Twice‐weekly glucocorticosteroids in infants and young boys with Duchenne muscular dystrophy

Cardiomyopathy in Duchenne Muscular Dystrophy and the Potential for Mitochondrial Therapeutics to Improve Treatment Response

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations to the dystrophin gene, resulting in deficiency of dystrophin protein, loss of myofiber integrity in skeletal and cardiac muscle, and eventual cell death and replacement with fibrotic tissue. Pathologic cardiac manifestations occur in nearly every DMD patient, with the development of cardiomyopathy-the leading cause of death-inevitable by adulthood. As early cardiac abnormalities are difficult to detect, timely diagnosis and appropriate treatment modalities remain a challenge. There is no cure for DMD; treatment is aimed at delaying disease progression and alleviating symptoms. A comprehensive understanding of the pathophysiological mechanisms is crucial to the development of targeted treatments. While established hypotheses of underlying mechanisms include sarcolemmal weakening, upregulation of pro-inflammatory cytokines, and perturbed ion homeostasis, mitochondrial dysfunction is thought to be a potential key contributor. Several experimental compounds targeting the skeletal muscle pathology of DMD are in development, but the effects of such agents on cardiac function remain unclear. The synergistic integration of small molecule- and gene-target-based drugs with metabolic-, immune-, or ion balance-enhancing compounds into a combinatorial therapy offers potential for treating dystrophin deficiency-induced cardiomyopathy, making it crucial to understand the underlying mechanisms driving the disorder.

Recent Advances in Pre-Clinical Development of Adiponectin Receptor Agonist Therapies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by genetic mutations in the cytoskeletal-sarcolemmal anchor protein dystrophin. Repeated cycles of sarcolemmal tearing and repair lead to a variety of secondary cellular and physiological stressors that are thought to contribute to weakness, atrophy, and fibrosis. Collectively, these stressors can contribute to a pro-inflammatory milieu in locomotor, cardiac, and respiratory muscles. Given the many unwanted side effects that accompany current anti-inflammatory steroid-based approaches for treating DMD (e.g., glucocorticoids), there is a need to develop new therapies that address inflammation and other cellular dysfunctions. Adiponectin receptor (AdipoR) agonists, which stimulate AdipoR1 and R2 isoforms on various cell types, have emerged as therapeutic candidates for DMD due to their anti-inflammatory, anti-fibrotic, and pro-myogenic properties in pre-clinical human and rodent DMD models. Although these molecules represent a new direction for therapeutic intervention, the mechanisms through which they elicit their beneficial effects are not yet fully understood, and DMD-specific data is limited. The overarching goal of this review is to investigate how adiponectin signaling may ameliorate pathology associated with dystrophin deficiency through inflammatory-dependent and -independent mechanisms and to determine if current data supports their future progression to clinical trials.

A review on mechanistic insights into structure and function of dystrophin protein in pathophysiology and therapeutic targeting of Duchenne muscular dystrophy

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive genetic disorder characterized by progressive and severe muscle weakening and degeneration. Among the various forms of muscular dystrophy, it stands out as one of the most common and impactful, predominantly affecting boys. The condition arises due to mutations in the dystrophin gene, a key player in maintaining the structure and function of muscle fibers. The manuscript explores the structural features of dystrophin protein and their pivotal roles in DMD. We present an in-depth analysis of promising therapeutic approaches targeting dystrophin and their implications for the therapeutic management of DMD. Several therapies aiming to restore dystrophin protein or address secondary pathology have obtained regulatory approval, and many others are ongoing clinical development. Notably, recent advancements in genetic approaches have demonstrated the potential to restore partially functional dystrophin forms. The review also provides a comprehensive overview of the status of clinical trials for major therapeutic genetic approaches for DMD. In addition, we have summarized the ongoing therapeutic approaches and advanced mechanisms of action for dystrophin restoration and the challenges associated with DMD therapeutics.

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum of Disease

Background

Duchenne muscular dystrophy (DMD) and related dystrophinopathies are neuromuscular conditions with great unmet medical needs that require the development of effective medical treatments.

Objective

To aid sponsors in clinical development of drugs and therapeutic biological products for treating DMD across the disease spectrum by integrating advancements, patient registries, natural history studies, and more into a comprehensive guidance.

Methods

This guidance emerged from collaboration between the FDA, the Duchenne community, and industry stakeholders. It entailed a structured approach, involving multiple committees and boards. From its inception in 2014, the guidance underwent revisions incorporating insights from gene therapy studies, cardiac function research, and innovative clinical trial designs.

Results

The guidance provides a deeper understanding of DMD and its variants, focusing on patient engagement, diagnostic criteria, natural history, biomarkers, and clinical trials. It underscores patient-focused drug development, the significance of dystrophin as a biomarker, and the pivotal role of magnetic resonance imaging in assessing disease progression. Additionally, the guidance addresses cardiomyopathy's prominence in DMD and the burgeoning field of gene therapy.

Conclusions

The updated guidance offers a comprehensive understanding of DMD, emphasizing patient-centric approaches, innovative trial designs, and the importance of biomarkers. The focus on cardiomyopathy and gene therapy signifies the evolving realm of DMD research. It acts as a crucial roadmap for sponsors, potentially leading to improved treatments for DMD.

The Early Care (0-3 Years) In Duchenne Muscular Dystrophy Meeting Report

Objective

This report summarizes the key discussions from the "Early Care (0-3 years) in Duchenne Muscular Dystrophy" meeting, which aimed to address the challenges and opportunities in the diagnosis and care of Duchenne muscular dystrophy (DMD) and female carriers within the 0-3-year age group.

Methods

The meeting brought together experts and healthcare providers who shared insights, discussed advancements in DMD care, and identified research needs. Presentations covered diagnostic challenges, approved therapies, clinical trials, identification of young female carriers, and the importance of clinical care and support for families.

Results

The meeting highlighted the importance of timely diagnosis and the lack of evidence-based guidelines for the care of children with DMD aged 0-3 years. Diagnostic challenges were discussed, including delays in receiving a DMD diagnosis and disparities based on ethnicity. The potential benefits and process of newborn screening were addressed.Approved therapeutic interventions, such as corticosteroids and exon-skipping drugs, were explored, with studies indicating the potential benefits of early initiation of corticosteroid therapy and the safety of exon-skipping drugs in DMD. Clinical trials involving infants and young boys were discussed, focusing on drugs like ataluren, vamorolone, and gene therapies.The meeting emphasized the importance of clinical care and support for families, including comprehensive information provision, early intervention services, and individualized support. The identification and care of young female carriers were also addressed.

Conclusion

The meeting provided a platform for experts and healthcare providers to discuss and identify key aspects of early care for children with DMD aged 0-3 years. The meeting emphasized the need for early diagnosis, evidence-based guidelines, and comprehensive care and support for affected children and their families. Further research, collaboration, and the development of consensus guidelines are needed to improve early diagnosis, treatment, and outcomes in this population.

Safety, tolerability and pharmacokinetics of eteplirsen in young boys aged 6–48 months with Duchenne muscular dystrophy amenable to exon 51 skipping

Eteplirsen is FDA-approved for the treatment of Duchenne muscular dystrophy (DMD) in exon 51 skip-amenable patients. Previous studies in boys > 4 years of age indicate eteplirsen is well tolerated and attenuates pulmonary and ambulatory decline compared with matched natural history cohorts. Here the safety, tolerability and pharmacokinetics of eteplirsen in boys aged 6-48 months is evaluated. In this open-label, multicenter, dose-escalation study (NCT03218995), boys with a confirmed mutation of the DMD gene amenable to exon 51 skipping (Cohort 1: aged 24-48 months, n = 9; Cohort 2: aged 6 to < 24 months, n = 6) received ascending doses (2, 4, 10, 20, 30 mg/kg) of once-weekly eteplirsen intravenously over 10 weeks, continuing at 30 mg/kg up to 96 weeks. Endpoints included safety (primary) and pharmacokinetics (secondary). All 15 participants completed the study. Eteplirsen was well tolerated with no treatment-related discontinuations, deaths or evidence of kidney toxicity. Most treatment-emergent adverse events were mild; most common were pyrexia, cough, nasopharyngitis, vomiting, and diarrhea. Eteplirsen pharmacokinetics were consistent between both cohorts and with previous clinical experience in boys with DMD > 4 years of age. These data support the safety and tolerability of eteplirsen at the approved 30-mg/kg dose in boys as young as 6 months old.

Modeling Early Heterogeneous Rates of Progression in Boys with Duchenne Muscular Dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) exhibits substantial variability in rates of disease progression and response to treatment. This has hindered treatment development and complicated interpretation of drug effects in clinical trials.

OBJECTIVE

We hypothesized that a multivariate combination of early-age clinical outcome measurements can explain differential disease progression.

METHODS

Data on boys with DMD (ages 4-<10 years), both treated with steroidal anti-inflammatories and untreated, were obtained from CINRG Duchenne Natural History Study (n = 209) and vamorolone VBP15-002/003/LTE (n = 46) studies. Velocities from three timed function tests (TFTs; stand from supine, run/walk 10 meters, and climb 4 stairs) were simultaneously modeled in a longitudinal latent class analysis.

RESULTS

Three classes of differentially progressing early age DMD motor trajectories were identified. Quicker decline/progression was associated with lower baseline TFT velocities, earlier loss of ability to finish a TFT, and lower predicted velocities. Earlier substantial steroid exposure was associated with greater TFT velocities while the moderate progression class was observed to have the largest difference in performance between boys treated early with steroids vs. not. Sample size calculations with the class showing the largest treatment response showed a large reduction in required sample size as compared to using summaries from all participants. Gene mutations were also investigated in post-hoc analyses, with mutations near the beginning of the DMD gene (Dp427 absent and Dp140/Dp71 present) found to be enriched in the slowest progressing class.

CONCLUSIONS

This study provides insight into the variation in DMD progression through a latent class analysis. Our findings show class-related trajectories of motor outcomes and pharmacological response to corticosteroids, and suggest that enrichment strategies and/or subgroup analyses could be considered further in design of therapeutic interventions in DMD.

Update of the Brazilian consensus recommendations on Duchenne muscular dystrophy

In the last few decades, there have been considerable improvements in the diagnosis and care of Duchenne muscular dystrophy (DMD), the most common childhood muscular dystrophy. International guidelines have been published and recently reviewed. A group of Brazilian experts has developed a standard of care based on a literature review with evidence-based graded recommendations in a two-part publication. Implementing best practice management has helped change the natural history of this chronic progressive disorder, in which the life expectancy for children of the male sex in the past used to be very limited. Since the previous publication, diagnosis, steroid treatment, rehabilitation, and systemic care have gained more significant insights with new original work in certain fields. Furthermore, the development of new drugs is ongoing, and some interventions have been approved for use in certain countries. Therefore, we have identified the need to review the previous care recommendations for Brazilian patients with DMD. Our objective was to create an evidence-based document that is an update on our previous consensus on those topics.

The Dystrophinopathies

PURPOSE OF REVIEW

This article reviews the history, epidemiology, genetics, clinical presentation, multidisciplinary management, and established and emerging therapies for the dystrophinopathies.

RECENT FINDINGS

The multidisciplinary care of individuals with dystrophinopathies continues to improve in many ways, including early surveillance and implementation of respiratory, cardiac, and orthopedic health management. The era of genetic therapeutics has altered the treatment landscape in neuromuscular disorders, including the dystrophinopathies.

SUMMARY

The dystrophinopathies are a spectrum of X-linked genetic disorders characterized by childhood-onset progressive weakness and variable cardiac and cognitive involvement. Corticosteroids are the mainstay of therapy to slow disease progression. Additional strategies for disease amelioration and dystrophin restoration, including gene replacement therapy, are under investigation.

Disease Progression Stages and Burden in Patients with Duchenne Muscular Dystrophy Using Administrative Claims Supplemented by Electronic Medical Records

INTRODUCTION

This study aims to identify stages of Duchenne muscular dystrophy (DMD) and assess the disease burden by progression stage using real-world administrative claims supplemented by relevant electronic medical record (EMR) data.

METHODS

Claims and EMR data from the Decision Resources Group's Real World Data Repository (2011-2020) were used to identify patients with DMD by diagnosis code and to stratify them into four disease stages by diagnosis and procedure markers reflective of DMD progression. Clinical and medical history data from the Cooperative International Neuromuscular Research Group (CINRG) were used to validate the developed claims-based staging algorithm. The distribution and drivers by disease stage, as well as disease burden, were examined.

RESULTS

A total of 938 (94%) of patients with DMD identified in claims/EMR data had sufficient information for stage classification. Patients were classified by stage based on patient characteristics and the presence or absence of progression markers such as genetic testing, wheelchair usage, scoliosis treatment, or ventilation assistance. Average ages at stages 1-4 are 7, 13, 18, and 23 years, respectively. Using natural history data, the claims-based staging algorithm was validated with high sensitivity and specificity rates. Both healthcare resource utilization and medical charges increased by stage. For example, the average annualized total charges were $17,688 (stage 1), $36,868 (stage 2), $72,801 (stage 3), and $167,285 (stage 4).

CONCLUSIONS

Large-scale claims data supplemented by EMR data can be used to characterize DMD progression and evaluate disease burden which may inform the design of future real-world studies about DMD.

Duchenne expert physician perspectives on Duchenne newborn screening and early Duchenne care

Duchenne muscular dystrophy (DMD) is a progressive, fatal neuromuscular disorder typically diagnosed between 4 and 5 years of age. DMD currently has five FDA approved therapies, which has led to increased interest in newborn screening (NBS) for DMD. Our objective was to explore the perspectives and predicted practices of physicians (primarily neurologists) who will likely be responsible for the follow-up of infants identified with DMD through NBS. A short survey was developed and distributed to physicians who are responsible for providing care for patients with Duchenne at Certified Duchenne Care Centers across the USA. Twenty-seven physicians responded to statements about benefit and readiness for dystrophinopathy NBS, which care recommendations they would make at initial infant visits, and when they would recommend initiating approved therapies. Most DMD physicians indicated they see benefit in NBS (82%) and believe the DMD care community is ready for NBS in dystrophinopathies (74%). The majority of physicians would recommend multiple interventions, including genetic counseling, maternal carrier testing, referral to early intervention services, screening siblings, discussion of clinical trials, exon skipping therapies, and assessment of social and language development at initial visits. The majority of physicians also indicated they would recommend initiating approved therapies much earlier than the typical age of diagnosis.

Cost of Illness in Patients with Duchenne Muscular Dystrophy in Portugal: The COIDUCH Study

OBJECTIVE

The aim of this study was to estimate the cost of illness (COI) of Duchenne muscular dystrophy (DMD) and its relation to disease progression, using age as a proxy, and according to the ambulatory status of patients.

METHODS

We conducted a cross-sectional study of patients diagnosed with DMD identified through the Portuguese Neuromuscular Patients Association (APN). Data regarding patient and caregiver demographics, patient health status, resource utilization and cost, and informal care were collected using a custom semistructured questionnaire. Labor productivity and absenteeism losses were captured using the Work Productivity and Activity Impairment questionnaire. Costs were valued using a societal perspective.

RESULTS

A total of 46 patient-caregiver pairs were included, of which eight of the patients were ambulant and 38 were nonambulant. Age had a decreasing effect on COI, independent of the patient's disease stage. Annualized lifetime costs were at their highest in nonambulant patients around the mean age of loss of ambulation (10 years of age). The mean per patient stage-specific costs (year 2019 values) of DMD were estimated at €48,991 in the nonambulant stage and €19,993 in the ambulant stage. Direct nonmedical costs were the main cost drivers, followed by indirect costs.

CONCLUSIONS

Our results indicate a close relation between overall disease costs and disease progression. DMD is associated with a substantial economic burden, which appears to be larger around the time ambulation is lost (10 years of age). The availability of new therapeutic options that delay disease progression, especially loss of ambulation, may prove to be highly beneficial for not only patients with DMD but also their families and society.

An Open Label Exploratory Clinical Trial Evaluating Safety and Tolerability of Once-Weekly Prednisone in Becker and Limb-Girdle Muscular Dystrophy

Background:

Glucocorticoid steroids are standard of care in Duchenne Muscular Dystrophy (DMD) to slow disease course. Use of glucocorticoids in other muscular dystrophies, including Becker (BMD) and Limb Girdle (LGMD), has been less explored. Recently, preclinical studies conducted in DMD and LGMD mouse models showed once-weekly prednisone was associated with improved muscle performance without activation of muscle atrophy genes.

Objective:

To determine safety and tolerability of once-weekly prednisone in patients with LGMD and BMD.

Methods:

We conducted an open label, exploratory single center study of of once-weekly prednisone at 0.75–1 mg/Kg in LGMD (n = 19) and BMD (n = 1) (mean age 35, range 18–60). The LGMD participants represented multiple different LGMD subtypes, and the study included ambulatory and non-ambulatory participants. Participants were assessed at baseline and 24 weeks for vital signs, blood biomarkers, and for patient-reported side effects. As secondary endpoints, functional muscle testing and body composition were measured.

Results:

Over the 24-week study, there were no significant changes in blood pressure, HgbA1C, or lipid profiles. We observed a reduction in serum creatine kinase over the study interval. Whole body DEXA scanning suggested a possible increase in lean mass and a reduction in adiposity. Functional measures suggested trends in improved muscle performance.

Conclusions:

In this single center, open label pilot study, once-weekly prednisone was safe and well tolerated. Additional investigation of once-weekly prednisone in a larger cohort and for a longer period of time is warranted.

Creatine kinase test diagnostic accuracy in neonatal screening for Duchenne Muscular Dystrophy: A systematic review

OBJECTIVES

to evaluate the accuracy of the creatine kinase test in neonatal screening for Duchenne Muscular Dystrophy.

METHODS

Investigations were carried out in six databases, gray literature and manual search. All studies and data extraction eligibility processes were carried out in paired mode. The methodological stringency of the studies was assessed using the modified QUADAS 2 tool. The performance measures of the test were calculated using the Meta-DiSc software, version 1.4.

RESULTS

11 studies were included, with a total sample of 1,416,123 newborns. The positive likelihood ratio was more than 10 in these studies. On the other hand, the negative likelihood ratio was up to 0.2 in 9/10 studies; however, when considering the upper limit of the confidence interval, only 4/10 studies showed a negative likelihood ratio less than 0.2 and in 6/11 it was greater than 0.5. Specificity was close to 1 in studies. The sensitivity was equal to or greater than 0.81 in 10/11 studies; however, when considering the reliability's minimum interval limit, only 6/10 studies showed sensitivity equal to or greater than 0.7. Ten studies were summarized on a ROC curve indicating good performance (Area under the curve = 0.9980 and Q index = 0.9846).

CONCLUSIONS

the creatine kinase test showed good accuracy in screening for cases of Duchenne Muscular Dystrophy and may be a useful alternative in the early diagnosis of the disease followed by confirmatory genetic testing.

Therapeutic Approaches for Duchenne Muscular Dystrophy: Old and New

Duchenne muscular dystrophy (DMD) is marked by pathogenic variants in the DMD gene, leading to reduced or absent dystrophin translation, muscle fiber destruction, loss of ambulation, cardiomyopathy, respiratory failure, and eventually death. Disease progression is slowed with use of prednisone or other corticosteroid agents. Gene replacement therapy, which is one of the focus points of this review, has emerged as the most promising potential treatment for DMD, though alternative RNA-based strategies have been employed for patients with specific pathogenic variants. While challenges remain, many of these novel therapeutic approaches hold promise for treating this devastating disease.

Overview of gene therapy in spinal muscular atrophy and Duchenne muscular dystrophy

Both 5q-linked spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD) are fatal monogenic neuromuscular disorders caused by loss-of-function mutations. SMA is an autosomal recessive disorder affecting motor neurons that is typically caused by homozygous whole-gene deletions of SMN1. DMD is an X-linked recessive muscle disease most often due to exon deletions, but also duplications and smaller sized variants within the DMD gene. Gene replacement therapy offers the opportunity to correct the underlying genetic defect by the introduction of a functional gene. We review the transformative work from clinical trials to United States Food and Drug Administration approval of onasemnogene abeparvovec-xioi in SMA and its application in clinical practice and the early results of microdystrophin delivery in DMD. We also review the introduction of antisense oligonucleotides to alter pre-messenger RNA splicing to promote exon inclusion (as in nusinersen in SMA) or exclusion (as in eteplirsen in DMD) into neuromuscular therapeutics. There are multiple promising novel genetically mediated therapies on the horizon, which in aggregate point towards a hopeful future for individuals with SMA and DMD.

Recent advances of glucocorticoids in the treatment of Duchenne muscular dystrophy (Review)

Duchenne muscular dystrophy (DMD) is the most common degenerative neuromuscular disease. The incidence of DMD in live births is 1/3,600-1/6,000. Although glucocorticoid-dependent medication is the mainstay treatment option for DMD, a standard treatment regimen has yet to be determined. The present review discusses the literature on the timing, methods and courses of glucocorticoid treatment for DMD. The review highlights the importance of the immediate commencement of glucocorticoid treatment following the diagnosis of DMD, with weekend-only administration being advantageous. Adherence to long-term single-glucocorticoid therapy can delay the loss of ambulation ability, and the side effects of the treatment are controllable. However, the standard medication for patients of different ages and stages of disease development, and the use of combination therapy require further investigation.

Duchenne muscular dystrophy

Duchenne muscular dystrophy is a severe, progressive, muscle-wasting disease that leads to difficulties with movement and, eventually, to the need for assisted ventilation and premature death. The disease is caused by mutations in DMD (encoding dystrophin) that abolish the production of dystrophin in muscle. Muscles without dystrophin are more sensitive to damage, resulting in progressive loss of muscle tissue and function, in addition to cardiomyopathy. Recent studies have greatly deepened our understanding of the primary and secondary pathogenetic mechanisms. Guidelines for the multidisciplinary care for Duchenne muscular dystrophy that address obtaining a genetic diagnosis and managing the various aspects of the disease have been established. In addition, a number of therapies that aim to restore the missing dystrophin protein or address secondary pathology have received regulatory approval and many others are in clinical development.

Mechanisms and Clinical Applications of Glucocorticoid Steroids in Muscular Dystrophy

Glucocorticoid steroids are widely used as immunomodulatory agents in acute and chronic conditions. Glucocorticoid steroids such as prednisone and deflazacort are recommended for treating Duchenne Muscular Dystrophy where their use prolongs ambulation and life expectancy. Despite this benefit, glucocorticoid use in Duchenne Muscular Dystrophy is also associated with significant adverse consequences including adrenal suppression, growth impairment, poor bone health and metabolic syndrome. For other forms of muscular dystrophy like the limb girdle dystrophies, glucocorticoids are not typically used. Here we review the experimental evidence supporting multiple mechanisms of glucocorticoid action in dystrophic muscle including their role in dampening inflammation and myofiber injury. We also discuss alternative dosing strategies as well as novel steroid agents that are in development and testing, with the goal to reduce adverse consequences of prolonged glucocorticoid exposure while maximizing beneficial outcomes.

Natural History of Steroid-Treated Young Boys With Duchenne Muscular Dystrophy Using the NSAA, 100m, and Timed Functional Tests

INTRODUCTION

Clinical trials targeting younger cohorts of boys with Duchenne muscular dystrophy are necessary as earlier intervention may maximize treatment effect. Boys with Duchenne muscular dystrophy often have gross motor delays very early in life, and although they gain skills, they are on a lower trajectory than typical peers. Quantifying the natural rate of motor maturation in Duchenne muscular dystrophy from an early age permits identification of deviations from the expected trajectory related to treatment effects.

METHODS

The purpose of our study was to define the natural history in boys aged from ≥3 to <8 years using the North Star Ambulatory Assessment (NSAA), 100-meter timed test (100m), 10-meter walk/run (10m), time to rise (Rise), and 4-stair climb (4SC). Assessments were completed as standard of care during regularly scheduled clinic visits.

RESULTS

One hundred sixty-two boys with DMD aged 3.1 to 7.9 years on glucocorticoids were evaluated using one or more of the following tests as appropriate for age: NSAA (N = 158; 3.1-7.9 years), 100m (N = 131; 3.4-7.9 years), 10m (N = 162; 3.1-7.9 years), Rise (N = 160; 3.1-7.9 years), and 4SC (N = 153; 3.1-7.9 years). Longitudinal data are presented by age in a subcohort (N = 64).

CONCLUSIONS

Our study documents the baseline function of boys with DMD who are being treated with corticosteroids. These data will be useful to compare ongoing and future therapeutic intervention(s) for DMD.

Pharmacotherapy of Duchenne Muscular Dystrophy

Drug development and pharmacotherapy of rare pediatric diseases have significantly expanded over the last decade, in part due to incentives and financial support provided by governments, regulators, and nonprofit foundations. Duchenne muscular dystrophy (DMD) is among the most common rare pediatric disorders, and clinical trials of therapeutic approaches have seen dramatic expansion. Pharmacotherapeutic standard of care has been limited to off-label prescription of high-dose, daily corticosteroids (prednisone, deflazacort). Deflazacort received FDA approval for DMD in 2016, although the price increases associated with formal FDA approval and the severe side effects associated with corticosteroid use have limited patient/physician uptake and insurance coverage in the USA. In Europe, EMA has given conditional marketing authorization for prescription of Translarna (a stop codon read-through drug prescribed to ~10% of DMD patients), although there is not yet evidence of clinical efficacy. The FDA awarded conditional approval to etiplirsen, an exon-skipping oligonucleotide drug, based on accelerated pathways (increased dystrophin production in patient muscle). Evidence of clinical efficacy remains the focus of post-marketing studies. There are many innovative pharmacotherapies under clinical development for DMD (Phase I, II, and III clinical trials). All are "disease modifying" in the sense that none seek to replace the full-length, normal DMD gene or dystrophin protein, but instead either seek to introduce an abnormal "Becker-like" version of the gene or protein or target pathophysiological pathways downstream of the primary defect. It is envisioned that the most significant benefit to DMD patients will be through multidrug approaches simultaneously aiming to introduce partially functional dystrophin in patient muscle while also targeting both chronic inflammation and the fibrofatty replacement of muscle.

Pulsed glucocorticoids enhance dystrophic muscle performance through epigenetic-metabolic reprogramming

In humans, chronic glucocorticoid use is associated with side effects like muscle wasting, obesity, and metabolic syndrome. Intermittent steroid dosing has been proposed in Duchenne Muscular Dystrophy patients to mitigate the side effects seen with daily steroid intake. We evaluated biomarkers from Duchenne Muscular Dystrophy patients, finding that, compared with chronic daily steroid use, weekend steroid use was associated with reduced serum insulin, free fatty acids, and branched chain amino acids, as well as reduction in fat mass despite having similar BMIs. We reasoned that intermittent prednisone administration in dystrophic mice would alter muscle epigenomic signatures, and we identified the coordinated action of the glucocorticoid receptor, KLF15 and MEF2C as mediators of a gene expression program driving metabolic reprogramming and enhanced nutrient utilization. Muscle lacking Klf15 failed to respond to intermittent steroids. Furthermore, coadministration of the histone acetyltransferase inhibitor anacardic acid with steroids in mdx mice eliminated steroid-specific epigenetic marks and abrogated the steroid response. Together, these findings indicate that intermittent, repeated exposure to glucocorticoids promotes performance in dystrophic muscle through an epigenetic program that enhances nutrient utilization.

Longitudinal natural history in young boys with Duchenne muscular dystrophy

The aim of this prospective multicentric study was to document disease progression in young boys affected by Duchenne muscular dystrophy (DMD) between age 3 and 6 years (±3 months) using the North Star Ambulatory Assessment scale. One hundred fifty-three DMD boys (573 assessments) younger than 6 years (mean: 4.68, SD: 0.84) with a genetically proven DMD diagnoses were included. Our results showed North Star Ambulatory Assessment scores progressively increased with age. The largest increase was observed between age 3 and 4 years but further increase was steadily observed until age of 6 years. Using a multiple linear regression analysis, we found that both the use of corticosteroids and the site of mutation significantly contributed to the North Star Ambulatory Assessment changes (p < 0.001). At each age point, boys on corticosteroid treatment had higher scores than corticosteroid naïve ones (p < 0.001). Similarly, patients with mutations downstream exon 44, had lower baseline scores and lower magnitude of changes compared to those with mutations located at the 5' end of the gene (p < 0,001). Very few boys achieved the age appropriate maximum score. These results provide useful information for the assessment and counselling of young DMD boys and for the design of clinical trials in this age group.

Duchenne Muscular Dystrophy Newborn Screening: Evaluation of a New GSP® Neonatal Creatine Kinase-MM Kit in a US and Danish Population

Duchenne muscular dystrophy (DMD/Duchenne) is a progressive X-linked disease and is the most common pediatric-onset form of muscular dystrophy, affecting approximately 1:5000 live male births. DNA testing for mutations in the dystrophin gene confirms the diagnosis of this disorder. This study involves assessment of screening newborns for DMD using an immunoassay for muscle-type (MM) creatine kinase (CK) isoform-the GSP Neonatal CK-MM kit. Comparisons were made with CK activity determination by fluorescence measurement. In addition, the study evaluated the effect of gestational age, age of infant at time of sampling and how stable the CK-MM was over time. This assay discriminates well between normal, unaffected and Duchenne affected populations and is suitable for Duchenne newborn screening.

Progress in treatment and newborn screening for Duchenne muscular dystrophy and spinal muscular atrophy

BACKGROUND

Advances in treatment for Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) hold promise for children with these disorders. Accurate genetic diagnosis, early in the disease process, will allow these treatments to be most effective. Newborn screening (NBS) for SMA has been recommended in the United States, and a pilot DMD NBS program is underway in Hangzhou, China.

DATA SOURCES

A PubMed search, limited to the past 5 years, was conducted to identify: (1) therapeutic advancements for DMD/SMA approved by the United States Food and Drug Administration or the European Medicine Agency and (2) The status of NBS for DMD/SMA.

RESULTS

We review the current state of approved treatments for DMD/SMA. We present recommendations regarding the future of NBS for these diseases, with a focus on the outcomes and challenges of SMA NBS in New York, USA, and the DMD NBS pilot program in Hangzhou, China.

CONCLUSIONS

Approved treatments for DMD and SMA may change the natural history of these diseases. Long-term studies of these treatments are underway. To avoid the known diagnostic delay associated with these disorders and provide optimal effectiveness of these treatments, early identification of patients through NBS will be necessary. Establishing comprehensive follow-up plans for positively identified patients will need to be in place for NBS programs to be successful.