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1.  Clearance of lysosomal glycogen accumulation by Transcription factor EB (TFEB) in muscle cells from lysosomal alpha-glucosidase deficient mice 
Biochemical and biophysical research communications  2013;S0006-291X(13)00272-6 10.1016/j.bbrc.2013.02.026.
A recently proposed therapeutic approach for lysosomal storage disorders (LSDs) relies upon the ability of transcription factor EB (TFEB) to stimulate autophagy and induce lysosomal exocytosis leading to cellular clearance. This approach is particularly attractive in Glycogen Storage Disease type II (a severe metabolic myopathy and a paradigm for LSDs, also called Pompe disease) as the currently available therapy, replacement of the missing enzyme acid alpha-glucosidase, fails to reverse skeletal muscle pathology. Pompe disease is characterized by both lysosomal abnormality and dysfunctional autophagy. Here we show that TFEB is a viable therapeutic target in Pompe disease: overexpression of TFEB in a newly established conditionally immortalized skeletal muscle cell model reduced glycogen load and lysosomal size; and in the muscle fibers of GFP-LC3 Pompe disease mouse model significantly increased the motility of lysosomes in the fibers, and stimulated the fusion between lysosomes and autophagosomes under stress. Hence, modulation of TFEB activity holds promise for the development of a better therapy. In addition, the newly developed mouse and cell models have many potential applications such as large-scale drug screening for Pompe disease.
PMCID: PMC3687018  PMID: 23416076
Pompe disease; acid alpha-glucosidase; autophagy; lysosomal storage; myoblast immortalization; TFEB
2.  Public support for neonatal screening for Pompe disease, a broad-phenotype condition 
Neonatal screening for Pompe disease has been introduced in Taiwan and a few U.S. states, while other jurisdictions including some European countries are piloting or considering this screening. First-tier screening flags both classic infantile and late-onset Pompe disease, which challenges current screening criteria. Previously, advocacy groups have sometimes supported expanded neonatal screening more than professional experts, while neutral citizens' views were unknown. This study aimed to measure support for neonatal screening for Pompe disease in the general public and to compare it to support among (parents of) patients with this condition. The study was done in the Netherlands, where newborns are not currently screened for Pompe disease. Newborn screening is not mandatory in the Netherlands but current uptake is almost universal.
A consumer panel (neutral group) and (parents of) patients with Pompe disease (Pompe group) were sent information and a questionnaire. Responses were analyzed of 555 neutral and 58 Pompe-experienced informants who had demonstrated sufficient understanding.
87% of the neutral group and 88% of the Pompe group supported the introduction of screening (95% CI of difference -10 to 7%). The groups were similar in their moral reasoning about screening and acceptance of false positives, but the Pompe-experienced group expected greater benefit from neonatal detection of late-onset disease. Multivariate regression analysis controlling for demographics confirmed that approval of the introduction of screening was independent of having (a child with) Pompe disease. Furthermore, respondents with university education, regardless of whether they have (a child with) Pompe disease, were more likely to be reluctant about the introduction of screening than those with less education, OR for approval 0.29 (95% CI 0.18 to 0.49, p < 0.001).
This survey suggests a rather high level of support for newborn screening for Pompe disease, not only among those who have personal experience of the disease but also among the general public in the Netherlands. Optional screening on the basis of informed parental consent is probably unrealistic, underlining the need for new guidelines to help policymakers in their consideration of newborn screening for broad phenotype conditions.
PMCID: PMC3351372  PMID: 22413814
Neonatal screening; Glycogen storage disease type II; Technology assessment; Biomedical; Health policy; Consumer participation
3.  Suppression of autophagy permits successful enzyme replacement therapy in a lysosomal storage disorder—murine Pompe disease 
Autophagy  2010;6(8):1078-1089.
Autophagy, an intracellular system for delivering portions of cytoplasm and damaged organelles to lysosomes for degradation/recycling, plays a role in many physiological processes and is disturbed in many diseases. We recently provided evidence for the role of autophagy in Pompe disease, a lysosomal storage disorder in which acid alpha-glucosidase, the enzyme involved in the breakdown of glycogen, is deficient or absent. Clinically the disease manifests as a cardiac and skeletal muscle myopathy. The current enzyme replacement therapy (ERT) clears lysosomal glycogen effectively from the heart but less so from skeletal muscle. In our Pompe model, the poor muscle response to therapy is associated with the presence of pools of autophagic debris. To clear the fibers of the autophagic debris, we have generated a Pompe model in which an autophagy gene, Atg7, is inactivated in muscle. Suppression of autophagy alone reduced the glycogen level by 50–60%. Following ERT, muscle glycogen was reduced to normal levels, an outcome not observed in Pompe mice with genetically intact autophagy. The suppression of autophagy, which has proven successful in the Pompe model, is a novel therapeutic approach that may be useful in other diseases with disturbed autophagy.
PMCID: PMC3039718  PMID: 20861693
Pompe disease; lysosomal glycogen storage; myopathy; Atg7; enzyme replacement therapy
4.  The clinical relevance of outcomes used in late-onset Pompe disease: can we do better? 
Pompe disease/glycogen storage disease type II, is a rare, lysosomal storage disorder associated with progressive proximal myopathy, causing a gradual loss of muscular function and respiratory insufficiency. Studies of patients with late-onset Pompe disease have used endpoints such as the 6-minute walking test (6MWT) and forced vital capacity (FVC) to assess muscular and respiratory function during disease progression or treatment. However, the relevance of these markers to late-onset Pompe disease and the minimal clinically important difference (MCID) for these endpoints in late-onset Pompe disease have not yet been established. A literature search was carried out to identify studies reporting the MCID (absolute and relative) for the 6MWT and FVC in other diseases. The MCIDs determined in studies of chronic respiratory diseases were used to analyze the results of clinical studies of enzyme replacement therapy in late-onset Pompe disease. In 9 of the 10 late-onset Pompe disease studies reviewed, changes from baseline in the 6MWT were above or within the MCID established in respiratory diseases. Clinical improvement was perceived by patients in 6 of the 10 studies. In 6 of the 9 late-onset Pompe disease studies that reported FVC, the changes from baseline in percentage predicted FVC were above or within the MCID established in respiratory diseases and the difference was perceived as either an improvement or stabilization by patients. However, applying the 6MWT and FVC MCIDs from studies of chronic respiratory diseases to late-onset Pompe disease has several important limitations. Outcome measures in muscular dystrophies include composite measures of muscle function and gait, as well as Rasch-designed and validated tools to assess disease-related quality of life and activities of daily living. Given that the relevance to patients with late-onset Pompe disease of the 6MWT or FVC MCIDs established for chronic respiratory diseases is unclear, these measures should be evaluated specifically in late-onset Pompe disease and alternative outcome measures more specific to neuromuscular disease considered.
PMCID: PMC4015278  PMID: 24119230
Late-onset Pompe disease; Minimal clinically important difference; Outcome measures
5.  Myostatin and Insulin-Like Growth Factor I: Potential Therapeutic Biomarkers for Pompe Disease 
PLoS ONE  2013;8(8):e71900.
Myostatin and insulin-like growth factor 1 (IGF-1) are serum markers for muscle growth and regeneration. However, their value in the clinical monitoring of Pompe disease – a muscle glycogen storage disease – is not known. In order to evaluate their possible utility for disease monitoring, we assessed the levels of these serum markers in Pompe disease patients receiving enzyme replacement therapy (ERT).
A case-control study that included 10 patients with Pompe disease and 10 gender- and age-matched non-Pompe disease control subjects was performed in a referral medical center. Average follow-up duration after ERT for Pompe disease patients was 11.7 months (range: 6–23 months). Measurements of serum myostatin, IGF-1, and creatine kinase levels were obtained, and examinations of muscle pathology were undertaken before and after ERT in the patient group.
Compared with control subjects, Pompe disease patients prior to undergoing ERT had significantly lower serum IGF-1 levels (98.6 ng/ml vs. 307.9 ng/ml, p = 0.010) and lower myostatin levels that bordered on significance (1.38 ng/ml vs. 3.32 ng/ml, p = 0.075). After ERT, respective myostatin and IGF-1 levels in Pompe disease patients increased significantly by 129% (from 1.38 ng/ml to 3.16 ng/ml, p = 0.047) and 74% (from 98.6 ng/ml to 171.1 ng/ml, p = 0.013); these values fall within age-matched normal ranges. In contrast, myostatin and IGF-1 serum markers did not increase in age-matched controls. Follistatin, a control marker unrelated to muscle, increased in both Pompe disease patients and control subjects. At the same time, the percentage of muscle fibers containing intracytoplasmic vacuoles decreased from 80.0±26.4% to 31.6±45.3%.
The increase in myostatin and IGF-1 levels in Pompe disease patients may reflect muscle regeneration after ERT. The role of these molecules as potential therapeutic biomarkers in Pompe disease and other neuromuscular diseases warrants further study.
PMCID: PMC3743802  PMID: 23967261
6.  siRNA Silencing of Proteasome Maturation Protein (POMP) Activates the Unfolded Protein Response and Constitutes a Model for KLICK Genodermatosis 
PLoS ONE  2012;7(1):e29471.
Keratosis linearis with ichthyosis congenita and keratoderma (KLICK) is an autosomal recessive skin disorder associated with a single-nucleotide deletion in the 5′untranslated region of the proteasome maturation protein (POMP) gene. The deletion causes a relative switch in transcription start sites for POMP, predicted to decrease levels of POMP protein in terminally differentiated keratinocytes. To investigate the pathophysiology behind KLICK we created an in vitro model of the disease using siRNA silencing of POMP in epidermal air-liquid cultures. Immunohistochemical analysis of the tissue constructs revealed aberrant staining of POMP, proteasome subunits and the skin differentiation marker filaggrin when compared to control tissue constructs. The staining patterns of POMP siRNA tissue constructs showed strong resemblance to those observed in skin biopsies from KLICK patients. Western blot analysis of lysates from the organotypic tissue constructs revealed an aberrant processing of profilaggrin to filaggrin in samples transfected with siRNA against POMP. Knock-down of POMP expression in regular cell cultures resulted in decreased amounts of proteasome subunits. Prolonged silencing of POMP in cultured cells induced C/EBP homologous protein (CHOP) expression consistent with an activation of the unfolded protein response and increased endoplasmic reticulum (ER) stress. The combined results indicate that KLICK is caused by reduced levels of POMP, leading to proteasome insufficiency in differentiating keratinocytes. Proteasome insufficiency disturbs terminal epidermal differentiation, presumably by increased ER stress, and leads to perturbed processing of profilaggrin. Our findings underline a critical role for the proteasome in human epidermal differentiation.
PMCID: PMC3250448  PMID: 22235297
7.  Teaching tolerance 
Human Vaccines & Immunotherapeutics  2012;8(10):1459-1464.
Babies born with Pompe disease require life-long treatment with enzyme-replacement therapy (ERT). Despite the human origin of the therapy, recombinant human lysosomal acid α glucosidase (GAA, rhGAA), ERT unfortunately leads to the development of high titers of anti-rhGAA antibody, decreased effectiveness of ERT, and a fatal outcome for a significant number of children who have Pompe disease. The severity of disease, anti-drug antibody (ADA) development, and the consequences thereof are directly related to the degree of the enzyme deficiency. Babies born with a complete deficiency GAA are said to have cross-reactive immunologic material (CRIM)–negative Pompe disease and are highly likely to develop GAA ADA. Less frequently, GAA ADA develop in CRIM-positive individuals. Currently, GAA-ADA sero-positive babies are treated with a combination of immunosuppressive drugs to induce immunological tolerance to ERT, but the long-term effect of these regimens is unknown. Alternative approaches that might redirect the immune response toward antigen-specific tolerance without immunosuppressive agents are needed. Methods leading to the induction of antigen-specific regulatory T cells (Tregs), using peptides such as Tregitopes (T regulatory cell epitopes) are under consideration for the future treatment of CRIM-negative Pompe disease. Tregitopes are natural T cell epitopes derived from immunoglobulin G (IgG) that cause the expansion and activation of regulatory T cells (Treg). Teaching the immune system to tolerate GAA by co-delivering GAA with Tregitope peptides might dramatically improve the lives of CRIM-negative babies and could be applied to other enzyme replacement therapies to which ADA have been induced.
PMCID: PMC3660767  PMID: 23095864
Pompe Disease; Anti-drug Antibodies; ADA; Lysosomal acid alpha glucosidase (GAA); Enzyme Replacement Therapy; ERT; Tregitope; Treg; Regulatory T cell; tolerance
8.  Pompe disease: from pathophysiology to therapy and back again 
Pompe disease is a lysosomal storage disorder in which acid alpha-glucosidase (GAA) is deficient or absent. Deficiency of this lysosomal enzyme results in progressive expansion of glycogen-filled lysosomes in multiple tissues, with cardiac and skeletal muscle being the most severely affected. The clinical spectrum ranges from fatal hypertrophic cardiomyopathy and skeletal muscle myopathy in infants to relatively attenuated forms, which manifest as a progressive myopathy without cardiac involvement. The currently available enzyme replacement therapy (ERT) proved to be successful in reversing cardiac but not skeletal muscle abnormalities. Although the overall understanding of the disease has progressed, the pathophysiology of muscle damage remains poorly understood. Lysosomal enlargement/rupture has long been considered a mechanism of relentless muscle damage in Pompe disease. In past years, it became clear that this simple view of the pathology is inadequate; the pathological cascade involves dysfunctional autophagy, a major lysosome-dependent intracellular degradative pathway. The autophagic process in Pompe skeletal muscle is affected at the termination stage—impaired autophagosomal-lysosomal fusion. Yet another abnormality in the diseased muscle is the accelerated production of large, unrelated to ageing, lipofuscin deposits—a marker of cellular oxidative damage and a sign of mitochondrial dysfunction. The massive autophagic buildup and lipofuscin inclusions appear to cause a greater effect on muscle architecture than the enlarged lysosomes outside the autophagic regions. Furthermore, the dysfunctional autophagy affects the trafficking of the replacement enzyme and interferes with its delivery to the lysosomes. Several new therapeutic approaches have been tested in Pompe mouse models: substrate reduction therapy, lysosomal exocytosis following the overexpression of transcription factor EB and a closely related but distinct factor E3, and genetic manipulation of autophagy.
PMCID: PMC4135233  PMID: 25183957
autophagy; lysosome; Pompe disease; lipofuscin; enzyme replacement therapy
9.  The respiratory neuromuscular system in Pompe disease☆ 
Pompe disease is due to mutations in the gene encoding the lysosomal enzyme acid α-glucosidase (GAA). Absence of functional GAA typically results in cardiorespiratory failure in the first year; reduced GAA activity is associated with progressive respiratory failure later in life. While skeletal muscle pathology contributes to respiratory insufficiency in Pompe disease, emerging evidence indicates that respiratory neuron dysfunction is also a significant part of dysfunction in motor units. Animal models show profound glycogen accumulation in spinal and medullary respiratory neurons and altered neural activity. Tissues from Pompe patients show central nervous system glycogen accumulation and motoneuron pathology. A neural mechanism raises considerations about the current clinical approach of enzyme replacement since the recombinant protein does not cross the blood-brain-barrier. Indeed, clinical data suggest that enzyme replacement therapy delays symptom progression, but many patients eventually require ventilatory assistance, especially during sleep. We propose that treatments which restore GAA activity to respiratory muscles, neurons and networks will be required to fully correct ventilatory insufficiency in Pompe disease.
PMCID: PMC4083814  PMID: 23797185
Pompe; Respiratory; Motoneurons; Plasticity; Therapy; Pathology
10.  Diffuse cerebral microhemorrhages in a patient with adult-onset Pompe’s disease: a case report 
Pompe’s disease is a glycogen storage disease that manifests as progressive neuropathy, and myopathy. There are a few reports of vasculopathy in this disease, thought to be from small- and medium-vessel arteriopathy. We present a case of late-onset Pompe’s disease with microhemorrhages and review of the pertinent literature.
We describe a case of microhemorrhages in a patient with known late-onset Pompe’s disease.
Our patient was noted to have numerous microhemorrhages concentrated in the posterior circulation distribution in what can best be described as central microhemorrhages, distinct from the pattern seen in amyloid angiopathy. Previous autopsy studies have found vacuoles in the vessel wall, resulting in small aneurysms as a part of the Pompe syndrome.
There is an accumulating body of evidence that suggests cerebral vasculopathy as one of the primary manifestations of adult-onset Pompe’s disease. This is manifested as dolichoectasia of basilar artery, aneurysms, and microhemorrhages that are central in distribution. The primary pathology is thought to be glycogen deposition in small- and medium-sized intracranial vessels. Controlling blood pressure aggressively and screening intracranial vascular imaging are recommended. Further definition of the syndrome is continuing from phenotypic and genotypic dimensions.
PMCID: PMC4280871  PMID: 25566347
11.  Hypertrophic Cardiomyopathy in Pompe Disease Is Not Limited to the Classic Infantile-Onset Phenotype 
JIMD Reports  2014;17:71-75.
Pompe disease is a genetic disorder caused by a deficiency of acid α-glucosidase (GAA). Patients with classic infantile-onset Pompe disease usually present with hypertrophic cardiomyopathy and die before 1 year of age, if not treated with enzyme replacement therapy (ERT). In comparison, patients with late-onset Pompe disease typically do not have hypertrophic cardiomyopathy. However, here we describe five patients who presented with hypertrophic cardiomyopathy but did not fit the criteria of classic infantile-onset Pompe disease. Their ages at diagnosis of cardiomyopathy were 1 month in two patients following detection of an audible cardiac murmur and 2–3 years in the three remaining patients. All patients survived for 5–8 years without ERT. Three patients died before the advent of ERT from causes other than congestive heart failure. One patient had a good response to ERT starting at 5 years of age. The sibling of one patient, who did not receive ERT and died at age seven, was diagnosed prenatally. At 3 months of age, the sibling had hypertrophic cardiomyopathy, and a muscle biopsy at that time revealed glycogen accumulation.
This case series demonstrates that Pompe disease is a continuum of disease, and the development of cardiomyopathy is not limited to classic infantile-onset Pompe disease. These patients do not fit into the discrete phenotypes of infantile- or late-onset Pompe disease, which may suggest reconsidering the nomenclature of Pompe disease.
PMCID: PMC4241200  PMID: 25213570
12.  Use of Cardiac Magnetic Resonance Imaging to Evaluate Cardiac Structure, Function and Fibrosis in Children with Infantile Pompe Disease on Enzyme Replacement Therapy 
Molecular genetics and metabolism  2010;101(4):332-337.
Pompe disease (acid α-glucosidase deficiency) is one of several lysosomal storage diseases amenable to treatment with enzyme replacement therapy (ERT). While echocardiography (echo) has been the standard method to evaluate the cardiac response to ERT, cardiac magnetic resonance imaging (CMR) has the advantage of better tissue definition and characterization of myocardial fibrosis. However, CMR for Pompe disease is not frequently performed due to the high risk of sedation. We report the first use of CMR in a feasible protocol to quantify left ventricular (LV) mass, function, and presence of myocardial fibrosis in the Pompe population.
Children with Pompe disease on ERT were assessed with transthoracic echo and CMR over a 3 year period at a single institution. Echocardiography was performed using standard techniques without sedation. CMR was performed using retrospectively gated and real-time imaging, with and without sedation. LV mass indexed to body surface area (LVMI) and ejection fraction (EF) were measured by both echo and CMR, and evaluated for change over time. Myocardial fibrosis was assessed with CMR by delayed enhancement imaging 5-10 min after gadolinium contrast using single-shot inversion recovery sequences with inversion time set to null the myocardium.
Seventeen CMR scans were successfully performed in 10 subjects with Pompe disease (median age at first CMR 9 months, range 1-38 months, 80% male), with sedation only performed for 4 studies. There was a median interval of 5 months (range 0-34 months) from start of ERT to first CMR (baseline). At baseline, median indexed LVMI by CMR (140.0 g/m2, range 43.8-334.0) tended to be lower than that assessed by echo (median 204.0 g/m2, range 52.0-385.0), but did not reach statistical significance. At baseline, CMR EF was similar to that assessed by echo (55% vs. 55%). Overall, there was not a significant decrease in CMR measured LVMI over time (CMR median LVMI at baseline 94 g/m2 (range 43.8-334) vs. CMR median at most recent study 44.5 g/m2 (range 34-303), p=0.44). In 5 patients with serial CMR scans over time, LVMI decreased in 2, was similar in 2, and increased in 1 patient with high sustained antibodies to exogenous enzyme. Delayed enhancement was noted in only l separate patient who also had high sustained antibodies to exogenous enzyme.
CMR is a useful imaging tool that is feasible to use to serially follow LVMI and EF in children with Pompe disease on ERT. Real-time imaging is adequate for quantification purposes in these patients and minimizes the need for sedation. Quantitative CMR LVMI is generally lower than echo derived LVMI. Delayed enhancement appears to be a rare finding by CMR in Pompe Disease. Further follow-up is necessary to better understand the long term effects of ERT in infantile Pompe survivors, especially those with high sustained antibody titers or advanced cardiac disease at treatment outset.
PMCID: PMC2991632  PMID: 20875764
Pompe Disease; Enzyme Replacement Therapy; Cardiac Magnetic Resonance Imaging; Echocardiography; Delayed Enhancement
13.  The values and limits of an in vitro model of Pompe disease 
Autophagy  2009;5(5):729-731.
In Pompe disease, a lysosomal glycogen storage disorder, cardiac and skeletal muscle abnormalities are responsible for premature death and severe weakness. Swollen glycogen-filled lysosomes, the expected pathology, are accompanied in skeletal muscle by a secondary pathology – massive accumulation of autophagic debris – that appears to contribute greatly to the weakness. We have tried to reproduce these defects in murine, Pompe myotubes derived from either primary myoblasts or myoblasts with extended proliferative capacity. The cells accumulated large lysosomes filled with glycogen, but, to our disappointment, did not have autophagic buildup even though basal autophagy was intact. When we suppressed autophagy by knocking down Atg7, we found that glycogen uptake by lysosomes was not affected, suggesting that macroautophagy is not the major pathway for glycogen delivery to lysosomes. But two apparently incidental observations – a peculiar distribution of both microinjected dextran and of small acidic structures adjacent to the interior membrane of large alkalinized glycogen-containing lysosomes – raised the possibility that glycogen traffics to the lysosomes by microautophagy or/and by the engulfment of small lysosomes by large ones. The cultured myotubes, therefore, appear to be a useful model for studying the mechanisms involved in glycogen accumulation in Pompe disease and to test substrate deprivation approaches.
PMCID: PMC2706922  PMID: 19571661
lysosomal storage; glycogen; Pompe disease; myotubes; Atg7
14.  Impaired clearance of accumulated lysosomal glycogen in advanced Pompe disease despite high-level vector-mediated transgene expression 
The journal of gene medicine  2009;11(10):913-920.
Infantile-onset glycogen storage disease type II (GSD-II; Pompe disease; MIM 232300) causes death early in childhood from cardiorespiratory failure in absence of effective treatment, whereas late-onset Pompe disease causes a progressive skeletal myopathy. The limitations of enzyme replacement therapy could potentially be addressed with adeno-associated virus (AAV) vector-mediated gene therapy.
AAV vectors containing tissue-specific regulatory cassettes, either liver-specific or muscle-specific, were administered to 12 and 17 month old Pompe disease mice to evaluate the efficacy of gene therapy in advanced Pompe disease. Biochemical correction was evaluated through GAA activity and glycogen content analyses of the heart and skeletal muscle. Western blotting, urinary biomarker, and Rotarod performance were evaluated following vector administration.
The AAV vector containing the liver-specific regulatory cassette secreted high-level hGAA into the blood and corrected glycogen storage in the heart and diaphragm. The biochemical correction of the heart and diaphragm was associated with efficacy, as reflected by increased Rotarod performance; however, the clearance of glycogen from skeletal muscles was relatively impaired, in comparison with younger Pompe disease mice. An alternative vector containing a muscle-specific regulatory cassette transduced skeletal muscle with high efficiency, but also failed to achieve complete clearance of accumulated glycogen. Decreased transduction of the heart and liver in older mice, especially in females, was implicated as a cause for reduced efficacy in advanced Pompe disease.
The impaired efficacy of AAV vector-mediated gene therapy in old Pompe disease mice emphasized the need for early treatment to achieve full efficacy.
PMCID: PMC3622249  PMID: 19621331
Glycogen storage disease type II; adeno-associated virus; acid alpha-glucosidase; acid maltase; Pompe disease
15.  Glycosylation-independent Lysosomal Targeting of Acid α-Glucosidase Enhances Muscle Glycogen Clearance in Pompe Mice* 
The Journal of Biological Chemistry  2012;288(3):1428-1438.
Background: Acid α-glucosidase, an enzyme replacement therapy for Pompe disease, is poorly targeted to lysosomes when relying on phosphomannose residues.
Results: Fusing IGF-II to acid α-glucosidase resulted in more efficient uptake and glycogen clearance from muscle of Pompe mice.
Conclusion: Enhanced binding to the cation-independent mannose 6-phosphate receptor (CI-MPR) enabled improved glycogen clearance in Pompe mice.
Significance: BMN 701 is now being tested for Pompe disease in human clinical studies.
We have used a peptide-based targeting system to improve lysosomal delivery of acid α-glucosidase (GAA), the enzyme deficient in patients with Pompe disease. Human GAA was fused to the glycosylation-independent lysosomal targeting (GILT) tag, which contains a portion of insulin-like growth factor II, to create an active, chimeric enzyme with high affinity for the cation-independent mannose 6-phosphate receptor. GILT-tagged GAA was taken up by L6 myoblasts about 25-fold more efficiently than was recombinant human GAA (rhGAA). Once delivered to the lysosome, the mature form of GILT-tagged GAA was indistinguishable from rhGAA and persisted with a half-life indistinguishable from rhGAA. GILT-tagged GAA was significantly more effective than rhGAA in clearing glycogen from numerous skeletal muscle tissues in the Pompe mouse model. The GILT-tagged GAA enzyme may provide an improved enzyme replacement therapy for Pompe disease patients.
PMCID: PMC3548456  PMID: 23188827
Glycogen; Lysosomal Storage Disease; Muscle; Muscular Dystrophy; Receptor Endocytosis; CI-MPR; Glycogen Storage Disease; IGF-II; Pompe; Enzyme Replacement Therapy
16.  Murine Muscle Cell Models for Pompe Disease and Their Use in Studying Therapeutic Approaches 
Molecular genetics and metabolism  2009;96(4):208-217.
Lysosomes filled with glycogen are a major pathologic feature of Pompe disease, a fatal myopathy and cardiomyopathy caused by a deficiency of the glycogen-degrading lysosomal enzyme, acid α-glucosidase (GAA). To facilitate studies germane to this genetic disorder, we developed two in vitro Pompe models: myotubes derived from cultured primary myoblasts isolated from Pompe (GAA KO) mice, and myotubes derived from primary myoblasts of the same genotype that had been transduced with cyclin-dependent kinase 4 (CDK4). This latter model is endowed with extended proliferative capacity. Both models showed extremely large alkalinized, glycogen-filled lysosomes as well as impaired trafficking to lysosomes. Although both Pompe tissue culture models were derived from fast muscles and were fast myosin positive, they strongly resemble slow fibers in terms of their pathologic phenotype and their response to therapy with recombinant human GAA (rhGAA). Autophagic buildup, a hallmark of Pompe disease in fast muscle fibers, was absent, but basal autophagy was functional. To evaluate substrate deprivation as a strategy to prevent the accumulation of lysosomal glycogen, we knocked down Atg7, a gene essential for autophagosome formation, via siRNA, but we observed no effect on the extent of glycogen accumulation, thus confirming our recent observation in autophagy deficient Pompe mice [1] that macroautophagy is not the major route of glycogen transport to lysosomes. The in vitro Pompe models should be useful in addressing fundamental questions regarding the pathway of glycogen to the lysosomes and testing panels of small molecules that could affect glycogen biosynthesis or speed delivery of the replacement enzyme to affected lysosomes.
PMCID: PMC2680079  PMID: 19167256
autophagy; lysosomes; myotubes; Pompe disease
17.  Recent Developments, Utilization, and Spending Trends for Pompe Disease Therapies 
American Health & Drug Benefits  2012;5(3):182-189.
Pompe disease is a rare condition, with an incidence rate estimated to be between 1 in 40,000 and 1 in 300,000 live births worldwide. For an infant who contracts the disease, which is an inherited metabolic myopathy caused by deficiency of the acid alpha-glucosidase (GAA) enzyme in lysosomal cells, the survival rate to age 1 year is estimated to be 25.7%. Before 2006, no therapies were available for this disease.
The goals of this study were to review recent developments in therapies for Pompe disease, including the US Food and Drug Administration (FDA) approval of 2 biologic drugs, and to describe the associated drug utilization and spending trends in the US Medicaid program for patients with this disease.
We reviewed 2 recently approved therapies for Pompe disease and compared their indications, as well as their efficacy and safety profiles. A retrospective analysis was performed using the national Medicaid pharmacy claims database. Quarterly prescriptions and reimbursement amounts were calculated for each drug from 2006 quarter 2 through 2011 quarter 2. Average per-prescription spending was calculated by dividing the drug reimbursement by the number of prescriptions written for that drug.
Myozyme (alglucosidase alfa, recombinant human GAA) and Lumizyme (alglucosidase alfa), the first 2 enzyme replacement therapies available for Pompe disease, were approved as orphan drugs by the FDA in 2006 and in 2010, respectively. Myozyme is indicated for infantile-onset Pompe disease; Lumizyme is indicated for patients aged ≥8 years. Although both drugs have been shown to improve patient survival rates, they both also have a boxed warning, because of the possibility of life-threatening allergic reactions. Moreover, Lumizyme has a restricted distribution system to ensure it is used by the correct patient population. In 2010, Medicaid spending for Myozyme was $3.6 million. In the first 2 quarters of 2011, Medicaid spending for Lumizyme was $1.8 million. Prescriptions for Myozyme increased from 1 in 2006 quarter 2 to 127 in 2011 quarter 2, whereas prescriptions for Lumizyme increased from 6 in 2010 quarter 3 to 60 in 2011 quarter 2. During the same period, expenditures rose from $9450 to $930,459 for Myozyme and from $119,691 to $1.16 million for Lumizyme. The average price per prescription was approximately $10,000 for Myozyme and approximately $20,000 for Lumizyme over the study period.
As can be expected after the FDA's approval of Myozyme and Lumizyme, Medicaid beneficiaries have experienced rising utilization of the 2 therapies. Spending by Medicaid has increased proportionately, implying a steady per-prescription average price for both drugs where if both numerator and denominator increase at the same rate, the ratio (price) should remain the same. New promising therapies for Pompe disease are currently being studied.
PMCID: PMC4046468  PMID: 24991319
18.  Burden of illness of Pompe disease in patients only receiving supportive care 
Pompe disease is an orphan disease for which enzyme replacement therapy (ERT) recently became available. This study aims to estimate all relevant aspects of burden of illness—societal costs, use of home care and informal care, productivity losses, and losses in health-related quality of life (HRQoL)—for adult Pompe patients only receiving supportive care.
We collected data on all relevant aspects of burden of illness via a questionnaire. We applied a societal perspective in calculating costs. The EQ-5D was used to estimate HRQoL.
Eighty adult patients (87% of the total Dutch adult Pompe population) completed a questionnaire. Disease severity ranged from mild to severe. Total annual costs were estimated at €22,475 (range €0–169,539) per adult Pompe patient. Patients on average received 8 h of home care and 19 h of informal care per week. Eighty-five percent of the patients received informal care from one or more caregivers; 40% had stopped working due to their disease; another 20% had reduced their working hours. HRQoL for Pompe patients who only received supportive care was estimated at 0.72, 17% lower than the Dutch population at large.
Adult Pompe disease is associated with a considerable burden of illness at both the societal and patient levels. The disease leads to substantial costs and dependency on medical devices, home care, and informal care, and has a high impact on the patient’s social network. In addition, patients are limited in their ability to work and have significantly reduced HRQoL.
PMCID: PMC3173621  PMID: 21499718
Muscle & nerve  2011;45(3):319-333.
Pompe disease is a rare, autosomal recessive disorder caused by deficiency of the glycogen-degrading lysosomal enzyme acid alpha-glucosidase. Late-onset Pompe disease is a multisystem condition, with a heterogeneous clinical presentation that mimics other neuromuscular disorders.
Objective is to propose consensus-based treatment and management recommendations for late-onset Pompe disease.
A systematic review of the literature by a panel of specialists with expertise in Pompe disease was undertaken.
A multidisciplinary team should be involved to properly treat the pulmonary, neuromuscular, orthopedic, and gastrointestinal elements of late-onset Pompe disease. Presymptomatic patients with subtle objective signs of Pompe disease (and patients symptomatic at diagnosis) should begin treatment with enzyme replacement therapy (ERT) immediately; presymptomatic patients without symptoms or signs should be observed without use of ERT. After 1 year of ERT, patients’ condition should be reevaluated to determine whether ERT should be continued.
PMCID: PMC3534745  PMID: 22173792
acid alpha-glucosidase; acid maltase deficiency; lysosomal storage disorder; neuromuscular disease; Pompe disease
20.  Clinical consequences of reduced dosing schedule during treatment of a patient with Pompe’s disease 
Biologics in Therapy  2011;1(1):1.
Pompe’s disease is a metabolic myopathy caused by a deficiency of the enzyme alpha-glucosidase. Patients with late-onset Pompe’s disease have progressive muscle weakness, which also affects pulmonary function. Since the advent of specific treatment for Pompe’s disease, enzyme replacement therapy with alpha-glucosidase, the prognosis of the disease has changed.
We report the case of the first patient treated in Spain with home therapy, and the effects on her clinical status of a reduction in treatment frequency.
A worsening was seen in the patient’s neuromuscular assessment on different scales, after two discontinuations during the patient’s usual administration frequency.
It is essential to keep an adequate administration schedule to maintain the clinical benefits of enzyme therapy.
PMCID: PMC3873020  PMID: 24392291
alpha-glucosidase replacement enzyme; maltase acid deficiency; neuromuscular disease; Pompe’s disease
21.  Clinical consequences of reduced dosing schedule during treatment of a patient with Pompe’s disease 
Biologics in Therapy  2011;1(1):1.
Pompe’s disease is a metabolic myopathy caused by a deficiency of the enzyme alpha-glucosidase. Patients with late-onset Pompe’s disease have progressive muscle weakness, which also affects pulmonary function. Since the advent of specific treatment for Pompe’s disease, enzyme replacement therapy with alpha-glucosidase, the prognosis of the disease has changed.
We report the case of the first patient treated in Spain with home therapy, and the effects on her clinical status of a reduction in treatment frequency.
A worsening was seen in the patient’s neuromuscular assessment on different scales, after two discontinuations during the patient’s usual administration frequency.
It is essential to keep an adequate administration schedule to maintain the clinical benefits of enzyme therapy.
PMCID: PMC3873020  PMID: 24392291
alpha-glucosidase replacement enzyme; maltase acid deficiency; neuromuscular disease; Pompe’s disease
22.  Therapeutic advances in the management of Pompe disease and other metabolic myopathies 
The world of metabolic myopathies has been dramatically modified by the advent of enzyme replacement therapy (ERT), the first causative treatment for glycogenosis type II (GSDII) or Pompe disease, which has given new impetus to research into that disease and also other pathologies. This article reviews new advances in the treatment of GSDII, the consensus about ERT, and its limitations. In addition, the most recent knowledge regarding the pathophysiology, phenotype, and genotype of the disease is discussed. Pharmacological, immunotherapy, nutritional, and physical/rehabilitative treatments for late-onset Pompe disease and other metabolic myopathies are covered, including treatments for defects in glycogen metabolism, such as glycogenosis type V (McArdle disease), and glycogenosis type III (debrancher enzyme deficiency), and defects in lipid metabolism, such as carnitine palmitoyltransferase II deficiency and electron transferring flavoprotein dehydrogenase deficiency, or riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency.
PMCID: PMC3755530  PMID: 23997816
Glycogenosis type II; McArdle disease; RR-MADD; glycogenosis type III; CPT2 deficiency
23.  Phenotypical variation within 22 families with Pompe disease 
Pompe disease has a broad clinical spectrum, in which the phenotype is partially explained by the genotype. The aim of this study was to describe phenotypical variation among siblings with non-classic Pompe disease. We hypothesized that siblings and families with the same genotype share more similar phenotypes than the total population of non-classic Pompe patients, and that this might reveal genotype-phenotype correlations.
We identified all Dutch families in which two or three siblings were diagnosed with Pompe disease and described genotype, acid α-glucosidase activity, age at symptom onset, presenting symptoms, specific clinical features, mobility and ventilator dependency.
We identified 22 families comprising two or three siblings. All carried the most common mutation c.-32-13 T > G in combination with another pathogenic mutation. The median age at symptom onset was 33 years (range 1–62 years). Within sibships symptom onset was either in childhood or in adulthood. The median variation in symptom onset between siblings was nine years (range 0–31 years). Presenting symptoms were similar across siblings in 14 out of 22 families. Limb girdle weakness was most frequently reported. In some families ptosis or bulbar weakness were present in all siblings. A large variation in disease severity (based on wheelchair/ventilator dependency) was observed in 11 families. This variation did not always result from a difference in duration of the disease since a third of the less affected siblings had a longer course of the disease. Enzyme activity could not explain this variation either. In most families male patients were more severely affected. Finally, symptom onset varied substantially in twelve families despite the same GAA genotype.
In most families with non-classic Pompe disease siblings share a similar phenotype regarding symptom onset, presenting symptoms and specific clinical features. However, in some families the course and severity of disease varied substantially. This phenotypical variation was also observed in families with identical GAA genotypes. The commonalities and differences indicate that besides genotype, other factors such as epigenetic and environmental effects influence the clinical presentation and disease course.
PMCID: PMC3843594  PMID: 24245577
Pompe disease; Glycogen storage disease type II; Lysosomal storage disorder; Acid α-glucosidase; Phenotype; Families; Siblings
24.  Autophagy in skeletal muscle: implications for Pompe disease 
Pompe disease is caused by an inherited deficiency of acid α-glucosidase (GAA), a lysosomal enzyme that catalyzes the breakdown of glycogen to glucose. In the absence of GAA, enlarged, glycogen-laden lysosomes accumulate in multiple tissues, although the major clinical manifestations are seen in cardiac and skeletal muscle. For many years, it was believed that the rupture of glycogen-filled lysosomes was the major cause of the profound muscle damage observed in patients with Pompe disease. Here, we present evidence that a failure of productive autophagy in muscle tissue contributes strongly to disease pathology in both patients with Pompe disease and GAA-knockout mice. In the GAA-knockout mouse model, progressive accumulation of autophagic vesicles is restricted to Type II-rich muscle fibers. Not only does this build-up of autophagosomes disrupt the contractile apparatus in the muscle fibers, it also interferes with enzyme replacement therapy by acting as a sink for the recombinant enzyme and preventing its efficient delivery to the lysosomes. Our data indicate that a re-examination of the presumed pathological mechanism in Pompe disease is necessary, and suggest that successful treatment of patients with Pompe disease will require consideration of the dramatic failure of autophagy that occurs in this disease.
PMCID: PMC2948975  PMID: 20040311
autophagy; enzyme replacement therapy; glycogen; Pompe disease; skeletal muscle
25.  In Vivo Bone Architecture in Pompe Disease Using High-Resolution Peripheral Computed Tomography 
JIMD Reports  2012;7:81-88.
Pompe disease (lysosomal acid alpha-glucosidase deficiency) in adolescents and adults presents primarily with muscle weakness. Bone weakness is an under-recognized finding in patients with Pompe disease, but there is emerging evidence that loss of muscle function and mobility can lead to loss of mineral content and a higher risk of fracture. In addition to the mineral content, architecture is also important in determining the overall strength of the bone. We present the results of the longest longitudinal duration study to date using a novel application of high-resolution peripheral quantitative computed tomography (HR-pQCT) in four patients with Pompe disease over 4 years of observation during the normal course of their disease management. The subjects varied in treatment status with recombinant human alpha-glucosidase (rhGAA), use of anti-resorptive therapy (such as bisphosphonates), mobility and weight-bearing status, and the use of side-alternating vibration therapy. Our observations were that HR-pQCT can measure trends in mineral density and architecture over a long period of observation and may be an early indicator of the response to interventional therapies. In addition, a combination of decreased loading forces due to decreased mobility likely contributes to the compromise of bone integrity in Pompe disease. These trends can be reversed by applying increased loading forces such as vibration therapy and maintaining weight-bearing and mobility. We conclude that HR-pQCT can serve as a valuable tool to monitor bone health in patients with Pompe disease.
PMCID: PMC3575046  PMID: 23430500

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