Pompe Disease: From Basic Science to Therapy

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.

Plant molecular farming: a promising frontier for orphan drug production

Orphan diseases comprise a range of disorders that individually affect a small percentage of people, but collectively impact millions of people worldwide. Patients with this disorder often face significant challenges in diagnosis, treatment, and access to care due to their rare nature and limited understanding and treatment options. In recent years, significant advancements have been made in the global healthcare in addressing the accessibility of essential treatments and medicines, but still challenges persist particularly related to orphan drugs (to treat rare diseases) in the developing world. The accessibility of orphan drugs remains a major challenge, where patients face barriers such as high costs, limited availability, and inadequate healthcare infrastructure. The high cost associated with orphan drugs presents a barrier to affordability for both patients and healthcare systems, causing disparities in access to life-saving treatments. The molecular farming approach utilizing plant-based production systems for recombinant protein production offers a hope for overcoming barriers to orphan drug access in resource-constrained settings. Molecular farming has the potential to produce a wide range of therapeutic proteins and biologics for the treatment of various rare diseases. The FDA approval of plant-derived proteins for the treatment of Gaucher disease (Elelyso) and Fabry disease (Elfabrio) highlights the potential of plant-based expression systems for the development of suitable drugs targeting niche and orphan diseases. This review examines the potential of the plant system in producing orphan drugs and also highlights the opportunities and challenges related to orphan drug manufacturing.

Bone disease and osteoporosis associated with Pompe disease

Pompe disease is a lysosomal storage disorder defined by a mutation in the GAA gene encoding alpha-1,4-glucosidase alpha (acid maltase). Pompe disease encompasses a range of clinical presentations that are broadly characterized as either classic infantile Pompe disease or late-onset Pompe disease (LOPD). LOPD is a milder manifestation of the disease that presents after the first year of life and is typically characterized by mild proximal muscle weakness and lack of cardiac involvement compared to the classic infantile form. The mainstay of treatment is enzyme replacement therapy (EnRT). Decreased bone mineral density (BMD) is frequently encountered in LOPD. While bone loss is thought to be due to mechanical unloading secondary to the progressive muscle weakness associated with the disease, there is a lack of tissue-level data in support of this mechanism. We describe a 60-yr-old female with LOPD managed with EnRT who presented with proximal muscle weakness and decreased BMD on dual-energy X-ray absorptiometry. Undecalcified bone histology showed low turnover osteoporosis, and treatment was initiated with romosozumab. Romosozumab specifically may provide a promising osteoporosis therapy for LOPD-associated osteoporosis. As a sclerostin inhibitor, it both inhibits bone resorption and promotes new bone formation. We additionally emphasize that bone biopsy should be considered as a useful diagnostic tool in the evaluation of osteoporosis associated with uncommon pathologies, since bone histology provides more specific tissue-level information over clinical and laboratory evaluation as well as substantive guidance for treatment.

Focus on the Forgotten Organelle: Regulation of Lysosomes in Skeletal Muscle

Research on the role of the lysosome as the terminal organelle in autophagy and in communicating with other organelles in skeletal muscle is in its infancy. We hypothesize that the lysosome can adapt positively to exercise to improve the clearance of cargo, like dysfunctional mitochondria, within muscle, representing an important therapy for protein homeostasis in aging and muscle disuse.

Simultaneous monitoring of glycogen, creatine, and phosphocreatine in type II glycogen storage disease using saturation transfer MRI

PURPOSE

There is a need for non-invasive approaches to assess the progression of glycogen storage diseases (GSD). Here, we use saturation transfer (ST) MRI via relayed nuclear Overhauser effects (glycoNOE) to detect abnormal changes in muscle glycogen of a GSD II mouse model. In addition to glycogen, the energy metabolites phosphocreatine (PCr) and creatine (Cr) were studied to assess the muscle disease.

METHODS

Water saturation (Z-spectra) and 1H MRS were acquired at 9.4 T on the skeletal muscle of healthy control mice and homozygous acidα $$ \upalpha $$ -glucosidase (GAA) knock-out mice (ages of 2-48 weeks). The glycoNOE (-1 ppm), total creatine (tCr)* (+2 ppm, = a × [Cr] + b × [PCr]), and PCr (+2.5 ppm) from Z-spectra and the ratio between tCr and taurine signals (tCr/Tau) from 1H MRS spectra were quantified by using multi-pool Lorentzian fitting methods. The concentrations of the metabolites were also measured via tissue assays.

RESULTS

The postnatal GSD II mice (age <12 weeks) showed a continued accumulation of muscle glycoNOE signal. GlycoNOE in adult GSD II mice (age ≥12 weeks) reached a plateau, at a level above 400% of that in normal mice. PCr, tCr*, and tCr/Tau gradually decreased in GSD II mice during the postnatal stage, then stabilized at levels comparable to adult control, yet PCr in adult GSD II mice was lower than that in controls.

CONCLUSION

This study demonstrates that ST MRI of glycogen can provide in situ non-invasive biomarkers for GSD II disease progression, with the potential to study the progression and treatment response of GSDs.

Antibodies to recombinant human alpha-L-iduronidase prevent disease correction in cortical bone in MPS I mice

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disorder caused by deficiency of the enzyme α-l-iduronidase (IDUA). Failure of enzyme replacement therapy (ERT) to treat skeletal disease may be due to development of anti-IDUA antibodies, found previously to alter tissue distribution of ERT in animal models. To test this hypothesis, immunocompromised (non-obese diabetic [NOD]-severe combined immunodeficiency [SCID]) MPS I mice were treated with weekly ERT from birth (ERT alone). Some mice also received weekly injections of rabbit immunoglobulin G (IgG) against IDUA (immunized rabbit immune globulin [IRIG]) concomitant with ERT, imitating antibodies developed in patients (ERT+IRIG). Mice treated with ERT+IRIG showed lower IDUA activity and higher disease burden than mice treated with ERT alone in most tissues. Femora were harvested at 20 weeks for ex vivo microcomputed tomography (μCT). Femoral cortical bone thickness and cortical bone area in MPS I mice were greater than in unaffected mice. Mice treated with ERT alone had values that were statistically indistinguishable from carrier mice, while mice that received ERT+IRIG had no significant differences compared to vehicle-treated MPS I mice. The data suggests that immune-modulatory or immune-suppressive therapy to prevent or reduce the humoral immune response against ERT may improve treatment of skeletal disease due to MPS I.

Metabolic and proteomic profiles provide insights on mechanism of late onset Pompe disease

Late onset Pompe disease (LOPD) is caused by a deficiency of the enzyme acid α-glucosidase, resulting in glycogen accumulation in lysosomes. The mechanism of LOPD has been less explored. In this study, we used an integrative analysis of the proteomics and metabolomics of LOPD muscle samples to reveal the potential mechanisms. Proteomic analysis identified 635 upregulated proteins and 89 downregulated proteins in the LOPD group. Similarly, metabolomic analysis revealed 15 upregulated and 143 downregulated metabolites; notably, L-arginine levels were significantly decreased in the LOPD group. Lysosome-related GO terms were significantly upregulated, while GO terms related to neurofilament, cytoskeleton, axon ensheathment, and myelin sheath were significantly downregulated. KEGG pathway analysis demonstrated that the lysosome, autophagy, and mTOR pathways were distinctly upregulated. Correlation analysis indicated that CALML3 showed a potential correlation with LOPD severity. Our study highlighted the potential crosstalk among these LOPD-related pathways. Supplementation with L-arginine could represent a promising therapeutic approach for LOPD, and CALML3 could serve as a potential biomarker for LOPD severity. These findings provide valuable insights into the pathogenesis of LOPD and suggest avenues for future therapeutic development.

Management of Pompe disease alongside and beyond ERT: a narrative review

Background

Pompe disease is a lysosomal storage disorder that primarily affects muscles, and its natural history has been transformed over the past 20 years by therapies designed to restore the deficient enzyme function, from the first enzyme replacement therapies (ERTs) to the gene therapy currently in development. However, despite these ground-breaking innovations, the importance of a multi-system and rehabilitative approach remains critical, as it addresses the complex systems involved in the disease and optimizes the success of pharmacological treatments.

Methods

We conducted a narrative review of the current pharmacological treatments approved for Pompe disease, as well as those undergoing clinical trials. We also reviewed international recommendations for managing respiratory, musculoskeletal, and cardiac function specially focusing on the late-onset form.

Results

There are no universally agreed guidelines for the multidisciplinary management and many recommendations are based on expert consensus and small interventional studies. Nevertheless, combined approaches involving ERT therapy along with specific rehabilitation and nutritional programs appear to yield beneficial effects.

Conclusions

Pompe disease, one of the first neuromuscular diseases to benefit from the approval of disease-modifying therapies, is a paradigm for the importance of an integrated therapeutic-rehabilitative approach.

A Real-World Data Analysis of Alglucosidase Alfa in the FDA Adverse Event Reporting System (FAERS) Database

BACKGROUND AND OBJECTIVE

Alglucosidase alfa for injection is used as an enzyme replacement therapy for the treatment of Pompe disease. The safety profile of alglucosidase alfa-associated adverse events requires a comprehensive evaluation. In this study, we aimed to identify drug safety alert signals and investigate the real-world safety of alglucosidase alfa to guide clinical decision making and optimize the risk-benefit balance.

METHODS

The adverse event reports from the first quarter of 2006 to the fourth quarter of 2023 were selected by exploring the Food and Drug Administration Adverse Event Reporting System (FAERS) database. The new and unexpected potential adverse event signals were detected using a disproportionality analysis, including the reporting odds ratio, the proportional reporting ratio, the Bayesian confidence propagation neural network, and the empirical Bayes geometric mean. Then, the Medical Dictionary for Regulatory Activities was used to systematically classify the results.

RESULTS

After analyzing 16,945,027 adverse event reports, a total of 4326 cases of adverse events related to alglucosidase alfa were identified, spanning 27 system organ classes. A total of 359 preferred terms of adverse events for glucosidase alpha were detected. Pyrexia ranked first, followed by pneumonia, dyspnea, respiratory failure, and disease progression according to occurrence frequency. The top three system organ classes were general disorders and administration-site conditions (n = 2466), respiratory, thoracic, and mediastinal disorders (n = 1749), and infections and infestations (n = 1551). In addition to adverse effects mentioned in the product label, our study also discovered rare but high signal intensity adverse events such as chronic recurrent multifocal osteomyelitis.

CONCLUSIONS

There are many adverse events associated with the clinical use of alglucosidase alfa, which should be closely monitored in the FAERS database. As the most effective enzyme replacement therapy for Pompe disease, it is crucial to closely monitor these adverse events. Ensuring patient safety while balancing drug effectiveness is particularly important.

Exploring the use of the National Institutes of Health Toolbox Cognition Battery with children and adolescents with Pompe disease: Preliminary findings

BACKGROUND

Although Pompe disease (PD) was originally characterized as a metabolic myopathy, there is now emerging evidence of neurological involvement in children and adolescents with infantile-onset Pompe disease (IOPD). Therefore, assessing cognition and detecting cognitive changes in these individuals over time have become important components of their care. The National Institutes of Health Toolbox Cognition Battery (NIHT-CB, Version 2) is a brief, standardized instrument designed to measure cognitive processes in individuals 3-85 years of age. With its availability and ease of administration by a trained provider, the NIHT-CB could potentially be used in a clinical health care setting to help screen/monitor cognition in individuals with PD. This is the first study to report the use of the NIHT-CB in children and adolescents with IOPD and late-onset Pompe disease (LOPD) and their performance on this instrument in comparison to traditional neuropsychological measures.

METHODS

Fourteen children with IOPD (median age = 10.5, range = 6-19 years) and eight with LOPD (median age = 12.5, range = 7-17 years) were administered the NIHT-CB and a neuropsychological battery by the same psychologist with expertise in PD.

RESULTS

On the NIHT-CB and selected neuropsychological measures, nearly all median scores for the IOPD group were lower than those of the LOPD group. However, none of the differences between the IOPD and LOPD groups were statistically significant. Consistent with previous reports, there was a wide range of scores among the IOPD and LOPD participants on both the neuropsychological measures and the NIHT-CB. The lowest median NIHT-CB score for both groups was on the Flanker Inhibitory Control and Attention Test (IOPD = 77.5, LOPD = 84), a measure of executive function and selective attention. Positive, significant relationships were found between the NIHT-CB and neuropsychological measures of overall cognition, reading decoding, and short-term working memory on the Wechsler Intelligence Test scales and the Woodcock-Johnson Tests of Achievement subtest for the IOPD group only.

CONCLUSIONS

Though not a replacement for an established neuropsychological battery, the NIHT-CB could potentially be used as a screening measure to provide a baseline level of cognitive functioning in children and adolescents with IOPD. Observed changes in the NIHT-CB Cognitive Function Composite or selected subtests over time may also signal the need for a more comprehensive neuropsychological battery and/or brain imaging studies as indicated. Longitudinal studies examining the performance of a larger cohort of IOPD and LOPD children and adults at multiple time points are needed.

Efficacy of transitioning from alglucosidase alfa to avalglucosidase alfa in infantile-onset Pompe disease: A single-center cohort analysis

PURPOSE

Although alglucosidase alfa (AGL) is the standard treatment for Pompe disease, its efficacy is limited, partially because of its low mannose-6-phosphate content. Avalglucosidase alfa (AVA), a glycoengineered recombinant human acid α-glucosidase, has shown improved receptor-mediated uptake compared with AGL. Herein, we report the long-term efficacy and safety of AVA in patients with infantile-onset Pompe disease (IOPD) previously treated with AGL.

METHODS

This retrospective cohort study included 9 patients with IOPD who transitioned from AGL to AVA; these patients were diagnosed and treated after being detected with IOPD via newborn screening. We analyzed the clinical status, biomarker levels (serum creatine kinase and urine glucose tetrasaccharide), and functional assessments before and after AVA treatment of these patients. Statistical analyses were performed using the Wilcoxon matched-pair signed-rank test.

RESULTS

Due to inadequate responses, all 9 patients received AGL at dosages exceeding the label recommendations, including one who also had tried cipaglucosidase alfa plus miglustat before transitioning to AVA. After transitioning to AVA at a dosage of 40 mg/kg every other week for a median duration of 4.9 years, the patients experienced significant reductions in biomarker levels (serum creatine kinase levels decreased by 63% and urine glucose tetrasaccharide levels decreased by 69%). Functional assessments, including pulmonary function and 6-minute walk tests, showed improvement in young patients but remained stable in older patients. Safety analyses revealed manageable infusion-associated reactions. Immune modulation therapy for antidrug antibodies was administered to 1 IOPD patient.

CONCLUSION

The transition from a high dose of AGL to AVA demonstrated sustained improvements in biomarker levels and motor function in patients with IOPD. Early initiation of AVA is crucial for patients with IOPD.

Rescue of common and rare exon 2 skipping variants of the GAA gene using modified U1 snRNA

BACKGROUND

Pompe disease (PD) is an autosomal recessive lysosomal storage disorder caused by the deficient activity of acid alpha glucosidase (GAA) enzyme due to mutations in the GAA gene. As a result, undigested glycogen accumulates within lysosomes causing their dysfunction. From a clinical point of view, the disease can be classified in infantile-onset (IO) and late-onset (LO) forms. The common GAA c.-32-13T>G variant, found in 40-70% of LO-PD alleles, is a leaky splicing mutation interfering with the correct GAA exon 2 recognition by the spliceosome leading to the production of non-functional GAA transcripts. In this study, we used modified, GAA-tailored U1 snRNAs to correct the aberrant splicing determined by the c.-32-13T>G and other GAA exon 2-skipping mutations.

METHODS

A set of constructs expressing 5 different engineered U1 snRNAs was generated. A functional splicing assay using a GAA hybrid minigene carrying different variants known to affect GAA exon 2 splicing was used to test the effect of engineered U1 snRNAs on exon 2 inclusion. The effect on endogenously expressed GAA transcript and GAA enzymatic activity was assessed by transfecting patient-derived fibroblasts bearing the common c.-32-13T>G with the best performing modified U1 snRNA.

RESULTS

Modified U1-3, U1+1 and U1+6 snRNAs were all able to increase, in a dose-dependent manner, the inclusion of exon 2 within the transcript derived from the GAA minigene harbouring the c.-32-13T>G variant. The U1+1 was the most effective one (2,5 fold increase). Moreover, U1+1 snRNA partially rescued the correct splicing of GAA minigenes harbouring mutations that affect the 3'ss (c.-32-3C>G, c.-32-2A>G) and the 5'ss (c.546G>A, c.546G>C, c.546G>T). Notably, the treatment of patient-derived fibroblasts carrying the c.-32-13T>G mutation with the U1+1 snRNA increased the amount of normal GAA mRNA by 1,8 fold and the GAA enzymatic activity by 70%.

CONCLUSIONS

we provide the proof-of-concept for the use of modified GAA-tailored U1 snRNAs, designed to potentiate the recognition of the GAA exon 2 5'ss, as therapeutic tools to correct the aberrant transcripts carrying variants that affect exon 2 splicing, including the common c.-32-13T>G variant.

Clinical manifestations in Egyptian Pompe disease patients: Molecular variability and enzyme replacement therapy (ERT) outcomes

BACKGROUND

Pompe disease is a rare genetic disorder caused by a deficiency of the enzyme acid alpha-glucosidase. This condition leads to muscle weakness, respiratory problems, and heart abnormalities in affected individuals.

METHODS

The aim of the study is to share our experience through cross sectional study of patients with infantile-onset Pompe disease (IOPD) with different genetic variations, resulting in diverse clinical presentations. We evaluated their phenotype, genotype, radiological and laboratory findings including their cross-reactive immunologic material (CRIM) status. Infantile Pompe disease was diagnosed by measurement of the activity of the enzyme alpha-glucosidase. The diagnosis was confirmed by molecular genetic testing using PCR amplification and sequencing of the acid alpha-glucosidase (GAA) gene. Routine two-D echocardiography, and multi-parametric ECG-gated cardiac magnetic resonance imaging (CMR) were done to patients six months after starting enzyme replacement therapy (ERT).

RESULTS

The results of our study revealed different genetic mutations among our patients, different CRIM status and also CMR abnormalities. CMR imaging revealed abnormalities in all cases that underwent the procedure, including myocardial and vascular changes, with feature tracking indicating issues across all parameters and LGE suggesting fibrosis. The patient with a positive immune response had the most severe cardiac abnormalities, despite improvements in muscle weakness and motor skills from ERT. This underscores that delayed diagnosis and ERT can lead to irreversible heart damage from autophagy buildup.

CONCLUSION

Pompe disease has various clinical presentations and results in significant CMR findings, which can be attributed to different genetic mutations. Early initiation of enzyme replacement therapy in infantile-onset Pompe disease is important to maximize its benefits.

Highlights of Precision Medicine, Genetics, Epigenetics and Artificial Intelligence in Pompe Disease

Pompe disease is a neuromuscular disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA), which leads to lysosomal glycogen accumulation and progressive development of muscle weakness. Two distinct isoforms have been identified. In the infantile form, the weakness is often severe and leads to motor difficulties from the first few months of life. In adult patients, the progression is slower but can still lead to significant loss of mobility. The current inherent difficulties of the disease lie in both early diagnosis and the use of biomarkers. Given that this is a multifactorial disease, a number of components may exert an influence on the disease process; from the degree of pre-ERT (enzyme replacement therapy) muscle damage to the damaged autophagic system and the different pathways involved. What methodology should be employed to study the complex characteristics of Pompe disease? Our approach relies on the application of genetic and epigenetic knowledge, with a progression from proteomics to transcriptomics. It is also becoming increasingly evident that artificial intelligence is a significant area of interest. The objective of this study is to conduct a comprehensive review of the existing literature on the known data and complications associated with the disease in patients with disorders attributed to Pompe disease.

A novel CD71 Centyrin:Gys1 siRNA conjugate reduces glycogen synthesis and glycogen levels in a mouse model of Pompe disease

Pompe disease is caused by acid alpha-glucosidase (GAA) deficiency, resulting in lysosomal glycogen accumulation. This disease is characterized by progressive skeletal muscle weakness, respiratory distress, and in the infantile-onset form, cardiomyopathy. The only approved treatment is enzyme replacement therapy (ERT) with human recombinant GAA. While ERT therapy extends life span, residual symptoms remain, with poor muscle uptake and immunogenicity limiting efficacy. We examined a novel Centyrin protein-short interfering ribonucleic acid (siRNA) conjugate targeting CD71 (transferrin receptor type 1, TfR1) and GYS1, a key enzyme involved in glycogen synthesis. Unlike existing ERTs designed to degrade aberrant glycogen deposits observed in Pompe patients, the CD71 Centyrin:Gys1 siRNA is designed to restore glycogen balance by inhibiting glycogen synthesis. To this end, we administered the CD71 Centyrin:Gys1 siRNA conjugate to the 6neo/6neo Pompe mouse model. Once bound to TfR1, siRNA-conjugated Centyrin is internalized into cells to facilitate gene knockdown. We found that treatment with this conjugate significantly reduced GYS1 protein expression, glycogen synthase enzymatic activity, and glycogen levels in muscle. In addition, impaired treadmill exercise performance of male Pompe mice was improved. These data suggest that Centyrin-mediated delivery of Gys1 siRNA may be an effective next generation therapy for late-onset Pompe disease or, in combination with ERT, for infantile-onset Pompe disease.

Clinical Reasoning: A 65-Year-Old Woman With Isolated Macroglossia as the Initial Presentation of a Rare Disease

Macroglossia can be seen in multiple conditions, but its evaluation becomes more challenging when approached as an isolated presenting symptom. This is a case of a 65-year-old patient with isolated progressive tongue hypertrophy of unclear etiology for 5 years. We navigate the causes of macroglossia and discuss the clinical and diagnostic procedures that helped us narrow the differential diagnoses for our patient. We emphasize searching for evidence of more systemic involvement and the use of appropriate genetic testing to change the course of the disease and avoid therapeutic delay.

Late onset of Pompe's disease: a rare cause of respiratory failure

A woman in her 30s was admitted acutely to the emergency department with severe respiratory failure of unknown cause. On arrival, the patient was severely compromised with a reduced Glasgow Coma scale and arterial pCO2 > 14 kPa. She was intubated and taken to the intensive care unit for respiratory support and further investigations.A detailed patient history revealed multiple admissions in the psychiatric sector with anxiety disorder, as well as numerous admissions to the emergency department with progressive tremors, muscle fatigue and dyspnoea, all of which were interpreted as anxiety attacks. Based on this history, we suspected a neurological disorder in our patient. Following extensive neurological investigation and additional genetic studies, the diagnosis of late-onset Pompe's disease was confirmed.Late-onset Pompe's disease can pose a diagnostic challenge due to its multifaceted presentation with non-specific symptoms. Any patient not responding to treatment should urge clinicians to re-evaluate their differential diagnoses.

Global birth prevalence of Pompe disease: A systematic review and meta-analysis

BACKGROUND

Pompe disease, also known as Glycogen storage disease type II, is an autosomal recessive disorder caused by defects in alpha-glucosidase, resulting in abnormal glycogen accumulation.

METHODS

To conduct a systematic review and meta-analysis of birth prevalence of Pompe disease, the MEDLINE and EMBASE databases were searched for original research articles on the epidemiology of Pompe disease from inception until July 01, 2024. Meta-analysis was performed to estimate global birth prevalence of Pompe disease. The funnel plot was used to describe potential publication bias.

RESULTS

Twenty-two studies, screened out of 945 records, were included for data extraction. Studies that fulfilled inclusion criteria involved 15 areas/countries. Global birth prevalence of Pompe disease was 2.0 cases (95% CI: 1.5-2.4) per 100,000 live births. Global birth prevalence of infantile-onset Pompe disease was 1.0 cases (95% CI: 0.5-1.5) per 100,000 live births. Global birth prevalence of late-onset Pompe disease was 2.4 cases (95% CI: 1.8-3.0) per 100,000 live births. The main limitations are that no study was assessed as high-quality and approximately half of the studies were from Europe.

CONCLUSIONS

Quantitative data on the global epidemiology of Pompe disease could be the fundamental to evaluate the global efforts on building a better world for Pompe disease patients.

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.

Clinical modeling of motor function to predict treatment efficacy and enable in silico treatment comparisons in infantile-onset Pompe disease

Infantile-onset Pompe disease (IOPD) is a rare, deadly, quickly-progressing degenerative disease. Even with life-sustaining treatment (e.g., alglucosidase alfa [ALGLU]), many patients experience continued motor impairment. The Mini-COMET trial evaluated avalglucosidase alfa (AVAL) versus ALGLU on motor and other outcomes in IOPD. However, treatment groups were imbalanced at baseline and the trial was not powered to directly compare treatments. To supplement this limited data, we developed a modeling and simulation approach to compare AVAL versus ALGLU head-to-head in in silico (i.e., computer-simulated) trials. We first developed a longitudinal clinical model to establish the relationship between changes in motor function and changes in urinary hexose tetrasaccharide (uHex4), an established biomarker in IOPD. This model was based on pooled data from Mini-COMET (n = 21) and COMET trials (n = 100 patients with late-onset Pompe disease, LOPD). We then conducted in silico trials mimicking Mini-COMET. Simulated trials were informed by motor data generated from the clinical model and uHex4 profiles simulated in a quantitative systems pharmacology model. The virtual IOPD population was based on observed Mini-COMET baseline characteristics but engineered to have well-balanced baseline characteristics across treatment cohorts. In silico trials showed that patients with IOPD would have the greatest improvements in motor function with AVAL 40 mg/kg every other week (Q2W), suboptimal improvement with ALGLU 40 mg/kg Q2W, and no improvement with ALGLU 20 mg/kg Q2W. This study provides information on the relative efficacy of IOPD treatments and mitigates the confounding effects of imbalanced treatment cohorts. Our approach could also be applied in other rare diseases.

Analyzing immune cell infiltrates in skeletal muscle of infantile-onset Pompe disease using bioinformatics and machine learning

Pompe disease, a severe lysosomal storage disorder, is marked by heart problems, muscle weakness, and respiratory difficulties. This study aimed to identify novel markers for infantile-onset Pompe disease by analyzing key genes and immune cells infiltrating affected skeletal muscles, building on existing research linking its progression to the immune cell infiltration. The datasets GSE38680 and GSE159062 were downloaded and differential expression genes (DEGs) were identified. Potential markers were screened using support vector machine recursive feature elimination (SVM-RFE) analysis and least absolute shrinkage and selection operator (LASSO) regression models. To analyze DEGs and immune processes, 22 immune cell types in affected tissues were examined using CIBERSORT. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed significant enrichment in the calcium signaling pathway, phosphatidylinositol signaling system, ubiquitin-mediated proteolysis and JAK-STAT signaling pathway. Machine learning identified GPNMB, CALML6 and TRIM7 as key genes. Immune cell infiltration analysis showed that the expression levels of the above three genes were closely related to immune cells in our target population under study, including T cells regulatory (Tregs), monocytes, macrophages M0, resting and activated dendritic cells, naive and memory B cells. Overall, our study results may provide new clues for exploring markers related to Pompe disease by highlighting key genes and their relationship with immune infiltration, offering insights into the disease's development. However, previous studies have shown limited evidence of significant immune cell infiltration in muscle biopsies from Pompe patients, and this lack of direct evidence necessitates further investigation and experimental validation in laboratory settings to confirm these associations.

Pompe disease: Unmet needs and emerging therapies

Pompe disease is a debilitating and life-threatening disease caused by aberrant accumulation of glycogen resulting from reduced acid alpha-glucosidase activity. The first treatment for Pompe disease, the enzyme replacement therapy, Myozyme® (recombinant human acid alpha-glucosidase, alglucosidase alfa), is a lifesaving treatment for the most severe form of the disease and provided clinically meaningful benefits to patients with milder phenotypes. Nonetheless, many patients display suboptimal responses or clinical decline following years of alglucosidase alfa treatment. The approval of avalglucosidase alfa (Nexviazyme®) and cipaglucosidase alfa (Pombiliti®) with miglustat (Opfolda®) represents a new generation of enzyme replacement therapies seeking to further improve patient outcomes beyond alglucosidase alfa. However, the emergence of a complicated new phenotype with central nervous system involvement following long-term treatment, coupled with known and anticipated unmet needs of patients receiving enzyme replacement therapy, has prompted development of innovative new treatments. This review provides an overview of the challenges of existing treatments and a summary of emerging therapies currently in preclinical or clinical development for Pompe disease and related lysosomal storage disorders. Key treatments include tissue-targeted enzyme replacement therapy, which seeks to enhance enzyme concentration in target tissues such as the central nervous system; substrate reduction therapy, which reduces intracellular glycogen concentrations via novel mechanisms; and gene therapy, which may restore endogenous production of deficient acid alpha-glucosidase. Each of these proposed treatments shows promise as a future therapeutic option to improve quality of life in Pompe disease by more efficiently treating the underlying cause of disease progression: glycogen accumulation.

Biochemical and Genetic Testing of GAA in Over 30.000 Symptomatic Patients Suspected to Be Affected With Pompe Disease

Pompe disease (PD) is a rare autosomal recessive lysosomal disorder caused by loss-of-function of the α-glucosidase (GAA) gene. The deficient GAA enzyme activity may result in potential life-threatening muscle weakness, thus requiring a rapid diagnosis to initiate therapeutic interventions. In this large retrospective study, we analyzed 30.836 PD suspect samples from 57 countries using a two-step approach utilizing dried blood spots (DBSs): biochemical testing of GAA activity followed by complementary genetic sequencing of GAA in biochemically conspicuous cases. Of these 30.836 samples, 2% (n = 639) were excluded; accordingly, this study consisted of 30.193 cases. Biochemical testing of GAA enzyme activity showed normal values in 28.354 (93.90%) and enzyme activity below the cut-off in 1843 (6.10%) cases. These biochemically suspicious cases were genetically analyzed. We identified 723 Pompe cases with 283 different GAA alterations, and 98 variants have been unpublished so far. The most common variant was the splice variant c.-32-13T>G (IVS1). Looking at the IVS1-genotype, the majority was compound heterozygous (n = 169) and identified in late-onset cases (n = 162). Comparison of early- versus late-onset cases to evaluate whether certain genotypes correlate with the age of onset revealed that homozygosity was predominantly found in infantile (85.65%) and compound heterozygosity in late-onset (76.9%) cases. Analysis of homozygous cases revealed 61% nonsense variants in the early stages and 87% missense variants in the late stages. Mapping of disease-associated (homozygous) missense variants to functional GAA protein domains showed that missense variants were found throughout GAA, but we identified enrichment in the catalytic domain. A strict genotype-phenotype correlation cannot be established; nevertheless, a phenotypic implication of some GAA variants could be drawn (e.g., c.896T>C/p.L299P, c.2015G>A/p.R672Q, and c.-32-13T>G). The combined enzyme activity and genetic testing from DBS cards can reliably identify PD and significantly accelerate diagnosis. We identified new genetic variants that contribute to the spectrum of pathogenic variants of the GAA gene.

Small molecule inhibition of glycogen synthase I reduces muscle glycogen content and improves biomarkers in a mouse model of Pompe disease

Pompe disease is a rare genetic disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA). This enzyme is responsible for breaking down glycogen, leading to the abnormal accumulation of glycogen, which results in progressive muscle weakness and metabolic dysregulation. In this study, we investigated the hypothesis that the small molecule inhibition of glycogen synthase I (GYS1) may reduce muscle glycogen content and improve metabolic dysregulation in a mouse model of Pompe disease. To address this hypothesis, we studied four groups of male mice: a control group of wild-type (WT) B6129SF1/J mice fed either regular chow or a GYS1 inhibitor (MZ-101) diet (WT-GYS1), and Pompe model mice B6;129-Gaatm1Rabn/J fed either regular chow (GAA-KO) or MZ-101 diet (GAA-GYS1) for 7 days. Our findings revealed that GAA-KO mice exhibited abnormal glycogen accumulation in the gastrocnemius, heart, and diaphragm. In contrast, inhibiting GYS1 reduced glycogen levels in all tissues compared with GAA-KO mice. Furthermore, GAA-KO mice displayed reduced spontaneous activity during the dark cycle compared with WT mice, whereas GYS1 inhibition counteracted this effect. Compared with GAA-KO mice, GAA-GYS1 mice exhibited improved glucose tolerance and whole body insulin sensitivity. These improvements in insulin sensitivity could be attributed to increased AMP-activated protein kinase phosphorylation in the gastrocnemius of WT-GYS1 and GAA-GYS1 mice. Additionally, the GYS1 inhibitor led to a reduction in the phosphorylation of GSS641 and the LC3 autophagy marker. Together, our results suggest that targeting GYS1 could serve as a potential strategy for treating glycogen storage disorders and metabolic dysregulation.NEW & NOTEWORTHY We investigated the effects of small molecule inhibition of glycogen synthase I (GYS1) on glucose metabolism in a mouse model of Pompe disease. GYS1 inhibition reduces abnormal glycogen accumulation and molecular biomarkers associated with Pompe disease while also improving glucose intolerance. Our results collectively demonstrate that the GYS1 inhibitor represents a novel approach to substrate reduction therapy for Pompe disease.

Non-invasive optoacoustic imaging of glycogen-storage and muscle degeneration in late-onset Pompe disease

Pompe disease (PD) is a rare autosomal recessive glycogen storage disorder that causes proximal muscle weakness and loss of respiratory function. While enzyme replacement therapy (ERT) is the only effective treatment, biomarkers for disease monitoring are scarce. Following ex vivo biomarker validation in phantom studies, we apply multispectral optoacoustic tomography (MSOT), a laser- and ultrasound-based non-invasive imaging approach, in a clinical trial (NCT05083806) to image the biceps muscles of 10 late-onset PD (LOPD) patients and 10 matched healthy controls. MSOT is compared with muscle magnetic resonance imaging (MRI), ultrasound, spirometry, muscle testing and quality of life scores. Next, results are validated in an independent LOPD patient cohort from a second clinical site. Our study demonstrates that MSOT enables imaging of subcellular disease pathology with increases in glycogen/water, collagen and lipid signals, providing higher sensitivity in detecting muscle degeneration than current methods. This translational approach suggests implementation in the complex care of these rare disease patients.

Clinical insight meets scientific innovation to develop a next generation ERT for Pompe disease

Years of research into the structure, processing, and function of acid alpha-glucosidase led to the development and 2006 approval of alglucosidase alfa (recombinant human acid alpha-glucosidase, Myozyme®/Lumizyme®), an enzyme replacement therapy and the first approved treatment for Pompe disease. Alglucosidase alfa has been a lifesaving treatment for patients with infantile-onset Pompe disease and radically improved daily life for patients with late-onset Pompe disease; however, long-term experience with alglucosidase alfa unraveled key unmet needs in these populations. Despite treatment, Pompe disease continues to progress, especially from a skeletal muscle perspective, resulting in a multitude of functional limitations. Strong collaboration between the scientific and patient communities led to increased awareness of Pompe disease, a better understanding of disease pathophysiology, knowledge of the clinical course of the disease as patients surpassed the first decade of life, and the strengths and limitations of enzyme replacement therapy. Taken together, these advancements spurred the need for development of a next generation of enzyme replacement therapy and provided a framework for progress toward other novel treatments. This review provides an overview of the development of avalglucosidase alfa as a model to highlight the interaction between clinical experience with existing treatments, the role of the clinician scientist, translational research at both system and cellular levels, and the iterative and collaborative process that optimizes the development of therapeutics.

Clinical features and genetic analysis of 5 cases of infantile-type glycogen storage disease type II: Case reports

OBJECTIVE

Clinical and genetic mutation analysis was performed on 5 infantile glycogen storage disease type II children in Chinese mainland.

METHODS

Clinical data of 5 children with infantile-type glycogen storage disease type II due to the acidic α-glucosidase (GAA) gene variants diagnosed and treated at Hebei Provincial Children's Hospital from January 2018 to April 2020 were retrospectively analyzed.

RESULTS

Among the 5 cases, 1 was female and 4 were male, and the age at first diagnosis was from 2 months to 7 months. The first symptoms of all 5 cases showed progressive muscle weakness, hypotonia, and motor developmental backwardness, and all of them had abnormally elevated creatine kinase, and the echocardiograms suggested different degrees of myocardial hypertrophy, with ejection fractions ranging from 44% to 67%. Analysis of GAA gene variations: all 5 cases were compound heterozygous, and a total of 12 variant loci were detected, of which c.2024_2026delACA, c.2853G > A, c.1124G > T, c.574G > A, c.2509C > T, and c.2013G > A were new mutations that had not been reported.

FOLLOWUP

All 5 children died before 1 year of age, and the age of death ranged from 7 months to 11.5 months, with a mean survival time of 9.8 months.

CONCLUSION

Peripheral blood GAA gene testing and alpha-glucosidase enzyme activity testing is an effective method for diagnosing this disease.

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.

Long term survival in patients with classic infantile Pompe disease reveals a spectrum with progressive brain abnormalities and changes in cognitive functioning

The aim of this longitudinal cohort study, is to provide more insight into the pattern of brain abnormalities, and possible consequences for cognitive functioning, in patients with classic infantile Pompe disease. We included 19 classic infantile Pompe patients (median age last assessment 8.9 years, range 1.5-22.5 years; 5/19 CRIM negative), treated with ERT. Using MR imaging of the brain (T1, T2, and FLAIR acquisitions), we classified progression of brain abnormalities on a 12-point rating scale at multiple time points throughout follow-up. Additionally we noted specific white matter patterns and examined atrophy. Cognitive development was studied using Wechsler IQ assessments obtained by certified neuropsychologists. The association between age and cognitive functioning, and MRI ratings and cognitive functioning was assessed by linear regression models. All but one patient developed brain abnormalities. The abnormalities progressed in a similar pattern throughout the brain, with early involvement of periventricular white matter, later followed by subcortical white matter, gray matter structures, and juxtacortical U-fibers. We found a significant decline (p < 0.01), with increasing age for full scale IQ, performance IQ and processing speed, but not for verbal IQ (p = 0.17). Each point increment in the 12-point MRI rating scale was associated with a significant decline (3.1-6.0 points) in all the IQ index scores (p < 0.05). The majority of long-term surviving patients in our cohort develop incremental brain MRI abnormalities and decline in cognitive functioning. This highlights the need for new therapies that can cross the blood-brain barrier in order to treat this CNS phenotype.

The Multi-Omic Approach to Newborn Screening: Opportunities and Challenges

Newborn screening programs have seen significant evolution since their initial implementation more than 60 years ago, with the primary goal of detecting treatable conditions within the earliest possible timeframe to ensure the optimal treatment and outcomes for the newborn. New technologies have driven the expansion of screening programs to cover additional conditions. In the current era, the breadth of screened conditions could be further expanded by integrating omic technologies such as untargeted metabolomics and genomics. Genomic screening could offer opportunities for lifelong care beyond the newborn period. For genomic newborn screening to be effective and ready for routine adoption, it must overcome barriers such as implementation cost, public acceptability, and scalability. Metabolomics approaches, on the other hand, can offer insight into disease phenotypes and could be used to identify known and novel biomarkers of disease. Given recent advances in metabolomic technologies, alongside advances in genomics including whole-genome sequencing, the combination of complementary multi-omic approaches may provide an exciting opportunity to leverage the best of both approaches and overcome their respective limitations. These techniques are described, along with the current outlook on multi-omic-based NBS research.

Acid α-glucosidase (GAA) activity and glycogen content in muscle biopsy specimens of patients with Pompe disease: A systematic review

Pompe disease is a rare genetic disorder characterized by a deficiency of acid α-glucosidase (GAA), leading to the accumulation of glycogen in various tissues, especially in skeletal muscles. The disease manifests as a large spectrum of phenotypes from infantile-onset Pompe disease (IOPD) to late-onset Pompe disease (LOPD), depending on the age of symptoms onset. Quantifying GAA activity and glycogen content in skeletal muscle provides important information about the disease severity. However, the distribution of GAA and glycogen levels in skeletal muscles from healthy individuals and those impacted by Pompe disease remains poorly understood, and there is currently no universally accepted standard assay for GAA activity measurement. This systematic literature review aims to provide an overview of the available information on GAA activity and glycogen content levels in skeletal muscle biopsies from patients with Pompe disease. A structured review of PubMed and Google Scholar literature (with the latter used to check that no additional publications were identified) was conducted to identify peer-reviewed publications on glycogen storage disease type II [MeSH term] + GAA, protein human (supplementary concept), Pompe, muscle; and muscle, acid alpha-glucosidase. A limit of English language was applied. Results were grouped by methodologies used to quantify GAA activity and glycogen content in skeletal muscle. The search and selection strategy were devised and carried out in line with Preferred Reporting of Items in Systematic Reviews and Meta-Analysis guidelines and documented using a flowchart. Bibliographies of papers included in the analysis were reviewed and applicable publications not already identified in the search were included. Of the 158 articles retrieved, 24 (comprising >100 muscle biopsies from >100 patients) were included in the analysis, with four different assays. Analysis revealed that patients with IOPD exhibited markedly lower GAA activity in skeletal muscles than those with LOPD, regardless of the measurement method employed. Additionally, patients with IOPD had notably higher glycogen content levels in skeletal muscles than those with LOPD. In general, however, it was difficult to fully characterize GAA activity because of the different methods used. The findings underscore the challenges in the interpretation and comparison of the results across studies because of the substantial methodological variations. There is a need to establish standardized reference ranges of GAA activity and glycogen content in healthy individuals and in Pompe disease patients based on globally standardized methods to improve comparability and reliability in assessing this rare disease.

Diaphragm weakness in late-onset Pompe disease: A complex interplay between lower motor neuron and muscle fibre degeneration

BACKGROUND

Late-onset Pompe disease (LOPD) patients may still need ventilation support at some point of their disease course, despite regular recombinant human alglucosidase alfa treatment. This suggest that other pathophysiological mechanisms than muscle fibre lesion can contribute to the respiratory failure process. We investigate through neurophysiology whether spinal phrenic motor neuron dysfunction could contribute to diaphragm weakness in LOPD patients.

MATERIAL AND METHODS

A group of symptomatic LOPD patients were prospectively studied in our centre from January 2022 to April 2023. We collected both demographic and clinical data, as well as neurophysiological parameters. Phrenic nerve conduction studies and needle EMG sampling of the diaphragm were perfomed.

RESULTS

Eight treated LOPD patients (3 males, 37.5%) were investigated. Three patients (37.5%) with no respiratory involvement had normal phrenic nerve motor responses [median phrenic compound muscle action potential (CMAP) amplitude of 0.49 mV; 1st-3rd interquartile range (IQR), 0.48-0.65]. Those with respiratory failure (under nocturnal non-invasive ventilation) had abnormal phrenic nerve motor responses (median phrenic CMAP amplitude of 0 mV; 1st-3rd IQR, 0-0.15), and were then investigated with EMG. Diaphragm needle EMG revealed both myopathic and neurogenic changes in 3 (60%) and myopathic potentials in 1 patient. In the last one, no motor unit potentials could be recruited.

CONCLUSIONS

Our study provide new insights regarding respiratory mechanisms in LOPD, suggesting a contribution of spinal phrenic motor neuron dysfunction for diaphragm weakness. If confirmed in further studies, our results recommend the need of new drugs crossing the blood-brain barrier.

Failure of Autophagy in Pompe Disease

Autophagy is an evolutionarily conserved lysosome-dependent degradation of cytoplasmic constituents. The system operates as a critical cellular pro-survival mechanism in response to nutrient deprivation and a variety of stress conditions. On top of that, autophagy is involved in maintaining cellular homeostasis through selective elimination of worn-out or damaged proteins and organelles. The autophagic pathway is largely responsible for the delivery of cytosolic glycogen to the lysosome where it is degraded to glucose via acid α-glucosidase. Although the physiological role of lysosomal glycogenolysis is not fully understood, its significance is highlighted by the manifestations of Pompe disease, which is caused by a deficiency of this lysosomal enzyme. Pompe disease is a severe lysosomal glycogen storage disorder that affects skeletal and cardiac muscles most. In this review, we discuss the basics of autophagy and describe its involvement in the pathogenesis of muscle damage in Pompe disease. Finally, we outline how autophagic pathology in the diseased muscles can be used as a tool to fast track the efficacy of therapeutic interventions.

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.

Treatment of infantile-onset Pompe disease in a rat model with muscle-directed AAV gene therapy

OBJECTIVE

Pompe disease (PD) is caused by deficiency of the lysosomal enzyme acid α-glucosidase (GAA), leading to progressive glycogen accumulation and severe myopathy with progressive muscle weakness. In the Infantile-Onset PD (IOPD), death generally occurs <1 year of age. There is no cure for IOPD. Mouse models of PD do not completely reproduce human IOPD severity. Our main objective was to generate the first IOPD rat model to assess an innovative muscle-directed adeno-associated viral (AAV) vector-mediated gene therapy.

METHODS

PD rats were generated by CRISPR/Cas9 technology. The novel highly myotropic bioengineered capsid AAVMYO3 and an optimized muscle-specific promoter in conjunction with a transcriptional cis-regulatory element were used to achieve robust Gaa expression in the entire muscular system. Several metabolic, molecular, histopathological, and functional parameters were measured.

RESULTS

PD rats showed early-onset widespread glycogen accumulation, hepato- and cardiomegaly, decreased body and tissue weight, severe impaired muscle function and decreased survival, closely resembling human IOPD. Treatment with AAVMYO3-Gaa vectors resulted in widespread expression of Gaa in muscle throughout the body, normalizing glycogen storage pathology, restoring muscle mass and strength, counteracting cardiomegaly and normalizing survival rate.

CONCLUSIONS

This gene therapy holds great potential to treat glycogen metabolism alterations in IOPD. Moreover, the AAV-mediated approach may be exploited for other inherited muscle diseases, which also are limited by the inefficient widespread delivery of therapeutic transgenes throughout the muscular system.

[Juvenile Pompe disease: Undescribed genotype. First report in Quintana Roo]

Background

Pompe disease (PD) is a rare autosomal recessive genetic disorder (1 in 14,000) which affects the synthesis of acid alpha-glucosidase (AGA), leading to intralysosomal glycogen accumulation in muscle tissue. The clinical presentation is heterogeneous, with variable degrees of involvement and progression, classifiable based on the age of onset into infantile (classic or non-classic) and late-onset forms (juvenile or adult). The diagnostic test of choice is the enzymatic analysis of AGA, and the only pharmacological treatment is enzyme replacement therapy (ERT). This document aims to report a clinical case of late-onset PD.

Clinical case

14-year-old male who started at the age of 5 with postural alterations, gait changes, and decreased physical performance compared to his peers. A diagnostic evaluation was initiated in 2022 due to worsening neuromuscular symptoms, accompanied by dyspnea, tachycardia, and chest pain. A suspicion of a lysosomal storage myopathy was established, and through enzymatic determination of AGA the diagnosis of PD was confirmed. The study of the GAA gene revealed the association of 2 previously unreported genomic variants. ERT was initiated, resulting in clinical improvement.

Conclusions

The age of symptom onset, severity of clinical presentation, and prognosis of the disease depend on the specific mutations involved. In this case, the identified genetic alterations are associated with different phenotypes. However, based on the clinical presentation, it is categorized as juvenile PD with an indeterminate prognosis.

Description of clinical and genetic features of 122 patients included in the Spanish Pompe registry

Pompe disease is a rare genetic disorder with an estimated prevalence of 1:60.000. The two main phenotypes are Infantile Onset Pompe Disease (IOPD) and Late Onset Pompe Disease (LOPD). There is no published data from Spain regarding the existing number of cases, regional distribution, clinical features or, access and response to the treatment. We created a registry to collect all these data from patients with Pompe in Spain. Here, we report the data of the 122 patients registered including nine IOPD and 113 LOPD patients. There was a high variability in how the diagnosis was obtained and how the follow-up was performed among different centres. Seven IOPD patients were still alive being all treated with enzymatic replacement therapy (ERT) at last visit. Ninety four of the 113 LOPD patients had muscle weakness of which 81 were receiving ERT. We observed a progressive decline in the results of muscle function tests during follow-up. Overall, the Spanish Pompe Registry is a valuable resource for understanding the demographics, patient's journey and clinical characteristics of patients in Spain. Our data supports the development of agreed guidelines to ensure that the care provided to the patients is standardized across the country.

Higher dose alglucosidase alfa is associated with improved overall survival in infantile-onset Pompe disease (IOPD): data from the Pompe Registry

BACKGROUND

Studies indicate that doses of alglucosidase alfa (ALGLU) higher than label dose (20 mg/kg every other week) improve clinical outcomes in infantile-onset Pompe disease (IOPD). We investigated data from the Pompe Registry to determine the association between ALGLU dose and survival in IOPD.

RESULTS

We included 332 IOPD patients from the Registry as of January 2022 who had cardiomyopathy and were first treated at age < 1 year. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between ALGLU as a time-varying exposure and survival, adjusting for age at first treatment, sex, and cross-reactive immunologic material (CRIM)/immune tolerance induction (ITI) status. Dose was measured as average relative dose received over time (in multiples of label dose, range > 0 to 4 times label dose), current dose, and lagged dose. 81% patients received label dose at treatment initiation. Over time, 52% received a higher dose. Higher ALGLU dose over time was associated with improved survival: adjusted HR 0.40 (95% CI 0.22-0.73, p = 0.003) per 1-unit increase in average relative dose, with similar results for invasive ventilation-free survival (adjusted HR 0.48, 95% CI 0.28-0.84; p = 0.010). The association was consistent in patients first treated before or after 3 months of age and did not vary significantly by CRIM status. Results for current and lagged dose were similar to average dose.

CONCLUSIONS

Higher ALGLU doses were associated with significantly improved overall and invasive ventilator-free survival in IOPD. Results were consistent across sensitivity analyses.

Intrauterine enzyme replacement therapies for lysosomal storage disorders: Current developments and promising future prospects

Lysosomal storage disorders (LSDs) are a group of monogenic condition, with many characterized by an enzyme deficiency leading to the accumulation of an undegraded substrate within the lysosomes. For those LSDs, postnatal enzyme replacement therapy (ERT) represents the standard of care, but this treatment has limitations when administered only postnatally because, at that point, prenatal disease sequelae may be irreversible. Furthermore, most forms of ERT, specifically those administered systemically, are currently unable to access certain tissues, such as the central nervous system (CNS), and furthermore, may initiate an immune response. In utero enzyme replacement therapy (IUERT) is a novel approach to address these challenges evaluated in a first-in-human clinical trial for IUERT in LSDs (NCT04532047). IUERT has numerous advantages: in-utero intervention may prevent early pathology; the CNS can be accessed before the blood-brain barrier forms; and the unique fetal immune system enables exposure to new proteins with the potential to prevent an immune response and may induce sustained tolerance. However, there are challenges and limitations for any fetal procedure that involves two patients. This article reviews the current state of IUERT for LSDs, including its advantages, limitations, and potential future directions for definitive therapies.

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.

Case report: Chronic pain in a pediatric patient with late-onset pompe disease

Pompe disease (PD) is a rare inherited metabolic disorder of deficient or absent acid alpha-glucosidase (GAA), resulting in defective lysosomal glycogen catabolism. Muscle weakness, respiratory deficiency and gastrointestinal symptoms are commonly monitored in PD. However, pain and associated psychological symptoms are less focused upon. A pediatric patient with late-onset Pompe disease (LOPD) comorbid with chronic pain is presented. Symptoms of pain in the feet were first reported between 6 and 7 years of age and were attributed to growing pains. Following progression of lower body pain, weakness, fatigue, and difficulties with ambulation, a thorough clinical assessment including genetic testing was performed, which led to a diagnosis of LOPD at 9 years of age. ERT with recombinant human alglucosidase alfa was subsequently started. The patient's clinical status is compounded by depressed mood, anxiety, and attention deficit hyperactivity disorder, which may further exacerbate pain. A multidisciplinary pain treatment approach consisting of orthopedics, physical therapy, and psychosocial therapy aimed at enhancing pain coping skills is described for this LOPD patient. This case highlights the need for a greater understanding of pain generation and identification of optimized pain treatment approaches in children with LOPD that can be implemented alongside ERT.

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.

Monitoring and Management of Respiratory Function in Pompe Disease: Current Perspectives

Pompe disease (PD) is a neuromuscular disorder caused by a deficiency of acid alpha-glucosidase (GAA) - a lysosomal enzyme responsible for hydrolyzing glycogen. GAA deficiency leads to accumulation of glycogen in lysosomes, causing cellular disruption. The severity of PD is directly related to the extent of GAA deficiency - if no or minimal GAA is produced, symptoms are severe and manifest in infancy, known as infantile onset PD (IOPD). If left untreated, infants with IOPD experience muscle hypotonia and cardio-respiratory failure leading to significant morbidity and mortality in the first year of life. In contrast, late-onset PD (LOPD) patients have more GAA activity and present later in life, but also have significant respiratory function decline. Despite FDA-approved enzyme replacement therapy, respiratory insufficiency remains a major cause of morbidity and mortality, emphasizing the importance of early detection and management of respiratory complications. These complications include impaired cough and airway clearance, respiratory muscle weakness, sleep-related breathing issues, and pulmonary infections. This review aims to provide an overview of the respiratory pathology, monitoring, and management of PD patients. In addition, we discuss the impact of novel approaches and therapies on respiratory function in PD.

Dissecting the multifaced function of transcription factor EB (TFEB) in human diseases: From molecular mechanism to pharmacological modulation

The transcription factor EB (TFEB) is a transcription factor of the MiT/TFE family that translocations from the cytoplasm to the nucleus in response to various stimuli, including lysosomal stress and nutrient starvation. By activating genes involved in lysosomal function, autophagy, and lipid metabolism, TFEB plays a crucial role in maintaining cellular homeostasis. Dysregulation of TFEB has been implicated in various diseases, including cancer, neurodegenerative diseases, metabolic diseases, cardiovascular diseases, infectious diseases, and inflammatory diseases. Therefore, modulating TFEB activity with agonists or inhibitors may have therapeutic potential. In this review, we reviewed the recently discovered regulatory mechanisms of TFEB and their impact on human diseases. Additionally, we also summarize the existing TFEB inhibitors and agonists (targeted and non-targeted) and discuss unresolved issues and future research directions in the field. In summary, this review sheds light on the crucial role of TFEB, which may pave the way for its translation from basic research to practical applications, bringing us closer to realizing the full potential of TFEB in various fields.

Screening for late-onset Pompe disease in Internal Medicine departments in Spain

BACKGROUND

The screening of high-risk populations using dried blood spots (DBS) has allowed the rapid identification of patients with Pompe disease, mostly in Neurology departments. The aim of the study was to determine the prevalence of late-onset Pompe disease (LOPD) among patients not previously diagnosed or tested for this entity despite presenting possible signs or symptoms of the disease in Internal Medicine departments in Spain.

METHODS

This epidemiological, observational, cross-sectional, multicenter study included a single cohort of individuals with clinical suspicion of LOPD seen at Internal Medicine departments in Spain. The diagnosis of LOPD was initially established on the basis of the result of DBS. If decreased enzyme acid-alpha-1,4-glucosidase (GAA) activity was detected in DBS, additional confirmatory diagnostic measurements were conducted, including GAA activity in lymphocytes, fibroblasts, or muscle and/or genetic testing.

RESULTS

The diagnosis of LOPD was confirmed in 2 out of 322 patients (0.6%). Reasons for suspecting LOPD diagnosis were polymyositis or any type of myopathy of unknown etiology (in one patient), and asymptomatic or pauci-symptomatic hyperCKemia (in the other). The time between symptom onset and LOPD diagnosis was 2.0 and 0.0 years. Both patients were asymptomatic, with no muscle weakness. Additionally, 19.7% of the non-LOPD cases received an alternative diagnosis.

CONCLUSIONS

Our study highlights the existence of a hidden population of LOPD patients in Internal Medicine departments who might benefit from early diagnosis and early initiation of potential treatments.

Omics-Based Approaches for the Characterization of Pompe Disease Metabolic Phenotypes

Lysosomal storage disorders (LSDs) constitute a large group of rare, multisystemic, inherited disorders of metabolism, characterized by defects in lysosomal enzymes, accessory proteins, membrane transporters or trafficking proteins. Pompe disease (PD) is produced by mutations in the acid alpha-glucosidase (GAA) lysosomal enzyme. This enzymatic deficiency leads to the aberrant accumulation of glycogen in the lysosome. The onset of symptoms, including a variety of neurological and multiple-organ pathologies, can range from birth to adulthood, and disease severity can vary between individuals. Although very significant advances related to the development of new treatments, and also to the improvement of newborn screening programs and tools for a more accurate diagnosis and follow-up of patients, have occurred over recent years, there exists an unmet need for further understanding the molecular mechanisms underlying the progression of the disease. Also, the reason why currently available treatments lose effectiveness over time in some patients is not completely understood. In this scenario, characterization of the metabolic phenotype is a valuable approach to gain insights into the global impact of lysosomal dysfunction, and its potential correlation with clinical progression and response to therapies. These approaches represent a discovery tool for investigating disease-induced modifications in the complete metabolic profile, including large numbers of metabolites that are simultaneously analyzed, enabling the identification of novel potential biomarkers associated with these conditions. This review aims to highlight the most relevant findings of recently published omics-based studies with a particular focus on describing the clinical potential of the specific metabolic phenotypes associated to different subgroups of PD patients.

Improved Enzyme Replacement Therapy with Cipaglucosidase Alfa/Miglustat in Infantile Pompe Disease

Pompe disease is a lysosomal storage disorder with impaired glycogen degradation caused by a deficiency of the enzyme acid α-glucosidase (GAA). Children with the severe infantile form do not survive beyond the first year of life without treatment. Since 2006, enzyme replacement therapy (ERT) with Alglucosidase alfa (Myozyme) has been available, which is a recombinant human GAA (rhGAA). Myozyme therapy has prolonged the life span of affected patients, but many patients showed a continuing, albeit slower, disease progression. A new generation of rhGAA, Cipaglucosidase alfa (Amicus) has a higher content of mannose-6-phosphate residues, which are necessary for efficient cellular uptake and lysosomal targeting. Cipaglucosidase alfa is co-administered with an enzyme stabilizer, Miglustat, which also optimizes the pharmacological properties. In mouse models, the superiority of Cipaglucosidase alfa/Miglustat compared to the previous standard therapy could be determined. Here, we report the disease course of a patient with severe infantile M. Pompe, who showed serious progression even with high-dose standard of care ERT. Changing the therapy to Cipaglucosidase alfa/Miglustat improved respiratory failure, cardiomyopathy, and motor functions significantly. The patient could be weaned from respiratory support and oxygen supplementation. Cardiac function was normalized. Most impressively, the patient, who had lost nearly all motor skills, acquired head control, learned to speak, and could move his wheelchair by himself. Overall, the patient's clinical situation has improved dramatically with the new ERT.

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.