Case Studies in Neuroscience: Neuropathology and diaphragm dysfunction in ventilatory failure from late-onset Pompe disease

Pharmacological modulation of respiratory control: Ampakines as a therapeutic strategy

Ampakines are a class of compounds that are positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and enhance glutamatergic neurotransmission. Glutamatergic synaptic transmission and AMPA receptor activation are fundamentally important to the genesis and propagation of the neural impulses driving breathing, including respiratory motoneuron depolarization. Ampakines therefore have the potential to modulate the neural control of breathing. In this paper, we describe the influence of ampakines on respiratory motor output in health and disease. We dissect the molecular mechanisms underlying ampakine action, delineate the diverse targets of ampakines along the respiratory neuraxis, survey the spectrum of respiratory disorders in which ampakines have been tested, and culminate with an examination of how ampakines modulate respiratory function after spinal cord injury. Collectively, the studies reviewed here indicate that ampakines may be a useful adjunctive strategy to pair with conventional respiratory rehabilitation approaches in conditions with impaired neural activation of the respiratory muscles.

Neonatal systemic gene therapy restores cardiorespiratory function in a rat model of Pompe disease

Absence of functional acid-α-glucosidase (GAA) leads to early-onset Pompe disease with cardiorespiratory and neuromuscular failure. A novel Pompe rat model (Gaa -/-) was used to test the hypothesis that neonatal gene therapy with adeno-associated virus serotype 9 (AAV9) restores cardiorespiratory neuromuscular function across the lifespan. Temporal vein administration of AAV9-DES-GAA or sham (saline) injection was done on post-natal day 1; rats were studied at 6-12 months old. Whole-body plethysmography showed that reduced inspiratory tidal volumes in Gaa -/- rats were corrected by AAV-GAA treatment. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI) revealed that AAV-GAA treatment normalized diaphragm muscle glycogen as well as glycans. Neurophysiological recordings of phrenic nerve output and immunohistochemical evaluation of the cervical spinal cord indicated a neurologic benefit of AAV-GAA treatment. In vivo magnetic resonance imaging demonstrated that impaired cardiac volumes in Gaa -/- rats were corrected by AAV-GAA treatment. Biochemical assays showed that AAV treatment increased GAA activity in the heart, diaphragm, quadriceps and spinal cord. We conclude that neonatal AAV9-DES-GAA therapy drives sustained, functional GAA expression and improved cardiorespiratory function in the Gaa -/- rat model of Pompe disease.

Preclinical lentiviral hematopoietic stem cell gene therapy corrects Pompe disease-related muscle and neurological manifestations

Pompe disease, a rare genetic neuromuscular disorder, is caused by a deficiency of acid alpha-glucosidase (GAA), leading to an accumulation of glycogen in lysosomes, and resulting in the progressive development of muscle weakness. The current standard treatment, enzyme replacement therapy (ERT), is not curative and has limitations such as poor penetration into skeletal muscle and both the central and peripheral nervous systems, a risk of immune responses against the recombinant enzyme, and the requirement for high doses and frequent infusions. To overcome these limitations, lentiviral vector-mediated hematopoietic stem and progenitor cell (HSPC) gene therapy has been proposed as a next-generation approach for treating Pompe disease. This study demonstrates the potential of lentiviral HSPC gene therapy to reverse the pathological effects of Pompe disease in a preclinical mouse model. It includes a comprehensive safety assessment via integration site analysis, along with single-cell RNA sequencing analysis of central nervous tissue samples to gain insights into the underlying mechanisms of phenotype correction.

Brain glycogen build-up measured by magnetic resonance spectroscopy in classic infantile Pompe disease

Classic infantile Pompe disease is caused by abnormal lysosomal glycogen accumulation in multiple tissues, including the brain due to a deficit in acid α-glucosidase. Although treatment with recombinant human acid α-glucosidase has dramatically improved survival, recombinant human acid α-glucosidase does not reach the brain, and surviving classic infantile Pompe patients develop progressive cognitive deficits and white matter lesions. We investigated the feasibility of measuring non-invasively glycogen build-up and other metabolic alterations in the brain of classic infantile Pompe patients. Four classic infantile patients (8-16 years old) and 4 age-matched healthy controls were scanned on a 7 T MRI scanner. We used T2-weighted MRI to assess the presence of white matter lesions as well as 1H magnetic resonance spectroscopy and magnetic resonance spectroscopy imaging to obtain the neurochemical profile and its spatial distribution, respectively. All patients had widespread white matter lesions on T2-weighted images. Magnetic resonance spectroscopy data from a single volume of interest positioned in the periventricular white matter showed a clear shift in the neurochemical profile, particularly a significant increase in glycogen (result of acid α-glucosidase deficiency) and decrease in N-acetyl-aspartate (marker of neuronal damage) in patients. Magnetic resonance spectroscopy imaging results were in line and showed a widespread accumulation of glycogen and a significant lower level of N-acetyl-aspartate in patients. Our results illustrate the unique potential of 1H magnetic resonance spectroscopy (imaging) to provide a non-invasive readout of the disease pathology in the brain. Further study will assess its potential to monitor disease progression and the correlation with cognitive decline.

Neurological glycogen storage diseases and emerging therapeutics

Glycogen storage diseases (GSDs) comprise a group of inherited metabolic disorders characterized by defects in glycogen metabolism, leading to abnormal glycogen accumulation in multiple tissues, most notably affecting the liver, skeletal muscle, and heart. Recent findings have uncovered the importance of glycogen metabolism in the brain, sustaining a myriad of physiological functions and linking its perturbation to central nervous system (CNS) pathology. This link resulted in classification of neurological-GSDs (n-GSDs), a group of diseases with shared deficits in neurological glycogen metabolism. The n-GSD patients exhibit a spectrum of clinical presentations with common etiology while requiring tailored therapeutic approaches from the traditional GSDs. Recent research has elucidated the genetic and biochemical mechanisms and pathophysiological basis underlying different n-GSDs. Further, the last decade has witnessed some promising developments in novel therapeutic approaches, including enzyme replacement therapy (ERT), substrate reduction therapy (SRT), small molecule drugs, and gene therapy targeting key aspects of glycogen metabolism in specific n-GSDs. This preclinical progress has generated noticeable success in potentially modifying disease course and improving clinical outcomes in patients. Herein, we provide an overview of current perspectives on n-GSDs, emphasizing recent advances in understanding their molecular basis, therapeutic developments, underscore key challenges and the need to deepen our understanding of n-GSDs pathogenesis to develop better therapeutic strategies that could offer improved treatment and sustainable benefits to the patients.

Current avenues of gene therapy in Pompe disease

PURPOSE OF REVIEW

Pompe disease is a rare, inherited, devastating condition that causes progressive weakness, cardiomyopathy and neuromotor disease due to the accumulation of glycogen in striated and smooth muscle, as well as neurons. While enzyme replacement therapy has dramatically changed the outcome of patients with the disease, this strategy has several limitations. Gene therapy in Pompe disease constitutes an attractive approach due to the multisystem aspects of the disease and need to address the central nervous system manifestations. This review highlights the recent work in this field, including methods, progress, shortcomings, and future directions.

RECENT FINDINGS

Recombinant adeno-associated virus (rAAV) and lentiviral vectors (LV) are well studied platforms for gene therapy in Pompe disease. These products can be further adapted for safe and efficient administration with concomitant immunosuppression, with the modification of specific receptors or codon optimization. rAAV has been studied in multiple clinical trials demonstrating safety and tolerability.

SUMMARY

Gene therapy for the treatment of patients with Pompe disease is feasible and offers an opportunity to fully correct the principal pathology leading to cellular glycogen accumulation. Further work is needed to overcome the limitations related to vector production, immunologic reactions and redosing.

Diaphragm pacing and independent breathing in individuals with severe Pompe disease

Introduction

Pompe disease is an inherited disease characterized by a deficit in acid-α-glucosidase (GAA), an enzyme which degrades lysosomal glycogen. The phrenic-diaphragm motor system is affected preferentially, and respiratory failure often occurs despite GAA enzyme replacement therapy. We hypothesized that the continued use of diaphragm pacing (DP) might improve ventilator-dependent subjects' respiratory outcomes and increase ventilator-free time tolerance.

Methods

Six patients (3 pediatric) underwent clinical DP implantation and started diaphragm conditioning, which involved progressively longer periods of daily, low intensity stimulation. Longitudinal respiratory breathing pattern, diaphragm electromyography, and pulmonary function tests were completed when possible, to assess feasibility of use, as well as diaphragm and ventilatory responses to conditioning.

Results

All subjects were eventually able to undergo full-time conditioning via DP and increase their maximal tolerated time off-ventilator, when compared to pre-implant function. Over time, 3 of 6 subjects also demonstrated increased or stable minute ventilation throughout the day, without positive-pressure ventilation assistance.

Discussion

Respiratory insufficiency is one of the main causes of death in patients with Pompe disease. Our results indicate that DP in Pompe disease was feasible, led to few adverse events and stabilized breathing for up to 7 years.

Phase I study of liver depot gene therapy in late-onset Pompe disease

Gene therapy with an adeno-associated virus serotype 8 (AAV8) vector (AAV8-LSPhGAA) could eliminate the need for enzyme replacement therapy (ERT) by creating a liver depot for acid α-glucosidase (GAA) production. We report initial safety and bioactivity of the first dose (1.6 × 1012 vector genomes/kg) cohort (n = 3) in a 52-week open-label, single-dose, dose-escalation study (NCT03533673) in patients with late-onset Pompe disease (LOPD). Subjects discontinued biweekly ERT after week 26 based on the detection of elevated serum GAA activity and the absence of clinically significant declines per protocol. Prednisone (60 mg/day) was administered as immunoprophylaxis through week 4, followed by an 11-week taper. All subjects demonstrated sustained serum GAA activities from 101% to 235% of baseline trough activity 2 weeks following the preceding ERT dose. There were no treatment-related serious adverse events. No subject had anti-capsid T cell responses that decreased transgene expression. Muscle biopsy at week 24 revealed unchanged muscle glycogen content in two of three subjects. At week 52, muscle GAA activity for the cohort was significantly increased (p < 0.05). Overall, these initial data support the safety and bioactivity of AAV8-LSPhGAA, the safety of withdrawing ERT, successful immunoprophylaxis, and justify continued clinical development of AAV8-LSPhGAA therapy in Pompe disease.

[Research progress of nervous system damage in Pompe disease]

Pompe disease, also known as glycogen storage disease type Ⅱ, is a rare autosomal recessive disease. With the application of enzyme replacement therapy, more and more patients with Pompe disease can survive to adulthood, and nervous system-related clinical manifestations gradually emerge. Nervous system involvement seriously affects the quality of life of patients with Pompe disease, and a systematic understanding of the clinical manifestations, imaging features and pathological changes of nervous system injury in Pompe disease is of great significance for the early identification and intervention of Pompe disease. This article reviews the research progress of neurological damage in Pompe disease.

An artificial intelligence-based approach for identifying rare disease patients using retrospective electronic health records applied for Pompe disease

Objective

We retrospectively screened 350,116 electronic health records (EHRs) to identify suspected patients for Pompe disease. Using these suspected patients, we then describe their phenotypical characteristics and estimate the prevalence in the respective population covered by the EHRs.

Methods

We applied Symptoma's Artificial Intelligence-based approach for identifying rare disease patients to retrospective anonymized EHRs provided by the "University Hospital Salzburg" clinic group. Within 1 month, the AI screened 350,116 EHRs reaching back 15 years from five hospitals, and 104 patients were flagged as probable for Pompe disease. Flagged patients were manually reviewed and assessed by generalist and specialist physicians for their likelihood for Pompe disease, from which the performance of the algorithms was evaluated.

Results

Of the 104 patients flagged by the algorithms, generalist physicians found five "diagnosed," 10 "suspected," and seven patients with "reduced suspicion." After feedback from Pompe disease specialist physicians, 19 patients remained clinically plausible for Pompe disease, resulting in a specificity of 18.27% for the AI. Estimating from the remaining plausible patients, the prevalence of Pompe disease for the greater Salzburg region [incl. Bavaria (Germany), Styria (Austria), and Upper Austria (Austria)] was one in every 18,427 people. Phenotypes for patient cohorts with an approximated onset of symptoms above or below 1 year of age were established, which correspond to infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), respectively.

Conclusion

Our study shows the feasibility of Symptoma's AI-based approach for identifying rare disease patients using retrospective EHRs. Via the algorithm's screening of an entire EHR population, a physician had only to manually review 5.47 patients on average to find one suspected candidate. This efficiency is crucial as Pompe disease, while rare, is a progressively debilitating but treatable neuromuscular disease. As such, we demonstrated both the efficiency of the approach and the potential of a scalable solution to the systematic identification of rare disease patients. Thus, similar implementation of this methodology should be encouraged to improve care for all rare disease patients.

Chemogenetic activation of hypoglossal motoneurons in a mouse model of Pompe disease

Pompe disease is a lysosomal storage disease resulting from absence or deficiency of acid α-glucosidase (GAA). Tongue-related disorders including dysarthria, dysphagia, and obstructive sleep apnea are common in Pompe disease. Our purpose was to determine if designer receptors exclusively activated by designer drugs (DREADDs) could be used to stimulate tongue motor output in a mouse model of Pompe disease. An adeno-associated virus serotype 9 (AAV9) encoding an excitatory DREADD (AAV9-hSyn-hM3D(Gq)-mCherry, 2.44 × 1010 vg) was administered to the posterior tongue of 5-7-wk-old Gaa null (Gaa-/-) mice. Lingual EMG responses to intraperitoneal injection of saline or a DREADD ligand (JHU37160-dihydrochloride, J60) were assessed 12 wk later during spontaneous breathing. Saline injection produced no consistent changes in lingual EMG. Following the DREADD ligand, there were statistically significant (P < 0.05) increases in both tonic and phasic inspiratory EMG activity recorded from the posterior tongue. Brainstem histology confirmed mCherry expression in hypoglossal (XII) motoneurons in all mice, thus verifying retrograde movement of the AAV9 vector. Morphologically, Gaa-/- XII motoneurons showed histological characteristics that are typical of Pompe disease, including an enlarged soma and vacuolization. We conclude that lingual delivery of AAV9 can be used to drive functional expression of DREADD in XII motoneurons in a mouse model of Pompe disease.NEW & NOTEWORTHY In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intraperitoneal delivery of a DREADD ligand stimulated tonic and phase tongue motor output.In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intravenous delivery of a DREADD ligand stimulated tonic and phase tongue motor output.

What's new and what's next for gene therapy in Pompe disease?

INTRODUCTION

Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome.

AREAS COVERED

Gene therapy offers several advantages including prolonged and consistent GAA expression and correction of skeletal muscle as well as the critical CNS pathology. We provide a systematic review of the preclinical and clinical outcomes of adeno-associated viral mediated gene therapy and alternative gene therapy strategies, highlighting what has been successful.

EXPERT OPINION

Although the preclinical and clinical studies so far have been promising, barriers exist that need to be addressed in gene therapy for Pompe disease. New strategies including novel capsids for better targeting, optimized DNA vectors, and adjuctive therapies will allow for a lower dose, and ameliorate the immune response.