A cross-sectional single-centre study on the spectrum of Pompe disease, German patients: molecular analysis of the GAA gene, manifestation and genotype-phenotype correlations

Drug Repurposing and Lysosomal Storage Disorders: A Trick to Treat

Rare diseases, or orphan diseases, are defined as diseases affecting a small number of people compared to the general population. Among these, we find lysosomal storage disorders (LSDs), a cluster of rare metabolic diseases characterized by enzyme mutations causing abnormal glycolipid storage. Drug repositioning involves repurposing existing approved drugs for new therapeutic applications, offering advantages in cost, time savings, and a lower risk of failure. We present a comprehensive analysis of existing drugs, their repurposing potential, and their clinical implications in the context of LSDs, highlighting the necessity of mutation-specific approaches. Our review systematically explores the landscape of drug repositioning as a means to enhance LSDs therapies. The findings advocate for the strategic repositioning of drugs, accentuating its role in expediting the discovery of effective treatments. We conclude that drug repurposing represents a viable pathway for accelerating therapeutic discovery for LSDs, emphasizing the need for the careful evaluation of drug efficacy and toxicity in disease-specific contexts.

Predicting disease severity in metachromatic leukodystrophy using protein activity and a patient phenotype matrix

BACKGROUND

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by mutations in the arylsulfatase A gene (ARSA) and categorized into three subtypes according to age of onset. The functional effect of most ARSA mutants remains unknown; better understanding of the genotype-phenotype relationship is required to support newborn screening (NBS) and guide treatment.

RESULTS

We collected a patient data set from the literature that relates disease severity to ARSA genotype in 489 individuals with MLD. Patient-based data were used to develop a phenotype matrix that predicts MLD phenotype given ARSA alleles in a patient's genotype with 76% accuracy. We then employed a high-throughput enzyme activity assay using mass spectrometry to explore the function of ARSA variants from the curated patient data set and the Genome Aggregation Database (gnomAD). We observed evidence that 36% of variants of unknown significance (VUS) in ARSA may be pathogenic. By classifying functional effects for 251 VUS from gnomAD, we reduced the incidence of genotypes of unknown significance (GUS) by over 98.5% in the overall population.

CONCLUSIONS

These results provide an additional tool for clinicians to anticipate the disease course in MLD patients, identifying individuals at high risk of severe disease to support treatment access. Our results suggest that more than 1 in 3 VUS in ARSA may be pathogenic. We show that combining genetic and biochemical information increases diagnostic yield. Our strategy may apply to other recessive diseases, providing a tool to address the challenge of interpreting VUS within genotype-phenotype relationships and NBS.

Distribution of Exonic Variants in Glycogen Synthesis and Catabolism Genes in Late Onset Pompe Disease (LOPD)

Pompe disease (PD) is a monogenic autosomal recessive disorder caused by biallelic pathogenic variants of the GAA gene encoding lysosomal alpha-glucosidase; its loss causes glycogen storage in lysosomes, mainly in the muscular tissue. The genotype–phenotype correlation has been extensively discussed, and caution is recommended when interpreting the clinical significance of any mutation in a single patient. As there is no evidence that environmental factors can modulate the phenotype, the observed clinical variability in PD suggests that genetic variants other than pathogenic GAA mutations influence the mechanisms of muscle damage/repair and the overall clinical picture. Genes encoding proteins involved in glycogen synthesis and catabolism may represent excellent candidates as phenotypic modifiers of PD. The genes analyzed for glycogen synthesis included UGP2, glycogenin (GYG1-muscle, GYG2, and other tissues), glycogen synthase (GYS1-muscle and GYS2-liver), GBE1, EPM2A, NHLRC1, GSK3A, and GSK3B. The only enzyme involved in glycogen catabolism in lysosomes is α-glucosidase, which is encoded by GAA, while two cytoplasmic enzymes, phosphorylase (PYGB-brain, PGL-liver, and PYGM-muscle) and glycogen debranching (AGL) are needed to obtain glucose 1-phosphate or free glucose. Here, we report the potentially relevant variants in genes related to glycogen synthesis and catabolism, identified by whole exome sequencing in a group of 30 patients with late-onset Pompe disease (LOPD). In our exploratory analysis, we observed a reduced number of variants in the genes expressed in muscles versus the genes expressed in other tissues, but we did not find a single variant that strongly affected the phenotype. From our work, it also appears that the current clinical scores used in LOPD do not describe muscle impairment with enough qualitative/quantitative details to correlate it with genes that, even with a slightly reduced function due to genetic variants, impact the phenotype.

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.

Induced pluripotent stem cell for modeling Pompe disease

Pompe disease (PD) is a rare, autosomal recessive, inherited, and progressive metabolic disorder caused by α-glucosidase defect in lysosomes, resulting in abnormal glycogen accumulation. Patients with PD characteristically have multisystem pathological disorders, particularly hypertrophic cardiomyopathy, muscle weakness, and hepatomegaly. Although the pathogenesis and clinical outcomes of PD are well-established, disease-modeling ability, mechanism elucidation, and drug development targeting PD have been substantially limited by the unavailable PD-relevant cell models. This obstacle has been overcome with the help of induced pluripotent stem cell (iPSC) reprogramming technology, thus providing a powerful tool for cell replacement therapy, disease modeling, drug screening, and drug toxicity assessment. This review focused on the exciting achievement of PD disease modeling and mechanism exploration using iPSC.

Beyond Sarcomeric Hypertrophic Cardiomyopathy: How to Diagnose and Manage Phenocopies

PURPOSE OF REVIEW

We describe the most common phenocopies of hypertrophic cardiomyopathy, their pathogenesis, and clinical presentation highlighting similarities and differences. We also suggest a step-by-step diagnostic work-up that can guide in differential diagnosis and management.

RECENT FINDINGS

In the last years, a wider application of genetic testing and the advances in cardiac imaging have significantly changed the diagnostic approach to HCM phenocopies. Different prognosis and management, with an increasing availability of disease-specific therapies, make differential diagnosis mandatory. The HCM phenotype can be the cardiac manifestation of different inherited and acquired disorders presenting different etiology, prognosis, and treatment. Differential diagnosis requires a cardiomyopathic mindset allowing to recognize red flags throughout the diagnostic work-up starting from clinical and family history and ending with advanced imaging and genetic testing. Different prognosis and management, with an increasing availability of disease-specific therapies make differential diagnosis mandatory.

Newborn screening for Pompe disease in Italy: Long-term results and future challenges

Pompe disease (PD) is a progressive neuromuscular disorder caused by a lysosomal acid α-glucosidase (GAA) deficiency. Enzymatic replacement therapy is available, but early diagnosis by newborn screening (NBS) is essential for early treatment and better outcomes, especially with more severe forms. We present results from 7 years of NBS for PD and the management of infantile-onset (IOPD) and late-onset (LOPD) patients, during which we sought candidate predictive parameters of phenotype severity at baseline and during follow-up. We used a tandem mass spectrometry assay for α-glucosidase activity to screen 206,741 newborns and identified 39 positive neonates (0.019%). Eleven had two pathogenic variants of the GAA gene (3 IOPD, 8 LOPD); six carried variants of uncertain significance (VUS). IOPD patients were treated promptly and had good outcomes. LOPD and infants with VUS were followed; all were asymptomatic at the last visit (mean age 3.4 years, range 0.5–5.5). Urinary glucose tetrasaccharide was a useful and biomarker for rapidly differentiating IOPD from LOPD and monitoring response to therapy during follow-up. Our study, the largest reported to date in Europe, presents data from longstanding NBS for PD, revealing an incidence in North East Italy of 1/18,795 (IOPD 1/68,914; LOPD 1/25,843), and the absence of mortality in IOPD treated from birth. In LOPD, rigorous long-term follow-up is needed to evaluate the best time to start therapy. The high pseudodeficiency frequency, ethical issues with early LOPD diagnosis, and difficulty predicting phenotypes based on biochemical parameters and genotypes, especially in LOPD, need further study.

The Clinical Management of Pompe Disease: A Pediatric Perspective

Pompe disease (PD) is an inherited metabolic disorder caused by a deficiency of acid α-glucosidase (GAA), leading to lysosomal accumulation of glycogen, mainly in skeletal and cardiac muscles as well as the nervous system. Patients with PD develop cellular dysfunction and muscle damage. PD can be classified into two classic forms, namely infantile-onset PD (IOPD) and late-onset PD (LOPD). Delayed treatment, particularly in IOPD, would result in significant organ damage and early death. Nonetheless, early diagnosis and timely treatment are often hampered by the rarity of PD and its wide variety of, but overlapping, symptoms. This article reviews the common clinical presentations of PD and outlines the essentials of PD management. In particular, the implications of newborn screening (NBS) and clinical performance of enzyme replacement therapy (ERT) are highlighted.

Pompe Disease: a Clinical, Diagnostic, and Therapeutic Overview

Purpose of Review

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

Recent Findings

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

Summary

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

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.

Correlation of GAA Genotype and Acid-α-Glucosidase Enzyme Activity in Hungarian Patients with Pompe Disease

Pompe disease is caused by the accumulation of glycogen in the lysosomes due to a deficiency of the lysosomal acid-α-glucosidase (GAA) enzyme. Depending on residual enzyme activity, the disease manifests two distinct phenotypes. In this study, we assess an enzymatic and genetic analysis of Hungarian patients with Pompe disease. Twenty-four patients diagnosed with Pompe disease were included. Enzyme activity of acid-α-glucosidase was measured by mass spectrometry. Sanger sequencing and an MLPA of the GAA gene were performed in all patients. Twenty (83.33%) patients were classified as having late-onset Pompe disease and four (16.66%) had infantile-onset Pompe disease. Fifteen different pathogenic GAA variants were detected. The most common finding was the c.-32-13 T > G splice site alteration. Comparing the α-glucosidase enzyme activity of homozygous cases to the compound heterozygous cases of the c.-32-13 T > G disease-causing variant, the mean GAA activity in homozygous cases was significantly higher. The lowest enzyme activity was found in cases where the c.-32-13 T > G variant was not present. The localization of the identified sequence variations in regions encoding the crucial protein domains of GAA correlates with severe effects on enzyme activity. A better understanding of the impact of pathogenic gene variations may help earlier initiation of enzyme replacement therapy (ERT) if subtle symptoms occur. Further information on the effect of GAA gene variation on the efficacy of treatment and the extent of immune response to ERT would be of importance for optimal disease management and designing effective treatment plans.

Genotype-phenotype correlation of 17 cases of Pompe disease in Spanish patients and identification of 4 novel GAA variants

Background

Pompe disease (PD) is an autosomal recessive metabolic disorder caused by pathogenic variants in the acid -glucosidase gene (GAA) that produces defects in the lysosomal acid -1,4-glucosidase. We aimed to identify genetic variations and clinical features in Spanish subjects to establish genotypephenotype correlation.

Methods

A total of 2637 samples of patients who showed symptoms or susceptible signs of PD were enrolled in this observational study. Enzymatic activity was detected by fluorometric techniques and the genetic study was carried out using Next-Generation Sequencing.

Results

Fourteen different variants from 17 diagnosed patients were identified, seven males and nine females with LOPD (mean age 36.07, SD 20.57, range 764) and a 2-day-old boy with IOPD, four genetic variants had not been described in the literature previously, including a homozygous variant. In all of them -glucosidase activity was decreased. Muscle weakness, respiratory distress, exercise intolerance, hypotonia, dysphagia and myalgia were commonly observed in patients.

Conclusions

This study report four new genetic variants that contribute to the pathogenic variants spectrum of the GAA gene. We confirm that patients in Spain have a characteristic profile of a European population, with c.-32-13T>G being the most prevalent variant. Furthermore, it was confirmed that the c.236_246delCCACACAGTGC pathogenic variant in homozygosity is associated with early disease and a worse prognosis.

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.

Rare Variants in Autophagy and Non-Autophagy Genes in Late-Onset Pompe Disease: Suggestions of Their Disease-Modifying Role in Two Italian Families

Pompe disease is an autosomal recessive disorder caused by a deficiency in the enzyme acid alpha-glucosidase. The late-onset form of Pompe disease (LOPD) is characterized by a slowly progressing proximal muscle weakness, often involving respiratory muscles. In LOPD, the levels of GAA enzyme activity and the severity of the clinical pictures may be highly variable among individuals, even in those who harbour the same combination of GAA mutations. The result is an unpredictable genotype–phenotype correlation. The purpose of this study was to identify the genetic factors responsible for the progression, severity and drug response in LOPD. We report here on a detailed clinical, morphological and genetic study, including a whole exome sequencing (WES) analysis of 11 adult LOPD siblings belonging to two Italian families carrying compound heterozygous GAA mutations. We disclosed a heterogeneous pattern of myopathic impairment, associated, among others, with cardiac defects, intracranial vessels abnormality, osteoporosis, vitamin D deficiency, obesity and adverse response to enzyme replacement therapy (ERT). We identified deleterious variants in the genes involved in autophagy, immunity and bone metabolism, which contributed to the severity of the clinical symptoms observed in the LOPD patients. This study emphasizes the multisystem nature of LOPD and highlights the polygenic nature of the complex phenotype disclosed in these patients.

Deferoxamine mesylate improves splicing and GAA activity of the common c.-32-13T>G allele in late-onset PD patient fibroblasts

Pompe disease (PD) is an autosomal recessive lysosomal storage disorder due to deficient activity of the acid alpha glucosidase enzyme (GAA). As a consequence of the enzymatic defect, undigested glycogen accumulates within lysosomes. Most patients affected by the late-onset (LO) phenotype carry in at least one allele the c.-32-13T>G variant, which leads to exon 2 exclusion from the pre-mRNA. These patients display a variable and suboptimal response to enzyme replacement therapy. To identify novel therapeutic approaches, we developed a fluorescent GAA exon 2 splicing assay and screened a library of US Food and Drug Administration (FDA)-approved compounds. This led to the identification of several drugs able to restore normal splicing. Among these, we further validated the effects of the iron chelator deferoxamine (Defe) in c.-32-13T>G fibroblasts. Defe treatment resulted in a 2-fold increase of GAA exon 2 inclusion and a 40% increase in enzymatic activity. Preliminary results suggest that this effect is mediated by the regulation of iron availability, at least partially. RNA-seq experiments also showed that Defe might shift the balance of splicing factor levels toward a profile promoting GAA exon 2 inclusion. This work provides the basis for drug repurposing and development of new chemically modified molecules aimed at improving the clinical outcome in LO-PD patients.

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

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

Enzymatic diagnosis of Pompe disease: lessons from 28 years of experience

Pompe disease is a lysosomal and neuromuscular disorder caused by deficiency of acid alpha-glucosidase (GAA), and causes classic infantile, childhood onset, or adulthood onset phenotypes. The biochemical diagnosis is based on GAA activity assays in dried blood spots, leukocytes, or fibroblasts. Diagnosis can be complicated by the existence of pseudodeficiencies, i.e., GAA variants that lower GAA activity but do not cause Pompe disease. A large-scale comparison between these assays for patient samples, including exceptions and borderline cases, along with clinical diagnoses has not been reported so far. Here we analyzed GAA activity in a total of 1709 diagnostic cases over the past 28 years using a total of 2591 analyses and we confirmed the clinical diagnosis in 174 patients. We compared the following assays: leukocytes using glycogen or 4MUG as substrate, fibroblasts using 4MUG as substrate, and dried blood spots using 4MUG as substrate. In 794 individuals, two or more assays were performed. We found that phenotypes could only be distinguished using fibroblasts with 4MUG as substrate. Pseudodeficiencies caused by the GAA2 allele could be ruled out using 4MUG rather than glycogen as substrate in leukocytes or fibroblasts. The Asian pseudodeficiency could only be ruled out in fibroblasts using 4MUG as substrate. We conclude that fibroblasts using 4MUG as substrate provides the most reliable assay for biochemical diagnosis and can serve to validate results from leukocytes or dried blood spots.

Pompe disease: pathogenesis, molecular genetics and diagnosis

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

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

A non-invasive diagnostic assay for rapid detection and characterization of aberrant mRNA-splicing by nonsense mediated decay inhibition

BACKGROUND

Interpretation of genetic variants detected by sequencing of genomic DNA, which may cause splicing defects, regularly requires mRNA analysis. Usually, only bioinformatic testing is provided, because simple and non-invasive assay protocols are lacking. Furthermore, the detection of mis-splicing is often hampered by nonsense mediated mRNA decay (NMD).

METHODS

Starting from a case of Pompe disease with two potential splicing variants an assay for the analysis of splice defects in general was developed. We analyzed the transcripts from the gene of interest by standard methods after short-term culture of the patient's lymphocytes in the presence and absence of a NMD inhibitor. Variant and wild type transcript expression were quantified by allele specific PCR in the patient and both parents and the expression ratio with/without NMD inhibition was calculated for each transcript.

RESULTS

NMD detection in lymphocytes was optimized and evaluated by analyzing a naturally occurring NMD transcript. Several compounds inhibited NMD successfully, including potential therapeutic agents. Sample storage for up to 4 days at room temperature prior to lymphocyte isolation did not affect results. In a proof of concept we identified two candidate variants as severe splicing variants in a patient with Pompe disease, but the strategy can also be used to screen for any mis-spliced transcripts prone to NMD.

CONCLUSIONS

We developed a simple, non-invasive assay for the detection and characterization of potential splicing variants. This is essential, because early and near-term diagnosis and disease classification is required to facilitate therapy in many genetic diseases.

Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human GM1-Gangliosidosis

G_M1-gangliosidosis is caused by a reduced activity of β-galactosidase (Glb1), resulting in intralysosomal accumulations of G_M1. The aim of this study was to reveal the pathogenic mechanisms of G_M1-gangliosidosis in a new Glb1 knockout mouse model. Glb1^−/− mice were analyzed clinically, histologically, immunohistochemically, electrophysiologically and biochemically. Morphological lesions in the central nervous system were already observed in two-month-old mice, whereas functional deficits, including ataxia and tremor, did not start before 3.5-months of age. This was most likely due to a reduced membrane resistance as a compensatory mechanism. Swollen neurons exhibited intralysosomal storage of lipids extending into axons and amyloid precursor protein positive spheroids. Additionally, axons showed a higher kinesin and lower dynein immunoreactivity compared to wildtype controls. Glb1^−/− mice also demonstrated loss of phosphorylated neurofilament positive axons and a mild increase in non-phosphorylated neurofilament positive axons. Moreover, marked astrogliosis and microgliosis were found, but no demyelination. In addition to the main storage material G_M1, G_A1, sphingomyelin, phosphatidylcholine and phosphatidylserine were elevated in the brain. In summary, the current Glb1^−/− mice exhibit a so far undescribed axonopathy and a reduced membrane resistance to compensate the functional effects of structural changes. They can be used for detailed examinations of axon–glial interactions and therapy trials of lysosomal storage diseases.

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

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

The First Year Experience of Newborn Screening for Pompe Disease in California

The California Department of Public Health started universal newborn screening for Pompe disease in August 2018 with a two-tier process including: (1) acid alpha-glucosidase (GAA) enzyme activity assay followed by, (2) GAA gene sequencing analysis. This study examines results from the first year of screening in a large and diverse screening population. With 453,152 screened newborns, the birth prevalence and GAA enzyme activity associated with various types of Pompe disease classifications are described. The frequency of GAA gene mutations and allele variants are reported. Of 88 screen positives, 18 newborns were resolved as Pompe disease, including 2 classic infantile-onset and 16 suspected late-onset form. The c.-32-13T>G variant was the most common pathogenic mutation reported. African American and Asian/Pacific Islander newborns had higher allele frequencies for both pathogenic and pseudodeficiency variants. After the first year of Pompe disease screening in California, the disease distribution in the population is now better understood. With the ongoing long-term follow-up system currently in place, our understanding of the complex genotype-phenotype relationships will become more evident in the future, and this should help us better understand the clinical significance of identified cases.

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.

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.

Variable clinical features and genotype-phenotype correlations in 18 patients with late-onset Pompe disease

Background

Pompe disease is a lysosomal storage disorder caused by the deficiency of enzyme acid alpha-glucosidase (GAA) which results in accumulation of glycogen, particularly in the skeletal, cardiac, and smooth muscles. The late-onset form with symptoms presenting in childhood through adulthood, is characterized by proximal muscle weakness, respiratory insufficiency, and unlike the infantile-onset form often with no cardiac involvement.

Methods

We report our experience with 18 adult patients (14 males/4 females) with Pompe disease, several of whom had unique findings and novel pathogenic variants. Patients ranged in ages from 22-74 years (mean 53.7 years) and were diagnosed at an age range of 11-65 years (mean 43.6 years), often after a history of progressive muscle disease of several years' duration. All 18 patients were treated with alglucosidase alfa (Lumizyme) and their response to treatment was monitored by measurements of their pulmonary function and muscle weakness, six-minute walk test (6MWT), and other functional studies.

Results

Genetic sequencing revealed that 16 out of 18 individuals had the common c.-32-13T>G splicing variant, and six patients, including two sibships had four novel pathogenic variants: c.1594G>A, c.2655_2656delCG, c.1951-1952delGGinsT, and c.1134C>G. A male with the c.1594G>A variant developed an intracerebral aneurysm at the age of 43 years treated with surgery. Two siblings with the c.2655_2656delCG developed very high antibody titers, one of whom developed a severe infusion reaction. Other clinical features included BiPAP requirement in twelve, tinnitus in seven, scoliosis in five, cardiomyopathy in three, one individual was diagnosed with a cerebral aneurysm who underwent successful Penumbra coil placement, and another individual was diagnosed with both Graves' disease and testicular cancer.

Conclusions

Our study illustrates significant variability in the range of clinical features, and the variable clinical response to enzyme replacement therapy. It also alerts us to the importance of careful monitoring and early management of complications. Possible genotype-phenotype associations with the novel mutations identified may emerge with larger studies.

A genetic modifier of symptom onset in Pompe disease

BACKGROUND

Neonatal screening for Pompe disease is complicated by difficulties in predicting symptom onset in patients with the common c.-32-13T>G (IVS1) variant/null (i.e. fully deleterious) acid α-glucosidase (GAA) genotype. This splicing variant occurs in 90% of Caucasian late onset patients, and is associated with a broad range of symptom onset.

METHODS

We analyzed a cohort of 143 compound heterozygous and 10 homozygous IVS1 patients, and we assessed ages at symptom onset, the presence of cis-acting single nucleotide variants (SNVs), and performed splicing analysis and enzyme activity assays.

FINDINGS

In compound heterozygous IVS1 patients, the synonymous variant c.510C>T was uniquely present on the IVS1 allele in 9/33 (27%) patients with childhood onset, but was absent from 110 patients with onset in adulthood. GAA enzyme activity was lower in fibroblasts from patients who contained c.510C>T than it was in patients without c.510C>T. By reducing the extent of leaky wild-type splicing, c.510C>T modulated aberrant splicing caused by the IVS1 variant. The deleterious effect of c.510C>T was also found in muscle cells, the main target cells in Pompe disease. In homozygous IVS1 patients, the c.510C>T variant was absent in 4/4 (100%) asymptomatic individuals and present in 3/6 (50%) symptomatic patients. In cells from homozygous IVS1 patients, c.510C>T caused reduced leaky wild-type splicing.

INTERPRETATION

c.510C>T is a genetic modifier in compound heterozygous and homozygous IVS1 patients. This finding is important for neonatal screening programs for Pompe disease. FUND: This work was funded by grants from Sophia Children's Hospital Foundation (SSWO, grant S17-32) and Metakids (2016-063).

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.

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.

A cross-sectional analysis of clinical evaluation in 35 individuals with mutations of the valosin-containing protein gene

Inclusion body myopathy (IBM) associated with Paget disease of the bone and frontotemporal dementia or IBMPFD is an autosomal dominant degenerative disorder caused by mutations in the valosin-containing protein (VCP) gene. We aim to establish a detailed clinical phenotype of VCP disease amongst 35 (28 affected individuals, 7 presymptomatic gene carriers) individuals versus 14 unaffected first-degree relatives in 14 families to establish useful biomarkers for IBMPFD and identify the most meaningful tests for monitoring disease progression in future clinical trials. Comprehensive studies included the Inclusion Body Myositis Functional Rating Scale (IBMFRS) and fatigue severity scale questionairres, strength measurements using the Manual Muscle Test with Medical Research Council (MRC) scales, hand-held dynamometry using the microFET and Biodex dynamometers, 6 minute walk test (6MWT), and pulmonary function studies. Strong correlation was observed between the IBMFRS and measurements of muscle strength with dynamometry and the other functional tests, indicating that it may be utilized in long-term follow-up assessments due to its relative simplicity. This cross-section study represents the most comprehensive evaluation of individuals with VCP disease to date and provides a useful guide for evaluating and possible monitoring of muscle weakness and pulmonary function progression in this unique cohort of individuals.

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.

Impact, Characterization, and Rescue of Pre-mRNA Splicing Mutations in Lysosomal Storage Disorders

Lysosomal storage disorders (LSDs) represent a group of more than 50 severe metabolic diseases caused by the deficiency of specific lysosomal hydrolases, activators, carriers, or lysosomal integral membrane proteins, leading to the abnormal accumulation of substrates within the lysosomes. Numerous mutations have been described in each disease-causing gene; among them, about 5-19% affect the pre-mRNA splicing process. In the last decade, several strategies to rescue/increase normal splicing of mutated transcripts have been developed and LSDs represent excellent candidates for this type of approach: (i) most of them are inherited in an autosomic recessive manner and patients affected by late-onset (LO) phenotypes often retain a fair amount of residual enzymatic activity; thus, even a small recovery of normal splicing may be beneficial in clinical settings; (ii) most LSDs still lack effective treatments or are currently treated with extremely expensive approaches; (iii) in few LSDs, a single splicing mutation accounts for up to 40-70% of pathogenic alleles. At present, numerous preclinical studies support the feasibility of reverting the pathological phenotype by partially rescuing splicing defects in LSDs. This review provides an overview of the impact of splicing mutations in LSDs and the related therapeutic approaches currently under investigation in these disorders.

Pompe disease in Austria: clinical, genetic and epidemiological aspects

In this study, we performed a survey of infantile and late-onset Pompe disease (IOPD and LOPD) in Austria. Paediatric and neuromuscular centres were contacted to provide a set of anonymized clinical and genetic data of patients with IOPD and LOPD. The number of patients receiving enzyme replacement therapy (ERT) was obtained from the pharmaceutical company providing alglucosidase alfa. We found 25 patients in 24 families, 4 IOPD and 21 LOPD with a resulting prevalence of 1:350,914. The most frequent clinical manifestation in LOPD was a lower limb-girdle phenotype combined with axial weakness. Three patients were clinically pauci- or asymptomatic and were diagnosed because of persistent hyperCKemia. Diagnostic delay in LOPD was 7.4 ± 9.7 years. The most common mutation was c.-32-13T > G. All IOPD and 17 symptomatic LOPD patients are receiving ERT. Standardized follow-up was only available in six LOPD patients for the 6-min walk test (6minWT) and in ten for the forced vital capacity (FVC). Mean FVC did not decline (before ERT; 63.6 ± 39.7%; last evaluation during ERT: 61.9 ± 26.9%; P = 0.5) while there was a trend to decline in the mean distance covered by the 6minWT (before ERT: 373.5 ± 117.9 m; last evaluation during ERT: 308.5 ± 120.8 m; P = 0.077). The study shows a lower prevalence of Pompe disease in Austria than in other European countries and corroborates a limb-girdle phenotype with axial weakness as the most common clinical presentation, although asymptomatic hyperCKemia may be the first indication of LOPD.

Insight into the phenotype of infants with Pompe disease identified by newborn screening with the common c.-32-13T>G "late-onset" GAA variant

OBJECTIVE

Newborn screening (NBS) has led to early diagnosis and early initiation of treatment for infantile onset Pompe Disease (IOPD). However, guidelines for management of late onset Pompe disease (LOPD) via NBS, especially with the IVS c.-32-13T>G are not clear. This IVS variant is noted in 68-90% cases with LOPD and has been presumed to result in "adult" disease in compound heterozygosity, with a few cases with earlier onset and a mild to no phenotype in homozygosity. Our study evaluates newborns with LOPD having IVS variant with a diligent multidisciplinary approach to determine if they have an early presentation.

METHODS

Seven children with LOPD identified by NBS with IVS variant (3 compound heterozygous, and 4 homozygous) were evaluated with clinical, biochemical (CK, AST, ALT, and urinary Glc₄), cardiac evaluation, physical therapy (PT), occupational, and speech/language therapy.

RESULTS

All seven patients demonstrated motor involvement by age 6months; the three patients with c.-32-13 T>G variant in compound heterozygosity had symptoms as neonates. Patients with c.-32-13 T>G variant in compound heterozygosity had more involvement with persistent hyperCKemia, elevated AST and ALT, swallowing difficulties, limb-girdle weakness, delayed motor milestones, and were initiated on ERT. The patients with c.-32-13T>G variant in homozygosity had normal laboratory parameters, and presented with very subtle yet LOPD specific signs, identified only by meticulous assessments.

CONCLUSION

This patient cohort represents the first carefully phenotyped cohort of infants with LOPD with the "late-onset" GAA variant c.-32-13T>G detected by NBS in the USA. It emphasizes not only the opportunity for early detection of skeletal and other muscle involvement in infants with c.-32-13T>G variant but also a high probability of overlooking or underestimating the significance of clinically present and detectable features. It can thus serve as a valuable contribution in the development of evaluation and treatment algorithms for infants with LOPD.

A molecular analysis of the GAA gene and clinical spectrum in 38 patients with Pompe disease in Japan

Pompe disease is an autosomal recessive disorder caused by acid α-glucosidase (GAA) deficiency, which results in the accumulation of glycogen in lysosomes in multiple tissues, including cardiac, skeletal, and smooth muscle cells. Thus far, 558 sequence variants of the GAA gene have been published in the Pompe Disease Mutation Database, and some mutations appear with considerable frequency in particular ethnic groups, such as Caucasians, Taiwanese, Chinese, and Koreans. However, the GAA mutation pattern in Japanese patients remains poorly understood. We analyzed the relationship between the genetic and clinical features of 38 mostly Japanese patients with Pompe disease from 35 unrelated families. We identified 28 different GAA gene mutations, including 7 novel mutations, by a GAA gene analysis. c.546G > T (22.9%) and c.1857C > G (14.3%) were the most common mutations and accounted for 37.1% of the total mutant alleles. In the six patients with infantile-onset Pompe disease (IOPD), c.1857C > G was also the most common mutation. In addition, there were 13 homozygotes (5 with the c.546G > T) among the 35 families, which is the highest frequency reported thus far. Regarding the initial symptoms, cardiomegaly was the most common (3/6 = 50%) in IOPD patients, while muscle weakness was observed the most frequently in patients with late-onset Pompe disease (LOPD) (15/30 = 50%). Notably, all IOPD patients who showed respiratory distress at the time of onset require respiratory assistance at present (4/4 = 100%). Regarding the presenting symptoms, cardiomegaly (6/6 = 100%) and hepatomegaly (4/6 = 66.7%) were more commonly seen in IOPD, and muscle weakness (24/29 = 82.7%) was observed more frequently in LOPD. Respiratory assistance is required at present in 33.3% of IOPD patients and 50% of LOPD patients, and 20% of IOPD patients and 29.6% of LOPD patients are wheelchair users. These individual clinical courses may be influenced by the timing of the diagnosis and treatment; for example, in 2007, an ERT orphan drug for treatment of Pompe disease, Alglucosidase alfa, was made available in Japan, and there were 5 (5/6 = 83.3%) wheelchair users diagnosed from 2008 to 2009 (cases 32–38) and 4 (4/27 = 14.8%) from 2010 to 2015 (cases 1–31). These findings underscore the importance of the early diagnosis and treatment.

[Clinical characteristics and GAA gene mutation in children with glycogen storage disease type II: an analysis of 3 cases]

Glycogen storage disease type II (GSD II) is an autosomal recessive disorder caused by a deficiency of the lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA) and can affect multiple systems including the heart and skeletal muscle. The aim of this study was to investigate three children with GSD II confirmed by GAA gene analysis and to report their clinical characteristics and gene mutations. One case was classified as infantile-onset GSD II, and two cases as late-onset GSD II. The infantile-onset patient (aged 4 months) showed no weight increase and had dyspnea, muscle hypotonia, and increased alanine aminotransferase and creatine kinase; echocardiography showed hypertrophic cardiomyopathy. The late-onset patients (aged 8 years and 13 years respectively) showed persistently elevated liver enzymes; one of them had recurrent respiratory tract infection and restrictive ventilation disorder, and the other case showed significantly increased creatase but normal electromyographic findings. Peripheral blood genetic testing for GAA gene showed six pathogenic mutations in the three cases, and the mutations c.2738C>T and c.568C>T had not been reported. Therefore, peripheral blood genetic testing for GAA gene is an effective diagnostic method.

First clinical and genetic description of a family diagnosed with late-onset Pompe disease from Costa Rica

Glycogen storage disease type II, also known as Pompe disease, is an autosomal recessive disorder caused by deficiency of enzymatic activity of acid alpha-glucosidase. The wide phenotypical variation of this disease relates to the amount of residual enzymatic activity depending on the combination of mutations on each allele. We confirmed Pompe disease in a patient that presented with progressive weakness, recurrent episodes of respiratory failure associated with pneumonia, a predominantly demyelinating mixed sensorimotor polyneuropathy and paraspinal complex repetitive discharges. Genetic analysis of the GAA gene from this patient revealed two pathogenic compound heterozygous mutations: c.-32-13T>G (rs386834236, intronic), c.2560C>T (rs121907943, p.Arg854Ter); and one variant of unknown significance: c.1551+42G>A (rs115427918, intronic). We found expected mutations in two siblings and two nieces. Genetic variants reported in this family reflect on the European and African ancestry that we carry in our Costa Rican population.

Effects of short-to-long term enzyme replacement therapy (ERT) on skeletal muscle tissue in late onset Pompe disease (LOPD)

AIMS

Pompe disease is an autosomal recessive lysosomal storage disorder resulting from deficiency of acid α-glucosidase (GAA) enzyme. Histopathological hallmarks in skeletal muscle tissue are fibre vacuolization and autophagy. Since 2006, enzyme replacement therapy (ERT) is the only approved treatment with human recombinant GAA alglucosidase alfa. We designed a study to examine ERT-related skeletal muscle changes in 18 modestly to moderately affected late onset Pompe disease (LOPD) patients along with the relationship between morphological/biochemical changes and clinical outcomes. Treatment duration was short-to-long term.

METHODS

We examined muscle biopsies from 18 LOPD patients at both histopathological and biochemical level. All patients underwent two muscle biopsies, before and after ERT administration respectively. The study is partially retrospective because the first biopsies were taken before the study was designed, whereas the second biopsy was always performed after at least 6 months of ERT administration.

RESULTS

After ERT, 15 out of 18 patients showed improved 6-min walking test (6MWT; P = 0.0007) and most of them achieved respiratory stabilization. Pretreatment muscle biopsies disclosed marked histopathological variability, ranging from an almost normal pattern to a severe vacuolar myopathy. After treatment, we detected morphological improvement in 15 patients and worsening in three patients. Post-ERT GAA enzymatic activity was mildly increased compared with pretreatment levels in all patients. Protein levels of the mature enzyme increased in 14 of the 18 patients (mean increase = +35%; P < 0.05). Additional studies demonstrated an improved autophagic flux after ERT in some patients.

CONCLUSIONS

ERT positively modified skeletal muscle pathology as well as motor and respiratory outcomes in the majority of LOPD patients.

Glycogen Reduction in Myotubes of Late-Onset Pompe Disease Patients Using Antisense Technology

Glycogen storage disease type II (GSDII) is a lysosomal disorder caused by the deficient activity of acid alpha-glucosidase (GAA) enzyme, leading to the accumulation of glycogen within the lysosomes. The disease has been classified in infantile and late-onset forms. Most late-onset patients share a splicing mutation c.-32-13T > G in intron 1 of the GAA gene that prevents efficient recognition of exon 2 by the spliceosome. In this study, we have mapped the splicing silencers of GAA exon 2 and developed antisense morpholino oligonucleotides (AMOs) to inhibit those regions and rescue normal splicing in the presence of the c.-32-13T > G mutation. Using a minigene approach and patient fibroblasts, we successfully increased inclusion of exon 2 in the mRNA and GAA enzyme production by targeting a specific silencer with a combination of AMOs. Most importantly, the use of these AMOs in patient myotubes results in a decreased accumulation of glycogen. To our knowledge, this is the only therapeutic approach resulting in a decrease of glycogen accumulation in patient tissues beside enzyme replacement therapy (ERT) and TFEB overexpression. As a result, it may represent a highly novel and promising therapeutic line for GSDII.

Prevalence of late-onset pompe disease in Portuguese patients with diaphragmatic paralysis - DIPPER study

Pompe disease is a rare autosomal recessive neuromuscular disorder caused by acid α-glucosidase enzyme (GAA) deficiency and divided into two distinct variants, infantile- and late-onset. The late-onset variant is characterized by a spectrum of phenotypic variation that may range from asymptomatic, to reduced muscle strength and/or diaphragmatic paralysis. Since muscle strength loss is characteristic of several different conditions, which may also cause diaphragmatic paralysis, a protocol was created to search for the diagnosis of Pompe disease and exclude other possible causes.

METHODS

We collected a sample size of 18 patients (10 females, 8 males) with a median age of 60 years and diagnosis of diaphragmatic paralysis of unknown etiology, followed in the Pulmonology outpatient consultation of 9 centers in Portugal, over a 24-month study period. We evaluated data from patient's clinical and demographic characteristics as well as complementary diagnostic tests including blood tests, imaging, neurophysiologic and respiratory function evaluation. All patients were evaluated for GAA activity with DBS (dried blood test) or serum quantification and positive results confirmed by serum quantification and sequencing.

RESULTS

Three patients were diagnosed with Pompe's disease and recommended for enzyme replacement therapy. The prevalence of Pompe, a rare disease, in our diaphragmatic paralysis patient sample was 16.8%.

CONCLUSION

We conclude that DBS test for GAA activity should be recommended for all patients with diaphragmatic paralysis which, despite looking at all the most common causes, remains of unknown etiology; this would improve both the timing and accuracy of diagnosis for Pompe disease in this patient population. Accurate diagnosis will lead to improved care for this rare, progressively debilitating but treatable neuromuscular disease.

Hereditary myopathies with early respiratory insufficiency in adults

INTRODUCTION

Hereditary myopathies with early respiratory insufficiency as a predominant feature of the clinical phenotype are uncommon and underestimated in adults.

METHODS

We reviewed the clinical and laboratory data of patients with hereditary myopathies who demonstrated early respiratory insufficiency before the need for ambulatory assistance. Only patients with disease-causing mutations or a specific histopathological diagnosis were included. Patients with cardiomyopathy were excluded.

RESULTS

We identified 22 patients; half had isolated respiratory symptoms at onset. The diagnosis of the myopathy was often delayed, resulting in delayed ventilatory support. The most common myopathies were adult-onset Pompe disease, myofibrillar myopathy, multi-minicore disease, and myotonic dystrophy type 1. Single cases of laminopathy, MELAS (mitochondrial encephalomyopathy with lactic acidosis and strokelike events), centronuclear myopathy, and cytoplasmic body myopathy were identified.

CONCLUSION

We highlighted the most common hereditary myopathies associated with early respiratory insufficiency as the predominant clinical feature, and underscored the importance of a timely diagnosis for patient care. Muscle Nerve 56: 881-886, 2017.

Late-onset pompe disease in Iran: A clinical and genetic report

INTRODUCTION

Pompe disease is characterized by absence or deficiency of acid α-glucosidase, and several causative mutations are known. In this study we report clinical and laboratory data in Iranian patients with late-onset Pompe disease (LOPD), focusing on population-specific mutations.

METHODS

Clinical and laboratory data of 14 patients from 10 families with the diagnosis of LOPD were recorded. All had reduced enzyme activity on dried blood spot (DBS) analysis. Genetic investigation was performed to identify the underlying mutations.

RESULTS

The age of onset ranged from <2 to 38 years. The clinical presentations were heterogeneous. Two siblings presented with foot drop. The most common mutation was c.(-32-13T>G). There were 4 novel mutations: c.(2040 + 2dup); c.(1650delG); c.(1837T>G); and c.(2596delG).

CONCLUSION

This is a comprehensive report of LOPD in Iranian patients. Distinct phenotypic and genotypic features in this population are highlighted. Muscle Nerve 55: 835-840, 2017.

From Cryptic Toward Canonical Pre-mRNA Splicing in Pompe Disease: a Pipeline for the Development of Antisense Oligonucleotides

While 9% of human pathogenic variants have an established effect on pre-mRNA splicing, it is suspected that an additional 20% of otherwise classified variants also affect splicing. Aberrant splicing includes disruption of splice sites or regulatory elements, or creation or strengthening of cryptic splice sites. For the majority of variants, it is poorly understood to what extent and how these may affect splicing. We have identified cryptic splicing in an unbiased manner. Three types of cryptic splicing were analyzed in the context of pathogenic variants in the acid α-glucosidase gene causing Pompe disease. These involved newly formed deep intronic or exonic cryptic splice sites, and a natural cryptic splice that was utilized due to weakening of a canonical splice site. Antisense oligonucleotides that targeted the identified cryptic splice sites repressed cryptic splicing at the expense of canonical splicing in all three cases, as shown by reverse-transcriptase-quantitative polymerase chain reaction analysis and by enhancement of acid α-glucosidase enzymatic activity. This argues for a competition model for available splice sites, including intact or weakened canonical sites and natural or newly formed cryptic sites. The pipeline described here can detect cryptic splicing and correct canonical splicing using antisense oligonucleotides to restore the gene defect.

A conceptual disease model for adult Pompe disease

Background

Studies in orphan diseases are, by nature, confronted with small patient populations, meaning that randomized controlled trials will have limited statistical power. In order to estimate the effectiveness of treatments in orphan diseases and extrapolate effects into the future, alternative models might be needed. The purpose of this study is to develop a conceptual disease model for Pompe disease in adults (an orphan disease). This conceptual model describes the associations between the most important levels of health concepts for Pompe disease in adults, from biological parameters via physiological parameters, symptoms and functional indicators to health perceptions and final health outcomes as measured in terms of health-related quality of life.

Methods

The structure of the Wilson-Cleary health outcomes model was used as a blueprint, and filled with clinically relevant aspects for Pompe disease based on literature and expert opinion. Multiple observations per patient from a Dutch cohort study in untreated patients were used to quantify the relationships between the different levels of health concepts in the model by means of regression analyses.

Results

Enzyme activity, muscle strength, respiratory function, fatigue, level of handicap, general health perceptions, mental and physical component scales and utility described the different levels of health concepts in the Wilson-Cleary model for Pompe disease. Regression analyses showed that functional status was affected by fatigue, muscle strength and respiratory function. Health perceptions were affected by handicap. In turn, self-reported quality of life was affected by health perceptions.

Conclusions

We conceptualized a disease model that incorporated the mechanisms believed to be responsible for impaired quality of life in Pompe disease. The model provides a comprehensive overview of various aspects of Pompe disease in adults, which can be useful for both clinicians and policymakers to support their multi-faceted decision making.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-015-0334-6) contains supplementary material, which is available to authorized users.

The Genetic Challenges and Opportunities in Advanced Heart Failure

The causes of heart failure are diverse. Inherited causes represent an important clinical entity and can be divided into 2 major categories: familial and metabolic cardiomyopathies. The distinct features that might be present in early disease states can become broadly overlapping with other diseases, such as in the case of inherited cardiomyopathies (ie, familial hypertrophic cardiomyopathy or mitochondrial diseases). In this review article, we focus on genetic issues related to advanced heart failure. Because of the emerging importance of this topic and its breadth, we sought to focus our discussion on the known genetic forms of heart failure syndromes, genetic testing, and newer data on pharmacogenetics and therapeutics in the treatment of heart failure, to primarily encourage clinicians to place a priority on the diagnosis and treatment of these potentially treatable conditions.

c.1437G>A intron 9 substitution on acid α-glucosidase gene associated with classic infantile-onset Pompe disease phenotype

Pompe disease, or glycogen storage disease type II (GSD2), an autosomal recessive disease first described by Joannes Cassianus Pompe (1901-1945), causes deficient activity of acid α-glucosidase (GAA) enzyme. GAA catalyses α 1,4 and α 1,6 glucosidic linkages in lysosomes; destruction of these linkages permits glycogen to be separated into glucose and later used for energy. Without proper function of this enzyme, glycogen accumulates in lysosome, causing muscle hypotonia. We report a previously undescribed association of c.1437G>A intron 9 substitution on the GAA gene with severe infantile-onset Pompe disease in a deceased proband and carrier status in four of five surviving family members. Previous authors have found late-onset or moderate severity infantile-onset Pompe disease associated with this allelic variation. Our proband's family's village was suspicious for locally endemic disease. While our proband developed all features of classic infantile onset GSD2, socioeconomic and geographic factors initially suggested an infectious aetiology.