Respiratory magnetic resonance imaging biomarkers in Duchenne muscular dystrophy

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum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

SEMPAI: a Self-Enhancing Multi-Photon Artificial Intelligence for Prior-Informed Assessment of Muscle Function and Pathology

Deep learning (DL) shows notable success in biomedical studies. However, most DL algorithms work as black boxes, exclude biomedical experts, and need extensive data. This is especially problematic for fundamental research in the laboratory, where often only small and sparse data are available and the objective is knowledge discovery rather than automation. Furthermore, basic research is usually hypothesis-driven and extensive prior knowledge (priors) exists. To address this, the Self-Enhancing Multi-Photon Artificial Intelligence (SEMPAI) that is designed for multiphoton microscopy (MPM)-based laboratory research is presented. It utilizes meta-learning to optimize prior (and hypothesis) integration, data representation, and neural network architecture simultaneously. By this, the method allows hypothesis testing with DL and provides interpretable feedback about the origin of biological information in 3D images. SEMPAI performs multi-task learning of several related tasks to enable prediction for small datasets. SEMPAI is applied on an extensive MPM database of single muscle fibers from a decade of experiments, resulting in the largest joint analysis of pathologies and function for single muscle fibers to date. It outperforms state-of-the-art biomarkers in six of seven prediction tasks, including those with scarce data. SEMPAI's DL models with integrated priors are superior to those without priors and to prior-only approaches.

Characteristics of Diaphragmatic and Chest Wall Motion in People with Normal Pulmonary Function: A Study with Free-Breathing Dynamic MRI

Objective: We aimed to quantitatively study the characteristic of diaphragm and chest wall motion using free-breathing dynamic magnetic resonance imaging (D-MRI) in Chinese people with normal lung function. Methods: 74 male subjects (mean age, 37 ± 11 years old) were prospectively enrolled, and they underwent high-resolution CT(HRCT), pulmonary functional tests (PFTs), and D-MRI in the same day. D-MRI was acquired with a gradient-echo sequence during the quiet and deep breathing. The motion of the diaphragm and chest wall were respectively assessed by measuring thoracic anteroposterior diameter (AP), left−right diameter (LR), cranial−caudal diameter (CC), and thoracic area ratios between end-inspiration and end-expiration. The effect of age, body mass index (BMI), and smoking on respiratory muscle function was also analyzed. Results: The mean ratio of right and left AP was greater than that of LR on three transversal planes during both quiet and deep breathing. The mean ratio at the anterior diaphragm (AND, Quiet: 1.04 ± 0.03; Deep: 1.15 ± 0.09) was weaker than that of the apex (vs. APD, Quiet: 1.08 ± 0.05, p < 0.001; Deep: 1.29 ± 0.12, p < 0.001) and posterior diaphragm (vs. POD, Quiet: 1.09 ± 0.04, p < 0.001; Deep: 1.30 ± 0.12, p < 0.001) both in quiet and deep breathing. Compared with non-smokers, the left AP and thoracic area ratios in smokers were significantly decreased (p < 0.05). However, the ratios of AP, LR, CC, and thoracic area on each plane were similar among groups in different age and BMI. Conclusions: During both quiet and deep breathing, the chest wall motion is prominent in the anteroposterior direction. The motions of diaphragm apex and posterior diaphragm were more prominent than that of the anterior diaphragm. Smoking may affect the respiratory muscle mobility. Dynamic MRI can quantitatively evaluate the motion of respiratory muscles.

Breathing in Duchenne muscular dystrophy: Translation to therapy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a deficiency in dystrophin - a structural protein which stabilizes muscle during contraction. Dystrophin deficiency adversely affects the respiratory system leading to sleep-disordered breathing, hypoventilation, and weakness of the expiratory and inspiratory musculature, which culminate in severe respiratory dysfunction. Muscle degeneration associated respiratory impairment in neuromuscular disease is a result of disruptions at multiple sites of the respiratory control network, including sensory and motor pathways. As a result of this pathology, respiratory failure is a leading cause of premature death in DMD patients. Currently available treatments for DMD respiratory insufficiency attenuate respiratory symptoms without completely reversing the underlying pathophysiology. This underscores the need to develop curative therapies to improve quality of life and longevity of DMD patients. This review summarises research findings on the pathophysiology of respiratory insufficiencies in DMD disease in humans and animal models, the clinical interventions available to ameliorate symptoms, and gene-based therapeutic strategies uncovered by preclinical animal studies. Abstract figure legend: Summary of the therapeutic strategies for respiratory insufficiency in DMD (Duchenne muscular dystrophy). Treatment options currently in clinical use only attenuate respiratory symptoms without reversing the underlying pathology of DMD-associated respiratory insufficiencies. Ongoing preclinical and clinical research is aimed at developing curative therapies that both improve quality of life and longevity of DMD patients. AAV - adeno-associated virus, PPMO - Peptide-conjugated phosphorodiamidate morpholino oligomer This article is protected by copyright. All rights reserved.

Precurved, Fiber-Reinforced Actuators Enable Pneumatically Efficient Replication of Complex Biological Motions

Much of the research on bioinspired soft robotics has focused on capturing the interplay of biological form and function. However, existing soft robotic actuators are mostly made with linear or planar fabrication orientations that do not represent the resting geometry of complex biological systems, such as curved musculature. This work introduces the ability to create fiber-reinforced actuators with precurved configurations. By tuning variables such as dimensions and fiber angles, an optimization algorithm can prescribe the mechanical fabrication parameters to create a fiber-reinforced actuator that can generate controlled motion to follow a desired input trajectory. Precurved configurations introduce an additional optimization parameter, the initial bend angle, allowing for a more accurate and robust algorithm and generating a median percent error of <1%. With a customized software tool, we can take existing motion data from biological systems-such as medical imaging-and build soft robotic actuators optimized to replicate these trajectories. We can predict the motion of precurved actuators both analytically and numerically and replicate the motion experimentally, with excellent trajectory matching between the three. In constructing actuators that better match the native forms found within biological systems, we find that precurved actuators are more efficient than their initially straight counterparts. This pneumatic efficiency allows for the use of control systems with lower power and precision, lowering the economic cost of the associated control hardware, while more accurately replicating the biological motion. Taking two examples from biology, that of the human diaphragm during respiration and that of a jellyfish bell during locomotion, we design and generate fiber reinforced actuators to mimic these motions.

Non-Invasive Respiratory Assessment in Duchenne Muscular Dystrophy: From Clinical Research to Outcome Measures

Ventilatory failure, due to the progressive wasting of respiratory muscles, is the main cause of death in patients with Duchenne muscular dystrophy (DMD). Reliable measures of lung function and respiratory muscle action are important to monitor disease progression, to identify early signs of ventilatory insufficiency and to plan individual respiratory management. Moreover, the current development of novel gene-modifying and pharmacological therapies highlighted the urgent need of respiratory outcomes to quantify the effects of these therapies. Pulmonary function tests represent the standard of care for lung function evaluation in DMD, but provide a global evaluation of respiratory involvement, which results from the interaction between different respiratory muscles. Currently, research studies have focused on finding novel outcome measures able to describe the behavior of individual respiratory muscles. This review overviews the measures currently identified in clinical research to follow the progressive respiratory decline in patients with DMD, from a global assessment to an individual structure–function muscle characterization. We aim to discuss their strengths and limitations, in relation to their current development and suitability as outcome measures for use in a clinical setting and as in upcoming drug trials in DMD.

Respiratory muscle imaging by ultrasound and MRI in neuromuscular disorders

Respiratory muscle weakness is common in neuromuscular disorders and leads to significant respiratory difficulties. Therefore, reliable and easy assessment of respiratory muscle structure and function in neuromuscular disorders is crucial. In the last decade, ultrasound and MRI emerged as promising imaging techniques to assess respiratory muscle structure and function. Respiratory muscle imaging directly measures the respiratory muscles and, in contrast to pulmonary function testing, is independent of patient effort. This makes respiratory muscle imaging suitable to use as tool in clinical respiratory management and as outcome parameter in upcoming drug trials for neuromuscular disorders, particularly in children. In this narrative review, we discuss the latest studies and technological developments in imaging of the respiratory muscles by US and MR, and its clinical application and limitations. We aim to increase understanding of respiratory muscle imaging and facilitate its use as outcome measure in daily practice and clinical trials.

Magnetic Resonance Imaging Studies in Duchenne Muscular Dystrophy: Linking Findings to the Physical Therapy Clinic

Duchenne muscular dystrophy (DMD) is a muscle degenerative disorder that manifests in early childhood and results in progressive muscle weakness. Physical therapists have long been an important component of the multidisciplinary team caring for people with DMD, providing expertise in areas of disease assessment, contracture management, assistive device prescription, and exercise prescription. Over the last decade, magnetic resonance imaging of muscles in people with DMD has led to an improved understanding of the muscle pathology underlying the clinical manifestations of DMD. Findings from magnetic resonance imaging (MRI) studies in DMD, paired with the clinical expertise of physical therapists, can help guide research that leads to improved physical therapist care for this unique patient population. The 2 main goals of this perspective article are to (1) summarize muscle pathology and disease progression findings from qualitative and quantitative muscle MRI studies in DMD and (2) link MRI findings of muscle pathology to the clinical manifestations observed by physical therapists with discussion of any potential implications of MRI findings on physical therapy management.

Echographic Assessment of Diaphragmatic Function in Duchenne Muscular Dystrophy from Childhood to Adulthood

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic muscle disorder. Respiratory muscle function is classically affected in this disease. Ultrasound recently emerged as a non-invasive tool to assess diaphragm function. However, there are only a few studies using diaphragm ultrasound (US) in DMD.

PURPOSE

We aimed to assess diaphragm ultrasound patterns in DMD, their relationship with age and their association with home mechanical ventilation (HMV).

METHODS

We included DMD patients followed at Raymond Poincaré Hospital who benefited from diaphragm ultrasound and pulmonary function tests.

RESULTS

There were 110 DMD patients and 17 male sex-matched healthy subjects included. In all, 94% of patients were permanent wheelchair users. Median body mass index (BMI) was 18 kg/m2. DMD patients disclosed a reduced forced vital capacity (VC) (12% of predicted value), and 78% of patients were on HMV. In patients, right and left diaphragmatic motions on deep inspiration were reduced and end expiratory diaphragm thickness was borderline normal. In patients, right and left diaphragmatic thickening fractions (TF) were reduced 12.7% and 15.5%, respectively. Age and end expiratory thickness were significantly inversely associated (p = 0.005 for the right diaphragm, p = 0.018 for the left diaphragm). Diaphragm TF was significantly inversely associated with age (p = 0.001 for the right side, p < 0.0001 for the left side). Right and left inspiratory diaphragm motions were significantly inversely associated with age (p < 0.0001).

CONCLUSION

This study describes the severity of diaphragm dysfunction in patients with DMD. Diaphragm US may be a non-invasive outcome measure for DMD.

Dynamic respiratory muscle function in late-onset Pompe disease

Maximal inspiratory pressure (PI_MAX) reflects inspiratory weakness in late-onset Pompe disease (LOPD). However, static pressure tests may not reveal specific respiratory muscle adaptations to disruptions in breathing. We hypothesized that dynamic respiratory muscle functional tests reflect distinct ventilatory compensations in LOPD. We evaluated LOPD (n = 7) and healthy controls (CON, n = 7) during pulmonary function tests, inspiratory endurance testing, dynamic kinematic MRI of the thorax, and ventilatory adjustments to single-breath inspiratory loads (inspiratory load compensation, ILC). We observed significantly lower static and dynamic respiratory function in LOPD. PI_MAX, spirometry, endurance time, and maximal diaphragm descent were significantly correlated. During single-breath inspiratory loads, inspiratory time and airflow acceleration increased to preserve volume, and in LOPD, the response magnitudes correlated to maximal chest wall kinematics. The results indicate that changes in diaphragmatic motor function and strength among LOPD subjects could be detected through dynamic respiratory testing. We concluded that neuromuscular function significantly influenced breathing endurance, timing and loading compensations.

Imaging respiratory muscle quality and function in Duchenne muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) is characterized by damage to muscles including the muscles involved in respiration. Dystrophic muscles become weak and infiltrated with fatty tissue, resulting in progressive respiratory impairment. The objective of this study was to assess respiratory muscle quality and function in DMD using magnetic resonance imaging and to determine the relationship to clinical respiratory function.

METHODS

Individuals with DMD (n = 36) and unaffected controls (n = 12) participated in this cross sectional magnetic resonance imaging study. Participants underwent dynamic imaging of the thorax to assess diaphragm and chest wall mobility and chemical shift-encoded imaging of the chest and abdomen to determine fatty infiltration of the accessory respiratory muscles. Additionally, clinical pulmonary function measures were obtained.

RESULTS

Thoracic cavity area was decreased in individuals with DMD compared to controls during tidal and maximal breathing. Individuals with DMD had reduced chest wall movement in the anterior-posterior direction during maximal inspirations and expirations, but diaphragm descent during maximal inspirations (normalized to height) was only decreased in a subset of individuals with maximal inspiratory pressures less than 60% predicted. Muscle fat fraction was elevated in all three expiratory muscles assessed (p < 0.001), and the degree of fatty infiltration correlated with percent predicted maximal expiratory pressures (r =  - 0.70, p < 0.001). The intercostal muscles demonstrated minimal visible fatty infiltration; however, this analysis was qualitative and resolution limited.

INTERPRETATION

This magnetic resonance imaging investigation of diaphragm movement, chest wall movement, and accessory respiratory muscle fatty infiltration provides new insights into the relationship between disease progression and clinical respiratory function.

Diaphragm Involvement in Duchenne Muscular Dystrophy (DMD): An MRI Study

BACKGROUND

Duchenne muscular dystrophy (DMD) is characterized by progressive weakness and wasting of skeletal, cardiac, and respiratory muscles, with consequent cardiopulmonary failure as the main cause of death. Reliable outcome measures able to demonstrate specific trends over disease progression are essential.

PURPOSE

To investigate MRI as a noninvasive imaging modality to assess diaphragm impairment in DMD. In particular, we sought to correlate MRI measurement of diaphragm structure and function with pulmonary function tests and with the abdominal volumes (V_AB ) measured by optoelectronic plethysmography, being an index of the action of the diaphragm.

STUDY TYPE

Cross-sectional study.

POPULATION

Twenty-six DMD patients (17.9 ± 6.2 years) and 12 age-matched controls (17.8 ± 5.9 years).

FIELD STRENGTH/SEQUENCE

3-Point gradient echo Dixon sequence at 3T.

ASSESSMENT

Images were acquired in breath-hold at full-expiration (EXP) and full-inspiration (INSP). INSP and EXP lung volumes were segmented and the diaphragm surface was reconstructed as the bottom surface of the left and the right lung. The inspiratory and the expiratory diaphragm surfaces were aligned by a nonrigid iterative closest point algorithm. On MRI we measured: 1) craniocaudal diaphragmatic excursion; 2) diaphragm fatty infiltration.

STATISTICAL TESTS

Three-parameter sigmoid regression, one-way analysis of variance (ANOVA), Spearman's correlation.

RESULTS

In patients, diaphragm excursion decreased with age (r² = 0.68, P < 0.0001) and fat fraction increased (r² = 0.51, P = 0.0002). In healthy subjects, diaphragm excursion and fat fraction had no relationship with age. Diaphragm excursion decreased with decreasing FEV₁ %pred (r = 0.78, P < 0.0001) and FVC %pred (r = 0.76, P < 0.0001) and correlated with V_AB (r = 0.60, P = 0.0002). Fatty infiltration increased with decreasing FEV1 %pred (r = -0.88, P < 0.0001) and FVC %pred (r = -0.88, P < 0.0001).

DATA CONCLUSION

The progressive structural and functional diaphragm impairment is highly related to pulmonary function tests and to V_AB . The results suggest that MRI might represent a new and noninvasive tool for the functional and structural assessment of the diaphragm.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2020;51:461-471.

Duchenne muscular dystrophy: genome editing gives new hope for treatment

Duchenne muscular dystrophy (DMD) is a progressive wasting disease of skeletal and cardiac muscles, representing one of the most common recessive fatal inherited genetic diseases with 1:3500–1:5000 in yearly incidence. It is caused by mutations in the DMD gene that encodes the membrane-associated dystrophin protein. Over the years, many have been the approaches to management of DMD, but despite all efforts, no effective treatment has yet been discovered. Hope for the development of potential therapeutics has followed the recent advances in genome editing and gene therapy. This review gives an overview to DMD and summarises current lines of evidence with regard to treatment and disease management alongside the appropriate considerations.