The new horizons for treatment of Late-Onset Pompe Disease (LOPD)

Splicing correction by peptide-conjugated morpholinos as a novel treatment for late-onset Pompe disease

Late-onset Pompe disease (LOPD) is overwhelmingly caused by a single mutation that disrupts splicing of acid-alpha glucosidase (GAA) and results in the accumulation of lysosomal glycogen in muscle cells leading to progressive muscle weakness in patients. Current therapeutics for LOPD do not meet the needs of patients and have largely been developed in mutant animal models lacking Gaa expression, which more closely mimic the less common infantile form of the disease. Here we design and evaluate peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) to target the causative mutation in GAA and correct pathogenic splicing in muscle tissue. We show PPMO compounds correct LOPD splicing in both patient induced pluripotent stem cell-derived muscle cells and in skeletal muscle tissue after intravenous dosing in a newly developed humanized LOPD animal model that recapitulates patient LOPD splicing.

Improving the treatment of Pompe disease with enzyme replacement therapy: current strategies and clinical evidence

INTRODUCTION

Pompe disease (PD) is a rare genetic disorder that leads to intralysosomal glycogen accumulation because of a deficiency in the lysosomal enzyme acid α-glucosidase (GAA), which is required to break down glycogen to glucose. Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) supplies exogenous GAA to reduce glycogen deposits, thereby improving motor and respiratory functioning.

AREA COVERED

The first approved ERT for PD was the rhGAA alglucosidase alfa. Limitations associated with this treatment led to the development of two other rhGAAs: avalglucosidase alfa and cipaglucosidase alfa. This review describes the limitations of alglucosidase alfa and focuses on the strategies used to overcome these limitations, including the conjugation of multiple synthetic bis-M6P - containing hexasaccharides to sialic acids present on the enzyme, thus enhancing M6PR targeting, enzyme uptake, glycogen clearance, and therapeutic outcomes. Efficacy and safety of avalglucosidase alfa in late-onset and infantile-onset PD are also discussed. A brief overview of the newest ERT, cipaglucosidase alfa, is also provided.

EXPERT OPINION

While ERT for PD continues to improve with more effective enzymes like avalglucosidase alfa, the future lies in integrated approaches that combine different therapeutic modalities (gene therapy, substrate reduction therapy) and the use of biomarkers to individualize treatment.

Exploring Quality of Life in Adults Living With Late-onset Pompe Disease: A Combined Quantitative and Qualitative Analysis of Patient Perceptions from Australia, France, Italy, and the Netherlands

Background: Late-onset Pompe disease (LOPD) is a rare, autosomal recessive metabolic disorder that is heterogeneous in disease presentation and progression. People with LOPD report a significantly lower physical, psychological, and social quality of life (QoL) than the general population. Objectives: This study investigated how individuals' self-reported LOPD status (improving, stable, declining) relates to their QoL. Participant experiences such as use of mobility or ventilation aids, caregivers, symptomology, and daily life impacts were also characterized. Methods: A 2-part observational study was conducted online between October and December 2023 using the 36-item short-form tool (SF-36) and a survey. Adults with LOPD (N=41) from Australia, France, Italy, and the Netherlands were recruited. Results: Participants reporting "declining" LOPD status (56%) had lower physical functioning SF-36 scores than those reporting as "stable" or "improving." Those self-reporting as stable or improving often described an acceptance of declining health in their responses. Physical functioning scores were generally stable in respondents who had been receiving enzyme replacement therapy (ERT) for 1-15 years, but those who had received ERT for >15 years had lower scores. Requiring ventilation and mobility aids had additive negative impacts on physical functioning. Difficulty swallowing, speaking, and scoliosis were the most burdensome symptoms reported by those on ERT for >15-25 years. Discussion: These results demonstrate the humanistic burden of LOPD; through declining physical functioning SF-36 scores over increasing time and increased use of aids, and also through factors related to self-reported LOPD status (where declining status was associated with lower scores) and symptomology variances. Taken holistically, these areas are valuable to explore when informing optimized care. Among a largely declining cohort, even those not self-reporting decline often assumed future deterioration, highlighting the need for improved therapies and the potential to initiate or switch ERT based on evolving symptomology and daily life impacts. Conclusion: Our results indicate that progressing LOPD leads to loss of QoL in ways that relate to time, use of aids, evolving symptomology, and the patient's own perspective. A holistic approach to assessing the individual can help ensure relevant factors are investigated and held in balance, supporting optimized care.

Significance of early diagnosis and treatment of adult late-onset Pompe disease on the effectiveness of enzyme replacement therapy in improving muscle strength and respiratory function: a case report

BACKGROUND

Pompe disease, a rare autosomal recessive disorder, is caused by mutations in the acid α-glucosidase gene. Pompe disease is a congenital metabolic disorder that affects all organs, particularly the striated muscle and nerve cells. Diagnosis is typically confirmed through enzyme assays that reveal reduced acid α-glucosidase activity. Enzyme replacement therapy utilizing human α-glucosidase is an available treatment option. Timely diagnosis and treatment in the early stages of the disease significantly impact the effectiveness of enzyme replacement therapy in enhancing patient condition. Here, we present a case of a patient with Pompe disease diagnosed 20 years after the onset of clinical symptoms.

CASE PRESENTATION

A 38-year-old Iranian Baloch woman referred to our rheumatology clinic with progressive muscle weakness presents with a complex medical history. On mechanical ventilation for 12 years, she has endured fatigue and limb weakness since the age of 16, exacerbated following an abortion at 19. Despite undergoing corticosteroid and azathioprine therapies, the suspected diagnosis of inflammatory myopathy did not yield improvement. Hospitalization at 23 due to respiratory failure post-pregnancy led to her continued reliance on a ventilator. A dried blood spot test indicated reduced GAA enzyme activity, confirming a diagnosis of Pompe disease through genetic testing. Treatment with myozyme for 2 years demonstrated limited efficacy, as the patient experienced improved breathing but no significant overall improvement in limb-girdle muscular weakness. This case underscores the challenges and complexities involved in diagnosing and managing rare neuromuscular disorders like Pompe disease.

CONCLUSION

Early intervention with enzyme replacement therapy plays a crucial role in halting further muscle loss and disease progression in Pompe disease patients. It is important to note that treatment during advanced stages of the disease may not yield substantial benefits. Nevertheless, enzyme instability and denaturation due to temperature and neutral pH levels, along with limited delivery to disease-relevant tissues, can pose challenges in treatment. However, timely diagnosis of Pompe disease is paramount for its effective management and improved outcomes.

Metabolic aspects of glycogenolysis with special attention to McArdle disease

The physiological function of muscle glycogen is to meet the energy demands of muscle contraction. The breakdown of glycogen occurs through two distinct pathways, primarily cytosolic and partially lysosomal. To obtain the necessary energy for their function, skeletal muscles utilise also fatty acids in the β-oxidation. Ketogenesis is an alternative metabolic pathway for fatty acids, which provides an energy source during fasting and starvation. Diseases arising from impaired glycogenolysis lead to muscle weakness and dysfunction. Here, we focused on the lack of muscle glycogen phosphorylase (PYGM), a rate-limiting enzyme for glycogenolysis in skeletal muscles, which leads to McArdle disease. Metabolic myopathies represent a group of genetic disorders characterised by the limited ability of skeletal muscles to generate energy. Here, we discuss the metabolic aspects of glycogenosis with a focus on McArdle disease, offering insights into its pathophysiology. Glycogen accumulation may influence the muscle metabolic dynamics in different ways. We emphasize that a proper treatment approach for such diseases requires addressing three important and interrelated aspects, which include: symptom relief therapy, elimination of the cause of the disease (lack of a functional enzyme) and effective and early diagnosis.

In vitro substrate reduction, chaperone and immunomodulation treatments reduce heparan sulfate in mucolipidosis III human fibroblasts

Mucolipidosis II and III (MLII and MLIII) are autosomal recessive diseases caused by pathogenic variants in GNPTAB and GNPTG genes that lead to defects in GlcNAc-1-phosphotransferase. This enzyme adds mannose 6-phosphate residues to lysosomal hydrolases, which allows enzymes to enter lysosomes. Defective GlcNAc-1-phosphotransferase causes substrate accumulation and inflammation. These diseases have no treatment, and we hypothesized that the use of substrate reduction therapy and immunomodulation may be beneficial at the cell level and as a future therapeutic approach. Fibroblasts from two patients with MLIII alpha/beta and 2 patients with MLIII gamma as well as from one healthy control were treated with 10 µM miglustat, 20 µM genistein, and 20 µM thalidomide independently. ELISA assay and confocal immunofluorescence microscopy were used to evaluate the presence of heparan sulfate (HS) and the impact on substrate accumulation. ELISA assay showed HS reduction in all patients with the different treatments used (p=0.05). HS reduction was also observed by immunofluorescence microscopy. Our study produced encouraging results, since the reduction in substrate accumulation, even partial, may offer benefits to the phenotype of patients with inborn errors of metabolism.

Variant Classification for Pompe disease; ACMG/AMP specifications from the ClinGen Lysosomal Diseases Variant Curation Expert Panel

Accurate determination of the clinical significance of genetic variants is critical to the integration of genomics in medicine. To facilitate this process, the NIH-funded Clinical Genome Resource (ClinGen) has assembled Variant Curation Expert Panels (VCEPs), groups of experts and biocurators which provide gene- and disease- specifications to the American College of Medical Genetics & Genomics and Association for Molecular Pathology's (ACMG/AMP) variation classification guidelines. With the goal of classifying the clinical significance of GAA variants in Pompe disease (Glycogen storage disease, type II), the ClinGen Lysosomal Diseases (LD) VCEP has specified the ACMG/AMP criteria for GAA. Variant classification can play an important role in confirming the diagnosis of Pompe disease as well as in the identification of carriers. Furthermore, since the inclusion of Pompe disease on the Recommended Uniform Screening Panel (RUSP) for newborns in the USA in 2015, the addition of molecular genetic testing has become an important component in the interpretation of newborn screening results, particularly for asymptomatic individuals. To date, the LD VCEP has submitted classifications and supporting data on 243 GAA variants to public databases, specifically ClinVar and the ClinGen Evidence Repository. Here, we describe the ACMG/AMP criteria specification process for GAA, an update of the GAA-specific variant classification guidelines, and comparison of the ClinGen LD VCEP's GAA variant classifications with variant classifications submitted to ClinVar. The LD VCEP has added to the publicly available knowledge on the pathogenicity of variants in GAA by increasing the number of expert-curated GAA variants present in ClinVar, and aids in resolving conflicting classifications and variants of uncertain clinical significance.

Metabolic Myopathies in the Era of Next-Generation Sequencing

Metabolic myopathies are rare inherited disorders that deserve more attention from neurologists and pediatricians. Pompe disease and McArdle disease represent some of the most common diseases in clinical practice; however, other less common diseases are now better-known. In general the pathophysiology of metabolic myopathies needs to be better understood. Thanks to the advent of next-generation sequencing (NGS), genetic testing has replaced more invasive investigations and sophisticated enzymatic assays to reach a final diagnosis in many cases. The current diagnostic algorithms for metabolic myopathies have integrated this paradigm shift and restrict invasive investigations for complicated cases. Moreover, NGS contributes to the discovery of novel genes and proteins, providing new insights into muscle metabolism and pathophysiology. More importantly, a growing number of these conditions are amenable to therapeutic approaches such as diets of different kinds, exercise training protocols, and enzyme replacement therapy or gene therapy. Prevention and management-notably of rhabdomyolysis-are key to avoiding serious and potentially life-threatening complications and improving patients' quality of life. Although not devoid of limitations, the newborn screening programs that are currently mushrooming across the globe show that early intervention in metabolic myopathies is a key factor for better therapeutic efficacy and long-term prognosis. As a whole NGS has largely increased the diagnostic yield of metabolic myopathies, but more invasive but classical investigations are still critical when the genetic diagnosis is unclear or when it comes to optimizing the follow-up and care of these muscular disorders.