Eteplirsen for paediatric patients with Duchenne muscular dystrophy: A pooled-analysis

Adverse events associated with eteplirsen: A disproportionality analysis using the 2016-2023 FAERS data

Background

Eteplirsen (Exondys 51) is an orphan drug approved for the treatment of Duchenne muscular dystrophy (DMD), having received accelerated approval from the U.S. Food and Drug Administration (FDA) in 2016. The primary aim of this study is to closely monitor adverse events (AEs) associated with eteplirsen and to identify emerging signals to better characterize their safety profile.

Methods

AEs due to eteplirsen usage reported from the third quarter (Q3) of 2016 to the fourth quarter (Q4) of 2023 were collected from the FDA Adverse Event Reporting System (FAERS). The role_code of AEs mainly includes primary suspect (PS), secondary suspect (SS), concomitant (C), and interaction (I). This study targeted reports with a role_cod of 'PS.' According to the FDA deduplication rule, the latest FDA_DT is selected when the CASEID is the same, and the higher PRIMARYID is selected when the CASEID and FDA_DT are the same. Disproportionality analyses, encompassing four algorithms for reporting odds ratio (ROR), proportional reporting ratio (PRR), Bayesian configuration promotion neural network (BCPNN), and multi-item gamma Poisson shrinker (MGPS), were utilized to quantify the signals of AEs associated with eteplirsen.

Results

From the FAERS database, a total of 13,205,369 reports were amassed throughout the study duration. Following the eradication of duplicates, the number of reports with eteplirsen designated as the PS amounted to 1480 encompassed 25 organ systems. Among these, "general disorders and administration site conditions," "injury, poisoning, and procedural complications," "respiratory, thoracic, and mediastinal disorders," "infections and infestations," "vascular disorders," and "product issues" met at least one of the four computational criteria. Additionally, 55 Preferred Terms (PTs) aligned with the prescribed algorithms. The median time to AEs in these patients was 903 days with an interquartile range (IQR) of 269-1575 days. Moreover, 70.04 % of AEs manifested one year or more after the initiation of treatment.

Conclusion

As an orphan drug granted accelerated approval, our study has confirmed well-known adverse drug reactions and identified potential safety issues associated with eteplirsen treatment. This has contributed to a deeper understanding of the complex interrelations between adverse reactions and the use of eteplirsen. The findings underscore the critical importance of ongoing monitoring and sustained observation to promptly detect and effectively manage AEs, thereby enhancing the overall safety and well-being of patients treated with eteplirsen for DMD.

Characteristics of Patients Receiving Novel Muscular Dystrophy Drugs in Trials vs Routine Care

Importance

The US Food and Drug Administration approved eteplirsen for Duchenne muscular dystrophy (DMD) in 2016 based on a controversial pivotal study that demonstrated a limited effect on the surrogate measure of dystrophin production. Other DMD treatments in the same class followed.

Objective

To assess how patients receiving novel DMD treatments in postapproval clinical settings compare with patients in the clinical trials.

Design, Setting, and Participants

This cross-sectional study collected data on patients who initiated 1 of 4 novel DMD treatments (eteplirsen, golodirsen, viltolarsen, and casimersen) using national claims databases of commercially insured (Merative MarketScan and Optum's Clinformatics Data Mart Database [CDM]) and Medicaid patients between September 19, 2016, and March 31, 2022. Patients were followed for 1 year after the date of first use of any novel DMD treatment. In addition, patients in pivotal DMD drug trials were identified for comparison.

Exposures

Age, sex, race and ethnicity, region, and DMD stage of patients receiving novel DMD treatment.

Main Outcome and Measures

The main outcome was health care costs and drug discontinuation as measured using descriptive statistics.

Results

A total of 223 routine care patients initiating novel DMD drugs (58 in MarketScan, 35 in CDM, and 130 in Medicaid) were identified. Among the 106 patients in the pivotal trials, the mean (SD) age was 8.5 (2.0) years (range, 4.0-13.0 years), which was younger than the mean age of patients in routine care (MarketScan: 13.7 [7.0] years [range, 1.8-33.3 years; P < .001]; CDM: 11.9 [5.7] years [range, 0.6-23.6 years; P < .001]; Medicaid: 13.4 [6.5] years [range, 1.8-46.1 years; P < .001]). The proportion of female patients identified in postapproval clinical settings was 2.9% (n = 1) in CDM (vs 34 male patients [97.1%]) and 1.5% (n = 2) in Medicaid (vs 128 male patients [98.5%]), which was not different from the pivotal trials. While nearly all patients in the pivotal trials had DMD disease stage 1 or 2 when initiating the DMD treatments (103 [97.2%]), in the postapproval clinical setting, slightly more than one-third of patients were in disease stage 3 or 4 (MarketScan, 17 [36.2%; P < .001]; CDM, 13 [41.9%; P < .001]; Medicaid, 54 [47.0%; P < .001]). The payer's cost for novel DMD treatments varied across the databases, with a mean (SD) of $634 764 ($607 101) in MarketScan, $482 749 ($582 350) in CDM, and $384 023 ($1 165 730) in Medicaid. Approximately one-third of routine care patients discontinued the treatments after approximately 7 months (mean [SD], 6.1 [4.4], 6.9 [3.9], and 7.2 [4.3] months in MarketScan, CDM, and Medicaid, respectively).

Conclusions and Relevance

These findings raise questions about the translation of DMD drug trial findings to routine care settings, with patients in routine care discontinuing the treatment within 1 year and payers incurring substantial expenses for these medications. More data are needed on whether these high costs are accompanied by corresponding clinical benefits.

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 Combined Efficacy of a Two-Year Period of Cybernic Treatment With a Wearable Cyborg Hybrid-Assistive Limb and Leuprorelin Therapy in a Patient With Spinal and Bulbar Muscular Atrophy: A Case Report

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a rare, slowly progressive, incurable, and hereditary neurodegenerative disease caused by the testosterone-dependent accumulation of pathogenic polyglutamine-expanded androgen receptor protein. After extensive review, two treatments for SBMA have recently been approved in Japan; this decision was based on the results of randomized controlled trials: First, anti-androgen therapy using leuprorelin acetate (leuprorelin), a disease-modifying drug that can inhibit the progression of dysphagia but has not yet been proved to improve gait function; second, cybernic treatment with a wearable cyborg hybrid assistive limb (HAL®) (Cyberdyne Inc. Tsukuba, Japan). The HAL is an innovative walking exercise system that has been shown to significantly improve gait function in eight neuromuscular diseases without reduction in muscle function, including SBMA. It is possible that the combination of these two approaches might yield better outcomes. However, the long-term effects of such a combined approach have yet to be clinically evaluated. Here, we describe the case of a 39-year-old male with SBMA who commenced anti-androgen therapy with leuprorelin 1 year previously; this was followed by cybernic treatment with HAL. The duration of walking exercise with HAL was 20–30 min a day in one session. Over 2 weeks, the patient underwent nine sessions (one course). The efficacy of HAL was evaluated by gait function tests before and after one course of cybernic treatment. Then, leuprorelin treatment was combined with cybernic sessions every 2 months for 2 years (13 courses in total). Walking ability, as evaluated by the 2-min walk test, improved by 20.3% in the first course and peaked 10 months after the commencement of combined therapy (a 59.0% improvement). Walking function was maintained throughout the period. Generally, SBMA is characterized by moderately increased serum levels of creatine kinase (CK), reflecting neuromuscular damage; interestingly, the patient's CK levels decreased dramatically with combined therapy, indicating remarkable functional improvement. Long-term combined therapy improved the patient's gait function with a steady reduction in CK levels. The combination of leuprorelin with cybernic treatment can, therefore, improve and maintain gait function without damaging the motor unit and may also suppress disease progression.

Long-Term Protective Effect of Human Dystrophin Expressing Chimeric (DEC) Cell Therapy on Amelioration of Function of Cardiac, Respiratory and Skeletal Muscles in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a lethal disease caused by mutations in dystrophin encoding gene, causing progressive degeneration of cardiac, respiratory, and skeletal muscles leading to premature death due to cardiac and respiratory failure. Currently, there is no cure for DMD. Therefore, novel therapeutic approaches are needed for DMD patients.

We have previously reported functional improvements which correlated with increased dystrophin expression following administration of dystrophin expressing chimeric (DEC) cells of myoblast origin to the mdx mouse models of DMD.

In the current study, we confirmed dose-dependent protective effect of human DEC therapy created from myoblasts of normal and DMD-affected donors, on restoration of dystrophin expression and amelioration of cardiac, respiratory, and skeletal muscle function at 180 days after systemic-intraosseous DEC administration to mdx/scid mouse model of DMD. Functional improvements included maintenance of ejection fraction and fractional shortening levels on echocardiography, reduced enhanced pause and expiration time on plethysmography and improved grip strength and maximum stretch induced contraction of skeletal muscles. Improved function was associated with amelioration of mdx muscle pathology revealed by reduced muscle fibrosis, reduced inflammation and improved muscle morphology confirmed by reduced number of centrally nucleated fibers and normalization of muscle fiber diameters. Our findings confirm the long-term systemic effect of DEC therapy in the most severely affected by DMD organs including heart, diaphragm, and long skeletal muscles.

These encouraging preclinical data introduces human DEC as a novel therapeutic modality of Advanced Therapy Medicinal Product (ATMP) with the potential to improve or halt the progression of DMD and enhance quality of life of DMD patients.

Cybernic treatment with wearable cyborg Hybrid Assistive Limb (HAL) improves ambulatory function in patients with slowly progressive rare neuromuscular diseases: a multicentre, randomised, controlled crossover trial for efficacy and safety (NCY-3001)

Background

Rare neuromuscular diseases such as spinal muscular atrophy, spinal bulbar muscular atrophy, muscular dystrophy, Charcot-Marie-Tooth disease, distal myopathy, sporadic inclusion body myositis, congenital myopathy, and amyotrophic lateral sclerosis lead to incurable amyotrophy and consequent loss of ambulation. Thus far, no therapeutic approaches have been successful in recovering the ambulatory ability. Thus, the aim of this trial was to evaluate the efficacy and safety of cybernic treatment with a wearable cyborg Hybrid Assistive Limb (HAL, Lower Limb Type) in improving the ambulatory function in those patients.

Results

We conducted an open-label, randomised, controlled crossover trial to test HAL at nine hospitals between March 6, 2013 and August 8, 2014. Eligible patients were older than 18 years and had a diagnosis of neuromuscular disease as specified above. They were unable to walk for 10 m independently and had neither respiratory failure nor rapid deterioration in gait. The primary endpoint was the distance passed during a two-minute walk test (2MWT). The secondary endpoints were walking speed, cadence, and step length during the 10-m walk test (10MWT), muscle strength by manual muscle testing (MMT), and a series of functional measures. Adverse events and failures/problems/errors with HAL were also evaluated. Thirty patients were randomly assigned to groups A or B, with each group of 15 receiving both treatments in a crossover design. The efficacy of a 40-min walking program performed nine times was compared between HAL plus a hoist and a hoist only. The final analysis included 13 and 11 patients in groups A and B, respectively. Cybernic treatment with HAL resulted in a 10.066% significantly improved distance in 2MWT (95% confidence interval, 0.667–19.464; p = 0.0369) compared with the hoist only treatment. Among the secondary endpoints, the total scores of MMT and cadence at 10MWT were the only ones that showed significant improvement. The only adverse effects were slight to mild myalgia, back pain, and contact skin troubles, which were easily remedied.

Conclusions

HAL is a new treatment device for walking exercise, proven to be more effective than the conventional method in patients with incurable neuromuscular diseases.

Trial registration: JMACTR, JMA-IIA00156

Restoring Protein Expression in Neuromuscular Conditions: A Review Assessing the Current State of Exon Skipping/Inclusion and Gene Therapies for Duchenne Muscular Dystrophy and Spinal Muscular Atrophy

The debilitating neuromuscular disorders Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA), which harm 1 in 5000 newborn males and 1 in 11,000 newborns, respectively, are marked by progressive muscle wasting among other complications. While DMD causes generalized muscle weakness due to the absence of the dystrophin protein, SMA patients generally face motor neuron degeneration because of the lack of the survival motor neuron (SMN) protein. Many of the most promising therapies for both conditions restore the absent proteins dystrophin and SMN. Antisense oligonucleotide-mediated exon skipping and inclusion therapies are advancing clinically with the approved DMD therapies casimersen, eteplirsen, golodirsen, and viltolarsen, and the SMA therapy nusinersen. Existing antisense therapies focus on skeletal muscle for DMD and motor neurons for SMA, respectively. Through innovative techniques, such as peptide conjugation and multi-exon skipping, these therapies could be optimized for efficacy and applicability. By contrast, gene replacement therapy is administered only once to patients during treatment. Currently, only onasemnogene abeparvovec for SMA has been approved. Safety shortcomings remain a major challenge for gene therapy. Nevertheless, gene therapy for DMD has strong potential to restore dystrophin expression in patients. In light of promising functional improvements, antisense and gene therapies stand poised to elevate the lives of patients with DMD and SMA.

Cholesterol metabolism is a potential therapeutic target in Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a lethal muscle disease detected in approximately 1:5000 male births. DMD is caused by mutations in the DMD gene, encoding a critical protein that links the cytoskeleton and the extracellular matrix in skeletal and cardiac muscles. The primary consequence of the disrupted link between the extracellular matrix and the myofibre actin cytoskeleton is thought to involve sarcolemma destabilization, perturbation of Ca2+ homeostasis, activation of proteases, mitochondrial damage, and tissue degeneration. A recently emphasized secondary aspect of the dystrophic process is a progressive metabolic change of the dystrophic tissue; however, the mechanism and nature of the metabolic dysregulation are yet poorly understood. In this study, we characterized a molecular mechanism of metabolic perturbation in DMD.

METHODS

We sequenced plasma miRNA in a DMD cohort, comprising 54 DMD patients treated or not by glucocorticoid, compared with 27 healthy controls, in three groups of the ages of 4-8, 8-12, and 12-20 years. We developed an original approach for the biological interpretation of miRNA dysregulation and produced a novel hypothesis concerning metabolic perturbation in DMD. We used the mdx mouse model for DMD for the investigation of this hypothesis.

RESULTS

We identified 96 dysregulated miRNAs (adjusted P-value <0.1), of which 74 were up-regulated and 22 were down-regulated in DMD. We confirmed the dysregulation in DMD of Dystro-miRs, Cardio-miRs, and a large number of the DLK1-DIO3 miRNAs. We also identified numerous dysregulated miRNAs yet unreported in DMD. Bioinformatics analysis of both target and host genes for dysregulated miRNAs predicted that lipid metabolism might be a critical metabolic perturbation in DMD. Investigation of skeletal muscles of the mdx mouse uncovered dysregulation of transcription factors of cholesterol and fatty acid metabolism (SREBP-1 and SREBP-2), perturbation of the mevalonate pathway, and the accumulation of cholesterol in the dystrophic muscles. Elevated cholesterol level was also found in muscle biopsies of DMD patients. Treatment of mdx mice with Simvastatin, a cholesterol-reducing agent, normalized these perturbations and partially restored the dystrophic parameters.

CONCLUSIONS

This investigation supports that cholesterol metabolism and the mevalonate pathway are potential therapeutic targets in DMD.

From traditional pharmacological towards nucleic acid-based therapies for cardiovascular diseases

Nucleic acid-based therapeutics are currently developed at large scale for prevention and management of cardiovascular diseases (CVDs), since: (i) genetic studies have highlighted novel therapeutic targets suggested to be causal for CVD; (ii) there is a substantial recent progress in delivery, efficacy, and safety of nucleic acid-based therapies; (iii) they enable effective modulation of therapeutic targets that cannot be sufficiently or optimally addressed using traditional small molecule drugs or antibodies. Nucleic acid-based therapeutics include (i) RNA-targeted therapeutics for gene silencing; (ii) microRNA-modulating and epigenetic therapies; (iii) gene therapies; and (iv) genome-editing approaches (e.g. CRISPR-Cas-based): (i) RNA-targeted therapeutics: several large-scale clinical development programmes, using antisense oligonucleotides (ASO) or short interfering RNA (siRNA) therapeutics for prevention and management of CVD have been initiated. These include ASO and/or siRNA molecules to lower apolipoprotein (a) [apo(a)], proprotein convertase subtilisin/kexin type 9 (PCSK9), apoCIII, ANGPTL3, or transthyretin (TTR) for prevention and treatment of patients with atherosclerotic CVD or TTR amyloidosis. (ii) MicroRNA-modulating and epigenetic therapies: novel potential therapeutic targets are continually arising from human non-coding genome and epigenetic research. First microRNA-based therapeutics or therapies targeting epigenetic regulatory pathways are in clinical studies. (iii) Gene therapies: EMA/FDA have approved gene therapies for non-cardiac monogenic diseases and LDL receptor gene therapy is currently being examined in patients with homozygous hypercholesterolaemia. In experimental studies, gene therapy has significantly improved cardiac function in heart failure animal models. (iv) Genome editing approaches: these technologies, such as using CRISPR-Cas, have proven powerful in stem cells, however, important challenges are remaining, e.g. low rates of homology-directed repair in somatic cells such as cardiomyocytes. In summary, RNA-targeted therapies (e.g. apo(a)-ASO and PCSK9-siRNA) are now in large-scale clinical outcome trials and will most likely become a novel effective and safe therapeutic option for CVD in the near future. MicroRNA-modulating, epigenetic, and gene therapies are tested in early clinical studies for CVD. CRISPR-Cas-mediated genome editing is highly effective in stem cells, but major challenges are remaining in somatic cells, however, this field is rapidly advancing.

Developing DMD therapeutics: a review of the effectiveness of small molecules, stop-codon readthrough, dystrophin gene replacement, and exon-skipping therapies

INTRODUCTION

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin (DMD) gene. Most patients die from respiratory failure or cardiomyopathy. There are significant unmet needs for treatments for DMD as the standard of care is principally limited to symptom relief through treatments including steroids.

AREAS COVERED

This review summarizes safety and efficacy in promising areas of DMD therapeutics - small molecules, stop codon readthrough, gene replacement, and exon skipping - under clinical examination from 2015-2020 as demonstrated in the NIH Clinical Trials and PubMed search engines.

EXPERT OPINION

Currently, steroids persist as the most accessible medicine for DMD. Stop-codon readthrough, gene replacement, and exon-skipping therapies all aim to restore dystrophin expression. Of these strategies, gene replacement therapy has recently gained momentum while exon-skipping retains great traction. The  FDA approval of three exon-skipping antisense oligonucleotides illustrate this regulatory momentum, though the effectiveness and sequence design of eteplirsen remain controversial. Cell-penetrating peptides promise to more efficaciously treat DMD-related cardiomyopathy.The recent success of antisense therapies, however, poses major regulatory challenges. To fully realize the benefits of exon-skipping, including cocktail oligonucleotide-mediated multiple exon-skipping and oligonucleotide drugs for very rare mutations, regulatory challenges need to be addressed in coordination with scientific advances.

Natural products, PGC-1 , and Duchenne muscular dystrophy

Peroxisome proliferator-activated receptor γ (PPARγ) is a transcriptional coactivator that binds to a diverse range of transcription factors. PPARγ coactivator 1 (PGC-1) coactivators possess an extensive range of biological effects in different tissues, and play a key part in the regulation of the oxidative metabolism, consequently modulating the production of reactive oxygen species, autophagy, and mitochondrial biogenesis. Owing to these findings, a large body of studies, aiming to establish the role of PGC-1 in the neuromuscular system, has shown that PGC-1 could be a promising target for therapies targeting neuromuscular diseases. Among these, some evidence has shown that various signaling pathways linked to PGC-1α are deregulated in muscular dystrophy, leading to a reduced capacity for mitochondrial oxidative phosphorylation and increased reactive oxygen species (ROS) production. In the light of these results, any intervention aimed at activating PGC-1 could contribute towards ameliorating the progression of muscular dystrophies. PGC-1α is influenced by different patho-physiological/pharmacological stimuli. Natural products have been reported to display modulatory effects on PPARγ activation with fewer side effects in comparison to synthetic drugs. Taken together, this review summarizes the current knowledge on Duchenne muscular dystrophy, focusing on the potential effects of natural compounds, acting as regulators of PGC-1α.

Recent Advances in the Treatment of Huntington's Disease: Targeting DNA and RNA

Huntington's disease is a dominantly inherited neurodegenerative disease caused by an unstable expanded trinucleotide repeat at the short end of the fourth chromosome. Central nervous system pathology begins in the striatum, eventually affecting the entire brain and occurs consequent to multiple intracellular derangements. The proximate cause is a mutant protein with an elongated polyglutamine tract. Pharmacological approaches targeting multiple domains of intracellular functions have universally been disappointing. However, recent developments in gene therapy, including antisense oligonucleotides, small interfering RNAs, and gene editing are bringing new hope to the Huntington's community. This review discusses the promises and challenges of these new potential treatments.

Therapies that are available and under development for Duchenne muscular dystrophy: What about lung function?

BACKGROUND

Respiratory failure is the principal source of morbidity and mortality among patients with Duchenne muscular dystrophy exerting a negative influence on their total quality of life. The aim of this review is to provide systematically current literature evidence about the effects of different treatment options (available or under development) for Duchenne muscular dystrophy on the pulmonary function of these patients.

METHODS

A comprehensive search was undertaken using multiple health-related databases, while two independent reviewers assessed the eligibility of studies. A third person addressed any disagreements between reviewers. The quality of the methodology of the included studies was also assessed.

RESULTS

A total of 19 original research papers (nine evaluating the role of steroids, six idebenone, three eteplirsen, one stem-cell therapy, and one ataluren) were found to fulfill our selection criteria with the majority of them (14 of 19) being prospective studies, not always including a control group. Endpoints mainly used in these studies were values of pulmonary function tests. Current and under development treatments proved to be safe and no significant adverse events were reported. A beneficial impact on pulmonary function was described by authors in the majority of these studies. The principal effect was slowing of lung disease progress, as expressed by spirometric values. However, the risk of bias was introduced in many of the above studies, while high heterogeneity in terms of treatment protocols and outcome measures limits the comparability of the results.

CONCLUSION

Glucocorticoids remain the best-studied pharmacologic therapy for Duchenne muscular dystrophy and very likely delay the expected decline in lung function. With regard to new therapeutic agents, initial study results are encouraging. However, larger clinical trials are needed that minimize the risk of study bias, optimize the comparability of treatment groups, examine clinically meaningful pulmonary outcome measures, and include long-term follow up.

Peptide-conjugate antisense based splice-correction for Duchenne muscular dystrophy and other neuromuscular diseases

Duchenne muscular dystrophy (DMD) is an X-linked disorder characterized by progressive muscle degeneration, caused by the absence of dystrophin. Exon skipping by antisense oligonucleotides (ASOs) has recently gained recognition as therapeutic approach in DMD. Conjugation of a peptide to the phosphorodiamidate morpholino backbone (PMO) of ASOs generated the peptide-conjugated PMOs (PPMOs) that exhibit a dramatically improved pharmacokinetic profile. When tested in animal models, PPMOs demonstrate effective exon skipping in target muscles and prolonged duration of dystrophin restoration after a treatment regime. Herein we summarize the main pathophysiological features of DMD and the emergence of PPMOs as promising exon skipping agents aiming to rescue defective gene expression in DMD and other neuromuscular diseases. The listed PPMO laboratory findings correspond to latest trends in the field and highlight the obstacles that must be overcome prior to translating the animal-based research into clinical trials tailored to the needs of patients suffering from neuromuscular diseases.

A new era in the management of Duchenne muscular dystrophy

The management of Duchenne muscular dystrophy (DMD) has changed considerably over the last few decades. Standards of care have recently been updated, based on systematic reviews of the literature and structured, case-based consensus discussions of experts. Besides addressing muscular function, these recommendations cover most areas of organ involvement and psychosocial issues. Studies employing animal models investigating basic disease mechanisms have increased considerably. Development of valid functional outcome measures enabled high-evidence, clinical trials in males with DMD. Stop codon readthrough with ataluren has revealed some effect in patients with moderate disability and has been approved for males with suitable mutations who are still ambulant. Exon 51 skipping with eteplirsen demonstrated a structural and functional effect in a small group of patients and received restricted approval in the USA. Further trials investigating a broad range of mechanisms are underway. However, much more work is needed to develop more active treatments that stop disease progression. Likewise, the distribution of complex and expensive therapies to underprivileged patients and those in poorer regions must be improved. WHAT THIS PAPER ADDS: Updated standards of care covering most clinical aspects of Duchenne muscular dystrophy (DMD) are available. Adequately controlled clinical trials have allowed initial approval of disease-modifying drugs for small groups of patients. Scientific, economic, and political efforts are needed to make effective therapies available more quickly. Effective therapies should be made available more quickly to patients in low-income regions.

Erythroid-Progenitor-Targeted Gene Therapy Using Bifunctional TFR1 Ligand-Peptides in Human Erythropoietic Protoporphyria

Erythropoietic protoporphyria (EPP) is a hereditary disease characterized by a deficiency in ferrochelatase (FECH) activity. FECH activity is responsible for the accumulation of protoporphyrin IX (PPIX). Without etiopathogenic treatment, EPP manifests as severe photosensitivity. 95% of affected individuals present a hypomorphic FECH allele trans to a loss-of-function (LOF) FECH mutation, resulting in a reduction in FECH activity in erythroblasts below a critical threshold. The hypomorphic allele promotes the use of a cryptic acceptor splice site, generating an aberrant FECH mRNA, which is responsible for the reduced level of wild-type FECH mRNA and, ultimately, FECH activity. We have previously identified an antisense oligonucleotide (AON), AON-V1 (V1), that redirects splicing to the physiological acceptor site and reduces the accumulation of PPIX. Here, we developed a specific strategy that uses transferrin receptor 1 (TRF1) as a Trojan horse to deliver V1 to erythroid progenitors. We designed a bifunctional peptide (P₁-9R) including a TFR1-targeting peptide coupled to a nine-arginine cell-penetrating peptide (CPP) that facilitates the release of the AON from TFR1 in endosomal vesicles. We demonstrated that the P₁-9R/V1 nanocomplex promotes the efficient and prolonged redirection of splicing towards the physiological splice site and subsequent normalization of WT FECH mRNA and protein levels. Finally, the P₁-9R/V1 nanocomplex increases WT FECH mRNA production and significantly decreases PPIX accumulation in primary cultures of differentiating erythroid progenitors from an overt EPP-affected individual. P₁-9R is a method designed to target erythroid progenitors and represents a potentially powerful tool for the in vivo delivery of therapeutic DNA in many erythroid disorders.

Clinical management of Duchenne muscular dystrophy: the state of the art

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a devastating, progressive neuromuscular disorder for which there is no cure. As the dystrophin gene is located on the X chromosome, DMD occurs predominately in males. DMD is caused by a lack of functional dystrophin protein resulting from mutations in the 2.2-Mb DMD gene, whichdisrupts the reading frame. Care considerations for DMD advocate a coordinated, multidisciplinary approach to the management of DMD in order to optimize management of the primary manifestations of DMD as well as any secondary complications that may arise.

METHODS

This review provides an overview of the multidisciplinary clinical management of DMD with regard to the respiratory, cardiology, orthopedic, and nutritional needs of patients with DMD. Recent advances in novel disease-modifying treatments for DMD are also discussed with specific reference to exon skipping and suppression of premature stop codons as promising genetic therapies.

RESULTS

The combination of multidisciplinary clinical management alongside novel gene therapiesoffers physicians a powerful armamentarium for the treatment of DMD.

Ambulatory function in spinal muscular atrophy: Age-related patterns of progression

Individuals with spinal muscular atrophy (SMA) type 3 are able to walk but they have weakness, gait impairments and fatigue. Our primary study objective was to examine longitudinal changes in the six-minute walk test (6MWT) and to evaluate whether age and SMA type 3 subtype are associated with decline in ambulatory function. Data from three prospective natural history studies were used. Seventy-three participants who performed the 6MWT more than once, at least 6 months apart, were included; follow-up ranged from 0.5-9 years. Only data from patients who completed the 6MWT were included. The mean age of the participants was 13.5 years (range 2.6-49.1), with 52 having disease onset before age 3 years (type 3A). At baseline, type 3A participants walked a shorter distance on average (257.1 m) than type 3B participants (390.2 m) (difference = 133.1 m, 95% confidence interval [CI] 71.8-194.3, p < 0.001). Distance walked was weakly associated with age (r = 0.25, p = 0.04). Linear mixed effects models were used to estimate the mean annual rate of change. The overall mean rate of change was -7.8 m/year (95% CI -13.6 --2.0, p = 0.009) and this did not differ by subtype (type 3A: -8.5 m/year, type 3B: -6.6 m/year, p = 0.78), but it did differ by age group (< 6: 9.8 m/year; 6-10: -7.9 m/year; 11-19: -20.8 m/year; ≥ 20: -9.7 m/year; p = 0.005). Our results showed an overall decline on the 6MWT over time, but different trajectories were observed depending on age. Young ambulant SMA patients gain function but in adolescence, patients lose function. Future clinical trials in ambulant SMA patients should consider in their design the different trajectories of ambulatory function over time, based on age.