Slow, progressive myopathy in neonatally treated patients with infantile-onset Pompe disease: a muscle magnetic resonance imaging study

The Importance of Early Treatment of Inherited Neuromuscular Conditions

There has been tremendous progress in treatment of neuromuscular diseases over the last 20 years, which has transformed the natural history of these severely debilitating conditions. Although the factors that determine the response to therapy are many and in some instance remain to be fully elucidated, early treatment clearly has a major impact on patient outcomes across a number of inherited neuromuscular conditions. To improve patient care and outcomes, clinicians should be aware of neuromuscular conditions that require prompt treatment initiation. This review describes data that underscore the importance of early treatment of children with inherited neuromuscular conditions with an emphasis on data resulting from newborn screening efforts.

A pilot study shows the positive effects of continuous airway pressure for treating hypernasal speech in children with infantile-onset Pompe disease

Children with infantile-onset Pompe disease (IOPD) demonstrate hypernasality. This study aimed to evaluate whether continuous positive airway pressure (CPAP) training may reduce hypernasality in children with IOPD. Five children with IOPD were enrolled in a single-subject experimental design of type A-B-A′. The intervention comprised an 8-week, 6-day-per-week regimen of CPAP training at home. Participants continued traditional speech therapy once per week throughout the 24-week study duration. The outcome measurements included the degree of hypernasality (DH), the percentage of consonants correct (PCC), and the speech intelligibility score (SIS). C-statistic analysis with an α of 0.05 was used along with visual analysis to assess speech changes. Three patients completed the study. During the CPAP training phase, the DH, PCC, and SIS were significantly improved compared with the baseline (p < 0.05). At the follow-up phase, both DH and SIS were improved compared with the baseline (p < 0.05), but the PCC had returned to the baseline level. CPAP training demonstrated effectiveness in reducing nasal sounds in IOPD patients. Further studies training younger children with normal hearing may help elucidate the persistence of the effects in children with IOPD.

Quantitative muscle ultrasound and electrical impedance myography in late onset Pompe disease: A pilot study of reliability, longitudinal change and correlation with function

Background/objectives

Late-onset Pompe disease (LOPD) is slowly progressive, making it difficult to assess clinical change and response to interventions. In this study, quantitative muscle ultrasonography (QMUS) and electrical impedance myography (EIM) were evaluated as potential biomarkers.

Methods

25 patients with confirmed LOPD were recruited from the Duke Pompe Clinic and evaluated with standard clinical measures, QMUS, standard EIM (sEIM) and hand-held EIM (hEIM). Patients were evaluated at baseline, 12 months and 24 months. MUS, sEIM and hEIM were compared with the clinical data. Five patients were given hEIM devices to perform measurements at home.

Results

QMUS and hEIM had good reliability as measures of muscle structure and conduction properties. Home, patient-performed hEIM measurements did not differ significantly from those performed in the clinic setting. Thirteen patients completed all follow-up measures. Most measures did not change over the study period, however, vastus lateralis echointensity increased 27%, a sign of declining muscle health. Additionally, significant correlations between QMUS, hEIM and measures of muscle strength and function were present.

Conclusions

QMUS and hEIM may provide useful outcome measures for future studies in LOPD with hEIM providing an opportunity to collect data at home. Larger, multicenter studies are needed to explore these possibilities.

Phenotypic implications of pathogenic variant types in Pompe disease

Newborn screening and therapies for Pompe disease (glycogen storage disease type II, acid maltase deficiency) will continue to expand in the future. It is thus important to determine whether enzyme activity or type of pathogenic genetic variant in GAA can best predict phenotypic severity, particularly the presence of infantile-onset Pompe disease (IOPD) versus late-onset Pompe disease (LOPD). We performed a retrospective analysis of 23 participants with genetically-confirmed cases of Pompe disease. The following data were collected: clinical details including presence or absence of cardiomyopathy, enzyme activity levels, and features of GAA variants including exon versus intron location and splice site versus non-splice site. Several combinations of GAA variant types for individual participants had significant associations with disease subtype, cardiomyopathy, age at diagnosis, gross motor function scale (GMFS), and stability of body weight. The presence of at least one splice site variant (c.546 G > C/p.T182 = , c.1076-22 T > G, c.2646 + 2 T > A, and the classic c.-32-13T > G variant) was associated with LOPD, while the presence of non-splice site variants on both alleles was associated with IOPD. Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features. To extend the findings of prior studies, we found that multiple types of splice site variants beyond the classic c.-32-13T > G variant are often associated with a milder phenotype. Enzyme activity levels continue to have utility for supporting the diagnosis when the genetic variants are ambiguous. It is important for newly diagnosed patients with Pompe disease to have complete genetic, cardiac, and neurological evaluations.

Endolysosomal N-glycan processing is critical to attain the most active form of the enzyme acid alpha-glucosidase

Acid alpha-glucosidase (GAA) is a lysosomal glycogen-catabolizing enzyme, the deficiency of which leads to Pompe disease. Pompe disease can be treated with systemic recombinant human GAA (rhGAA) enzyme replacement therapy (ERT), but the current standard of care exhibits poor uptake in skeletal muscles, limiting its clinical efficacy. Furthermore, it is unclear how the specific cellular processing steps of GAA after delivery to lysosomes impact its efficacy. GAA undergoes both proteolytic cleavage and glycan trimming within the endolysosomal pathway, yielding an enzyme that is more efficient in hydrolyzing its natural substrate, glycogen. Here, we developed a tool kit of modified rhGAAs that allowed us to dissect the individual contributions of glycan trimming and proteolysis on maturation-associated increases in glycogen hydrolysis using in vitro and in cellulo enzyme processing, glycopeptide analysis by MS, and high-pH anion-exchange chromatography with pulsed amperometric detection for enzyme kinetics. Chemical modifications of terminal sialic acids on N-glycans blocked sialidase activity in vitro and in cellulo, thereby preventing downstream glycan trimming without affecting proteolysis. This sialidase-resistant rhGAA displayed only partial activation after endolysosomal processing, as evidenced by reduced catalytic efficiency. We also generated enzymatically deglycosylated rhGAA that was shown to be partially activated despite not undergoing proteolytic processing. Taken together, these data suggest that an optimal rhGAA ERT would require both N-glycan and proteolytic processing to attain the most efficient enzyme for glycogen hydrolysis and treatment of Pompe disease. Future studies should examine the amenability of next-generation ERTs to both types of cellular processing.

Transforming the clinical outcome in CRIM-negative infantile Pompe disease identified via newborn screening: the benefits of early treatment with enzyme replacement therapy and immune tolerance induction

Purpose:

To assess the magnitude of benefit to early treatment initiation, enabled by newborn screening or prenatal diagnosis, in patients with cross-reactive immunological material (CRIM)-negative infantile Pompe disease (IPD), treated with enzyme replacement therapy (ERT) and prophylactic immune tolerance induction (ITI) with rituximab, methotrexate, and IVIG.

Methods:

A total of 41 CRIM-negative IPD patients were evaluated. Amongst patients who were treated with ERT+ITI (n=30), those who were invasive ventilator-free at baseline and had ≥6 months of follow-up were stratified based on age at treatment initiation: 1) early (≤4 weeks), 2) intermediate (>4 and ≤15 weeks), and 3) late (>15 weeks). A historical cohort of 11 CRIM-negative patients with IPD treated with ERT monotherapy served as an additional comparator group.

Results:

Twenty patients were included; five, seven, and eight in early, intermediate, and late treatment groups, respectively. Genotypes were similar across the three groups. Early-treated patients showed significant improvements in left ventricular mass index, motor and pulmonary outcomes, as well as biomarkers creatine kinase and urinary glucose tetrasaccharide, compared to those treated later.

Conclusion:

Our preliminary data suggest that early treatment with ERT+ITI can transform the long-term CRIM-negative IPD phenotype, which represents the most severe end of the Pompe disease spectrum.

Quantitative whole-body magnetic resonance imaging in children with Pompe disease: Clinical tools to evaluate severity of muscle disease

OBJECTIVE

Since the introduction of enzyme replacement therapy (ERT) with alglucosidase alfa, there has been increased survival in patients with Pompe disease. It is essential to characterize and quantify the burden of disease in these patients. Here, we report a measure of muscle fat infiltration in children with infantile and pediatric late-onset Pompe disease (IPD and LOPD, respectively) to better understand the extent of muscle involvement.

METHODS

Eleven pediatric patients with Pompe disease (five IPD, six LOPD), ages 7-17 years, received whole-body magnetic resonance imaging (WBMRI), muscle strength testing using the modified Medical Research Council (mMRC) scale, functional assessment using gait, stairs, gowers, chair (GSGC), and urine glucose tetrasaccharide (Glc4) testing. The intramuscular fat seen on WBMRI was quantified using proton density fat fraction (PDFF) and correlated to appropriate muscle strength and functional tests, and urine Glc4.

RESULTS

Patients with IPD, although younger, had higher mean PDFF values than LOPD patients (11.61% vs 8.52%). Significant correlation existed between PDFF and the GSGC assessment (r = .9273, P = .0003). Moderate correlation existed between PDFF and mMRC (r = -.667, P = .0831), and PDFF and urine Glc4 (r = .6121, P = .0667). Anterior tibialis was in the top quartile of muscle involvement for patients with LOPD.

CONCLUSION

In the past, physical therapy assessments alone have been used to track disease progression. Here, we show the clinical utility of WBMRI in quantifying muscle involvement in children with Pompe disease, especially regarding the novel involvement of anterior tibialis in children with LOPD, to better assess baseline muscle burden and mapping disease progression in children treated with ERT.

Targeted Therapies for Metabolic Myopathies Related to Glycogen Storage and Lipid Metabolism: a Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Metabolic myopathies are a heterogenous group of muscle diseases typically characterized by exercise intolerance, myalgia and progressive muscle weakness. Effective treatments for some of these diseases are available, but while our understanding of the pathogenesis of metabolic myopathies related to glycogen storage, lipid metabolism and β-oxidation is well established, evidence linking treatments with the precise causative genetic defect is lacking.

OBJECTIVE

The objective of this study was to collate all published evidence on pharmacological therapies for the aforementioned metabolic myopathies and link this to the genetic mutation in a format amenable to databasing for further computational use in line with the principles of the "treatabolome" project.

METHODS

A systematic literature review was conducted to retrieve all levels of evidence examining the therapeutic efficacy of pharmacological treatments on metabolic myopathies related to glycogen storage and lipid metabolism. A key inclusion criterion was the availability of the genetic variant of the treated patients in order to link treatment outcome with the genetic defect.

RESULTS

Of the 1,085 articles initially identified, 268 full-text articles were assessed for eligibility, of which 87 were carried over into the final data extraction. The most studied metabolic myopathies were Pompe disease (45 articles), multiple acyl-CoA dehydrogenase deficiency related to mutations in the ETFDH gene (15 articles) and systemic primary carnitine deficiency (8 articles). The most studied therapeutic management strategies for these diseases were enzyme replacement therapy, riboflavin, and carnitine supplementation, respectively.

CONCLUSIONS

This systematic review provides evidence for treatments of metabolic myopathies linked with the genetic defect in a computationally accessible format suitable for databasing in the treatabolome system, which will enable clinicians to acquire evidence on appropriate therapeutic options for their patient at the time of diagnosis.

Ultrastructural and diffusion tensor imaging studies reveal axon abnormalities in Pompe disease mice

Pompe disease (PD) is caused by lysosomal glycogen accumulation in tissues, including muscles and the central nervous system (CNS). The intravenous infusion of recombinant human acid alpha-glucosidase (rhGAA) rescues the muscle pathologies in PD but does not treat the CNS because rhGAA does not cross the blood–brain barrier (BBB). To understand the CNS pathologies in PD, control and PD mice were followed and analyzed at 9 and 18 months with brain structural and ultrastructural studies. T2-weighted brain magnetic resonance imaging studies revealed the progressive dilatation of the lateral ventricles and thinning of the corpus callosum in PD mice. Electron microscopy (EM) studies at the genu of the corpus callosum revealed glycogen accumulation, an increase in nerve fiber size variation, a decrease in the g-ratio (axon diameter/total fiber diameter), and myelin sheath decompaction. The morphology of oligodendrocytes was normal. Diffusion tensor imaging (DTI) studies at the corpus callosum revealed an increase in axial diffusivity (AD) and mean diffusivity (MD) more significantly in 9-month-old PD mice. The current study suggests that axon degeneration and axon loss occur in aged PD mice and are probably caused by glycogen accumulation in neurons. A drug crossing the BBB or a treatment for directly targeting the brain might be necessary in PD.

Skeletal muscle magnetic resonance imaging in Pompe disease

Pompe disease is characterized by a deficiency of acid alpha-glucosidase that results in muscle weakness and a variable degree of disability. There is an approved therapy based on enzymatic replacement that has modified disease progression. Several reports describing muscle magnetic resonance imaging (MRI) features of Pompe patients have been published. Most of the studies have focused on late-onset Pompe disease (LOPD) and identified a characteristic pattern of muscle involvement useful for the diagnosis. In addition, quantitative MRI studies have shown a progressive increase in fat in skeletal muscles of LOPD over time and they are increasingly considered a good tool to monitor progression of the disease. The studies performed in infantile-onset Pompe disease patients have shown less consistent changes. Other more sophisticated muscle MRI sequences, such as diffusion tensor imaging or glycogen spectroscopy, have also been used in Pompe patients and have shown promising results.

Using human Pompe disease-induced pluripotent stem cell-derived neural cells to identify compounds with therapeutic potential

Pompe disease (OMIM # 232300) is a glycogen storage disease caused by autosomal recessive mutations of the gene encoding alpha-1,4-glucosidase (GAA; EC 3.2.1.20). Despite the relatively effective employment of enzyme replacement therapy, some critical medical issues still exist in patients with this disease, including the persistence of abnormalities in the central nervous system (CNS), probably because of the inability of the recombinant GAA to pass through the blood-brain barrier. To address this issue, identification of more therapeutic agents that target the CNS of patients with Pompe disease may be required. In this study, we derived neuronal cells from Pompe disease-induced pluripotent stem cells (Pom-iPSCs) and proved that they are able to recapitulate the hallmark cellular and biochemical phenotypes of Pompe disease. Using the Pom-iPSC-derived neurons as an in vitro drug-testing model, we then identified three compounds, ebselen, wortmannin and PX-866, with therapeutic potential to alleviate Pompe disease-associated pathological phenotypes in the neurons derived from Pom-iPSCs. We confirmed that all three compounds were able to enhance the GAA activity in the Pom-iPSC-derived neurons. Moreover, they were able to enhance the GAA activity in several important internal organs of GAA-deficient mice when co-injected with recombinant human GAA, and we found that intraperitoneal injection of ebselen was able to promote the GAA activity of the GAA-heterozygous mouse brain. Our results prove the usefulness of Pom-iPSC-derived neuronal populations for identifying new compounds with therapeutic potential.

Earlier and higher dosing of alglucosidase alfa improve outcomes in patients with infantile-onset Pompe disease: Evidence from real-world experiences

Objective

Enzyme replacement therapy (ERT), the only approved therapy for infantile-onset Pompe disease (IOPD), had heterogeneous clinical effects due to factors such as severity, age at first treatment, dosage, and dosing regimens. We report the clinical and biochemical outcomes of a cohort of IOPD patients identified through newborn screening, and evaluating the dosage effect.

Study design

A retrospective observational study was designed to describe the long-term clinical and biochemical outcomes of a uniform cohort of IOPD patients who have been treated with high-dosage of ERT.

Results

Twenty-eight patients received alglucosidase alpha at either the labeled dosage followed by a high dosage (n = 23) or a high dosage exclusively (n = 5). At a median age of 8.3 years (0.8–17.3), 15 patients were walkers, 8 were weak walkers, and 5 were nonwalkers. The three groups exhibited a significant difference in the age of gross motor decline (p < .001). In patients with classical IOPD diagnosed through newborn screening, those late in ERT initiation (p = .006) or late in high-dosage ERT initiation (p = .044) had a higher risk of motor decline. At the latest assessment, both serum creatine kinase (CK) and urinary glucose tetrasaccharide (uGlc4) levels were lowest in the walkers. During follow up, the biomarker levels, once rose, never returned to normal.

Conclusion

Low CK and uGlc4 levels were correlated with favorable response to ERT in IOPD patients, although CK may be more fluctuated than uGlc4. High-dose ERT instituted immediately at newborn screening seems to give the best outcome, and a dosage increase is necessary upon – or, even better, before – a rise in biomarker levels.

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CK and uGlc4 levels were correlated with favorable response to ERT in IOPD patients.

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Once these biomarkers rose, they never returned to normal.

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High-dose ERT instituted immediately at newborn screening seems to give the best outcome.

Newborn screening: Taiwanese experience

Newborn screening (NBS) aims to diagnose patients with Pompe disease earlier so that timely treatment can be applied. We describe the evolution of the screening methods in Taiwan with a population in which a pseudodeficiency variant is prevalent. We review and update the outcome of NBS-identified patients and discuss the limitations of the current therapy. We also address the challenges associated with caring for the babies with diagnosed acid alpha-glucosidase deficiency but yet without significant clinical manifestations. Further modifications of the current treatment and better predictive biomarkers should be explored.

Challenges in treating Pompe disease: an industry perspective

Pompe disease is a rare inherited metabolic disorder of defective lysosomal glycogen catabolism due to a deficiency in acid alpha-glucosidase (GAA). Alglucosidase alfa enzyme replacement therapy (ERT) using recombinant human GAA (rhGAA ERT) is the only approved treatment for Pompe disease. Alglucosidase alfa has provided irrefutable clinical benefits, but has not been an optimal treatment primarily due to poor drug targeting of ERT to skeletal muscles. Several critical factors contribute to this inefficiency. Some are inherent to the anatomy of the body that cannot be altered, while others may be addressed with better drug design and engineering. The knowledge gained from alglucosidase alfa ERT over the past 2 decades has allowed us to better understand the challenges that hinder its effectiveness. In this review, we detail the problems which must be overcome for improving drug targeting and clinical efficacy. These same issues may also impact therapeutic enzymes derived from gene therapies, and thus, have important implications for the development of next generation therapies for Pompe.

Improved efficacy of a next-generation ERT in murine Pompe disease

Pompe disease is a rare inherited disorder of lysosomal glycogen metabolism due to acid α-glucosidase (GAA) deficiency. Enzyme replacement therapy (ERT) using alglucosidase alfa, a recombinant human GAA (rhGAA), is the only approved treatment for Pompe disease. Although alglucosidase alfa has provided clinical benefits, its poor targeting to key disease-relevant skeletal muscles results in suboptimal efficacy. We are developing an rhGAA, ATB200 (Amicus proprietary rhGAA), with high levels of mannose-6-phosphate that are required for efficient cellular uptake and lysosomal trafficking. When administered in combination with the pharmacological chaperone AT2221 (miglustat), which stabilizes the enzyme and improves its pharmacokinetic properties, ATB200/AT2221 was substantially more potent than alglucosidase alfa in a mouse model of Pompe disease. The new investigational therapy is more effective at reversing the primary abnormality - intralysosomal glycogen accumulation - in multiple muscles. Furthermore, unlike the current standard of care, ATB200/AT2221 dramatically reduces autophagic buildup, a major secondary defect in the diseased muscles. The reversal of lysosomal and autophagic pathologies leads to improved muscle function. These data demonstrate the superiority of ATB200/AT2221 over the currently approved ERT in the murine model.

Therapeutic Benefit of Autophagy Modulation in Pompe Disease

The complexity of the pathogenic cascade in lysosomal storage disorders suggests that combination therapy will be needed to target various aspects of pathogenesis. The standard of care for Pompe disease (glycogen storage disease type II), a deficiency of lysosomal acid alpha glucosidase, is enzyme replacement therapy (ERT). Many patients have poor outcomes due to limited efficacy of the drug in clearing muscle glycogen stores. The resistance to therapy is linked to massive autophagic buildup in the diseased muscle. We have explored two strategies to address the problem. Genetic suppression of autophagy in muscle of knockout mice resulted in the removal of autophagic buildup, increase in muscle force, decrease in glycogen level, and near-complete clearance of lysosomal glycogen following ERT. However, this approach leads to accumulation of ubiquitinated proteins, oxidative stress, and exacerbation of muscle atrophy. Another approach involves AAV-mediated TSC knockdown in knockout muscle leading to upregulation of mTOR, inhibition of autophagy, reversal of atrophy, and efficient cellular clearance on ERT. Importantly, this approach reveals the possibility of reversing already established autophagic buildup, rather than preventing its development.

Long term clinical history of an Italian cohort of infantile onset Pompe disease treated with enzyme replacement therapy

Background

Enzyme replacement therapy (ERT) has deeply modified the clinical history of Infantile Onset Pompe Disease (IOPD). However, its long-term effectiveness is still not completely defined. Available data shows a close relationship between clinical outcome and patients’ cross-reactive immunological status (CRIM), being CRIM-negative status a negative prognostic factor. At the same time limited data are available on the long-term treatment in CRIM-positive infants.

Methods

A retrospective multicentre observational study was designed to analyse the long-term effectiveness of ERT in IOPD. Thirteen Italian centres spread throughout the country were involved and a cohort of 28 patients (15 females, 13 males, born in the period: February 2002–January 2013) was enrolled. IOPD diagnosis was based on clinical symptoms, enzymatic and molecular analysis. All patients received ERT within the first year of life. Clinical, laboratory, and functional data (motor, cardiac and respiratory) were collected and followed for a median period of 71 months (5 years 11 months).

Results

Median age at onset, diagnosis and start of ERT were 2, 3 and 4 months, respectively. CRIM status was available for 24/28 patients: 17/24 (71%) were CRIM-positive. Nineteen patients (67%) survived > 2 years: 4 were CRIM-negative, 14 CRIM-positive and one unknown. Six patients (5 CRIM-positive and one unknown) never needed ventilation support (21,4%) and seven (6 CRIM-positive and one unknown: 25%) developed independent ambulation although one subsequently lost this function. Brain imaging study was performed in 6 patients and showed peri-ventricular white matter abnormalities in all of them. Clinical follow-up confirmed the better prognosis for CRIM-positive patients, though a slow, progressive worsening of motor and/or respiratory functions was detected in 8 patients.

Conclusions

These data are the result of the longest independent retrospective study on ERT in IOPD reported so far outside clinical trials. The data obtained confirmed the better outcome of the CRIM-positive patients but at the same time, showed the inability of the current therapeutic approach to reverse or stabilize the disease progression. The results also evidenced the involvement of central nervous system in Pompe disease. To better understand the disease clinical history and to improve treatment efficacy larger multicentre studies are needed as well as the development of new therapeutic approaches.

Causally treatable, hereditary neuropathies in Fabry's disease, transthyretin-related familial amyloidosis, and Pompe's disease

OBJECTIVES

Most acquired neuropathies are treatable, whereas genetic neuropathies respond to treatment in Fabry's disease (FD), transthyretin-related familial amyloidosis (TTR-FA), and Pompe's disease (PD). This review summarizes and discusses recent findings and future perspectives concerning etiology, pathophysiology, clinical presentation, diagnosis, treatment, and outcome of neuropathy in FD, TTR-FA, and PD.

METHODS

Literature review.

RESULTS

Neuropathy in FD concerns particularly small, unmyelinated, or myelinated sensory fibers (small fiber neuropathy [SFN]) and autonomic fibers, manifesting as acroparesthesias, Fabry's crises, or autonomous disturbances. FD neuropathy benefits from agalsidase alpha (0.2 mg/kg every second week intravenously) or from beta (1.0 mg/kg every second week intravenously). Neuropathy in TTR-FA is axonal and affects large and small sensory, motor, and autonomous fibers. Neuropathy in TTR-FA profits from liver transplantation and the TTR kinetic stabilizer tafamidis (20 mg/d). Neuropathy in PD particularly occurs in late-onset PD and manifests as mononeuropathy, polyneuropathy, or SFN. PD neuropathy presumably responds to alglucosidase-alpha (20 mg/kg every second week intravenously).

CONCLUSIONS

Neuropathy in FD, TTR-FA, and PD is predominantly a SFN and can be the dominant feature in FD and TTR-FA. SFN in FD, TTR-FA, and PD needs to be recognized and benefits from enzyme replacement treatment or TT-kinetic stabilizers.

A Neuron-Specific Gene Therapy Relieves Motor Deficits in Pompe Disease Mice

In Pompe disease, deficient lysosomal acid α-glucosidase (GAA) activity causes glycogen accumulation in the muscles, which leads to weakness, cardiomyopathy, and respiratory failure. Although glycogen accumulation also occurs in the nervous system, the burden of neurological deficits in Pompe disease remains obscure. In this study, a neuron-specific gene therapy was administered to Pompe mice through intracerebroventricular injection of a viral vector carrying a neuron-specific promoter. The results revealed that gene therapy increased GAA activity and decreased glycogen content in the brain and spinal cord but not in the muscles of Pompe mice. Gene therapy only slightly increased the muscle strength of Pompe mice but substantially improved their performance on the rotarod, a test measuring motor coordination. Gene therapy also decreased astrogliosis and increased myelination in the brain and spinal cord of Pompe mice. Therefore, a neuron-specific treatment improved the motor coordination of Pompe mice by lowering glycogen accumulation, decreasing astrogliosis, and increasing myelination. These findings indicate that neurological deficits are responsible for a significant burden in Pompe disease.

Albuterol as an adjunctive treatment to enzyme replacement therapy in infantile-onset Pompe disease

BACKGROUND

Early initiation of enzyme replacement therapy (ERT) with recombinant human acid alpha-glucosidase is an effective treatment for patients with infantile-onset Pompe disease (IOPD) but cannot prevent a slow progression of myopathy. Albuterol has been shown to be helpful in adult patients with Pompe disease, and therefore, we administered an open-label adjunctive therapy with albuterol in IOPD patients undergoing ERT.

METHODS

Fourteen patients, aged 2 to 12 years, were enrolled in this study; all of them had a disease onset before 12 months of life, and 13 of them were ambulatory because of early initiation of ERT. All patients received albuterol (also referred to as salbutamol) 12 mg daily for 26 weeks. The outcome measurements included a 6-minute walk test, four-stair climb test (SCT), the standing/walking/running/jumping domains of Gross Motor Function Measure-88, speech quality, serum creatine kinase, and urinary glucose tetrasaccharide. Outcome and safety measurements were evaluated at baseline, and at 1, 3, and 6 months (26 weeks) after entering the trial.

RESULTS

After a period of 26 weeks, among the 12 patients who were able to complete the SCT, the median time needed decreased by 22% (p = 0.034). Other parameters inconsistently improved in a variety of individuals. Eleven adverse events, including nausea, urinary frequency, and tachycardia, were potentially related to the study drug, but all were mild and disappeared after a brief drug withdrawal. One patient was actively withdrawn from the trial because of poor compliance.

CONCLUSIONS

The results of our study suggest that albuterol showed a good safety profile as an adjunctive treatment in our IOPD cohort, although the benefits are limited.