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Background: Classical infantile-onset Pompe disease (IOPD) is the most severe form of Pompe disease. Enzyme replacement therapy (ERT) has significantly increased survival but only a few studies have reported long-term outcomes., Methods: We retrospectively analyzed the outcomes of classical IOPD patients diagnosed in France between 2004 and 2020., Results: Sixty-four patients were identified. At diagnosis (median age 4 months) all patients had cardiomyopathy and most had severe hypotonia (57 of 62 patients, 92%). ERT was initiated in 50 (78%) patients and stopped later due to being ineffective in 10 (21%). Thirty-seven (58%) patients died during follow-up, including all untreated and discontinued ERT patients, and 13 additional patients. Mortality was higher during the first 3 years of life and after the age of 12 years. Persistence of cardiomyopathy during follow-up and/or the presence of heart failure were highly associated with an increased risk of death. In contrast, cross-reactive immunologic material (CRIM)-negative status (n = 16, 26%) was unrelated to increased mortality, presumably because immunomodulation protocols prevent the emergence of high antibody titers to ERT. Besides survival, decreased ERT efficacy appeared after the age of 6 years, with a progressive decline in motor and pulmonary functions for most survivors., Conclusions: This study reports the long-term follow-up of one of the largest cohorts of classical IOPD patients and demonstrates high long-term mortality and morbidity rates with a secondary decline in muscular and respiratory functions. This decreased efficacy seems to be multifactorial, highlighting the importance of developing new therapeutic approaches targeting various aspects of pathogenesis., (© 2023 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)

In the search of a better enzyme therapy in Pompe disease, the conjugation of mannose 6-phosphonates to the recombinant enzyme appeared as an enhancer of its efficacy. Here, we demonstrated that the increased efficacy of the conjugated enzyme is partly due to a higher intracellular maturation because of its insensitiveness to acid phosphatases during the routing to lysosomes., (© 2019 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Pompe disease (PD) is caused by a deficiency of lysosomal acid α-glucosidase resulting from mutations in the GAA gene. The clinical spectrum ranges from a rapidly fatal multisystemic disorder (classic PD, onset < 1 year) to a milder adult onset myopathy. The aims of this study were to characterize the GAA mutations, to establish the disease epidemiology, and to identify potential genotype-phenotype correlations in French late-onset PD patients (onset ≥ 2 years) diagnosed since the 1970s. Data were collected from the two main laboratories involved in PD diagnosis and from the French Pompe registry. Two hundred forty-six patients (130 females and 116 males) were included, with a mean age at diagnosis of 43 years. Eighty-three different mutations were identified in the GAA gene, among which 28 were novel. These variants were spread all over the sequence and included 42 missense (one affecting start codon), 8 nonsense, 15 frameshift, 14 splice mutations, 3 small in-frame deletions, and one large deletion. The common c.-32-13T>G mutation was detected in 151/170 index cases. Other frequent mutations included the exon 18 deletion, the c.525del, and the missense mutations c.1927G>A (p.Gly643Arg) and c.655G>A (p.Gly219Arg). Patients carrying the c.-32-13T>G mutation had an older mean age at onset than patients non-exhibiting this mutation (36 versus 25 years). Patients with the same genotype had a highly variable age at onset. We estimated the frequency of late-onset PD in France around 1/69,927 newborns. In conclusion, we characterized the French cohort of late-onset PD patients through a nationwide study covering more than 40 years.

Pompe disease is a rare disorder due to deficiency of the acid α-glucosidase (GAA) treated by enzyme replacement therapy. The present authorized treatment with rhGAA, the recombinant human enzyme, provides an important benefit in the infantile onset; however, the juvenile and adult forms of the disease corresponding to >80% of the patients are less responsive to this treatment. This resistance has been mainly attributed to an insufficiency of mannose 6-phosphate residues in rhGAA to address lysosomes through the cation-independent mannose 6-phosphate receptor (CI-M6PR). As yet, several attempts to improve the enzyme delivery by increasing the number of mannose 6-phosphate on the enzyme were poorly effective on the late onset form of the disease. Here, we show that chemical conjugation of a synthetic analogue of the mannose 6-phosphate, named AMFA, onto rhGAA improves the affinity for CI-M6PR and the uptake of the enzyme in fibroblasts and myoblasts of adult Pompe patients. More importantly, only the conjugated rhGAA-AMFA was effective in aged Pompe mice when compared to rhGAA. Weekly treatment with 5-20mg·kg -1 rhGAA-AMFA provided major improvements of the motor function and of the myofiber structure, whereas rhGAA was inactive. Finally, AMFA addition did not induce supplementary immune response to the enzyme. This modified enzyme, displaying a muscle recovery in aged Pompe mice that was never attained before, could be considered as a potential therapy for the late onset Pompe disease., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Improving therapeutics delivery in enzyme replacement therapy (ERT) for lysosomal storage disorders is a challenge. Herein, we present the synthesis of novel analogues of mannose 6-phosphate (M6P), known as AMFAs and functionalized at the anomeric position for enzyme grafting. AMFAs are non-phosphate serum-resistant derivatives that efficiently bind the cation-independent mannose 6-phosphate receptor (CI-M6PR), which is the main pathway to address enzymes to lysosomes. One of the AMFAs was used to improve the treatment of the lysosomal myopathy Pompe disease, in which acid α-glucosidase (GAA) is defective. AMFA grafting on a M6P-free recombinant GAA led to a higher uptake of the GAA in adult Pompe fibroblasts in culture as compared to Myozyme, the M6P recombinant GAA. Moreover, the treatment of Pompe adult mice with the AMFA-grafted recombinant enzyme led to a remarkable improvement, even at low doses, in muscle functionality and regeneration, whereas Myozyme had limited efficacy., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Immunogenicity of recombinant human acid-alpha glucosidase (rhGAA) in enzyme replacement therapy (ERT) is a safety and efficacy concern in the management of late-onset Pompe disease (LOPD). However, long-term effects of ERT on humoral and cellular responses to rhGAA are still poorly understood. To better understand the impact of immunogenicity of rhGAA on the efficacy of ERT, clinical data and blood samples from LOPD patients undergoing ERT for >4 years (n = 28) or untreated (n = 10) were collected and analyzed. In treated LOPD patients, anti-rhGAA antibodies peaked within the first 1000 days of ERT, while long-term exposure to rhGAA resulted in clearance of antibodies with residual production of non-neutralizing IgG. Analysis of  T cell responses to rhGAA showed detectable T cell reactivity only after in vitro restimulation. Upregulation of several cytokines and chemokines was detectable in both treated and untreated LOPD subjects, while IL2 secretion was detectable only in subjects who received ERT. These results indicate that long-term ERT in LOPD patients results in a decrease in antibody titers and residual production of non-inhibitory IgGs. Immune responses to GAA following long-term ERT do not seem to affect efficacy of ERT and are consistent with an immunomodulatory effect possibly mediated by regulatory T cells., Competing Interests: Pascal Laforet has received grants and honoraria from Genzyme Company, and honoraria from BioMarin and Amicus Therapeutics and all the other authors declare no competing financial interests.

Glycogen storage disease type II or Pompe disease (GSD II, MIM 232300) is a rare inherited metabolic myopathy caused by a deficiency of lysosomal acid α-glucosidase or acid maltase (GAA; EC 3.2.1.20), resulting in a massive lysosomal glycogen accumulation in cardiac and skeletal muscles. Affected individuals exhibit either severe hypotonia associated with hypertrophic cardiomyopathy (infantile forms) or progressive muscle weakness (late-onset forms). Even if enzyme replacement therapy has recently become a standard treatment, it suffers from several limitations. This review will present the main results of enzyme replacement therapy and the recent findings concerning alternative treatments for Pompe disease, such as gene therapy, enzyme enhancement therapy, and substrate reduction therapy., (Copyright © 2011 Wiley Periodicals, Inc.)

Glycogen storage disease type II (GSDII) or Pompe disease is an autosomal recessive disorder caused by acid alpha-glucosidase (GAA) deficiency, leading to lysosomal glycogen accumulation. Affected individuals store glycogen mainly in cardiac and skeletal muscle tissues resulting in fatal hypertrophic cardiomyopathy and respiratory failure in the most severe infantile form. Enzyme replacement therapy has already proved some efficacy, but results remain variable especially in skeletal muscle. Substrate reduction therapy was successfully used to improve the phenotype in several lysosomal storage disorders. We have recently demonstrated that shRNA-mediated reduction of glycogen synthesis led to a significant reduction of glycogen accumulation in skeletal muscle of GSDII mice. In this paper, we analyzed the effect of a complete genetic elimination of glycogen synthesis in the same GSDII model. GAA and glycogen synthase 1 (GYS1) KO mice were inter-crossed to generate a new double-KO model. GAA/GYS1-KO mice exhibited a profound reduction of the amount of glycogen in the heart and skeletal muscles, a significant decrease in lysosomal swelling and autophagic build-up as well as a complete correction of cardiomegaly. In addition, the abnormalities in glucose metabolism and insulin tolerance observed in the GSDII model were corrected in double-KO mice. Muscle atrophy observed in 11-month-old GSDII mice was less pronounced in GAA/GYS1-KO mice, resulting in improved exercise capacity. These data demonstrate that long-term elimination of muscle glycogen synthesis leads to a significant improvement of structural, metabolic and functional defects in GSDII mice and offers a new perspective for the treatment of Pompe disease.

The authors describe a 50-year-old man who was evaluated for a rigid spine syndrome with onset at age 15, and subsequent walking difficulties. Cardiac and pulmonary functions were normal. Deltoid biopsy revealed the presence of small vacuoles and increased glycogen with Periodic Acid Schiff staining in a limited number of fibers. Acid alpha-glucosidase staining was decreased in leucocytes, and genetic analysis identified the presence of two mutations in that gene. This observation suggests that Pompe disease should be considered in the differential diagnosis of rigid spine syndrome, even in patients without respiratory involvement or with a muscle biopsy showing only mild histopathological changes., (Copyright 2009 Elsevier B.V. All rights reserved.)

Glycogen storage disease type II (GSDII) is an autosomal recessive disorder caused by defects in the acid alpha-glucosidase (GAA) gene leading to lysosomal glycogen accumulation, mainly in cardiac and muscle tissues. In order to facilitate biological investigation on this disease and to avoid time-consuming direct cell isolation and culture, we have established murine myogenic GSDII cell lines. Lentiviral/retroviral expression of SV40 T antigen, Bmi-1 or cyclin-dependent kinase 4 (CDK4) genes was used to induce the immortalization of primary satellite cells from GSDII mice. The resulting immortalized myoblasts exhibit phenotypic characteristics of their parental cells, including profound GAA deficiency, glycogen accumulation and the ability to fully differentiate into myotubes when placed in proper culture conditions. These cell lines will constitute a powerful tool for both basic and applied studies focused on a better understanding of the pathophysiological mechanisms involved in GSDII and for assessing putative therapeutic strategies.

Background: Glycogen storage disease type II (GSDII) or Pompe disease is an inherited disease of glycogen metabolism caused by a lack of functional lysosomal acid alpha-glucosidase (GAA). Affected individuals store glycogen in lysosomes resulting in fatal hypertrophic cardiomyopathy and respiratory failure in the most severe form. Even if enzyme replacement therapy (ERT) has already proven some efficacy, its results remain heterogeneous in skeletal muscle, especially in cross reactive immunological material (CRIM)-negative patients. We investigated for the first time the use of hematopoietic stem cell (HSC) gene therapy in a murine model of GSDII., Methods: Deficient HSC were transduced with a lentiviral vector expressing human GAA or enhanced green fluorescent protein (GFP) under the control of the retroviral MND promoter and transplanted into lethally irradiated GSDII mice. Animals were then subjected to an ERT protocol for 5 weeks and monitored for metabolic correction and GAA-induced immune reaction., Results: GAA was expressed as a correctly processed protein, allowing a complete enzymatic correction in transduced deficient cells without toxicity. Seventeen weeks after transplantation, a partial restoration of the GAA enzymatic activity was observed in bone marrow and peripheral blood cells of GSDII mice, allowing a significant glycogen clearance in skeletal muscle. ERT induced a robust antibody response in GFP-transplanted mice, whereas no immune reaction could be detected in GAA-transplanted mice., Conclusions: Lentiviral vector-mediated HSC gene therapy leads to a partial metabolic correction and induces a tolerance to ERT in GSDII mice. This strategy could enhance the efficacy of ERT in CRIM-negative Pompe patients.

Glycogen storage disease type II (GSDII) or Pompe disease is an autosomal recessive disorder caused by defects in the acid alpha-glucosidase gene, which leads to lysosomal glycogen accumulation and enlargement of the lysosomes mainly in cardiac and muscle tissues, resulting in fatal hypertrophic cardiomyopathy and respiratory failure in the most severely affected patients. Enzyme replacement therapy has already proven to be beneficial in this disease, but correction of pathology in skeletal muscle still remains a challenge. As substrate deprivation was successfully used to improve the phenotype in other lysosomal storage disorders, we explore here a novel therapeutic approach for GSDII based on a modulation of muscle glycogen synthesis. Short hairpin ribonucleic acids (shRNAs) targeted to the two major enzymes involved in glycogen synthesis, i.e. glycogenin (shGYG) and glycogen synthase (shGYS), were selected. C2C12 cells and primary myoblasts from GSDII mice were stably transduced with lentiviral vectors expressing both the shRNAs and the enhanced green fluorescent protein (EGFP) reporter gene. Efficient and specific inhibition of GYG and GYS was associated not only with a decrease in cytoplasmic and lysosomal glycogen accumulation in transduced cells, but also with a strong reduction in the lysosomal size, as demonstrated by confocal microscopy analysis. A single intramuscular injection of recombinant AAV-1 (adeno-associated virus-1) vectors expressing shGYS into newborn GSDII mice led to a significant reduction in glycogen accumulation, demonstrating the in vivo therapeutic efficiency. These data offer new perspectives for the treatment of GSDII and could be relevant to other muscle glycogenoses.

Glycogen storage disease type II (GSDII) or Pompe disease is an inherited disease of glycogen metabolism caused by a lack of functional lysosomal acid alpha-glucosidase (GAA). Affected individuals store glycogen in lysosomes resulting in fatal hypertrophic cardiomyopathy and respiratory failure in the most severe form. We investigated for the first time the use of lentiviral vectors to correct the GSDII phenotype in human and murine GAA-deficient cells. Fibroblasts from infantile and adult GSDII patients were efficiently transduced by a GAA-expressing lentiviral vector placed under the control of the strong MND promoter, leading to a complete restoration of enzymatic activity. We also developed a muscle-specific lentiviral vector based on the synthetic C5-12 promoter and tested it on deficient myogenic satellite cells derived from a GSDII mouse model. GAA was expressed as a correctly processed protein allowing a complete enzymatic and metabolic correction in myoblasts and differentiated myotubes, as well as a significant mannose-6-phosphate (M6P)-dependent secretion reuptake by naive cells. Transduced cells showed lysosomal glycogen clearance, as demonstrated by electron microscopy. These results form the basis for a therapeutic approach of GSDII using lentiviral vector-mediated gene transfer into muscle stem cells.

Muscle glycogen storage was measured by in vivo, natural abundance 13C nuclear magnetic resonance spectroscopy in distal and proximal lower limb segments of patients suffering from adult-onset acid maltase deficiency. Interleaved T1-weighted acquisitions of glycogen and creatine served to quantify glycogen excess. For acid maltase deficient patients (n=11), glycogen:creatine was higher than controls (n=12), (1.20+/-0.39 vs. 0.83+/-0.18, P=0.0005). Glycogen storage was above the normal 95% confidence limits in at least one site for 7/11 patients. The intra-individual coefficient of reproducibility was 12%. This totally atraumatic measurement of glycogen allows repeated measurement at different muscle sites of acid maltase deficient patients, despite selective fatty replacement of tissue. This could provide an additional parameter to follow the development of disease in individual patients, including in the perspective of forthcoming therapeutic trials. It may also offer an appropriate tool to study the role of glycogen accumulation in progression of the pathology.

In Infantile Onset Pompe Disease (IOPD), enzyme replacement therapy (ERT) may improve survival, cardiac function, and motor development. However, even with early enzyme replacement therapy, some patients experienced poor response to ERT and abnormal motor milestones that could be due to motor neuron involvement. In this long-term retrospective study, we analyzed concomitant clinical motor outcomes and electroneuromyography (ENMG) findings in patients with IOPD and Juvenile Onset Pompe Disease (JOPD). Twenty-nine pediatric patients were included and 20 surviving were analyzed for neuromotor studies: 12 had IOPD (group 1), 4 had JOPD (group 2) and 4 (group 3) received ERT in the first month of age. Motor nerve conduction studies were mostly normal. Needle EMG performed at diagnosis always indicated the existence of myopathy that responded to ERT. Two IOPD patients (group 1) presenting with mixed motor neuropathy and myopathy displayed a poor outcome and never walked. Two patients became non-walkers (one IOPD patient and one patient of group 3) at respectively 9 and 3 years of age. One JOPD patient is about to lose walking ability. This motor deterioration was associated with the development of a motor neuropathy. Patients older than 10 years of age develop a motor neuropathy. Initial or secondary motor neuron involvement seems to be associated with a poor motor outcome showing that ERT may fail to prevent the accumulation of glycogen in motor neuron. Neurophysiological findings are important to assess severity of motor neuron damage in all Pompe pediatric patients and should be systematically performed. [ABSTRACT FROM AUTHOR]

Muscle glycogen storage was measured by in vivo, natural abundance 13C nuclear magnetic resonance spectroscopy in distal and proximal lower limb segments of patients suffering from adult-onset acid maltase deficiency. Interleaved T1-weighted acquisitions of glycogen and creatine served to quantify glycogen excess. For acid maltase deficient patients (n=11), glycogen:creatine was higher than controls (n=12), (1.20±0.39 vs. 0.83±0.18, P=0.0005). Glycogen storage was above the normal 95% confidence limits in at least one site for 7/11 patients. The intra-individual coefficient of reproducibility was 12%. This totally atraumatic measurement of glycogen allows repeated measurement at different muscle sites of acid maltase deficient patients, despite selective fatty replacement of tissue. This could provide an additional parameter to follow the development of disease in individual patients, including in the perspective of forthcoming therapeutic trials. It may also offer an appropriate tool to study the role of glycogen accumulation in progression of the pathology. [Copyright &y& Elsevier]