Progress and challenges of gene therapy for Pompe disease

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.

Lysosomal Dysfunction: Connecting the Dots in the Landscape of Human Diseases

Lysosomes are the main organelles responsible for the degradation of macromolecules in eukaryotic cells. Beyond their fundamental role in degradation, lysosomes are involved in different physiological processes such as autophagy, nutrient sensing, and intracellular signaling. In some circumstances, lysosomal abnormalities underlie several human pathologies with different etiologies known as known as lysosomal storage disorders (LSDs). These disorders can result from deficiencies in primary lysosomal enzymes, dysfunction of lysosomal enzyme activators, alterations in modifiers that impact lysosomal function, or changes in membrane-associated proteins, among other factors. The clinical phenotype observed in affected patients hinges on the type and location of the accumulating substrate, influenced by genetic mutations and residual enzyme activity. In this context, the scientific community is dedicated to exploring potential therapeutic approaches, striving not only to extend lifespan but also to enhance the overall quality of life for individuals afflicted with LSDs. This review provides insights into lysosomal dysfunction from a molecular perspective, particularly in the context of human diseases, and highlights recent advancements and breakthroughs in this field.

Muscle-specific, liver-detargeted adeno-associated virus gene therapy rescues Pompe phenotype in adult and neonate Gaa-/- mice

Pompe disease (PD) is a neuromuscular disorder caused by acid α-glucosidase (GAA) deficiency. Reduced GAA activity leads to pathological glycogen accumulation in cardiac and skeletal muscles responsible for severe heart impairment, respiratory defects, and muscle weakness. Enzyme replacement therapy with recombinant human GAA (rhGAA) is the standard-of-care treatment for PD, however, its efficacy is limited due to poor uptake in muscle and the development of an immune response. Multiple clinical trials are ongoing in PD with adeno-associated virus (AAV) vectors based on liver- and muscle-targeting. Current gene therapy approaches are limited by liver proliferation, poor muscle targeting, and the potential immune response to the hGAA transgene. To generate a treatment tailored to infantile-onset PD, we took advantage of a novel AAV capsid able to increase skeletal muscle targeting compared to AAV9 while reducing liver overload. When combined with a liver-muscle tandem promoter (LiMP), and despite the extensive liver-detargeting, this vector had a limited immune response to the hGAA transgene. This combination of capsid and promoter with improved muscle expression and specificity allowed for glycogen clearance in cardiac and skeletal muscles of Gaa-/- adult mice. In neonate Gaa-/- , complete rescue of glycogen content and muscle strength was observed 6 months after AAV vector injection. Our work highlights the importance of residual liver expression to control the immune response toward a potentially immunogenic transgene expressed in muscle. In conclusion, the demonstration of the efficacy of a muscle-specific AAV capsid-promoter combination for the full rescue of PD manifestation in both neonate and adult Gaa-/- provides a potential therapeutic avenue for the infantile-onset form of this devastating disease.

Glycogen storage diseases: An update

Glycogen storage diseases (GSDs), also referred to as glycogenoses, are inherited metabolic disorders of glycogen metabolism caused by deficiency of enzymes or transporters involved in the synthesis or degradation of glycogen leading to aberrant storage and/or utilization. The overall estimated GSD incidence is 1 case per 20000-43000 live births. There are over 20 types of GSD including the subtypes. This heterogeneous group of rare diseases represents inborn errors of carbohydrate metabolism and are classified based on the deficient enzyme and affected tissues. GSDs primarily affect liver or muscle or both as glycogen is particularly abundant in these tissues. However, besides liver and skeletal muscle, depending on the affected enzyme and its expression in various tissues, multiorgan involvement including heart, kidney and/or brain may be seen. Although GSDs share similar clinical features to some extent, there is a wide spectrum of clinical phenotypes. Currently, the goal of treatment is to maintain glucose homeostasis by dietary management and the use of uncooked cornstarch. In addition to nutritional interventions, pharmacological treatment, physical and supportive therapies, enzyme replacement therapy (ERT) and organ transplantation are other treatment approaches for both disease manifestations and long-term complications. The lack of a specific therapy for GSDs has prompted efforts to develop new treatment strategies like gene therapy. Since early diagnosis and aggressive treatment are related to better prognosis, physicians should be aware of these conditions and include GSDs in the differential diagnosis of patients with relevant manifestations including fasting hypoglycemia, hepatomegaly, hypertransaminasemia, hyperlipidemia, exercise intolerance, muscle cramps/pain, rhabdomyolysis, and muscle weakness. Here, we aim to provide a comprehensive review of GSDs. This review provides general characteristics of all types of GSDs with a focus on those with liver involvement.

Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective

This consensus statement by a panel of neurology experts aimed to provide a practical and implementable guidance document to assist clinicians with the best clinical practice in terms of diagnosis, treatment, and monitoring of late-onset Pompe disease (LOPD). The participating experts consider the clinical suspicion of LOPD by the physician to be of utmost importance in the prevention of diagnostic and therapeutic delay in LOPD patients. A diagnostic algorithm is proposed to facilitate the diagnosis of LOPD in patients presenting with unexplained proximal/axial weakness (with or without respiratory symptoms) or restrictive respiratory insufficiency with hyperCKemia and/or exercise intolerance as the red flag symptoms/signs that raise the index of suspicion for LOPD diagnosis. The diagnosis is based on the subsequent use of dried blood spot (DBS) assay, and the DBS assay can be confirmed by acid alpha-glucosidase (GAA) tissue analysis in leukocytes, fibroblasts, or muscle fibers and/or genetic mutation analysis. Accordingly, experts consider increased awareness among physicians about potential presenting characteristics with a high index of suspicion for LOPD to be crucial to suspect and consider LOPD in the differential diagnosis, while strongly suggesting the use of a diagnostic algorithm combined with DBS assay and confirmatory tests in the timely diagnosis of LOPD and implementation of best practice patterns.

Sudden cardiac death in childhood hypertrophic cardiomyopathy

The most prevalent cause of mortality in children with hypertrophic cardiomyopathy (HCM) is sudden cardiac death (SCD), which happens more frequently than in adult patients. Risk stratification tactics have generally been drawn from adult practice, however emerging data has revealed significant disparities between children and adult cohorts, implying the need for pediatric-specific risk stratification methodologies. We conducted an all-language literature search on Medline, Cochrane, Embase, and Google Scholar until October 2021. The following search strings and Medical Subject Heading (MeSH) terms were used: "HCM," "SCD," "Sudden Cardiac Death," and "Childhood Onset HCM." We explored the literature on the risk of SCD in HCM for its epidemiology, pathophysiology, the role of various genes and their influence, associated complications leading to SCD and preventive and treatment modalities. Childhood-onset HCM is linked to significant life-long morbidity and mortality, including a higher SCD rate in children than in adults. The present focus is on symptom relief and avoiding illness-related consequences, but the prospect of future disease-modifying medicines offers an intriguing opportunity to alter disease expression and outcomes in these young individuals. Current preventive recommendations promote implantable cardioverter defibrillator placement based on cumulative risk factor thresholds, although they have been demonstrated to have weak discriminating capacity. This article addresses questions and discusses the etiology, risk factors, and method to risk stratification for SCD in children with HCM.

Therapeutic Options for the Management of Pompe Disease: Current Challenges and Clinical Evidence in Therapeutics and Clinical Risk Management

Pompe disease is a genetic disorder produced by mutations in the GAA gene leading to absence or reduced expression of acid alpha-glucosidase, an enzyme that metabolizes the breakdown of glycogen into glucose. There are two main phenotypes, the infantile consisting of early onset severe weakness and cardiomyopathy, and the adult which is characterized by slowly progressive skeletal and respiratory muscle weakness. Enzymatic replacement therapy (ERT) has been available for Pompe disease for more than 15 years. Although the treatment has improved many aspects of the disease, such as prolonged survival through improved cardiomyopathy and acquisition of motor milestones in infants and slower progression rate in adults, ERT is far from being a cure as both infantile and adult patients continue to progress. This fact has prompted the development of improved or new enzymes and other treatments such as gene therapy or substrate reduction strategies. Here, we review the data obtained from randomized clinical trials but also from open-label studies published so far that have assessed the advantages and limitations of this therapy. Moreover, we also review the new therapeutic strategies that are under development and provide our opinion on which are the unmet needs for patients with this disease.

Transcriptomic analysis of the innate immune response to in vitro transfection of plasmid DNA

The innate immune response to cytosolic DNA is intended to protect the host from viral infections, but it can also inhibit the delivery and expression of therapeutic transgenes in gene and cell therapies. The goal of this work was to use mRNA sequencing to identify genes that may influence transfection efficiency in four different cell types (PC-3, Jurkat, HEK-293T, and primary T cells). The highest transfection efficiency was observed in HEK-293T cells, which upregulated only 142 genes with no known antiviral functions after transfection with lipofectamine. Lipofection upregulated 1,057 cytokine-stimulated genes (CSGs) in PC-3 cells, which exhibited a significantly lower transfection efficiency. However, when PC-3 cells were transfected in serum-containing media or electroporated, the observed transfection efficiencies were significantly higher while the expression levels of cytokines and CSGs decreased. In contrast, lipofection of Jurkat and primary T cells only upregulated a few genes, but several of the antiviral CSGs that were absent in HEK-293T cells and upregulated in PC-3 cells were observed to be constitutively expressed in T cells, which may explain the relatively low Lipofection efficiencies observed with T cells (8%-21% GFP⁺). Indeed, overexpression of one CSG (IFI16) significantly decreased transfection efficiency in HEK-293T cells.

[Application of adeno-associated virus-mediated gene therapy in lysosomal storage diseases]

Lysosomal storage disorders (LSDs) are a group of single-gene inherited metabolic diseases caused by defects in lysosomal enzymes or function-related proteins. Enzyme replacement therapy is the main treatment method in clinical practice, but it has a poor effect in patients with neurological symptoms. With the rapid development of multi-omics, sequencing technology, and bioengineering, gene therapy has been applied in patients with LSDs. As one of the vectors of gene therapy, adeno-associated virus (AAV) has good prospects in the treatment of genetic and metabolic diseases. More and more studies have shown that AAV-mediated gene therapy is effective in LSDs. This article reviews the application of AAV-mediated gene therapy in LSDs.

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.

Therapeutic thoroughfares for adults living with Pompe disease

PURPOSE OF REVIEW

Pompe disease is caused by autosomal recessive mutations in the acid α-glucosidase gene leading to a multiorgan deficiency of the enzyme acid glucosidase alfa. To recover to a nondiseased status, a lift over a threshold of 25% acid glucosidase alfa enzyme activity is required. This update on therapeutic thoroughfares for adult Pompe disease aims to assist neuromuscular and metabolic specialists.

RECENT FINDINGS

We reviewed the recent studies covering enzyme replacement therapy, gene therapy, and substrate reduction therapy in adult Pompe disease. Results of phase 3 studies and the first sets of long-term data of both novel enzyme replacement therapies, avalglucosidase alfa, and ciplaglucodsidase alfa combined with miglustat, are public. First gene therapy trials are ongoing. Substrate reduction therapy is in early transition to the clinical trial phase. We still miss dose escalation and intensification of frequency trials on enzyme replacement therapy in adults, probably suitable to echo current results in infantile and juvenile Pompe disease.

SUMMARY

Therapy of Pompe disease reaches new thoroughfares reducing the overall disease burden of patients; however, individualization of these novel therapeutic options remains challenging. Consensus-based and shared decision-based recommendations need to be established based on reliable real-world data to allow the best standards of care worldwide.

A favorable outcome in an infantile-onset Pompe patient with cross reactive immunological material (CRIM) negative disease with high dose enzyme replacement therapy and adjusted immunomodulation

Infantile onset Pompe disease (IOPD) is a rare devastating disease that presents in early infancy with rapidly progressive hypertrophic cardiomyopathy, severe generalized myopathy and death within the first year of life. The emergence of enzyme replacement therapy (ERT) with recombinant human acid alpha glucosidase (rhGAA) has improved the natural course of IOPD with a significant impact on cardiomyopathy but has a more limited effect on the progression of myopathy and consequently the later deterioration of the disease. Possible reasons for reduced ERT efficacy include insufficient enzyme, partial targeting of skeletal muscle and the development of IgG rhGAA antibodies especially in patients who are cross-reactive immunological material (CRIM) negative. We report a CRIM-negative IOPD female patient who started treatment upon diagnosis at 4.5 months with ERT at 20 mg/kg every other week and a course of combined immunomodulation with rituximab, methotrexate and IVIG according to the published Duke protocol and increased ERT within a month to 40 mg/kg/week. Despite initial good clinical response to ERT and immunomodulation, monthly monitoring identified a gradual increase of serum antibody titers to rhGAA necessitating a second course of immunomodulation with bortezomib and maintenance rituximab and methotrexate. A gradual reduction in frequency of immunotherapy was instituted and over a period of 14 months was discontinued. Serum anti-rhGAA antibody titers remained negative for 5 months since cessation of immunomodulation and the patient is now immune tolerant with recovery of CD19. At the age of 30 months the patient is walking independently and has normal cardiac function and anatomy. We recommend initiating ERT at 40 mg/kg/week in CRIM-negative IOPD patients, concomitant with immunomodulation and monthly monitoring of serum anti-rhGAA IgG titers upon confirmation of the diagnosis.

Pompe Disease: a Clinical, Diagnostic, and Therapeutic Overview

Purpose of Review

This review summarizes the clinical presentation and provides an update on the current strategies for diagnosis of Pompe disease. We will review the available treatment options. We examine newly approved treatments as well as upcoming therapies in this condition. We also provide commentary on the unmet needs in clinical management and research for this disease.

Recent Findings

In March 2015, Pompe disease was added to the Recommended Uniform Screening Panel (RUSP) and since then a number of states have added Pompe disease to their slate of diseases for their Newborn Screening (NBS) program. Data emerging from these programs is revising our knowledge of incidence of Pompe disease. In 2021, two randomized controlled trials involving new forms of enzyme replacement therapy (ERT) were completed and one new product is already FDA-approved and on the market, whereas the other product will come up for FDA review in the fall. Neither of the new ERT were shown to be superior to the standard of care product, alglucosidase. The long-term effectiveness of these newer forms of ERT is unclear. Newer versions of the ERT are in development in addition to multiple different strategies of gene therapy to deliver GAA, the gene responsible for producing acid alpha-glucosidase, the defective protein in Pompe Disease. Glycogen substrate reduction is also in development in Pompe disease and other glycogen storage disorders.

Summary

There are significant unmet needs as it relates to clinical care and therapeutics in Pompe disease as well as in research. The currently available treatments lose effectiveness over the long run and do not have penetration into neuronal tissues and inconsistent penetration in certain muscles. More definitive gene therapy and enzyme replacement strategies are currently in development and testing.

Atypical infantile-onset Pompe disease with good prognosis from mainland China: A case report

BACKGROUND

Pompe disease has a broad disease spectrum, including infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD) forms. It is a type of glycogen storage disorder belonging to autosomal recessive genetic disease, for an estimated incidence of 1/40000 among the neonatal population. In severe cases, the natural course is characterized by death due to cardiopulmonary failure in the first year after birth. However, the clinical outcomes have improved since the emergence of enzyme replacement therapy (ERT) was widely used.

CASE SUMMARY

The reported female case in China was an atypical IOPD, which demonstrates an unusual presentation of glycogen accumulation syndrome type II without obvious skeletal muscle involvement, and reviewed physical examination, biochemical examinations, chest radiograph, and acid α-glucosidase (GAA) mutation analysis. After 4-mo specific ERT, the case received 12-mo follow-up. Moreover, the patient has obtained a very good prognosis under ERT.

CONCLUSION

For the atypical IOPD patients, early diagnosis and treatment may contribute to good prognosis.

Hypertrophic Cardiomyopathy in Children: Pathophysiology, Diagnosis, and Treatment of Non-sarcomeric Causes

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy not solely explained by abnormal loading conditions. Despite its rare prevalence in pediatric age, HCM carries a relevant risk of mortality and morbidity in both infants and children. Pediatric HCM is a large heterogeneous group of disorders. Other than mutations in sarcomeric genes, which represent the most important cause of HCM in adults, childhood HCM includes a high prevalence of non-sarcomeric causes, including inherited errors of metabolism (i.e., glycogen storage diseases, lysosomal storage diseases, and fatty acid oxidation disorders), malformation syndromes, neuromuscular diseases, and mitochondrial disease, which globally represent up to 35% of children with HCM. The age of presentation and the underlying etiology significantly impact the prognosis of children with HCM. Moreover, in recent years, different targeted approaches for non-sarcomeric etiologies of HCM have emerged. Therefore, the etiological diagnosis is a fundamental step in designing specific management and therapy in these subjects. The present review aims to provide an overview of the non-sarcomeric causes of HCM in children, focusing on the pathophysiology, clinical features, diagnosis, and treatment of these rare disorders.

Impaired autophagy: The collateral damage of lysosomal storage disorders

Lysosomal storage disorders (LSDs), which number over fifty, are monogenically inherited and caused by mutations in genes encoding proteins that are involved in lysosomal function. Lack of the functional protein results in storage of a distinctive material within the lysosomes, which for years was thought to determine the pathophysiology of the disorder. However, our current view posits that the primary storage material disrupts the normal role of the lysosome in the autophagic pathway resulting in the secondary storage of autophagic debris. It is this "collateral damage" which is common to the LSDs but nonetheless intricately nuanced in each. We have selected five LSDs resulting from defective proteins that govern widely different lysosomal functions including glycogen degradation (Pompe), lysosomal transport (Cystinosis), lysosomal trafficking (Danon), glycolipid degradation (Gaucher) and an unidentified function (Batten) and argue that despite the disparate functions, these proteins, when mutant, all impair the autophagic process uniquely.

Design of efficacious somatic cell genome editing strategies for recessive and polygenic diseases

Compound heterozygous recessive or polygenic diseases could be addressed through gene correction of multiple alleles. However, targeting of multiple alleles using genome editors could lead to mixed genotypes and adverse events that amplify during tissue morphogenesis. Here we demonstrate that Cas9-ribonucleoprotein-based genome editors can correct two distinct mutant alleles within a single human cell precisely. Gene-corrected cells in an induced pluripotent stem cell model of Pompe disease expressed the corrected transcript from both corrected alleles, leading to enzymatic cross-correction of diseased cells. Using a quantitative in silico model for the in vivo delivery of genome editors into the developing human infant liver, we identify progenitor targeting, delivery efficiencies, and suppression of imprecise editing outcomes at the on-target site as key design parameters that control the efficacy of various therapeutic strategies. This work establishes that precise gene editing to correct multiple distinct gene variants could be highly efficacious if designed appropriately.

Characterization of Gait and Postural Regulation in Late-Onset Pompe Disease

Pompe disease is a multisystemic disorder with the hallmark of progressive skeletal muscle weakness that often results in difficulties in walking and balance. However, detailed characterization of gait and postural regulation with this disease is lacking. The objective of this investigation was to determine if differences exist between the gait and postural regulation of LOPD patients and a matched control group. The gaits of 16 patients with LOPD were assessed using a gait analysis mobile system (RehaGait) and a dynamometric treadmill (FDM-T 1.8). The Interactive Balance System (IBS) was used to evaluate postural regulation and stability. All measures were compared to individual reference data. Demographic (age, gender), morphological (body height, body mass) and clinical data (muscle strength according to the Medical Research Council Scale (MRC Scale), as well as the 6-min walking test and a 10-m fast walk) were also recorded. Compared to individual reference data, LOPD patients presented with reduced gait velocity, cadence and time in single stand. A total of 87% of LOPD patients had abnormalities during posturographic analysis presenting with differences in postural subsystems. This study provides objective data demonstrating impaired gait and posture in LOPD patients. For follow-up analysis and as outcome measurements during medical or physiotherapeutic interventions, the findings of this investigation may be useful.

Pompe Disease: New Developments in an Old Lysosomal Storage Disorder

Pompe disease, also known as glycogen storage disease type II, is caused by the lack or deficiency of a single enzyme, lysosomal acid alpha-glucosidase, leading to severe cardiac and skeletal muscle myopathy due to progressive accumulation of glycogen. The discovery that acid alpha-glucosidase resides in the lysosome gave rise to the concept of lysosomal storage diseases, and Pompe disease became the first among many monogenic diseases caused by loss of lysosomal enzyme activities. The only disease-specific treatment available for Pompe disease patients is enzyme replacement therapy (ERT) which aims to halt the natural course of the illness. Both the success and limitations of ERT provided novel insights in the pathophysiology of the disease and motivated the scientific community to develop the next generation of therapies that have already progressed to the clinic.

Diagnostic challenges in metabolic myopathies

INTRODUCTION

Metabolic myopathies comprise a clinically etiological diverse group of disorders caused by defects in cellular energy metabolism including the breakdown of carbohydrates and fatty acids, which include glycogen storage diseases and fatty acid oxidation disorders. Their wide clinical spectrum ranges from infantile severe multisystemic disorders to adult-onset myopathies. To suspect in adults these disorders, clinical features such as exercise intolerance and recurrent myoglobinuria need investigation while another group presents fixed weakness and cardiomyopathy as a clinical pattern.

AREAS COVERED

In metabolic myopathies, clinical manifestations are important to guide diagnostic tests used in order to lead to the correct diagnosis. The authors searched in literature the most recent techniques developed. The authors present an overview of the most common phenotypes of Pompe disease and what is currently known about the mechanism of ERT treatment. The most common disorders of lipid metabolism are overviewed, with their possible dietary or supplementary treatments.

EXPERT COMMENTARY

The clinical suspicion is the clue to conduct in-depth investigations in suspected cases of metabolic myopathies that lead to the final diagnosis with biochemical molecular studies and often nowadays by the use of Next Generation Sequencing (NGS) to determine gene mutations.

Lentiviral Hematopoietic Stem Cell Gene Therapy Rescues Clinical Phenotypes in a Murine Model of Pompe Disease

Pompe disease is a lysosomal storage disorder caused by malfunctions of the acid alpha-glucosidase (GAA) enzyme with a consequent toxic accumulation of glycogen in cells. Muscle wasting and hypertrophic cardiomyopathy are the most common clinical signs that can lead to cardiac and respiratory failure within the first year of age in the more severe infantile forms. Currently available treatments have significant limitations and are not curative, highlighting a need for the development of alternative therapies. In this study, we investigated the use of a clinically relevant lentiviral vector to deliver systemically GAA through genetic modification of hematopoietic stem and progenitor cells (HSPCs). The overexpression of GAA in human HSPCs did not exert any toxic effect on this cell population, which conserved its stem cell capacity in xenograft experiments. In a murine model of Pompe disease treated at young age, we observed phenotypic correction of heart and muscle function with a significant reduction of glycogen accumulation in tissues after 6 months of treatment. These findings suggest that lentiviral-mediated HSPC gene therapy can be a safe alternative therapy for Pompe disease.

Pompe disease: pathogenesis, molecular genetics and diagnosis

Pompe disease (PD) is a rare autosomal recessive disorder caused by mutations in the GAA gene, localized on chromosome 17 and encoding for acid alpha-1,4-glucosidase (GAA). Currently, more than 560 mutations spread throughout GAA gene have been reported. GAA catalyzes the hydrolysis of α-1,4 and α-1,6-glucosidic bonds of glycogen and its deficiency leads to lysosomal storage of glycogen in several tissues, particularly in muscle. PD is a chronic and progressive pathology usually characterized by limb-girdle muscle weakness and respiratory failure. PD is classified as infantile and childhood/adult forms. PD patients exhibit a multisystemic manifestation that depends on age of onset.

Early diagnosis is essential to prevent or reduce the irreversible organ damage associated with PD progression. Here, we make an overview of PD focusing on pathogenesis, clinical phenotypes, molecular genetics, diagnosis, therapies, autophagy and the role of miRNAs as potential biomarkers for PD.

Rescue of Advanced Pompe Disease in Mice with Hepatic Expression of Secretable Acid α-Glucosidase

Pompe disease is a neuromuscular disorder caused by disease-associated variants in the gene encoding for the lysosomal enzyme acid α-glucosidase (GAA), which converts lysosomal glycogen to glucose. We previously reported full rescue of Pompe disease in symptomatic 4-month-old Gaa knockout (Gaa^−/−) mice by adeno-associated virus (AAV) vector-mediated liver gene transfer of an engineered secretable form of GAA (secGAA). Here, we showed that hepatic expression of secGAA rescues the phenotype of 4-month-old Gaa^−/− mice at vector doses at which the native form of GAA has little to no therapeutic effect. Based on these results, we then treated severely affected 9-month-old Gaa^−/− mice with an AAV vector expressing secGAA and followed the animals for 9 months thereafter. AAV-treated Gaa^−/− mice showed complete reversal of the Pompe phenotype, with rescue of glycogen accumulation in most tissues, including the central nervous system, and normalization of muscle strength. Transcriptomic profiling of skeletal muscle showed rescue of most altered pathways, including those involved in mitochondrial defects, a finding supported by structural and biochemical analyses, which also showed restoration of lysosomal function. Together, these results provide insight into the reversibility of advanced Pompe disease in the Gaa^−/− mouse model via liver gene transfer of secGAA.

Splice modulating antisense oligonucleotides restore some acid-alpha-glucosidase activity in cells derived from patients with late-onset Pompe disease

Pompe disease is caused by mutations in the GAA gene, resulting in deficient lysosomal acid-α-glucosidase activity in patients, and a progressive decline in mobility and respiratory function. Enzyme replacement therapy is one therapeutic option, but since not all patients respond to this treatment, alternative interventions should be considered. One GAA mutation, c.-32-13T > G, impacts upon normal exon 2 splicing and is found in two-thirds of late-onset cases. We and others have explored a therapeutic strategy using splice modulating phosphorodiamidate morpholino oligomers to enhance GAA exon 2 inclusion in the mature mRNA of patients with one c.-32-13T > G allele. We designed 20 oligomers and treated fibroblasts derived from five patients to identify an oligomer sequence that maximally increased enzyme activity in all fibroblasts. The most effective splice correcting oligomer was chosen to treat forced-myogenic cells, derived from fibroblasts from nine patients carrying the c.-32-13T > G mutation. After transfection, we show increased levels of the full-length GAA transcript, acid-α-glucosidase protein, and enzyme activity in all patients’ myogenic cells, regardless of the nature of the mutation in the other allele. This data encourages the initiation of clinical trials to assess the therapeutic efficacy of this oligomer for those patients carrying the c.-32-13T > G mutation.

Ultrasound assessment of diaphragm function in patients with late-onset Pompe disease

INTRODUCTION

Late-Onset Pompe Disease (LOPD) is characterized by progressive limb-girdle muscle weakness and respiratory dysfunction. Diaphragm is the most impaired muscle in LOPD and its dysfunction cause major respiratory symptoms. The aim of this study was to evaluate the correlation between diaphragm thickness and mobility assessed by ultrasonography and respiratory function and muscle strength tests in patients with LOPD.

METHODS

17 patients with LOPD (9 female, 47 ± 15 years) and 17 age and gender-matched healthy controls underwent spirometry, muscle strength testing, and ultrasound evaluation of diaphragm excursion and thickness.

RESULTS

The following parameters were significantly reduced in LOPD patients versus controls (all p < 0.001): forced vital capacity (FVC) in seated and supine position, maximum inspiratory and expiratory pressure (MIP and MEP), diaphragm excursion, thickness at functional residual capacity (FRC) and total lung capacity (TLC), and thickness fraction (TF). Ultrasound studies of diaphragm thickness at FRC correlated with MIP (r = 0.74; p < 0.0001) and seated FVC(r = 0.73; p < 0.05). Diaphragm thickness at TLC correlated with MIP (r = 0.85; p < 0.0001) and FVC in both seated (r = 0.77; p < 0.0001) and supine position (r = 0.68; p < 0.05). TF correlated significantly with MIP (r = 0.80; p < 0.001), FVC in both seated (r = 0.66; p < 0,005) and supine position (r = 0.61; p < 0.05). Interestingly diaphragm thickness at FRC correlated with disease duration (years) in LOPD patients (r = -0.53; p < 0,05). Ultrasound diaphragm mobility correlated with diaphragm thickness at TLC(r = 0.87; p < 0.0001), FRC (r = 0.84; p < 0.005) and TF (r = 0.73; p < 0.05). Moreover diaphragm mobility correlated with FVC in seated(r = 0.79; p < 0.005) and supine position(r = 0.74; p < 0.05) and MIP (r = 0.81; p < 0.005).

CONCLUSION

Diaphragm ultrasonography is a simple and reproducible technique for manage respiratory dysfunction in LOPD patients.

AAV Vector Immunogenicity in Humans: A Long Journey to Successful Gene Transfer

Gene therapy with adeno-associated virus (AAV) vectors has demonstrated safety and long-term efficacy in a number of trials across target organs, including eye, liver, skeletal muscle, and the central nervous system. Since the initial evidence that AAV vectors can elicit capsid T cell responses in humans, which can affect the duration of transgene expression, much progress has been made in understanding and modulating AAV vector immunogenicity. It is now well established that exposure to wild-type AAV results in priming of the immune system against the virus, with development of both humoral and T cell immunity. Aside from the neutralizing effect of antibodies, the impact of pre-existing immunity to AAV on gene transfer is still poorly understood. Herein, we review data emerging from clinical trials across a broad range of gene therapy applications. Common features of immune responses to AAV can be found, suggesting, for example, that vector immunogenicity is dose-dependent, and that innate immunity plays an important role in the outcome of gene transfer. A range of host-specific factors are also likely to be important, and a comprehensive understanding of the mechanisms driving AAV vector immunogenicity in humans will be key to unlocking the full potential of in vivo gene therapy.

Is Newborn Screening the Ultimate Strategy to Reduce Diagnostic Delays in Pompe Disease? The Parent and Patient Perspective

Pompe disease (PD) is a rare, autosomal-recessively inherited deficiency in the enzyme acid α-glucosidase. It is a spectrum disorder; age at symptom onset and rate of deterioration can vary considerably. In affected infants prognosis is poor, such that without treatment most infants die within the first year of life. To lose a baby in their first year of life to a rare disease causes much regret, guilt, and loneliness to parents, family, and friends. To lose a baby needlessly when there is an effective treatment amplifies this sadness. With so little experience of rare disease in the community, once a baby transfers to their home they are subject to a very uncertain and unyielding diagnostic journey while their symptomology progresses and their health deteriorates. With a rare disease like PD, the best opportunity to diagnose a baby is at birth. PD is not yet included in the current newborn screening (NBS) panel in Australia. Should it be? In late 2018 the Australian Pompe Association applied to the Australian Standing committee on Newborn Screening to have PD included. The application was not upheld. Here we provide an overview of the rationale for NBS, drawing on the scientific literature and perspectives from The Australian Pompe Association, its patients and their families. In doing so, we hope to bring a new voice to this very important debate.

New Therapeutics Options for Pediatric Neuromuscular Disorders

Neuromuscular disorders (NMDs) of Childhood onset are a genetically heterogeneous group of diseases affecting the anterior horn cell, the peripheral nerve, the neuromuscular junction, or the muscle. For many decades, treatment of NMDs has been exclusively symptomatic. But this has changed fundamentally in recent years due to the development of new drugs attempting either to ameliorate secondary pathophysiologic consequences or to modify the underlying genetic defect itself. While the effects on the course of disease are still modest in some NMDs (e.g., Duchenne muscular dystrophy), new therapies have substantially prolonged life expectancy and improved motor function in others (e.g., spinal muscular atrophy and infantile onset Pompe disease). This review summarizes recently approved medicaments and provides an outlook for new therapies that are on the horizon in this field.

Links between autophagy and disorders of glycogen metabolism - Perspectives on pathogenesis and possible treatments

The glycogen storage diseases are a group of inherited metabolic disorders that are characterized by specific enzymatic defects involving the synthesis or degradation of glycogen. Each disorder presents with a set of symptoms that are due to the underlying enzyme deficiency and the particular tissues that are affected. Autophagy is a process by which cells degrade and recycle unneeded or damaged intracellular components such as lipids, glycogen, and damaged mitochondria. Recent studies showed that several of the glycogen storage disorders have abnormal autophagy which can disturb normal cellular metabolism and/or mitochondrial function. Here, we provide a clinical overview of the glycogen storage disorders, a brief description of autophagy, and the known links between specific glycogen storage disorders and autophagy.