Pompe Disease: New Developments in an Old Lysosomal Storage Disorder

Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression

Late-onset Pompe disease (LOPD) is a rare genetic disorder caused by the deficiency of acid alpha-glucosidase leading to progressive cellular dysfunction owing to the accumulation of glycogen in the lysosome. The mechanism of relentless muscle damage (a classic manifestation of the disease) has been studied extensively by analysing the whole-muscle tissue; however, little, if anything, is known about transcriptional heterogeneity among nuclei within the multinucleated skeletal muscle cells. This is the first report of application of single-nucleus RNA sequencing to uncover changes in the gene expression profile in muscle biopsies from eight patients with LOPD and four muscle samples from age- and sex-matched healthy controls. We matched these changes with histological findings using GeoMx spatial transcriptomics to compare the transcriptome of control myofibres from healthy individuals with non-vacuolated (histologically unaffected) and vacuolated (histologically affected) myofibres of LODP patients. We observed an increase in the proportion of slow and regenerative muscle fibres and macrophages in LOPD muscles. The expression of the genes involved in glycolysis was reduced, whereas the expression of the genes involved in the metabolism of lipids and amino acids was increased in non-vacuolated fibres, indicating early metabolic abnormalities. Additionally, we detected upregulation of autophagy genes and downregulation of the genes involved in ribosomal and mitochondrial function leading to defective oxidative phosphorylation. Upregulation of genes associated with inflammation, apoptosis and muscle regeneration was observed only in vacuolated fibres. Notably, enzyme replacement therapy (the only available therapy for the disease) showed a tendency to restore dysregulated metabolism, particularly within slow fibres. A combination of single-nucleus RNA sequencing and spatial transcriptomics revealed the landscape of the normal and diseased muscle and highlighted the early abnormalities associated with disease progression. Thus, the application of these two new cutting-edge technologies provided insight into the molecular pathophysiology of muscle damage in LOPD and identified potential avenues for therapeutic intervention.

Exercise Intolerance in McArdle Disease: A Role for Cardiac Impairment? A Preliminary Study in Humans and Mice

INTRODUCTION

Whether cardiac impairment can be fully discarded in McArdle disease-the paradigm of "exercise intolerance," caused by inherited deficiency of the skeletal muscle-specific glycogen phosphorylase isoform ("myophosphorylase")-remains to be determined.

METHODS

Eight patients with McArdle disease and seven age/sex-matched controls performed a 15-min moderate, constant-load cycle-ergometer exercise bout followed by a maximal ramp test. Electrocardiographic and two-dimensional transthoracic (for cardiac dimension's assessment) and speckle tracking (for left ventricular global longitudinal strain (GLS) assessments) echocardiographic evaluations were performed at baseline. Electrocardiographic and GLS assessments were also performed during constant-load exercise and immediately upon maximal exertion. Four human heart biopsies were obtained in individuals without McArdle disease, and in-depth histological/molecular analyses were performed in McArdle and wild-type mouse hearts.

RESULTS

Exercise intolerance was confirmed in patients ("second wind" during constant-load exercise, -55% peak power output vs controls). As opposed to controls, patients showed a decrease in GLS during constant-load exercise, especially upon second wind occurrence, but with no other between-group difference in cardiac structure/function. Human cardiac biopsies showed that all three glycogen phosphorylase-myophosphorylase, but also liver and especially brain-isoforms are expressed in the normal adult heart, thereby theoretically compensating for eventual myophosphorylase deficiency. No overall histological (including glycogen depots), cytoskeleton, metabolic, or mitochondrial (morphology/network/distribution) differences were found between McArdle and wild-type mouse hearts, except for lower levels of pyruvate kinase M2 and translocase of outer-membrane 20-kDa subunit in the former.

CONCLUSIONS

This study provides preliminary evidence that cardiac structure and function seem to be preserved in patients with McArdle disease. However, the role for an impaired cardiac contractility associated with the second wind phenomenon should be further explored.

Chaperone therapy: Stabilization and enhancement of endogenous and exogenous lysosomal enzymes

Chaperone therapy is a new concept of molecular therapeutic approach to protein misfolding diseases, particularly to lysosomal diseases. Initially we started molecular analysis of culture cells, model animals and patients with Fabry disease and GM1-gangliosidosis. Some mutant enzyme proteins did not express the catalytic activity because of unstable molecular structure in somatic cells. The small molecule compound (chaperone) corrected misfolding of the unstable mutant protein, resulting in restoration of the enzyme activity (chaperone therapy). This pathological molecular event was studied first in endogenous mutant enzymes. Then a similar molecular interaction was found between the chaperone and the exogenous protein supplied for enzyme replacement therapy (ERT) in Pompe disease. This new chaperone-ERT combination therapy will become another useful technology in order to expand the application of chaperone therapy to a wide range of lysosomal diseases. Thus, chaperone therapy is expected in future for stabilization and enhancement of exogenously supplied ERT enzymes as well as endogenous mutant enzymes.

Lysosomal enzyme binding to the cation-independent mannose 6-phosphate receptor is regulated allosterically by insulin-like growth factor 2

The cation-independent mannose 6-phosphate receptor (CI-MPR) is clinically significant in the treatment of patients with lysosomal storage diseases because it functions in the biogenesis of lysosomes by transporting mannose 6-phosphate (M6P)-containing lysosomal enzymes to endosomal compartments. CI-MPR is multifunctional and modulates embryonic growth and fetal size by downregulating circulating levels of the peptide hormone insulin-like growth factor 2 (IGF2). The extracellular region of CI-MPR comprises 15 homologous domains with binding sites for M6P-containing ligands located in domains 3, 5, 9, and 15, whereas IGF2 interacts with residues in domain 11. How a particular ligand affects the receptor's conformation or its ability to bind other ligands remains poorly understood. To address these questions, we purified a soluble form of the receptor from newborn calf serum, carried out glycoproteomics to define the N-glycans at its 19 potential glycosylation sites, probed its ability to bind lysosomal enzymes in the presence and absence of IGF2 using surface plasmon resonance, and assessed its conformation in the presence and absence of IGF2 by negative-staining electron microscopy and hydroxyl radical protein footprinting studies. Together, our findings support the hypothesis that IGF2 acts as an allosteric inhibitor of lysosomal enzyme binding by inducing global conformational changes of CI-MPR.

Targeting lysosomal quality control as a therapeutic strategy against aging and diseases

Previously, lysosomes were primarily referred to as the digestive organelles and recycling centers within cells. Recent discoveries have expanded the lysosomal functional scope and revealed their critical roles in nutrient sensing, epigenetic regulation, plasma membrane repair, lipid transport, ion homeostasis, and cellular stress response. Lysosomal dysfunction is also found to be associated with aging and several diseases. Therefore, function of macroautophagy, a lysosome-dependent intracellular degradation system, has been identified as one of the updated twelve hallmarks of aging. In this review, we begin by introducing the concept of lysosomal quality control (LQC), which is a cellular machinery that maintains the number, morphology, and function of lysosomes through different processes such as lysosomal biogenesis, reformation, fission, fusion, turnover, lysophagy, exocytosis, and membrane permeabilization and repair. Next, we summarize the results from studies reporting the association between LQC dysregulation and aging/various disorders. Subsequently, we explore the emerging therapeutic strategies that target distinct aspects of LQC for treating diseases and combatting aging. Lastly, we underscore the existing knowledge gap and propose potential avenues for future research.

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.

Decoding the molecular mechanism of selective autophagy of glycogen mediated by autophagy receptor STBD1

Autophagy of glycogen (glycophagy) is crucial for the maintenance of cellular glucose homeostasis and physiology in mammals. STBD1 can serve as an autophagy receptor to mediate glycophagy by specifically recognizing glycogen and relevant key autophagic factors, but with poorly understood mechanisms. Here, we systematically characterize the interactions of STBD1 with glycogen and related saccharides, and determine the crystal structure of the STBD1 CBM20 domain with maltotetraose, uncovering a unique binding mode involving two different oligosaccharide-binding sites adopted by STBD1 CBM20 for recognizing glycogen. In addition, we demonstrate that the LC3-interacting region (LIR) motif of STBD1 can selectively bind to six mammalian ATG8 family members. We elucidate the detailed molecular mechanism underlying the selective interactions of STBD1 with ATG8 family proteins by solving the STBD1 LIR/GABARAPL1 complex structure. Importantly, our cell-based assays reveal that both the STBD1 LIR/GABARAPL1 interaction and the intact two oligosaccharide binding sites of STBD1 CBM20 are essential for the effective association of STBD1, GABARAPL1, and glycogen in cells. Finally, through mass spectrometry, biochemical, and structural modeling analyses, we unveil that STBD1 can directly bind to the Claw domain of RB1CC1 through its LIR, thereby recruiting the key autophagy initiation factor RB1CC1. In all, our findings provide mechanistic insights into the recognitions of glycogen, ATG8 family proteins, and RB1CC1 by STBD1 and shed light on the potential working mechanism of STBD1-mediated glycophagy.

Efficacy of avalglucosidase alfa on forced vital capacity percent predicted in treatment-naïve patients with late-onset Pompe disease: A pooled analysis of clinical trials

Background

The efficacy of avalglucosidase alfa (AVA) versus alglucosidase alfa (ALG) on forced vital capacity percent predicted (FVCpp) in patients with late-onset Pompe disease (LOPD) has been assessed in the Phase 3 COMET trial (NCT02782741). Due to the rarity of LOPD and thus small sample size in COMET, additional data were analyzed to gain further insights into the efficacy of AVA versus ALG.

Methods

Data from treatment-naive patients with LOPD were pooled from COMET and Phase 1/2 NEO1/NEO-EXT (NCT01898364/NCT02032524) trials for patients treated with AVA, and Phase 3 LOTS trial (NCT00158600) for patients treated with ALG. Regression analyses using mixed models with repeated measures consistent with those pre-specified in COMET were performed post-hoc. Analyses were adjusted for trials and differences in baseline characteristics. Four models were developed: Model 1 considered all trials; Model 2 included Phase 3 trials; Model 3 included Phase 3 trials and was adjusted for baseline ventilation use; Model 4 included COMET and NEO1/NEO-EXT (i.e., AVA trials only).

Results

Overall, 100 randomized patients from COMET (AVA, n = 51, ALG, n = 49), 60 from LOTS (ALG arm only), and three patients from NEO1/NEO-EXT (who received open-label AVA only) were considered for analysis. Mean age at enrollment was similar across trials (45.3-50.3 years); however, patients from LOTS had a longer mean duration of disease versus COMET and NEO1/NEO-EXT trials (9.0 years and 0.5-2.2 years, respectively) and younger mean age at diagnosis (36.2 years and 44.7-48.6 years, respectively). Least squares mean (95% confidence interval) improvement from baseline in FVCpp at Week 49-52 for AVA versus ALG was 2.43 (-0.13; 4.99) for COMET (n = 98); 2.31 (0.06; 4.57) for Model 1 (n = 160); 2.43 (0.21; 4.65) for Model 2 (n = 157); 2.80 (0.54; 5.05) for Model 3 (n = 154); and 2.27 (-0.30; 4.45) for Model 4 (n = 101).

Conclusions

Models 1 to 3, which had an increased sample size versus COMET, demonstrated a nominally significant effect on FVCpp favoring AVA versus ALG after 1 year of treatment, consistent with results from COMET.

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.

Mitochondrial Dysfunction in Glycogen Storage Disorders (GSDs)

Glycogen storage disorders (GSDs) are a group of inherited metabolic disorders characterized by defects in enzymes involved in glycogen metabolism. Deficiencies in enzymes responsible for glycogen breakdown and synthesis can impair mitochondrial function. For instance, in GSD type II (Pompe disease), acid alpha-glucosidase deficiency leads to lysosomal glycogen accumulation, which secondarily impacts mitochondrial function through dysfunctional mitophagy, which disrupts mitochondrial quality control, generating oxidative stress. In GSD type III (Cori disease), the lack of the debranching enzyme causes glycogen accumulation and affects mitochondrial dynamics and biogenesis by disrupting the integrity of muscle fibers. Malfunctional glycogen metabolism can disrupt various cascades, thus causing mitochondrial and cell metabolic dysfunction through various mechanisms. These dysfunctions include altered mitochondrial morphology, impaired oxidative phosphorylation, increased production of reactive oxygen species (ROS), and defective mitophagy. The oxidative burden typical of GSDs compromises mitochondrial integrity and exacerbates the metabolic derangements observed in GSDs. The intertwining of mitochondrial dysfunction and GSDs underscores the complexity of these disorders and has significant clinical implications. GSD patients often present with multisystem manifestations, including hepatomegaly, hypoglycemia, and muscle weakness, which can be exacerbated by mitochondrial impairment. Moreover, mitochondrial dysfunction may contribute to the progression of GSD-related complications, such as cardiomyopathy and neurocognitive deficits. Targeting mitochondrial dysfunction thus represents a promising therapeutic avenue in GSDs. Potential strategies include antioxidants to mitigate oxidative stress, compounds that enhance mitochondrial biogenesis, and gene therapy to correct the underlying mitochondrial enzyme deficiencies. Mitochondrial dysfunction plays a critical role in the pathophysiology of GSDs. Recognizing and addressing this aspect can lead to more comprehensive and effective treatments, improving the quality of life of GSD patients. This review aims to elaborate on the intricate relationship between mitochondrial dysfunction and various types of GSDs. The review presents challenges and treatment options for several GSDs.

Systematic Review of Genetic Substrate Reduction Therapy in Lysosomal Storage Diseases: Opportunities, Challenges and Delivery Systems

BACKGROUND

Genetic substrate reduction therapy (gSRT), which involves the use of nucleic acids to downregulate the genes involved in the biosynthesis of storage substances, has been investigated in the treatment of lysosomal storage diseases (LSDs).

OBJECTIVE

To analyze the application of gSRT to the treatment of LSDs, identifying the silencing tools and delivery systems used, and the main challenges for its development and clinical translation, highlighting the contribution of nanotechnology to overcome them.

METHODS

A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines was performed. PubMed, Scopus, and Web of Science databases were used for searching terms related to LSDs and gene-silencing strategies and tools.

RESULTS

Fabry, Gaucher, and Pompe diseases and mucopolysaccharidoses I and III are the only LSDs for which gSRT has been studied, siRNA and lipid nanoparticles being the silencing strategy and the delivery system most frequently employed, respectively. Only in one recently published study was CRISPR/Cas9 applied to treat Fabry disease. Specific tissue targeting, availability of relevant cell and animal LSD models, and the rare disease condition are the main challenges with gSRT for the treatment of these diseases. Out of the 11 studies identified, only two gSRT studies were evaluated in animal models.

CONCLUSIONS

Nucleic acid therapies are expanding the clinical tools and therapies currently available for LSDs. Recent advances in CRISPR/Cas9 technology and the growing impact of nanotechnology are expected to boost the clinical translation of gSRT in the near future, and not only for LSDs.

Mutation Spectrum of GAA Gene in Pompe Disease: Current Knowledge and Results of an Italian Study

Studying a patient with Pompe disease (PD) is like opening Pandora's box. The specialist is faced with numerous clinical features similar to those of several diseases, and very often the symptoms are well hidden and none is associated with this rare disease. In recent years, scientific interest in this disease has been growing more and more, but still no symptom is recognized as key to a correct diagnosis of it, nor is there any specific disease marker to date. New diagnostic/therapeutic proposals on disease allow for the diffusion of knowledge of this pathology for timely diagnosis of the patient. Due to unawareness and difficulty in diagnosis, many adults with PD are diagnosed with great delay. In this article, we report and discuss current knowledge of PD and provide new data from work conducted on a cohort of 2934 Italian subjects recruited in recent years. A genetic analysis of the GAA gene was performed on patients with significant clinical signs and pathological enzyme activity to define the genetic profile of subjects. This identified 39 symptomatic PD subjects with low acid alpha-glucosidase enzyme activity and the presence of two causative mutations in GAA gene regions. Furthermore, 22 subjects with genetic variants of uncertain significance (GVUS) were identified.

Adult Pompe disease: Analysis of 13 patients

INTRODUCTION

Pompe Disease (PD) is a lysosomal disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA), primarily manifesting as a progressive myopathy with early respiratory involvement. Enzyme replacement therapy (ERT) is available since 2006.

MATERIALS AND METHODS

We describe 13 patients with partial GAA deficiency, followed at Hospital 12 de Octubre, 8 of whom were receiving treatment.

RESULTS

8 patients exhibit symptoms, all with late onset. They display axial and proximal weakness predominantly in the lower limbs but maintain autonomous gait. Five patients require non-invasive mechanical ventilation due to respiratory insufficiency. All symptomatic patients receive ERT, and in 7/8 (87.5%), there is a decline in motor and pulmonary function after an average of 8.25 years of treatment (baseline and post-treatment FVC and 6MWT mean 86.6% vs 70.8% and 498 vs 430 meters, respectively).

CONCLUSION

Not all patients with partial GAA deficiency experience symptoms of PD, and symptomatic patients, despite ERT with recombinant alpha-glucosidase, mostly experience a gradual decline in motor and respiratory function.

Restoring immune balance with Tregitopes: A new approach to treating immunological disorders

The induction of immunological tolerance is a promising strategy for managing autoimmune diseases, allergies, and transplant rejection. Tregitopes, a class of peptides, have emerged as potential agents for this purpose. They activate regulatory T cells, which are pivotal in reducing inflammation and promoting tolerance, by binding to MHC II molecules and facilitating their processing and presentation to Treg cells, thereby encouraging their proliferation. Moreover, Tregitopes influence the phenotype of antigen-presenting cells by attenuating the expression of CD80, CD86, and MHC class II while enhancing ILT3, resulting in the inhibition of NF-kappa B signaling pathways. Various techniques, including in vitro and in silico methods, are applied to identify Tregitope candidates. Currently, Tregitopes play a vital role in balancing immune activation and tolerance in clinical applications such as Pompe disease, diabetes-related antigens, and the prevention of spontaneous abortions in autoimmune diseases. Similarly, Tregitopes can induce antigen-specific regulatory T cells. Their anti-inflammatory effects are significant in conditions such as autoimmune encephalomyelitis, inflammatory bowel disease, and Guillain-Barré syndrome. Additionally, Tregitopes have been leveraged to enhance vaccine design and efficacy. Recent advancements in understanding the potential benefits and drawbacks of IVIG and the discovery of the function and mechanism of Tregitopes have introduced Tregitopes as a popular option for immune system modulation. It is expected that they will bring about a significant revolution in the management and treatment of autoimmune and immunological diseases. This article is a comprehensive review of Tregitopes, concluding with the potential of these epitopes as a therapeutic avenue for immunological disorders.

Bioluminescent Assay for the Quantification of Cellular Glycogen Levels

Glycogen is a large polymer of glucose that functions as an important means of storing energy and maintaining glucose homeostasis. Glycogen synthesis and degradation pathways are highly regulated and their dysregulation can contribute to disease. Glycogen storage diseases are a set of disorders that arise from improper glycogen metabolism. Glycogen storage disease II, known as Pompe disease, is caused by a genetic mutation that leads to increased glycogen storage in cells and tissues, resulting in progressive muscle atrophy and respiratory decline for patients. One approach for treating Pompe disease is to reduce glycogen levels by interfering with the glycogen synthesis pathway through glycogen synthase inhibitors. To facilitate the study of glycogen synthase inhibitors in biological samples, such as cultured cells, a high-throughput approach for measuring cellular glycogen was developed. A bioluminescent glycogen detection assay was automated and used to measure the glycogen content in cells grown in 384-well plates. The assay successfully quantified reduced glycogen stores in cells treated with a series of glycogen synthase 1 inhibitors, validating the utility of the assay for drug screening efforts and demonstrating its value for therapy development and glycogen metabolism research.

104-week efficacy and safety of cipaglucosidase alfa plus miglustat in adults with late-onset Pompe disease: a phase III open-label extension study (ATB200-07)

The phase III double-blind PROPEL study compared the novel two-component therapy cipaglucosidase alfa + miglustat (cipa + mig) with alglucosidase alfa + placebo (alg + pbo) in adults with late-onset Pompe disease (LOPD). This ongoing open-label extension (OLE; NCT04138277) evaluates long-term safety and efficacy of cipa + mig. Outcomes include 6-min walk distance (6MWD), forced vital capacity (FVC), creatine kinase (CK) and hexose tetrasaccharide (Hex4) levels, patient-reported outcomes and safety. Data are reported as change from PROPEL baseline to OLE week 52 (104 weeks post-PROPEL baseline). Of 118 patients treated in the OLE, 81 continued cipa + mig treatment from PROPEL (cipa + mig group; 61 enzyme replacement therapy [ERT] experienced prior to PROPEL; 20 ERT naïve) and 37 switched from alg + pbo to cipa + mig (switch group; 29 ERT experienced; 8 ERT naive). Mean (standard deviation [SD]) change in % predicted 6MWD from baseline to week 104 was + 3.1 (8.1) for cipa + mig and - 0.5 (7.8) for the ERT-experienced switch group, and + 8.6 (8.6) for cipa + mig and + 8.9 (11.7) for the ERT-naïve switch group. Mean (SD) change in % predicted FVC was - 0.6 (7.5) for cipa + mig and - 3.8 (6.2) for the ERT-experienced switch group, and - 4.8 (6.5) and - 3.1 (6.7), respectively, in ERT-naïve patients. CK and Hex4 levels improved in both treatment groups by week 104 with cipa + mig treatment. Three patients discontinued the OLE due to infusion-associated reactions. No new safety signals were identified. Cipa + mig treatment up to 104 weeks was associated with overall maintained improvements (6MWD, biomarkers) or stabilization (FVC) from baseline with continued durability, and was well tolerated, supporting long-term benefits for patients with LOPD.Trial registration number: NCT04138277; trial start date: December 18, 2019.

Defect in degradation of glycogenin-exposed residual glycogen in lysosomes is the fundamental pathomechanism of Pompe disease

Pompe disease is a lysosomal storage disorder that preferentially affects muscles, and it is caused by GAA mutation coding acid alpha-glucosidase in lysosome and glycophagy deficiency. While the initial pathology of Pompe disease is glycogen accumulation in lysosomes, the special role of the lysosomal pathway in glycogen degradation is not fully understood. Hence, we investigated the characteristics of accumulated glycogen and the mechanism underlying glycophagy disturbance in Pompe disease. Skeletal muscle specimens were obtained from the affected sites of patients and mouse models with Pompe disease. Histological analysis, immunoblot analysis, immunofluorescence assay, and lysosome isolation were utilized to analyze the characteristics of accumulated glycogen. Cell culture, lentiviral infection, and the CRISPR/Cas9 approach were utilized to investigate the regulation of glycophagy accumulation. We demonstrated residual glycogen, which was distinguishable from mature glycogen by exposed glycogenin and more α-amylase resistance, accumulated in the skeletal muscle of Pompe disease. Lysosome isolation revealed glycogen-free glycogenin in wild type mouse lysosomes and variously sized glycogenin in Gaa-/- mouse lysosomes. Our study identified that a defect in the degradation of glycogenin-exposed residual glycogen in lysosomes was the fundamental pathological mechanism of Pompe disease. Meanwhile, glycogenin-exposed residual glycogen was absent in other glycogen storage diseases caused by cytoplasmic glycogenolysis deficiencies. In vitro, the generation of residual glycogen resulted from cytoplasmic glycogenolysis. Notably, the inhibition of glycogen phosphorylase led to a reduction in glycogenin-exposed residual glycogen and glycophagy accumulations in cellular models of Pompe disease. Therefore, the lysosomal hydrolysis pathway played a crucial role in the degradation of residual glycogen into glycogenin, which took place in tandem with cytoplasmic glycogenolysis. These findings may offer a novel substrate reduction therapeutic strategy for Pompe disease. © 2024 The Pathological Society of Great Britain and Ireland.

Using an In Vivo Mouse Model to Determine the Exclusion Criteria of Preexisting Anti-AAV9 Neutralizing Antibody Titer of Pompe Disease Patients in Clinical Trials

The efficacy of adeno-associated virus (AAV)-based gene therapy is dependent on effective viral transduction, which might be inhibited by preexisting immunity to AAV acquired from infection or maternal delivery. Anti-AAV neutralizing Abs (NAbs) titer is usually measured by in vitro assay and used for patient enroll; however, this assay could not evaluate NAbs' impacts on AAV pharmacology and potential harm in vivo. Here, we infused a mouse anti-AAV9 monoclonal antibody into Balb/C mice 2 h before receiving 1.2 × 1014 or 3 × 1013 vg/kg of rAAV9-coGAA by tail vein, a drug for our ongoing clinical trials for Pompe disease. The pharmacokinetics, pharmacodynamics, and cellular responses combined with in vitro NAb assay validated the different impacts of preexisting NAbs at different levels in vivo. Sustained GAA expression in the heart, liver, diaphragm, and quadriceps were observed. The presence of high-level NAb, a titer about 1:1000, accelerated vector clearance in blood and completely blocked transduction. The AAV-specific T cell responses tended to increase when the titer of NAb exceeded 1:200. A low-level NAbs, near 1:100, had no effect on transduction in the heart and liver as well as cellular responses, but decreased transduction in muscles slightly. Therefore, we propose to preclude patients with NAb titers > 1:100 from rAAV9-coGAA clinical trials.

Small-molecule inhibition of glycogen synthase 1 for the treatment of Pompe disease and other glycogen storage disorders

Glycogen synthase 1 (GYS1), the rate-limiting enzyme in muscle glycogen synthesis, plays a central role in energy homeostasis and has been proposed as a therapeutic target in multiple glycogen storage diseases. Despite decades of investigation, there are no known potent, selective small-molecule inhibitors of this enzyme. Here, we report the preclinical characterization of MZ-101, a small molecule that potently inhibits GYS1 in vitro and in vivo without inhibiting GYS2, a related isoform essential for synthesizing liver glycogen. Chronic treatment with MZ-101 depleted muscle glycogen and was well tolerated in mice. Pompe disease, a glycogen storage disease caused by mutations in acid α glucosidase (GAA), results in pathological accumulation of glycogen and consequent autophagolysosomal abnormalities, metabolic dysregulation, and muscle atrophy. Enzyme replacement therapy (ERT) with recombinant GAA is the only approved treatment for Pompe disease, but it requires frequent infusions, and efficacy is limited by suboptimal skeletal muscle distribution. In a mouse model of Pompe disease, chronic oral administration of MZ-101 alone reduced glycogen buildup in skeletal muscle with comparable efficacy to ERT. In addition, treatment with MZ-101 in combination with ERT had an additive effect and could normalize muscle glycogen concentrations. Biochemical, metabolomic, and transcriptomic analyses of muscle tissue demonstrated that lowering of glycogen concentrations with MZ-101, alone or in combination with ERT, corrected the cellular pathology in this mouse model. These data suggest that substrate reduction therapy with GYS1 inhibition may be a promising therapeutic approach for Pompe disease and other glycogen storage diseases.

Nutritional Approach in Selected Inherited Metabolic Cardiac Disorders-A Concise Summary of Available Scientific Evidence

Inborn errors of metabolism (IMDs) are a group of inherited diseases that manifest themselves through a myriad of signs and symptoms, including structural or functional cardiovascular damage. The therapy of these diseases is currently based on enzyme-replacement therapy, chaperone therapy or the administration of supplements and the establishment of personalized dietary plans. Starting from the major signs identified by the pediatric cardiologist that can indicate the presence of such a metabolic disease-cardiomyopathies, conduction disorders or valvular dysplasias-we tried to paint the portrait of dietary interventions that can improve the course of patients with mitochondrial diseases or lysosomal abnormalities. The choice of the two categories of inborn errors of metabolism is not accidental and reflects the experience and concern of the authors regarding the management of patients with such diagnoses. A ketogenic diet offers promising results in selected cases, although, to date, studies have failed to bring enough evidence to support generalized recommendations. Other diets have been successfully utilized in patients with IMDs, but their specific effect on the cardiac phenotype and function is not yet fully understood. Significant prospective studies are necessary in order to understand and establish which diet best suits every patient depending on the inherited metabolic disorder. The most suitable imagistic monitoring method for the impact of different diets on the cardiovascular system is still under debate, with no protocols yet available. Echocardiography is readily available in most hospital settings and brings important information regarding the impact of diets on the left ventricular parameters. Cardiac MRI (magnetic resonance imaging) could better characterize the cardiac tissue and bring forth both functional and structural information.

Late-Onset Pompe Disease with Normal Creatine Kinase Levels: The Importance of Rheumatological Suspicion

Pompe disease (PD), also defined as acid maltase deficiency, is a rare autosomal recessive disease that causes glycogen accumulation due to a deficiency of the lysosomal enzyme acid α-glucosidase. An excessive amount of undisposed glycogen causes progressive muscle weakness throughout the body. It particularly affects skeletal muscles and the nervous system, especially in the late-onset phase. Here, we present a clinical case of late-onset PD (LOPD) with normal CK (creatinine kinase) values treated after a misdiagnosis of demyelinating motor polyneuropathy and chronic inflammatory neuropathy. The suspicion of possible fibromyalgia induced the patient to seek a rheumatology consultation, and the investigations performed led to the diagnosis of PD. The patient was investigated for genetic and enzymatic studies. PD was diagnosed using the α-glucosidase assay on DBS. In LOPD, clinical manifestations, such as muscle weakness, exercise intolerance, myalgia, or even high hyperCKemia, often appear as nonspecific and may mimic a wide variety of other muscle disorders, such as limb muscle dystrophies, congenital, metabolic, or inflammatory myopathies. In our case, the patient had CK values in the normal range but with continued complaints typical of PD. An analysis of enzyme activity revealed a pathologic value, and genetic analysis identified the c.-32-13T>G mutation in homozygosis. The association of the pathological enzyme value and mutation in homozygosity with LOPD led to a familial segregation study. Our results contribute to the characterization of PD in Italy and support the importance of rheumatologic attention. This suggests further studies are needed to define the broad clinical and pathological spectrum observed in this disease.

Glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of rare, monogenic disorders that share a defect in the synthesis or breakdown of glycogen. This Primer describes the multi-organ clinical features of hepatic GSDs and muscle GSDs, in addition to their epidemiology, biochemistry and mechanisms of disease, diagnosis, management, quality of life and future research directions. Some GSDs have available guidelines for diagnosis and management. Diagnostic considerations include phenotypic characterization, biomarkers, imaging, genetic testing, enzyme activity analysis and histology. Management includes surveillance for development of characteristic disease sequelae, avoidance of fasting in several hepatic GSDs, medically prescribed diets, appropriate exercise regimens and emergency letters. Specific therapeutic interventions are available for some diseases, such as enzyme replacement therapy to correct enzyme deficiency in Pompe disease and SGLT2 inhibitors for neutropenia and neutrophil dysfunction in GSD Ib. Progress in diagnosis, management and definitive therapies affects the natural course and hence morbidity and mortality. The natural history of GSDs is still being described. The quality of life of patients with these conditions varies, and standard sets of patient-centred outcomes have not yet been developed. The landscape of novel therapeutics and GSD clinical trials is vast, and emerging research is discussed herein.

GAA variants associated with reduced enzymatic activity but lack of Pompe-related symptoms, incidentally identified by exome sequencing

Pompe disease is a rare metabolic myopathy caused by pathogenic variants affecting the activity of the lysosomal glycogen-degrading enzyme acid alpha-glucosidase (GAA). Impaired GAA function results in the accumulation of undegraded glycogen within lysosomes in multiple tissues but predominantly affects the skeletal, smooth and cardiac muscle. The degree of residual enzymatic activity appears to roughly correlate with the age of onset and the severity of the clinical symptoms. Here, we report four siblings in which the GAA variants NM_000152.5:c.2237G > C p.(Trp746Ser) and NM_000152.5:c.266G > A p.(Arg89His) were identified as an incidental finding of clinical exome sequencing. These variants are listed in the ClinVar and the Pompe disease GAA variant databases but are reported here for the first time in compound heterozygosity. All four siblings displayed normal urine tetrasaccharide levels and no clinical manifestations related to Pompe disease. Nevertheless, GAA enzymatic activity was within the range for late onset Pompe patients. Our report shows an association between a novel genotype and attenuated GAA enzymatic activity. The clinical significance can only be established by the regular monitoring of these individuals. The study highlights the major challenges for clinical care arising from incidental findings of next generation sequencing.

Glycogen-binding protein STBD1: Molecule and role in pathophysiology

Starch-binding domain-containing protein 1 (STBD1) is a glycogen-binding protein discovered in skeletal muscle gene differential expression that is pivotal to cellular energy metabolism. Recent studies have indicated that STBD1 is involved in many physiological processes, such as glycophagy, glycogen accumulation, and lipid droplet formation. Moreover, dysregulation of STBD1 causes multiple diseases, including cardiovascular disease, metabolic disease, and even cancer. Deletions and/or mutations in STBD1 promote tumorigenesis. Therefore, STBD1 has garnered considerable interest in the pathology community. In this review, we first summarized the current understanding of STBD1, including its structure, subcellular localization, tissue distribution, and biological functions. Next, we examined the roles and molecular mechanisms of STBD1 in related diseases. Based on available research, we discussed the novel function and future of STBD1, including its potential application as a therapeutic target in glycogen-related diseases. Given the significance of STBD1 in energy metabolism, an in-depth understanding of the protein is crucial for understanding physiological processes and developing therapeutic strategies for related diseases.

Screening data from 19 patients with late-onset Pompe disease for a phase I clinical trial of AAV8 vector-mediated gene therapy

Late-onset Pompe disease (LOPD) is a multisystem disorder with significant myopathy. The standard treatment is enzyme replacement therapy (ERT), a therapy that is lifesaving, yet with limitations. Clinical trials have emerged for other potential treatment options, including adeno-associated virus (AAV) gene therapy. We present clinical parameters and AAV antibody titers for 19 individuals with LOPD undergoing screening for a Phase I clinical trial with an AAV serotype 8 vector targeting hepatic transduction (AAV2/8-LSPhGAA). Reported clinical parameters included GAA genotype, assessments of muscle function, upright and supine spirometry, anti-recombinant human GAA antibody titers, and biomarkers. Variability in measured parameters and phenotypes of screened individuals was evident. Eligibility criteria required that all participants have six-minute walk test (6MWT) and upright forced vital capacity (FVC) below the expected range for normal individuals, and were stably treated with ERT for >2 years. All participants had Pompe disease diagnosed by enzyme deficiency, and all had the common c.-32-13T>G LOPD pathogenic variant. Screening identified 14 patients (74%) with no or minimal detectable neutralizing antibodies against AAV8 (titer ≤1:5). 6MWT distance varied significantly (percent of expected distance ranging from 24% to 91% with an average of 60 and standard deviation of 21). Upright FVC percent predicted ranged from 35% predicted to 91% predicted with an average of 66 and standard deviation of 18. None of the participants had significantly elevated alanine transaminase, which has been associated with LOPD and could complicate screening for hepatitis related to AAV gene therapy. We review the parameters considered in screening for eligibility for a clinical trial of AAV8 vector-mediated gene therapy.

Glycoproteomics of a Single Protein: Revealing Tens of Thousands of Myozyme Glycoforms by Hybrid HPLC-MS Approaches

Characterization of highly glycosylated biopharma-ceuticals by mass spectrometry is challenging because of the huge chemical space of coexistent glycoforms present. Here, we report the use of an array of HPLC-mass spectrometry-based approaches at different structural levels of released glycan, glycopeptide, and hitherto unexplored intact glycoforms to scrutinize the biopharmaceutical Myozyme, containing the highly complex lysosomal enzyme recombinant acid α-glucosidase. The intrinsic heterogeneity of recombinant acid α-glucosidase glycoforms was unraveled using a novel strong anion exchange HPLC-mass spectrometry approach involving a pH-gradient of volatile buffers to facilitate chromatographic separation of glycoforms based on their degree of sialylation, followed by the acquisition of native mass spectra in an Orbitrap mass spectrometer. Upon considering the structures of 60 different glycans attached to seven glycosylation sites in the intact protein, the large set of interdependent data acquired at different structural levels was integrated using a set of bioinformatic tools and allowed the annotation of intact glycoforms unraveling more than 1,000,000 putative intact glycoforms. Detectable isoforms also included several mannose-6-phosphate variants, which are essential for directing the drug toward its target, the lysosomes. Finally, for the first time, we sought to validate the intact glycoform annotations by integrating experimental data on the enzymatically dissected proteoforms, which reduced the number of glycoforms supported by experimental evidence to 42,104. The latter verification clearly revealed the strengths but also intrinsic limitations of this approach for fully characterizing such highly complex glycoproteins by mass spectrometry.

A Comprehensive Update on Late-Onset Pompe Disease

Pompe disease (PD) is an autosomal recessive disorder caused by mutations in the GAA gene that lead to a deficiency in the acid alpha-glucosidase enzyme. Two clinical presentations are usually considered, named infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), which differ in age of onset, organ involvement, and severity of disease. Assessment of acid alpha-glucosidase activity on a dried blood spot is the first-line screening test, which needs to be confirmed by genetic analysis in case of suspected deficiency. LOPD is a multi-system disease, thus requiring a multidisciplinary approach for efficacious management. Enzyme replacement therapy (ERT), which was introduced over 15 years ago, changes the natural progression of the disease. However, it has limitations, including a reduction in efficacy over time and heterogeneous therapeutic responses among patients. Novel therapeutic approaches, such as gene therapy, are currently under study. We provide a comprehensive review of diagnostic advances in LOPD and a critical discussion about the advantages and limitations of current and future treatments.

AAV-mediated delivery of secreted acid α-glucosidase with enhanced uptake corrects neuromuscular pathology in Pompe mice

Gene therapy is under advanced clinical development for several lysosomal storage disorders. Pompe disease, a debilitating neuromuscular illness affecting infants, children, and adults with different severity, is caused by a deficiency of lysosomal glycogen-degrading enzyme acid α-glucosidase (GAA). Here, we demonstrated that adeno-associated virus-mediated (AAV-mediated) systemic gene transfer reversed glycogen storage in all key therapeutic targets - skeletal and cardiac muscles, the diaphragm, and the central nervous system - in both young and severely affected old Gaa-knockout mice. Furthermore, the therapy reversed secondary cellular abnormalities in skeletal muscle, such as those in autophagy and mTORC1/AMPK signaling. We used an AAV9 vector encoding a chimeric human GAA protein with enhanced uptake and secretion to facilitate efficient spread of the expressed protein among multiple target tissues. These results lay the groundwork for a future clinical development strategy in Pompe disease.

Therapeutic Role of Pharmacological Chaperones in Lysosomal Storage Disorders: A Review of the Evidence and Informed Approach to Reclassification

The treatment landscape for lysosomal storage disorders (LSDs) is rapidly evolving. An increase in the number of preclinical and clinical studies in the last decade has demonstrated that pharmacological chaperones are a feasible alternative to enzyme replacement therapy (ERT) for individuals with LSDs. A systematic search was performed to retrieve and critically assess the evidence from preclinical and clinical applications of pharmacological chaperones in the treatment of LSDs and to elucidate the mechanisms by which they could be effective in clinical practice. Publications were screened according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) reporting guidelines. Fifty-two articles evaluating 12 small molecules for the treatment of seven LSDs are included in this review. Overall, a substantial amount of preclinical and clinical data support the potential of pharmacological chaperones as treatments for Fabry disease, Gaucher disease, and Pompe disease. Most of the available clinical evidence evaluated migalastat for the treatment of Fabry disease. There was a lack of consistency in the terminology used to describe pharmacological chaperones in the literature. Therefore, the new small molecule chaperone (SMC) classification system is proposed to inform a standardized approach for new, emerging small molecule therapies in LSDs.

From Acid Alpha-Glucosidase Deficiency to Autophagy: Understanding the Bases of POMPE Disease

Pompe disease (PD) is caused by mutations in the GAA gene, which encodes the lysosomal enzyme acid alpha-glucosidase, causing lysosomal glycogen accumulation, mainly in muscular tissue. Autophagic buildup is considered the main factor affecting skeletal muscle, although other processes are also involved. Uncovering how these mechanisms are interconnected could be an approximation to address long-lasting concerns, like the differential skeletal and cardiac involvement in each clinical phenotype. In this sense, a network reconstruction based on a comprehensive literature review of evidence found in PD enriched with the STRING database and other scientific articles is presented. The role of autophagic lysosome reformation, PGC-1α, MCOLN1, calcineurin, and Keap1 as intermediates between the events involved in the pathologic cascade is discussed and contextualized within their relationship with mTORC1/AMPK. The intermediates and mechanisms found open the possibility of new hypotheses and questions that can be addressed in future experimental studies of PD.

Targeted Therapies in Pediatric and Adult Patients With Hypertrophic Heart Disease: From Molecular Pathophysiology to Personalized Medicine

Hypertrophic cardiomyopathy is a myocardial disease defined by an increased left ventricular wall thickness not solely explained by abnormal loading conditions. It is often genetically determined, with sarcomeric gene mutations accounting for around 50% of cases. Several conditions, including syndromic, metabolic, infiltrative, and neuromuscular diseases, may present with left ventricular hypertrophy, mimicking the hypertrophic cardiomyopathy phenotype but showing a different pathophysiology, clinical course, and outcome. Despite being rare, they are collectively responsible for a large proportion of patients presenting with hypertrophic heart disease, and their timely diagnosis can significantly impact patients' management. The understanding of disease pathophysiology has advanced over the last few years, and several therapeutic targets have been identified, leading to a new era of tailored treatments applying to different etiologies associated with left ventricular hypertrophy. This review aims to provide an overview of the existing and emerging therapies for the principal causes of hypertrophic heart disease, discussing the potential impact on patients' management and clinical outcome.

The role of GPLD1 in chronic diseases

Glycosylphosphatidylinositol-specific phospholipase D (GPLD1) is a specific enzyme for glycosylphosphatidylinositol (GPI) anchors, thereby exerting its biological functions by cleaving membrane-associated GPI molecules. GPLD1 is abundant in serum, with a concentration of approximately 5-10 µg/mL. Previous studies have demonstrated that GPLD1 plays a crucial role in the pathogenesis of numerous chronic diseases including disorders of lipid and glucose metabolism, cancer, and neurological disorders. In the present study, we reviewed the structure, functions, and localization of GPLD1 in chronic diseases, as well as exercise-mediated regulation of GPLD1, thus providing a theoretical support to develop GPLD1 as a new therapeutic target for chronic diseases.

Cipaglucosidase Alfa: First Approval

Cipaglucosidase alfa (Pombiliti^™) is a recombinant human acid α-glucosidase (GAA) product being developed by Amicus Therapeutics along with the enzyme stabilizer miglustat as a two-component therapy for Pompe disease. Pompe disease is a rare, inherited lysosomal disease caused by a deficiency of the enzyme GAA, which leads to accumulation of glycogen in various tissues. On 27 March 2023, cipaglucosidase alfa was approved in the EU as a long-term enzyme replacement therapy (ERT) used in combination with miglustat for the treatment of adults with late-onset Pompe disease. This article summarizes the milestones in the development of cipaglucosidase alfa leading to this first approval.

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.

Quality of Life with Late-Onset Pompe Disease: Qualitative Interviews and General Public Utility Estimation in the United Kingdom

Background: Late-onset Pompe disease (LOPD) is a rare, progressive neuromuscular condition typically characterized by weakness of skeletal muscles, including those involved in respiration and diaphragmatic dysfunction. Individuals with LOPD typically eventually require mobility and/or ventilatory support. Objectives: This study aimed to develop health state vignettes and estimate health state utility values for LOPD in the United Kingdom. Methods: Vignettes were developed for 7 health states of LOPD with states defined in terms of mobility and/or ventilatory support. Vignettes were drafted based on patient-reported outcome data from the Phase 3 PROPEL trial (NCT03729362) and supplemented by a literature review. Qualitative interviews with individuals living with LOPD and clinical experts were conducted to explore the health-related quality-of-life (HRQoL) impact of LOPD and to review the draft vignettes. Vignettes were finalized following a second round of interviews with individuals living with LOPD and used in health state valuation exercises with people of the UK population. Participants rated the health states using the EQ-5D-5L, visual analogue scale, and time trade-off interviews. Results: Twelve individuals living with LOPD and 2 clinical experts were interviewed. Following the interviews, 4 new statements were added regarding dependence on others, bladder control problems, balance issues/fear of falling, and frustration. One hundred interviews with a representative UK population sample were completed. Mean time trade-off utilities ranged from 0.754 (SD = 0.31) (no support) to 0.132 (SD = 0.50) (invasive ventilatory and mobility support-dependent). Similarly, EQ-5D-5L utilities ranged from 0.608 (SD = 0.12) to -0.078 (SD = 0.22). Discussion: The utilities obtained in the study are consistent with utilities reported in the literature (0.670-0.853 for nonsupport state). The vignette content was based on robust quantitative and qualitative evidence and captured the main HRQoL impacts of LOPD. The general public rated the health states consistently lower with increasing disease progression. There was greater uncertainty around utility estimates for the severe states, suggesting that participants found it harder to rate them. Conclusion: This study provides utility estimates for LOPD that can be used in economic modeling of treatments for LOPD. Our findings highlight the high disease burden of LOPD and reinforce the societal value of slowing disease progression.

Induced pluripotent stem cell for modeling Pompe disease

Pompe disease (PD) is a rare, autosomal recessive, inherited, and progressive metabolic disorder caused by α-glucosidase defect in lysosomes, resulting in abnormal glycogen accumulation. Patients with PD characteristically have multisystem pathological disorders, particularly hypertrophic cardiomyopathy, muscle weakness, and hepatomegaly. Although the pathogenesis and clinical outcomes of PD are well-established, disease-modeling ability, mechanism elucidation, and drug development targeting PD have been substantially limited by the unavailable PD-relevant cell models. This obstacle has been overcome with the help of induced pluripotent stem cell (iPSC) reprogramming technology, thus providing a powerful tool for cell replacement therapy, disease modeling, drug screening, and drug toxicity assessment. This review focused on the exciting achievement of PD disease modeling and mechanism exploration using iPSC.

CONVENTIONAL APPROACHES TO THE THERAPY OF HEREDITARY MYOPATHIES

The aim of the work was to analyze the available therapeutic options for the conventional therapy of hereditary myopathies.

Materials and methods. When searching for the material for writing a review article, such abstract databases as PubMed and Google Scholar were used. The search was carried out on the publications during the period from 1980 to September 2022. The following words and their combinations were selected as parameters for the literature selection: “myopathy”, “Duchenne”, “myodystrophy”, “metabolic”, “mitochondrial”, “congenital”, “symptoms”, “replacement”, “recombinant”, “corticosteroids”, “vitamins”, “tirasemtiv”, “therapy”, “treatment”, “evidence”, “clinical trials”, “patients”, “dichloracetate”.

Results. Congenital myopathies are a heterogeneous group of pathologies that are caused by atrophy and degeneration of muscle fibers due to mutations in genes. Based on a number of clinical and pathogenetic features, hereditary myopathies are divided into: 1) congenital myopathies; 2) muscular dystrophy; 3) mitochondrial and 4) metabolic myopathies. At the same time, treatment approaches vary significantly depending on the type of myopathy and can be based on 1) substitution of the mutant protein; 2) an increase in its expression; 3) stimulation of the internal compensatory pathways expression; 4) restoration of the compounds balance associated with the mutant protein function (for enzymes); 5) impact on the mitochondrial function (with metabolic and mitochondrial myopathies); 6) reduction of inflammation and fibrosis (with muscular dystrophies); as well as 7) an increase in muscle mass and strength. The current review presents current data on each of the listed approaches, as well as specific pharmacological agents with a description of their action mechanisms.

Conclusion. Currently, the following pharmacological groups are used or undergoing clinical trials for the treatment of various myopathies types: inotropic, anti-inflammatory and antifibrotic drugs, antimyostatin therapy and the drugs that promote translation through stop codons (applicable for nonsense mutations). In addition, metabolic drugs, metabolic enzyme cofactors, mitochondrial biogenesis stimulators, and antioxidants can be used to treat myopathies. Finally, the recombinant drugs alglucosidase and avalglucosidase have been clinically approved for the replacement therapy of metabolic myopathies (Pompe’s disease).

Infantile Pompe disease with intrauterine onset: a case report and literature review

BACKGROUND

Pompe disease is a rare autosomal recessive disease. Acid alpha-glucosidase (GAA) deficiency leads to glycogen storage in lysosomes, causing skeletal, cardiac, and smooth muscle lesions. Pompe disease is progressive, and its severity depends on the age of onset. Classic infantile Pompe disease, the most severe form, is characterized by an age of onset before 12 months. Pompe disease with intrauterine onset has rarely been reported.

CASE PRESENTATION

The proband was born at a gestational age of 40 weeks and 3 days and admitted to our hospital because of intrauterine cardiac hypertrophy, shortness of breath, and cyanosis until 13 min postnatally. Physical examination at admission revealed poor responsiveness, pale skin, shortness of breath, reduced limb muscle tone, and bilateral pedal edema. The heart sounds were weak, and no heart murmur was heard. Echocardiography showed left (9 mm) and right (5 mm) ventricular hypertrophies. The patient was subjected to non-invasive ventilator-assisted respiration, fluid restriction, diuresis, and metoprolol treatment. Infantile Pompe disease was diagnosed on day 16 with a GAA enzymatic activity of 0.31 µmol/L/h and with the full-penetrance genetic test showing the homozygous gene mutation c.1844G>T(p.Gly615Val). Enzyme replacement therapy was refused by the patient's parents, and the patient died at seven months of age from cardiopulmonary failure.

CONCLUSION

Infants with intrauterine-onset Pompe disease usually have early manifestations of heart disease. Prompt GAA enzymatic activity determination and molecular genetic testing are helpful in aiding the parents' decision and planning the treatment.

Liposomal formulations for treating lysosomal storage disorders

Lysosomal storage disorders (LSD) are a group of rare life-threatening diseases caused by a lysosomal dysfunction, usually due to the lack of a single enzyme required for the metabolism of macromolecules, which leads to a lysosomal accumulation of specific substrates, resulting in severe disease manifestations and early death. There is currently no definitive cure for LSD, and despite the approval of certain therapies, their effectiveness is limited. Therefore, an appropriate nanocarrier could help improve the efficacy of some of these therapies. Liposomes show excellent properties as drug carriers, because they can entrap active therapeutic compounds offering protection, biocompatibility, and selectivity. Here, we discuss the potential of liposomes for LSD treatment and conduct a detailed analysis of promising liposomal formulations still in the preclinical development stage from various perspectives, including treatment strategy, manufacturing, characterization, and future directions for implementing liposomal formulations for LSD.

Lysosomal positioning diseases: beyond substrate storage

Lysosomal storage diseases (LSDs) comprise a group of inherited monogenic disorders characterized by lysosomal dysfunctions due to undegraded substrate accumulation. They are caused by a deficiency in specific lysosomal hydrolases involved in cellular catabolism, or non-enzymatic proteins essential for normal lysosomal functions. In LSDs, the lack of degradation of the accumulated substrate and its lysosomal storage impairs lysosome functions resulting in the perturbation of cellular homeostasis and, in turn, the damage of multiple organ systems. A substantial number of studies on the pathogenesis of LSDs has highlighted how the accumulation of lysosomal substrates is only the first event of a cascade of processes including the accumulation of secondary metabolites and the impairment of cellular trafficking, cell signalling, autophagic flux, mitochondria functionality and calcium homeostasis, that significantly contribute to the onset and progression of these diseases. Emerging studies on lysosomal biology have described the fundamental roles of these organelles in a variety of physiological functions and pathological conditions beyond their canonical activity in cellular waste clearance. Here, we discuss recent advances in the knowledge of cellular and molecular mechanisms linking lysosomal positioning and trafficking to LSDs.

Nutritional co-therapy with 1,3-butanediol and multi-ingredient antioxidants enhances autophagic clearance in Pompe disease

Alglucosidase alpha is an orphan drug approved for enzyme replacement therapy (ERT) in Pompe disease (PD); however, its efficacy is limited in skeletal muscle because of a partial blockage of autophagic flux that hinders intracellular trafficking and enzyme delivery. Adjunctive therapies that enhance autophagic flux and protect mitochondrial integrity may alleviate autophagic blockage and oxidative stress and thereby improve ERT efficacy in PD. In this study, we compared the benefits of ERT combined with a ketogenic diet (ERT-KETO), daily administration of an oral ketone precursor (1,3-butanediol; ERT-BD), a multi-ingredient antioxidant diet (ERT-MITO; CoQ10, α-lipoic acid, vitamin E, beetroot extract, HMB, creatine, and citrulline), or co-therapy with the ketone precursor and multi-ingredient antioxidants (ERT-BD-MITO) on skeletal muscle pathology in GAA-KO mice. We found that two months of 1,3-BD administration raised circulatory ketone levels to ≥1.2 mM, attenuated autophagic buildup in type 2 muscle fibers, and preserved muscle strength and function in ERT-treated GAA-KO mice. Collectively, ERT-BD was more effective vs. standard ERT and ERT-KETO in terms of autophagic clearance, dampening of oxidative stress, and muscle maintenance. However, the addition of multi-ingredient antioxidants (ERT-BD-MITO) provided the most consistent benefits across all outcome measures and normalized mitochondrial protein expression in GAA-KO mice. We therefore conclude that nutritional co-therapy with 1,3-butanediol and multi-ingredient antioxidants may provide an alternative to ketogenic diets for inducing ketosis and enhancing autophagic flux in PD patients.

1,6-epi-Cyclophellitol Cyclosulfamidate Is a Bona Fide Lysosomal α-Glucosidase Stabilizer for the Treatment of Pompe Disease

α-Glucosidase inhibitors are potential therapeutics for the treatment of diabetes, viral infections, and Pompe disease. Herein, we report a 1,6-epi-cyclophellitol cyclosulfamidate as a new class of reversible α-glucosidase inhibitors that displays enzyme inhibitory activity by virtue of its conformational mimicry of the substrate when bound in the Michaelis complex. The α-d-glc-configured cyclophellitol cyclosulfamidate 4 binds in a competitive manner the human lysosomal acid α-glucosidase (GAA), ER α-glucosidases, and, at higher concentrations, intestinal α-glucosidases, displaying an excellent selectivity over the human β-glucosidases GBA and GBA2 and glucosylceramide synthase (GCS). Cyclosulfamidate 4 stabilizes recombinant human GAA (rhGAA, alglucosidase alfa, Myozyme) in cell medium and plasma and facilitates enzyme trafficking to lysosomes. It stabilizes rhGAA more effectively than existing small-molecule chaperones and does so in vitro, in cellulo, and in vivo in zebrafish, thus representing a promising therapeutic alternative to Miglustat for Pompe disease.

A Multidisciplinary Perspective Addressing the Diagnostic Challenges of Late-Onset Pompe Disease in the Arabian Peninsula Region Developed From an Expert Group Meeting

Pompe disease is a rare, metabolic, autosomal recessive disorder. Early diagnosis is critical for progressive Pompe disease as delays can significantly alter the clinical course of the disease. Diagnostic modalities, including dried blood spot testing and genetic testing, are available and are effective for diagnosing patients with late-onset Pompe disease (LOPD). However, clinicians face numerous clinical challenges related to the diagnosis of the disease. Two expert group committee meetings, involving 11 experts from the United Arab Emirates, Kuwait, the Kingdom of Saudi Arabia, and Oman, were convened in October 2019 and November 2020 respectively to develop a uniform diagnostic algorithm for the diagnosis of pediatric and adult LOPD in the Arabian Peninsula region. During the first meeting, the specialty-specific clinical presentation of LOPD was defined. During the second meeting, a diagnostic algorithm was developed after a thorough validation of clinical presentation or symptoms, which was performed with the aid of existing literature and expert judgement. A consensus was reached on the diagnostic algorithm for field specialists, such as neurologists, rheumatologists, general practitioners/internal medicine specialists, orthopedic specialists, and pulmonologists. This specialty-specific diagnostic referral algorithm for pediatric and adult LOPD will guide clinicians in the differential diagnosis of LOPD.

Glycogen-autophagy: Molecular machinery and cellular mechanisms of glycophagy

Autophagy is an essential cellular process involving degradation of superfluous or defective macromolecules and organelles as a form of homeostatic recycling. Initially proposed to be a “bulk” degradation pathway, a more nuanced appreciation of selective autophagy pathways has developed in the literature in recent years. As a glycogen-selective autophagy process, “glycophagy” is emerging as a key metabolic route of transport and delivery of glycolytic fuel substrate. Study of glycophagy is at an early stage. Enhanced understanding of this major noncanonical pathway of glycogen flux will provide important opportunities for new insights into cellular energy metabolism. In addition, glycogen metabolic mishandling is centrally involved in the pathophysiology of several metabolic diseases in a wide range of tissues, including the liver, skeletal muscle, cardiac muscle, and brain. Thus, advances in this exciting new field are of broad multidisciplinary interest relevant to many cell types and metabolic states. Here, we review the current evidence of glycophagy involvement in homeostatic cellular metabolic processes and of molecular mediators participating in glycophagy flux. We integrate information from a variety of settings including cell lines, primary cell culture systems, ex vivo tissue preparations, genetic disease models, and clinical glycogen disease states.

The lysosome as an imperative regulator of autophagy and cell death

Lysosomes are single membrane-bound organelles containing acid hydrolases responsible for the degradation of cellular cargo and maintenance of cellular homeostasis. Lysosomes could originate from pre-existing endolysosomes or autolysosomes, acting as a critical juncture between autophagy and endocytosis. Stress that triggers lysosomal membrane permeabilization can be altered by ESCRT complexes; however, irreparable damage to the membrane results in the induction of a selective lysosomal degradation pathway, specifically lysophagy. Lysosomes play an indispensable role in different types of autophagy, including microautophagy, macroautophagy, and chaperone-mediated autophagy, and various cell death pathways such as lysosomal cell death, apoptotic cell death, and autophagic cell death. In this review, we discuss lysosomal reformation, maintenance, and degradation pathways following the involvement of the lysosome in autophagy and cell death, which are related to several pathophysiological conditions observed in humans.

Targeting neurological abnormalities in lysosomal storage diseases

Central nervous system (CNS) abnormalities and corresponding neurological and psychiatric symptoms are frequently observed in lysosomal storage disorders (LSDs). The genetic background of individual LSDs is indeed unique to each illness. However, resulting defective lysosomal function within the CNS can transition normal cellular processes (i.e., autophagy) into aberrant mechanisms, facilitating overlapping downstream consequences including neurocircuitry dysfunction, neurodegeneration as well as sensory, motor, cognitive, and psychological symptoms. Here, the neurological and biobehavioral phenotypes of major classes of LSDs are discussed alongside therapeutic strategies in development that aim to tackle neuropathology among other disease elements. Finally, focused ultrasound blood-brain barrier opening is proposed to enhance therapeutic delivery thereby overcoming the key hurdle of central distribution of disease modifying therapies in LSDs.

Correction of oxidative stress enhances enzyme replacement therapy in Pompe disease

Pompe disease is a metabolic myopathy due to acid alpha-glucosidase deficiency. In addition to glycogen storage, secondary dysregulation of cellular functions, such as autophagy and oxidative stress, contributes to the disease pathophysiology. We have tested whether oxidative stress impacts on enzyme replacement therapy with recombinant human alpha-glucosidase (rhGAA), currently the standard of care for Pompe disease patients, and whether correction of oxidative stress may be beneficial for rhGAA therapy. We found elevated oxidative stress levels in tissues from the Pompe disease murine model and in patients' cells. In cells, stress levels inversely correlated with the ability of rhGAA to correct the enzymatic deficiency. Antioxidants (N-acetylcysteine, idebenone, resveratrol, edaravone) improved alpha-glucosidase activity in rhGAA-treated cells, enhanced enzyme processing, and improved mannose-6-phosphate receptor localization. When co-administered with rhGAA, antioxidants improved alpha-glucosidase activity in tissues from the Pompe disease mouse model. These results indicate that oxidative stress impacts on the efficacy of enzyme replacement therapy in Pompe disease and that manipulation of secondary abnormalities may represent a strategy to improve the efficacy of therapies for this disorder.