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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of rare, monogenic disorders that share a defect in the synthesis or breakdown of glycogen. This Primer describes the multi-organ clinical features of hepatic GSDs and muscle GSDs, in addition to their epidemiology, biochemistry and mechanisms of disease, diagnosis, management, quality of life and future research directions. Some GSDs have available guidelines for diagnosis and management. Diagnostic considerations include phenotypic characterization, biomarkers, imaging, genetic testing, enzyme activity analysis and histology. Management includes surveillance for development of characteristic disease sequelae, avoidance of fasting in several hepatic GSDs, medically prescribed diets, appropriate exercise regimens and emergency letters. Specific therapeutic interventions are available for some diseases, such as enzyme replacement therapy to correct enzyme deficiency in Pompe disease and SGLT2 inhibitors for neutropenia and neutrophil dysfunction in GSD Ib. Progress in diagnosis, management and definitive therapies affects the natural course and hence morbidity and mortality. The natural history of GSDs is still being described. The quality of life of patients with these conditions varies, and standard sets of patient-centred outcomes have not yet been developed. The landscape of novel therapeutics and GSD clinical trials is vast, and emerging research is discussed herein.

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

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

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

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

Variant Classification for Pompe disease; ACMG/AMP specifications from the ClinGen Lysosomal Diseases Variant Curation Expert Panel

Accurate determination of the clinical significance of genetic variants is critical to the integration of genomics in medicine. To facilitate this process, the NIH-funded Clinical Genome Resource (ClinGen) has assembled Variant Curation Expert Panels (VCEPs), groups of experts and biocurators which provide gene- and disease- specifications to the American College of Medical Genetics & Genomics and Association for Molecular Pathology's (ACMG/AMP) variation classification guidelines. With the goal of classifying the clinical significance of GAA variants in Pompe disease (Glycogen storage disease, type II), the ClinGen Lysosomal Diseases (LD) VCEP has specified the ACMG/AMP criteria for GAA. Variant classification can play an important role in confirming the diagnosis of Pompe disease as well as in the identification of carriers. Furthermore, since the inclusion of Pompe disease on the Recommended Uniform Screening Panel (RUSP) for newborns in the USA in 2015, the addition of molecular genetic testing has become an important component in the interpretation of newborn screening results, particularly for asymptomatic individuals. To date, the LD VCEP has submitted classifications and supporting data on 243 GAA variants to public databases, specifically ClinVar and the ClinGen Evidence Repository. Here, we describe the ACMG/AMP criteria specification process for GAA, an update of the GAA-specific variant classification guidelines, and comparison of the ClinGen LD VCEP's GAA variant classifications with variant classifications submitted to ClinVar. The LD VCEP has added to the publicly available knowledge on the pathogenicity of variants in GAA by increasing the number of expert-curated GAA variants present in ClinVar, and aids in resolving conflicting classifications and variants of uncertain clinical significance.

Enzyme Replacement Therapy (ERT) on Heart Function Changes the Outcome in Patients with Infantile-Onset Pompe Disease: A Familial History

Background

Lysosomal acid alpha-glucosidase (GAA) deficiency, also known as Pompe disease, is an autosomal recessive disorder that leads to the accumulation of glycogen in lysosomes and cytoplasm, resulting in tissue destruction. Infantile-onset GAA deficiency is characterized by cardiomyopathy and severe generalized hypotonia. Without treatment, most patients die within the first two years of life. The demonstration of reduced GAA activity, followed by sequencing of the GAA gene, confirms the disease. GAA deficiency is currently treated with enzyme replacement therapy (ERT) with improved clinical outcomes and survival. Case Presentation. We describe the case of DGAA in two siblings, in which the diagnostic time point, treatment, and outcomes were completely different. The girl was diagnosed with DGAA at the age of 6 months during investigations for poor weight gain and excessive sleepiness. The finding of severe cardiomyopathy through EKG and echocardiography led to the suspicion of storage disease, and the GAA deficiency was later confirmed by genetic analysis. The girl died of complications due to the clinical picture before starting ERT. Conversely, her younger brother had the opportunity to receive an early diagnosis and the rapid onset of ERT. He is showing a regression of cardiac hypertrophy.

Conclusion

The advent of ERT improved clinical outcomes and survival in infantile-onset PD. Its impact on cardiac function is still under study, but different reports in the literature have shown encouraging data. Early recognition of DGAA and prompt initiation of ERT is therefore crucial to prevent the progression of the disease and improve the outcomes.

An artificial intelligence-based approach for identifying rare disease patients using retrospective electronic health records applied for Pompe disease

Objective

We retrospectively screened 350,116 electronic health records (EHRs) to identify suspected patients for Pompe disease. Using these suspected patients, we then describe their phenotypical characteristics and estimate the prevalence in the respective population covered by the EHRs.

Methods

We applied Symptoma's Artificial Intelligence-based approach for identifying rare disease patients to retrospective anonymized EHRs provided by the "University Hospital Salzburg" clinic group. Within 1 month, the AI screened 350,116 EHRs reaching back 15 years from five hospitals, and 104 patients were flagged as probable for Pompe disease. Flagged patients were manually reviewed and assessed by generalist and specialist physicians for their likelihood for Pompe disease, from which the performance of the algorithms was evaluated.

Results

Of the 104 patients flagged by the algorithms, generalist physicians found five "diagnosed," 10 "suspected," and seven patients with "reduced suspicion." After feedback from Pompe disease specialist physicians, 19 patients remained clinically plausible for Pompe disease, resulting in a specificity of 18.27% for the AI. Estimating from the remaining plausible patients, the prevalence of Pompe disease for the greater Salzburg region [incl. Bavaria (Germany), Styria (Austria), and Upper Austria (Austria)] was one in every 18,427 people. Phenotypes for patient cohorts with an approximated onset of symptoms above or below 1 year of age were established, which correspond to infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), respectively.

Conclusion

Our study shows the feasibility of Symptoma's AI-based approach for identifying rare disease patients using retrospective EHRs. Via the algorithm's screening of an entire EHR population, a physician had only to manually review 5.47 patients on average to find one suspected candidate. This efficiency is crucial as Pompe disease, while rare, is a progressively debilitating but treatable neuromuscular disease. As such, we demonstrated both the efficiency of the approach and the potential of a scalable solution to the systematic identification of rare disease patients. Thus, similar implementation of this methodology should be encouraged to improve care for all rare disease patients.

Development of a clinically validated in vitro functional assay to assess pathogenicity of novel GAA variants in patients with Pompe disease identified via newborn screening

Purpose: The addition of Pompe disease (Glycogen Storage Disease Type II) to the Recommended Uniform Screening Panel in the United States has led to an increase in the number of variants of uncertain significance (VUS) and novel variants identified in the GAA gene. This presents a diagnostic challenge, especially in the setting of late-onset Pompe disease when symptoms are rarely apparent at birth. There is an unmet need for validated functional studies to aid in classification of GAA variants.

Methods: We developed an in vitro mammalian cell expression and functional analysis system based on guidelines established by the Clinical Genome Resource (ClinGen) Sequence Variant Interpretation Working Group for PS3/BS3. We validated the assay with 12 control variants and subsequently analyzed eight VUS or novel variants in GAA identified in patients with a positive newborn screen for Pompe disease without phenotypic evidence of infantile-onset disease.

Results: The control variants were analyzed in our expression system and an activity range was established. The pathogenic controls had GAA activity between 0% and 11% of normal. The benign or likely benign controls had an activity range of 54%–100%. The pseudodeficiency variant had activity of 17%. These ranges were then applied to the variants selected for functional studies. Using the threshold of <11%, we were able to apply PS3_ supporting to classify two variants as likely pathogenic (c.316C > T and c.1103G > A) and provide further evidence to support the classification of likely pathogenic for two variants (c.1721T > C and c.1048G > A). One variant (c.1123C > T) was able to be reclassified based on other supporting evidence. We were unable to reclassify three variants (c.664G > A, c.2450A > G, and c.1378G > A) due to insufficient or conflicting evidence.

Conclusion: We investigated eight GAA variants as proof of concept using our validated and reproducible in vitro expression and functional analysis system. While additional work is needed to further refine our system with additional controls and different variant types in order to apply the PS3/BS3 criteria at a higher level, this tool can be utilized for variant classification to meet the growing need for novel GAA variant classification in the era of newborn screening for Pompe disease.

Lentiviral gene therapy prevents anti-human acid α-glucosidase antibody formation in murine Pompe disease

Enzyme replacement therapy (ERT) is the current standard treatment for Pompe disease, a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). ERT has shown to be lifesaving in patients with classic infantile Pompe disease. However, a major drawback is the development of neutralizing antibodies against ERT. Hematopoietic stem and progenitor cell-mediated lentiviral gene therapy (HSPC-LVGT) provides a novel, potential lifelong therapy with a single intervention and may induce immune tolerance. Here, we investigated whether ERT can be safely applied as additional or alternative therapy following HSPC-LVGT in a murine model of Pompe disease. We found that lentiviral expression at subtherapeutic dose was sufficient to induce tolerance to the transgene product, as well as to subsequently administered ERT. Immune tolerance was established within 4–6 weeks after gene therapy. The mice tolerated ERT doses up to 100 mg/kg, allowing ERT to eliminate glycogen accumulation in cardiac and skeletal muscle and normalizing locomotor function. The presence of HSPC-derived cells expressing GAA in the thymus suggested the establishment of central immune tolerance. These findings demonstrate that lentiviral gene therapy in murine Pompe disease induced robust and long-term immune tolerance to GAA either expressed by a transgene or supplied as ERT.

Small fiber involvement is independent from clinical pain in late-onset Pompe disease

BACKGROUND

Pain occurs in the majority of patients with late onset Pompe disease (LOPD) and is associated with a reduced quality of life. The aim of this study was to analyse the pain characteristics and its relation to a small nerve fiber involvement in LOPD patients.

METHODS

In 35 patients with LOPD under enzyme replacement therapy without clinical signs of polyneuropathy (19 females; 51 ± 15 years), pain characteristics as well as depressive and anxiety symptoms were assessed using the PainDetect questionnaire (PDQ) and the hospital anxiety and depression scale (HADS), respectively. Distal skin biopsies were analysed for intraepidermal nerve fiber density (IENFD) and compared to age- and gender-matched reference data. Skin biopsies from 20 healthy subjects served as controls to assure validity of the morphometric analysis.

RESULTS

Pain was reported in 69% of the patients with an average intensity of 4.1 ± 1.1 on the numeric rating scale (NRS; anchors: 0-10). According to PDQ, neuropathic pain was likely in one patient, possible in 29%, and unlikely in 67%. Relevant depression and anxiety symptoms occurred in 31% and 23%, respectively, and correlated with pain intensity. Distal IENFD (3.98 ± 1.95 fibers/mm) was reduced in 57% of the patients. The degree of IENFD reduction did not correlate with the durations of symptoms to ERT or duration of ERT to biopsy.

CONCLUSIONS

Pain is a frequent symptom in treated LOPD on ERT, though a screening questionnaire seldom indicated neuropathic pain. The high frequency of small nerve fiber pathology in a treated LOPD cohort was found regardless of the presence of pain or comorbid risk factors for SFN and needs further exploration in terms of clinical context, exact mechanisms and when developing novel therapeutic options for LOPD.

A subcellular cookie cutter for spatial genomics in human tissue

Intracellular heterogeneity contributes significantly to cellular physiology and, in a number of debilitating diseases, cellular pathophysiology. This is greatly influenced by distinct organelle populations and to understand the aetiology of disease, it is important to have tools able to isolate and differentially analyse organelles from precise location within tissues. Here, we report the development of a subcellular biopsy technology that facilitates the isolation of organelles, such as mitochondria, from human tissue. We compared the subcellular biopsy technology to laser capture microdissection (LCM) that is the state-of-the-art technique for the isolation of cells from their surrounding tissues. We demonstrate an operational limit of  >20 µm for LCM and then, for the first time in human tissue, show that subcellular biopsy can be used to isolate mitochondria beyond this limit.

Infantile-onset Pompe disease complicated by sickle cell anemia: Case report and management considerations

Infantile-onset Pompe disease (IOPD) is a rare, severe disorder of lysosomal storage of glycogen that leads to progressive cardiac and skeletal myopathy. IOPD is a fatal disease in childhood unless treated with enzyme replacement therapy (ERT) from an early age. Sickle cell anemia (SCA) is a relatively common hemoglobinopathy caused by a specific variant in the hemoglobin beta-chain. Here we report a case of a male newborn of African ancestry diagnosed and treated for IOPD and SCA. Molecular testing confirmed two GAA variants, NM_000152.5: c.842G>C, p.(Arg281Pro) and NM_000152.5: c.2560C>T, p.(Arg854^*) in trans, and homozygosity for the HBB variant causative of SCA, consistent with his diagnosis. An acute neonatal presentation of hypotonia and cardiomyopathy required ERT with alglucosidase alfa infusions preceded by immune tolerance induction (ITI), as well as chronic red blood cell transfusions and penicillin V potassium prophylaxis for treatment of IOPD and SCA. Clinical course was further complicated by multiple respiratory infections. We review the current guidelines and interventions taken to optimize his care and the pitfalls of those guidelines when treating patients with concomitant conditions. To the best of our knowledge, no other case reports of the concomitance of these two disorders was found. This report emphasizes the importance of newborn screening, early intervention, and treatment considerations for this complex patient presentation of IOPD and SCA.

Variable Genotype-Phenotype Correlation of Pompe's Disease Caused by a c.2015 G > A (p.Arg672Gln) Mutation in the GAA Gene

Pompe's disease occurs due to an autosomal recessive trait resulting from numerous distinctive mutations in the GAA gene. It manifests as a broad spectrum of clinical phenotypes with progressive weakness that impairs motor and respiratory functions being common for all its forms. Cardiac hypertrophy is a prominent feature of its classic infantile form. To date, the pathogenic variant c.2015G > A (p.Arg672Gln) in exon 14 of the GAA gene has been described in 10 children of different ethnic groups, with variable phenotypic presentations. This work describes three children from two unrelated families of Arab ethnicity who presented with infantile-onset Pompe's disease as a result of a c.2015G > A (p.Arg672Gln) mutation. The clinical course of the children we report was more severe than previous reports. This further emphasizes the lack of a strict genotype-phenotype correlation in regard to the unique c.2015G > A (p.R672Q) mutation that causes Pompe's disease. This information contributes to the knowledge of the phenotypic expression of the specific mutation c.2015G > A (p.Arg672Gln) that causes Pompe's disease.

Broad variation in phenotypes for common GAA genotypes in Pompe disease

Patients with the common c.-32-13T > G/null GAA genotype have a broad variation in age at symptom onset, ranging from early childhood to late adulthood. Phenotypic variation for other common GAA genotypes remains largely unexplored. Here, we analyzed variation in age at symptom onset for the most common GAA genotypes using the updated and extended Pompe GAA variant database. Patients with the c.2647-7G > A/null genotype invariably presented symptoms at adulthood, while the c.-32-13T > G/null, c.546G > T/null, c.1076-22T > G/null, c.2238G > C/null, and c.2173C > T/null genotypes led to presentations from early childhood up to late adulthood. The c.1309C > T/null genotype was associated with onset at early to late childhood. Symptom onset shifted toward higher ages in homozygous patients. These findings indicate that a broad variation in symptom onset occurs for various common GAA genotypes, suggesting the presence of modifying factors. We identified three new compound heterozygous c.-32-13T > G/null patients who carried the genetic modifier c.510C > T and who showed symptom onset at childhood. While c.510C > T acted by lowering GAA enzyme activity, other putative genetic modifiers did not at the group level, suggesting that these act in trans on processes downstream of GAA enzyme activity.

Case Studies in Neuroscience: Neuropathology and diaphragm dysfunction in ventilatory failure from late-onset Pompe disease

Pompe disease (PD) is a neuromuscular disorder caused by a mutation in the acid alpha-glucosidase (GAA) gene. Patients with late-onset PD retain some GAA activity and present symptoms later in life, with fatality mainly associated with respiratory failure. This case study presents diaphragm electrophysiology and a histological analysis of the brainstem, spinal cord, and diaphragm, from a male PD patient diagnosed with late-onset PD at age 35. The patient was wheelchair dependent by age 38, required nocturnal ventilation at age 40, 24-h noninvasive ventilation by age 43, and passed away from respiratory failure at age 54. Diaphragm electromyography recorded using indwelling "pacing" wires showed asynchronous bursting between the left and right diaphragm during brief periods of independent breathing. The synchrony declined over a 4-yr period preceding respiratory failure. Histological assessment indicated motoneuron atrophy in the medulla and rostral spinal cord. Hypoglossal (soma size: 421 ± 159 µm²) and cervical motoneurons (soma size: 487 ± 189 µm²) had an atrophied, elongated appearance. In contrast, lumbar (soma size: 1,363 ± 677 µm²) and sacral motoneurons (soma size: 1,411 ± 633 µm²) had the ballooned morphology typical of early-onset PD. Diaphragm histology indicated loss of myofibers. These results are consistent with neuromuscular degeneration and the concept that effective PD therapy will need to target the central nervous system, in addition to skeletal and cardiac muscle.NEW & NOTEWORTHY This case study offered a unique opportunity to investigate longitudinal changes in phrenic neurophysiology in an individual with severe, ventilator-dependent, late-onset Pompe disease. Additional diaphragm and neural tissue histology upon autopsy confirmed significant neuromuscular degeneration, and it provided novel insights regarding rostral to caudal variability in the neuropathology. These findings suggest that a successful treatment approach for ventilator-dependent Pompe disease should target the central nervous system, in addition to skeletal muscle.

Next-Generation Sequencing in Newborn Screening: A Review of Current State

Newborn screening was first introduced at the beginning of the 1960s with the successful implementation of the first phenylketonuria screening programs. Early expansion of the included disorders was slow because each additional disorder screened required a separate test. Subsequently, the technological advancements of biochemical methodology enabled the scaling-up of newborn screening, most notably with the implementation of tandem mass spectrometry. In recent years, we have witnessed a remarkable progression of high-throughput sequencing technologies, which has resulted in a continuous decrease of both cost and time required for genetic analysis. This has enabled more widespread use of the massive multiparallel sequencing. Genomic sequencing is now frequently used in clinical applications, and its implementation in newborn screening has been intensively advocated. The expansion of newborn screening has raised many clinical, ethical, legal, psychological, sociological, and technological concerns over time. This review provides an overview of the current state of next-generation sequencing regarding newborn screening including current recommendations and potential challenges for the use of such technologies in newborn screening.

Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease

In Pompe disease, the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) causes skeletal and cardiac muscle weakness, respiratory failure, and premature death. While enzyme replacement therapy using recombinant human GAA (rhGAA) can significantly improve patient outcomes, detailed disease mechanisms and incomplete therapeutic effects require further studies. Here we report a three-dimensional primary human skeletal muscle ("myobundle") model of infantile-onset Pompe disease (IOPD) that recapitulates hallmark pathological features including reduced GAA enzyme activity, elevated glycogen content and lysosome abundance, and increased sensitivity of muscle contractile function to metabolic stress. In vitro treatment of IOPD myobundles with rhGAA or adeno-associated virus (AAV)-mediated hGAA expression yields increased GAA activity and robust glycogen clearance, but no improvements in stress-induced functional deficits. We also apply RNA sequencing analysis to the quadriceps of untreated and AAV-treated GAA-/- mice and wild-type controls to establish a Pompe disease-specific transcriptional signature and reveal novel disease pathways. The mouse-derived signature is enriched in the transcriptomic profile of IOPD vs. healthy myobundles and partially reversed by in vitro rhGAA treatment, further confirming the utility of the human myobundle model for studies of Pompe disease and therapy.

Muscle Proteomic Profile before and after Enzyme Replacement Therapy in Late-Onset Pompe Disease

Mutations in the acidic alpha-glucosidase (GAA) coding gene cause Pompe disease. Late-onset Pompe disease (LOPD) is characterized by progressive proximal and axial muscle weakness and atrophy, causing respiratory failure. Enzyme replacement therapy (ERT), based on recombinant human GAA infusions, is the only available treatment; however, the efficacy of ERT is variable. Here we address the question whether proteins at variance in LOPD muscle of patients before and after 1 year of ERT, compared withhealthy age-matched subjects (CTR), reveal a specific signature. Proteins extracted from skeletal muscle of LOPD patients and CTR were analyzed by combining gel based (two-dimensional difference gel electrophoresis) and label-free (liquid chromatography-mass spectrometry) proteomic approaches, and ingenuity pathway analysis. Upstream regulators targeting autophagy and lysosomal tethering were assessed by immunoblotting. 178 proteins were changed in abundance in LOPD patients, 47 of them recovered normal level after ERT. Defects in oxidative metabolism, muscle contractile protein regulation, cytoskeletal rearrangement, and membrane reorganization persisted. Metabolic changes, ER stress and UPR (unfolded protein response) contribute to muscle proteostasis dysregulation with active membrane remodeling (high levels of LC3BII/LC3BI) and accumulation of p62, suggesting imbalance in the autophagic process. Active lysosome biogenesis characterizes both LOPD PRE and POST, unparalleled by molecules involved in lysosome tethering (VAMP8, SNAP29, STX17, and GORASP2) and BNIP3. In conclusion this study reveals a specific signature that suggests ERT prolongation and molecular targets to ameliorate patient’s outcome.

A generic assay for the identification of splicing variants that induce nonsense-mediated decay in Pompe disease

DNA variants affecting mRNA expression and processing in genetic diseases are often missed or poorly characterized. We previously reported a generic assay to identify variants that affect mRNA expression and splicing in Pompe disease, a monogenic disorder caused by deficiency of acid α-glucosidase (GAA). However, this assay could miss mRNA that is subjected to degradation. Here, we inhibited mRNA degradation using cycloheximide and performed unbiased splicing analysis of all GAA exons using exon flanking RT-PCR and exon internal RT-qPCR. In four patients that were suspected of harboring splicing variants but for which aberrant splicing could not be detected in normally growing cells, we detected a total of 10 novel splicing events in cells treated with cycloheximide. In addition, we found that sequences of GAA introns 6 and 12 were naturally included in a subset of transcripts from patients and healthy controls, indicating inefficient canonical splicing. Identification of aberrant splicing caused by the common Asian variant c.546G>T allowed the development of an antisense oligonucleotide that promoted canonical GAA pre-mRNA splicing and elevated GAA enzymatic activity. Our results indicate that this extended generic splicing assay allows the detection of aberrant splicing in cases of mRNA degradation to enable functional analysis of unknown splicing variants and the development of targeted treatment options.

The rapidly evolving view of lysosomal storage diseases

Lysosomal storage diseases are a group of metabolic disorders caused by deficiencies of several components of lysosomal function. Most commonly affected are lysosomal hydrolases, which are involved in the breakdown and recycling of a variety of complex molecules and cellular structures. The understanding of lysosomal biology has progressively improved over time. Lysosomes are no longer viewed as organelles exclusively involved in catabolic pathways, but rather as highly dynamic elements of the autophagic-lysosomal pathway, involved in multiple cellular functions, including signaling, and able to adapt to environmental stimuli. This refined vision of lysosomes has substantially impacted on our understanding of the pathophysiology of lysosomal disorders. It is now clear that substrate accumulation triggers complex pathogenetic cascades that are responsible for disease pathology, such as aberrant vesicle trafficking, impairment of autophagy, dysregulation of signaling pathways, abnormalities of calcium homeostasis, and mitochondrial dysfunction. Novel technologies, in most cases based on high-throughput approaches, have significantly contributed to the characterization of lysosomal biology or lysosomal dysfunction and have the potential to facilitate diagnostic processes, and to enable the identification of new therapeutic targets.

Update of the Pompe variant database for the prediction of clinical phenotypes: Novel disease-associated variants, common sequence variants, and results from newborn screening

Pompe disease is an inherited disorder caused by disease-associated variants in the acid α-glucosidase gene (GAA). The Pompe disease GAA variant database (http://www.pompevariantdatabase.nl) is a curated, open-source, disease-specific database, and lists disease-associated GAA variants, in silico predictions, and clinical phenotypes reported until 2016. Here, we provide an update to include 226 disease-associated variants that were published until 2020. We also listed 148 common GAA sequence variants that do not cause Pompe disease. GAA variants with unknown severity that were identified only in newborn screening programs were listed as a new feature to indicate the reason why phenotypes were still unknown. Expression studies were performed for common missense variants to predict their severity. The updated Pompe disease GAA variant database now includes 648 disease-associated variants, 26 variants from newborn screening, and 237 variants with unknown severity. Regular updates of the Pompe disease GAA variant database will be required to improve genetic counseling and the study of genotype-phenotype relationships.

Advancements in AAV-mediated Gene Therapy for Pompe Disease

Pompe disease (glycogen storage disease type II) is caused by mutations in acid α-glucosidase (GAA) resulting in lysosomal pathology and impairment of the muscular and cardio-pulmonary systems. Enzyme replacement therapy (ERT), the only approved therapy for Pompe disease, improves muscle function by reducing glycogen accumulation but this approach entails several limitations including a short drug half-life and an antibody response that results in reduced efficacy. To address these limitations, new treatments such as gene therapy are under development to increase the intrinsic ability of the affected cells to produce GAA. Key components to gene therapy strategies include the choice of vector, promoter, and the route of administration. The efficacy of gene therapy depends on the ability of the vector to drive gene expression in the target tissue and also on the recipient's immune tolerance to the transgene protein. In this review, we discuss the preclinical and clinical studies that are paving the way for the development of a gene therapy strategy for patients with early and late onset Pompe disease as well as some of the challenges for advancing gene therapy.

Gene therapy with secreted acid alpha-glucosidase rescues Pompe disease in a novel mouse model with early-onset spinal cord and respiratory defects

Background

Pompe disease (PD) is a neuromuscular disorder caused by deficiency of acidalpha-glucosidase (GAA), leading to motor and respiratory dysfunctions. Available Gaa knock-out (KO) mouse models do not accurately mimic PD, particularly its highly impaired respiratory phenotype.

Methods

Here we developed a new mouse model of PD crossing Gaa KO^B6;129 with DBA2/J mice. We subsequently treated Gaa KO^DBA2/J mice with adeno-associated virus (AAV) vectors expressing a secretable form of GAA (secGAA).

Findings

Male Gaa KO^DBA2/J mice present most of the key features of the human disease, including early lethality, severe respiratory impairment, cardiac hypertrophy and muscle weakness. Transcriptome analyses of Gaa KO^DBA2/J, compared to the parental Gaa KO^B6;129 mice, revealed a profoundly impaired gene signature in the spinal cord and a similarly deregulated gene expression in skeletal muscle. Muscle and spinal cord transcriptome changes, biochemical defects, respiratory and muscle function in the Gaa KO^DBA2/J model were significantly improved upon gene therapy with AAV vectors expressing secGAA.

Interpretation

These data show that the genetic background impacts on the severity of respiratory function and neuroglial spinal cord defects in the Gaa KO mouse model of PD. Our findings have implications for PD prognosis and treatment, show novel molecular pathophysiology mechanisms of the disease and provide a unique model to study PD respiratory defects, which majorly affect patients.

Funding

This work was supported by Genethon, the French Muscular Dystrophy Association (AFM), the European Commission (grant nos. 667751, 617432, and 797144), and Spark Therapeutics.

GAA gene mutation detection following clinical evaluation and enzyme activity analysis in Azeri Turkish patients with Pompe disease

Pompe disease (PD) is a rare autosomal recessive multi-systemic lysosomal storage disorder, caused by mutations in the acid alpha-glucosidase (GAA) gene located on 17q25.2-q25.3. It is one of about 50 rare genetic diseases categorized as lysosomal storage disorders. This disease is characterized by a range of different symptoms related to acid alpha-glucosidase deficiency. Mutation recognition in the GAA gene can be very significant for purposes such as therapeutic interference, early diagnosis and genotype-phenotype relationship. In the current study, peripheral blood samples were gathered from patients with PD and healthy members of three families. Enzymatic activity of GAA was checked. Then, mutation detection was performed by polymerase chain reaction followed by direct sequencing of all exons in samples with decreased enzyme activity. The identified mutations were investigated using bioinformatics tools to predict possible effects on the protein product and also to compare the mutated sequence with near species. Three novel mutations (c.1966-1968delGAG, c.2011-2012delAT and c.1475-1481dupACCCCAC) were identified in the GAA gene. Assessment of the effects of these mutations on protein structure and function showed the possibility of harmful effects and their significant alterations in the protein structure. The three novel GAA gene mutations detected in this study expand the information about the molecular genetics of PD and can be used to helpdiagnosis and genetic counseling of affected families.

Plant Glycosides and Glycosidases: A Treasure-Trove for Therapeutics

Plants contain numerous glycoconjugates that are metabolized by specific glucosyltransferases and hydrolyzed by specific glycosidases, some also catalyzing synthetic transglycosylation reactions. The documented value of plant-derived glycoconjugates to beneficially modulate metabolism is first addressed. Next, focus is given to glycosidases, the central theme of the review. The therapeutic value of plant glycosidases is discussed as well as the present production in plant platforms of therapeutic human glycosidases used in enzyme replacement therapies. The increasing knowledge on glycosidases, including structure and catalytic mechanism, is described. The novel insights have allowed the design of functionalized highly specific suicide inhibitors of glycosidases. These so-called activity-based probes allow unprecedented visualization of glycosidases cross-species. Here, special attention is paid on the use of such probes in plant science that promote the discovery of novel enzymes and the identification of potential therapeutic inhibitors and chaperones.

Mutations in GAA Gene in Tunisian Families with Infantile Onset Pompe Disease: Novel Mutation and Structural Modeling Investigations

Pompe disease, a rare, autosomal, recessive, inherited, lysosomal storage disorder, is caused by mutations in the acid α-glucosidase (GAA) gene leading to a deficiency of the lysosomal GAA enzyme. Some GAA mutations eliminate all enzymatic activities, causing severe infantile Pompe disease; others allow residual GAA activity and lead to middle adulthood forms. Here, we report a cohort of 12 patients, belonging to 11 unrelated families, with infantile Pompe disease. The mutational analysis of GAA gene revealed a novel c.1494G > A (p.Trp498X) mutation in one patient and three known mutatio,ns including the c.1497G > A (p.Trp499X) mutation, in two patients, the c.1927G > A (p.Gly643Arg) mutation in one patient and the common c.236_246del (p.Pro79ArgfsX13) mutation in eight patients. The high prevalence of c.236_246del mutation in our cohort (58%) was supported by the existence of a common founder ancestor that was confirmed by its segregation of similar SNPs haplotype, including four intragenic SNPs of GAA gene. In addition, a 3D structure model and a docking were generated for the mutant p.Gly643Arg using the crystal structure of human GAA as template and the 4-methylumbelliferyl-α-D-glucopyranoside as substrate. The results showed that the arginine at position 643 caused electrostatic changes in neighboring regions, leading to the repulsion between the amino acids located in the catalytic cavity of the GAA enzyme, thus restricting access to its substrate. These structural defects could cause the impairment of the transport and maturation previously reported for p.Gly643Arg mutation.

Novel Mutations Found in Individuals with Adult-Onset Pompe Disease

Pompe disease, or glycogen storage disease II is a rare, progressive disease leading to skeletal muscle weakness due to deficiency of the acid α-1,4-glucosidase enzyme (GAA). The severity of disease and observed time of onset is subject to the various combinations of heterozygous GAA alleles. Here we have characterized two novel mutations: c.2074C>T and c.1910_1918del, and a previously reported c.1082C>G mutation of uncertain clinical significance. These mutations were found in three unrelated patients with adult-onset Pompe disease carrying the common c.-32-13T>G mutation. The c.2074 C>T nonsense mutation has obvious consequences on GAA expression but the c.1910_1918del (deletion of 3 amino acids) and c.1082C>G missense variants are more subtle DNA changes with catastrophic consequences on GAA activity. Molecular and clinical analyses from the three patients corresponded with the anticipated pathogenicity of each mutation.

Molecular Approaches for the Treatment of Pompe Disease

Glycogen storage disease type II (GSDII, Pompe disease) is a rare metabolic disorder caused by a deficiency of acid alpha-glucosidase (GAA), an enzyme localized within lysosomes that is solely responsible for glycogen degradation in this compartment. The manifestations of GSDII are heterogeneous but are classified as early or late onset. The natural course of early-onset Pompe disease (EOPD) is severe and rapidly fatal if left untreated. Currently, one therapeutic approach, namely, enzyme replacement therapy, is available, but advances in molecular medicine approaches hold promise for even more effective therapeutic strategies. These approaches, which we review here, comprise splicing modification by antisense oligonucleotides, chaperone therapy, stop codon readthrough therapy, and the use of viral vectors to introduce wild-type genes. Considering the high rate at which innovations are translated from bench to bedside, it is reasonable to expect substantial improvements in the treatment of this illness in the foreseeable future.

An integrative correlation of myopathology, phenotype and genotype in late onset Pompe disease

AIMS

Pompe disease is caused by pathogenic mutations in the alpha 1,4-glucosidase (GAA) gene and in patients with late onset Pome disease (LOPD), genotype-phenotype correlations are unpredictable. Skeletal muscle pathology includes glycogen accumulation and altered autophagy of various degrees. A correlation of the muscle morphology with clinical features and the genetic background in GAA may contribute to the understanding of the phenotypic variability.

METHODS

Muscle biopsies taken before enzyme replacement therapy were analysed from 53 patients with LOPD. On resin sections, glycogen accumulation, fibrosis, autophagic vacuoles and the degree of muscle damage (morphology-score) were analysed and the results were compared with clinical findings. Additional autophagy markers microtubule-associated protein 1A/1B-light chain 3, p62 and Bcl2-associated athanogene 3 were analysed on cryosections from 22 LOPD biopsies.

RESULTS

The myopathology showed a high variability with, in most patients, a moderate glycogen accumulation and a low morphology-score. High morphology-scores were associated with increased fibrosis and autophagy highlighting the role of autophagy in severe stages of skeletal muscle damage. The morphology-score did not correlate with the patient's age at biopsy, disease duration, nor with the residual GAA enzyme activity or creatine-kinase levels. In 37 patients with LOPD, genetic analysis identified the most frequent mutation, c.-32-13T>G, in 95%, most commonly in combination with c.525delT (19%). No significant correlation was found between the different GAA genotypes and muscle morphology type.

CONCLUSIONS

Muscle morphology in LOPD patients shows a high variability with, in most cases, moderate pathology. Increased pathology is associated with more fibrosis and autophagy.

GAA variants and phenotypes among 1,079 patients with Pompe disease: Data from the Pompe Registry

Identification of variants in the acid α‐glucosidase (GAA) gene in Pompe disease provides valuable insights and systematic overviews are needed. We report on the number, nature, frequency, and geographic distribution of GAA sequence variants listed in the Pompe Registry, a long‐term, observational program and the largest global repository of Pompe disease data. Variant information was reviewed and compared with publicly available GAA databases/resources. Among 1,079 eligible patients, 2,075 GAA variants (80 unique novel) were reported. Variants were listed by groups representing Pompe disease phenotypes. Patients were classified as Group A: Symptom onset ≤ 12 months of age with cardiomyopathy; Group B: Symptom onset ≤ 12 years of age (includes patients with symptom onset ≤ 12 months of age without cardiomyopathy); or Group C: Symptom onset > 12 years of age. Likely impact of novel variants was predicted using bioinformatics algorithms. Variants were classified by pathogenicity using ACMG guidelines. Data reported from the Pompe Registry provide new information about the distribution of GAA variants globally and across the clinical spectrum, add to the number and diversity of GAA variants registered in public databases through published data sharing, provide a first indication of the severity of novel variants, and assist in diagnostic practice and outcome prediction.

CAGI5: Objective performance assessments of predictions based on the Evolutionary Action equation

Many computational approaches estimate the effect of coding variants, but their predictions often disagree with each other. These contradictions confound users and raise questions regarding reliability. Performance assessments can indicate the expected accuracy for each method and highlight advantages and limitations. The Critical Assessment of Genome Interpretation (CAGI) community aims to organize objective and systematic assessments: They challenge predictors on unpublished experimental and clinical data and assign independent assessors to evaluate the submissions. We participated in CAGI experiments as predictors, using the Evolutionary Action (EA) method to estimate the fitness effect of coding mutations. EA is untrained, uses homology information, and relies on a formal equation: The fitness effect equals the functional sensitivity to residue changes multiplied by the magnitude of the substitution. In previous CAGI experiments (between 2011 and 2016), our submissions aimed to predict the protein activity of single mutants. In 2018 (CAGI5), we also submitted predictions regarding clinical associations, folding stability, and matching genomic data with phenotype. For all these diverse challenges, we used EA to predict the fitness effect of variants, adjusted to specifically address each question. Our submissions had consistently good performance, suggesting that EA predicts reliably the effects of genetic variants.

Assessment of the functional impact on the pre-mRNA splicing process of 28 nucleotide variants associated with Pompe disease in GAA exon 2 and their recovery using antisense technology

Glycogen storage disease II (GSDII), also called Pompe disease, is an autosomal recessive inherited disease caused by a defect in glycogen metabolism due to the deficiency of the enzyme acid alpha-glucosidase (GAA) responsible for its degradation. So far, more than 500 sequence variants of the GAA gene have been reported but their possible involvement on the pre-messenger RNA splicing mechanism has not been extensively studied. In this work, we have investigated, by an in vitro functional assay, all putative splicing variants within GAA exon 2 and flanking introns. Our results show that many variants falling in the canonical splice site or the exon can induce GAA exon 2 skipping. In these cases, therefore, therapeutic strategies aimed at restoring protein folding of partially active mutated GAA proteins might not be sufficient. Regarding this issue, we have tested the effect of antisense oligonucleotides (AMOs) that were previously shown capable of rescuing splicing misregulation caused by the common c.-32-13T>G variant associated with the childhood/adult phenotype of GSDII. Interestingly, our results show that these AMOs are also quite effective in rescuing the splicing impairment of several exonic splicing variants, thus widening the potential use of these effectors for GSDII treatment.

Molecular genetics of Pompe disease: a comprehensive overview

Pompe disease (PD) is an autosomal recessive lysosomal disorder caused by the deficient activity of acid alpha-glucosidase (GAA) enzyme due to mutations in the GAA gene. The enzymatic deficiency leads to the accumulation of glycogen within the lysosomes. Clinically, the disease has been classically classified in infantile and childhood/adult forms. The GAA gene has been localized to chromosome 17q25.2-q25.3 and to date, 582 mutations distributed throughout the whole gene have been reported (HGMD: http://www.hgmd.cf.ac.uk/ac/). All types of mutations have been described; missense variants are the most frequent type followed by small deletions. Most GAA mutations are private or found in a small number of families. However, an exception is represented by the c.-32-13T>G splice mutation that is very common in patients of Caucasian origin affected by the childhood/adult form of the disease, with an allelic frequency ranging from 40% to 70%. In this article, we review the spectrum of GAA mutations, their distribution in different populations, and their classification according to their impact on GAA splicing process, protein expression and activity. In addition, whenever possible, we discuss the phenotype/genotype correlation. The information collected in this review provides an overview of the molecular genetics of PD and can be used to facilitate diagnosis and genetic counseling of families affected by this disorder.

The ACE I/D polymorphism does not explain heterogeneity of natural course and response to enzyme replacement therapy in Pompe disease

The majority of children and adults with Pompe disease in the population of European descent carry the leaky splicing GAA variant c.-32-13T>G (IVS1) in combination with a fully deleterious GAA variant on the second allele. The phenotypic spectrum of this patient group is exceptionally broad, with symptom onset ranging from early infancy to late adulthood. In addition, the response to enzyme replacement therapy (ERT) varies between patients. The insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme (ACE) has been suggested to be a modifier of disease onset and/or response to ERT. Here, we have investigated the effect of the ACE I/D polymorphism in a relatively large cohort of 131 children and adults with Pompe disease, of whom 112 were followed during treatment with ERT for 5 years. We assessed the use of wheelchair and mechanical ventilation, muscle strength assessed via manual muscle testing and hand-held dynamometry (HHD), distance walked on the six-minute walk test (6MWT), forced vital capacity (FVC) in sitting and supine position and daily-life activities assessed by R-PAct. Cross sectional analysis at first visit showed no differences between the genotypes with respect to age at first symptoms, diagnosis, wheelchair use, or ventilator use. Also response to ERT over 5 years assessed by linear mixed model analyses showed no significant differences between ACE groups for any of the outcome measures. The patient cohort contained 24 families with 54 siblings. Differences in ACE genotype could neither explain inter nor intra familial differences. We conclude that the ACE I/D polymorphism does not explain the large variation in disease severity and response to ERT observed among Pompe patients with the same c.-32-13T>G GAA variant.

Lysosomal storage disorders affecting the heart: a review

Lysosomal storage disorders (LSD) comprise a group of diseases caused by a deficiency of lysosomal enzymes, membrane transporters or other proteins involved in lysosomal biology. Lysosomal storage disorders result from an accumulation of specific substrates, due to the inability to break them down. The diseases are classified according to the type of material that is accumulated; for example, lipid storage disorders, mucopolysaccharidoses and glycoproteinoses. Cardiac disease is particularly important in lysosomal glycogen storage diseases (Pompe and Danon disease), mucopolysaccharidoses and in glycosphingolipidoses (Anderson-Fabry disease). Various disease manifestations may be observed including hypertrophic and dilated cardiomyopathy, coronary artery disease and valvular diseases. Endomyocardial biopsies can play an important role in the diagnosis of these diseases. Microscopic features along with ancillary tests like special stains and ultrastructural studies help in the diagnosis of these disorders. Diagnosis is further confirmed based upon enzymatic and molecular genetic analysis. Emerging evidence suggests that Enzyme replacement therapy (ERT) substantially improves many of the features of the disease, including some aspects of cardiac involvement. The identification of these disorders is important due to the availability of ERT, the need for family screening, as well as appropriate patient management and counseling.

Glycogen metabolism and glycogen storage disorders

Glucose is the main energy fuel for the human brain. Maintenance of glucose homeostasis is therefore, crucial to meet cellular energy demands in both - normal physiological states and during stress or increased demands. Glucose is stored as glycogen primarily in the liver and skeletal muscle with a small amount stored in the brain. Liver glycogen primarily maintains blood glucose levels, while skeletal muscle glycogen is utilized during high-intensity exertion, and brain glycogen is an emergency cerebral energy source. Glycogen and glucose transform into one another through glycogen synthesis and degradation pathways. Thus, enzymatic defects along these pathways are associated with altered glucose metabolism and breakdown leading to hypoglycemia ± hepatomegaly and or liver disease in hepatic forms of glycogen storage disorder (GSD) and skeletal ± cardiac myopathy, depending on the site of the enzyme defects. Overall, defects in glycogen metabolism mainly present as GSDs and are a heterogenous group of inborn errors of carbohydrate metabolism. In this article we review the genetics, epidemiology, clinical and metabolic findings of various types of GSD, and glycolysis defects emphasizing current treatment and implications for future directions.

Late-onset Pompe disease in France: molecular features and epidemiology from a nationwide study

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.

Cough Effectiveness and Pulmonary Hygiene Practices in Patients with Pompe Disease

PURPOSE

While factors leading to hypoventilation have been well studied in Pompe disease, cough effectiveness and airway clearance practices are less understood. We aimed to identify significant factors that influence peak cough flow (PCF) in Pompe, and to detect whether pulmonary hygiene practices were reflective of reduced PCF.

METHODS

This is a prospective observational study of 20 subjects with Pompe disease (infantile-onset: 7, juvenile-onset: 6, adult-onset: 14). Subjects performed spirometry, maximal respiratory pressures, and cough (voluntary: n = 24, spontaneous: n = 3). Subjects or their parents reported airway clearance and secretion management practices. Relationships between disease variables, pulmonary function, and cough parameters as well as group differences in cough parameters were evaluated.

RESULTS

Subjects with infantile-onset disease had significantly lower PCF (p < 0.05) and tended to require more external ventilatory support (p = 0.07). In juvenile- and adult-onset disease, PCF differed according to external ventilatory requirement [daytime: 83.6 L/min (95% CI 41.2-126.0); nighttime: 224.6 L/min (95% CI 139.1-310.2); none: 340.2 L/min (95% CI 193.3-487.6), p < 0.005]. Cough inspiratory volume also differed significantly by ventilatory requirement [daytime: 5.5 mL/kg (95% CI 3.0-8.0); nighttime: 16.0 mL/kg (95% CI 11.8-20.2); none: 26.8 mL/kg (95% CI 11.9-41.7), p < 0.001]. However, routine airway clearance or secretion management practices were only consistently reported among patients with infantile-onset disease (infantile: 86%, juvenile: 0%, adult: 14%, p < 0.005).

CONCLUSIONS

Cough weakness was detected in the majority of patients with Pompe disease and was influenced by both inspiratory and expiratory muscle function. Patients at risk for problems or with ineffective PCF should be urged to complete routine pulmonary hygiene.

Clinical and molecular characterization of Korean children with infantile and late-onset Pompe disease: 10 years of experience with enzyme replacement therapy at a single center

Purpose

Pompe disease (PD) is an autosomal recessive disorder caused by a deficiency of acid alphaglucosidase resulting from pathogenic GAA variants. This study describes the clinical features, genotypes, changes before and after enzyme replacement therapy (ERT), and long-term outcomes in patients with infantile-onset PD (IOPD) and late-onset PD (LOPD) at a tertiary medical center.

Methods

The medical records of 5 Korean patients (2 male, 3 female patients) diagnosed with PD between 2002 and 2013 at Samsung Medical Center in Seoul, Republic of Korea were retrospectively reviewed for data, including clinical and genetic characteristics at diagnosis and clinical course after ERT.

Results

Common initial symptoms included hypotonia, cyanosis, and tachycardia in patients with IOPD and limb girdle weakness in patients with LOPD. Electrocardiography at diagnosis revealed hypertrophic cardiomyopathy in all patients with IOPD who showed a stable disease course during a median follow-up period of 10 years. Patients with LOPD showed improved hepatomegaly and liver transaminase level after ERT.

Conclusion

As ERT is effective for treatment of PD, early identification of this disease is very important. Thus, patients with IOPD should be considered candidates for clinical trials of new drugs in the future.

Pompe Disease: From Basic Science to Therapy

Pompe disease is a rare and deadly muscle disorder. As a clinical entity, the disease has been known for over 75 years. While an optimist might be excited about the advances made during this time, a pessimist would note that we have yet to find a cure. However, both sides would agree that many findings in basic science-such as the Nobel prize-winning discoveries of glycogen metabolism, the lysosome, and autophagy-have become the foundation of our understanding of Pompe disease. The disease is a glycogen storage disorder, a lysosomal disorder, and an autophagic myopathy. In this review, we will discuss how these past discoveries have guided Pompe research and impacted recent therapeutic developments.

Identification of Seven Novel Mutations in the Acid Alpha-glucosidase Gene in Five Chinese Patients with Late-onset Pompe Disease

Background:

Pompe disease is a rare lysosomal glycogen storage disorder linked to the acid alpha-glucosidase gene (GAA). A wide clinical and genetic variability exists between patients from different ethnic populations, and the genotype-phenotype correlations are still not well understood. The aim of this study was to report the clinicopathological and genetic characteristics of five Chinese patients with late-onset Pompe disease (LOPD) who carried novel GAA gene mutations.

Methods:

Clinical and pathological data of patients diagnosed with glycogen storage disease at our institution from April 1986 to August 2017 were collected, and next-generation sequencing of frozen muscle specimens was conducted.

Results:

Of the five patients included in the study, the median disease onset age was 13 years, with a median 5 years delay in diagnosis. The patients mainly manifested as progressive weakness in the proximal and axial muscles, while one patient developed respiratory insufficiency that required artificial ventilation. In muscle biopsies, vacuoles with variable sizes and shapes appeared inside muscle fibers, and they stained positive for both periodic acid-Schiff and acid phosphatase staining. Ten GAA gene mutations, including seven novel ones (c.796C>A, c.1057C>T, c.1201C>A, c.1780C>T, c.1799G>C, c.2051C>A, c.2235dupG), were identified by genetic tests.

Conclusions:

The seven novel GAA gene mutations revealed in this study broaden the genetic spectrum of LOPD and highlight the genetic heterogeneity in Chinese LOPD patients.

Safety of Intradiaphragmatic Delivery of Adeno-Associated Virus-Mediated Alpha-Glucosidase (rAAV1-CMV-hGAA) Gene Therapy in Children Affected by Pompe Disease

A first-in-human trial of diaphragmatic gene therapy (AAV1-CMV-GAA) to treat respiratory and neural dysfunction in early-onset Pompe disease was conducted. The primary objective of this study was to assess the safety of rAAV1-CMV-hGAA vector delivered to the diaphragm muscle of Pompe disease subjects with ventilatory insufficiency. Safety was assessed by measurement of change in serum chemistries and hematology, urinalysis, and immune response to GAA and AAV, as well as change in level of health. The data demonstrate that the AAV treatment was safe and there were no adverse events related to the study agent. Adverse events related to the study procedure were observed in subjects with lower baseline neuromuscular function. All adverse events were resolved before the end of the study, except for one severe adverse event determined not to be related to either the study agent or the study procedure. In addition, an anti-capsid and anti-transgene antibody response was observed in all subjects who received rAAV1-CMV-hGAA, except for subjects who received concomitant immunomodulation to manage reaction to enzyme replacement therapy, as per their standard of care. This observation is significant for future gene therapy studies and serves to establish a clinically relevant approach to blocking immune responses to both the AAV capsid protein and transgene product.

Mitochondrial Variants in Pompe Disease: A Comparison between Classic and Non-Classic Forms

Objective

Pompe disease (PD) is a progressive neuromuscular disorder that is caused by glucosidase acid alpha (GAA) deleterious mutations. Mitochondrial involvement is an important contributor to neuromuscular diseases. In this study the sequence of MT-ATP 6/8 and Cytochrome C oxidase I/II genes along with the expression levels of the former genes were compared in classic and non-classic patients.

Materials and Methods

In this case-control study, the sequence of MT-ATP 6/8 and Cytochrome C oxidase was analyzed by polymerase chain reaction (PCR)-Sanger sequencing and expression of MT-ATP genes were quantified by real time-PCR (RT-PCR) in 28 Pompe patients. The results were then compared with 100 controls. All sequences were compared with the revised Cambridge reference sequence as reference.

Results

Screening of MT-ATP6/8 resulted in the identification of three novel variants, namely T9117A, A8456C and A8524C. There was a significant decrease in MT-ATP6 expression between classic (i.e. adult) and control groups (P=0.030). Additionally, the MT-ATP8 expression was significantly decreased in classic (P=0.004) and non-classic (i.e. infant) patients (P=0.013). In total, 22 variants were observed in Cytochrome C oxidase, five of which were non- synonymous, one leading to a stop codon and another (C9227G) being a novel heteroplasmic variant. The A8302G in the lysine tRNA gene was found in two brothers in a pedigree, while a T7572C variant in the aspartate tRNA gene was observed in two brothers in another pedigree.

Conclusion

The extent of mitochondrial involvement in the classic group was more significant than in the non-classic form. Beside GAA deleterious mutations, it seems that mtDNA variants have a secondary effect on PD. Understanding, the role of mitochondria in the pathogenesis of Pompe may potentially be helpful in developing new therapeutic strategies.

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.

Using Decision Analysis to Support Newborn Screening Policy Decisions: A Case Study for Pompe Disease

Background: Newborn screening is a public health program to identify conditions associated with significant morbidity or mortality that benefit from early intervention. Policy decisions about which conditions to include in newborn screening are complex because data regarding epidemiology and outcomes of early identification are often incomplete. Objectives: To describe expected outcomes of Pompe disease newborn screening and how a decision analysis informed recommendations by a federal advisory committee. Methods: We developed a decision tree to compare Pompe disease newborn screening with clinical identification of Pompe disease in the absence of screening. Cases of Pompe disease were classified into three types: classic infantile-onset disease with cardiomyopathy, nonclassic infantile-onset disease, and late-onset disease. Screening results and 36-month health outcomes were projected for classic and nonclassic infantile-onset cases. Input parameters were based on published and unpublished data supplemented by expert opinion. Results: We estimated that screening 4 million babies born each year in the United States would detect 40 cases (range: 13–56) of infantile-onset Pompe disease compared with 36 cases (range: 13–56) detected clinically without screening. Newborn screening would also identify 94 cases of late-onset Pompe disease that might not become symptomatic for decades. By 36 months, newborn screening would avert 13 deaths (range: 8–19) and decrease the number of individuals requiring mechanical ventilation by 26 (range: 20–28). Conclusions: Pompe disease is a rare condition, but early identification can improve health outcomes. Decision analytic modeling provided a quantitative data synthesis that informed the recommendation of Pompe disease newborn screening.

Sensitivity of whole exome sequencing in detecting infantile- and late-onset Pompe disease

Pompe disease is a metabolic myopathy with a wide spectrum of clinical presentation. The gold-standard diagnostic test is acid alpha-glucosidase assay on skin fibroblasts, muscle or blood. Identification of two GAA pathogenic variants in-trans is confirmatory. Optimal effectiveness of enzyme replacement therapy hinges on early diagnosis, which is challenging in late-onset form of the disease due to non-specific presentation. Next-generation sequencing-based panels effectively facilitate diagnosis, but the sensitivity of whole-exome sequencing (WES) in detecting pathogenic GAA variants remains unknown. We analyzed WES data from 93 patients with confirmed Pompe disease and GAA genotypes based on PCR/Sanger sequencing. After ensuring that the common intronic variant c.-32-13T>G is not filtered out, whole-exome sequencing identified both GAA pathogenic variants in 77/93 (83%) patients. However, one variant was missed in 14/93 (15%), and both variants were missed in 2/93 (2%). One complex indel leading to a severe phenotype was incorrectly called a nonsynonymous substitution c.-32-13T>C due to misalignment. These results demonstrate that WES may fail to diagnose Pompe disease. Clinicians need to be aware of limitations of WES, and consider tests specific to Pompe disease when WES does not provide a diagnosis in patients with proximal myopathy, progressive respiratory failure or other subtle symptoms.

Infantile-onset Pompe disease with neonatal debut: A case report and literature review

RATIONALE

Infantile-onset Pompe disease, also known as glycogen storage disease type II, is a progressive and fatal disorder without treatment. Enzyme replacement therapy with recombinant human acid alpha-glucosidase (GAA) enhances survival; however, the best outcomes have been achieved with early treatment.

PATIENT CONCERNS

We report a case of a newborn with infantile-onset Pompe disease diagnosed in the first days of life who did not undergo universal neonatal screening. The patient was asymptomatic, with a general physical examination revealing only a murmur. The clinical presentation was dominated by the neonatal detection of hypertrophic cardiomyopathy, without hypotonia or macroglossia.

DIAGNOSES

Pompe disease was confirmed in the first week of life by GAA activity in dried blood spots, and a GAA genetic study showed the homozygous mutation p.Arg854X.

INTERVENTIONS

Parents initially refused replacement therapy.

OUTCOMES

The patient experienced recurrent episodes of ventricular fibrillation during central line placement and could not be resuscitated.

LESSONS

Although Pompe disease is rare, and universal screening has not been established, neonatologists should be alerted to the diagnosis of Pompe in the presence of hypertrophic cardiomyopathy. Diagnosis is achieved in a few days with the aid of dried blood spots.

Respiratory manifestations in late-onset Pompe disease: a case series conducted in Brazil

Objective:

To describe respiratory function in a series of patients with late-onset Pompe disease after the definitive diagnosis and before enzyme replacement therapy.

Methods:

This was a cross-sectional study involving patients with a definitive molecular diagnosis of late-onset Pompe disease. The data analyzed included age at symptom onset; age at definitive diagnosis; type of initial symptoms; time from symptom onset to diagnosis; FVC in the sitting and supine positions; six-minute walk distance; and locomotor ability. Analyses were carried out using frequencies, medians, minimum values, and maximum values.

Results:

Six patients were included in the study. The median age at symptom onset was 15 years (range, 13-50 years), and the median age at diagnosis was 39.5 years (range, 10-64 years). The median time from symptom onset to diagnosis was 8 years (range, 0-45 years). In all cases, the initial manifestation of the disease had been motor weakness. The median FVC in percentage of the predicted value (FVC%) in the sitting and supine positions was 71.0% (range, 22.9-104.6%) and 58.0% (range, 10.9-106.9%), respectively. The median ΔFVC% was 24.5% (range, −4.59 to 52.40%).The median six-minute walk distance was 391.7 m (range, 97-702 m) .

Conclusions:

In this case series, the time from symptom onset to diagnosis was long. Although respiratory signs or symptoms were not the initial manifestations of the disease, 66.7% of the patients showed reduced FVC% in the sitting and supine positions at diagnosis.