Myotonic dystrophy type 2: molecular, diagnostic and clinical spectrum

Disturbance of the human gut microbiota in patients with Myotonic Dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a rare autosomal dominant genetic disorder. Although DM1 is primarily characterized by progressive muscular weakness, it exhibits many multisystemic manifestations, such as cognitive deficits, cardiac conduction abnormalities, and cataracts, as well as endocrine and reproductive issues. Additionally, the gastrointestinal (GI) tract is frequently affected, encompassing the entire digestive tract. However, the underlying causes of these GI symptoms remain uncertain, whether it is biomechanical problems of the intestine, involvement of bacterial communities, or both. The primary objective of this study is to investigate the structural changes in the gut microbiome of DM1 patients. To achieve this purpose, 35 patients with DM1 were recruited from the DM-Scope registry of the neuromuscular clinic in the Saguenay-Lac-St-Jean region of the province of Québec, Canada. Stool samples from these 35 patients, including 15 paired samples with family members living with them as controls, were collected. Subsequently, these samples were sequenced by 16S MiSeq and were analyzed with DADA2 to generate taxonomic signatures. Our analysis revealed that the DM1 status correlated with changes in gut bacterial community. Notably, there were differences in the relative abundance of Bacteroidota, Euryarchaeota, Fusobacteriota, and Cyanobacteria Phyla compared to healthy controls. However, no significant shift in gut microbiome community structure was observed between DM1 phenotypes. These findings provide valuable insights into how the gut bacterial community, in conjunction with biomechanical factors, could potentially influence the gastrointestinal tract of DM1 patients.

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.

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.

Life Expectancy and Causes of Death in Patients with Myotonic Dystrophy Type 2

Background

Myotonic Dystrophy type 2 (DM2) is a dominantly inherited multisystem disease caused by a CCTG repeat expansion in intron 1 of the CNBP gene. Although in the last two decades over 1500 patients with DM2 have been diagnosed worldwide, our clinical impression of a reduced life expectancy in DM2 has not been investigated previously.

Objective

The aim of this observational study was to determine the life expectancy and the causes of death in patients with genetically confirmed DM2.

Methods

We identified the data of all deceased patients with DM2 in the Dutch neuromuscular database between 2000 and 2023. Ages and causes of death and the patients' clinical features during lifetime were determined. Age of death in DM2 was compared to the general population by using life tables with prognostic cohort life expectancy (CLE) and period life expectancy (PLE) data of the Dutch electronic database of statistics (CBS StatLine).

Results

Twenty-six deceased patients were identified in the Dutch DM2 cohort (n = 125). Median age of death in DM2 (70.9 years) was significantly lower compared to sex- and age-matched CLE (78.1 years) and PLE (82.1 years) in the Netherlands. Main causes of death were cardiac diseases (31%) and pneumonia (27%). Seven patients (27%) had a malignancy at the time of death.

Conclusion

These results provide new insights into the phenotype of DM2. Life expectancy in patients with DM2 is reduced, possibly attributable to multiple causes including increased risk of cardiac disease, pneumonia, and malignancies. The occurrence of a significantly reduced life expectancy has implications for clinical practice and may form a basis for advanced care planning, including end-of-life care, to optimize quality of life for patients with DM2 and their family. Research in larger cohorts should be done to confirm these findings and to ascertain more about the natural course in DM2.

Effectiveness and safety of mexiletine versus placebo in patients with myotonia: a systematic review and meta-analysis

BACKGROUND

The rare nature of dystrophic and non-dystrophic myotonia has limited the available evidence on the efficacy of mexiletine as a potential treatment. To address this gap, we conducted a systematic review and meta-analysis to evaluate the effectiveness and safety of mexiletine for both dystrophic and non-dystrophic myotonic patients.

METHODS

The search was conducted on various electronic databases up to March 2023, for randomized clinical trials (RCTs) comparing mexiletine versus placebo in myotonic patients. A risk of bias assessment was carried out, and relevant data was extracted manually into an online sheet. RevMan software (version 5.4) was employed for analysis.

RESULTS

A total of five studies, comprising 186 patients, were included in the meta-analysis. Our findings showed that mexiletine was significantly more effective than placebo in improving stiffness score (SMD =  - 1.19, 95% CI [- 1.53, - 0.85]), as well as in reducing hand grip myotonia (MD =  - 1.36 s, 95% CI [- 1.83, - 0.89]). Mexiletine also significantly improved SF-36 Physical and Mental Component Score in patients with non-dystrophic myotonia only. Regarding safety, mexiletine did not significantly alter ECG parameters but was associated with greater gastrointestinal symptoms (GIT) compared to placebo (RR 3.7, 95% CI [1.79, 7.64]). Other adverse events showed no significant differences.

CONCLUSION

The results support that mexiletine is effective and safe in myotonic patients; however, it is associated with a higher risk of GIT symptoms. Due to the scarcity of published RCTs and the prevalence of GIT symptoms, we recommend further well-designed RCTs testing various drug combinations to reduce GIT symptoms.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Sequence composition changes in short tandem repeats: heterogeneity, detection, mechanisms and clinical implications

Short tandem repeats (STRs) are a class of repetitive elements, composed of tandem arrays of 1-6 base pair sequence motifs, that comprise a substantial fraction of the human genome. STR expansions can cause a wide range of neurological and neuromuscular conditions, known as repeat expansion disorders, whose age of onset, severity, penetrance and/or clinical phenotype are influenced by the length of the repeats and their sequence composition. The presence of non-canonical motifs, depending on the type, frequency and position within the repeat tract, can alter clinical outcomes by modifying somatic and intergenerational repeat stability, gene expression and mutant transcript-mediated and/or protein-mediated toxicities. Here, we review the diverse structural conformations of repeat expansions, technological advances for the characterization of changes in sequence composition, their clinical correlations and the impact on disease mechanisms.

Massive contractions of myotonic dystrophy type 2-associated CCTG tetranucleotide repeats occur via double-strand break repair with distinct requirements for DNA helicases

Myotonic dystrophy type 2 (DM2) is a genetic disease caused by expanded CCTG DNA repeats in the first intron of CNBP. The number of CCTG repeats in DM2 patients ranges from 75 to 11,000, yet little is known about the molecular mechanisms responsible for repeat expansions or contractions. We developed an experimental system in Saccharomyces cerevisiae that enables the selection of large-scale contractions of (CCTG)100 within the intron of a reporter gene and subsequent genetic analysis. Contractions exceeded 80 repeat units, causing the final repetitive tract to be well below the threshold for disease. We found that Rad51 and Rad52 are involved in these massive contractions, indicating a mechanism that uses homologous recombination. Srs2 helicase was shown previously to stabilize CTG, CAG, and CGG repeats. Loss of Srs2 did not significantly affect CCTG contraction rates in unperturbed conditions. In contrast, loss of the RecQ helicase Sgs1 resulted in a 6-fold decrease in contraction rate with specific evidence that helicase activity is required for large-scale contractions. Using a genetic assay to evaluate chromosome arm loss, we determined that CCTG and reverse complementary CAGG repeats elevate the rate of chromosomal fragility compared to a short-track control. Overall, our results demonstrate that the genetic control of CCTG repeat contractions is notably distinct among disease-causing microsatellite repeat sequences.

Inherited myotonias

The inherited myotonias are a complex group of diseases caused by variations in genes that encode or modulate the expression of ion channels that regulate muscle excitability. These variations alter muscle membrane excitability allowing mild depolarization, causing myotonic discharges. There are two groups of inherited myotonia, the dystrophic and the nondystrophic myotonias (NDM). Patients with NDM have a pure muscle phenotype with variations in channel genes expressed in muscle. The dystrophic myotonias are caused by genes that alter splicing leading to more systemic effects with myotonia being one of a number of systemic symptoms. This chapter therefore focuses on the key aspects of the NDMs. The NDMs manifest with varying clinical phenotypes, which change from infancy to adulthood. The pathogenicity of different variants can be determined using heterologous expression systems to understand the alteration in channel properties and predict the likelihood of causing disease. Myotonia itself can be managed by lifestyle modifications. A number of randomized controlled trials demonstrate efficacy of mexiletine and lamotrigine in treating myotonia, but there is an evidence that specific variants may be more or less well-treated by the different agents because of how they alter the channel kinetics. More work is needed to develop more targeted genetic treatments.

Expert Insights from a Delphi-driven Neurologists' Panel: Real-world Mexiletine use in Patients with Myotonic Disorders in Italy

Background

Myotonic disorders, such as non-dystrophic myotonias (NDMs) and myotonic dystrophies (DMs) are characterized by a delay in muscle relaxation after a contraction stimulus. There is general consensus that protocols to treat myotonia need to be implemented.

Objective

Mexiletine is the only pharmacological agent approved for the symptomatic treatment of myotonia in adult patients with NDM and is considered to be the first-line treatment for DMs; however, its production in Italy was halted in 2022 making its availability to patients problematic.

Methods

A panel of 8 Italian neurologists took part in a two-round Delphi panel between June and October 2022, analyzing the current use of mexiletine in Italian clinical practice.

Results

The panelists assist 1126 patients (69% DM type1, 18% NDM and 13% DM type2). Adult NDM patients receive, on average, 400-600 mg of mexiletine hydrochloride (HCl) while adult DM patients receive 100-600 mg, per day in the long-term. The severity of symptoms is considered the main reason to start mexiletine treatment for both NDM and DM patients. Mexiletine is reckoned to have a clinical impact for both NDM and DM patients, but currently drug access is problematic.

Conclusions

Mexiletine treatment is recognized to have a role in the reduction of the symptomatic burden for NDM and DM patients. Patient management could be improved by facilitating access to therapy and developing new drug formulations.

Sleep in pediatric neuromuscular disorders

Sleep disordered breathing (SDB) is prevalent among children with neuromuscular disorders (NMD). The combination of respiratory muscle weakness, altered drive, and chest wall distortion due to scoliosis make sleep a stressful state in this population. Symptomatology can range from absent to snoring, nocturnal awakenings, morning headaches, and excessive daytime sleepiness. Sequelae of untreated SDB includes cardiovascular effects, metabolic derangements, and neurocognitive concerns which can be compounded by those innate to the NMD. The clinician should have a low threshold for obtaining polysomnography and recognize the nuances of individual disorders due to disproportionately impacted muscle groups such as hypoventilation in ambulating patients from diaphragm weakness. Non-invasive or invasive ventilation are the mainstay of treatment. In this review we explore the diagnosis and treatment of SDB in children with various NMD.

Exploring challenges in the management and treatment of inclusion body myositis

PURPOSE OF REVIEW

This review provides an overview of the management and treatment landscape of inclusion body myositis (IBM), while highlighting the current challenges and future directions.

RECENT FINDINGS

IBM is a slowly progressive myopathy that predominantly affects patients over the age of 40, leading to increased morbidity and mortality. Unfortunately, a definitive cure for IBM remains elusive. Various clinical trials targeting inflammatory and some of the noninflammatory pathways have failed. The search for effective disease-modifying treatments faces numerous hurdles including variability in presentation, diagnostic challenges, poor understanding of pathogenesis, scarcity of disease models, a lack of validated outcome measures, and challenges related to clinical trial design. Close monitoring of swallowing and respiratory function, adapting an exercise routine, and addressing mobility issues are the mainstay of management at this time.

SUMMARY

Addressing the obstacles encountered by patients with IBM and the medical community presents a multitude of challenges. Effectively surmounting these hurdles requires embracing cutting-edge research strategies aimed at enhancing the management and treatment of IBM, while elevating the quality of life for those affected.

Sporadic Myotonic Dystrophy Type 2 in a Japanese Patient

We herein report a Japanese patient with myotonic dystrophy type 2 (DM2), which is rare in Japan. A 64-year-oldman had proximal muscle weakness and grip myotonia. Electromyography showed myotonic discharges, but dystrophia-myotonica protein kinase (DMPK) was negative for CTG repeats. A muscle biopsy revealed increased central nuclei, pyknotic nuclear clumps and muscle fiber atrophy, mainly in type 2 fibers, raising the possibility of DM2. The diagnosis was genetically confirmed by the abnormal CCTG repeat size in cellular nucleic acid-binding protein (CNBP) on repeat-primed polymerase chain reaction, which was estimated to be around 4,500 repeats by Southern blotting.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Massive contractions of Myotonic Dystrophy Type 2-associated CCTG tetranucleotide repeats occur via double strand break repair with distinct requirements for helicases

Myotonic Dystrophy Type 2 (DM2) is a genetic disease caused by expanded CCTG DNA repeats in the first intron of CNBP. The number of CCTG repeats in DM2 patients ranges from 75-11,000, yet little is known about the molecular mechanisms responsible for repeat expansions or contractions. We developed an experimental system in Saccharomyces cerevisiae that enables selection of large-scale contractions of (CCTG)100 within the intron of a reporter gene and subsequent genetic analysis. Contractions exceeded 80 repeat units, causing the final repetitive tract to be well below the threshold for disease. We found that Rad51 and Rad52 are required for these massive contractions, indicating a mechanism that involves homologous recombination. Srs2 helicase was shown previously to stabilize CTG, CAG, and CGG repeats. Loss of Srs2 did not significantly affect CCTG contraction rates in unperturbed conditions. In contrast, loss of the RecQ helicase Sgs1 resulted in a 6-fold decrease in contraction rate with specific evidence that helicase activity is required for large-scale contractions. Using a genetic assay to evaluate chromosome arm loss, we determined that CCTG and reverse complementary CAGG repeats elevate the rate of chromosomal fragility compared to a low-repeat control. Overall, our results demonstrate that the genetic control of CCTG repeat contractions is notably distinct among disease-causing microsatellite repeat sequences.

Associations between lower extremity muscle fat fraction and motor performance in myotonic dystrophy type 2: A pilot study

INTRODUCTION/AIMS

Although muscle structure measures from magnetic resonance imaging (MRI) have been used to assess disease severity in muscular dystrophies, little is known about how these measures are affected in myotonic dystrophy type 2 (DM2). We aim to characterize lower extremity muscle fat fraction (MFF) as a potential biomarker of disease severity, and evaluate its relationship with motor performance in DM2.

METHODS

3-Tesla MRIs were obtained from nine patients with DM2 and six controls using a T1W-Dixon protocol. To calculate MFF, muscle volumes were segmented from proximal, middle, and distal regions of the thigh and calf. Associations between MFF and motor performance were calculated using Spearman's correlations (ρ).

RESULTS

Mean age of DM2 participants was 62 ± 11 y (89% female), and mean symptom duration was 20 ± 12 y. Compared to controls, the DM2 group had significantly higher MFF in the thigh and the calf segments (p-value = .002). The highest MFF at the thigh in DM2 was located in the posterior compartment (39.7 ± 12.9%) and at the calf was the lateral compartment (31.5 ± 8.7%). In the DM2 group, we found a strong correlation between the posterior thigh MFF and the 6-min walk test (ρ = -.90, p-value = .001). The lateral calf MFF was also strongly correlated with the step test (ρ = -0.82, p-value = .006).

DISCUSSION

Our pilot data suggest a potential correlation between lower extremity MFF and some motor performance tests in DM2. Longitudinal studies with larger sample sizes are required to validate MFF as a marker of disease severity in DM2.

Clinical score for early diagnosis of myotonic dystrophy type 2

INTRODUCTION

Myotonic dystrophy type 2 (DM2) is a rare, multisystemic, autosomal dominant disease with highly variable clinical presentation. DM2 is considered to be highly underdiagnosed.

OBJECTIVE

The aim of this study was to determine which symptoms, signs, and diagnostic findings in patients referred to neurological outpatient units are the most indicative to arouse suspicion of DM2. We tried to make a useful and easy-to-administer clinical scoring system for early diagnosis of DM2-DM2 early diagnosis score (DM2-EDS).

PATIENTS AND METHODS

Two hundred ninety-one patients with a clinical suspicion of DM2 were included: 69 were genetically confirmed to have DM2, and 222 patients were DM2 negative. Relevant history, neurological, and paraclinical data were obtained from the electronic medical records.

RESULTS

The following parameters appeared as significant predictors of DM2 diagnosis: cataracts (beta = 0.410, p < 0.001), myotonia on needle EMG (beta = 0.298, p < 0.001), hand tremor (beta = 0.211, p = 0.001), positive family history (beta = 0.171, p = 0.012), and calf hypertrophy (beta = 0.120, p = 0.043). In the final DM2-EDS, based on the beta values, symptoms were associated with the following values: cataracts (present 3.4, absent 0), myotonia (present 2.5, absent 0), tremor (present 1.7, absent 0), family history (positive 1.4, negative 0), and calf hypertrophy (present 1.0, absent 0). A cut-off value on DM2-EDS of 3.25 of maximum 10 points had a sensitivity of 84% and specificity of 81% to diagnose DM2.

CONCLUSION

Significant predictors of DM2 diagnosis in the neurology outpatient unit were identified. We made an easy-to-administer DM2-EDS score for early diagnosis of DM2.

Unexpected diagnosis of myotonic dystrophy type 2 repeat expansion by genome sequencing

Several neurological disorders, such as myotonic dystrophy are caused by expansions of short tandem repeats (STRs) which can be difficult to detect by molecular tools. Methodological advances have made repeat expansion (RE) detection with whole genome sequencing (WGS) feasible. We recruited a multi-generational family (family A) ascertained for genetic studies of autism spectrum disorder. WGS was performed on seven children from four nuclear families from family A and analyzed for REs of STRs known to cause neurological disorders. We detected an expansion of a heterozygous intronic CCTG STR in CNBP in two siblings. This STR causes myotonic dystrophy type 2 (DM2). The expansion did not segregate with the ASD phenotype. Repeat-primed PCR showed that the DM2 CCTG motif was expanded above the pathogenic threshold in both children and their mother. On subsequent examination, the mother had mild features of DM2. We show that screening of STRs in WGS datasets has diagnostic utility, both in the clinical and research domain, with potential management and genetic counseling implications.

Myotonic Dystrophy

PURPOSE OF REVIEW

Myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2) are genetic disorders affecting skeletal and smooth muscle, heart, brain, eyes, and other organs. The multisystem involvement and disease variability of myotonic dystrophy have presented challenges for clinical care and research. This article focuses on the diagnosis and management of the disease. In addition, recent advances in characterizing the diverse clinical manifestations and variability of the disease are discussed.

RECENT FINDINGS

Studies of the multisystem involvement of myotonic dystrophy, including the most lethal cardiac and respiratory manifestations and their molecular underpinnings, expand our understanding of the myotonic dystrophy phenotype. Advances have been made in understanding the molecular mechanisms of both types of myotonic dystrophy, providing opportunities for developing targeted therapeutics, some of which have entered clinical trials in DM1.

SUMMARY

Continued efforts focus on advancing our molecular and clinical understanding of DM1 and DM2. Accurately measuring and monitoring the diverse and variable clinical manifestations of myotonic dystrophy in clinic and in research is important to provide adequate care, prevent complications, and find treatments that improve symptoms and life quality.

Development of Therapeutic Approaches for Myotonic Dystrophies Type 1 and Type 2

Myotonic Dystrophies type 1 (DM1) and type 2 (DM2) are complex multisystem diseases without disease-based therapies. These disorders are caused by the expansions of unstable CTG (DM1) and CCTG (DM2) repeats outside of the coding regions of the disease genes: DMPK in DM1 and CNBP in DM2. Multiple clinical and molecular studies provided a consensus for DM1 pathogenesis, showing that the molecular pathophysiology of DM1 is associated with the toxicity of RNA CUG repeats, which cause multiple disturbances in RNA metabolism in patients' cells. As a result, splicing, translation, RNA stability and transcription of multiple genes are misregulated in DM1 cells. While mutant CCUG repeats are the main cause of DM2, additional factors might play a role in DM2 pathogenesis. This review describes current progress in the translation of mechanistic knowledge in DM1 and DM2 to clinical trials, with a focus on the development of disease-specific therapies for patients with adult forms of DM1 and congenital DM1 (CDM1).

Characterization of full-length CNBP expanded alleles in myotonic dystrophy type 2 patients by Cas9-mediated enrichment and nanopore sequencing

Myotonic dystrophy type 2 (DM2) is caused by CCTG repeat expansions in the CNBP gene, comprising 75 to >11,000 units and featuring extensive mosaicism, making it challenging to sequence fully expanded alleles. To overcome these limitations, we used PCR-free Cas9-mediated nanopore sequencing to characterize CNBP repeat expansions at the single-nucleotide level in nine DM2 patients. The length of normal and expanded alleles can be assessed precisely using this strategy, agreeing with traditional methods, and revealing the degree of mosaicism. We also sequenced an entire ~50 kbp expansion, which has not been achieved previously for DM2 or any other repeat-expansion disorders. Our approach precisely counted the repeats and identified the repeat pattern for both short interrupted and uninterrupted alleles. Interestingly, in the expanded alleles, only two DM2 samples featured the expected pure CCTG repeat pattern, while the other seven presented also TCTG blocks at the 3′ end, which have not been reported before in DM2 patients, but confirmed hereby with orthogonal methods. The demonstrated approach simultaneously determines repeat length, structure/motif, and the extent of somatic mosaicism, promising to improve the molecular diagnosis of DM2 and achieve more accurate genotype–phenotype correlations for the better stratification of DM2 patients in clinical trials.

Autoimmune Diseases in Patients With Myotonic Dystrophy Type 2

Introduction

Myotonic dystrophy type 2 (DM2) is a rare autosomal dominant multisystemic disease with highly variable clinical presentation. Several case reports and one cohort study suggested a significant association between DM2 and autoimmune diseases (AIDs).

Aim

The aim of this study is to analyze the frequency and type of AIDs in patients with DM2 from the Serbian DM registry.

Patients and Methods

A total of 131 patients with DM2 from 108 families were included, [62.6% women, mean age at DM2 onset 40.4 (with standard deviation 13) years, age at entering the registry 52 (12.8) years, and age at analysis 58.4 (12.8) years]. Data were obtained from Akhenaten, the Serbian registry for DM, and through the hospital electronic data system.

Results

Upon entering the registry, 35 (26.7%) of the 131 patients with DM2 had AIDs including Hashimoto thyroiditis (18.1%), rheumatoid arthritis, diabetes mellitus type 1, systemic lupus, Sjogren's disease, localized scleroderma, psoriasis, celiac disease, Graves's disease, neuromyelitis optica, myasthenia gravis, and Guillain-Barre syndrome. At the time of data analysis, one additional patient developed new AIDs, so eventually, 36 (28.8%) of 125 DM2 survivors had AIDs. Antinuclear antibodies (ANAs) were found in 14 (10.7%) of 63 tested patients, including 12 without defined corresponding AID (all in low titers, 1:40 to 1:160). Antineutrophil cytoplasmic antibodies (ANCAs) were negative in all 50 tested cases. The percentage of women was significantly higher among patients with AIDs (82.9% vs. 55.2%, p <0.01).

Conclusion

AIDs were present in as high as 30% of the patients with DM2. Thus, screening for AIDs in DM2 seems reasonable. Presence of AIDs and/or ANAs may lead to under-diagnosis of DM2.

Milestones of progression in myotonic dystrophy type 1 and type 2

INTRODUCTION/AIMS

Disease progression in myotonic dystrophy (DM) is marked by milestone events, when functional thresholds are crossed. DM type 2 (DM2) is considered less severe than DM type 1 (DM1), but whether this applies uniformly to all features is unknown. We compared the age-dependent risk for milestone events in DM1 and DM2, and tested for associations with age of onset and sex.

METHODS

We studied a large cohort of adult participants in a national registry of DM1 and DM2. Using annual surveys from participants, we ascertained milestone events for motor involvement (use of cane, walker, ankle brace, wheelchair, or ventilatory device), systemic involvement (diabetes, pacemaker, cancer), loss of employment due to DM, and death.

RESULTS

Mean follow-up of registry participants (DM1 = 929, DM2=222) was 7 years. Disability and motor milestones occurred at earlier ages in DM1 than in DM2. In contrast, the risk of diabetes was higher and tended to occur earlier in DM2 (HR=0.56, p=<0.001). In DM1, the milestone events tended to occur earlier, and life expectancy was reduced, when symptoms began at younger ages. In DM1, men were at greater risk for disability (HR=1.34, p=<0.01), use of ankle braces (HR=1.41, p=0.02), and diabetes (HR=2.2, p=<0.0001), whereas women were at greater risk for using walkers (HR=0.68, p=0.001) or malignancy (0.66, p=<0.01).

DISCUSSION

Milestone events recorded through registries can be used to assess long-term impact of DM in large cohorts. Except for diabetes, the age-related risk of milestone events is greater in DM1 than in DM2.

Non-dystrophic myotonia: 2-year clinical and patient reported outcomes

INTRODUCTION/AIMS

Consistency of differences between non-dystrophic myotonias over time measured by standardized clinical/patient-reported outcomes is lacking. Evaluation of longitudinal data could establish clinically relevant endpoints for future research.

METHODS

Data from prospective observational study of 95 definite/clinically suspected non-dystrophic myotonia participants (six sites in the United States, United Kingdom, and Canada) between March 2006 and March 2009 were analyzed. Outcomes included: standardized symptom interview/exam, Short Form-36, Individualized Neuromuscular Quality of Life (INQoL), electrophysiological short/prolonged exercise tests, manual muscle testing, quantitative grip strength, modified get-up-and-go test. Patterns were assigned as described by Fournier et al. Comparisons were restricted to confirmed sodium channelopathies (SCN4A, baseline, year 1, year 2: n = 34, 19, 13), chloride channelopathies (CLCN1, n = 32, 26, 18), and myotonic dystrophy type 2 (DM2, n = 9, 6, 2).

RESULTS

Muscle stiffness was the most frequent symptom over time (54.7%-64.7%). Eyelid myotonia and paradoxical handgrip/eyelid myotonia were more frequent in SCN4A. Grip strength and combined manual muscle testing remained stable. Modified get-up-and-go showed less warm up in SCN4A but remained stable. Median post short exercise decrement was stable, except for SCN4A (baseline to year 2 decrement difference 16.6% [Q1, Q3: 9.5, 39.2]). Fournier patterns type 2 (CLCN1) and 1 (SCN4A) were most specific; 40.4% of participants had a change in pattern over time. INQoL showed higher impact for SCN4A and DM2 with scores stable over time.

DISCUSSION

Symptom frequency and clinical outcome assessments were stable with defined variability in myotonia measures supporting trial designs like cross over or combined n-of-1 as important for rare disorders.

Molecular characterization of myotonic dystrophy fibroblast cell lines for use in small molecule screening

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are common forms of adult onset muscular dystrophy. Pathogenesis in both diseases is largely driven by production of toxic-expanded repeat RNAs that sequester MBNL RNA-binding proteins, causing mis-splicing. Given this shared pathogenesis, we hypothesized that diamidines, small molecules that rescue mis-splicing in DM1 models, could also rescue mis-splicing in DM2 models. While several DM1 cell models exist, few are available for DM2 limiting research and therapeutic development. Here, we characterize DM1 and DM2 patient-derived fibroblasts for use in small molecule screens and therapeutic studies. We identify mis-splicing events unique to DM2 fibroblasts and common events shared with DM1 fibroblasts. We show that diamidines can partially rescue molecular phenotypes in both DM1 and DM2 fibroblasts. This study demonstrates the potential of fibroblasts as models for DM1 and DM2, which will help meet an important need for well-characterized DM2 cell models.

Circulating small RNA signatures differentiate accurately the subtypes of muscular dystrophies: small-RNA next-generation sequencing analytics and functional insights

Muscular dystrophies are a group of rare and severe inherited disorders mainly affecting the muscle tissue. Duchene Muscular Dystrophy, Myotonic Dystrophy types 1 and 2, Limb Girdle Muscular Dystrophy and Facioscapulohumeral Muscular Dystrophy are some of the members of this family of disorders. In addition to the current diagnostic tools, there is an increasing interest for the development of novel non-invasive biomarkers for the diagnosis and monitoring of these diseases. miRNAs are small RNA molecules characterized by high stability in blood thus making them ideal biomarker candidates for various diseases. In this study, we present the first genome-wide next-generation small RNA sequencing in serum samples of five different types of muscular dystrophy patients and healthy individuals. We identified many small RNAs including miRNAs, lncRNAs, tRNAs, snoRNAs and snRNAs, that differentially discriminate the muscular dystrophy patients from the healthy individuals. Further analysis of the identified miRNAs showed that some miRNAs can distinguish the muscular dystrophy patients from controls and other miRNAs are specific to the type of muscular dystrophy. Bioinformatics analysis of the target genes for the most significant miRNAs and the biological role of these genes revealed different pathways that the dysregulated miRNAs are involved in each type of muscular dystrophy investigated. In conclusion, this study shows unique signatures of small RNAs circulating in five types of muscular dystrophy patients and provides a useful resource for future studies for the development of miRNA biomarkers in muscular dystrophies and for their involvement in the pathogenesis of the disorders.

Cutaneous findings in myotonic dystrophy

Myotonic dystrophy types 1 and 2 are a group of complex genetic disorders resulting from the expansion of (CTG)_n nucleotide repeats in the DMPK gene. In addition to the hallmark manifestations of myotonia and skeletal muscle atrophy, myotonic dystrophy also affects a myriad of other organs including the heart, lungs, as well as the skin. The most common cutaneous manifestations of myotonic dystrophy are early male frontal alopecia and adult-onset pilomatricomas. Myotonic dystrophy also increases the risk of developing malignant skin diseases such as basal cell carcinoma and melanoma. To aid in the diagnosis and treatment of myotonic dystrophy related skin conditions, it is important for the dermatologist to become cognizant of the common and rare cutaneous manifestations of this genetic disorder. We performed a PubMed search using the key terms “myotonic dystrophy” AND “cutaneous” OR “skin” OR “dermatologic” AND “manifestation” OR “finding.” The resulting publications were manually reviewed for additional relevant publications, and subsequent additional searches were performed as needed, especially regarding the molecular mechanisms of pathogenesis. In this review, we aim to provide an overview of myotonic dystrophy types 1 and 2 and summarize their cutaneous manifestations as well as potential mechanisms of pathogenesis.

Myotonic Dystrophies: A Genetic Overview

Myotonic dystrophies (DM) are the most common muscular dystrophies in adults, which can affect other non-skeletal muscle organs such as the heart, brain and gastrointestinal system. There are two genetically distinct types of myotonic dystrophy: myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2), both dominantly inherited with significant overlap in clinical manifestations. DM1 results from CTG repeat expansions in the 3'-untranslated region (3'UTR) of the DMPK (dystrophia myotonica protein kinase) gene on chromosome 19, while DM2 is caused by CCTG repeat expansions in intron 1 of the CNBP (cellular nucleic acid-binding protein) gene on chromosome 3. Recent advances in genetics and molecular biology, especially in the field of RNA biology, have allowed better understanding of the potential pathomechanisms involved in DM. In this review article, core clinical features and genetics of DM are presented followed by a discussion on the current postulated pathomechanisms and therapeutic approaches used in DM, including the ones currently in human clinical trial phase.

Hereditary myopathies associated with hematological abnormalities

The diagnostic evaluation of a patient with suspected hereditary muscle disease can be challenging. Clinicians rely largely on clinical history and examination features, with additional serological, electrodiagnostic, radiologic, histopathologic, and genetic investigations assisting in definitive diagnosis. Hematological testing is inexpensive and widely available, but frequently overlooked in the hereditary myopathy evaluation. Hematological abnormalities are infrequently encountered in this setting; however, their presence provides a valuable clue, helps refine the differential diagnosis, tailors further investigation, and assists interpretation of variants of uncertain significance. A diverse spectrum of hematological abnormalities is associated with hereditary myopathies, including anemias, leukocyte abnormalities, and thrombocytopenia. Recurrent rhabdomyolysis in certain glycolytic enzymopathies co-occurs with hemolytic anemia, often chronic and mild in phosphofructokinase and phosphoglycerate kinase deficiencies, or acute and fever-associated in aldolase-A and triosephosphate isomerase deficiency. Sideroblastic anemia, commonly severe, accompanies congenital-to-childhood onset mitochondrial myopathies including Pearson marrow-pancreas syndrome and mitochondrial myopathy, lactic acidosis, and sideroblastic anemia phenotypes. Congenital megaloblastic macrocytic anemia and mitochondrial dysfunction characterize SFXN4-related myopathy. Neutropenia, chronic or cyclical, with recurrent infections, infantile-to-childhood onset skeletal myopathy and cardiomyopathy are typical of Barth syndrome, while chronic neutropenia without infection occurs rarely in DNM2-centronuclear myopathy. Peripheral eosinophilia may accompany eosinophilic inflammation in recessive calpainopathy. Lipid accumulation in leukocytes on peripheral blood smear (Jordans' anomaly) is pathognomonic for neutral lipid storage diseases. Mild thrombocytopenia occurs in autosomal dominant, childhood-onset STIM1 tubular aggregate myopathy, STIM1 and ORAI1 deficiency syndromes, and GNE myopathy. Herein, we review these hereditary myopathies in which hematological features play a prominent role.

Progressive myocardial injury in myotonic dystrophy type II and facioscapulohumeral muscular dystrophy 1: a cardiovascular magnetic resonance follow-up study

AIM

Muscular dystrophy (MD) is a progressive disease with predominantly muscular symptoms. Myotonic dystrophy type II (MD2) and facioscapulohumeral muscular dystrophy type 1 (FSHD1) are gaining an increasing awareness, but data on cardiac involvement are conflicting. The aim of this study was to determine a progression of cardiac remodeling in both entities by applying cardiovascular magnetic resonance (CMR) and evaluate its potential relation to arrhythmias as well as to conduction abnormalities.

METHODS AND RESULTS

83 MD2 and FSHD1 patients were followed. The participation was 87% in MD2 and 80% in FSHD1. 1.5 T CMR was performed to assess functional parameters as well as myocardial tissue characterization applying T1 and T2 mapping, fat/water-separated imaging and late gadolinium enhancement. Focal fibrosis was detected in 23% of MD2) and 33% of FSHD1 subjects and fat infiltration in 32% of MD2 and 28% of FSHD1 subjects, respectively. The incidence of all focal findings was higher at follow-up. T2 decreased, whereas native T1 remained stable. Global extracellular volume fraction (ECV) decreased similarly to the fibrosis volume while the total cell volume remained unchanged. All patients with focal fibrosis showed a significant increase in left ventricular (LV) and right ventricular (RV) volumes. An increase of arrhythmic events was observed. All patients with ventricular arrhythmias had focal myocardial changes and an increased volume of both ventricles (LV end-diastolic volume (EDV) p = 0.003, RVEDV p = 0.031). Patients with supraventricular tachycardias had a significantly higher left atrial volume (p = 0.047).

CONCLUSION

We observed a remarkably fast and progressive decline of cardiac morphology and function as well as a progression of rhythm disturbances, even in asymptomatic patients with a potential association between an increase in arrhythmias and progression of myocardial tissue damage, such as focal fibrosis and fat infiltration, exists. These results suggest that MD2 and FSHD1 patients should be carefully followed-up to identify early development of remodeling and potential risks for the development of further cardiac events even in the absence of symptoms. Trial registration ISRCTN, ID ISRCTN16491505. Registered 29 November 2017 - Retrospectively registered, http://www.isrctn.com/ISRCTN16491505.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Current Treatment Options for Patients with Myotonic Dystrophy Type 2

Purpose of the review

Myotonic dystrophy types 1 and 2 are frequent forms of muscular dystrophies in adulthood. Their clinical differences need to be taken into account for the most appropriate treatment of patients. The aim of this article is to provide an overview on the current and upcoming therapeutic options for patients with myotonic dystrophy type 2 (DM2).

Recent findings

At the moment, no disease-modifying therapies are available for DM2; next-generation therapies may however be available in the near future. In the meanwhile, the symptomatic management of patients has greatly improved, thank to the production of consensus-based standards of care and the growing evidence of efficacy of anti-myotonic drugs, promising employment of cannabinoids for symptom’s relief, regular monitoring, and early detection of treatable extra-muscular manifestations.

Summary

The treatment of DM2 is currently symptomatic and relies on the coordinated intervention of a multidisciplinary team. It remains to be determined whether upcoming causal therapies for myotonic dystrophy type 1 will be applicable also in DM2.

Genetic syndromes with diabetes: A systematic review

Previous reviews and clinical guidelines have identified 10-20 genetic syndromes associated with diabetes, but no systematic review has been conducted to date. We provide the first comprehensive catalog for syndromes with diabetes mellitus. We conducted a systematic review of MEDLINE, Embase, CENTRAL, PubMed, OMIM, and Orphanet databases for case reports, case series, and observational studies published between 1946 and January 15, 2020, that described diabetes mellitus in adults and children with monogenic or chromosomal syndromes. Our literature search identified 7,122 studies, of which 160 fulfilled inclusion criteria. Our analysis of these studies found 69 distinct diabetes syndromes. Thirty (43.5%) syndromes included diabetes mellitus as a cardinal clinical feature, and 56 (81.2%) were fully genetically elucidated. Sixty-three syndromes (91.3%) were described more than once in independent case reports, of which 59 (93.7%) demonstrated clinical heterogeneity. Syndromes associated with diabetes mellitus are more numerous and diverse than previously anticipated. While knowledge of the syndromes is limited by their low prevalence, future reviews will be needed as more cases are identified. The genetic etiologies of these syndromes are well elucidated and provide potential avenues for future gene identification efforts, aid in diagnosis and management, gene therapy research, and developing personalized medicine treatments.

Role of CMR Imaging in Diagnostics and Evaluation of Cardiac Involvement in Muscle Dystrophies

PURPOSE OF REVIEW

This review aims to outline the utility of cardiac magnetic resonance (CMR) in patients with different types of muscular dystrophies for the assessment of myocardial involvement, risk stratification and in guiding therapeutic decisions.

RECENT FINDINGS

In patients suffering from muscular dystrophies (MD), even mild initial dysfunction may lead to severe heart failure over a time course of years. CMR plays an increasing role in the diagnosis and clinical care of these patients, mostly due to its unique capability to precisely characterize subclinical and progressive changes in cardiac geometry, function in order to differentiate myocardial injury it allows the identification of inflammation, focal and diffuse fibrosis as well as fatty infiltration. CMR may provide additional information in addition to the physical examination, laboratory tests, ECG, and echocardiography. Further trials are needed to investigate the potential impact of CMR on the therapeutic decision-making as well as the assessment of long-term prognosis in different forms of muscular dystrophies. In addition to the basic cardiovascular evaluation, CMR can provide a robust, non-invasive technique for the evaluation of subclinical myocardial tissue injury like fat infiltration and focal and diffuse fibrosis. Furthermore, CMR has a unique capability to detect the progression of myocardial tissue damage in patients with a preserved systolic function.

Ancestral Origin of the First Indian Families with Myotonic Dystrophy Type 2

BACKGROUND

Myotonic dystrophy type 2 (DM2) is caused by a CCTG repeat expansion in intron 1 of the CCHC-Type Zinc Finger Nucleic Acid Binding Protein (CNBP) gene. Previous studies indicated that this repeat expansion originates from separate founders.

OBJECTIVE

This study was set out to determine whether or not patients with DM2 originating from European and non-European countries carry the previously described European founder haplotypes.

METHODS

Haplotype analysis was performed in 59 DM2 patients from 29 unrelated families. Twenty-three families were from European descent and 6 families originated from non-European countries (India, Suriname and Morocco). Seven short tandem repeats (CL3N122, CL3N99, CL3N59, CL3N117, CL3N119, CL3N19 and CL3N23) and 4 single nucleotide polymorphisms (SNP) (rs1871922, rs1384313, rs4303883 and CGAP_886192) in and around the CNBP gene were used to construct patients' haplotypes. These haplotypes were compared to the known DM2 haplotypes to determine the ancestral origin of the CNBP repeat expansion.

RESULTS

Of 41 patients, the haplotype could be assigned to the previously described Caucasian haplotypes. Three patients from Morocco and Portugal had a haplotype identical to the earlier reported Moroccan haplotype. Twelve patients from India and Suriname, however, carried a haplotype that seems distinct from the previously reported haplotypes. Three individuals could not be assigned to a specific haplotype.

CONCLUSION

The ancestral origin of DM2 in India might be distinct from the Caucasian families and the solely described Japanese patient. However, we were unable to establish this firmly due to the limited genetic variation in the region surrounding the CNBP gene.

New diagnostic and therapeutic modalities in neuromuscular disorders in children

Pediatric neuromuscular disorders are a diverse group of conditions that affect how muscle and nerve function. They involve the motor neurons, nerves, neuromuscular junction and muscles. Pathology of any of these regions leads to the inability to perform voluntary movements. Over time, the natural progression of most of these disorders is followed by significant disability, and at the most extreme, almost complete paralysis and death secondary to complications. Diagnostic measures for pediatric neuromuscular disorders, like that of most medical conditions, relies heavily on clinical presentation, history and a detailed physical examination. Primary additional diagnostic measures have included serum creatine kinase (CK) levels, electromyography (EMG), nerve conduction studies (NCS) and muscle or nerve biopsies, which has historically been the gold standard. In the last several decades less invasive testing has become more common such as muscle magnetic resonance imaging (MRI) and genetic testing.  The advances of molecular genetics, such as next generation sequencing (NGS) which includes whole-exome sequencing (WES) and whole-genome sequencing (WGS), enable clinicians to pinpoint more accurately exact gene mutations. The advent of genetic testing enhances personalized medicine. The field of pediatric neuromuscular disorders is also undergoing a remarkable evolution in therapeutic modalities including novel targeted therapies such as exon skipping/inclusion and gene replacement therapies. This is a review of the initial approach to suspected neuromuscular disorders in children as well as up to date diagnostic and therapeutic modalities for the most common pediatric neuromuscular disorders. As the world enters the new decade, there are encouraging therapeutic results. However, there remain key challenges to these modalities including limitations in its applicability, optimization for delivery of gene replacement therapies and in its effectiveness.

Comparison of Shear Wave Elastography and Dynamometer Test in Muscle Tissue Characterization for Potential Medical and Sport Application

Skeletal muscle status and its dynamic follow up are of particular importance in the management of several diseases where weight and muscle mass loss and, consequently, immobilization occurs, as in cancer and its treatment, as well as in neurodegenerative disorders. But immobilization is not the direct result of body and muscle mass loss, but rather the loss of the maximal tension capabilities of the skeletal muscle. Therefore, the development of a non-invasive and real-time method which can measure muscle tension capabilities in immobile patients is highly anticipated. Our aim was to introduce and evaluate a special ultrasound measurement technique to estimate a maximal muscle tension characteristic which can be used in medicine and also in sports diagnostics. Therefore, we determined the relationship between the results of shear wave elastography measurements and the dynamometric data of individuals. The measurements were concluded on the m. vastus lateralis. Twelve healthy elite athletes took part in our preliminary proof of principle study—five endurance (S) and seven strength (F) athletes showing unambiguously different muscle composition features, nine healthy subjects (H) without prior sports background, and four cancer patients in treatment for a stage 3 brain tumor (T). Results showed a high correlation between the maximal dynamometric isometric torque (Mmax) and mean elasticity value (E) for the non-athletes [(H + T), (r = 0.795)] and for the athletes [(S + F), (r = 0.79)]. For the athletes (S + F), the rate of tension development at contraction (RTDk) and E correlation was also determined (r = 0.84, p < 0.05). Our measurements showed significantly greater E values for the strength athletes with fast muscle fiber dominance than endurance athletes with slow muscle fiber dominance (p < 0.05). Our findings suggest that shear wave ultrasound elastography is a promising method for estimating maximal muscle tension and, also, the human skeletal muscle fiber ratio. These results warrant further investigations with a larger number of individuals, both in medicine and in sports science.

A 14-Year Italian Experience in DM2 Genetic Testing: Frequency and Distribution of Normal and Premutated CNBP Alleles

Myotonic dystrophy type 2 (DM2) is a multisystemic disorder caused by a (CCTG)_n in intron 1 of the CNBP gene. The CCTG repeat tract is part of a complex (TG)_v(TCTG)_w(CCTG)_x(NCTG)_y(CCTG)_z motif generally interrupted in CNBP healthy range alleles. Here we report our 14-year experience of DM2 postnatal genetic testing in a total of 570 individuals. The DM2 locus has been analyzed by a combination of SR-PCR, TP-PCR, LR-PCR, and Sanger sequencing of CNBP alleles. DM2 molecular diagnosis has been confirmed in 187/570 samples analyzed (32.8%) and is mainly associated with the presence of myotonia in patients. This set of CNBP alleles showed unimodal distribution with 25 different alleles ranging from 108 to 168 bp, in accordance with previous studies on European populations. The most frequent CNBP alleles consisted of 138, 134, 140, and 136 bps with an overall locus heterozygosity of 90%. Sequencing of 103 unexpanded CNBP alleles in DM2-positive patients revealed that (CCTG)₅(NCTG)₃(CCTG)₇ and (CCTG)₆(NCTG)₃(CCTG)₇ are the most common interruption motifs. We also characterized five CNBP premutated alleles with (CCTG)_n repetitions from n = 36 to n = 53. However, the molecular and clinical consequences in our cohort of samples are not unequivocal. Data that emerged from this study are representative of the Italian population and are useful tools for National and European centers offering DM2 genetic testing and counseling.

Cerebral involvement and related aspects in myotonic dystrophy type 2

Myotonic dystrophy type 2 (DM2) is an autosomal dominant multisystemic disorder caused by CCTG repeats expansion in the first intron of the CNBP gene. In this review we focus on the brain involvement in DM2, including its pathogenic mechanisms, microstructural, macrostructural and functional brain changes, as well as the effects of all these impairments on patients' everyday life. We also try to understand how brain abnormalities in DM2 should be adequately measured and potentially treated. The most important pathogenetic mechanisms in DM2 are RNA gain-of-function and repeat-associated non-ATG (RAN) translation. One of the main neuroimaging findings in DM2 is the presence of diffuse periventricular white matter hyperintensity lesions (WMHLs). Brain atrophy has been described in DM2 patients, but it is not clear if it is mostly caused by a decrease of the white or gray matter volume. The most commonly reported specific cognitive symptoms in DM2 are dysexecutive syndrome, visuospatial and memory impairments. Fatigue, sleep-related disorders and pain are also frequent in DM2. The majority of key symptoms and signs in DM2 has a great influence on patients' daily lives, their psychological status, economic situation and quality of life.

Regulatory Potential of Competing Endogenous RNAs in Myotonic Dystrophies

Non-coding RNAs (ncRNAs) have been reported to be implicated in cell fate determination and various human diseases. All ncRNA molecules are emerging as key regulators of diverse cellular processes; however, little is known about the regulatory interaction among these various classes of RNAs. It has been proposed that the large-scale regulatory network across the whole transcriptome is mediated by competing endogenous RNA (ceRNA) activity attributed to both protein-coding and ncRNAs. ceRNAs are considered to be natural sponges of miRNAs that can influence the expression and availability of multiple miRNAs and, consequently, the global mRNA and protein levels. In this review, we summarize the current understanding of the role of ncRNAs in two neuromuscular diseases, myotonic dystrophy type 1 and 2 (DM1 and DM2), and the involvement of expanded CUG and CCUG repeat-containing transcripts in miRNA-mediated RNA crosstalk. More specifically, we discuss the possibility that long repeat tracts present in mutant transcripts can be potent miRNA sponges and may affect ceRNA crosstalk in these diseases. Moreover, we highlight practical information related to innovative disease modelling and studying RNA regulatory networks in cells. Extending knowledge of gene regulation by ncRNAs, and of complex regulatory ceRNA networks in DM1 and DM2, will help to address many questions pertinent to pathogenesis and treatment of these disorders; it may also help to better understand general rules of gene expression and to discover new rules of gene control.

New developments in myotonic dystrophies from a multisystemic perspective

PURPOSE OF REVIEW

The multisystemic involvement of myotonic dystrophies (DMs) intricates disease monitoring, patients' care and trial design. This update of the multifaceted comorbidities observed in DMs aims to assist neurologists in the complex management of patients and to encourage further studies for still under-investigated aspects of the disease.

RECENT FINDINGS

We reviewed the most recent studies covering pathogenesis and clinical aspects of extra-muscular involvement in DM1 and DM2. The largest body of evidence regards the cardiac and respiratory features, for which experts' recommendations have been produced. Gastrointestinal symptoms emerge as one of the most prevalent complaints in DMs. The alteration of insulin signaling pathways, involved in gastrointestinal manifestations, carcinogenesis, muscle function, cognitive and endocrinological aspects, gain further relevance in the light of recent evidence of metformin efficacy in DM1. Still, too few studies are performed on large DM2 cohorts, so that current recommendations mainly rely on data gathered in DM1 that cannot be fully translated to DM2.

SUMMARY

Extra-muscular manifestations greatly contribute to the overall disease burden. A multidisciplinary approach is the key for the management of patients. Consensus-based recommendations for DM1 and DM2 allow high standards of care but further evidence are needed to implement these recommendations.

Degradation of Toxic RNA in Myotonic Dystrophy Using Gapmer Antisense Oligonucleotides

Myotonic dystrophy (DM) types 1 (DM1) and 2 (DM2) are caused by autosomal dominant gain-of-function RNA which are, in turn, created by the expansion of repeat sequences in the DMPK and ZNF9 genes, respectively. The expansions are highly unstable and biased for further expansion in somatic cells and across generations. Despite the different genes involved, DM1 and DM2 share several clinical features due to having the similar underlying mechanism of repetitive RNA-mediated toxicity. Both disorders manifest as multisystemic conditions with features including myotonia, cataract development, and abnormalities in cardiac conduction. At present, there is no cure for DM and treatments mostly aim at symptom management. Among the therapeutics being developed, antisense therapy using gapmers is one of the most promising. Compared to other antisense oligonucleotides, gapmers maintain the ability to induce RNase H cleavage while having enhanced target binding affinity and nuclease resistance. This chapter will consolidate the different strategies studied thus far to develop a treatment for DM1 through the targeting of toxic repetitive RNA using gapmers.

Myotonic Muscular Dystrophy Type 2 in CT, USA: A Single-Center Experience With 50 Patients

ABSTRACT

Myotonic dystrophy type 2 (DM2) is an autosomal dominant disorder due to a (CCTG)n repeat expansion in intron 1 of the CNBP gene. In this article, we report the clinicopathologic findings in 50 patients seen at a single site over a 27 year period. DM2 was the fifth most common type of muscular dystrophy seen at our center with a 5-fold lower frequency as compared to DM1. Age of symptom onset ranged from 15 to 72 years, and the mean duration between symptom onset and diagnosis was 7.4 years. Weakness referable to the proximal lower extremities was the presenting symptom in 62% of patients. The degree of generalized weakness varied from severe in 30% to no weakness in 20% of patients. Clinical myotonia was noted in 18% and myotonic discharges on electromyography in 97% of patients. Pain symptoms were uncommon in our cohort. A significant correlation was noted between limb weakness and degree of muscle pathologic changes. There was no correlation between CCTG repeat size and other clinicopathologic findings. Six patients (12%) had cardiac abnormalities including one who developed progressive nonischemic dilated cardiomyopathy ultimately leading to cardiac transplantation. In 21 patients followed for 2 or more years, we noted a mean rate of decline in total Medical Research Council score of about 1% per year.

Myotonic dystrophy type 2: the 2020 update

The myotonic dystrophies are the commonest cause of adult-onset muscular dystrophy. Phenotypes of DM1 and DM2 are similar, but there are some important differences, including the presence or absence of congenital form, muscles primarily affected (distal vs proximal), involved muscle fiber types (type 1 vs type 2 fibers), and some associated multisystemic phenotypes. There is currently no cure for the myotonic dystrophies but effective management significantly reduces the morbidity and mortality of patients. For the enormous understanding of the molecular pathogenesis of myotonic dystrophy type 1 and myotonic dystrophy type 2, these diseases are now called "spliceopathies" and are mediated by a primary disorder of RNA rather than proteins. Despite clinical and genetic similarities, myotonic dystrophy type 1 and type 2 are distinct disorders requiring different diagnostic and management strategies. Gene therapy for myotonic dystrophy type 1 and myotonic dystrophy type 2 appears to be very close and the near future is an exciting time for clinicians and patients.

Utility and Results from a Patient-Reported Online Survey in Myotonic Dystrophies Types 1 and 2

INTRODUCTION

Myotonic dystrophies (DMs) are the most frequent autosomal dominant neuromuscular disorders in adults. Our objective was to evaluate the utility of an online survey in a rare disease as well as to assess and compare the onset and the progression of clinical symptoms in patients with myotonic dystrophy types 1 (DM1) and 2 (DM2).

METHODS

We conducted a patient's reported online survey assessing demographics, disease-related symptoms (age of onset, first symptom, time of diagnosis, current symptoms, inheritance, and family history) combined with capturing current symptoms by validated questionnaires. The questionnaire consisted of open, closed, single- and multiple-choice questions. Multiple answers were possible in some cases. Patients with genetically confirmed DM1 or DM2 who were registered in the German DM registry or the Deutsche Gesellschaft für Muskelkranke e.V. - Diagnostic Group for DMs were invited to participate in this online survey. We calculated descriptive and exploratory analysis, where applicable.

RESULTS

Out of 677 data sets from respondents, 394 were suitable for final analysis, containing completed questionnaires from 207 DM1 (56% female) and 187 DM2 patients (71% female). The median age of onset was 28 years for DM1 and 35 years for DM2. Muscular symptoms were most frequently reported as the first symptom. The onset of myotonia was earlier than the onset of muscle weakness in both DM1 and DM2. Forty-four percent of patients with DM1 and one-third of patients with DM2 indicated muscle weakness as the first symptom. Patients with DM1 were significantly younger when experiencing muscle weakness as first symptom. Fatigue was only mentioned by a small fraction of patients as a first symptom but increased significantly in the course of the disease. There was no statistically significant difference in the incidence of cataracts, cardiac symptoms, and gastrointestinal symptoms between DM1 and DM2. Falls were reported almost equally in both groups, and most of the patients reported 2-3 falls within the past year.

DISCUSSION

Overall, as our results are consistent with the results of clinical studies and online registries, it can be assumed that this type of systematic gathering of data from patients with rare diseases is useful and provides realistic and appropriate results. Due to the nature of online surveys and the absence of an assessor, some uncertainty remains. Furthermore, survey frauds cannot be completely excluded. An additional clinical assessment could confirm the given information and will improve the utility and validity of reported symptoms participants provide in online surveys. Therefore, we recommend a combination of data collecting by online surveys and clinical assessments.

How to capture activities of daily living in myotonic dystrophy type 2?

Myotonic dystrophy type 2 (DM2) lacks validated patients´ reported outcomes (PROs). This represents a limit for monitoring disease progression and perceived efficacy of symptomatic treatments. Our aim was to investigate whether PROs for activities of daily living designed for other neuromuscular diseases could be used in DM2. Sixty-six DM2 patients completed the following PROs: DM1-Activ-c, Rasch-built Pompe-specific activity (R-PAct) scale, McGill-pain questionnaire, fatigue and daytime sleepiness scale and Beck depression inventory (BDI-II). Clinical data and motor outcome measures (6-minutes walking test - 6MWT, manual muscle testing, quick motor function test and myotonia behavior scale) were collected as well. Patients underwent one visit at baseline and one after 10 months. Ceiling/flooring effects, criterion validity and discriminant validity were calculated. DM1-activ-c and R-PAct showed acceptable ceiling effects despite being built for myotonic dystrophy type 1 and Pompe disease, respectively. The difficulty hierarchy of the single items was better preserved in R-PAct than in DM1-Activ-c. Both tests showed excellent criterion validity highly correlating with 6MWT, quick motor function test, myalgia and disease duration. They could partially discriminate patients with different disability grades. These results suggest that DM1-Activ-c, slightly better than R-PAct, might be adopted for monitoring activities of daily living also in DM2, at least until disease-specific PROs will be available.

Myopathies with finger flexor weakness: Not only inclusion-body myositis

Muscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion-body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion-body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis.