Clinical Manifestations and Overall Management Strategies for Duchenne Muscular Dystrophy

Hematopoietic Prostaglandin D Synthase Is Increased in Mast Cells and Pericytes in Autopsy Myocardial Specimens from Patients with Duchenne Muscular Dystrophy

The leading cause of death for patients with Duchenne muscular dystrophy (DMD), a progressive muscle disease, is heart failure. Prostaglandin (PG) D2, a physiologically active fatty acid, is synthesized from the precursor PGH2 by hematopoietic prostaglandin D synthase (HPGDS). Using a DMD animal model (mdx mice), we previously found that HPGDS expression is increased not only in injured muscle but also in the heart. Moreover, HPGDS inhibitors can slow the progression of muscle injury and cardiomyopathy. However, the location of HPGDS in the heart is still unknown. Thus, this study investigated HPGDS expression in autopsy myocardial samples from DMD patients. We confirmed the presence of fibrosis, a characteristic phenotype of DMD, in the autopsy myocardial sections. Additionally, HPGDS was expressed in mast cells, pericytes, and myeloid cells of the myocardial specimens but not in the myocardium. Compared with the non-DMD group, the DMD group showed increased HPGDS expression in mast cells and pericytes. Our findings confirm the possibility of using HPGDS inhibitor therapy to suppress PGD2 production to treat skeletal muscle disorders and cardiomyopathy. It thus provides significant insights for developing therapeutic drugs for DMD.

Duchenne muscular dystrophy: disease mechanism and therapeutic strategies

Duchenne muscular dystrophy (DMD) is a severe, progressive, and ultimately fatal disease of skeletal muscle wasting, respiratory insufficiency, and cardiomyopathy. The identification of the dystrophin gene as central to DMD pathogenesis has led to the understanding of the muscle membrane and the proteins involved in membrane stability as the focal point of the disease. The lessons learned from decades of research in human genetics, biochemistry, and physiology have culminated in establishing the myriad functionalities of dystrophin in striated muscle biology. Here, we review the pathophysiological basis of DMD and discuss recent progress toward the development of therapeutic strategies for DMD that are currently close to or are in human clinical trials. The first section of the review focuses on DMD and the mechanisms contributing to membrane instability, inflammation, and fibrosis. The second section discusses therapeutic strategies currently used to treat DMD. This includes a focus on outlining the strengths and limitations of approaches directed at correcting the genetic defect through dystrophin gene replacement, modification, repair, and/or a range of dystrophin-independent approaches. The final section highlights the different therapeutic strategies for DMD currently in clinical trials.

Longitudinal study of multi-parameter quantitative magnetic resonance imaging in Duchenne muscular dystrophy: hyperresponsiveness of gluteus maximus and detection of subclinical disease progression in functionally stable patients

OBJECTIVE

To describe the disease progression of Duchenne muscular dystrophy (DMD) in the pelvic and thigh muscles over 1-year using multiple-parameter quantitative magnetic resonance imaging (qMRI), and to determine the most responsive muscle and predict subclinical disease progression in functionally stable patients.

METHODS

Fifty-four DMD patients (mean age 8.9 ± 2.5, range 5-15 years) completed baseline and 1-year follow-up qMRI examinations/biomarkers [3-point Dixon/fat fraction (FF); T1 mapping/T1; T2 mapping/T2]. Meanwhile, clinical assessments [NorthStar ambulatory assessment (NSAA) score] and timed function tests were performed in DMD patients. Twenty-four healthy male controls (range 5-15 years) accomplished baseline qMRI examinations. Group differences were compared using the Wilcoxon test. The standardized response mean (SRM) was taken as the responsiveness to the disease progression index.

RESULTS

FF, T1, and T2 in all DMD age subgroups changed significantly over 1-year (P < 0.05). Even in functionally stable patients (NSAA score increased, unchanged, or decreased by 1-point) over 1-year, significant increases in FF and T2 and decreases in T1 were observed in gluteus maximus (GMa), gluteus medius, vastus lateralis, and adductor magnus (P < 0.05). Overall, the SRM of FF, T1, and T2 was all the highest in GMa, which were 1.25, - 0.92, and 0.93, respectively.

CONCLUSIONS

qMRI biomarkers are responsive to disease progression and can also detect subclinical disease progression in functionally stable DMD patients over 1-year. GMa is the most responsive to disease progression of all the muscles analyzed.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ( http://www.chictr.org.cn/index.aspx ) ChiCTR1800018340, 09/12/2018, prospectively registered.

Utilization of T1-Mapping for the pelvic and thigh muscles in Duchenne Muscular Dystrophy: a quantitative biomarker for disease involvement and correlation with clinical assessments

BACKGROUND

Little is known about the disease distribution and severity detected by T1-mapping in Duchenne muscular dystrophy (DMD). Furthermore, the correlation between skeletal muscle T1-values and clinical assessments is less studied. Hence, the purposes of our study are to investigate quantitative T1-mapping in detecting the degree of disease involvement by detailed analyzing the hip and thigh muscle, future exploring the predicting value of T1-mapping for the clinical status of DMD.

METHODS

Ninety-two DMD patients were included. Grading fat infiltration and measuring the T1-values of 19 pelvic and thigh muscles (right side) in axial T1-weighted images (T1WI) and T1-maps, respectively, the disease distribution and severity were evaluated and compared. Clinical assessments included age, height, weight, BMI, wheelchair use, timed functional tests, NorthStar ambulatory assessment (NSAA) score, serum creatine kinase (CK) level. Correlation analysis were performed between the muscle T1-value and clinical assessments. Multiple linear regression analysis was conducted for the independent association of T1-value and motor function.

RESULTS

The gluteus maximus had the lowest T1-value, and the gracilis had the highest T1-value. T1-value decreased as the grade of fat infiltration increased scored by T1WI (P < 0.001). The decreasing of T1-values was correlated with the increase of age, height, weight, wheelchair use, and timed functional tests (P < 0.05). T1-value correlated with NSAA (r = 0.232-0.721, P < 0.05) and CK (r = 0.208-0.491, P < 0.05) positively. T1-value of gluteus maximus, tensor fascia, vastus lateralis, vastus intermedius, vastus medialis, and adductor magnus was independently associated with the clinical motor function tests (P < 0.05). Interclass correlation coefficient (ICC) analysis and Bland-Altman plots showed excellent inter-rater reliability of T1-value region of interest (ROI) measurements.

CONCLUSION

T1-mapping can be used as a quantitative biomarker for disease involvement, further assessing the disease severity and predicting motor function in DMD.

Delays in pulmonary decline in eteplirsen-treated patients with Duchenne muscular dystrophy

INTRODUCTION/AIMS

Pulmonary decline is an important issue in patients with Duchenne muscular dystrophy (DMD). Eteplirsen is a US-approved treatment for patients with DMD and exon 51 skip-amenable mutations. Previous analyses have shown that eteplirsen is associated with statistically significant attenuation of pulmonary decline. This study evaluates the effect of eteplirsen treatment from newly available data sources on pulmonary function over time in patients with DMD.

METHODS

This study uses a post hoc pooled analysis to compare the percentage of predicted forced vital capacity (FVC%p) and projected time to pulmonary function milestones in patients with DMD and exon 51 skip-amenable mutations receiving eteplirsen (Studies 204 and 301) or standard of care (SoC; Cooperative International Neuromuscular Research Group Duchenne Natural History Study). A mixed model for repeated measures framework was applied to evaluate the impact of eteplirsen.

RESULTS

An average annual rate of FVC%p decline for eteplirsen-treated patients was estimated to be 3.47%, which was a statistically significant attenuation from the 5.95% rate of decline estimated in SoC patients (P = 0.0001). Using linear extrapolations of the model-estimated decline in FVC%p, the attenuation in FVC%p decline for eteplirsen-treated patients corresponded to a delay of 5.72 years in time to needing continuous ventilation, 3.31 years in time to needing nighttime ventilation, and 2.11 years in time to needing a cough assist device compared with SoC patients.

DISCUSSION

The attenuation of FVC%p decline suggests that eteplirsen-treated patients experienced statistically significant and clinically meaningful attenuations in pulmonary decline compared with SoC patients. This article is protected by copyright. All rights reserved.

Case Report: Identification of Maternal Low-Level Mosaicism in the Dystrophin Gene by Droplet Digital Polymerase Chain Reaction

Germline mosaicism should be suspected when the same de novo mutations are identified in a second pregnancy with asymptomatic parents. Our study aims to find a feasible approach to reveal the existence of germline mosaicism. Multiplex Ligation-dependent Probe Amplification was performed on a Duchenne muscular dystrophy affected pedigree to detect deletion mutations. Then gap-polymerase chain reaction was performed to amplify the breakpoints junction sequence. Droplet digital polymerase chain reaction was utilized to identify the mutation frequencies in healthy parents. The same deletion in the exon 51 of the dystrophin gene, which was 50,035 bp in size, was detected in the proband and the fetus but not in their parents. Droplet digital polymerase chain reaction analysis of peripheral blood samples revealed mutant alleles of 3.53% in maternal blood cells. We here report a case of maternal low-level mosaicism confirmed by droplet digital polymerase chain reaction in peripheral blood samples, which reveals the existence of germline mosaicism. Gap-polymerase chain reaction combined with droplet digital polymerase chain reaction provide insights into the detection of germline mosaicism.

PMO-based let-7c site blocking oligonucleotide (SBO) mediated utrophin upregulation in mdx mice, a therapeutic approach for Duchenne muscular dystrophy (DMD)

Upregulation of utrophin, a dystrophin related protein, is considered a promising therapeutic approach for Duchenne muscular dystrophy (DMD). Utrophin expression is repressed at the post-transcriptional level by a set of miRNAs, among which let-7c is evolutionarily highly conserved. We designed PMO-based SBOs complementary to the let-7c binding site in UTRN 3′UTR, with the goal of inhibiting let-7c interaction with UTRN mRNA and thus upregulating utrophin. We used the C2C12UTRN5′luc3′ reporter cell line in which the 5′- and 3′-UTRs of human UTRN sequences flank luciferase, for reporter assays and the C2C12 cell line for utrophin western blots, to independently evaluate the site blocking efficiency of a series of let-7c PMOs in vitro. Treatment of one-month old mdx mice with the most effective let-7c PMO (i.e. S56) resulted in ca. two-fold higher utrophin protein expression in skeletal muscles and the improvement in dystrophic pathophysiology in mdx mice, in vivo. In summary, we show that PMO-based let-7c SBO has potential applicability for upregulating utrophin expression as a therapeutic approach for DMD.

The exploration of aza-quinolines as hematopoietic prostaglandin D synthase (H-PGDS) inhibitors with low brain exposure

GlaxoSmithKline and Astex Pharmaceuticals recently disclosed the discovery of the potent H-PGDS inhibitor GSK2894631A 1a (IC₅₀ = 9.9 nM) as part of a fragment-based drug discovery collaboration with Astex Pharmaceuticals. This molecule exhibited good murine pharmacokinetics, allowing it to be utilized to explore H-PGDS pharmacology in vivo. Yet, with prolonged dosing at higher concentrations, 1a induced CNS toxicity. Looking to attenuate brain penetration in this series, aza-quinolines, were prepared with the intent of increasing polar surface area. Nitrogen substitutions at the 6- and 8-positions of the quinoline were discovered to be tolerated by the enzyme. Subsequent structure activity studies in these aza-quinoline scaffolds led to the identification of 1,8-naphthyridine 1y (IC₅₀ = 9.4 nM) as a potent peripherally restricted H-PGDS inhibitor. Compound 1y is efficacious in four in vivo inflammatory models and exhibits no CNS toxicity.

Genotype and age at diagnosis in Thai boys with Duchenne muscular dystrophy (DMD)

Gene-based therapy is a treatment for Duchenne muscular dystrophy (DMD) has become lately available; limited use for specific of mutation and percentages of the patients. Diagnosis in Thailand is made by muscle biopsy or multiplex ligation-dependent probe amplification (MLPA). Appropriate treatment in developing countries is difficult because gene sequencing is expensive and has limited availability. We aimed to identify the clinical and genetic characteristics of Thai DMD. Patients aged 0-22 years were recruited from the pediatric neuromuscular clinic of Siriraj Hospital during 2017-2019. Ninety-four charts were reviewed for clinical and laboratory data. Patients with negative MLPA who underwent next generation sequencing were consented. The mean age at onset and diagnosis was 4 and 7 years, respectively. Approximately 70% of patients had loss of ambulation by the mean age of 9.6 ± 1.8 years. Eighty percent were treated with glucocorticoids. Genetic testing was performed in 70 patients. Molecular analysis revealed mutations in 90% of cases, including exon deletions in 48.57%, nonsense mutations in 20%, frameshift mutations in 12.86%, splice site in 7.14%, exon duplications in 5.71%, and in-frame deletion in 2.86%. Gene sequencing should be performed because baseline genetic mutation data is essential for gene-based therapies that will become available in the future.

Genome Editing-Mediated Utrophin Upregulation in Duchenne Muscular Dystrophy Stem Cells

Utrophin upregulation is considered a promising therapeutic strategy for Duchenne muscular dystrophy (DMD). A number of microRNAs (miRNAs) post-transcriptionally regulate utrophin expression by binding their cognate sites in the 3′ UTR. Previously we have shown that miRNA: UTRN repression can be alleviated using miRNA let-7c site blocking oligonucleotides (SBOs) to achieve utrophin upregulation and functional improvement in mdx mice. Here, we used CRISPR/Cas9-mediated genome editing to delete five miRNA binding sites (miR-150, miR-296-5p, miR-133b, let-7c, miR-196b) clustered in a 500 bp inhibitory miRNA target region (IMTR) within the UTRN 3′ UTR, for achieving higher expression of endogenous utrophin. Deleting the UTRN IMTR in DMD patient-derived human induced pluripotent stem cells (DMD-hiPSCs) resulted in ca. 2-fold higher levels of utrophin protein. Differentiation of the UTRN edited DMD-hiPSCs (UTRNΔIMTR) by MyoD overexpression resulted in increased sarcolemmal α-sarcoglycan staining consistent with improved dystrophin glycoprotein complex (DGC) restoration. These results demonstrate that CRISPR/Cas9-based UTRN genome editing offers a novel utrophin upregulation therapeutic strategy applicable to all DMD patients, irrespective of the dystrophin mutation status.

Alpha-1 Adrenergic-Antagonist Use Increases the Risk of Sleep Apnea: A Nationwide Population-Based Cohort Study

STUDY OBJECTIVES

Decreased upper-airway muscle responsiveness is one of the major phenotypes of obstructive sleep apnea. Use of α1-adrenergic antagonists is correlated with decreased muscle responsiveness in animal studies, but this association has not yet been demonstrated in humans. This study examined whether use of α1-adrenergic antagonists is an independent risk factor for sleep apnea in humans.

METHODS

Data for this retrospective cohort study were obtained from the National Health Insurance Research Database from Taiwan. Between 2000 and 2012, 25,466 patients with hypertension and 18,930 patients without hypertension were enrolled. These groups were divided into α1-adrenergic antagonist users and nonusers, matched by age, sex, and index year. Individuals were monitored for diagnosis of sleep apnea until 2013.

RESULTS

After adjusting for propensity score and potential confounders, including age, geographic location, enrollee category, income, urbanization level, comorbidities, and medication, the adjusted hazard ratios (HRs) for development of sleep apnea with α1-adrenergic antagonist use were 2.38 (95% confidence interval [CI] 1.82-3.10) and 2.82 (95% CI 1.79-4.44) in the hypertension and nonhypertension groups, respectively. Similarly, the adjusted HRs for development of severe sleep apnea with α1-adrenergic antagonist use were 2.74 (95% CI 1.78-4.22) and 4.23 (95% CI 1.57-11.40) in hypertension and nonhypertension patient groups, respectively. The interaction between α1-adrenergic-antagonist user and patients with hypertension was tested using multivariable Cox regression. The results showed that there are positive additive interactions for developing sleep apnea and severe sleep apnea, respectively.

CONCLUSIONS

Our study suggests that patients with hypertension using α1-adrenergic antagonists have a higher risk of sleep apnea. Routine sleep apnea screening would be beneficial for patients with hypertension who take α1-adrenergic antagonists.

From fiction to science: clinical potentials and regulatory considerations of gene editing

Gene editing technologies such as CRISPR/Cas9 have emerged as an attractive tool not only for scientific research but also for the development of medicinal products. Their ability to induce precise double strand breaks into DNA enables targeted modifications of the genome including selective knockout of genes, correction of mutations or precise insertion of new genetic material into specific loci. Gene editing-based therapies hold a great potential for the treatment of numerous diseases and the first products are already being tested in clinical trials. The treatment indications include oncological malignancies, HIV, diseases of the hematopoietic system and metabolic disorders. This article reviews ongoing preclinical and clinical studies and discusses how gene editing technologies are altering the gene therapy landscape. In addition, it focusses on the regulatory challenges associated with such therapies and how they can be tackled during the drug development process.

Oxidative muscles have better mitochondrial homeostasis than glycolytic muscles throughout life and maintain mitochondrial function during aging

Preservation of mitochondrial function, which is dependent on mitochondrial homeostasis (biogenesis, dynamics, disposal/recycling), is critical for maintenance of skeletal muscle function. Skeletal muscle performance declines upon aging (sarcopenia) and is accompanied by decreased mitochondrial function in fast-glycolytic muscles. Oxidative metabolism promotes mitochondrial homeostasis, so we investigated whether mitochondrial function is preserved in oxidative muscles. We compared tibialis anterior (predominantly glycolytic) and soleus (oxidative) muscles from young (3 mo) and old (28-29 mo) C57BL/6J mice. Throughout life, the soleus remained more oxidative than the tibialis anterior and expressed higher levels of markers of mitochondrial biogenesis, fission/fusion and autophagy. The respiratory capacity of mitochondria isolated from the tibialis anterior, but not the soleus, declined upon aging. The soleus and tibialis anterior exhibited similar aging-associated changes in mitochondrial biogenesis, fission/fusion, disposal and autophagy marker expression, but opposite changes in fiber composition: the most oxidative fibers declined in the tibialis anterior, while the more glycolytic fibers declined in the soleus. In conclusion, oxidative muscles are protected from mitochondrial aging, probably due to better mitochondrial homeostasis ab initio and aging-associated changes in fiber composition. Exercise training aimed at enriching oxidative fibers may be valuable in preventing mitochondria-related aging and its contribution to sarcopenia.