetic divergence from primary cells, iPSC modeling of myotonic dystrophy (DM) may be essential to mechanistic understanding and development of treatments for the disease, particular when patient tissues are difficult to impossible to access (e.g., CNS and heart). MDF has facilitated the development of human DM1 iPSC lines, now available through RUCDR Infinite Biologics, with DM2 lines to follow.

Development of iPSC-Derived Cardiomyocytes

Reported in a newly published study, Dr. Federica Sangiuolo (University of Rome Tor Vergata) and colleagues have developed iPSC lines from two DM1 patients and two healthy controls. They characterized cardiomyocytes derived from these lines, with the goal of determining whether they could recapitulate at least some of the major traits of the DM1 heart. Myocyte characterization included RT-qPCR to quantify RNA expression, FISH and IF for nuclear foci, RT-PCR for splice variants, whole-cell patch clamp to characterize cardiomyocyte electrophysiology, and atomic force microscopy (AFM) to characterize biomechanical traits.

Traits of iPSC-Derived Cardiomyocytes—DM1 versus Wild Type

Most iPSC-derived cardiomyocytes exhibited a ventricular-like phenotype. DM1-derived cardiomyocytes contrasted with wild type controls in expressing nuclear foci and mis-slicing of each transcript evaluated (MBNL1, MBNL2, TNNT2 and SCN5A); DM1 derivatives also showed down-regulation of key cardiac ion channel transcripts (CACNA1C, KCNH2, KCNQ1, KCND3, and SCH5A) compared with controls. The research team noted novel differences in nuclear morphology in DM1 derivatives, potentially related to altered expression of lamin A.

Whole-cell patch clamp recordings of disaggregated single cardiomyocytes showed an abnormal electrophysiological profile only in the DM1 derivatives. DM1 ventricular myocyte-like derivatives exhibited lower spontaneous action potential rates, lower peak amplitude, and longer time to reach peak from threshold. Electrophysiologic parameters of DM1 cardiomyocytes could be altered by drugs targeting cardiac ion channels.

Using AFM, the research team identified differences in beat frequency and synchronicity of beats in DM1 iPSC-derived cardiomyocytes—describing the overall pattern as indicative of instability, with reduced frequency and the appearance of non-synchronous oscillation patterns when compared to wild type. The predominance of ventricular-like myocytes, and relative absence of nodal or other conduction system-related cardiomyocytes, may make it more difficult for iPSC-based models to be informative of the conduction system-specific abnormalities known to characterize DM1.

Overall, DM1 iPSC-derived cardiomyocytes recapitulated the main morphologic and molecular markers of the disease, including CTG expansions, nuclear foci, splicopathy of the mRNAs evaluated, and altered expression of several known cardiac ion channels. Alterations in electrophysiological parameters and biomechanical behavior were interpreted as consistent with unstable beating.

Reference:

Modelling the pathogenesis of Myotonic Dystrophy type 1 cardiac phenotype through human iPSC-derived cardiomyocytes.
Spitalieri P, Talarico RV, Caioli S, Murdocca M, Serafino A, Girasole M, Dinarelli S, Longo G, Pucci S, Botta A, Novelli G, Zona C, Mango R, Sangiuolo F.
J Mol Cell Cardiol. 2018 Mar 15. pii: S0022-2828(18)30083-X. doi: 10.1016/j.yjmcc.2018.03.012. [Epub ahead of print]

Role of Muscleblind Proteins in Health and Disease

Muscleblind (MBNL) proteins play a central role in the pathogenesis of myotonic dystrophy (DM), as MBNL depletion below a threshold level triggers a range of mRNA splicing, polyadenylation, localization, and processing defects and, thereby, the production of temporally inappropriate protein isoforms. This compromise of function for a wide range of proteins, in turn, leads to the multi-organ system phenotypes that characterize DM. To understand MBNL’s roles in normal development and function, and dysfunction in DM, it is essential to elucidate mechanisms underlying its spatial and temporal localization and steps necessary for its functional activation/inactivation.

Dissecting the Role of MBNL in the CNS

Understanding the regulation and functional roles of MBNL proteins in the CNS represents a critically important problem in determining pathogenic mechanisms underlying the nervous system phenotype in DM. Dr. Guey-Shin Wang at National Yang-Ming University and Academia Sinica (Taiwan) have published an article in Cell Reports that MBNL1 localized to the cytoplasm, but not that retained in the nucleus, plays a key role in neurite morphogenesis and show that this role is disrupted in DM1.

Using FLAG-tagged isoforms of MBNL1 (with and without exon 5) expressed in hippocampal neuron cultures, Dr. Wang and colleagues demonstrated that MBNL1 that included exon 5 was retained in the nucleus and had no impact on neuronal development, while exon 5-deleted MBNL1, which translocates to the cytoplasm, enhanced dendrite and axon morphogenesis.

Consistent with this role for MBNL1 in regulating neurite differentiation and the differentiation failure in DM1, the research team showed that either MBNL1 knockdown or overexpression of 960-repeat DMPK mRNA (DMPK-CUG⁹⁶⁰) resulted in delayed neurite maturation. Moreover, the cytoplasmic (exon 5 deleted) MBNL1 isoform, but not the nuclear-localized isoform, was found to rescue maturation defects in neurons expressing DMPK-CUG⁹⁶⁰ in a dose-dependent manner.

Mechanisms Regulating Neuronal Subcellular Distribution of MBNL1

Analysis of the developmental distribution of the two MBNL1 isoforms led to the puzzling finding that nuclear or cytoplasmic localization was independent of exon 5 inclusion/exclusion, suggesting that another factor regulated MBNL1 localization in the developing brain. The research team then demonstrated that Lys 63-linked ubiquitination of MBNL1 and neuronal activity level regulated its cellular localization. Finally, it was shown that deubiquitination caused by expanded repeat mRNA resulted in a cytoplasmic-to-nuclear translocation of MBNL1 and corresponding alterations in neurite morphogenesis—these consequences were prevented by deubiquitination inhibitors.

Taken together, Dr. Wang and colleagues have shown that MBNL1 plays a key role in neuronal differentiation and that disruption of its cellular localization alters functionally significant steps in neuronal structure and function that likely underlie the CNS consequences of DM. Moreover, their identification of the regulatory role that the ubiquitination/deubiquitination status plays in the cytoplasmic localization of MBNL1 suggests a novel potential target for therapeutic development in DM1.

Reference:

Ubiquitination of MBNL1 Is Required for Its Cytoplasmic Localization and Function in Promoting Neurite Outgrowth.
Wang PY, Chang KT, Lin YM, Kuo TY, Wang GS.
Cell Rep. 2018 Feb 27;22(9):2294-2306. doi: 10.1016/j.celrep.2018.02.025.

The Myotonic Dystrophy Foundation is excited to introduce Understanding Myotonic Dystrophy, a new series of short educational animations designed to educate people living with myotonic dystrophy (DM) and their healthcare providers!

Our second animation “Understanding Myotonic Dystrophy – Inheritance of Myotonic Dystrophy Type 1 (DM1)”, explains how DM1 is passed down from generation to generation and highlights the importance of genetic testing. This animation is a valuable resource for individuals and families living with DM1, helping them deepen their understanding of DM, raise awareness within their families, and educate others about myotonic dystrophy.

Stay tuned—our next video on Myotonic Dystrophy Type 2 (DM2) is coming soon!

We are sincerely thankful to all physicians, care providers, and patients for their help providing suggestions, opinions, and input regarding content and design throughout this process. Please let us know what topics you would like us to cover in a future animation. Click here to share your feedback! 

Read the Transcript - Understanding Myotonic Dystrophy: Inheritance of Myotonic Dystrophy Type 1 (DM1)

Dr. Smith: "I have Emma's genetic test results . She has myotonic dystrophy type 1. It is caused by an expanded repeat in a gene. This leads to Emma's symptoms."

Sarah: "How did she get it?"

Dr. Smith: "It is inherited. If one parent has it, there's a 50% chance of passing it to their children with each pregnancy."

Sarah: "Did I give it to Emma or did John?"

Dr. Smith: "Emma could have inherited myotonic dystrophy from either of you. Sarah, You mentioned your father had early cataracts and muscle weakness; both could have been symptoms of myotonic dystrophy."

Sarah: "How can we find out?"

Dr. Smith: " You and John should get tested. You may have inherited the expanded gene from your dad and passed it on to Emma. Or John, may have inherited it from his mother or father and passed it on to Emma."

Sarah: "If we don't have any symptoms, why is Emma sick?"

Dr. Smith: "Symptoms can manifest later in life and may worsen from one generation to the next. Doctors call this anticipation. Testing will provide clarity and this will help us understand the risk for your family and future children."

Joel R. Chamberlain, Ph.D. is a Research Associate Professor at the University of Washington (UW) in Seattle, WA, where she has been a vital contributor to the fields of muscular dystrophy and molecular therapies for over 15 years. Starting her career at UW as a postdoctoral scholar in 2001, Dr. Chamberlain has dedicated her research to developing gene-based therapies for the two most common dominant muscular dystrophies: myotonic dystrophy (DM) and facioscapulohumeral muscular dystrophy (FSHD).

At UW’s cutting-edge South Lake Union research campus, Dr. Chamberlain, who earned her PhD at the University of Michigan in Ann Arbor, is part of a world-class facility that includes the Institute for Stem Cell and Regenerative Medicine, the Center for Cardiovascular Biology, the Center for Translational Muscle Research, the Center for Innate Immunity and Disease, the Diabetes Center, and others.

As an MDF Pilot Grant recipient, Dr. Chamberlain is leading an exciting project titled “Efficacy Testing of Cell-Derived Nanovesicle Delivery of Small Interfering RNAs for Treatment of DM1.” Her team is pioneering a novel approach to treat DM1 by utilizing natural cell-derived vesicles to deliver therapies aimed at eliminating toxic RNA structures in the muscles and tissues of DM1 patients. By testing these carriers in DM1-derived stem cells and transforming them into muscle-like cells, her team hopes to determine whether this innovative delivery system can successfully neutralize the harmful effects of the disease. This groundbreaking research holds tremendous potential to revolutionize treatment for DM1, offering a promising non-invasive approach that targets the root cause of the condition.

Click here to learn more about MDF's research funding opportunities and prior grant recipients.

Understanding Tissue Specificity in Repeat Expansion Disorders

The instability of short tandem repeats and consequent somatic expansion underlies an entire class of neurological disorders. In DM1, the interaction between expanded repeat transcripts and the RNA binding protein/splicing regulator MBNL determines subsequent pathogenic events. Although the inherited (progenitor) repeat length is independent of cell/tissue type, tissue specificity in somatic expansion defines both the timing and severity of organ systems impacted by DM1. Questions of the spatial and temporal patterns of disease pathophysiology are difficult to ask and answer in studies of patients. Yet, most model organisms used to study DM1 to date are not capable of interrogating mechanisms that underlie such cell type- and tissue-specific effects.

New Mouse Models to DM1 Study Tissue Specificity

New technologies, rolling circle amplification and CRISPR/Cas9 genome editing, have been used by Dr Maury Swanson (University of Florida) and colleagues to develop novel Dmpk 3’UTR CTG^exp knock-in mouse models of DM1. Mice expressing 170 (Dmpk^170/170) and 480 (Dmpk^480/480) repeats were selected. These new models enable study of repeat expansion, MBNL sequestration, mis-splicing, and pathophysiology on specific cell and tissue type levels. Dr. Curtis Nutter, recipient of a 2018 MDF Fellowship, was lead author on this work.

Dmpk^exp mice exhibited nuclear foci and reduced Dmpk mRNA and protein levels, but disrupted splicing regulation was not observed and downstream muscle phenotypic changes (myotonia, central nuclei) were absent. Similar reductions in Dmpk mRNA and protein were seen in cultured myoblasts and myotubes. In contrast to absent splicing changes in adult mice, MBNL sequestration and mis-splicing were seen in Dmpk^480/480 but not in Dmpk^170/170 mouse myotubes. To reconcile their findings, the authors found that MBNL activity might be more effectively damped in myoblasts/myotubes than in mature muscle—reinforcing the notion that pathology reflects both tissue and developmental stage specificity due to interactions of relative repeat load (expansion length and gene expression level) with MBNL protein levels. Crosses resulting in Dmpk^480/480 mice haploinsufficient for MBNL supported this idea.

Given the severity of the CNS phenotype in DM1, the research team also evaluated choroid plexus (a CNS tissue expressing high Dmpk levels) in the Dmpk^exp mice. Nuclear foci were prominent and DM1-related splicing anomalies detected in choroid plexus of these mice.

Insights into Cell Type Specificity and Pathogenesis of DM1

 The Dmpk^exp mice have not, to date, shown evidence of repeat instability—in keeping with the absence of an in vivo phenotype. Larger repeat loads may be necessary to trigger mouse phenotypes. Perhaps more importantly, these data help establish a link between DMPK CTG^exp length and the cell/tissue patterns of pathology in DM1. That choroid plexus may be affected earlier (i.e., at lower repeat load) than skeletal muscle helps solidify understanding of the spatial and temporal patterning of DM1. It’s now highly likely that the repeat load in other cell/tissue types can be more directly linked to their disease phenotype. Finally, these results also make it clear that there is a need to explore potential involvement of affected choroid plexus function (CSF production) in the CNS consequences of DM1.

Reference:

Cell-type-specific dysregulation of RNA alternative splicing in short tandem repeat mouse knockin models of myotonic dystrophy.
Nutter CA, Bubenik JL, Oliveira R, Ivankovic F, Sznajder ŁJ, Kidd BM, Pinto BS, Otero BA, Carter HA, Vitriol EA, Wang ET, Swanson MS.
Genes Dev. 2019 Oct 17. doi: 10.1101/gad.328963.119. [Epub ahead of print]

Cardiac Biomarkers and DM

Cardiac rhythm disturbances represent a cardinal feature and a leading cause of death in DM. To elevate the level of patient cardiac care, consensus-based care recommendations are now available for DM1, children with CDM or DM1, and DM2. The molecular basis of cardiac dysfunction in DM, however, has been difficult to discern. It has been suggested that serum levels of high-sensitive cardiac troponin T and N-terminal pro B-type natriuretic peptide may be predictive of cardiac risk and potentially useful for stratification (Valaperta et al., 2016 and 2017), but these have not yet shown promise as efficacy biomarkers for interventional clinical trials. Similarly, mis-splicing of SCN5A has been implicated in DM cardiac conduction defects (Freyermuth et al., 2016; Pang et al., 2018), but its value as a clinical trial tool has not been determined. Thus, specific biomarkers for cardiac involvement in DM have not yet been established and their absence represents an important gap in the ability to assess candidate therapeutics for a key phenotype in this patient group.

Assessing Mis-Splicing of Cardiac-Relevant Transcripts

Drs. Rosanna Cardani and Giovanni Meola (IRCCS-Policlinico San Donato and University of Milan) and colleagues initiated a study of alternative splicing of several genes that could be used to follow the cardiac phenotype in DM1 or DM2 patients. Analyses were performed in patients with and without cardiac involvement; molecular analyses focused on TNNT2 expression, in part because it is mis-spliced in both skeletal and cardiac muscle in DM.  Dr. Laura Valentina Renna, a former MDF fellow, contributed to this work.

The research team evaluated skeletal muscle biopsies in 24 DM1, 9 DM2 patients, and 10 age-matched controls; subjects also underwent muscle strength evaluations (MRC scale), staging of DM1 (MIRS), ECG, and Holter tests. Their study also included a range of histologic and immunocytochemical markers to establish correlations between observed splicopathies and skeletal muscle status.

TNNT2 encodes cardiac troponin T (cTnT). The research team showed that TNNT2 mis-splicing was more evident in skeletal muscle biopsies from DM1 subjects (where the fetal isoform was > 50% of total transcript) versus DM2. The authors suggest that greater mis-splicing in DM1 may relate not only to the more severe myopathy, but to the general disease severity, including cardiac involvement, in DM1. Finally, the level of TNNT2 mis-splicing strongly correlated with QRS duration abnormalities in DM1 (but not DM2), suggesting that alternative splicing of TNNT2 may have value as a cardiac biomarker.

TNNT2 as a Biomarker of DM1 Severity?

Overall, the authors cannot conclude that TNNT2 mis-splicing is a specific biomarker of cardiac involvement in DM, only that data are suggestive that it may be when further data are acquired. They do argue that TNNT2 mis-splicing may function as a biomarker of disease severity in DM1, the potential of which should be explored in natural history studies and interventional clinical trials.

References:

High-sensitive cardiac troponin T (hs-cTnT) assay as serum biomarker to predict cardiac risk in myotonic dystrophy: A case-control study.
Valaperta R, Gaeta M, Cardani R, Lombardi F, Rampoldi B, De Siena C, Mori F, Fossati B, Gaia P, Ferraro OE, Villani S, Iachettini S, Piccoli M, Cirillo F, Pusineri E, Meola G, Costa E.
Clin Chim Acta. 2016 Dec 1;463:122-128. doi: 10.1016/j.cca.2016.10.026. Epub 2016 Oct 22.

Cardiac involvement in myotonic dystrophy: The role of troponins and N-terminal pro B-type natriuretic peptide.
Valaperta R, De Siena C, Cardani R, Lombardia F, Cenko E, Rampoldi B, Fossati B, Brigonzi E, Rigolini R, Gaia P, Meola G, Costa E, Bugiardini R.
Atherosclerosis. 2017 Dec;267:110-115. doi: 10.1016/j.atherosclerosis.2017.10.020. Epub 2017 Oct 21.

Splicing misregulation of SCN5A contributes to cardiac-conduction delay and heart arrhythmia in myotonic dystrophy.
Freyermuth F, Rau F, Kokunai Y, Linke T, Sellier C, Nakamori M, Kino Y, Arandel L, Jollet A, Thibault C, Philipps M, Vicaire S, Jost B, Udd B, Day JW, Duboc D, Wahbi K, Matsumura T, Fujimura H, Mochizuki H, Deryckere F, Kimura T, Nukina N, Ishiura S, Lacroix V, Campan-Fournier A, Navratil V, Chautard E, Auboeuf D, Horie M, Imoto K, Lee KY, Swanson MS, de Munain AL, Inada S, Itoh H, Nakazawa K, Ashihara T, Wang E, Zimmer T, Furling D, Takahashi MP, Charlet-Berguerand N.
Nat Commun. 2016 Apr 11;7:11067. doi: 10.1038/ncomms11067.

CRISPR -Mediated Expression of the Fetal Scn5a Isoform in Adult Mice Causes Conduction Defects and Arrhythmias.
Pang PD, Alsina KM, Cao S, Koushik AB, Wehrens XHT, Cooper TA.
J Am Heart Assoc. 2018 Oct 2;7(19):e010393. doi: 10.1161/JAHA.118.010393.

TNNT2 Missplicing in Skeletal Muscle as a Cardiac Biomarker in Myotonic Dystrophy Type 1 but Not in Myotonic Dystrophy Type 2.
Bosè F, Renna LV, Fossati B, Arpa G, Labate V, Milani V, Botta A, Micaglio E, Meola G, Cardani R.
Front Neurol. 2019 Sep 27;10:992. doi: 10.3389/fneur.2019.00992. eCollection 2019.

MDF has strongly supported the inclusion of the patient voice in both care and therapy development for DM. The most recent examples of these efforts are the Patient Focused Drug Development meeting held with FDA, and its subsequent Voice of the Patient report, and the development of DM Care Considerations to drive improved clinical management of patients living with DM. MDF also has long focused on collecting patient- and caregiver-reported data through the Myotonic Dystrophy Family Registry.

To provide the highest level of support to those living with DM, it is important to not only utilize registries for collection of both patient/care provider-reported and clinical data, but to ensure the utilization and sharing of these data to meet the goals of improved care and optimized clinical trials.

The Canadian Neuromuscular Disease Registry (CNDR)

The CNDR is a clinic-based enrollment and data entry registry focused on regular clinical contact with registrants and accurate retrospective data collection from patient charts. Dr. Craig Campbell (University of Western Ontario) and colleagues have recently published information on the CNDR’s efforts to support research into potential therapies for a wide range of neuromuscular diseases, including DM (Wei et al., 2018).

The CNDR’s website reports a current total of 3,440 registrants (https://cndr.org); the publication by Dr. Campbell and colleagues reports out on details of the overall registry (including design, consent, data collection and management, and access policies) and data from its pediatric registrants. The CNDR’s pediatric registrants include 249 with dystrophinopathies, 57 with DM, 98 with SMA, and 65 with LGMD. The CNDR houses clinical data obtained from retrospective chart evaluation and data obtained during clinic visits. CNDR data is used to support both research proposal and statistical data requests.

CNDR has supported 30 study requests for pediatric data (20 clinical trials, 5 mail surveys, and 5 other studies). Two of the mail surveys have focused on DM (parent reported burden of disease in CDM and childhood-onset DM1, Johnson et al., 2016; access to technology survey in DM). The ‘other’ studies included a study of CDM and a study of ventilator support use in pediatric patients with DM1. The paper’s authors note that they are exploring post-marketing surveillance models as a potential resource for companies engaging in clinical trials in neuromuscular diseases.

Moving Forward with Registries

The success of individual registries like the CNDR is laudable in fostering improved care and therapy development for rare neuromuscular diseases. As for many neuromuscular diseases, the DM field has harmonized clinical study and registry data collection. Thus, there’s a firm basis for data sharing and meta-analysis of the smaller cohorts that are spread among multiple DM registries. For any rare disease, it is especially important that data not remain siloed, as that’s a hindrance to assembling cohorts that are sufficient to reach meaningful conclusions about disease course and clinical trial endpoints. The DM field will only meet the expectations and trust of the patients who so willingly share their data when cultural changes occur and analysis of internationally shared data is possible (Larkindale and Porter, 2018).

References:

The Canadian Neuromuscular Disease Registry: Connecting patients to national and international research opportunities.
Wei Y, McCormick A, MacKenzie A, O'Ferrall E, Venance S, Mah JK, Selby K, McMillan HJ, Smith G, Oskoui M, Hogan G, McAdam L, Mabaya G, Hodgkinson V, Lounsberry J, Korngut L, Campbell C.
Paediatr Child Health. 2018 Feb;23(1):20-26. doi: 10.1093/pch/pxx125. Epub 2017 Dec 8.

Parent-reported multi-national study of the impact of congenital and childhood onset myotonic dystrophy.
Johnson NE, Ekstrom AB, Campbell C, Hung M, Adams HR, Chen W, Luebbe E, Hilbert J, Moxley RT 3rd, Heatwole CR.
Dev Med Child Neurol. 2016 Jul;58(7):698-705. doi: 10.1111/dmcn.12948. Epub 2015 Oct 28.

Seeking a better landscape for therapy development in neuromuscular disorders.
Larkindale J, Porter JD.
Muscle Nerve. 2018 Jan;57(1):16-19. doi: 10.1002/mus.25961. Epub 2017 Sep 23.

Analysis of phenotypic variability in the presentation of DM1 has led to the conclusion that disease types based upon age of onset represent a continuum, but that there are recognizable patterns in symptom onset and progression (De Antonio et al., 2016) that impact prognosis. Gender is also a major modifier of symptomatology and, ultimately, of mortality rates (Dogan et al., 2016). Understanding these risk factors and how they contribute toward the clinical spectrum and stages of DM1 is critically important for appropriate management of patient care and for the design of clinical trials.

Implementation of the care considerations developed by the MDF in partnership with an international group of physicians represents a critically important step in improving the quality of life for those living with myotonic dystrophy. Development of a means to quantitatively assess the risk factors of and long-term prognosis for this multi-systemic disease at the individual patient level would provide an important tool for patient management.

Towards a Prognostic System for DM1 Patient Survival

To determine whether a clinical scoring model might predict long-term survival, Dr. Karim Wahbi (Cochin Hospital, Sorbonne Paris Cité University) and colleagues assessed a cohort of 1296 consecutive adult patients with molecular confirmation of DM1 and included in the French DM1 Heart Registry (Wahbi et al., 2018). 1066 patients were used in a derivation cohort to identify and assign weighting of variables that would comprise a survival index, while the remainder of patients, all from two other clinics, served as a validation cohort. The primary study endpoint was survival and ten variables collected in the DM1 Heart Registry were evaluated for inclusion in a prognostic index.

The commonly available variables of age, diabetes, need for support when walking, heart rate, systolic blood pressure, first-degree atrioventricular block, bundle-branch block, and lung vital capacity were associated with death. These factors were associated with survival by multiple variable Cox modeling and found to contribute to a prognostic model. CTG length, atrial fibrillation, left ventricular dysfunction, and dysphagia did not add to the predictive value of the scoring system and were excluded. Scores ranging from 1 or less to 15 or more were associated with 10-year survival probabilities from 98.1% to 22.5%, respectively. Thus, the model exhibited a wide dynamic range in predicting survival. Survivors and non-survivors were similarly well discriminated in the validation cohort.

A Simplified Tool for Patient Management and Clinical Trial Design

The research team emphasized the value of the DM1 survival score by noting that just eight common patient traits typically collected in clinical examinations are needed to determine a score. Moreover, the reliability and long-term prognostic capability may make this system an essential tool in the management of care in a multi-disciplinary setting.

References:

Unravelling the myotonic dystrophy type 1 clinical spectrum: A systematic registry-based study with implications for disease classification.
De Antonio M, Dogan C, Hamroun D, Mati M, Zerrouki S, Eymard B, Katsahian S, Bassez G; French Myotonic Dystrophy Clinical Network.
Rev Neurol (Paris). 2016 Oct;172(10):572-580. doi: 10.1016/j.neurol.2016.08.003. Epub 2016 Sep 21. Review.

Gender as a Modifying Factor Influencing Myotonic Dystrophy Type 1 Phenotype Severity and Mortality: A Nationwide Multiple Databases Cross-Sectional Observational Study.
Dogan C, De Antonio M, Hamroun D, Varet H, Fabbro M, Rougier F, Amarof K, Arne Bes MC, Bedat-Millet AL, Behin A, Bellance R, Bouhour F, Boutte C, Boyer F, Campana-Salort E, Chapon F, Cintas P, Desnuelle C, Deschamps R, Drouin-Garraud V, Ferrer X, Gervais-Bernard H, Ghorab K, Laforet P, Magot A, Magy L, Menard D, Minot MC, Nadaj-Pakleza A, Pellieux S, Pereon Y, Preudhomme M, Pouget J, Sacconi S, Sole G, Stojkovich T, Tiffreau V, Urtizberea A, Vial C, Zagnoli F, Caranhac G, Bourlier C, Riviere G, Geille A, Gherardi RK, Eymard B, Puymirat J, Katsahian S, Bassez G.
PLoS One. 2016 Feb 5;11(2):e0148264. doi: 10.1371/journal.pone.0148264. eCollection 2016.

Development and Validation of a New Scoring System to Predict Survival in Patients With Myotonic Dystrophy Type 1.
Wahbi K, Porcher R, Laforêt P, Fayssoil A, Bécane HM, Lazarus A, Sochala M, Stojkovic T, Béhin A, Leonard-Louis S, Arnaud P, Furling D, Probst V, Babuty D, Pellieux S, Clementy N, Bassez G, Péréon Y, Eymard B, Duboc D.
JAMA Neurol. 2018 Feb 5. doi: 10.1001/jamaneurol.2017.4778. [Epub ahead of print]

Speech disorders (dysarthria) in CDM and childhood-onset DM1 have long been recognized and surveillance by speech and language therapists is an important aspect of patient care. Facial weakness and myotonia, and involvement of oral cavity, palatopharyngeal and respiratory muscles, are known to contribute to speech impairment.

The Three Major Contributors to Speech Disorders 

In a recent review of speech disorders in DM1 (Lopes Cardos and Baptista, 2017), three major contributors to speech disorders were identified—myotonia as a hindrance to the initiation of speech, muscle weakness leading to reductions of lip force, and atrophy of tongue muscles. The authors note that few studies have evaluated the effectiveness of various speech therapies. There is no consensus on whether oral muscle exercises can improve lip strength. Other reports have shown that warming up reduced myotonia and led to increased speech rate and decreased variability in speech, but there were some concerns that this strategy could increase fatigue and thereby be counterproductive. Finally, increasing lip strength through exercising with an oral screen has been reported to increase lip force, but had no apparent effect on lip articulation. The authors concluded that strategies of warming up facial muscles and lip exercises can help, but used alone are insufficient to correct speech disorders in DM1 and therefore speech therapy is advised.

In this context, a new study has characterized the characteristics of speech in 50 subjects with CDM and childhood-onset DM1 (Sjőgreen et al., 2018). All subjects with CDM showed impairments of the intelligibility of their speech and nearly 80% of those with childhood DM1 were similarly impaired. The authors further characterized key speech components, identifying deficits in producing sounds: (1) that require coordinated function of both lips (bilabial consonants), (2) that require placing the tip of the tongue between the teeth (interdental consonants), and (3) that are due to increased airflow through the nose during speech (hypernasal speech). They also established a correlation between maximum lip force (as an indicator of how oral and facial muscles are affected in DM patients) and the intelligibility of speech. Some patients employed a variety of compensatory strategies to improve speech, including placing their tongue between their lips or biting the lower lip, to produce appropriate speech sounds—in some these strategies were very effective, but still did not reduce poor intelligibility in others.

The Connection Between DM and Speech Disorders

The researchers conclude that most children with CDM or childhood-onset DM1 will need speech therapy starting at a young age and that the most those with the severe manifestations will require training in alternative means of communication. Taken together, they show that weakness of oral and facial muscles is the primary cause of disordered speech in congenital and early-onset DM1. These findings suggest that therapies under development to improve muscle function in DM may also have positive effects on speech disorders. Finally, the research team reaffirmed conclusions of prior studies in that this patient group will require speech therapy from an early age.

References:

Myotonic dystrophy type 1 (DM1) and speech problems.
Lopes Cardoso I, Baptista H.
JSM Communication Dis. 1(1): 1003.
https://www.jscimedcentral.com/CommunicationDisorders/communicationdiso…

Speech characteristics in the congenital and childhood-onset forms of myotonic dystrophy type 1.
Sjögreen L, Mårtensson Å, Ekström AB.
Int J Lang Commun Disord. 2018 Jan 12. doi: 10.1111/1460-6984.12370. [Epub ahead of print]

Since a neuropsychological study in 2008 (Ekström et al., 2008), there have been few studies of pediatric cohorts to assess potential links between congenital and childhood-onset DM1 with autism spectrum disorders. The Ekström analysis of 57 children and adolescents with DM1 showed that 53% exhibited autism spectrum or other neuropsychiatric disorders (e.g., attention deficit hyperactivity disorder or Tourette's syndrome). The authors concluded that awareness of potential autism spectrum disorder comorbidity in DM1 was essential to patient care. There has been little literature on this issue since 2008.

A New Cohort Study of Autism and Childhood DM1

Dr. Nathalie Angeard (Paris Descartes University and Institut de Myologie) and colleagues recently published a review of nine studies focused on cognitive disorders in childhood DM1, compromising 175 cases (Angeard et al., 2017).

Emotional and behavioral disorders were prominent among reports in childhood DM1—the earlier study by Ekström and colleagues found that 36% of a cohort containing congenital (CDM) and juvenile-onset DM1 had autism spectrum disorders, although other studies did not report that high a prevalence. Angeard suggests that the association between and difficulties in the differential diagnoses of intellectual disability and autism spectrum might contribute to differences in reports of autism spectrum in CDM and juvenile DM1.

Cognitive function studies in CDM have reported moderate to severe intellectual disability in greater than half of patients studied. Considerable information is available regarding the characterization of specific cognitive function deficits and is reported in this meta-analysis. Patients with autism spectrum comorbidity did not fit a narrow profile, but rather exhibited a range of severity of symptoms, cognitive abilities and functional adaptations. The authors suggest that a considerable gap exists in understanding executive function and social cognition in childhood DM1, making it difficult to compare these patients with those with autism spectrum disorder. Likewise, a dearth of neuroanatomic and brain function studies in childhood DM1 also makes it difficult to compare their profile with that of autism spectrum disorder children. Where comparisons can be made based on available publications, the authors compare and contrast the social/communication, cognitive function and brain abnormality profiles between the two disorders (Table 2 in Angeard et al., 2017).

It’s Not Yet Clear Whether Childhood DM1 and Autism Spectrum Disorders are Comorbid

Overall, Angeard and colleagues note that only the Ekström paper reports high prevalence of autism spectrum disorder in childhood DM1 (36% versus 1% in the general population). Most publications agree, however, upon moderate prevalence of autism spectrum disorders in CDM. An evolving definition of autism spectrum over the time of the publications assessed here complicates any clear conclusion regarding comorbidity. The authors note that the prevalence of intellectual disability among childhood DM1 and autism spectrum may lead to biases in diagnosis. Taken together, they regard the question of comorbidity of childhood DM1 and autism as still open, requiring more careful cross-sectional and longitudinal natural history studies of the cognitive and behavioral phenotype of childhood DM1. For now, earlier attention to the cognitive, developmental, and social/emotional profiles of those at risk for CDM and juvenile-onset DM1 is warranted.

References:

Autism spectrum conditions in myotonic dystrophy type 1: a study on 57 individuals with congenital and childhood forms.
Ekström AB, Hakenäs-Plate L, Samuelsson L, Tulinius M, Wentz E.
Am J Med Genet B Neuropsychiatr Genet. 2008 Sep 5;147B(6):918-26. doi: 10.1002/ajmg.b.30698.

Childhood-onset form of myotonic dystrophy type 1 and autism spectrum disorder: Is there comorbidity?
Angeard N, Huerta E, Jacquette A, Cohen D, Xavier J, Gargiulo M, Servais L, Eymard B, Héron D.
Neuromuscul Disord. 2017 Dec 15. pii: S0960-8966(17)31337-8. doi: 10.1016/j.nmd.2017.12.006. [Epub ahead of print]