Myotonic Dystrophy Type Research Articles

Heterogeneity of cognitive impairments in myotonic dystrophy type 1 explained by three distinct cognitive profiles.

Severity and nature of cognitive impairments in Myotonic dystrophy type 1 (DM1) are heterogeneous among studies. We hypothesized that this heterogeneity is explained by different cognitive profiles in DM1, with different clinical, biological and behavioral features. Adult patients with genetically proven DM1 underwent a clinical, neuropsychological and behavioral assessment. We conducted a k-means clustering analysis on 9 cognitive tests representative of different domains (verbal/non-verbal episodic memory, visuo-constructive abilities, visual gnosis, executive functions, information processing speed). We included 124 DM1 patients. Mean age was 45.1 ± 13.5years [19.8-73.2], mean age of onset was 30.4 ± 15.7years [5-72], and mean CTG triplets' expansion size was 489.7 ± 351.8 [50-1600]. We found 3 cognitive clusters, including, respectively, 84, 29 and 11 patients. The first cluster included patients with more preserved cognitive functions; the second included patients with worse cognitive performances which predominate on executive functions; and the third even more pronounced and diffuse cognitive deficits. Younger patients, with a more recent DM1 clinical onset, higher educational level were more frequently classified in the cluster with more preserved cognitive functions. There were no significant differences between clusters regarding CTG triplets' expansion, neither age at DM1 onset, nor most of behavioral measures. We found different cognitive profiles in our DM1 population, which seem influenced by age and DM1 duration. Our findings may explain the heterogeneity of studies about cognition in DM1, and suggest a potential neurodegenerative mechanism in DM1 adults.

Phosphorylated neurofilament heavy chain in cerebrospinal fluid and plasma as a Nusinersen treatment response marker in childhood-onset SMA individuals from Serbia

IntroductionBiomarkers capable of reflecting disease onset and short- and long-term therapeutic effects in individuals with spinal muscular atrophy (SMA) are still an unmet need and phosphorylated neurofilament heavy chain (pNF-H) holds significant promise.MethodsWe conducted a longitudinal prospective study to evaluate pNF-H levels in the cerebrospinal fluid (CSF) and plasma of 29 individuals with childhood-onset SMA treated with Nuinersen (SMA type 1: n = 6, 2: n = 17, 3: n = 6). pNF-H levels before and during treatment were compared with the levels of controls (n = 22), patients with Duchenne muscular dystrophy (n = 17), myotonic dystrophy type 1 (n = 11), untreated SMA individuals with chronic type 3 disease (n = 8), and children with presymptomatic SMA (n = 3).ResultsSMA type 1 showed the highest mean CSF pNF-H levels before treatment initiation. All Nusinersen-treated individuals (types 1, 2, and 3) showed significantly elevated mean baseline CSF pNF-H compared to controls, which inversely correlated with age at disease onset, age at first dose, disease duration and the initial CHOP INTEND result (SMA type 1 and 2). During 22 months of treatment, CSF pNF-H levels declined during loading doses, stabilizing at reduced levels from the initial maintenance dose in all individuals. Baseline plasma pNF-H levels in type 1 and 2 SMA were significantly increased compared to other cohorts and decreased notably in type 1 after 2 months of treatment and type 2 after 14 months. Conversely, SMA type 3, characterized by lower baseline pNF-H levels, did not show significant fluctuations in plasma pNF-H levels after 14 months of treatment.ConclusionOur findings suggest that CSF pNF-H levels in untreated SMA individuals are significantly higher than in controls and that monitoring of CSF pNF-H levels may serve as an indicator of rapid short-term treatment response in childhood-onset SMA individuals, irrespective of the subtype of the disease, while also suggesting its potential for assessing long-term suppression of neurodegeneration. Plasma pNF-H may serve as an appropriate outcome measure for disease progression and/or response to treatment in types 1 and 2 but not in type 3. Presymptomatic infants with SMA may show elevated pNF-H levels, confirming early neuronal degeneration.

Bruno 1/CELF regulates splicing and cytoskeleton dynamics to ensure correct sarcomere assembly Drosophila flight muscles.

Muscles undergo developmental transitions in gene expression and alternative splicing that are necessary to refine sarcomere structure and contractility. CUG-BP and ETR-3-like (CELF) family RNA-binding proteins are important regulators of RNA processing during myogenesis that are misregulated in diseases such as Myotonic Dystrophy Type I (DM1). Here, we report a conserved function for Bruno 1 (Bru1, Arrest), a CELF1/2 family homolog in Drosophila, during early muscle myogenesis. Loss of Bru1 in flight muscles results in disorganization of the actin cytoskeleton leading to aberrant myofiber compaction and defects in pre-myofibril formation. Temporally restricted rescue and RNAi knockdown demonstrate that early cytoskeletal defects interfere with subsequent steps in sarcomere growth and maturation. Early defects are distinct from a later requirement for bru1 to regulate sarcomere assembly dynamics during myofiber maturation. We identify an imbalance in growth in sarcomere length and width during later stages of development as the mechanism driving abnormal radial growth, myofibril fusion, and the formation of hollow myofibrils in bru1 mutant muscle. Molecularly, we characterize a genome-wide transition from immature to mature sarcomere gene isoform expression in flight muscle development that is blocked in bru1 mutants. We further demonstrate that temporally restricted Bru1 rescue can partially alleviate hypercontraction in late pupal and adult stages, but it cannot restore myofiber function or correct structural deficits. Our results reveal the conserved nature of CELF function in regulating cytoskeletal dynamics in muscle development and demonstrate that defective RNA processing due to misexpression of CELF proteins causes wide-reaching structural defects and progressive malfunction of affected muscles that cannot be rescued by late-stage gene replacement.

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

BackgroundCardiac 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. MethodsPatients 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. ResultsWe 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. ConclusionsIn 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 perspectiveWhat is new?•After 10 years of follow-up cardiac involvement increased from 42% to 66%.•Conduction abnormalities, arrhythmias, and left ventricular dysfunction are common despite most patients not reporting any symptoms.•Addition of Holter monitoring and echocardiography to the standard 12‑lead ECG increases the diagnostic yield for detecting cardiac involvement.What are the clinical implications?•Systematic screening for cardiac involvement with 12‑lead ECG, Holter monitoring, and echocardiography is justified in patients with myotonic dystrophy type 1.•All-cause mortality remains high despite cardiac screening which underlines the need improved risk stratification and multidisciplinary care.

Prevalence of Steinert's Myotonic Dystrophy and Utilization of Healthcare Services: A Population-Based Cross-Sectional Study.

Myotonic dystrophy type I (MDI) is the most common muscular dystrophy in adults. The main objectives of this study were to determine the prevalence of MDI in the Community of Madrid (CM) (Spain) and to analyze the use of public healthcare services; a population-based cross-sectional descriptive study was carried out on patients with MDI in CM and data were obtained from a population-based registry (2010-2017). A total of 1101 patients were studied (49.1% women) with average age of 47.8 years; the prevalence of MDI was 14.4/100,000 inhabitants. In the women lineal regression model for hospital admissions, being in the fourth quartile of the deprivation index, was a risk factor (regression coef (rc): 0.80; 95%CI 0.25-1.37). In the overall multiple lineal regression model for primary health care (PHC) attendance, being a woman increased the probability of having a higher number of consultations (rc: 3.99; 95%CI: 3.95-5.04), as did being in the fourth quartile of the deprivation index (rc: 2.10; 95%CI: 0.58-3.63); having received influenza vaccines was a protective factor (rc: -0.46; 95%CI: -0.66-(-0.25)). The prevalence of MDI in the CM is high compared to other settings. Moreover, having any level of risk stratification of becoming ill (high, medium or low) has a positive association with increased PHC consultations and hospital admissions.

Differentiation shifts from a reversible to an irreversible heterochromatin state at the DM1 locus

Epigenetic defects caused by hereditary or de novo mutations are implicated in various human diseases. It remains uncertain whether correcting the underlying mutation can reverse these defects in patient cells. Here we show by the analysis of myotonic dystrophy type 1 (DM1)-related locus that in mutant human embryonic stem cells (hESCs), DNA methylation and H3K9me3 enrichments are completely abolished by repeat excision (CTG2000 expansion), whereas in patient myoblasts (CTG2600 expansion), repeat deletion fails to do so. This distinction between undifferentiated and differentiated cells arises during cell differentiation, and can be reversed by reprogramming of gene-edited myoblasts. We demonstrate that abnormal methylation in DM1 is distinctively maintained in the undifferentiated state by the activity of the de novo DNMTs (DNMT3b in tandem with DNMT3a). Overall, the findings highlight a crucial difference in heterochromatin maintenance between undifferentiated (sequence-dependent) and differentiated (sequence-independent) cells, thus underscoring the role of differentiation as a locking mechanism for repressive epigenetic modifications at the DM1 locus.

Coexistence Of Anti-Musk-Positive Bulbar Myasthenia Gravis And Myotonic Dystrophy Type 1: The First Case Report from Turkey

Muscle-specific tyrosine kinase (MuSK) myasthenia gravis (MG) is an acute-onset subtype of MG that primarily affects the fasciobulbar muscles and begins with progressive velopharyngeal and respiratory symptoms such as early respiratory crises, swallowing, and speaking difficulties. Myotonic dystrophy Type 1 (DM1) is an autosomal dominantly inherited autoimmune neuromuscular disease characterized by distal-dominant muscle weakness, cardiovascular pathologies, and corneal disorders. In this case report, we discussed 42-year-old female patient with a previous diagnosis of DM1, and diagnosed with MuSK-MG as a result of electroneuromyographic and antibody tests upon the development of bulbar symptoms and thymus hyperplasia. The patient underwent video-assisted thymectomy, and medical treatment was started with a combination of pyridostigmine and methylprednisolone. The coexistence of anti-MuSK positive MG with thymoid hyperplasia and DM 1 has not been reported so far, and it has been predicted that both diseases may trigger each other through neuroinflammatory mechanisms on an autoimmunergic basis.

Myotonic dystrophy type 1 in South Korea: a comprehensive analysis of cancer and comorbidity risks.

Myotonic dystrophy type 1 (DM1) is an inherited neuromuscular disorder characterized by myotonia and progressive muscle weakness. Beyond the primary symptoms, there is growing concern regarding a higher incidence of certain comorbidities in DM1 patients, including cancer, diabetes, thyroid dysfunction, and cataracts. This study was designed to examine the occurrence of these conditions among patients diagnosed with DM1 in South Korea, using data from the National Health Insurance Service database. The study undertook a comprehensive review of 3,842 patients diagnosed with DM1 between 2012 and 2018. We assessed the incidence of cancer and the prevalence of diabetes, thyroid dysfunction, and cataracts among these patients, comparing their rates to those in the general population. In the study cohort, 463 out of 3,842 DM1 patients (12.04%) were diagnosed with cancer, indicating a substantial elevation in cancer risk with an overall standard incidence ratio of 1.9 (95% CI = 1.6-2.3, p < 0.01) when compared to the expected rates in the general population. Moreover, the prevalence of diabetes (15.2%) and thyroid dysfunction (17.6%) was noteworthy in the DM1 population. The mean age at which DM1 patients underwent cataract surgery was 55.07years, noticeably younger than the mean age of 69.25years for cataract surgery in the general population. DM1 patients have a noteworthy occurrence of several comorbidities such as cancer, diabetes, thyroid dysfunction, and earlier cataract surgery. This highlights the importance of a comprehensive and integrative approach to the management and treatment of DM1, going beyond addressing only the primary neuromuscular symptoms. More research is required to understand the underlying mechanisms contributing to these comorbidities in DM1 patients, which may inform preventative measures and guide improvements in patient care.

MicroRNA-mRNA expression profiles in the skeletal muscle of myotonic dystrophy type 1

ABSTRACT Objectives Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults, yet there are currently no disease-modifying treatments. Disrupted miRNA expressions may lead to dysregulation of target mRNAs and dysfunction involved in DM1 pathogenic mechanism. Methods We used microarray platforms to examine the miRNA/mRNA expression profiles in skeletal muscle biopsies derived from DM1 patients and matched controls. Bioinformatics analysis and dual-luciferase reporter assay were conducted to provide insight into miRNA-mRNA regulatory networks altered in DM1. Results Twenty-three differentially expressed miRNAs and 135 differentially expressed genes were identified. qPCR confirmed that miR-3201, myogenic factor 5 (MYF5), myogenic differentiation 1 (MYOD1), CUGBP, Elav-like family member 1 (CELF1), and CELF2 were significantly up-regulated, while miR-196a, miR-200c, and miR-146a were significantly down-regulated. Enriched functions and pathways such as multicellular organismal development, RNA splicing, cell differentiation, and spliceosome are relevant to DM1. The miRNA-mRNA interaction network revealed that miR-182, miR-30c-2, and miR-200c were the critical nodes that potentially interacted with hub genes. Luciferase reporter assay confirmed the direct interaction between miR-196a and CELF2. Conclusion Those results implied that the observed miRNA/mRNA dysregulation could contribute to specific functions and pathways related to DM1 pathogenesis, highlighting the dysfunction of miR-196a and CELF2.

Treatment Approaches for Altered Facial Expression: A Systematic Review in Facioscapulohumeral Muscular Dystrophy and Other Neurological Diseases.

Facial weakness is a key feature of facioscapulohumeral muscular dystrophy (FSHD) and may lead to altered facial expression and subsequent psychosocial impairment. There is no cure and supportive treatments focus on optimizing physical fitness and compensation of functional disabilities. We hypothesize that symptomatic treatment options and psychosocial interventions for other neurological diseases with altered facial expression could be applicable to FSHD. Therefore, the aim of this review is to collect symptomatic treatment approaches that target facial muscle function and psychosocial interventions in various neurological diseases with altered facial expression in order to discuss the applicability to FSHD. A systematic search was performed. Selected studies had to include FSHD, Bell's palsy, Moebius syndrome, myotonic dystrophy type 1, or Parkinson's disease and treatment options which target altered facial expression. Data was extracted for study and patients' characteristics, outcome assessment tools, treatment, outcome of facial expression and or psychosocial functioning. Forty studies met the inclusion criteria, of which only three studies included FSHD patients exclusively. Most, twenty-one, studies were performed in patients with Bell's palsy. Studies included twelve different therapy categories and results were assessed with different outcomes measures. Five therapy categories were considered applicable to FSHD: training of (non-verbal) communication compensation strategies, speech training, physical therapy, conference attendance, and smile restoration surgery. Further research is needed to establish the effect of these therapies in FSHD. We recommend to include outcome measures in these studies that cover at least cosmetic, functional, communication, and quality of life domains.

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

BackgroundAs 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.MethodsBased 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.ResultsAmong 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.ConclusionThe 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.

Small and large fiber neuropathy in adults with myotonic dystrophy type 1.

Myotonic dystrophy type 1 (DM1) is an inherited neuromuscular disorder that affects multiple organs. In this study, we investigated symptoms of pain and presence of small and large fiber neuropathy in the juvenile and adult form of DM1. Twenty genetically verified DM1 patients were included. Pain was assessed, and neurological examination and investigations of the peripheral nervous system by quantification of small nerve fibers in skin biopsy, quantitative sensory testing and nerve conduction studies were performed. Results from skin biopsies were compared to healthy controls. Seventeen patients reported chronic pain. Large and/or small fiber abnormalities were present in 50% of the patients. The intraepidermal nerve fiber density was significantly lower in the whole group of patients compared to healthy controls. Small-fiber neuropathy might be an important cause of pain in DM1.

Generation of three myotonic dystrophy type 1 patient iPSC lines (CBRCULi018-A, CBRCULi019-A, CBRCULi020-A) derived from lymphoblastoid cell lines for disease modelling and therapeutic research

Myotonic dystrophy type 1 (DM1) is the most prevalent adult-onset muscular dystrophy affecting 1 in 8,000 individuals. It is characterized by multisystemic symptoms, primarily myopathy. The root cause of DM1 is a heterozygous CTG triplet expansion beyond the normal size threshold in the non-coding region of the DM1 protein kinase gene (DMPK). In our study, we generated and characterized three distinct DM1 induced pluripotent stem cell (iPSC) lines with CTG repeat expansions ranging from 900 to 2000 in the DMPK gene. These iPSC lines maintained normal karyotypes, exhibited distinctive colony morphology, robustly expressed pluripotency markers, differentiated into the three primary germ layers, and lacked residual viral vectors.

Studying the Effect of MBNL1 and MBNL2 Loss in Skeletal Muscle Regeneration.

Loss of function of members of the muscleblind-like (MBNL) family of RNA binding proteins has been shown to play a key role in the spliceopathy of RNA toxicity in myotonic dystrophy type 1 (DM1), the most common muscular dystrophy affecting adults and children. MBNL1 and MBNL2 are the most abundantly expressed members in skeletal muscle. A key aspect of DM1 is poor muscle regeneration and repair, leading to dystrophy. We used a BaCl2-induced damage model of muscle injury to study regeneration and effects on skeletal muscle satellite cells (MuSCs) in Mbnl1∆E3/∆E3 and Mbnl2∆E2/∆E2 knockout mice. Similar experiments have previously shown deleterious effects on these parameters in mouse models of RNA toxicity. Muscle regeneration in Mbnl1 and Mbnl2 knockout mice progressed normally with no obvious deleterious effects on MuSC numbers or increased expression of markers of fibrosis. Skeletal muscles in Mbnl1∆E3/∆E3/ Mbnl2∆E2/+ mice showed increased histopathology but no deleterious reductions in MuSC numbers and only a slight increase in collagen deposition. These results suggest that factors beyond the loss of MBNL1/MBNL2 and the associated spliceopathy are likely to play a key role in the defects in skeletal muscle regeneration and deleterious effects on MuSCs that are seen in mouse models of RNA toxicity due to expanded CUG repeats.

Проявления клинического полиморфизма миотонической дистрофии 1-го типа на примере двух семейных случаев

Myotonic dystrophy type 1 (DM1) is one of the most common hereditary forms of MD both among adult patients and in pediatric practice. Due to clinical heterogeneity as well as polymorphism of symptoms in different forms of DM1 there is a problem of insufficient detection of this disease. An earlier onset and a more severe course usually suggest maternal inheritance of the disease, as is clearly shown in the first clinical case described in the Article. However, the other described case demonstrates the phenomenon of anticipation that can be traced during the transmission of DM1 on the paternal side, which is not typical for DM1. The two presented clinical cases, in addition to muscle symptoms, demonstrate many manifestations from various organs and systems, including heart rhythm disturbances, respiratory failure, breathing disorders during sleep, cognitive and emotional disorders, early cataracts, diabetes mellitus, gastrointestinal tract dysfunction, orthopedic complications. Focal white matter lesions and cortical atrophy identified by neuroimaging using magnetic resonance imaging in patients from the presented cases were not associated with the presence of neuropsychological disorders. The multisystem nature of manifestations confirms the need for increasing awareness of healthcare specialists about this disease as well as the monitoring of patients with DM1 by a multidisciplinary team of experts.

Chronic endoplasmic reticulum stress in myotonic dystrophy type 2 promotes autoimmunity via mitochondrial DNA release

Myotonic dystrophy type 2 (DM2) is a tetranucleotide CCTG repeat expansion disease associated with an increased prevalence of autoimmunity. Here, we identified an elevated type I interferon (IFN) signature in peripheral blood mononuclear cells and primary fibroblasts of DM2 patients as a trigger of chronic immune stimulation. Although RNA-repeat accumulation was prevalent in the cytosol of DM2-patient fibroblasts, type-I IFN release did not depend on innate RNA immune sensors but rather the DNA sensor cGAS and the prevalence of mitochondrial DNA (mtDNA) in the cytoplasm. Sublethal mtDNA release was promoted by a chronic activation of the ATF6 branch of the unfolded protein response (UPR) in reaction to RNA-repeat accumulation and non-AUG translated tetrapeptide expansion proteins. ATF6-dependent mtDNA release and resulting cGAS/STING activation could also be recapitulated in human THP-1 monocytes exposed to chronic endoplasmic reticulum (ER) stress. Altogether, our study demonstrates a novel mechanism by which large repeat expansions cause chronic endoplasmic reticulum stress and associated mtDNA leakage. This mtDNA is, in turn, sensed by the cGAS/STING pathway and induces a type-I IFN response predisposing to autoimmunity. Elucidating this pathway reveals new potential therapeutic targets for autoimmune disorders associated with repeat expansion diseases.

Comprehensive Cardiovascular Management of Myotonic Dystrophy Type 1 Patients: A Report from the Italian Neuro-Cardiology Network.

Myotonic dystrophy is a hereditary disorder with systemic involvement. The Italian Neuro-Cardiology Network-"Rete delle Neurocardiologie" (INCN-RNC) is a unique collaborative experience involving neurology units combined with cardio-arrhythmology units. The INCN facilitates the creation of integrated neuro-cardiac teams in Neuromuscular Disease Centers for the management of cardiovascular involvement in the treatment of myotonic dystrophy type 1 (MD1).

Diagnostic uplift through the implementation of short tandem repeat analysis using exome sequencing

To date, approximately 50 short tandem repeat (STR) disorders have been identified; yet, clinical laboratories rarely conduct STR analysis on exomes. To assess its diagnostic value, we analyzed STRs in 6099 exomes from 2510 families with mostly suspected neurogenetic disorders. We employed ExpansionHunter and REViewer to detect pathogenic repeat expansions, confirming them using orthogonal methods. Genotype-phenotype correlations led to the diagnosis of thirteen individuals in seven previously undiagnosed families, identifying three autosomal dominant disorders: dentatorubral-pallidoluysian atrophy (n = 3), spinocerebellar ataxia type 7 (n = 2), and myotonic dystrophy type 1 (n = 2), resulting in a diagnostic gain of 0.28% (7/2510). Additionally, we found expanded ATXN1 alleles (≥39 repeats) with varying patterns of CAT interruptions in twelve individuals, accounting for approximately 0.19% in the Korean population. Our study underscores the importance of integrating STR analysis into exome sequencing pipeline, broadening the application of exome sequencing for STR assessments.

Electrophysiological aspects of myotonic dystrophy type 1 in cardiomyocytes derived from patient-specific induced pluripotent stem cells

Electrophysiological aspects of myotonic dystrophy type 1 in cardiomyocytes derived from patient-specific induced pluripotent stem cells

Multi-level profiling unravels mitochondrial dysfunction in myotonic dystrophy type 2

Myotonic dystrophy type 2 (DM2) is an autosomal-dominant multisystemic disease with a core manifestation of proximal muscle weakness, muscle atrophy, myotonia, and myalgia. The disease-causing CCTG tetranucleotide expansion within the CNBP gene on chromosome 3 leads to an RNA-dominated spliceopathy, which is currently untreatable. Research exploring the pathophysiological mechanisms in myotonic dystrophy type 1 has resulted in new insights into disease mechanisms and identified mitochondrial dysfunction as a promising therapeutic target. It remains unclear whether similar mechanisms underlie DM2 and, if so, whether these might also serve as potential therapeutic targets. In this cross-sectional study, we studied DM2 skeletal muscle biopsy specimens on proteomic, molecular, and morphological, including ultrastructural levels in two separate patient cohorts consisting of 8 (explorative cohort) and 40 (confirmatory cohort) patients. Seven muscle biopsy specimens from four female and three male DM2 patients underwent proteomic analysis and respiratory chain enzymology. We performed bulk RNA sequencing, immunoblotting of respiratory chain complexes, mitochondrial DNA copy number determination, and long-range PCR (LR-PCR) to study mitochondrial DNA deletions on six biopsies. Proteomic and transcriptomic analyses revealed a downregulation of essential mitochondrial proteins and their respective RNA transcripts, namely of subunits of respiratory chain complexes I, III, and IV (e.g., mt-CO1, mt-ND1, mt-CYB, NDUFB6) and associated translation factors (TACO1). Light microscopy showed mitochondrial abnormalities (e.g., an age-inappropriate amount of COX-deficient fibers, subsarcolemmal accumulation) in most biopsy specimens. Electron microscopy revealed widespread ultrastructural mitochondrial abnormalities, including dysmorphic mitochondria with paracrystalline inclusions. Immunofluorescence studies with co-localization of autophagy (p62, LC-3) and mitochondrial marker proteins (TOM20, COX-IV), as well as immunohistochemistry for mitophagy marker BNIP3 indicated impaired mitophagic flux. Immunoblotting and LR-PCR did not reveal significant differences between patients and controls. In contrast, mtDNA copy number measurement showed a reduction of mtDNA copy numbers in the patient group compared to controls. This first multi-level study of DM2 unravels thus far undescribed functional and structural mitochondrial abnormalities. However, the molecular link between the tetranucleotide expansion and mitochondrial dysfunction needs to be further elucidated.