Duchenne Muscular Dystrophy: A Practice Update

The Role of MicroRNA in the Pathogenesis of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked progressive disorder associated with muscle wasting and degeneration. The disease is caused by mutations in the gene that encodes dystrophin, a protein that links the cytoskeleton with cell membrane proteins. The current treatment methods aim to relieve the symptoms of the disease or partially rescue muscle functionality. However, they are insufficient to suppress disease progression. In recent years, studies have uncovered an important role for non-coding RNAs (ncRNAs) in regulating the progression of numerous diseases. ncRNAs, such as micro-RNAs (miRNAs), bind to their target messenger RNAs (mRNAs) to suppress translation. Understanding the mechanisms involving dysregulated miRNAs can improve diagnosis and suggest novel treatment methods for patients with DMD. This review presents the available evidence on the role of altered expression of miRNAs in the pathogenesis of DMD. We discuss the involvement of these molecules in the processes associated with muscle physiology and DMD-associated cardiomyopathy.

Implication of Corneal Refractive Surgery in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked disorder due to a dystrophin mutation and is the leading cause of muscular dystrophy. DMD presents with characteristic systemic effects, including severe muscular atrophy, cardiomyopathy, and ocular manifestations. Performing corneal refractive surgeries in patients with DMD raises concerns regarding patient positioning, risk of cataracts, and other comorbid conditions. Published reports of photorefractive keratectomy, laser-assisted in situ keratomileuses, and small incision lenticule extraction are lacking in this population. Here, we discuss a patient being evaluated for a corneal refractive surgery. This article also discusses the current understanding of DMD, known ocular manifestations, and factors to consider when evaluating a patient for potential corrective vision laser surgery.

Analysis of Long Noncoding RNAs-Related Regulatory Mechanisms in Duchenne Muscular Dystrophy Using a Disease-Related lncRNA-mRNA Pathway Network

Objective

This study aimed to investigate the molecular regulatory mechanisms underpinning Duchenne muscular dystrophy (DMD).

Methods

Using microarray data, differentially expressed long noncoding RNAs (DELs) and DMD-related differentially expressed mRNAs (DEMs) were screened based on the comparative toxicogenomics database, using a cutoff of |log₂ fold change| > 1 and false discovery rate (FDR) < 0.05. Then, protein-protein interaction (PPI), coexpression network of lncRNA-mRNA, and DMD-related lncRNA-mRNA pathway networks were constructed, and functional analyses of the genes in the network were performed. Finally, the proportions of immune cells infiltrating the muscle tissues in DMD were analyzed, and the correlation between the immune cells and expression of the DELs/DEMs was studied.

Results

A total of 46 DELs and 313 DMD-related DEMs were identified. The PPI network revealed STAT1, VEGFA, and CCL2 to be the top three hub genes. The DMD-related lncRNA-mRNA pathway network comprising two pathways, nine DELs, and nine DMD-related DEMs showed that PYCARD, RIPK2, and CASP1 were significantly enriched in the NOD-like receptor signaling pathway, whereas MAP2K2, LUM, RPS6, PDCD4, TWIST1, and HIF1A were significantly enriched with proteoglycans in cancers. The nine DELs in this network were DBET, MBNL1-AS1, MIR29B2CHG, CCDC18-AS1, FAM111A-DT, GAS5, LINC01290, ATP2B1-AS1, and PSMB8-AS1.

Conclusion

The nine DMD-related DEMs and DELs identified in this study may play important roles in the occurrence and progression of DMD through the two pathways of the NOD-like receptor signaling pathway and proteoglycans in cancers.

The Refinement of Home Exercise Program for Children and Adolescents With Muscular Dystrophy in the Present COVID-19 Pandemic Scenario: A Scoping Review

Muscular dystrophies (MDs) are a category of hereditary illnesses characterized by the gradual malfunction and/or weakening of the skeletal muscles. This disease of the muscles also results in hypotonia and joint contracture, along with raised serum creatine kinase (CK) levels. To prevent complications, continuous physiotherapy is advised for children with muscular dystrophy, which is even asked to perform at home as a home exercise program (HEP). As a result, the home exercise program (HEP) is critical in maintaining the optimal health of children with Duchenne muscular dystrophy (DMD). The present coronavirus (COVID-19) pandemic has adversely affected these children as there was very little scope to get direct help from a physiotherapist. Meanwhile, the home program was continued by many to compensate for the direct benefit. However, because of the lack of specific guidelines and structured methodology to follow for a home program, there was a deterioration in the health status of many children. There is a need to understand how the children are getting affected and the way the home program can be refined to help needy children with muscular dystrophy. Our scoping review aims to identify the present home program patterns being followed for children with DMD and their scope for refinement. The data were collected from electronic databases including PubMed, ProQuest, Cochrane, and Web of Science. We searched four electronic databases until September 2021. We included the published case studies, observational and experimental studies that described the positive impact of home exercise programs, and the methodology they followed as an alternative to institution-based physiotherapy. One hundred thirty-eight titles were screened, and 58 met the inclusion criteria. Along with regular physiotherapy, the incorporation of HEP helped in early complication prevention in patients with muscular dystrophy. The HEP was found to be a successful adjunct in the COVID-19 scenario. This review presents different therapeutic measures that can be taken for the prevention of complications in patients with MD and how the HEP plays an important role in removing the gaps on how HEP is beneficial in the COVID-19 scenario and a scope to refine the present methodologies for more accurate management.

Development and economic evaluation of a patient-centered care model for children with Duchenne’s Muscular Dystrophy: A quasi-experimental study protocol (Preprint)

BACKGROUND

Duchenne muscular dystrophy (DMD) is a rare progressive muscular disease that primarily affects boys. A lack of comprehensive care for patients living with DMD is directly associated with a compromised quality of life (QoL) for those affected and their caregivers. This disease also has a huge economic impact on families as its treatment requires substantial direct, indirect, and informal care costs.

OBJECTIVE

This study presents a protocol developed to evaluate the feasibility and efficacy of a patient-centered care (PCC) model for children with DMD. The care model was designed with the aim to empower families, improve QoL, and reduce economic burden on their families.

METHODS

This study is planned as a quasi-experimental study that will enroll 70 consecutive families with boys (aged 5-15 years) with DMD visiting a tertiary care center. The study is being conducted in 2 phases (preintervention and postintervention phases, referred to as phase 1 and phase 2, respectively). During phase 1, the patients received routine care. The study is now in phase 2, with the intervention currently being administered. The intervention is based on the PCC model individualized by the intervention team. The model has a comprehensive DMD telecare component that includes teleconsultation as one of its key components to reduce in-person physician visits at the health facility. Teleconsultation is especially beneficial for late-ambulatory and nonambulatory patients. Data on economic burden are being collected for out-of-pocket expenses for both phases during in-person visits via telephone or messaging apps on a monthly basis. QoL data for patients and their primary caregivers are being collected at 3 time points (ie, time of enrollment, end of phase 1, and end of phase 2). Outcome measures are being assessed as changes in economic burden on families and changes in QoL scores.

RESULTS

Participant recruitment began in July 2021. The study is ongoing and expected to be completed by March 2023. The findings based on baseline data are expected to be submitted for publication in 2023.

CONCLUSIONS

This paper outlines a research proposal developed to study the impact of a PCC model for patients with DMD in low- and middle-income countries (LMICs). This study is expected to provide evidence of whether a multicomponent, patient-centric intervention could reduce economic burdens on families and improve their QoL. The results of this study could guide policy makers and health professionals in India and other LMICs to facilitate a comprehensive care program for patients living with DMD. The economic impact of a rare disease is an important consideration to formulate or evaluate any health policy or intervention related to new treatments and financial support schemes.

TRIAL REGISTRATION

Clinical Trials Registry India (ICMR-NIMS) CTRI/2021/06/034274; https://www.ctri.nic.in/Clinicaltrials/pmaindet2.php?trialid=56650.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/42491.

Ambulatory Duchenne muscular dystrophy children: cross-sectional correlation between function, quantitative muscle ultrasound and MRI

Duchenne muscular dystrophy (DMD) is a progressive genetic muscle disease. Quantitative muscle ultrasound (US), muscle MRI, and functional tools are important to delineate characteristics of muscle involvement. We aimed to establish correlations between clinical/functional and above-named imaging tools respecting their diagnostic and prognostic role in DMD children. A cross-sectional retrospective study of 27 steroid-naive, ambulant male children/adolescents with genetically-confirmed DMD (mean age, 8.8 ± 3.3 years). Functional performance was assessed using motor function measure (MFM) which assess standing/transfer (D1), proximal (D2) and distal (D3) motor function, and six-minute walk test (6MWT). Imaging evaluation included quantitative muscle MRI which measured muscle fat content in a specific location of right rectus femoris by mDixon sequence. Quantitative muscle US measured right rectus femoris muscle brightness in standardized US image as an indicator of muscle fat content. We found a highly significant positive correlation between the mean MFM total score and 6MWT (R = 0.537, p = 0.007), and a highly significant negative correlation between fat content by muscle US and MFM total score (R = -0.603, p = 0.006) and its D1 subscore (R =-0.712, p = 0.001), and a significant negative correlation between fat content by US and 6MWT (R = -0.529, p = 0.02), and a significant positive correlation between muscle fat content by mDixon MRI and patient's age (R = 0.617, p = 0.01). Quantitative muscle US correlates significantly with clinical/functional assessment tools as MFM and 6MWT, and augments their role in disease-tracking of DMD. Quantitative muscle US has the potential to act as a substitute to functional assessment tools.

Cardiac MRI and Echocardiography for Early Diagnosis of Cardiomyopathy Among Boys With Duchenne Muscular Dystrophy: A Cross-Sectional Study

BACKGROUND

Cardiomyopathy is an important cause of morbidity and mortality in boys with Duchenne muscular dystrophy (DMD). Early diagnosis is a prerequisite for timely institution of cardioprotective therapies.

OBJECTIVE

We compared cardiac MRI (CMRI) with transthoracic echocardiography (TTE) including tissue Doppler imaging (TDI) and speckle tracking echocardiography (STE) for diagnosis of cardiomyopathy in early ambulatory boys with DMD.

METHODOLOGY

This cross-sectional study was conducted between June 2018 and December 2020. Consecutive boys between 7 and 15 years of age with DMD were enrolled. Percentage ejection fraction (EF), fractional shortening, wall motion abnormalities, early diastolic mitral annulus velocity (Ea), medial mitral annulus ratio (E/Ea), and global strain were measured with STE. CMRI-derived EF, segmental hypokinesia, and late gadolinium enhancement (LGE) were studied and compared.

RESULTS

A total of 38 ambulatory boys with DMD were enrolled. The mean age was 8.8 ± 1.6 years, and none had clinical features suggestive of cardiac dysfunction. In the TTE, EF was ≤55% in 5 (15%), FS was ≤28% in 3 (9%), and one each had left ventricular wall thinning and wall hypokinesia. In TDI, none had diastolic dysfunction, and STE showed reduced global strain of < 18% in 3 (9%) boys. CMRI-derived EF was ≤55% in 20 (53%) boys and CMRI showed the presence of left ventricular wall hypokinesia in 9 (24%) and LGE in 4 (11%) boys.

CONCLUSION

Cardiomyopathy remains clinically asymptomatic among early ambulatory boys with DMD. A significantly higher percentage of boys revealed early features of DMD-related cardiomyopathy in CMRI in comparison with echocardiography.

Alteration of skeletal and cardiac muscles function in DBA/2J mdx mice background: a focus on high intensity interval training

Duchenne muscular dystrophy (DMD) is a recessive hereditary myopathy due to deficiency of functional dystrophin. Current therapeutic interventions need more investigation to slow down the progression of skeletal and cardiac muscle weakness. In humans, there is a lack of an adapted training program. In animals, the murine Mdx model with a DBA/2J background (D2-mdx) was recently suggested to present pathological features closer to that of humans. In this study, we characterized skeletal and cardiac muscle functions in males and females D2-mdx mice compared to control groups. We also evaluated the impact of high intensity interval training (HIIT) in these muscles in females and males. HIIT was performed 5 times per week during a month on a motorized treadmill. Specific maximal isometric force production and weakness were measured in the tibialis anterior muscle (TA). Sedentary male and female D2-mdx mice produced lower absolute and specific maximal force compared to control mice. Dystrophic mice showed a decline of force generation during repetitive stimulation compared to controls. This reduction was greater for male D2-mdx mice than females. Furthermore, trained D2-mdx males showed an improvement in force generation after the fifth lengthening contraction compared to sedentary D2-mdx males. Moreover, echocardiography measures revealed a decrease in left ventricular end-diastolic volume, left ventricular ejection volume and left ventricular end-diastolic diameter in sedentary male and female D2-mdx mice. Overall, our results showed a serious muscle function alteration in female and male D2-mdx mice compared to controls. HIIT may delay force loss especially in male D2-mdx mice.

The expanding spectrum of dystrophinopathies: HyperCKemia to manifest female carriers

Background:

X-linked dystrophinopathies have a wide spectrum of manifestation. The most common forms are severe Duchenne muscular dystrophy (DMD) and Becker’s muscular dystrophy (BMD). However, less common manifestations are isolated cardiomyopathy, myalgia, cramps, rhabdomyolysis, hyperCKemia, and manifest female carriers.

Materials and Methods:

This case series is a part of an ongoing long-term prospective cohort of children with DMD and BMD from the year 2013. The clinical details are maintained in the clinic files and standard management protocols are followed. For this case series, clinical details were collected from the clinic files and recorded on a case record proforma. Details of cardiology, radiology, and genetic investigations were collected.

Results:

We report cases of classical DMD, BMD, manifest female carrier with proximal pelvic girdle weakness, a female carrier with isolated dilated cardiomyopathy, and infantile-onset asymptomatic hyperCKemia. We also report less common but notable clinical presentations of DMD, autism, intellectual disability, epilepsy, and asymptomatic transaminitis.

Conclusions:

It is important for clinicians to be aware of these less common clinical presentations for prompt diagnosis, and to avoid unnecessary investigations. Here, we report the clinical spectrum of dystrophinopathies seen in pediatric neuromuscular clinic and emphasize the variability and expanding knowledge about different manifestations of dystrophinopathies.

DMD-related muscular dystrophy in Cameroon: Clinical and genetic profiles

BACKGROUND

Most of the previous studies on Duchenne Muscular Dystrophy (DMD) were conducted in Caucasian, Asian, and Arab populations. Therefore, little is known about the features of this disease in Africans. In this study, we aimed to determine the clinical characteristics of DMD, and the common mutations associated with this condition in a group of Cameroonian patients.

METHODS

We recruited DMD patients and performed a general physical examination on each of them. Multiplex ligand-dependant probe amplification was carried out to investigate exon deletions and duplications in the DMD gene (OMIM: 300377) of patients and their mothers.

RESULTS

A total of 17 male patients from 14 families were recruited, aged 14 ± 5.1 (8-23) years. The mean age at onset of symptoms was 4.6 ± 1.5 years, and the mean age at diagnosis was 12.1 ± 5.2 years. Proximal muscle weakness was noted in all patients and calf hypertrophy in the large majority of them (88.2%; 15/17). Flexion contractures were particularly frequent on the ankle (85.7%; 12/14). Wasting of shoulder girdle and thigh muscles was present in 50% (6/12) and 46.2% (6/13) of patients, respectively. No patient presented with hearing impairment. Deletions in DMD gene (OMIM: 300377) occurred in 45.5% of patients (5/11), while duplications were observed in 27.3% (3/11). Both mutation types were clustered between exons 45 and 50, and the proportion of de novo mutation was estimated at 18.2% (2/11).

CONCLUSION

Despite the first symptoms of DMD occurring in infancy, the diagnosis is frequently made later in adolescence, indicating an underestimation of the number of cases of DMD in Cameroon. Future screening of deletions and duplications in patients from Cameroon should focus on the distal part of the gene.

Implications of Insulin-Like Growth Factor-1 in Skeletal Muscle and Various Diseases

Skeletal muscle is an essential tissue that attaches to bones and facilitates body movements. Insulin-like growth factor-1 (IGF-1) is a hormone found in blood that plays an important role in skeletal myogenesis and is importantly associated with muscle mass entity, strength development, and degeneration and increases the proliferative capacity of muscle satellite cells (MSCs). IGF-1R is an IGF-1 receptor with a transmembrane location that activates PI3K/Akt signaling and possesses tyrosine kinase activity, and its expression is significant in terms of myoblast proliferation and normal muscle mass maintenance. IGF-1 synthesis is elevated in MSCs of injured muscles and stimulates MSCs proliferation and myogenic differentiation. Mechanical loading also affects skeletal muscle production by IGF-1, and low IGF-1 levels are associated with low handgrip strength and poor physical performance. IGF-1 is potentially useful in the management of Duchenne muscular dystrophy, muscle atrophy, and promotes neurite development. This review highlights the role of IGF-1 in skeletal muscle, its importance during myogenesis, and its involvement in different disease conditions.

Funcionalidade de membro superior em pacientes deambuladores e não deambuladores com distrofia muscular de Duchenne

RESUMO Novos tratamentos propostos para os pacientes com distrofia muscular de Duchenne (DMD) têm sua eficácia avaliada por testes de membros inferiores. Contudo, os testes funcionais de membros superiores (MMSS) avaliam tanto deambuladores (D) como não deambuladores (ND). Assim, este estudo se propôs a comparar a funcionalidade de MMSS de pacientes D e ND com DMD e correlacionar o estadiamento da doença e a função de MMSS. Trata-se de um estudo transversal no qual os pacientes foram divididos em D e ND de acordo com a escala Vignos. Posteriormente, a funcionalidade dos MMSS foi avaliada pela escala performace of upper limb (PUL). Foi realizado o teste t independente, teste qui-quadrado, teste Mann-Whitney, regressão linear e teste de correlação de Spearman pelo programa SPSS, versão 22. A pesquisa foi composta de 51 pacientes, sendo 20 D e 31 ND. Houve diferença entre os grupos em relação à idade (p=0,001), ao índice de massa corporal (IMC) (p=0,016), à escolaridade (p=0,011), quanto ao escore na escala Vignos (p<0,001) e na função dos MMSS (p<0,001). Na análise de regressão linear observamos que o paciente ser D ou ND influencia na função dos MMSS em 18 pontos na escala PUL. Houve forte correlação entre o estadiamento da doença e a função de MMSS (r2=−0,769, p<0,001). A condição funcional dos MMSS depende se o paciente é D ou ND, sendo pior nos ND. Concluiu-se que a função de MMSS tem forte correlação com o estadiamento da doença.

[Clinical features and LAMA2 mutations of patients with congenital muscular dystrophy type 1A: a case report and literature review]

Biallelic pathogenic mutations of the LAMA2 gene result in congenital muscular dystrophy type 1A (CMD1A). The patient in this study was a boy aged 19 months, with the clinical manifestations of motor development delay and increases in the serum levels of creatine kinase, aminotransferases, and lactate dehydrogenase. Genetic analysis showed that the patient had compound heterozygous mutations in the LAMA2 gene, among which c.7147C>T (p.Ala2383Ter) from his mother was a known nonsense mutation, and c.8551_8552insAA (p.Ile2852ArgfsTer2) from his father was a frameshift mutation which had never been reported before and was identified as a pathogenic mutation based on the ACMG guideline. The boy was confirmed with CMD1A. A literature review of related articles in China and overseas revealed that most children with CMD1A have disease onset within 6 months after birth, with the features of motor developmental delay, elevated serum creatine kinase, and white matter impairment on imaging examination. The mutations of the LAMA2 gene have remarkable heterogeneity, the majority of which are null mutations. There are no specific treatment methods for CMD1A currently, and children with CMD1A usually have a poor long-term prognosis.