Myotonic Dystrophy Type 1 Management and Therapeutics

Treatments and therapies for symptoms and clinical manifestations of adult type 1 myotonic dystrophy: A scoping review

Myotonic Dystrophy is the most common adult-onset muscular dystrophy, with a broad, multi-systemic presentation. There is no cure, so quality-of-life improvements rely on treatment of symptoms and clinical manifestations. This review aimed to synthesize primary research evaluating treatments or therapies for symptoms and clinical manifestations of adult type 1 Myotonic Dystrophy and map targets against patient-reported symptom burden. Embase, MEDLINE, Web of Science, CINAHL, CENTRAL, and PsycINFO were searched for relevant studies published to 16th of October 2024. Two independent reviewers screened title and abstract, then full-text records for eligibility and conflicts were settled by group discussion. Study information was extracted, and treatment targets were mapped against patient-reported symptom burden as reported by Hagerman et al. The literature was limited to only 86 studies; 2/3 conducted in cohorts of <30 participants. Main target symptoms were muscle (50 %), respiratory (15.1 %), central nervous system (12.7 %) and cardiac conduction disorders (10.5 %). Most treatments were pharmacotherapies (43 %), followed by physical training (15.1 %), Non-invasive Ventilation (11.5 %), and Cardiac Resynchronization Therapy (10.5 %). The distribution of treatment targets was poorly representative of patient-reported symptoms. Outcome measures, clinical and patient-reported, were varied and utilized without standardization within treatment categories. These findings emphasize the need for evidence-based clinical management targeting patient priorities to produce quality-of-life improvements.

Use of HSALR female mice as a model for the study of myotonic dystrophy type I

HSALR mice are the most broadly used animal model for studying myotonic dystrophy type I (DM1). However, so far, HSALR preclinical studies have often excluded female mice or failed to document the biological sex of the animals. This leaves an unwanted knowledge gap concerning the differential development of DM1 in males and females, particularly considering that the disease has a different clinical presentation in men and women. Here we compared typical functional measurements, histological features, molecular phenotypes and biochemical plasma profiles in the muscles of male and female HSALR mice in search of any significant between-sex differences that could justify this exclusion of female mice in HSALR studies and, critically, in candidate therapy assays performed with this model. We found no fundamental differences between HSALR males and females during disease development. Both sexes presented comparable functional and tissue phenotypes, with similar molecular muscle profiles. The only sex differences and significant interactions observed were in plasma biochemical parameters, which are also intrinsically variable in patients with DM1. In addition, we tested the influence of age on these measurements. We therefore suggest including female HSALR mice in regular DM1 studies, and recommend documenting the sex of animals, especially in studies focusing on metabolic alterations. This will allow researchers to detect and report any potential differences between male and female HSALR mice, especially regarding the efficacy of experimental treatments that could be relevant to patients with DM1.

Intellectual Profile in Myotonic Dystrophy Type 1 and Its Association With Its Onset: A Systematic Review and Meta-Analysis

BACKGROUND

Myotonic dystrophy type 1 (DM1) is caused by mutations in the DMPK gene, and it is associated with cognitive deficits and intelligence below normative values. The objective of this systematic review and meta-analysis was to estimate the overall intelligence and proportion of intellectual development disorder (IDD) in the population with DM1 and its association with its onset.

METHODS

Systematic searches of Medline, Scopus, Web of Science, and Cochrane Library were performed from inception to January 2023. Studies that determined the full intelligence quotient (FIQ) or the IDD proportion in populations with DM1 were included. Meta-analyses of the FIQ and IDD and the FIQ mean difference and IDD prevalence ratios (PRs) by disease onset, inheritance, and genotype were conducted.

RESULTS

Forty-five studies were included in the meta-analyses, and all were performed in the DM1 population. The FIQ and IDD in DM1 were 77.90 (71.98, 83.81) and 0.44 (0.27, 0.60), respectively. Furthermore, DM1 onset was negatively associated with intelligence. Thus, the comparison "Congenital versus Adult" onsets resulted in an intelligence quotient of -41.61 (-47.81, -35.40) points and a PR of IDD of 9.49 (3.23, 27.89). Finally, maternal inheritance was also negatively associated, but the genotype did not have a statistically significant association.

CONCLUSIONS

The alterations in intelligence in DM1 are highly associated with the onset of the disease. However, the genotype did not explain these alterations well and there may be other genetic or epigenetic factors that should be considered.

A meta-analysis of the prevalence of neuropsychiatric disorders and their association with disease onset in myotonic dystrophy

There is a high prevalence of neuropsychiatric disorders in myotonic dystrophy types 1 and 2 (DM1 and DM2), including autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) in DM1, and depression and anxiety in both DMs. The aim of this systematic review and meta-analysis was to estimate the prevalence of ASD, ADHD, depression and anxiety in the population with DM, and their association with disease onset. A systematic search of Medline, Scopus, Web of Science, and the Cochrane Library was conducted from inception to November 2023. Observational studies estimating the prevalence of these disorders in DM1 or DM2 were included. A meta-analysis of the prevalence of these disorders and an association study with disease onset by prevalence ratio meta-analysis were performed. Thirty-eight studies were included. In DM1, the prevalence of ASD was 14%, with congenital onset being 79% more common than juvenile onset, while the prevalence of ADHD was 21%, with no difference between congenital and juvenile onset, and the prevalence of depression and anxiety were 14% and 16%. Depression was more common in the adult onset. Finally, the prevalence of depression in DM2 was 16%. A higher prevalence of neuropsychiatric disorders is observed in individuals with DM1 and DM2 than in the general population. Therefore, actively screening for congenital and juvenile neurodevelopmental disorders in DM1 and emotional disorders in DM1 and DM2 may improve the quality of life of those affected.

Therapeutic potential of oleic acid supplementation in myotonic dystrophy muscle cell models

BACKGROUND

We recently reported that upregulation of Musashi 2 (MSI2) protein in the rare neuromuscular disease myotonic dystrophy type 1 contributes to the hyperactivation of the muscle catabolic processes autophagy and UPS through a reduction in miR-7 levels. Because oleic acid (OA) is a known allosteric regulator of MSI2 activity in the biogenesis of miR-7, here we sought to evaluate endogenous levels of this fatty acid and its therapeutic potential in rescuing cell differentiation phenotypes in vitro. In this work, four muscle cell lines derived from DM1 patients were treated with OA for 24 h, and autophagy and muscle differentiation parameters were analyzed.

RESULTS

We demonstrate a reduction of OA levels in different cell models of the disease. OA supplementation rescued disease-related phenotypes such as fusion index, myotube diameter, and repressed autophagy. This involved inhibiting MSI2 regulation of direct molecular target miR-7 since OA isoschizomer, elaidic acid (EA) could not cause the same rescues. Reduction of OA levels seems to stem from impaired biogenesis since levels of the enzyme stearoyl-CoA desaturase 1 (SCD1), responsible for converting stearic acid to oleic acid, are decreased in DM1 and correlate with OA amounts.

CONCLUSIONS

For the first time in DM1, we describe a fatty acid metabolism impairment that originated, at least in part, from a decrease in SCD1. Because OA allosterically inhibits MSI2 binding to molecular targets, reduced OA levels synergize with the overexpression of MSI2 and contribute to the MSI2 > miR-7 > autophagy axis that we proposed to explain the muscle atrophy phenotype.

Myotonic dystrophy type 1: 13 years of experience at a tertiary hospital. Clinical and epidemiological study and genotype-phenotype correlation

INTRODUCTION

The incidence of myotonic dystrophy type 1 (DM1), a disease with great phenotypic variety, in our region is unknown. This study aims to estimate the incidence of DM1 at our hospital (a reference centre in Aragon, Spain) and to identify the characteristics of our population (genotype-phenotype correlation).

METHODS

Retrospective, descriptive study of 459 patients classified according to the number of CTG repeats, as follows: normal (5-35), premutation (36-50), protomutation (51-80), small expansions (81-150), intermediate expansions (151-1000), and large expansions (> 1000). Furthermore, according to clinical phenotype, patients were categorised as unaffected (5-50 CTG repeats), mild form or asymptomatic (51-150), classical form (151-1000), and severe form (> 1000).

RESULTS

The incidence of DM1 was 20.61 cases per million person-years (95% CI, 19.59-21.63). An inverse correlation was observed between the number of CTG repeats and the age at genetic diagnosis (ρ = -0.547; 95% CI, -0.610 to -0.375; P < .001). CTG5 was the most frequent polymorphic allele in healthy individuals. Of all patients with DM1, 28.3% presented the mild or asymptomatic form, 59.1% the classical form, and 12.6% the severe form. Inheritance was maternal in 35.1% of cases, paternal in 59.4%, and uncertain in 5.5%. In mild forms, frontal balding in men was the most prevalent phenotypic trait, as well as myotonia and cataracts, while in the classical form, ptosis, facial weakness, voice and pronunciation alterations, myotonia, and fatigue/sleepiness were most frequent.

CONCLUSIONS

The incidence of DM1 in Aragon is significant. Multidisciplinary study of the phenotype of patients with DM1 is key to early diagnosis and personalised management.

Gastrointestinal and nutritional care in pediatric neuromuscular disorders

Neuromuscular diseases (NMDs) affect the development and growth of the neuromuscular system in children. The pathology can occur anywhere along the neuromuscular pathway, from the brain to the nerves to the muscle fibers. These diseases have a profound impact on the quality of life not only of children but also of their families. The predominant manifestation in NMDs is hypotonia, which leads to muscle weakness and fatigue, reduced mobility, and decreased physical performance. However, multiple organ systems can be affected, with resulting orthopedic, cardiac, infectious, respiratory, and nutritional problems. Children with NMD present an increased risk for several dietary and feeding difficulties because of their neuromuscular diagnosis, presentation, and severity. These problems include chronic gastrointestinal issues (constipation, dysphagia, gastroesophageal reflux, and diarrhea), dysphagia, malnutrition, and body composition alterations. As a result, compared to the overall pediatric population, infants and children with NMD are more likely to be malnourished, ranging from failure to thrive to overweight or obesity. Disease-specific guidelines vary in level of detail and recommendations for dietary management. Overall, nutritional data available are sparse, with the exception of Duchenne muscular dystrophy, spinal muscular atrophy, and congenital muscular dystrophy. The purpose of this review is to describe the spectrum of nutritional challenges in children with NMD and to summarize the main dietary and gastrointestinal recommendations for each neuromuscular disorder to provide guidance for daily clinical practice.

Individual-specific levels of CTG•CAG somatic instability are shared across multiple tissues in myotonic dystrophy type 1

Myotonic dystrophy type 1 is a complex disease caused by a genetically unstable CTG repeat expansion in the 3'-untranslated region of the DMPK gene. Age-dependent, tissue-specific somatic instability has confounded genotype-phenotype associations, but growing evidence suggests that it also contributes directly toward disease progression. Using a well-characterized clinical cohort of DM1 patients from Costa Rica, we quantified somatic instability in blood, buccal cells, skin and skeletal muscle. Whilst skeletal muscle showed the largest expansions, modal allele lengths in skin were also very large and frequently exceeded 2000 CTG repeats. Similarly, the degree of somatic expansion in blood, muscle and skin were associated with each other. Notably, we found that the degree of somatic expansion in skin was highly predictive of that in skeletal muscle. More importantly, we established that individuals whose repeat expanded more rapidly than expected in one tissue (after correction for progenitor allele length and age) also expanded more rapidly than expected in other tissues. We also provide evidence suggesting that individuals in whom the repeat expanded more rapidly than expected in skeletal muscle have an earlier age at onset than expected (after correction for the progenitor allele length). Pyrosequencing analyses of the genomic DNA flanking the CTG repeat revealed that the degree of methylation in muscle was well predicted by the muscle modal allele length and age, but that neither methylation of the flanking DNA nor levels of DMPK sense and anti-sense transcripts could obviously explain individual- or tissue-specific patterns of somatic instability.

Quantitative magnetic resonance imaging assessment of muscle composition in myotonic dystrophy mice

Myotonic dystrophy type 1 (DM1) is a severe autosomal dominant neuromuscular disease in which the musculoskeletal system contributes substantially to overall mortality and morbidity. DM1 stems from a noncoding CTG trinucleotide repeat expansion in the DMPK gene. The human skeletal actin long repeat (HSA^LR) mouse model reproduces several aspects of the disease, but the muscle-wasting phenotype of this model has never been characterized in vivo. Herein, we used quantitative MRI to measure the fat and muscle volumes in the leg compartment (LC) of mice. These acquired data were processed to extract relevant parameters such as fat fraction and fat infiltration (fat LC/LC) in HSA^LR and control (FBV) muscles. These results showed increased fat volume (fat LC) and fat infiltration within the muscle tissue of the leg compartment (muscle LC), in agreement with necropsies, in which fatty clumps were observed, and consistent with previous findings in DM1 patients. Model mice did not reproduce the characteristic impaired fat fraction, widespread fat replacement through the muscles, or reduced muscle volume reported in patients. Taken together, the observed abnormal replacement of skeletal muscle by fat in the HSA^LR mice indicates that these mice partially reproduced the muscle phenotype observed in humans.

Calcitriol increases MBNL1 expression and alleviates myotonic dystrophy phenotypes in HSALR mouse models

BACKGROUND

Myotonic dystrophy type 1 (DM1), one of the most common forms of adult-onset muscular dystrophy, is caused by abnormally expanded CTG repeats in the 3' untranslated region of the DMPK gene. The CUG repeats transcribed from the expanded CTG repeats sequestrate a splicing factor, MBNL1, causing the clinical symptoms in DM1. Nowadays, only symptomatic treatments are available for DM1, and no rational therapy is available. Recently, upregulation of MBNL1 expression has been found to be one of the promising therapies for DM1.

METHODS

All experiments were conducted in the C2C12 myoblasts and HSA^LR mice, a DM1 mouse model. Real-time PCR and western blot were used to detect the mRNA and protein level, respectively. The rotarod exercise, grip strength and hanging time were used to evaluate the muscle strength of mice.

RESULTS

In this study, we demonstrated that calcitriol, an active form of vitamin D3, increased MBNL1 in C2C12 mouse myoblasts as well as in HSA^LR mice model for DM1. In HSA^LR mice model, calcitriol improved muscle strength, and corrected aberrant splicing in skeletal muscle. Besides, calcitriol reduced the number of central nuclei, and improved muscle histopathology in HSA^LR mice. In addition, we identified that calcitriol upregulated MBNL1 expression via activating the promoter of Mbnl1 in C2C12 myogenic cells.

CONCLUSION

Our study suggests that calcitriol is a potential pharmacological strategy for DM1 that enhances MBNL1 expression.

Prevention of Adverse Outcomes and Treatment Side Effects in Patients with Neuromuscular Disorders

In this article, we review prevention of serious adverse clinical outcomes and treatment side effects in patients with neuromuscular disorders including myopathies and myasthenia gravis. While neither of these entities is preventable, their course can often be modified, and severe sequelae may be prevented, with the identification of risk factors and proactive attention toward treatment planning.

[Rare diseases in the differential diagnosis of myalgia]

Myalgia describes pain in the skeletal muscles. According to the current German clinical guidelines from 2020 (AWMF register number: 030/051), the initial diagnostic assessment consists of the anamnesis, clinical examination, electrophysiological examination and standard laboratory tests. Additional special examinations, such as molecular genetic investigations, special laboratory tests, medical imaging and muscle biopsy are only needed in certain cases. This article focuses on rare neurological diseases that are classically associated with myalgia. In this context etiologically different diseases are considered, whereby some genetically linked diseases (fascioscapulohumeral dystrophy, FSHD, dystrophia myotonica, McArdle's disease, Pompe's disease, limb girdle muscular dystrophy) are contrasted with diseases with an (auto)immune-related pathogenesis (stiff-person syndrome, Isaacs syndrome). The aspects relevant for the diagnosis are particularly highlighted. The therapeutic aspects of the diseases are not part of this article.

Condensation properties of stress granules and processing bodies are compromised in Myotonic Dystrophy Type 1

RNA regulation in mammalian cells requires complex physical compartmentalisation, using structures thought to be formed by liquid-liquid phase separation. Disruption of these structures is implicated in numerous degenerative diseases. Myotonic dystrophy type 1 (DM1) is a multi-systemic trinucleotide repeat disorder resulting from an expansion of nucleotides CTG (CTGexp) in the DNA encoding DM1 protein kinase (DMPK). The cellular hallmark of DM1 is the formation of nuclear foci that contain expanded DMPK RNA (CUGexp) (with thymine instead of uracil). We report here the deregulation of stress granules (SGs) and processing bodies (P-bodies), two cytoplasmic structures key for mRNA regulation, in cell culture models of DM1. Alterations to the rates of formation and dispersal of SGs suggest an altered ability of cells to respond to stress associated with DM1, while changes to the structure and dynamics of SGs and P-bodies suggest that a widespread alteration to the biophysical properties of cellular structures is a consequence of the presence of CUGexp RNA.

Summary: Validation of an inducible model of myotonic dystrophy type 1 that shows altered cellular stress responses. These involve phase-separated cellular structures also implicated in other degenerative conditions.

[Rare diseases in the differential diagnosis of myalgia]

Myalgia describes pain in the skeletal muscles. According to the current German clinical guidelines from 2020 (AWMF register number: 030/051), the initial diagnostic assessment consists of the anamnesis, clinical examination, electrophysiological examination and standard laboratory tests. Additional special examinations, such as molecular genetic investigations, special laboratory tests, medical imaging and muscle biopsy are only needed in certain cases. This article focuses on rare neurological diseases that are classically associated with myalgia. In this context etiologically different diseases are considered, whereby some genetically linked diseases (fascioscapulohumeral dystrophy, FSHD, dystrophia myotonica, McArdle's disease, Pompe's disease, limb girdle muscular dystrophy) are contrasted with diseases with an (auto)immune-related pathogenesis (stiff-person syndrome, Isaacs syndrome). The aspects relevant for the diagnosis are particularly highlighted. The therapeutic aspects of the diseases are not part of this article.

Targeting Myotonic Dystrophy Type 1 with Metformin

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder of genetic origin. Progressive muscular weakness, atrophy and myotonia are its most prominent neuromuscular features, while additional clinical manifestations in multiple organs are also common. Overall, DM1 features resemble accelerated aging. There is currently no cure or specific treatment for myotonic dystrophy patients. However, in recent years a great effort has been made to identify potential new therapeutic strategies for DM1 patients. Metformin is a biguanide antidiabetic drug, with potential to delay aging at cellular and organismal levels. In DM1, different studies revealed that metformin rescues multiple phenotypes of the disease. This review provides an overview of recent findings describing metformin as a novel therapy to combat DM1 and their link with aging.

Healthcare resource utilization, total costs, and comorbidities among patients with myotonic dystrophy using U.S. insurance claims data from 2012 to 2019

Background

Myotonic dystrophy (DM) is a rare, inherited disorder with multi-systemic effects that impact the skeletal muscles, eyes, heart, skin and gastrointestinal, endocrine, respiratory, and central nervous systems. DM is divided into two subtypes: DM1 can present from early childhood through adulthood and also has a congenital form (cDM) while DM2 typically manifests during mid-adulthood. Both forms are progressive with no approved treatments, and unmet need for disease-modifying therapies remains high. This study interrogated health insurance claims data to explore the clinical experience, healthcare resource utilization (HCRU), and all-cause costs for DM.

Results

A total of 8541 patients with DM and 242 patients with cDM and their matched controls were selected from a database of over 200 million claimants. HCRU and all-cause costs, including pharmacy, outpatient, and inpatient services, were analyzed across four years in 12-month follow-up periods. Mean all-cause costs per DM patient were high in each of the four periods (range $14,640–$16,704) and showed a steady increase from 13 to 23 months on, while the control group mean costs declined from $9671 in the first 12 months after the index event, to approach the US population average ($5193) over time. For cDM, the highest mean costs were in the first 12-months ($66,496 vs. $2818 for controls), and remained high (above $17,944) across all subsequent periods, while control mean costs approached $0. For DM and cDM, HCRU was higher compared to controls across all study periods and all-cause healthcare costs were mostly driven by inpatient and outpatient encounters. Analysis of all diagnosis codes over the study period (comorbidities) demonstrated an elevated comorbidity profile consistent with the clinical profile of DM.

Conclusions

This study is among the first to utilize claims data to increase understanding of the clinical experience and health economic outcomes associated with DM. The markedly elevated HCRU patterns and comorbidity profile presented here add to the broad body of scientific and clinical knowledge on DM. These insights can inform clinical care and support the development of disease modifying and/or symptom-targeting therapies that address the multi-systemic, progressive nature of DM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02241-9.

Cellular Senescence and Aging in Myotonic Dystrophy

Myotonic dystrophy (DM) is a dominantly inherited multisystemic disorder affecting various organs, such as skeletal muscle, heart, the nervous system, and the eye. Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are caused by expanded CTG and CCTG repeats, respectively. In both forms, the mutant transcripts containing expanded repeats aggregate as nuclear foci and sequester several RNA-binding proteins, resulting in alternative splicing dysregulation. Although certain alternative splicing events are linked to the clinical DM phenotypes, the molecular mechanisms underlying multiple DM symptoms remain unclear. Interestingly, multi-systemic DM manifestations, including muscle weakness, cognitive impairment, cataract, and frontal baldness, resemble premature aging. Furthermore, cellular senescence, a critical contributor to aging, is suggested to play a key role in DM cellular pathophysiology. In particular, several senescence inducers including telomere shortening, mitochondrial dysfunction, and oxidative stress and senescence biomarkers such as cell cycle inhibitors, senescence-associated secretory phenotype, chromatin reorganization, and microRNA have been implicated in DM pathogenesis. In this review, we focus on the clinical similarities between DM and aging, and summarize the involvement of cellular senescence in DM and the potential application of anti-aging DM therapies.

RNA-binding proteins and post-transcriptional regulation in lens biology and cataract: Mediating spatiotemporal expression of key factors that control the cell cycle, transcription, cytoskeleton and transparency

Development of the ocular lens - a transparent tissue capable of sustaining frequent shape changes for optimal focusing power - pushes the boundaries of what cells can achieve using the molecular toolkit encoded by their genomes. The mammalian lens contains broadly two types of cells, the anteriorly located monolayer of epithelial cells which, at the equatorial region of the lens, initiate differentiation into fiber cells that contribute to the bulk of the tissue. This differentiation program involves massive upregulation of select fiber cell-expressed RNAs and their subsequent translation into high amounts of proteins, such as crystallins. But intriguingly, fiber cells achieve this while also simultaneously undergoing significant morphological changes such as elongation - involving about 1000-fold length-wise increase - and migration, which requires modulation of cytoskeletal and cell adhesion factors. Adding further to the challenges, these molecular and cellular events have to be coordinated as fiber cells progress toward loss of their nuclei and organelles, which irreversibly compromises their potential for harnessing genetically hardwired information. A long-standing question is how processes downstream of signaling and transcription, which may also participate in feedback regulation, contribute toward orchestrating these cellular differentiation events in the lens. It is now becoming clear from findings over the past decade that post-transcriptional gene expression regulatory mechanisms are critical in controlling cellular proteomes and coordinating key processes in lens development and fiber cell differentiation. Indeed, RNA-binding proteins (RBPs) such as Caprin2, Celf1, Rbm24 and Tdrd7 have now been described in mediating post-transcriptional control over key factors (e.g. Actn2, Cdkn1a (p21Cip1), Cdkn1b (p27Kip1), various crystallins, Dnase2b, Hspb1, Pax6, Prox1, Sox2) that are variously involved in cell cycle, transcription, cytoskeleton maintenance and differentiation in the lens. Furthermore, deficiencies of these RBPs have been shown to result in various eye and lens defects and/or cataract. Because fiber cell differentiation in the lens occurs throughout life, the underlying regulatory mechanisms operational in development are expected to also be recruited for the maintenance of transparency in aged lenses. Indeed, in support of this, TDRD7 and CAPRIN2 loci have been linked to age-related cataract in humans. Here, I will review the role of key RBPs in the lens and their importance in understanding the pathology of lens defects. I will discuss advances in RBP-based gene expression control, in general, and the important challenges that need to be addressed in the lens to define the mechanisms that determine the epithelial and fiber cell proteome. Finally, I will also discuss in detail several key future directions including the application of bioinformatics approaches such as iSyTE to study RBP-based post-transcriptional gene expression control in the aging lens and in the context of age-related cataract.

Preclinical characterization of antagomiR-218 as a potential treatment for myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a rare neuromuscular disease caused by expansion of unstable CTG repeats in a non-coding region of the DMPK gene. CUG expansions in mutant DMPK transcripts sequester MBNL1 proteins in ribonuclear foci. Depletion of this protein is a primary contributor to disease symptoms such as muscle weakness and atrophy and myotonia, yet upregulation of endogenous MBNL1 levels may compensate for this sequestration. Having previously demonstrated that antisense oligonucleotides against miR-218 boost MBNL1 expression and rescue phenotypes in disease models, here we provide preclinical characterization of an antagomiR-218 molecule using the HSA^LR mouse model and patient-derived myotubes. In HSA^LR, antagomiR-218 reached 40–60 pM 2 weeks after injection, rescued molecular and functional phenotypes in a dose- and time-dependent manner, and showed a good toxicity profile after a single subcutaneous administration. In muscle tissue, antagomiR rescued the normal subcellular distribution of Mbnl1 and did not alter the proportion of myonuclei containing CUG foci. In patient-derived cells, antagomiR-218 improved defective fusion and differentiation and rescued up to 34% of the gene expression alterations found in the transcriptome of patient cells. Importantly, miR-218 was found to be upregulated in DM1 muscle biopsies, pinpointing this microRNA (miRNA) as a relevant therapeutic target.

Musashi-2 contributes to myotonic dystrophy muscle dysfunction by promoting excessive autophagy through miR-7 biogenesis repression

Skeletal muscle symptoms strongly contribute to mortality of myotonic dystrophy type 1 (DM1) patients. DM1 is a neuromuscular genetic disease caused by CTG repeat expansions that, upon transcription, sequester the Muscleblind-like family of proteins and dysregulate alternative splicing of hundreds of genes. However, mis-splicing does not satisfactorily explain muscle atrophy and wasting, and several other contributing factors have been suggested, including hyperactivated autophagy leading to excessive catabolism. MicroRNA (miR)-7 has been demonstrated to be necessary and sufficient to repress the autophagy pathway in cell models of the disease, but the origin of its low levels in DM1 was unknown. We have found that the RNA-binding protein Musashi-2 (MSI2) is upregulated in patient-derived myoblasts and biopsy samples. Because it has been previously reported that MSI2 controls miR-7 biogenesis, we tested the hypothesis that excessive MSI2 was repressing miR-7 maturation. Using gene-silencing strategies (small interfering RNAs [siRNAs] and gapmers) and the small molecule MSI2-inhibitor Ro 08-2750, we demonstrate that reducing MSI2 levels or activity boosts miR-7 expression, represses excessive autophagy, and downregulates atrophy-related genes of the UPS system. We also detect a significant upregulation of MBNL1 upon MSI2 silencing. Taken together, we propose MSI2 as a new therapeutic target to treat muscle dysfunction in DM1.

Multifocal Noninvasive Magnetic Stimulation of the Primary Motor Cortex in Type 1 Myotonic Dystrophy -A Proof of Concept Pilot Study

BACKGROUND

Repeated neuromuscular electrical stimulation in type 1 Myotonic Dystrophy (DM1) has previously been shown to cause an increase in strength and a decrease in hyperexcitability of the tibialis anterior muscle.

OBJECTIVE

In this proof-of-principle study our objective was to test the hypothesis that noninvasive repetitive transcranial magnetic stimulation of the primary motor cortex (M1) with a new portable wearable multifocal stimulator causes improvement in muscle function in DM1 patients.

METHODS

We performed repetitive stimulation of M1, localized by magnetic resonance imaging, with a newly developed Transcranial Rotating Permanent Magnet Stimulator (TRPMS). Using a randomized within-patient placebo-controlled double-blind TRPMS protocol, we performed unilateral active stimulation along with contralateral sham stimulation every weekday for two weeks in 6 adults. Methods for evaluation of muscle function involved electromyography (EMG), hand dynamometry and clinical assessment using the Medical Research Council scale.

RESULTS

All participants tolerated the treatment well. While there were no significant changes clinically, EMG showed significant improvement in nerve stimulus-evoked compound muscle action potential amplitude of the first dorsal interosseous muscle and a similar but non-significant trend in the trapezius muscle, after a short exercise test, with active but not sham stimulation.

CONCLUSIONS

We conclude that two-week repeated multifocal cortical stimulation with a new wearable transcranial magnetic stimulator can be safely conducted in DM1 patients to investigate potential improvement of muscle strength and activity. The results obtained, if confirmed and extended by future safety and efficacy trials with larger patient samples, could offer a potential supportive TRPMS treatment in DM1.

Myotonic dystrophy type1: 13years of experience at a tertiary hospital. Clinical and epidemiological study and genotype-phenotype correlation

INTRODUCTION

The incidence of myotonic dystrophy type1 (DM1), a disease with great phenotypic variety, in our region is unknown. This study aims to estimate the incidence of DM1 at our hospital (a reference centre in Aragon, Spain) and to identify the characteristics of our population (genotype-phenotype correlation).

METHODS

Retrospective, descriptive study of 459 patients classified according to the number of CTG repeats, as follows: normal (5-35), premutation (36-50), protomutation (51-80), small expansions (81-150), intermediate expansions (151-1000), and large expansions (>1000). Furthermore, according to clinical phenotype, patients were categorised as unaffected (5-50 CTG repeats), mild form or asymptomatic (51-150), classical form (151-1000), and severe form (>1000).

RESULTS

The incidence of DM1 was 20.61 cases per million person-years (95%CI: 19.59-21.63). An inverse correlation was observed between the number of CTG repeats and the age at genetic diagnosis (ρ=-0.547; 95%CI: -0.610 to -0.375; P<.001). CTG5 was the most frequent polymorphic allele in healthy individuals. Of all patients with DM1, 28.3% presented the mild or asymptomatic form, 59.1% the classical form, and 12.6% the severe form. Inheritance was maternal in 35.1% of cases, paternal in 59.4%, and uncertain in 5.5%. In mild forms, frontal balding in men was the most prevalent phenotypic trait, as well as myotonia and cataracts, while in the classical form, ptosis, facial weakness, voice and pronunciation alterations, myotonia, and fatigue/sleepiness were most frequent.

CONCLUSIONS

The incidence of DM1 in Aragon is significant. Multidisciplinary study of the phenotype of patients with DM1 is key to early diagnosis and personalised management.

Genetic burden linked to founder effects in Saguenay-Lac-Saint-Jean illustrates the importance of genetic screening test availability

The Saguenay–Lac-Saint-Jean (SLSJ) region located in the province of Quebec was settled in the 19th century by pioneers issued from successive migration waves starting in France in the 17th century and continuing within Quebec until the beginning of the 20th century. The genetic structure of the SLSJ population is considered to be the product of a triple founder effect and is characterised by a higher prevalence of some rare genetic diseases. Several studies were performed to elucidate the historical, demographic and genetic background of current SLSJ inhabitants to assess the origins of these rare disorders and their distribution in the population. Thanks to the development of new sequencing technologies, the genes and the variants responsible for the most prevalent conditions were identified. Combined with other resources such as the BALSAC population database, identifying the causal genes and the pathogenic variants allowed to assess the impacts of some of these founder mutations on the population health and to design precision medicine public health strategies based on carrier testing. Furthermore, it stimulated the establishment of many public programmes.

We report here a review and an update of a subset of inherited disorders and founder mutations in the SLSJ region. Data were collected from published scientific sources. This work expands the knowledge about the current frequencies of these rare disorders, the frequencies of other rare genetic diseases in this population, the relevance of the carrier tests offered to the population, as well as the current available treatments and research about future therapeutic avenues for these inherited disorders.

Characterization of cannabis use by patients with myotonic dystrophy type 1: A pilot study

The treatment of myotonic dystrophy type 1 (DM1) focuses on reducing symptom burden. However, since medication often fails to produce satisfying symptom relief, some patients seek alternatives, such as cannabis, to help reduce some of these symptoms. The aim of this study was to provide an accurate profile of cannabis use among DM1 patients. Phone interviews were conducted to identify current and former users, and to assess reasons for cannabis use. Characteristics of cannabis use were also investigated. Briefly, among the 72 study participants, 22.2% currently used cannabis and a majority of them (56.9%) reported using it to relieve symptoms associated with DM1. These users, classified as therapeutic users, reported poorer health status (EQ-5D index scores: 0.532±0.230 vs. 0.823±0.208, p = 0.020; EQ-VAS scale 50.56±10.74 vs. 75.57±21.50, p = 0.009) than non-therapeutic users. Finally, differences among sex were also highlighted. While the therapeutic effects of cannabis were not explored in our study, our results support the potential role of cannabis and cannabinoids in the treatment of DM1-associated symptoms which will need to be thoroughly investigated.

miR-322/miR-503 clusters regulate defective myoblast differentiation in myotonic dystrophy RNA-toxic by targeting Celf1

Myotonic dystrophy (DM) is a genetic disorder featured by muscular dystrophy. It is caused by CUG expansion in the myotonic dystrophy protein kinase gene that leads to aberrant signaling and impaired myocyte differentiation. Many studies have shown that microRNAs are involved in the differentiation process of myoblasts. The purpose of this study was to investigate how the miR-322/miR-503 cluster regulates intracellular signaling to affect cell differentiation. The cell model of DM1 was employed by expressing GFP-CUG200 or CUGBP Elav-like family member 1 (Celf1) in myoblasts. Immunostaining of MF-20 was performed to examine myocyte differentiation. qRT-PCR and western blot were used to determine the levels of Celf1, MyoD, MyoG, Mef2c, miR-322/miR-503, and mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK) signaling. Dual luciferase assay was performed to validate the interaction between miR-322/miR-503 and Celf1. CUG expansion in myoblasts impaired the cell differentiation, increased the Celf1 level, but it decreased the miR-322/miR-503 levels. miR-322/miR-503 mimics restored the impaired differentiation caused by CUG expansion, while miR-322/miR-503 inhibitors further suppressed. miR-322/miR-503 directly targeted Celf1 and negatively regulated its expression. Knockdown of Celf1 promoted myocyte differentiation. Further, miR-322/miR-503 mimics rescued the impaired differentiation of myocytes caused by CUG expansion or Celf1 overexpression through suppressing of MEK/ERK signaling. miR-322/miR-503 cluster recover the defective myocyte differentiation caused by RNA-toxic via targeting Celf1. Restoring miR-322/miR-503 levels could be an avenue for DM1 therapy.

DNA methylation at the DMPK gene locus is associated with cognitive functions in myotonic dystrophy type 1

Aim: Myotonic dystrophy type 1 (DM1) is caused by an unstable trinucleotide (CTG) expansion at the DMPK gene locus. Cognitive dysfunctions are often observed in the condition. We investigated the association between DMPK blood DNA methylation (DNAm) and cognitive functions in DM1, considering expansion length and variant repeats (VRs). Method: Data were obtained from 115 adult-onset DM1 patients. Molecular analyses consisted of pyrosequencing, small pool PCR and Southern blot hybridization. Cognitive functions were assessed by validated neuropsychological tests. Results: For patients without VRs (n = 103), blood DNAm at baseline independently contributed to predict cognitive functions 9 years later. Patients with VRs (n = 12) had different DNAm and cognitive profiles. Conclusion: DNAm allows to better understand DM1-related cognitive dysfunction etiology.

Nutritional practices in pediatric patients with neuromuscular disorders

Children with neuromuscular disorders (NMDs) may experience a spectrum of nutritional issues with adverse health consequences. This review summarizes the current understanding of nutritional care in pediatric NMDs, recognizing disease-specific aspects of nutrition alongside the challenges and needs in dietetic care. General or disease-related nutritional issues for children with NMDs include being underweight, overweight, or obese and having swallowing difficulty, gastroesophageal reflux, diarrhea, and/or constipation. Specific challenges in NMD nutritional assessment include alterations in body composition and energy requirements and difficulties in measuring anthropometry. Multidisciplinary dietetic intervention focuses on optimizing nutrient intakes to avert growth failure or obesity and managing feeding difficulties and gastrointestinal problems. Care guidelines are disease specific and vary in approach and detail. To promote best clinical practice across diverse settings, a standardized approach to assessing growth and nutrition across all pediatric NMDs is needed to direct optimal care centered on individual requirements. Future studies should focus on determining the prevalence of specific nutritional issues and the effectiveness of specific interventions among various pediatric NMD populations.

Variant repeats within the DMPK CTG expansion protect function in myotonic dystrophy type 1

Objective

We tested the hypothesis that variant repeat interruptions (RIs) within the DMPK CTG repeat tract lead to milder symptoms compared with pure repeats (PRs) in myotonic dystrophy type 1 (DM1).

Methods

We evaluated motor, neurocognitive, and behavioral outcomes in a group of 6 participants with DM1 with RI compared with a case-matched sample of 12 participants with DM1 with PR and a case-matched sample of 12 unaffected healthy comparison participants (UA).

Results

In every measure, the RI participants were intermediate between UA and PR participants. For muscle strength, the RI group was significantly less impaired than the PR group. For measures of Full Scale IQ, depression, and sleepiness, all 3 groups were significantly different from each other with UA > RI > PR in order of impairment. The RI group was different from unaffected, but not significantly different from PR (UA > RI = PR) in apathy and working memory. Finally, in finger tapping and processing speed, RI did not differ from UA comparisons, but PR had significantly lower scores than the UA comparisons (UA = RI > PR).

Conclusions

Our results support the notion that patients affected by DM1 with RI demonstrate a milder phenotype with the same pattern of deficits as those with PR indicating a similar disease process.

Skeletal Muscle Channelopathies

Skeletal muscle channelopathies are rare genetic neuromuscular conditions that include the nondystrophic myotonias and periodic paralyses. They cause disabling muscle symptoms and can limit educational potential, work opportunities, socialization, and quality of life. Effective therapy is available, making it essential to recognize and treat this group of disorders. Here, the authors highlight important aspects regarding diagnosis and management using illustrative case reports.

Intrarater reliability and validity of outcome measures in myotonic dystrophy type 1

OBJECTIVE

To investigate intrarater reliability and concurrent and construct validity of muscle strength, balance, and functional mobility measures in individuals with noncongenital myotonic dystrophy type 1 (DM1).

METHODS

Seventy-eight adults with noncongenital DM1 participated in visit 1, and 73 of the them participated in visit 2 separated by 1 to 2 weeks. The assessments consisted of muscle strength tests with handheld dynamometry (HHD) and stationary dynamometry in the lower limb. The balance tests consisted of the step test, Timed Up and Go test, feet-together stance, tandem stance, 1-leg stance, and modified Clinical Test of Sensory Integration and Balance on a balance platform. The functional mobility tests consisted of the 10-m walk test (10mWT) and 10-times Sit-to-Stand test.

RESULTS

The HHD and stationary dynamometry had sufficient intrarater reliability for most muscle groups on a group (SEM_% ≤15%) and individual (minimal detectable difference [MDD_95%] ≤30%) level, but the HHD was most reliable. Stationary dynamometry measured a higher torque than HHD for all extensor muscles, but for single individuals, none of the devices were favored. Overall, intrarater reliability and validity were sufficient only for the dynamic balance tests, not the static balance tests. Both functional mobility tests were sufficiently reliable and valid, but the 10mWT was most reliable.

CONCLUSION

Overall, HHD is recommended as a reliable and valid tool for single individuals and for flexor muscles on a group level. For balance assessments, the dynamic balance tests are recommended as the most valid and reliable balance tests. Both functional mobility tests are recommended for valid and reliable outcomes, but the 10mWT was superior for reliability.

Multisystemic Impairments in 93 Chinese Patients With Myotonic Dystrophy Type 1

Background: Myotonic dystrophy type 1 (DM1) is an autosomal dominant neuromuscular disease characterized by muscle weakness and multisystemic impairments, which significantly impact the quality of life. There is currently an increasing consensus on the necessity of a multidisciplinary assessment in patients with DM1, to improve the management of the disease.

Methods: To analyze the prevalence and pairwise relationships between various organs involved, we performed a retrospective study by reviewing demographic and clinical information of DM1 patients including age, disease duration, clinical history, muscular impairment rating scale score (MIRS), results of blood biochemistry, electrocardiogram, echocardiography, and ophthalmologic examination.

Results: Ninety three DM1 patients (60 males and 33 females), aged 34.7 ± 12.6 (mean ± standard deviation) years were recruited. Of which, two congenital cases were of maternal and paternal inheritance, respectively. In the other 91 patients, cataract was found in 44.1% of patients, followed by hypogonadism (40.8%), frontal balding (40.7%), and cardiac abnormalities (34.5%). Thyroid dysfunction and insulin insensitivity were relatively uncommon. Age (p < 0.001) is independently correlated with cataract, and MIRS correlates positively with cardiac abnormalities (p = 0.005) and frontal balding (p = 0.015). Male patients more frequently had frontal balding (Risk ratio, 3.98; 95% confidence interval, 1.493–10.611) compared with female patients. Male patients with cataract presented more frequent cardiac abnormalities (Risk ratio, 4.40; 95% confidence interval, 1.055–18.358) compared with non-cataract male patients. Hypogonadism in male patients was characterized as decreased testosterone level, accompanied by elevated levels of luteinizing hormone and follicle-stimulating hormone.

Conclusions: In Chinese patients with DM1, we conclude that (1) cataract, hypogonadism, frontal balding and cardiac abnormalities are frequently observed; (2) age is an independent indicator to cataract and MIRS is the only predictor for cardiac abnormalities and frontal balding; (3) a positive correlation between ophthalmologic and cardiac impairments in male patients is found; (4) endocrine abnormalities show diverse manifestations and hormone tests are recommended; (5) particular attention should be given to patients with older age and higher MIRS score.

Health-Related Quality of Life in Patients with Adult-Onset Myotonic Dystrophy Type 1: A Systematic Review

Background

Adult-onset myotonic dystrophy type 1 (DM1) is a chronic, multisystem disorder that leads to disability and premature death.

Objectives

The objective of our study was to conduct a systematic literature review of the health-related quality of life (HRQoL) of patients with DM1.

Methods

We searched Embase, Web of Science, and PubMed for English language full-text articles reporting results from studies of HRQoL in patients with adult-onset DM1 published between 1 January 2000 and 21 February 2018. We excluded reviews, editorials, and studies reporting results for a sample with fewer than five patients (to allow for meaningful inference).

Results

The search identified 266 unique publications. Of these, 231 were excluded following title and abstract screening and 16 after full-text review, leaving 19 articles for data synthesis. We found 15 articles measuring the HRQoL of patients with adult-onset DM1 using the 36-Item Short Form Health Survey (SF-36), six using the Individualized Neuromuscular Quality of Life Questionnaire (INQoL), and one using Cantril’s Ladder. Available evidence shows that patient HRQoL is impaired in DM1, mainly due to compromised physical health, but also reveals that substantial heterogeneity exists in estimates across studies.

Conclusions

HRQoL in adult-onset DM1 has been extensively studied using the SF-36 and the INQoL, but current estimates are inconclusive, and little is known of the impact of the disease as measured using other instruments. Our data synthesis should help characterize the patient burden of DM1 and inform future studies of HRQoL in this indication.

Electronic supplementary material

The online version of this article (10.1007/s40271-019-00357-y) contains supplementary material, which is available to authorized users.

Summary of Selected Healthcare Encounters among a Selection of Patients with Myotonic Muscular Dystrophy

OBJECTIVE

Research has not examined the use of health care by patients with myotonic muscular dystrophy (MMD), but it would provide insights into this population, which is prone to comorbidities and high service needs. This study is an analysis of this understudied subgroup, using a unique linked dataset to examine the characteristics and healthcare utilization patterns for people with MMD.

METHODS

This analysis used 3 South Carolina datasets (2009-2014). The subjects included individuals with at least 1 encounter with an International Classification of Diseases, Ninth Revision, Clinical Modification code of 359.21. The variables included sex, race, visit type, payer, and diagnoses. The analyses examined characteristics and number of encounters.

RESULTS

The subjects were predominately female, white, and 45 to 64 years old. A total of 44.6% of the study population had at least 1 inpatient visit, whereas 64.2% had at least 1 emergency department visit. A majority of the subjects had at least 1 office visit (55.0%), and most (85.3%) did not have a home health encounter.

CONCLUSIONS

Investigation of the reasons for these inpatient and emergency department encounters may be helpful in identifying ways to deliver high-quality care.

Gender difference in clinical conditions among hospitalized adults with myotonic dystrophy

INTRODUCTION

In this study we examined gender differences in adult hospitalizations with myotonic dystrophy (DM).

METHODS

From the Nationwide Inpatient Sample (NIS) 2010-2014, we identified 1,891 adult hospitalizations with a DM diagnosis and constructed a comparison group of hospitalizations without DM using propensity score matching. We calculated relative risk by gender for 44 clinical diagnoses that each accounted for at least 5% of DM hospitalizations.

RESULTS

Hospitalizations with DM were longer (4.8 vs. 4.1 days, P < 0.0001) and more costly ($13,241 vs. $11,458, P < 0.0001) than those without DM. More than half (25 of 44) of the conditions co-occurring with DM hospitalizations did not differ in their relative risks by gender. For those that differed by gender, only 5 were specific to DM, compared with hospitalizations without DM.

DISCUSSION

Our findings highlight the importance of comprehensive and coordinated care for DM rather than gender-oriented care in the inpatient setting. Muscle Nerve 59:348-353, 2019.

Genotype-phenotype correlations in pediatric patients with myotonic dystrophy type 1

PURPOSE

Myotonic dystrophy, also known as dystrophia myotonica (DM), is an autosomal dominant disorder with 2 genetically distinct forms. DM type 1 (DM1) is the more common form and is caused by abnormal expansion of cytosine/thymine/guanine (CTG) repeats in the DM protein kinase (DMPK ) gene. Our study aimed to determine whether the age of onset is correlated with CTG repeat length in a population of pediatric patients with DM1.

METHODS

We retrospectively identified 30 pediatric patients with DM1 that underwent DMPK testing, of which the clinical data of 17 was sufficient. The cohort was divided into 2 subgroups based on the clinical phenotype (congenital-onset vs. late-onset) and number of CTG repeats (<1,000 vs. ≥1,000).

RESULTS

We found no significant difference between the age of onset and CTG repeat length in our pediatric patient population. Based on clinical subgrouping, we found that the congenital-onset subgroup was statistically different with respect to several variables, including prematurity, rate of admission to neonatal intensive care unit, need for respiratory support at birth, hypotonia, dysphagia, ventilator dependence, and functional status on last visit, compared to the late-onset subgroup. Based on genetic subgrouping, we found a single variable (poor feeding in neonate) that was significantly different in the large CTG subgroup than that in the small CTG subgroup.

CONCLUSION

Clinical variables exhibiting statistically significant differences between the subgroups should be focused on prognosis and designing tailored management approaches for the patients; our findings will contribute to achieve this important goal for treating patients with DM1.

Daunorubicin reduces MBNL1 sequestration caused by CUG-repeat expansion and rescues cardiac dysfunctions in a Drosophila model of myotonic dystrophy

Myotonic dystrophy (DM) is a dominantly inherited neuromuscular disorder caused by expression of mutant myotonin-protein kinase (DMPK) transcripts containing expanded CUG repeats. Pathogenic DMPK RNA sequesters the muscleblind-like (MBNL) proteins, causing alterations in metabolism of various RNAs. Cardiac dysfunction represents the second most common cause of death in DM type 1 (DM1) patients. However, the contribution of MBNL sequestration in DM1 cardiac dysfunction is unclear. We overexpressed Muscleblind (Mbl), the DrosophilaMBNL orthologue, in cardiomyocytes of DM1 model flies and observed a rescue of heart dysfunctions, which are characteristic of these model flies and resemble cardiac defects observed in patients. We also identified a drug – daunorubicin hydrochloride – that directly binds to CUG repeats and alleviates Mbl sequestration in Drosophila DM1 cardiomyocytes, resulting in mis-splicing rescue and cardiac function recovery. These results demonstrate the relevance of Mbl sequestration caused by expanded-CUG-repeat RNA in cardiac dysfunctions in DM1, and highlight the potential of strategies aimed at inhibiting this protein-RNA interaction to recover normal cardiac function.

Summary: MBNL protein sequestration by expanded CUG RNA contributes towards cardiac dysfunction in a myotonic dystrophy Drosophila model. Here, the authors identify the anticancer drug daunorubicin as a candidate therapeutic for the disease.

What the internist should know about hereditary muscle channelopathies

OBJECTIVES

Non-dystrophic myotonia, periodic paralysis and, to a certain extent, myotonic dystrophies are rare hereditary skeletal muscle channelopathies, charactarized by myotonia or episodic muscle weakness. This review highlights the diagnostic challenges and treatment options.

RESULTS

Some of these rare skeletal muscle disorders are associated with a broad range of systemic and nonspecific muscle symptoms. Consequently, patients are often referred to the internist before seeing a neurologist. This article provides clinical clues to better diagnose an tackle these unique disorders.

CONCLUSION

A increased knowledge will reduce the diagnostic delay, improve monitoring and treatment, and might even prevent potentially life-threatening conditions as seen in DM.

Identification of exosomal muscle-specific miRNAs in serum of myotonic dystrophy patients relating to muscle disease progress

Myotonic dystrophy type 1 (DM1) is the most common form of adult-onset muscular dystrophy, which is characterised by progressive muscle wasting and the discovery of reliable blood-based biomarkers could be useful for the disease progress monitoring. There have been some reports showing that the presence of specific miRNAs in blood correlates with DM1. In one of these, our group identified four muscle-specific miRNAs, miR-1, miR-133a, miR-133b and miR-206, which correlated with the progression of muscle wasting observed in DM1 patients. The levels of the four muscle-specific miRNAs were elevated in the serum of DM1 patients compared to healthy participants and were also elevated in the serum of progressive muscle wasting DM1 patients compared to disease-stable DM1 patients. The aim of this work was to characterise the ontology of these four muscle-specific miRNAs in the blood circulation of DM1 patients. Here we show that the four muscle-specific miRNAs are encapsulated within exosomes isolated from DM1 patients. Our results show for the first time, the presence of miRNAs encapsulated within exosomes in blood circulation of DM1 patients. More interestingly, the levels of the four exosomal muscle-specific miRNAs are associated with the progression of muscle wasting in DM1 patients. We propose that exosomal muscle-specific miRNAs may be useful molecular biomarkers for monitoring the progress of muscle wasting in DM1 patients. There has been a growing interest regarding the clinical applications of exosomes and their role in prognosis and therapy of various diseases and the above results contribute towards this way.

Dystrophia myotonica type 1 presenting with dysarthria: A case report and literature review

Dystrophia myotonica (DM) type 1 is an autosomal dominant disorder, caused by a trinucleotide CTG repeat expansion in the 3′ untranslated region of the dystrophia myotonica protein kinase (DMPK) gene (chromosome 19q13.3). The disorder affects different organ systems, including the skeletal muscles, ocular lens, lungs, heart and gastrointestinal tract, as well as the endocrine and central nervous systems. The skeletal muscles are most frequently involved, whereby the disorder manifests as myotonia, muscle weakness and amyotrophy. However, DM type 1 presenting with dysarthria is rare. The current study presents a case of a 28-year-old male with DM type 1 presenting with dysarthria and associated multifocal hyperintense lesions in the white matter. Although electromyogram measurements identified myotonic discharges in all extremities, a muscle biopsy failed to detect the characteristic pathological features of DM type 1. A lack of a positive family history for DM type 1 also obscured diagnosis. However, genetic analysis detected a single allele in the P12 segment of the DMPK gene that included a CTG expansion of 13 repeats and a three-base gradient fragment in the P134 segment that included a CTG expansion of >600 repeats. According to the characteristics of dysarthria, multifocal hyperintense lesions in the white matter, electromyogram measurement results and genetic testing results, a diagnosis of DM type 1 was confirmed.

Close encounters: Moving along bumps, breaks, and bubbles on expanded trinucleotide tracts

Expansion of simple triplet repeats (TNR) underlies more than 30 severe degenerative diseases. There is a good understanding of the major pathways generating an expansion, and the associated polymerases that operate during gap filling synthesis at these "difficult to copy" sequences. However, the mechanism by which a TNR is repaired depends on the type of lesion, the structural features imposed by the lesion, the assembled replication/repair complex, and the polymerase that encounters it. The relationships among these parameters are exceptionally complex and how they direct pathway choice is poorly understood. In this review, we consider the properties of polymerases, and how encounters with GC-rich or abnormal structures might influence polymerase choice and the success of replication and repair. Insights over the last three years have highlighted new mechanisms that provide interesting choices to consider in protecting genome stability.