Correction of exon 2, exon 2-9 and exons 8-9 duplications in DMD patient myogenic cells by a single CRISPR/Cas9 system.

Duchenne Muscular dystrophy (DMD), a yet-incurable X-linked recessive disorder that results in muscle wasting and loss of ambulation is due to mutations in the dystrophin gene. Exonic duplications of dystrophin gene are a common type of mutations found in DMD patients. In this study, we utilized a single guide RNA CRISPR strategy targeting intronic regions to delete the extra duplicated regions in patient myogenic cells carrying duplication of exon 2, exons 2-9, and exons 8-9 in the DMD gene. Immunostaining on CRISPR-corrected derived myotubes demonstrated the rescue of dystrophin protein. Subsequent RNA sequencing of the DMD cells indicated rescue of genes of dystrophin related pathways. Examination of predicted close-match off-targets evidenced no aberrant gene editing at these loci. Here, we further demonstrate the efficiency of a single guide CRISPR strategy capable of deleting multi-exon duplications in the DMD gene without significant off target effect. Our study contributes valuable insights into the safety and efficacy of using single guide CRISPR strategy as a potential therapeutic approach for DMD patients with duplications of variable size.

Distribution of MRI-derived T2 values as a biomarker for in vivo rapid screening of phenotype severity in mdx mice.

BACKGROUND: The pathology in Duchenne muscular dystrophy (DMD) is characterized by degenerating muscle fibers, inflammation, fibro-fatty infiltrate, and edema, and these pathological processes replace normal healthy muscle tissue. The mdx mouse model is one of the most commonly used preclinical models to study DMD. Mounting evidence has emerged illustrating that muscle disease progression varies considerably in mdx mice, with inter-animal differences as well as intra-muscular differences in pathology in individual mdx mice. This variation is important to consider when conducting assessments of drug efficacy and in longitudinal studies. We developed a magnetic resonance imaging (MRI) segmentation and analysis pipeline to rapidly and non-invasively measure the severity of muscle disease in mdx mice. METHODS: Wildtype and mdx mice were imaged with MRI and T2 maps were obtained axially across the hindlimbs. A neural network was trained to rapidly and semi-automatically segment the muscle tissue, and the distribution of resulting T2 values was analyzed. Interdecile range and Pearson Skew were identified as biomarkers to quickly and accurately estimate muscle disease severity in mice. RESULTS: The semiautomated segmentation tool reduced image processing time approximately tenfold. Measures of Pearson skew and interdecile range based on that segmentation were repeatable and reflected muscle disease severity in healthy wildtype and diseased mdx mice based on both qualitative observation of images and correlation with Evans blue dye uptake. CONCLUSION: Use of this rapid, non-invasive, semi-automated MR image segmentation and analysis pipeline has the potential to transform preclinical studies, allowing for pre-screening of dystrophic mice prior to study enrollment to ensure more uniform muscle disease pathology across treatment groups, improving study outcomes.

Cell transplantation-mediated dystrophin supplementation efficacy in Duchenne muscular dystrophy mouse motor function improvement demonstrated by enhanced skeletal muscle fatigue tolerance.

BACKGROUND: Duchenne muscular dystrophy (DMD) is an incurable neuromuscular disease leading to progressive skeletal muscle weakness and fatigue. Cell transplantation in murine models has shown promise in supplementing the lack of the dystrophin protein in DMD muscles. However, the establishment of novel, long-term, relevant methods is needed to assess its efficiency on the DMD motor function. By applying newly developed methods, this study aimed to evaluate the functional and molecular effects of cell therapy-mediated dystrophin supplementation on DMD muscles. METHODS: Dystrophin was supplemented in the gastrocnemius of a 5-week-old immunodeficient DMD mouse model (Dmd-null/NSG) by intramuscular xenotransplantation of healthy human immortalized myoblasts (Hu5/KD3). A long-term time-course comparative study was conducted between wild-type, untreated DMD, and dystrophin supplemented-DMD mouse muscle functions and histology. A novel GO-ATeam2 transgenic DMD mouse model was also generated to assess in vivo real-time ATP levels in gastrocnemius muscles during repeated contractions. RESULTS: We found that 10.6% dystrophin supplementation in DMD muscles was sufficient to prevent low values of gastrocnemius maximal isometric contraction torque (MCT) at rest, while muscle fatigue tolerance, assessed by MCT decline after treadmill running, was fully ameliorated in 21-week-old transplanted mice. None of the dystrophin-supplemented fibers were positive for muscle damage markers after treadmill running, with 85.4% demonstrating the utilization of oxidative metabolism. Furthermore, ATP levels in response to repeated muscle contractions tended to improve, and mitochondrial activity was significantly enhanced in dystrophin supplemented-fibers. CONCLUSIONS: Cell therapy-mediated dystrophin supplementation efficiently improved DMD muscle functions, as evaluated using newly developed evaluation methods. The enhanced muscle fatigue tolerance in 21-week-old mice was associated with the preferential regeneration of damage-resistant and oxidative fibers, highlighting increased mitochondrial activity, after cell transplantation. These findings significantly contribute to a more in-depth understanding of DMD pathogenesis.

LED therapy modulates M1/M2 macrophage phenotypes and mitigates dystrophic features in treadmill-trained mdx mice.

The mdx mouse phenotype, aggravated by chronic exercise on a treadmill, makes this murine model more reliable for the study of Duchenne muscular dystrophy (DMD) and allows the efficacy of therapeutic interventions to be evaluated. This study aims to investigate the effects of photobiomodulation by light-emitting diode (LED) therapy on functional, biochemical and morphological parameters in treadmill-trained adult mdx animals. Mdx mice were trained for 30 min of treadmill running at a speed of 12 m/min, twice a week for 4 weeks. The LED therapy (850 nm) was applied twice a week to the quadriceps muscle throughout the treadmill running period. LED therapy improved behavioral activity (open field) and muscle function (grip strength and four limb hanging test). Functional benefits correlated with reduced muscle damage; a decrease in the inflammatory process; modulation of the regenerative muscular process and calcium signalling pathways; and a decrease in oxidative stress markers. The striking finding of this work is that LED therapy leads to a shift from the M1 to M2 macrophage phenotype in the treadmill-trained mdx mice, enhancing tissue repair and mitigating the dystrophic features. Our data also imply that the beneficial effects of LED therapy in the dystrophic muscle correlate with the interplay between calcium, oxidative stress and inflammation signalling pathways. Together, these results suggest that photobiomodulation could be a potential adjuvant therapy for dystrophinopathies.

The cryptic complex rearrangements involving the DMD gene: etiologic clues about phenotypical differences revealed by optical genome mapping.

BACKGROUND: Deletion or duplication in the DMD gene is one of the most common causes of Duchenne and Becker muscular dystrophy (DMD/BMD). However, the pathogenicity of complex rearrangements involving DMD, especially segmental duplications with unknown breakpoints, is not well understood. This study aimed to evaluate the structure, pattern, and potential impact of rearrangements involving DMD duplication. METHODS: Two families with DMD segmental duplications exhibiting phenotypical differences were recruited. Optical genome mapping (OGM) was used to explore the cryptic pattern of the rearrangements. Breakpoints were validated using long-range polymerase chain reaction combined with next-generation sequencing and Sanger sequencing. RESULTS: A multi-copy duplication involving exons 64-79 of DMD was identified in Family A without obvious clinical symptoms. Family B exhibited typical DMD neuromuscular manifestations and presented a duplication involving exons 10-13 of DMD. The rearrangement in Family A involved complex in-cis tandem repeats shown by OGM but retained a complete copy (reading frame) of DMD inferred from breakpoint validation. A reversed insertion with a segmental repeat was identified in Family B by OGM, which was predicted to disrupt the normal structure and reading frame of DMD after confirming the breakpoints. CONCLUSIONS: Validating breakpoint and rearrangement pattern is crucial for the functional annotation and pathogenic classification of genomic structural variations. OGM provides valuable insights into etiological analysis of DMD/BMD and enhances our understanding for cryptic effects of complex rearrangements.

Engineering TadA ortholog-derived cytosine base editor without motif preference and adenosine activity limitation.

The engineered TadA variants used in cytosine base editors (CBEs) present distinctive advantages, including a smaller size and fewer off-target effects compared to cytosine base editors that rely on natural deaminases. However, the current TadA variants demonstrate a preference for base editing in DNA with specific motif sequences and possess dual deaminase activity, acting on both cytosine and adenosine in adjacent positions, limiting their application scope. To address these issues, we employ TadA orthologs screening and multi sequence alignment (MSA)-guided protein engineering techniques to create a highly effective cytosine base editor (aTdCBE) without motif and adenosine deaminase activity limitations. Notably, the delivery of aTdCBE to a humanized mouse model of Duchenne muscular dystrophy (DMD) mice achieves robust exon 55 skipping and restoration of dystrophin expression. Our advancement in engineering TadA ortholog for cytosine editing enriches the base editing toolkits for gene-editing therapy and other potential applications.

Musculoskeletal Issues in Children and Adolescents: Genetic Musculoskeletal Disorders.

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder with progressive proximal weakness as the principal sign. Glucocorticoids and physical therapy are the mainstay of treatment. Exercise intolerance is the hallmark of metabolic myopathies, which require a combination of laboratory testing, electrodiagnostic testing, and muscle biopsy for diagnosis. Joint hypermobility may be an isolated finding or be associated with hypermobility Ehlers-Danlos syndrome (EDS), other variants of EDS, or marfanoid syndromes. The latter conditions are associated with aortic and cardiac valvular abnormalities. Osteogenesis imperfecta encompasses a group of disorders characterized by bone fragility presenting with a low-impact fracture as a result of minimal trauma. Management includes multidiscipline specialists. Down syndrome (DS), or trisomy 21, is the most common chromosome abnormality identified in live births. Routine evaluation of atlantoaxial instability with x-ray is no longer recommended for children with DS without symptoms of atlantoaxial instability; however, clinical evaluation of symptoms is required for sports preparticipation. Achondroplasia is the most common skeletal dysplasia. Clinical signs are macrocephaly, short limb, short stature with disproportionately shorter humerus and femur, along with characteristic findings in pelvis and lumbar spine x-rays. Caregivers should be educated on proper positioning and handling to avoid complications, including car seat-related deaths.

Identifying inversions with breakpoints in the Dystrophin gene through long-read sequencing: report of two cases.

BACKGROUND: Duchenne Muscular Dystrophy (DMD) is an X-linked disorder caused by mutations in the DMD gene, with large deletions being the most common type of mutation. Inversions involving the DMD gene are a less frequent cause of the disorder, largely because they often evade detection by standard diagnostic methods such as multiplex ligation probe amplification (MLPA) and whole exome sequencing (WES). CASE PRESENTATION: Our research identified two intrachromosomal inversions involving the dystrophin gene in two unrelated families through Long-read sequencing (LRS). These variants were subsequently confirmed via Sanger sequencing. The first case involved a pericentric inversion extending from DMD intron 47 to Xq27.3. The second case featured a paracentric inversion between DMD intron 42 and Xp21.1, inherited from the mother. In both cases, simple repeat sequences (SRS) were present at the breakpoints of these inversions. CONCLUSIONS: Our findings demonstrate that LRS is an effective tool for detecting atypical mutations. The identification of SRS at the breakpoints in DMD patients enhances our understanding of the mechanisms underlying structural variations, thereby facilitating the exploration of potential treatments.

Cataloging health state utility estimates for Duchenne muscular dystrophy and related conditions.

BACKGROUND: Duchenne muscular dystrophy (DMD) is a genetic disease resulting in progressive muscle weakness, loss of ambulation, and cardiorespiratory complications. Direct estimation of health-related quality of life for patients with DMD is challenging, highlighting the need for proxy measures. This study aims to catalog and compare existing published health state utility estimates for DMD and related conditions. METHODS: Using two search strategies, relevant utilities were extracted from the Tufts Cost-Effectiveness Analysis Registry, including health states, utility estimates, and study and patient characteristics. Analysis One identified health states with comparable utility estimates to a set of published US patient population utility estimates for DMD. A minimal clinically important difference of ± 0.03 was applied to each DMD utility estimate to establish a range, and the registry was searched to identify other health states with associated utilities that fell within each range. Analysis Two used pre-defined search terms to identify health states clinically similar to DMD. Mapping was based on the degree of clinical similarity. RESULTS: Analysis One identified 4,308 unique utilities across 2,322 cost-effectiveness publications. The health states captured a wide range of acute and chronic conditions; 34% of utility records were extrapolated for US populations (n = 1,451); 1% were related to pediatric populations (n = 61). Analysis Two identified 153 utilities with health states clinically similar to DMD. The median utility estimates varied among identified health states. Health states similar to the early non-ambulatory DMD phase exhibited the greatest difference between the median estimate of the sample (0.39) and the existing estimate from published literature (0.21). CONCLUSIONS: When available estimates are limited, using novel search strategies to identify utilities of clinically similar conditions could be an approach for overcoming the information gap. However, it requires careful evaluation of the utility instruments, tariffs, and raters (proxy or self).

Cognitive and emotional-behavioural outcomes of Turkish Duchenne muscular dystrophy population and its association with motor function.

PURPOSE: The aim of this study was to examine the cognitive and emotional-behavioural outcomes of Turkish children with Duchenne muscular dystrophy (DMD) in comparison with healthy peers, to determine its relationship with motor functions, and to analyse the difference of cognitive and emotional-behavioural outcomes according to the site of mutations. METHOD: Children aged 7-16 years with DMD (n = 68) and age-matched typically developing children (n = 33) were included in the study. The cognitive and emotional-behavioural status and the motor functions were assessed in detail. Children with DMD also divided into two groups as "proximal" and "distal" site mutation groups to compare the cognitive and emotional-behavioural outcomes. RESULTS: The children with DMD and typically developing children were similar in terms of age and body mass index (p > 0.05). Significant differences were found between children with DMD and typically developing peers in almost all subtests of both cognitive and emotional-behavioural assessments (p < 0.05). Cognitive and emotional-behavioural parameters were weakly correlated with specific motor parameters responsive to cognitive functioning (p < 0.05). Children with distal site mutation performed significantly worser than those with proximal site mutation in particular cognitive subtest (p < 0.05). CONCLUSIONS: It is concluded that comprehensive and detailed evaluation of cognitive and emotional-behavioural features of children with DMD is essential for better implementation of rehabilitation programs to maintain motor function which especially requires cognitive ability, since a Turkish cohort represented challenges in particular domains of cognitive and emotional-behavioural areas. CLINICAL TRIAL REGISTRATION NUMBER: NCT05661071.

A novel deep intronic variant in the DMD gene causes Duchenne muscular dystrophy by pseudoexon activation encoding a nonsense codon.

Dystrophinopathies are a group of neuromuscular disorders, inherited in an X-linked recessive manner, caused by pathogenic variants in the DMD gene. Copy number variation detection and next generation sequencing allow the detection of around 99 % of the pathogenic variants. However, some patients require mRNA studies from muscle biopsies to identify deep intronic pathogenic variants. Here, we report a child suspected of having Duchenne muscular dystrophy, with a muscle biopsy showing dystrophin deficiency, and negative molecular testing for deletions, duplications, and small variants. mRNA analysis from muscle biopsy revealed a pseudoexon activation that introduce a premature stop codon into the reading frame. gDNA sequencing allowed to identified a novel variant, c.832-186 T>G, which creates a cryptic donor splice site, recognizing the underlying mechanism causing the pseudoexon insertion. This case highlights the usefulness of the mRNA analysis from muscle biopsy when routine genetic testing is negative and clinical suspicion of dystrophinopathies remains the main clinical diagnosis suspicion.

Comprehensive analysis of 2097 patients with dystrophinopathy based on a database from 2011 to 2021.

BACKGROUND: An increasing number of clinical trials for new therapeutic strategies are underway or being considered for dystrophinopathy. Having detailed data on the natural progression of this condition is crucial for assessing the effectiveness of new drugs. However, there's a lack of data regarding the long-term data on the natural course and how it's managed in China. In this study, we offer a comprehensive overview of clinical and molecular findings, as well as treatment outcomes in the Chinese population. METHODS: Institutional data on all patients with dystrophinopathy from August 2011 to August 2021 were retrospectively reviewed. The data included geographic distribution, age at diagnosis, molecular findings, and treatment options, such as corticosteroids, cardiac interventions, and clinical outcomes. RESULTS: In total, 2097 patients with dystrophinopathy, including 1703 cases of Duchenne muscular dystrophy (DMD), 311 cases of Becker muscular dystrophy (BMD), 46 cases of intermediate muscular dystrophy (IMD), and 37 cases categorized as "pending" (individuals with an undetermined phenotype), were registered in the Children's Hospital of Fudan University database for dystrophinopathy from August 2011 to August 2021. The spectrum of identified variants included exonic deletions (66.6%), exonic duplications (10.7%), nonsense variants (10.3%), splice-site variants (4.5%), small deletions (3.5%), small insertions/duplications (1.8%), and missense variants (0.9%). Four deep intronic variants and two inversion variants were identified. Regarding treatment, glucocorticoids were administered to 54.4% of DMD patients and 39.1% of IMD patients. The median age at loss of ambulation was 2.5 years later in DMD patients who received glucocorticoid treatment. Overall, one cardiac medicine at least was prescribed to 7.4% of DMD patients, 8.3% of IMD patients, and 2.6% of BMD patients. Additionally, ventilator support was required by four DMD patients. Eligibility for exon skipping therapy was found in 55.3% of DMD patients, with 12.9%, 10%, and 9.6% of these patients being eligible for skipping exons 51, 53, and 45, respectively. CONCLUSIONS: This is one of the largest studies to have evaluated the natural history of dystrophinopathy in China, which is particularly conducive to the recruitment of eligible patients for clinical trials and the provision of real-world data to support drug development.

Diarylpropionitrile-stimulated ERß nuclear accumulation promotes MyoD-induced muscle regeneration in mdx mice by interacting with FOXO3A.

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive degenerative disease of skeletal muscle, characterized by intramuscular inflammation, muscle regeneration disorder and replacement of muscle with fibroadipose tissue. DMD is caused by the absence of normal dystrophy. Impaired self-renew ability and limited differentiation capacity of satellite cells are proved as main reasons for muscle regeneration failure. The deficiency of estrogen impedes the process of muscle regeneration. However, the role of estrogen receptor ß (ERß) in muscle regeneration is still unclear. This study aims to investigate the role and the pharmacological effect of ERß activation on muscle regeneration in mdx mice. This study showed that mRNA levels of ERß and myogenic-related genes both witnessed increasing trends in dystrophic context. Our results revealed that treatment with selective ERß agonist (DPN, diarylpropionitrile) significantly increased myogenic differentiation 1 (MyoD-1) level and promoted muscle regeneration in mdx mice. Similarly, in mdx mice with muscle-specific estrogen receptor α (ERα) ablation, DPN treatment still promoted muscle regeneration. Moreover, we demonstrated that myoblasts differentiation was accompanied by raised nuclear accumulation of ERß. DPN treatment augmented the nuclear accumulation of ERß and, thus, contributed to myotubes formation. One important finding was that forkhead box O3A (FOXO3A), as a pivotal transcription factor in Myod-1 transcription, participated in the ERß-promoted muscle regeneration. Overall, we offered an interesting explanation about the crucial role of ERß during myogenesis.

Caveolin and NOS in the Development of Muscular Dystrophy.

Caveolin is a structural protein within caveolae that may be involved in transmembrane molecular transport and/or various intercellular interactions within cells. Specific mutations of caveolin-3 in muscle fibers are well known to cause limb-girdle muscular dystrophy. Altered expression of caveolin-3 has also been detected in Duchenne muscular dystrophy, which may be a part of the pathological process leading to muscle weakness. Interestingly, it has been shown that the renovation of nitric oxide synthase (NOS) in sarcolemma with muscular dystrophy could improve muscle health, suggesting that NOS may be involved in the pathology of muscular dystrophy. Here, we summarize the notable function of caveolin and/or NOS in skeletal muscle fibers and discuss their involvement in the pathology as well as possible tactics for the innovative treatment of muscular dystrophies.

Comparison of hand dexterity and hand laterality task in duchenne muscular dystrophy patients with typically developing peers.

BACKGROUND: Hand dexterity is important with Duchenne muscular dystrophy (DMD). OBJECTIVE: The aim of this study was to compare hand dexterity and hand laterality task assessments in patients with DMD with typically-developing peers. METHODS: The study included 25 DMD with a mean age of 10.2±2.38 and 21 typically-developing peers with a mean age of 10.33±2.26. Functional levels of DMD patients were determined by Brooke Upper Extremity Functional Classification Scale and Brooke Lower Extremity Functional Scale. The ABILHAND-Kids and 9-hole peg test were used to assess the hand dexterity of all participants, and assess the hand laterality task. RESULTS: Patients with DMD had lower ABILHAND-Kids scores than their typically-developing peers (p < 0.001). Patients with DMD had higher 9-hole peg test duration on the dominant and non-dominant extremity compared to typically-developing peers (p < 0.001). Patients with DMD were found to be different from their typically-developing peers (p < 0.001) in lateralization response time and accuracy. CONCLUSION: Patients with DMD were found to have lower manual dexterity and hand laterality task skills compared to their typically-developing peers. It is recommended that hand dexterity and upper extremity recognition capacities should be considered in assessment and intervention programs for physiotherapists and clinicians working in this field.

Impact of Disease-modifying Therapies on Respiratory Function in People with Neuromuscular Disorders.

Spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD) are neuromuscular disorders that affect muscular function. The most common causes of morbidity and mortality are respiratory complications, including restrictive lung disease, ineffective cough, and sleep-disordered breathing. The paradigm of care is changing as new disease-modifying therapies are altering disease trajectory, outcomes, expectations, as well as patient and caregiver experiences. This article provides an overview on therapeutic advances for SMA and DMD in the last 10 years, with a focus on the effects of disease-modifying therapies on respiratory function.

Effects of cycling training on balance and gait in children with Duchenne muscular dystrophy: A randomized controlled study.

BACKGROUND AND AIMS: Although aerobic exercises such as cycling and swimming are increasingly being recommended in Duchenne muscular dystrophy (DMD), their effect on gait and balance parameters is unclear. This study was aimed to investigate the effect of cycling training on balance and spatio-temporal gait parameters in children with DMD. METHODS: Ambulant children (age range: 6.17-11.33 years) were randomly divided into two groups: home-based exercise training applied in the control group (n = 12) while 12 weeks of supervised submaximal lower extremity cycling training in addition to home-based exercise training performed in the study group (n = 11). Gait and balance parameters were evaluated using the GAITRite electronic walkway system and the Bertec Balance Check Screener™, respectively. Assessments were applied before and after 12 weeks of training. RESULTS: The mean ages of the children in the study and control groups were 8.20 (SD:1.34) and 8.86 (SD:1.30) years, consecutively (p > 0.05). Considering the baseline values, the balance and spatio-temporal gait parameters of the children were similar except for the antero-posterior postural sway on the perturbed surface with eyes open (p > 0.05). There was a significant time x group interaction effect in favor of the study group for the antero-posterior postural sway of children on the normal surface with eyes open (F (1,58) = 12.62, p = 0.002). It was found that the antero-posterior postural sway on the normal surface with eyes open was improved in the study group within group comparison (F (1,10) = 8.50, p = 0.015). CONCLUSIONS: The study showed that both the cycling and the home-based exercise training groups may maintain gait and balance parameters during the study. Adding a cycling training to the rehabilitation program can also provide additional contribution to improve antero-posterior balance.