Gender as a Modifying Factor Influencing Myotonic Dystrophy Type 1 Phenotype Severity and Mortality: A Nationwide Multiple Databases Cross-Sectional Observational Study

Natural history of cardiac involvement in myotonic dystrophy type 1 - Emphasis on the need for lifelong follow-up

BACKGROUND

Cardiac involvement represents a major cause of morbidity and mortality in patients with myotonic dystrophy type 1 (DM1) and prevention of sudden cardiac death (SCD) is a central part of patient care. We investigated the natural history of cardiac involvement in patients with DM1 to provide an evidence-based foundation for adjustment of follow-up protocols.

METHODS

Patients with genetically confirmed DM1 were identified. Data on patient characteristics, performed investigations (12 lead ECG, Holter monitoring and echocardiography), and clinical outcomes were retrospectively collected from electronic health records.

RESULTS

We included 195 patients (52% men) with a mean age at baseline evaluation of 41 years (range 14-79). The overall prevalence of cardiac involvement increased from 42% to 66% after a median follow-up of 10.5 years. There was a male predominance for cardiac involvement at end of follow-up (74 vs. 44%, p < 0.001). The most common types of cardiac involvement were conduction abnormalities (48%), arrhythmias (35%), and left ventricular systolic dysfunction (21%). Only 17% of patients reported cardiac symptoms. The standard 12‑lead ECG was the most sensitive diagnostic modality and documented cardiac involvement in 24% at baseline and in 49% at latest follow-up. However, addition of Holter monitoring and echocardiography significantly increased the diagnostic yield with 18 and 13% points at baseline and latest follow-up, respectively. Despite surveillance 35 patients (18%) died during follow-up; seven due to SCD.

CONCLUSIONS

In patients with DM1 cardiac involvement was highly prevalent and developed during follow-up. These findings justify lifelong follow-up with ECG, Holter, and echocardiography.

CLINICAL PERSPECTIVE

What is new? What are the clinical implications?

Resistance training in women with myotonic dystrophy type 1: a multisystemic therapeutic avenue

Myotonic dystrophy type 1 (DM1) is a hereditary disease characterized by muscular impairments. Fundamental and clinical positive effects of strength training have been reported in men with DM1, but its impact on women remains unknown. We evaluated the effects of a 12-week supervised strength training on physical and neuropsychiatric health. Women with DM1 performed a twice-weekly supervised resistance training program (3 series of 6-8 repetitions of squat, leg press, plantar flexion, knee extension, and hip abduction). Lower limb muscle strength, physical function, apathy, anxiety and depression, fatigue and excessive somnolence, pain, and patient-reported outcomes were assessed before and after the intervention, as well as three and six months after completion of the training program. Muscle biopsies of the vastus lateralis were also taken before and after the training program to assess muscle fiber growth. Eleven participants completed the program (attendance: 98.5 %). Maximal hip and knee extension strength (p < 0.006), all One-Repetition Maximum strength measures (p < 0.001), apathy (p = 0.0005), depression (p = 0.02), pain interference (p = 0.01) and perception of the lower limb function (p = 0.003) were significantly improved by training. Some of these gains were maintained up to six months after the training program. Strength training is a good therapeutic strategy for women with DM1.

Main features and disease outcome of congenital myotonic dystrophy - experience from a single tertiary center

Congenital myotonic dystrophy type 1 (CDM1) is a rare neuromuscular disease. The aim of our study was to evaluate clinical variability of CDM1 and factors that may influence survival in CDM1. Research included 24 pediatric patients with CDM1. Most of our patients had some form of hypoxic ischemic encephalopathy (HIE) (74 %), from mild to severe. Prolonged and complicated deliveries (75 %), high percentage of children resuscitated at birth (57 %) and respiratory insufficiency (46 %) with consequent hypoxia were the main reasons that could explain high percentage of HIE. Therapeutic hypothermia was applied in three children with poor outcome. Median survival of all CDM1 was 14.2 ± 1.5 years. Six patients had a fatal outcome (25 %). Their mean age of death was 3.0 ± 2.8 years. Poor prognostic factors for the survival of our CDM1 patients were: preterm delivery, resuscitation at birth, severe HIE, hypothermia treatment and permanent mechanical ventilation. Respiratory insufficiency was the main life-threatening factor. Our data clearly indicates the need to develop natural history studies in CDM1 in order to enhance the standards of care and to develop clinical trials investigating causative therapies in pediatric patients with CDM1.

CNS involvement in myotonic dystrophy type 1: does sex play a role?

Introduction

Myotonic dystrophy type 1 (DM1) is a hereditary neuromuscular disorder affecting the central nervous system (CNS). Although sex differences have been explored in other neuromuscular disorders, research on this topic in DM1 remains limited. The present study aims to analyze sex differences (both the patient's and disease-transmitting parent's sex) with a focus on CNS outcomes.

Methods

Retrospective data from 146 non-congenital DM1 patients were analyzed, including clinical, molecular, neuropsychological, and neuroradiological data. Sex and inheritance pattern differences were analyzed using t-tests, and ANOVA analyses were conducted to address the interactions.

Results

Overall, no significant sex differences were observed except in certain cognitive domains. However, individuals with maternal inheritance showed larger CTG expansion size, lower estimated IQs, and poorer performance on visual memory, executive functions, and language domains than those with paternal inheritance. Notably, IQ performance was independently influenced by inheritance pattern and CTG expansion.

Discussion

This study is the first to delve into sex differences in DM1 with a focus on CNS outcomes. While the results revealed the absence of a sex-specific clinic-molecular profile, more substantial CNS differences were observed between patients with maternal and paternal inheritance patterns. The hypothetical existence of genomic imprinting and its potential mechanism are discussed. These findings hold potential implications for aiding clinical management by improving genetic counseling and predicting disease severity and prognosis.

Expert opinion on mexiletine treatment in adult patients with myotonic dystrophy

In France, mexiletine - a class I antiarrhythmic drug - can be prescribed for the symptomatic treatment of myotonia of the skeletal muscles in adult patients with myotonic dystrophy under a compassionate use programme. Mexiletine is used according to its summary of product characteristics, which describes its use for myotonia treatment in adult patients with non-dystrophic myotonia, a different neuromuscular condition without cardiac involvement. A cardiac assessment is required prior to initiation and throughout treatment due to potential proarrhythmic effects. The presence of conduction system disease, the most common cardiac manifestation of myotonic dystrophy, mandates repeated cardiac evaluations in patients with this condition, and becomes even more important when they are given mexiletine. A group of experts, including three neurologists and five cardiologists from French neuromuscular reference centres, were involved in a task force to develop a treatment algorithm to guide mexiletine use in myotonic dystrophy. The recommendations are based on data from a literature review of the safety of mexiletine-treated patients with myotonic dystrophy, the compassionate use protocol for mexiletine and the personal clinical experience of the experts. The main conclusion of the expert group is that, although existing safety data in mexiletine-treated patients with myotonic dystrophy are reassuring, cardiac assessments should be reinforced in such patients compared with mexiletine-treated patients with non-dystrophic myotonia. This expert opinion to guide mexiletine treatment in patients with myotonic dystrophy should help to reduce the risk of severe adverse events and facilitate interactions between specialists involved in the routine care of patients with myotonic dystrophy.

Clinical features and genetic spectrum of a multicenter Chinese cohort with myotonic dystrophy type 1

BACKGROUND

As the most common subtype of adult muscular dystrophy worldwide, large cohort reports on myotonic dystrophy type I (DM1) in China are still lacking. This study aims to analyze the genetic and clinical characteristics of Chinese Han DM1 patients.

METHODS

Based on the multicenter collaborating effort of the Pan-Yangtze River Delta Alliance for Neuromuscular Disorders, patients with suspected clinical diagnoses of DM1 were genetically confirmed from January 2020 to April 2023. Peak CTG repeats in the DMPK gene were analyzed using triplet repeat-primed PCR (TP-PCR) and flanking PCR. Time-to-event analysis of onset age in females and males was performed. Additionally, detailed clinical features and longitudinal changes from the disease onset in 64 DM1 patients were retrospectively collected and analyzed. The Epworth Sleepiness Scale and Fatigue Severity Scale were used to quantify the severity of daytime sleepiness and fatigue.

RESULTS

Among the 211 genetically confirmed DM1 patients, the mean age at diagnosis was 40.9 ± 12.2 (range: 12-74) with a male-to-female ratio of 124:87. The average size of CTG repeats was 511.3 (range: 92-1945). Among the DM1 patients with comprehensive clinical data (n = 64, mean age 41.0 ± 12.0), the age at onset was significantly earlier in males than in females (4.8 years earlier, p = 0.026). Muscle weakness (92.2%), myotonia (85.9%), and fatigue (73.4%) were the most prevalent clinical features. The predominant involved muscles at onset are hands (weakness or myotonia) (52.6%) and legs (walking disability) (42.1%). Of them, 70.3% of patients had daytime sleepiness, 14.1% had cataract surgery, 7.8% used wheelchairs, 4.7% required ventilatory support, and 1.6% required gastric tubes. Regarding the comorbidities, 4.7% of patients had tumors, 17.2% had diabetes, 23.4% had dyspnea, 28.1% had intermittent insomnia, 43.8% experienced dysphagia, and 25% exhibited cognitive impairment. Chinese patients exhibited smaller size of CTG repeats (468 ± 139) than those reported in Italy (613 ± 623), the US (629 ± 386), and Japan (625 [302, 1047]), and milder phenotypes with less multisystem involvement.

CONCLUSION

The Chinese Han DM1 patients presented milder phenotypes compared to their Caucasian and Japanese counterparts. A male predominance and an early age of onset were identified in male Chinese Han DM1 patients.

Impact of gastrointestinal and urological symptoms in children with myotonic dystrophy type 1

Gastrointestinal and urological symptoms are frequently reported by people with myotonic dystrophy type 1 (DM1) but have remained understudied. In a cross-sectional study, frequency, nature, treatment and impact of gastrointestinal and urological symptoms in children with DM1 aged 5-18 years were assessed. We included 58 children (30 males, 28 females) with a mean age of 13 years; 74.1 % reported at least one gastrointestinal symptom. Abdominal pain was the most frequently reported symptom (51.7 %), followed by dysphagia (41.8 %), diarrhoea (36.2 %), encopresis (36.0 %), constipation (32.7 %), bloating and flatulence (both 25.9 %). The most frequently reported urological symptoms were difficulty with toilet training (59.3 %), urinary incontinence (22.0 %), enuresis nocturna (10.3 %) and voiding (23.5 % hesitancy, 4.8 % intermittency and 13.8 % dysuria). The majority considered urological and gastrointestinal symptoms to have a negative influence on their daily life; 22.4 % of parents reported severe influence on daily family life (shame, social restrictions, school absence and concerns for their children's future). Considering the high prevalence of urological and gastrointestinal symptoms in children with DM1 and their influence on daily life it is key to correctly recognize, diagnose and treat these symptoms. We recommend screening for gastrointestinal and urological symptoms in the standard of care for children with DM1.

Individual transcriptomic response to strength training for patients with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1), the most common form of adult-onset muscular dystrophy, is caused by a CTG expansion resulting in significant transcriptomic dysregulation that leads to muscle weakness and wasting. While strength training is clinically beneficial in DM1, molecular effects had not been studied. To determine whether training rescued transcriptomic defects, RNA-Seq was performed on vastus lateralis samples from 9 male patients with DM1 before and after a 12-week strength-training program and 6 male controls who did not undergo training. Differential gene expression and alternative splicing analysis were correlated with the one-repetition maximum strength evaluation method (leg extension, leg press, hip abduction, and squat). While training program-induced improvements in splicing were similar among most individuals, rescued splicing events varied considerably between individuals. Gene expression improvements were highly varied between individuals, and the percentage of differentially expressed genes rescued after training were strongly correlated with strength improvements. Evaluating transcriptome changes individually revealed responses to the training not evident from grouped analysis, likely due to disease heterogeneity and individual exercise response differences. Our analyses indicate that transcriptomic changes are associated with clinical outcomes in patients with DM1 undergoing training and that these changes are often specific to the individual and should be analyzed accordingly.

Sex differences in neuromuscular disorders

The prevalence, onset, pathophysiology, and clinical course of many neuromuscular disorders (NMDs) may significantly differ between males and females. Some NMDs are more frequently observed in females, and characterized to show a higher grade of severity during or after the pregnancy. Meanwhile, others tend to have an earlier onset in males and exhibit a more variable progression. Prevalently, sex differences in NMDs have a familiar character given from genetic inheritance. However, they may also influence clinical presentation and disease severity of acquired NMD forms, and are represented by both hormonal and genetic factors. Consequently, to shed light on the distinctive role of biological factors in the different clinical phenotypes, we summarize in this review the sex related differences and their distinctive biological roles emerging from the current literature in both acquired and inherited NMDs.

The current status of medical care for myotonic dystrophy type 1 in the national registry of Japan

INTRODUCTION/AIMS

Myotonic dystrophy (DM) is a systemic disease with multiple organ complications, making the standardization of medical care a challenge. We analyzed data from Japan's national registry to clarify the current treatment patterns and demographic features of Japanese DM patients.

METHODS

Using the Japanese National Registry of Muscular Dystrophy (Remudy), we analyzed medical care practice for the multisystemic issues associated with adult DM type 1 patients, excluding congenital DM.

RESULTS

We included 809 patients with a median age of 44.2 years. Among these patients, 15.8% used ventilators; 31.7% met the index considered at risk for sudden death due to cardiac conduction defects (PR interval over 240 milliseconds or QRS duration over 120 milliseconds) and 2.8% had implanted cardiac devices. Medication for heart failure was prescribed to 9.6% of patients. Overall, 21.2% of patients had abnormal glucose metabolism, of whom 42.9% were treated with oral medications. Among the oral medications, dipeptidyl peptidase-4 inhibitors were the most common. Cancers were observed in 3.7% of the patients, and endometrial and breast cancers were dominant. Mexiletine was prescribed for myotonia in 1.9% of the patients, and only 1% of the patients received medication for daytime sleepiness.

DISCUSSION

This study shows difference in treatment patterns for DM1 in Japan compared with other countries, such as lower rates of use of implantable cardiac devices and higher rates of ventilator use. These data may be useful in discussions aimed at standardizing medical care for patients with DM.

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.

Combinatorial treatment with exercise and AICAR potentiates the rescue of myotonic dystrophy type 1 mouse muscles in a sex-specific manner

Targeting AMP-activated protein kinase (AMPK) is emerging as a promising strategy for treating myotonic dystrophy type 1 (DM1), the most prevalent form of adult-onset muscular dystrophy. We previously demonstrated that 5-aminomidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) and exercise, two potent AMPK activators, improve disease features in DM1 mouse skeletal muscles. Here, we employed a combinatorial approach with these AMPK activators and examined their joint impact on disease severity in male and female DM1 mice. Our data reveal that swimming exercise additively enhances the effect of AICAR in mitigating the nuclear accumulation of toxic CUGexp RNA foci. In addition, our findings show a trend towards an enhanced reversal of MBNL1 sequestration and correction in pathogenic alternative splicing events. Our results further demonstrate that the combinatorial impact of exercise and AICAR promotes muscle fiber hypertrophy in DM1 skeletal muscle. Importantly, these improvements occur in a sex-specific manner with greater benefits observed in female DM1 mice. Our findings demonstrate that combining AMPK-activating interventions may prove optimal for rescuing the DM1 muscle phenotype and uncover important sex differences in the response to AMPK-based therapeutic strategies in DM1 mice.

Longitudinal Changes in Neuropsychological Functioning in Japanese Patients with Myotonic Dystrophy Type 1: A Five Year Follow-Up Study

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a form of muscular dystrophy that causes various symptoms, including those of the central nervous system. Some studies have reported cognitive decline in patients with DM1, although the available evidence is limited.

OBJECTIVE

This study aimed to describe longitudinal differences in neuropsychological function in patients with DM1.

METHODS

A total of 66 Japanese adult patients with DM1 were investigated using a neuropsychological battery to assess several cognitive domains, including memory, processing speed, and executive function. The patients underwent neuropsychological evaluation approximately five years after baseline (Times 1 and 2).

RESULTS

Thirty-eight patients underwent a second neuropsychological evaluation. The participants in the Time 2 evaluation were younger than those who did not participate in Time 2. Patients showed a decline in the Mini-Mental State Examination, Trail Making Test (TMT), Block Design, and Symbol Digit Modalities Test at Time 2 (P < 0.05). Age at Time 1 was associated with a decline in TMT-A and TMT-B scores (rho = 0.57 and 0.45, respectively).

CONCLUSION

These results suggest a cognitive decline in patients with DM1 and warrant further investigation into the possible effects of age-related changes.

Prevalence of urinary incontinence and other pelvic floor disorders in women with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a neuromuscular disease that can affect the pelvic floor muscles but few studies have investigated pelvic floor disorders, including urinary incontinence. The main purpose of this study was to document the prevalence, characteristics, and impacts of urinary incontinence and other pelvic floor disorders in women with DM1. Associations between pelvic floor disorders and phenotypes, considering age and parity, were explored. Eighty adult women aged 47,1±13,7 years old participated in a cross-sectional study using validated questionnaires, including the International Consultation Incontinence Questionnaire - Urinary Incontinence short form (ICIQ-UI-SF)), the Pelvic Floor Disorder Inventory (PFDI), and the Pelvic Floor Impact Questionnaire short form (PFIQ-SF). The mean score for the ICIQ-UI-SF was 4.3. The mean scores for the subscales of the PFDI were 36.8 for the urinary distress inventory, 74.1 for the colorectal-anal distress inventory, and 43.8 for the pelvic organ prolapse distress inventory. A total of 60% of women reported urinary incontinence and 56.3% anal incontinence. Pelvic prolapse symptoms (>1 symptom) were reported by 25% of women. Findings reveal high prevalence and significant related impacts of these disorders. This provides evidence regarding the importance of screening for these disorders in a clinical setting and the need to explore treatment approaches.

Resistance Exercise Training Rescues Mitochondrial Dysfunction in Skeletal Muscle of Patients with Myotonic Dystrophy Type 1

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a dominant autosomal neuromuscular disorder caused by the inheritance of a CTG triplet repeat expansion in the Dystrophia Myotonica Protein Kinase (DMPK) gene. At present, no cure currently exists for DM1 disease.

OBJECTIVE

This study investigates the effects of 12-week resistance exercise training on mitochondrial oxidative phosphorylation in skeletal muscle in a cohort of DM1 patients (n = 11, men) in comparison to control muscle with normal oxidative phosphorylation.

METHODS

Immunofluorescence was used to assess protein levels of key respiratory chain subunits of complex I (CI) and complex IV (CIV), and markers of mitochondrial mass and cell membrane in individual myofibres sampled from muscle biopsies. Using control's skeletal muscle fibers population, we classified each patient's fibers as having normal, low or high levels of CI and CIV and compared the proportions of fibers before and after exercise training. The significance of changes observed between pre- and post-exercise within patients was estimated using a permutation test.

RESULTS

At baseline, DM1 patients present with significantly decreased mitochondrial mass, and isolated or combined CI and CIV deficiency. After resistance exercise training, in most patients a significant increase in mitochondrial mass was observed, and all patients showed a significant increase in CI and/or CIV protein levels. Moreover, improvements in mitochondrial mass were correlated with the one-repetition maximum strength evaluation.

CONCLUSIONS

Remarkably, 12-week resistance exercise training is sufficient to partially rescue mitochondrial dysfunction in DM1 patients, suggesting that the response to exercise is in part be due to changes in mitochondria.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

Excessive rest time during active phase is reliably detected in a mouse model of myotonic dystrophy type 1 using home cage monitoring

Myotonic dystrophy type 1 (DM1) is a dominantly inherited neuromuscular disease caused by the abnormal expansion of CTG-repeats in the 3'-untranslated region of the Dystrophia Myotonica Protein Kinase (DMPK) gene, characterized by multisystemic symptoms including muscle weakness, myotonia, cardio-respiratory problems, hypersomnia, cognitive dysfunction and behavioral abnormalities. Sleep-related disturbances are among the most reported symptoms that negatively affect the quality of life of patients and that are present in early and adult-onset forms of the disease. DMSXL mice carry a mutated human DMPK transgene containing >1,000 CTGrepeats, modeling an early onset, severe form of DM1. They exhibit a pathologic neuromuscular phenotype and also synaptic dysfunction resulting in neurological and behavioral deficits similar to those observed in patients. Additionally, they are underweight with a very high mortality within the first month after birth presenting several welfare issues. To specifically explore sleep/rest-related behaviors of this frail DM1 mouse model we used an automated home cage-based system that allows 24/7 monitoring of their activity non-invasively. We tested male and female DMSXL mice and their wild-type (WT) littermates in Digital Ventilated Cages (DVCR) assessing activity and rest parameters on day and night for 5 weeks. We demonstrated that DMSXL mice show reduced activity and regularity disruption index (RDI), higher percentage of zero activity per each hour and longer periods of rest during the active phase compared to WT. This novel rest-related phenotype in DMSXL mice, assessed unobtrusively, could be valuable to further explore mechanisms and potential therapeutic interventions to alleviate the very common symptom of excessive daytime sleepiness in DM1 patients.

A Greek National Cross-Sectional Study on Myotonic Dystrophies

Myotonic Dystrophies (DM, Dystrophia Myotonia) are autosomal dominant inherited myopathies with a high prevalence across different ethnic regions. Despite some differences, mainly due to the pattern of muscle involvement and the age of onset, both forms, DM1 and DM2, share many clinical and genetic similarities. In this study, we retrospectively analyzed the medical record files of 561 Greek patients, 434 with DM1 and 127 with DM2 diagnosed in two large academic centers between 1994-2020. The mean age at onset of symptoms was 26.2 ± 15.3 years in DM1 versus 44.4 ± 17.0 years in DM2 patients, while the delay of diagnosis was 10 and 7 years for DM1 and DM2 patients, respectively. Muscle weakness was the first symptom in both types, while myotonia was more frequent in DM1 patients. Multisystemic involvement was detected in the great majority of patients, with cataracts being one of the most common extramuscular manifestations, even in the early stages of disease expression. In conclusion, the present work, despite some limitations arising from the retrospective collection of data, is the first record of a large number of Greek patients with myotonic dystrophy and emphasizes the need for specialized neuromuscular centers that can provide genetic counseling and a multidisciplinary approach.

Masseter muscle volume as a disease marker in adult-onset myotonic dystrophy type 1

The advent of clinical trials in myotonic dystrophy type 1 (DM1) necessitates the identification of reliable outcome measures to quantify different disease manifestations using minimal number of assessments. In this study, clinical correlations of mean masseter volume (mMV) were explored to evaluate its potential as a marker of muscle involvement in adult-onset DM1 patients. We utilised data from a preceding study, pertaining to 39 DM1 patients and 20 age-matched control participants. In this study participants had undergone MRI of the brain, completed various clinical outcome measures and had CTG repeats measured by small-pool PCR. Manual segmentation of masseter muscles was performed by a single rater to estimate mMV. The masseter muscle was atrophied in DM1 patients when compared to controls (p<0.001). Significant correlations were found between mMV and estimated progenitor allele length (p = 0.001), modal allele length (p = 0.003), disease duration (p = 0.009) and and the Muscle Impairment Rating Scale (p = 0.008). After correction for lean body mass, mMV was also inversely correlated with self-reported myotonia (p = 0.014). This study demonstrates that changes in mMV are sensitive in reflecting the underlying disease process. Quantitative MRI methods demonstrate that data concerning both central and peripheral disease could be acquired from MR brain imaging studies in DM1 patients.

Delay of EGF-Stimulated EGFR Degradation in Myotonic Dystrophy Type 1 (DM1)

Myotonic dystrophy type 1 (DM1) is an autosomal dominant disease caused by a CTG repeat expansion in the 3′ untranslated region of the dystrophia myotonica protein kinase gene. AKT dephosphorylation and autophagy are associated with DM1. Autophagy has been widely studied in DM1, although the endocytic pathway has not. AKT has a critical role in endocytosis, and its phosphorylation is mediated by the activation of tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR). EGF-activated EGFR triggers the internalization and degradation of ligand–receptor complexes that serve as a PI3K/AKT signaling platform. Here, we used primary fibroblasts from healthy subjects and DM1 patients. DM1-derived fibroblasts showed increased autophagy flux, with enlarged endosomes and lysosomes. Thereafter, cells were stimulated with a high concentration of EGF to promote EGFR internalization and degradation. Interestingly, EGF binding to EGFR was reduced in DM1 cells and EGFR internalization was also slowed during the early steps of endocytosis. However, EGF-activated EGFR enhanced AKT and ERK1/2 phosphorylation levels in the DM1-derived fibroblasts. Therefore, there was a delay in EGF-stimulated EGFR endocytosis in DM1 cells; this alteration might be due to the decrease in the binding of EGF to EGFR, and not to a decrease in AKT phosphorylation.

Assessment of body composition, metabolism, and pulmonary function in patients with myotonic dystrophy type 1

Abnormal body composition in myotonic dystrophy type 1 (DM1) are affected by energy intake above resting energy expenditure (REE). We aim to investigate the characteristics and relationship between body composition, REE, and pulmonary function in patients with DM1, and to examine their changes in 1 year. The study design was a single-center, cross-sectional, and longitudinal study of body composition, REE characteristics, and pulmonary function. Twenty-one male patients with DM1 and 16 healthy volunteers were registered in the study. Body composition was measured using dual-energy X-ray absorptiometry (DEXA). Fat mass (FM) index (kg/m2), fat-FM index (kg/m2), and skeletal mass index (kg/m2) were calculated. The measurements were taken breath by breath with a portable indirect calorimeter. The REE was calculated using the oxygen intake (VO2) and carbon dioxide output (VCO2) in the Weir equation. Basal energy expenditure (BEE) was calculated by substituting height, weight, and age into the Harris-Benedict equation. The study enrolled male patients with DM1 (n = 12) and healthy male volunteers (n = 16). Patients with DM1 (n = 7) and healthy volunteers (n = 14) could be followed in 1 year. The body composition of patients with DM1 was significantly higher in the FM index and significantly lower in the fat-FM index and skeletal mass index. The REE of patients with DM1 was significantly lower and was not associated with body composition. Patients with DM1 had poor metabolism that was not related to body composition. FM was high and lean body mass was low.

Intergenerational Influence of Gender and the DM1 Phenotype of the Transmitting Parent in Korean Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common autosomal-dominant disorder caused by the CTG repeat expansion of the DMPK, and it has been categorized into three phenotypes: mild, classic, and congenital DM1. Here, we reviewed the intergenerational influence of gender and phenotype of the transmitting parent on the occurrence of Korean DM1. A total of 44 parent–child pairs matched for the gender of the transmitting parent and the affected child and 29 parent–child pairs matched for the gender and DM1 phenotype of the transmitting parent were reviewed. The CTG repeat size of the DMPK in the affected child was found to be significantly greater when transmitted by a female parent to a female child (DM1-FF) (median, 1309 repeats; range, 400–2083) than when transmitted by a male parent to a male child (650; 160–1030; p = 0.038 and 0.048 using the Tukey HSD and the Bonferroni test) or by a male parent to a female child (480; 94–1140; p = 0.003). The difference in the CTG repeat size of the DMPK between the transmitting parent and the affected child was also lower when transmitted from a male parent with classic DM1 (−235; −280 to 0) compared to when it was transmitted from a female parent with mild DM1 (866; 612–905; p = 0.015 and 0.019) or from a female parent with classic DM1 (DM1-FC) (605; 10–1393; p = 0.005). This study highlights that gender and the DM1 phenotype of the transmitting parent had an impact on the CTG repeat size of the DMPK in the affected child, with greater increases being inherited from the DM1-FF or DM1-FC situations in Korean DM1.

An evaluation of 24 h Holter monitoring in patients with myotonic dystrophy type 1

AIMS

To evaluate the clinical effectiveness of routine 24 h Holter monitoring to screen for conduction disturbances and arrhythmias in patients with myotonic dystrophy type 1 (DM1).

METHODS AND RESULTS

A retrospective two-centre study was conducted including DM1-affected individuals undergoing routine cardiac screening with at least one 24 h Holter monitoring between January 2010 and December 2020. For each individual, the following data were collected: Holter results, results of electrocardiograms (ECGs) performed at the same year as Holter monitoring, presence of cardiac complaints, and neuromuscular status. Holter findings were compared with the results of cardiac screening (ECG + history taking) performed at the same year. Cardiac conduction abnormalities and/or arrhythmias that would have remained undiagnosed based on history taking and ECG alone were considered de novo findings. A total 235 genetically confirmed DM1 patients were included. Abnormal Holter results were discovered in 126 (54%) patients after a mean follow-up of 64 ± 28 months in which an average of 3 ± 1 Holter recordings per patient was performed. Abnormalities upon Holter mainly consisted of conduction disorders (70%) such as atrioventricular (AV) block. Out of 126 patients with abnormal Holter findings, 74 (59%) patients had de novo Holter findings including second-degree AV block, atrial fibrillation/flutter and non-sustained ventricular tachycardia. Patient characteristics were unable to predict the occurrence of de novo Holter findings. In 39 out of 133 (29%) patients with normal ECGs upon yearly cardiac screening, abnormalities were found on Holter monitoring during follow-up.

CONCLUSION

Twenty-four hour Holter monitoring is of added value to routine cardiac screening for all DM1 patients.

Pharmacological and exercise-induced activation of AMPK as emerging therapies for myotonic dystrophy type 1 patients

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder with variable clinical features. Currently, there is no cure or effective treatment for DM1. The disease is caused by an expansion of CUG repeats in the 3' UTR of DMPK mRNAs. Mutant DMPK mRNAs accumulate in nuclei as RNA foci and trigger an imbalance in the level and localization of RNA-binding proteins causing the characteristic missplicing events that account for the varied DM1 symptoms, a disease mechanism referred to as RNA toxicity. In recent years, multiple signalling pathways have been identified as being aberrantly regulated in skeletal muscle in response to the CUG expansion, including AMPK, a sensor of energy status, as well as a master regulator of cellular energy homeostasis. Converging lines of evidence highlight the benefits of activating AMPK signalling pharmacologically on RNA toxicity, as well as on muscle histology and function, in preclinical DM1 models. Importantly, a clinical trial with metformin, an activator of AMPK, resulted in functional benefits in DM1 patients. In addition, exercise, a known AMPK activator, has shown promising effects on RNA toxicity and muscle function in DM1 mice. Finally, clinical trials involving moderate-intensity exercise also induced functional benefits for DM1 patients. Taken together, these studies clearly demonstrate the molecular, histological and functional benefits of AMPK activation and exercise-based interventions on the DM1 phenotype. Despite these advances, several key questions remain; in particular, the extent of the true implication of AMPK in the observed beneficial improvements, as well as how, mechanistically, activation of AMPK signalling improves the DM1 pathophysiology.

Explanatory factors of dynamic balance impairment in myotonic dystrophy type 1

INTRODUCTION/AIMS

Myotonic dystrophy type 1 (DM1) is a neuromuscular disease affecting many systems and for which muscle weakness is one of the cardinal symptoms. People with DM1 also present with balance-related impairments and high fall risk. The aim of this study was to explore explanatory factors of dynamic balance impairment in the DM1 population.

METHODS

A secondary analysis of data collected as part of a larger study was performed. The Mini Balance Evaluation System Test (Mini-BESTest) was used to assess dynamic balance. Age, sex, and CTG repeat length in blood were retrieved from medical records and research files. The maximal isometric muscle strength of five lower limb muscle groups (hip flexors and extensors, knee flexors and extensors, and ankle dorsiflexors) was quantitatively assessed as well as fatigue. Standard multiple regression analysis was used.

RESULTS

Fifty-two individuals (31 men) aged between 24 and 81 years were included. The final model explains 65.9% of the balance score; ankle dorsiflexor muscle strength was the strongest explanatory factor, followed by CTG repeat length, age and fatigue to a lesser extent.

DISCUSSION

Dynamic balance is impaired in people with DM1. Results of this study suggest that rehabilitation interventions aimed at improving strength of the ankle dorsiflexors and managing fatigue could help to improve dynamic balance in this specific population.

Mice lacking MBNL1 and MBNL2 exhibit sudden cardiac death and molecular signatures recapitulating myotonic dystrophy

Myotonic dystrophy (DM) is caused by expansions of C(C)TG repeats in the non-coding regions of the DMPK and CNBP genes, and DM patients often suffer from sudden cardiac death due to lethal conduction block or arrhythmia. Specific molecular changes that underlie DM cardiac pathology have been linked to repeat-associated depletion of Muscleblind-like (MBNL) 1 and 2 proteins and upregulation of CUGBP, Elav-like family member 1 (CELF1). Hypothesis solely targeting MBNL1 or CELF1 pathways that could address all the consequences of repeat expansion in heart remained inconclusive, particularly when the direct cause of mortality and results of transcriptome analyses remained undetermined in Mbnl compound knockout (KO) mice with cardiac phenotypes. Here, we develop Myh6-Cre double KO (DKO) (Mbnl1^−/−; Mbnl2^cond/cond; Myh6-Cre^+/−) mice to eliminate Mbnl1/2 in cardiomyocytes and observe spontaneous lethal cardiac events under no anesthesia. RNA sequencing recapitulates DM heart spliceopathy and shows gene expression changes that were previously undescribed in DM heart studies. Notably, immunoblotting reveals a nearly 6-fold increase of Calsequestrin 1 and 50% reduction of epidermal growth factor proteins. Our findings demonstrate that complete ablation of MBNL1/2 in cardiomyocytes is essential for generating sudden death due to lethal cardiac rhythms and reveal potential mechanisms for DM heart pathogenesis.

Overview of the Complex Relationship between Epigenetics Markers, CTG Repeat Instability and Symptoms in Myotonic Dystrophy Type 1

Among the trinucleotide repeat disorders, myotonic dystrophy type 1 (DM1) is one of the most complex neuromuscular diseases caused by an unstable CTG repeat expansion in the DMPK gene. DM1 patients exhibit high variability in the dynamics of CTG repeat instability and in the manifestations and progression of the disease. The largest expanded alleles are generally associated with the earliest and most severe clinical form. However, CTG repeat length alone is not sufficient to predict disease severity and progression, suggesting the involvement of other factors. Several data support the role of epigenetic alterations in clinical and genetic variability. By highlighting epigenetic alterations in DM1, this review provides a new avenue on how these changes can serve as biomarkers to predict clinical features and the mutation behavior.

Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1)

The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.

Characteristics of myotonic dystrophy patients in the national registry of Japan

Myotonic dystrophies (DM) are inherited autosomal dominant disorders affecting multiple organs. Currently available therapeutics for DM are limited; therefore, a patient registry is essential for therapeutic development and success of clinical trials targeting the diseases. We have developed a nationwide DM registry in Japan under the Registry of Muscular Dystrophy (Remudy). The registration process was patient-initiated; however, physicians certified the clinical information. The dataset includes all Naarden and TREAT-NMD core datasets and additional items covering major DM clinical features. As of March 2020, we enrolled 976 patients with genetically confirmed DM. The majority (99.9%) of these patients had DM1, with 11.4% having the congenital form. However, 1 patient had DM2. Upon classifying 969 symptomatic DM1 patients based on their age at onset, an earlier onset was associated with a longer CTG repeat length. Myotonia was the most frequent symptom, followed by hand disability, fatigue, and daytime sleepiness. The frequency of hand disabilities, constipation, and visual disturbances was higher for patients with congenital DM. According to a multiple regression analysis of objective clinical measurements related to prognosis and activities of daily living, CTG repeat length strongly influenced the grip strength, forced vital capacity, and QRS time in an electrocardiogram. However, the grip strength was only modestly related to disease duration. This report will shed light on the Japanese national DM registry, which has recruited a significant number of patients. The registry will provide invaluable data for planning clinical trials and improving the standard of care for patients.

Static Postural Control Deficits in Adults with Myotonic Dystrophy Type 1, Steinert Disease

BACKGROUND

Myotonic dystrophy type 1 (DM1) is characterized by progressive and predominantly distal muscle atrophy and myotonia. Gait and balance impairments, resulting in falls, are frequently reported in this population. However, the extent to which individuals with DM1 rely more on a specific sensory system for balance than asymptomatic individuals (AI) is unknown.

OBJECTIVE

Evaluate postural control performance in individuals with DM1 and its dependence on vision compared to AI.

METHODS

20 participants with DM1, divided into two groups based on their diagnosis, i.e. adult and congenital phenotype, and 12 AI participants were recruited. Quiet standing postural control was assessed in two visual conditions: eyes-open and eyes-closed. The outcomes measures were center of pressure (CoP) mean velocity, CoP range of displacement in anteroposterior and mediolateral axis, and the 95% confidence ellipse's surface. Friedman and Kruskal-Wallis analysis of variance were used to compare outcomes between conditions and groups, respectively.

RESULTS

Significant group effect and condition effect were observed on postural control performance. No significant difference was observed between the two DM1 groups. The significant differences observed between the AI group and the two DM1 groups in the eyes-open condition were also observed in the eyes-closed condition.

CONCLUSIONS

The result revealed poorer postural control performance in people with DM1 compared to AI. The DM1 group also showed similar decrease in performance than AI in eyes-closed condition, suggesting no excessive visual dependency.

Cardiac Manifestations of Myotonic Dystrophy in a Pediatric Cohort

Myotonic dystrophy type 1 (DM1) is the most prevalent inherited neuromuscular dystrophy in adults. It is a multisystem disease with cardiac manifestations. Whilst these are well-defined in adults, there are scarce published data in the pediatric population. This study aimed to investigate the yield and progression of cardiac disease in pediatric DM1 patients, focusing on congenital DM1 (cDM1).

METHODS

A retrospective observational study of all pediatric DM1 patients referred to our center (December 2000-November 2020) was conducted. Patients were classified into DM1 forms according to age of symptom onset and disease severity. Patients underwent clinical and cardiac evaluation with 12-lead ECG, transthoracic echocardiography and 24-h ECG Holter monitoring.

RESULTS

67 DM1 pediatric patients were included: 56 (83.6%) cDM1 and 11 (16.4%) non-cDM1. Median follow-up time of cDM1 patients was 8.0 [3.25-11.0] years. 49 (87.5%) cDM1 patients had baseline 12-lead ECG and 44 (78.6%) had a follow-up 12-lead-ECG, with a median follow-up time from diagnosis to baseline ECG of 2.8 [1.0-8.5] years and to follow-up ECG of 10.9 [5.7-14.2] years. Overall, 43 (87.8%) presented ECG abnormalities, most commonly in the form of asymptomatic conduction disease (n = 23, 46.9%), of which 21 (42.9%) had first degree atrioventricular block (1^st AVB). There was an increase of prevalence from baseline to follow-up ECG in low QRS voltage (16.7%), poor R wave progression (13.9%), abnormal repolarisation (11.9%) and 1^st AVB (7.6%). one patient (1.8%) underwent pacemaker implantation for syncope in the context of progressive conduction disease. No patients developed left ventricular systolic dysfunction. 4 (7.1%) cDM1 patients died during follow up, including three who died suddenly with no clear cause of death.

CONCLUSIONS

This study is the first to analyse the prevalence and progression of ECG abnormalities in cDM1 pediatric patients. The high prevalence of abnormal findings, progressive changes and number of potentially associated events (1 pacemaker implantation and 3 unexplained sudden deaths) stresses the importance of systematic and continued cardiac evaluation of these patients.

[Multidisciplinary care of patients with Myotonic Dystrophy type 1 (DM1) in South Aquitaine]

DM1 is characterized by a multisystemic involvement. Our objective was to determine the proportion of adequate follow-up for each affected organ in DM1 patients based on the recently published American and Spanish recommendations. To this end, we conducted a descriptive cross-sectional survey by phone in adult, genetically proven DM1 patients followed in the two French neuromuscular centers of Bayonne and Hendaye located in South Aquitaine, France. The questionnaire selected the most stringent criteria of the two international recommendations for each item of follow-up. Seventy-three patients were included, 55% of which were women (mean age of 48 years) with an average number of 467 CTG repeats. The proportion of patients receiving clinical follow-up in accordance with the recommendations was 90% in cardiology, 60% in neurology, 68% in ophthalmology, 53% in physiotherapy, 23% in pneumology, and 12% in rehabilitation. The high rate of neurological, cardiological, and ophthalmological monitoring might be explained by a locally dense medical demography whereas low rate of respiratory follow up and rehabilitation may reflect an incomplete knowledge of both the disease and the questionnaire. These results should be carefully interpretated as cognitive status may influence such a declarative study. Our study nevertheless disclosed important disparities according to the recommended multidisciplinary follow-up criteria in this French cohort of adult DM1 patients. These results highlight the major role of a multidisciplinary care and monitoring in DM1.

Modifiers of CAG/CTG Repeat Instability: Insights from Mammalian Models

At fifteen different genomic locations, the expansion of a CAG/CTG repeat causes a neurodegenerative or neuromuscular disease, the most common being Huntington's disease and myotonic dystrophy type 1. These disorders are characterized by germline and somatic instability of the causative CAG/CTG repeat mutations. Repeat lengthening, or expansion, in the germline leads to an earlier age of onset or more severe symptoms in the next generation. In somatic cells, repeat expansion is thought to precipitate the rate of disease. The mechanisms underlying repeat instability are not well understood. Here we review the mammalian model systems that have been used to study CAG/CTG repeat instability, and the modifiers identified in these systems. Mouse models have demonstrated prominent roles for proteins in the mismatch repair pathway as critical drivers of CAG/CTG instability, which is also suggested by recent genome-wide association studies in humans. We draw attention to a network of connections between modifiers identified across several systems that might indicate pathway crosstalk in the context of repeat instability, and which could provide hypotheses for further validation or discovery. Overall, the data indicate that repeat dynamics might be modulated by altering the levels of DNA metabolic proteins, their regulation, their interaction with chromatin, or by direct perturbation of the repeat tract. Applying novel methodologies and technologies to this exciting area of research will be needed to gain deeper mechanistic insight that can be harnessed for therapies aimed at preventing repeat expansion or promoting repeat contraction.

Nationwide incidence of myotonic dystrophy type 1 and the status of multi-organ involvement

PURPOSE

This study aimed to investigate the incidence of myotonic dystrophy type 1 (DM1) and the status of multi-organ involvement.

METHODS

This was a nationwide, population-based, cohort study using data from the Korean National Health Claims database. All patients with DM1 from the entire population aged ≤ 80 years were included. To identify possible systemic diseases along with DM1, we searched for concurrent codes for systemic diseases. To assess the recent status of systemic evaluation, concurrent codes for various diagnostic and treatment modalities were collected. Cumulative incidence during 2016-2019 was first evaluated then systemic evaluation for those patients was assessed during 2010-2019.

RESULTS

A total of 387 patients (47.8% men) during the recent 4-year study period (2016-2019) were diagnosed with DM1. The cumulative incidence in the general population was 0.77 (95% confidence interval: 0.76-0.77) per 100,000 persons. In newly developed incidental cases, cardiac involvement developed in 51.2%, pneumonia in 30.7%, diabetes in 26.9%, brain involvement in 18.1%, cataract in 13.7%, and cancers in 5.4% of total patients. Electrocardiography was performed in 93.8%, Holter in 33.9%, and echocardiography in 31.3% of the total patients for cardiac evaluation.

CONCLUSIONS

The incidence estimates of DM1 in the Asian population were lower than those of Caucasians. This study provides the real situation of screening and treatment for systemic diseases related to DM1. These detailed estimates could promote an understanding of the current disease status and allow for appropriate planning within the healthcare system.

Deciphering the mechanisms underlying brain alterations and cognitive impairment in congenital myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.

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.

Assessment of muscular strength and functional capacity in the juvenile and adult myotonic dystrophy type 1 population: a 3-year follow-up study

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is a progressive, multisystemic, and autosomal dominant disease. Muscle wasting and weakness have been associated with impaired functional capacity and restricted social participation in affected individuals. The disease's presentation is very heterogenous and its progression is still under-documented.

OBJECTIVE

The aim of the study was to document the progression of muscular strength and functional capacity in the DM1 population over a 3-year period.

METHODS

Twenty-three individuals with juvenile or adult phenotypes of DM1 were recruited to complete clinical assessments in 2016 and 2019. Maximal isometric muscle strength (MIMS) was evaluated with quantified muscle testing and functional capacity was evaluated with the Mini-BESTest, the 10-m walk test at comfortable and maximal speeds, the Timed Up and Go and the 6-min walk test. Participants also completed three questionnaires: DM1-Activ, Upper Extremity Functional Index and Lower Extremity Functional Scale (LEFS). Subgroup analyses were evaluated for sex, phenotype, and type of physical activity practiced during the 3-year period.

RESULTS

For the whole group, there was a significant decline in the scores of the Mini-BESTest and the LEFS. Also, MIMS significantly declined for prehension, lateral pinch as well as for hip abductors, knee extensors and ankle dorsiflexors muscle groups. Subgroups analyses revealed that men lost more MIMS than women, and that adult phenotype lost more MIMS than juvenile phenotype.

CONCLUSION

Quantified muscle testing is a better indicator of disease progression over a 3-year period than functional tests. Phenotype and sex are important factors that influence the progression of DM1.

microRNA-mRNA Profile of Skeletal Muscle Differentiation and Relevance to Congenital Myotonic Dystrophy

microRNAs (miRNAs) regulate messenger RNA (mRNA) abundance and translation during key developmental processes including muscle differentiation. Assessment of miRNA targets can provide insight into muscle biology and gene expression profiles altered by disease. mRNA and miRNA libraries were generated from C2C12 myoblasts during differentiation, and predicted miRNA targets were identified based on presence of miRNA binding sites and reciprocal expression. Seventeen miRNAs were differentially expressed at all time intervals (comparing days 0, 2, and 5) of differentiation. mRNA targets of differentially expressed miRNAs were enriched for functions related to calcium signaling and sarcomere formation. To evaluate this relationship in a disease state, we evaluated the miRNAs differentially expressed in human congenital myotonic dystrophy (CMD) myoblasts and compared with normal control. Seventy-four miRNAs were differentially expressed during healthy human myocyte maturation, of which only 12 were also up- or downregulated in CMD patient cells. The 62 miRNAs that were only differentially expressed in healthy cells were compared with differentiating C2C12 cells. Eighteen of the 62 were conserved in mouse and up- or down-regulated during mouse myoblast differentiation, and their C2C12 targets were enriched for functions related to muscle differentiation and contraction.

Robust Detection of Somatic Mosaicism and Repeat Interruptions by Long-Read Targeted Sequencing in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most complex and variable trinucleotide repeat disorder caused by an unstable CTG repeat expansion, reaching up to 4000 CTG in the most severe cases. The genetic and clinical variability of DM1 depend on the sex and age of the transmitting parent, but also on the CTG repeat number, presence of repeat interruptions and/or on the degree of somatic instability. Currently, it is difficult to simultaneously and accurately determine these contributing factors in DM1 patients due to the limitations of gold standard methods used in molecular diagnostics and research laboratories. Our study showed the efficiency of the latest PacBio long-read sequencing technology to sequence large CTG trinucleotides, detect multiple and single repeat interruptions and estimate the levels of somatic mosaicism in DM1 patients carrying complex CTG repeat expansions inaccessible to most methods. Using this innovative approach, we revealed the existence of de novo CCG interruptions associated with CTG stabilization/contraction across generations in a new DM1 family. We also demonstrated that our method is suitable to sequence the DM1 locus and measure somatic mosaicism in DM1 families carrying more than 1000 pure CTG repeats. Better characterization of expanded alleles in DM1 patients can significantly improve prognosis and genetic counseling, not only in DM1 but also for other tandem DNA repeat disorders.

Pain in adult myotonic dystrophy type 1: relation to function and gender

Background

Pain is prevalent in myotonic dystrophy 1 (DM1). This study investigated whether CTG repeat size, disease duration, BMI and motor and psychological function were related to pain in adult patients with DM1, and if there were gender differences regarding intensity and location of pain.

Method

Cross-sectional design. Pain was investigated in 50 genetically confirmed DM1 patients by combining clinical assessment and self-reports of pain intensity and locations. Pain scoring results were related to CTG size, disease duration, muscle strength, walking capacity measured by 6-min walk test, activity of daily life by Katz ADL Index, respiratory function by Forced Vital Capacity and BMI. In addition, the degree of reported pain was related to Quality of life measured by WHOQOL-BREF; fatigue was measured by Fatigue severity scale; psychological functions were measured by Beck Depression Inventory, Beck Anxiety Inventory, IQ and Autism spectrum Quotient.

Results

Pain was reported in 84% of the patients and was significantly correlated with CTG size (r = 0.28 p = 0.050), disease duration (r = 0.38 p = 0.007), quality of life (r = − 0.37 p = 0.009), fatigue (r = 0.33 p = 0.02) and forced vital capacity (r = − 0.51, p = 0.005). Significant gender differences, with higher scores for females, were documented. In male subjects the number of pain locations was significantly correlated with quality of life and the autism quotient. In females, pain intensity was significantly correlated with activity, respiratory function and BMI.

Conclusions

Pain in DM1 was prevalent, with a strong association to lung function and other aspects of the disease. Significant gender differences were present for pain intensity and number of pain locations. How pain was related to other symptoms differed between male and female subjects. Our findings highlight the importance of assessments of pain in DM1 patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02124-9.

Predictors of respiratory decline in myotonic dystrophy type 1 (DM1): a longitudinal cohort study

We studied 33 patients affected by juvenile and adult myotonic dystrophy type 1 (DM1). The aim of the study was to assess clinical and laboratory parameters that could predict the requirement of noninvasive ventilation (NIV) in DM1. Secondary outcome was to assess the interplay between genetic profile, muscle impairment severity and presence of cardiac comorbidities.Patients with genetic diagnosis of DM1 were recruited. An abnormal trinucleotide repeat (CTG) expansion of dystrophy protein kinase gene (DMPK) on chromosome 19q13.3 was the prerequisite for inclusion. The number of triplet repeats was measured in genomic DNA to classify subjects. A multidisciplinary team evaluated the patients every 6-8 months up to 18 years with serial cardiological and respiratory function assessments. Neurological progression was monitored using a validated DM1-specific rating scale (MIRS). Independent variables considered for the study outcomes were gender, genetic status, age of presentation, MIRS scores, and results of pulmonary function tests (PFTs).Patients were 17 males (51.5%) and 16 females (48.5%). 16 cases were younger than mean age of 31.4 years, the remaining 17 were up to 65. 12 subjects (36.4%) underwent NIV during follow up. Cardiac comorbidities were detected in 63.6% of cases and in 91% of patients in NIV. Among PFTs, forced vital capacity (FVC) was a reliable indicator of respiratory decline. FVC values were significantly associated with clinical muscle severity assessed by MIRS.Severity of muscular impairment, CTG expansion size, age and presence of cardiac comorbidities predict respiratory impairment in DM1.

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.

Transcriptome Analysis Reveals Altered Inflammatory Pathway in an Inducible Glial Cell Model of Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1), the most frequent inherited muscular dystrophy in adults, is caused by the CTG repeat expansion in the 3′UTR of the DMPK gene. Mutant DMPK RNA accumulates in nuclear foci altering diverse cellular functions including alternative splicing regulation. DM1 is a multisystemic condition, with debilitating central nervous system alterations. Although a defective neuroglia communication has been described as a contributor of the brain pathology in DM1, the specific cellular and molecular events potentially affected in glia cells have not been totally recognized. Thus, to study the effects of DM1 mutation on glial physiology, in this work, we have established an inducible DM1 model derived from the MIO-M1 cell line expressing 648 CUG repeats. This new model recreated the molecular hallmarks of DM1 elicited by a toxic RNA gain-of-function mechanism: accumulation of RNA foci colocalized with MBNL proteins and dysregulation of alternative splicing. By applying a microarray whole-transcriptome approach, we identified several gene changes associated with DM1 mutation in MIO-M1 cells, including the immune mediators CXCL10, CCL5, CXCL8, TNFAIP3, and TNFRSF9, as well as the microRNAs miR-222, miR-448, among others, as potential regulators. A gene ontology enrichment analyses revealed that inflammation and immune response emerged as major cellular deregulated processes in the MIO-M1 DM1 cells. Our findings indicate the involvement of an altered immune response in glia cells, opening new windows for the study of glia as potential contributor of the CNS symptoms in DM1.

Mexiletine in Myotonic Dystrophy Type 1: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

To assess mexiletine's long-term safety and effect on 6-minute walk distance in a well-defined cohort of patients with myotonic dystrophy type 1 (DM1).

METHODS

We performed a randomized, double-blind, placebo-controlled trial of mexiletine (150 mg 3 times daily) to evaluate its efficacy and safety in a homogenous cohort of adult ambulatory patients with DM1. The primary outcome was change in 6-minute walk distance at 6 months. Secondary outcomes included changes in hand grip myotonia, strength, swallowing, forced vital capacity, lean muscle mass, Myotonic Dystrophy Health Index scores, and 24-hour Holter and ECG results at 3 and 6 months.

RESULTS

Forty-two participants were randomized and 40 completed the 6-month follow-up (n = 20 in both groups). No significant effects of mexiletine were observed on 6-minute walk distance, but hand grip myotonia was improved with mexiletine treatment. There were no differences between the mexiletine and placebo groups with respect to the frequency or type of adverse events. Changes in PR, QRS, and QTc intervals were similar in mexiletine- and placebo-treated participants.

CONCLUSIONS

There was no benefit of mexiletine on 6-minute walk distance at 6 months. Although mexiletine had a sustained positive effect on objectively measured hand grip myotonia, this was not seen in measures reflecting participants' perceptions of their myotonia. No effects of mexiletine on cardiac conduction measures were seen over the 6-month follow-up period.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for ambulatory patients with DM1, mexiletine does not significantly change 6-minute walk distance at 6 months.

Effects and Acceptability of an Individualized Home-Based 10-Week Training Program in Adults with Myotonic Dystrophy Type 1

Background: Muscle weakness is a cardinal sign of myotonic dystrophy type 1, causing important functional mobility limitations and increasing the risk of falling. As a non-pharmacological, accessible and safe treatment for this population, strength training is an intervention of choice. Objective: To document the effects and acceptability of an individualized semi-supervised home-based exercise program on functional mobility, balance and lower limb strength, and to determine if an assistive training device has a significant impact on outcomes. Methods: This study used a pre-post test design and men with the adult form of DM1 were randomly assigned to the control or device group. The training program was performed three times a week for 10 weeks and included three exercises (sit-to-stand, squat, and alternated lunges). Outcome measures included maximal isometric muscle strength, 10-Meter Walk Test, Mini-BESTest, 30-Second Chair Stand Test and 6-minute walk test. Results: No outcome measures showed a significant difference, except for the strength of the knee flexors muscle group between the two assessments. All participants improved beyond the standard error of measurement in at least two outcome measures. The program and the device were well accepted and all participants reported many perceived improvements at the end of the program. Conclusions: Our results provide encouraging data on the effects and acceptability of a home-based training program for men with the adult form of DM1. These programs would reduce the financial burden on the health system while improving the clinical services offered to this population.

Gender effect on cardiac involvement in myotonic dystrophy type 1

BACKGROUND AND PURPOSE

Cardiac involvement is observed in about 80% of subjects with myotonic dystrophy type 1 (DM1) and is mainly characterized by cardiac conduction and/or rhythm abnormalities (CCRAs), possibly leading to sudden cardiac death (SCD). Our objective was to investigate whether the gender difference may influence the cardiac involvement and SCD in DM1.

METHODS

We analyzed prevalence and incidence of cardiological abnormalities in males versus females in 151 consecutive DM1 patients over a 35-year follow-up period.

RESULTS

Fifty-five patients, 35 males (62.5%) and 20 females (42.5%), developed some type of CCRA during the follow-up period (mean 7.82 ± 6.21 years). CCRA overall, and specifically cardiac conduction abnormalities (CCAs), were significantly more frequent in males than in females (p = 0.043 and p = 0.031, respectively). CCRAs progressed in 16 males (45.7%) and six females (30%). Twenty-four patients, 14 males (25.0%) and 10 females (21.3%), died during the follow-up. Nine of them, six males (10.7%) and three females (6.4%), had SCD. After correction for Muscular Impairment Rating Scale progression, cytosine thymine-guanine expansion, and follow-up duration, a higher prevalence of CCAs was independently associated with male gender (p = 0.039), but independent association with gender was not detected for CCRAs overall, cardiac rhythm abnormalities, and SCD prevalence, even if prevalence was higher in males than females.

CONCLUSIONS

The overall risk of occurrence of CCAs in DM1 is significantly higher in males than females regardless of genetic background and disease severity and progression. Moreover, the data also suggest a similar impact for male gender for CCRAs overall, CCAs, and SCD even if not statistically significant.