The French Pompe registry. Baseline characteristics of a cohort of 126 patients with adult Pompe disease

Lysosomal storage disorders identified in adult population from India: Experience of a tertiary genetic centre and review of literature

Lysosomal storage disorders (LSDs) in adults have milder phenotype and variable age at presentation. Several studies have described the phenotype, genotype and treatment outcomes for adult-onset LSDs like Gaucher, Fabry, Pompe disease and others. We describe the first systematic study on the occurrence of LSDs in an adult population from India. It describes, the key clinical signs seen in these patients and those from literature review that can aid in early detection. Of 2102 biochemically diagnosed LSDs cases, 32 adult patients were identified with LSDs. Based on the clinical suspicion, screening test and enzyme study was carried out. Twenty-two patients were subjected to a genetic study to identify the causative variant in a respective gene. Of the 32 adult patients, we observed a maximum percentage of 37.5% (n = 12) cases with Gaucher disease, followed by 13% (n = 4) with Fabry disease. We found 10% of cases with MPS IVA and MPS I, and 9% cases with Pompe. Single case of adult mucolipidosis III and two cases each of Type 1 Sialidosis, Niemann-Pick disease B and metachromatic leukodystrophy were identified. We observed two common variants p.Leu483Pro and p.Ala487Thr in the GBA1 gene in 23% of Indian patients with adult Gaucher disease. No common variants were observed in other aforementioned LSDs. Study identified 50% of Fabry patients and 4% of Gaucher patients diagnosed at our centre to be adults. The prevalence of adult Pompe patients was low (3.4%) as compared to 80% reported in the Caucasian population. Adult LSDs such as, MPS III, GM1/GM2 gangliosidosis and Krabbe disease were not identified in our cohort.

Description of clinical and genetic features of 122 patients included in the Spanish Pompe registry

Pompe disease is a rare genetic disorder with an estimated prevalence of 1:60.000. The two main phenotypes are Infantile Onset Pompe Disease (IOPD) and Late Onset Pompe Disease (LOPD). There is no published data from Spain regarding the existing number of cases, regional distribution, clinical features or, access and response to the treatment. We created a registry to collect all these data from patients with Pompe in Spain. Here, we report the data of the 122 patients registered including nine IOPD and 113 LOPD patients. There was a high variability in how the diagnosis was obtained and how the follow-up was performed among different centres. Seven IOPD patients were still alive being all treated with enzymatic replacement therapy (ERT) at last visit. Ninety four of the 113 LOPD patients had muscle weakness of which 81 were receiving ERT. We observed a progressive decline in the results of muscle function tests during follow-up. Overall, the Spanish Pompe Registry is a valuable resource for understanding the demographics, patient's journey and clinical characteristics of patients in Spain. Our data supports the development of agreed guidelines to ensure that the care provided to the patients is standardized across the country.

Muscle ultrasound in patients with late-onset Pompe disease identified by newborn screening

Importance

Implementation of newborn screening (NBS) in the United States now detects infants with late-onset Pompe disease (LOPD), a lysosomal storage disease characterized by slowly progressive muscle weakness, and detailed clinical evaluation has identified early muscle weakness. Biomarkers may be uninformative; thus, non-invasive imaging is needed to assess early LOPD muscle changes. Muscle ultrasound (US) measuring echointensity (EI) is a non-invasive measure of muscle health.

Objective

In this study, we aimed to evaluate if EI can identify characteristic patterns of muscle involvement in LOPD patients identified by NBS.

Design/setting

Prospective, cross-sectional, single time point study.

Setting

One-center study.

Participants

We examined 20 infants with NBS-identified LOPD (ages 5-20 months). All had standardized physical therapy assessments.

Exposures

Creatine Kinase (CK) and Urine Hexose Tetrasaccharide (Glc4) were obtained. Muscle US of deltoid, biceps brachii, forearm flexors, thoracic paraspinals, gluteus maximus, quadriceps, tibialis anterior and medial gastrocnemius was performed.

Main outcomes and measures

Mean EI was calculated for all involved muscle groups. Quantitative EI Sum Scores were calculated as total EI divided by number of muscle groups assessed. We performed a comprehensive literature review to compare our results to previous LOPD muscle ultrasound studies.

Results

Six of 20 participants had elevated CK and 15 had ≥ 50% of the most common concerning kinematic physical findings; with normal urine Glc4 in all except one. Based upon muscle EI, the most affected muscles were quadriceps and medial gastrocnemius, with notable elevated EI in thoracic paraspinals. Biceps brachii was the most frequently affected upper extremity muscle. EI sum scores correlated moderately with increasing CK. Statistically significant positive correlation was found between posterior pelvic tilt in sitting and EI of gluteus maximus. Sonographic pattern of muscle involvement was similar to previous studies assessing older patients with LOPD.

Conclusions and relevance

In this study, muscle EI was elevated most often in the quadriceps, tibialis anterior, medial gastrocnemius, thoracic paraspinals, and biceps brachii. Involved muscles generally fit the profile of physical and muscle ultrasound/MRI exam findings in LOPD patients. Muscle ultrasound is recommended for rapid, focused muscle assessment in LOPD, especially those identified via NBS. Future studies should focus on this pattern of ultrasonographic abnormality and changes over time.

Characteristics of Patients With Late-Onset Pompe Disease in France: Insights From the French Pompe Registry in 2022

BACKGROUND AND OBJECTIVES

The French Pompe disease registry was created in 2004 for study of the natural course of the disease in patients. It rapidly became a major tool for assessing the long-term efficacy of enzyme replacement therapy (ERT) after the market release of alglucosidase-alfa.

METHODS

Approximately 10 years after publication of the baseline characteristics of the 126 initial patients of the French Late-Onset Pompe Disease registry, we provide here an update of the clinical and biological features of patients included in this registry.

RESULTS

We describe 210 patients followed at 31 hospital-based French neuromuscular or metabolic centers. The median age at inclusion was 48.67 ± 14.91 years. The first symptom was progressive lower limb muscle weakness, either isolated (50%) or associated with respiratory symptoms (18%), at a median age of 38 ± 14.9 years. At inclusion, 64% of the patients were able to walk independently and 14% needed a wheelchair. Positive associations were found between motor function measure, manual motor test, and 6-minute walk test (6MWT) results, and these parameters were inversely associated with the time taken to sit up from a lying position at inclusion. Seventy-two patients had been followed for at least 10 years in the registry. Thirty-three patients remained untreated a median of 12 years after symptom onset. The standard ERT dose was administered for 177 patients.

DISCUSSION

This update confirms previous findings for the adult population included in the French Pompe disease registry, but with a lower clinical severity at inclusion, suggesting that this rare disease is now diagnosed earlier; thanks to greater awareness among physicians. The 6MWT remains an important method for assessing motor performance and walking ability. The French Pompe disease registry provides an exhaustive, nationwide overview of Pompe disease and can be used to assess individual and global responses to future treatments.

Motor Function Characteristics of Adults With Late-Onset Pompe Disease: A Systematic Scoping Review

BACKGROUND AND OBJECTIVES

Pompe disease is a rare neuromuscular disease caused by a deficiency of the lysosomal enzyme acid α-glucosidase. The late-onset Pompe disease (LOPD) in adults is characterized by weakness of ventilatory, axial, and proximal extremity muscles. These muscle impairments progressively impair various motor functions such as locomotion and postural control. Nearly 87% of adults with LOPD (aLOPD) report walking problems, and more than 80% report instability and falls. Knowledge of these motor functions is now sufficient to provide a clear and comprehensive overview of motor function in aLOPD. Therefore, this scoping review aimed to summarize current knowledge about motor function in aLOPD. It specifically targeted neuromuscular performance, locomotion, and postural control.

METHODS

A systematic search in MEDLINE (through PubMed), EMBASE, and Cochrane databases was conducted until May 2021. We included studies providing primary data on at least 4 participants, exploring neuromuscular performance, locomotion, and/or postural control in aLOPD. Risk of bias analysis was assessed using tools appropriate to the study designs; the risk of bias 2 (Cochrane tool) for randomized controlled trials, risk of bias in Nonrandomized Studies - of Interventions (Cochrane tool) for nonrandomized interventional trials, and the Newcastle-Ottawa Scale for cohort studies and case-control studies.

RESULTS

The search identified 2,885 articles. After screening, 58 articles were included in the analysis. In these studies, 88% explored locomotion, 83% neuromuscular performance, and 3% postural control. This review showed that aLOPD experience symmetrical weakness, concerning especially the hip and lumbar muscles. Locomotor activities are limited with a distance reduction, spatiotemporal gait parameter modification, and an increased pelvic drop and tilt. Balance disorders are also observed especially in the anteroposterior direction.

DISCUSSION

We performed the first review on motor function characteristics in aLOPD. Although a significant amount of knowledge was synthesized in this review, our study also highlighted the lack of current research on this topic. Maximal muscle strength was the only neuromuscular performance studied, and gait biomechanics and postural control were poorly explored in LOPD. Relationships between the degree of muscle weakness and motor function alterations also remain to be determined in aLOPD.

Determinants and Characterization of Locomotion in Adults with Late-Onset Pompe Disease: New Clinical Biomarkers

BACKGROUND

The late-onset form of Pompe disease (LOPD) is characterized by muscle weakness, locomotor limitations and a risk of falls. The mechanisms responsible for altered locomotion in adults with LOPD are unknown. The identification of clinical biomarkers is essential for clinical follow-up and research.

OBJECTIVES

To identify muscle determinants of impaired locomotor performance, gait stability and gait pattern, and biomechanical determinants of falls in adults with LOPD.

METHODS

In this cross-sectional, case-control study, LOPD and control participants underwent 3D gait analysis, locomotor performance tests and muscle strength measurements (isokinetic dynamometer). We explored the muscular determinants of locomotor performance (gait speed, 6-minute walk test distance and timed up and go test), gait stability (spatiotemporal gait variables) and the gait pattern. We also explored biomechanical gait determinants of falls. After intergroup comparisons, determinants were sought to use forward stepwise multiple regression.

RESULTS

Eighteen participants with LOPD and 20 control participants were included. Locomotor performance, gait stability, and the gait pattern were significantly altered in LOPD compared to control participants. Hip abductor strength was the main common determinant of locomotor performance, gait stability and pelvic instability. Hip flexor strength was the main determinant of abnormal gait kinematics at the hip and knee. Percentage duration of single support phase during the gait cycle was the main determinant of falls.

CONCLUSIONS

Hip abductor strength and percentage duration of single support during gait were the major determinants of locomotor performance, gait stability, falls and the gait pattern in LOPD. These new clinical biomarkers should therefore be systematically assessed using instrumented tools to improve the follow-up of adults with LOPD. They should also be considered in future studies to accurately assess the effects of new therapies. Hip abductor strength and single support phase should also be priority targets for rehabilitation.

The new horizons for treatment of Late-Onset Pompe Disease (LOPD)

Late-onset Pompe disease (LOPD) is a genetic myopathy causing skeletal muscle weakness and severe respiratory impairment, due to the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) leading to lysosomal glycogen accumulation along with other complex pathophysiological processes. A major step for treatment of Pompe disease was reached in 2006 with the marketing of alglucosidase alfa, a first enzyme replacement therapy (ERT) that showed a significant motor and respiratory benefit. However, efficacy of alglucosidase alfa is limited in LOPD with a loss of efficacy over time, promoting research on new treatments. Next-generation ERT are new enzymes biochemically modified to increase the uptake of exogenous enzyme by target tissues, and the benefit of two recombinant enzymes (avalglucosidase alfa and cipaglucosidase alfa) has been recently studied in large phase III clinical trials, the latest combined with miglustat. Several innovative therapies, based on GAA gene transfer, antisense oligonucleotides or inhibition of glycogen synthesis with substrate reduction therapy, are currently under study, but are still at an early stage of development. Overall, active research for new treatments raises hope for LOPD patients but challenges remain for the clinician with the need for reliable efficacy assessment tools, long-term registry data, and evidence-based recommendations for the best use of these new molecules recently available or under development.

Early clinical phenotype of late onset Pompe disease: Lessons learned from newborn screening

PURPOSE

Thoroughly phenotype children with late-onset Pompe disease (LOPD) diagnosed via newborn screening (NBS) to provide guidance for long-term follow up.

METHODS

Twenty infants ages 6-21 months with LOPD diagnosed by NBS underwent systematic clinical evaluation at Duke University including cardiac imaging, biomarker testing, physical therapy evaluation, and speech-language pathology evaluation.

RESULTS

Of the 20 infants, four were homozygous for the "late-onset" IVS1 splice site variant c.-32-13 T > G, fourteen were compound heterozygous, and two did not have any copies of this variant. None of the patients had evidence of cardiomyopathy or cardiac rhythm disturbances. Biomarker testing showed an increase in CK, AST, and ALT in 8 patients (40%) and increase in Glc4 in two patients (10%). All patients demonstrated postural and kinematic concerns. Three patients (17%) scored below the 10%ile on the Alberta Infant Motor Scale (AIMS) and 15 patients (83%) scored above the 10%ile. Speech-language pathology assessments were normal in all patients and mild feeding/swallowing abnormalities were noted in nine patients (45%).

CONCLUSION

Our data show high variability among children with LOPD diagnosed via NBS. Careful physical therapy evaluation is necessary to monitor for subtle musculoskeletal signs that may reflect early muscle involvement. Patients should be monitored closely for symptom progression.

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.

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.

Standardized nursing management of enzyme replacement therapy for late-onset Pompe disease

ABSTRACT

Pompe disease or glycogen storage disease type II is a rare autosomal recessive disorder caused by a deficiency of the lysosomal enzyme a-glucosidase. Although enzyme replacement therapy (ERT) with 2 weekly intervals following was considered an effective treatment for Pompe disease in 2006, few patients can afford to receive treatment in China because of the high cost. This study aimed to examine the standard management of enzyme replacement therapy for late-onset Pompe disease among patients over the age of 14 years from a nursing perspective in order to assess operating procedures. ERT injection fluid dispensing and infusion procedures using different methods were analyzed and compared in 3 patients with advanced Pompe disease for forming standard operation procedures. In addition, the impact of different methods on time consumption was analyzed by 1-way analysis of variance. There were significant differences in time consumption between different dispensing and infusion methods. The time of dispensing and infusing the injection fluids using the cooperative method was 15.97 minutes shorter than that using the conventional method (95% CI: 4.51-27.43, P = .012); the time using the modified method was 20.93 minutes shorter than that using the conventional method (95% CI: 9.47-32.39, P = .012); and there was no significant difference between the cooperative and modified methods (P = .431). Enzyme replacement therapy entails frequent treatment and strict nursing requirements related to the intravenous infusion process. In this context, a standard operating procedure can be used to control nursing times and labor costs effectively while ensuring a safe and effective infusion process.

Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review

Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness. It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure. In untreated LOPD, the most common cause of death is respiratory failure. Patients suffering from respiratory compromise may present with symptoms of sleep-disordered breathing (SDB) before overt signs of respiratory failure. Diaphragm weakness leads to nocturnal hypoventilation, which can result in sleep disruption. Both subjective and objective sleep quality can be impaired with associated excessive daytime sleepiness (EDS). Health-related quality of life worsens as sleep disturbance increases. The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure. These patients are at risk of acute deterioration due to lower respiratory tract infections; effective secretion clearance and vaccination against common pathogens is an important facet of care. Whilst disease-modifying enzyme replacement therapy (ERT) delays progression of locomotor dysfunction and prolongs life, its effect on respiratory function and SDB remains unclear. There are no data demonstrating the impact of ERT on sleep quality or SDB.

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.

Long-term benefit of enzyme replacement therapy with alglucosidase alfa in adults with Pompe disease: Prospective analysis from the French Pompe Registry

Despite a wide clinical spectrum, the adult form of Pompe disease is the most common one, and represents more than 90% of diagnosed patients in France. Since the marketing of enzyme replacement therapy (alglucosidase alfa, Myozyme), all reports to date in adults demonstrated an improvement of the walking distance, and a trend toward stabilization of respiratory function, but the majority of these studies were less than 5 years of duration. We report here the findings from 158 treated patients included in the French Pompe Registry, who underwent regular clinical assessments based on commonly used standardized tests (6-minute walking test, MFM scale, sitting vital capacity, MIP and MEP). For longitudinal analyses, the linear mixed effects models were used to assess trends in primary endpoints over time under ERT. A two-phase model better described the changes in distance traveled in the 6-minute walk test and MFM. 6MWT showed an initial significant increase (1.4% ± 0.5/year) followed by a progressive decline (-2.3%/year), with a cut-off point at 2.2 years. A similar pattern was observed in total MFM score (6.6% ± 2.3/year followed by a - 1.1%/year decline after 0.5 years). A single-phase decline with a slope of -0.9 ± 0.1%/year (P < .001) was observed for FVC, and MEP remained stable over the all duration of follow-up. This study provides further evidence that ERT improves walking abilities and likely stabilizes respiratory function in adult patients with Pompe disease, with a ceiling effect for the 6MWT in the first 3 years of treatment.

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.

Clouds over IMD? Perspectives for inherited metabolic diseases in adults from a retrospective cohort study in two Swiss adult metabolic clinics

Background

Inherited metabolic diseases (IMD) are complex medical conditions. Thanks to improvements in diagnosis and treatment, a growing number of pediatric IMD patients reach adulthood. Thus, clinical care of adults with IMD has emerged as a new and challenging reality. This purpose of this study of adults with IMD in an adult metabolic clinic at two academic hospitals (Lausanne and Geneva) was to help inform decisions on the future organization of health care for this group of patients.

Methods

All adult patients with a biochemical and/or genetic diagnosis of IMD followed at the clinics were included in the study. Electronic patient records were reviewed for clinical features, diagnostic studies, treatment and long-term outcome. Data of undiagnosed patients referred for suspected IMD were analyzed separately.

Results

126 patients were included in the study. The most prevalent group of diseases was small molecules disorders with 82 (65%) patients, followed by energy defects disorders with 29 (23%) patients and complex molecules disorders with 15 (12%) patients. Overall, 64% of patients were diagnosed before, and 36% after the age 16 years. Among the 126 cases, 51% suffered from medical complications. 79% of the patients were receiving a specific treatment for their disease. Among the 138 undiagnosed patients referred for suspicion of IMD, investigations lead to a genetic diagnosis in 24 (17%) patients. 19 had confirmation of an IMD, 5 were found to have another genetic condition.

Conclusions

This retrospective study reveals significant features of adult IMD cohort. The disorders are heterogeneous, and there is no one-size-fits-all approach – treatment must be tailored to fit each specific disorder in each individual patient. Even patients who are followed at the dedicated clinic are not protected from metabolic decompensations and/or chronic organ-specific complications. While it is commonly assumed that patients with IMD are more stable once they become adults, our data show that the diseases continue to exact a lifelong toll. A coordinated monitoring of target organs by a multidisciplinary team is needed. To ensure that the success in diagnosis and treatment of individuals with IMD is sustained, there is a clear requirement for adequately staffed adult IMD clinics.

Pulmonary outcome measures in long-term survivors of infantile Pompe disease on enzyme replacement therapy: A case series

OBJECTIVES

To report the respiratory function of school-aged children with infantile Pompe disease (IPD) who started enzyme replacement therapy (ERT) in infancy and early childhood.

STUDY DESIGN

This is a retrospective chart review of pulmonary function tests of: (a) patients with IPD 5 to 18 years of age, (b) who were not ventilator dependent, and (c) were able to perform upright and supine spirometry. Subjects were divided into a younger (5-9 years) and older cohort (10-18 years) for the analysis. Upright and supine forced vital capacity (FVC), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP) were analyzed.

RESULTS

Fourteen patients, all cross-reactive immunologic material (CRIM)-positive, met the inclusion criteria and were included in this study. Mean upright and supine FVC were 70.3% and 64.9% predicted, respectively, in the 5- to 9-year-old cohort; and 61.5% and 52.5% predicted, respectively, in the 10- to 18-year-old group. Individual patient trends showed stability in FVC overtime in six of the 14 patients. MIPs and MEPs were consistent with inspiratory and expiratory muscle weakness in the younger and older age group but did not decline with age.

CONCLUSION

Data from this cohort of CRIM-positive patients with IPD showed that ERT is able to maintain respiratory function in a subgroup of patients whereas others had a steady decline. There was a statistically significant decline in FVC from the upright to a supine position in both the younger and older age groups of CRIM-positive ERT-treated patients. Before ERT, patients with IPD were unable to maintain independent ventilation beyond the first few years of life.

Gene Therapy for Pompe Disease: The Time is now

Pompe disease (PD) is caused by the deficiency of the lysosomal enzyme acid α-glucosidase (GAA), resulting in systemic pathological glycogen accumulation. PD can present with cardiac, skeletal muscle, and central nervous system manifestations, as a continuum of phenotypes among two main forms: classical infantile-onset PD (IOPD) and late-onset PD (LOPD). IOPD is caused by severe GAA deficiency and presents at birth with cardiac hypertrophy, muscle hypotonia, and severe respiratory impairment, leading to premature death, if not treated. LOPD is characterized by levels of residual GAA activity up to ∼20% of normal and presents both in children and adults with a varied severity of muscle weakness and motor and respiratory deficit. Enzyme replacement therapy (ERT), based on repeated intravenous (i.v.) infusions of recombinant human GAA (rhGAA), represents the only available treatment for PD. Upon more than 10 years from its launch, it is becoming evident that ERT can extend the life span of IOPD and stabilize disease progression in LOPD; however, it does not represent a cure for PD. The limited uptake of the enzyme in key affected tissues and the high immunogenicity of rhGAA are some of the hurdles that limit ERT efficacy. GAA gene transfer with adeno-associated virus (AAV) vectors has been shown to reduce glycogen storage and improve the PD phenotype in preclinical studies following different approaches. Here, we present an overview of the different gene therapy approaches for PD, focusing on in vivo gene transfer with AAV vectors and discussing the potential opportunities and challenges in developing safe and effective gene therapies for the disease. Based on emerging safety and efficacy data from clinical trials for other protein deficiencies, in vivo gene therapy with AAV vectors appears to have the potential to provide a therapeutically relevant, stable source of GAA enzyme, which could be highly beneficial in PD.

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.

Spanish Pompe registry: Baseline characteristics of first 49 patients with adult onset of Pompe disease

INTRODUCTION AND OBJECTIVES

Pompe disease is a rare autosomal recessive disorder produced by a deficiency of acid maltase. This deficit produces an accumulation of glycogen in tissues. Clinically it is mainly characterized by limb girdle and respiratory muscle weakness. In 2013, we developed the Spanish Pompe Registry. The objective of this article was to analyse the characteristics of the first 49 patients and disclose the existence of this registry within the medical community.

MATERIAL AND METHODS

An observational retrospective study was undertaken. We analysed the 49 patients included in the Spanish Registry of Pompe Disease from May 2013 to October 2018.

RESULTS

Patients were visited at 7 different Spanish hospitals. Twenty-six patients were women and 23 were men. The average age at the time of the analysis was 47.2 years. Ten patients were asymptomatic. The mean age of onset of symptoms was 29, and low limb girdle weakness was the most frequent initial symptom. Of the patients, 49% had respiratory involvement, and 70.8% of them required non-invasive mechanical ventilation. The most common mutation found was IVS1-13T>G in 85.3% of the patients. All symptomatic patients received treatment with ERT.

CONCLUSIONS

This registry allows us to know the clinical and genetic characteristics of adult patients with Pompe disease in Spain. Moreover, it can be the basis for future studies of natural history to understand the impact of ERT in the course of the disease.

[Which follow-up for innovative treatments?]

Suivre les bénéfices et la tolérance d’une thérapie innovante constitue un exercice relativement récent dans le champ des maladies neuromusculaires. Fonction respiratoire, capacités musculaires et fonctionnelles, qualité de vie, effets indésirables, pour chaque paramètre à évaluer s’esquisse un panel de mesures idéales.

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).

Early-onset of symptoms and clinical course of Pompe disease associated with the c.-32-13 T > G variant

BACKGROUND

Individuals with late-onset Pompe disease (LOPD) and the common c.-32-13 T > G variant are widely thought to have milder, adult-onset disease. This belief, and the consequent low suspicion of clinical involvement in children, has led to delays in diagnosis and treatment initiation in patients with early onset of symptoms. Previous reports of LOPD in children do not include description of the early-onset phenotype. This description of signs and symptoms, some of which are subtle and less known, is important to facilitate prompt identification and appropriate treatment in symptomatic children.

METHODS

Retrospective chart review of a cohort of 84 LOPD patients with the c.-32-13 T > G variant was conducted to identify patients diagnosed clinically (as opposed to through newborn screening) who had clinically documented symptom-onset within the first two years of life.

RESULTS

Four patients had early onset of symptoms, with age at onset ranging from 10 days to 20 months. Initial symptoms included delay in achievement of gross motor milestones, signs of proximal muscle weakness, swallow and feeding difficulties, and sleep apnea. Early and characteristic alterations in posture and movement were identified in all patients. Age at diagnosis ranged from 10 months to 26 months. Median age at enzyme replacement therapy (ERT) initiation was 23.5 months. Despite ERT, progression of musculoskeletal involvement and residual muscle weakness was evident in all patients, as evidenced by ptosis, myopathic facies, scoliosis, lumbar lordosis, scapular winging, and trunk and lower extremity weakness. Standardized functional assessments showed gross motor function below age level as measured by the Alberta Infant Motor Scales, the Peabody Developmental Motor Scales-2, the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition, and the six-minute walk test.

CONCLUSIONS

Onset of symptoms including delay in achievement of gross motor milestones, signs of proximal muscle weakness, swallow and feeding difficulties, and sleep apnea in the first two years of life is not uncommon in individuals with LOPD and the c.-32-13 T > G variant. Patients with early-onset disease appear to have a more, rapid and severe progression of disease with persistent residual muscle deficits which partially improve with higher doses of ERT. Careful evaluation for specific and characteristic patterns of posture and movement in patients with this variant is necessary to identify those who have early onset of disease. Increased awareness of the early-onset signs and symptoms may also enable early identification of disease onset in children who are diagnosed through newborn screening.

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.

Severe Cardiac Involvement Is Rare in Patients with Late-Onset Pompe Disease and the Common c.-32-13T>G Variant: Implications for Newborn Screening

Based on a review of a large patient cohort, published literature, and 3 newborn screening cohorts, we concluded that children diagnosed through newborn screening with late-onset Pompe disease and the common heterozygous c.-32-13T>G variant require frequent cardiac follow-up with electrocardiography for arrhythmias. However, there is limited evidence for performing repeated echocardiography for cardiomyopathy.

Therapeutic Potential of Tricyclo-DNA antisense oligonucleotides

Oligonucleotide therapeutics hold great promise for the treatment of various diseases and the antisense field is constantly gaining interest due to the development of more potent and nuclease resistant chemistries. Despite a rather low success rate with only three antisense drugs being clinically approved, the frontiers of AON therapeutic applications have increased over the past three decades and continue to expand thanks to a steady increase in understanding the mechanisms of action of these molecules, progress in chemical modification and delivery.

In this review, we will examine the recent advances obtained with the tricyclo-DNA chemistry which displays unique pharmacological properties and unprecedented uptake in many tissues after systemic administration. We will review their specific properties and their therapeutic applications mainly for neuromuscular disorders, including exon-skipping for Duchenne muscular dystrophy and exon-inclusion for spinal muscular atrophy, but also aberrant splicing correction for Pompe disease. Finally, we will discuss their advantages and potential limitations, with a focus on the need for careful toxicological screen early in the process of AON drug development.

A database for screening and registering late onset Pompe disease in Turkey

The aim of this study was to search for the frequency of late onset Pompe disease (LOPD) among patients who had a myopathy with unknown diagnosis registered in the pre-diagnostic part of a novel registry for LOPD within a collaborative study of neurologists working throughout Turkey. Included in the study were 350 patients older than 18 years who have a myopathic syndrome without a proven diagnosis by serum creatine kinase (CK) levels, electrodiagnostic studies, and/or muscle pathology, and/or genetic tests for myopathies other than LOPD. Acid alpha glucosidase (GAA) in dried blood spot was measured in each patient at two different university laboratories. LOPD was confirmed by mutation analysis in patients with decreased GAA levels from either both or one of the laboratories. Pre-diagnostic data, recorded by 45 investigators from 32 centers on 350 patients revealed low GAA levels in a total of 21 patients; from both laboratories in 6 and from either one of the laboratories in 15. Among them, genetic testing proved LOPD in 3 of 6 patients and 1 of 15 patients with decreased GAA levels from both or one of the laboratories respectively. Registry was transferred to Turkish Neurological Association after completion of the study for possible future use and development. Our collaborative study enabled collection of a considerable amount of data on the registry in a short time. GAA levels by dried blood spot even from two different laboratories in the same patient may not prove LOPD. LOPD seemed to be rarer in Turkey than in Europe.

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.

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.

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.

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.

Clinical Analysis of Algerian Patients with Pompe Disease

Pompe's disease is a metabolic myopathy caused by a deficiency of acid alpha-glucosidase (GAA), also called acid maltase, an enzyme that degrades lysosomal glycogen. The clinical presentation of Pompe's disease is variable with respect to the age of onset and rate of disease progression. Patients with onset of symptoms in early infancy (infantile-onset Pompe disease (IOPD)) typically exhibit rapidly progressive hypertrophic cardiomyopathy and marked muscle weakness. Most of them die within the first year of life from cardiac and/or respiratory failure. In the majority of cases of Pompe's disease, onset of symptoms occurs after infancy, ranging widely from the first to sixth decade of life (late-onset Pompe's disease or LOPD). Progression of the disease is relentless and patients eventually progress to loss of ambulation and death due to respiratory failure. The objective of this study was to characterize the clinical presentation of 6 patients (3 with EOPD and the other 3 with LOPD) of 5 families from the East of Algeria. All our patients were diagnosed as having Pompe's disease based on biochemical confirmations of GAA deficiency by dried blood spots (DBS) and GAA gene mutations were analyzed in all patients who consented (n = 4). Our results are similar to other ethnic groups.

Intracranial arterial abnormalities in patients with late onset Pompe disease (LOPD)

BACKGROUND AND OBJECTIVES

Pompe disease is a rare metabolic disorder due to lysosomal alpha-glucosidase (GAA) deficiency. It is considered as a multi-systemic disease since, although glycogen accumulation is largely prominent in heart, skeletal and respiratory muscles, other organs can also be affected. As regards the vascular system, few reports have documented cerebrovascular malformations in Pompe patients. The aim of this study was to define the presence and type of intracranial arterial abnormalities in a cohort of late onset Pompe disease (LOPD) patients.

METHODS

We have studied 21 LOPD patients with cerebral CT angiography (CTA), using maximum intensity projection and volume rendering technique for 3D-image reconstruction.

RESULTS

We found intracranial arterial abnormalities in 13/21 patients (62 %), of whom: 2/21 patients (9.5 %) showed an unruptured intracranial aneurysm (respectively 2 and 4 mm), 10/21 (47 %) had a vertebrobasilar dolichoectasia (VBD) and 1/21 a basilar artery fenestration. Signs of lacunar encephalopathy (insular, capsular and frontal subcortical lesions) were detected in 13/21 patients (62 %) and this correlated with the presence of respiratory impairment (p = 0.017).

CONCLUSIONS

These findings differ from what has been previously observed in healthy, aged-matched populations and confirm that cerebral arteries abnormalities, mainly involving the posterior circle, are not so rare in LOPD patients and are often accompanied by a lacunar encephalopathy that might represent a hypoxic-ischemic origin. A CTA or an MRA is recommended, in LOPD patients, for early detection of cerebrovascular malformations as they could lead to life-threatening events such as sub-arachnoid haemorrhage or brainstem compression.

Reevaluating Muscle Biopsies in the Diagnosis of Pompe Disease: A Corroborative Report

Background: Previous reports suggest that although a diagnostic muscle biopsy can confirm the presence of Pompe disease, the absence of a definitive biopsy result does not rule out the diagnosis. Methods: In this study, we reviewed patients with a limb-girdle syndrome who demonstrated nonspecific abnormalities of muscle, without evidence of the classical changes of acid maltase deficiency. These patients were rescreened for Pompe disease using dried blood spot (DBS) testing. Results: Twenty-seven patients provided blood samples for the DBS test. Four patients underwent subsequent genetic testing. Genetic analysis demonstrated that one patient tested positive for Pompe disease and one patient had one copy of a pathogenic variant. Conclusions: In conclusion, the ability of a diagnostic muscle biopsy to definitively rule out the presence of Pompe disease is limited. There is a role for a screening DBS in all patients presenting with a limb-girdle syndrome without a clear diagnosis.

Altered activation of the tibialis anterior in individuals with Pompe disease: Implications for motor unit dysfunction

INTRODUCTION

Pompe disease is a progressive disease that affects skeletal muscles and leads to loss of ambulation. We investigated the activation of the tibialis anterior (TA) in late-onset Pompe disease (LOPD) individuals during maximal voluntary contraction (MVC) and evoked involuntary responses.

METHODS

Four LOPD patients and matched control subjects performed MVC of the TA using dorsiflexion and TA evoked responses. Activation of the TA was recorded with surface electromyography.

RESULTS

The Pompe patients exhibited greater power at frequencies below 60 Hz and reduced power above 100 Hz. They also exhibited a reduced increase in M-wave and prolonged M-wave latency and duration in response to stimulation.

CONCLUSIONS

These results provide evidence that LOPD individuals have an altered activation pattern of the TA during maximal contractions. The observed activation pattern may reflect impairments in voluntary command, neuromuscular junction pathology, or compensatory drive due to a reduced number of functional motoneurons.

Pompe disease: literature review and case series

Pompe disease is a rare multi-systemic metabolic myopathy caused by autosomal recessive mutations in the acidic alpha glucosidase (GAA) gene. Significant progress had been made in the diagnosis and management of patients with Pompe disease. Here, we describe our experience with 12 patients with various forms of Pompe disease including 4 potentially pathogenic, novel GAA variants. We also review the recent the recent advances in the pathogenesis, diagnosis, and treatment of individuals with Pompe disease.

Identification and characterization of aberrant GAA pre-mRNA splicing in pompe disease using a generic approach

Identification of pathogenic variants in monogenic diseases is an important aspect of diagnosis, genetic counseling, and prediction of disease severity. Pathogenic mechanisms involved include changes in gene expression, RNA processing, and protein translation. Variants affecting pre-mRNA splicing are difficult to predict due to the complex mechanism of splicing regulation. A generic approach to systematically detect and characterize effects of sequence variants on splicing would improve current diagnostic practice. Here, it is shown that such approach is feasible by combining flanking exon RT-PCR, sequence analysis of PCR products, and exon-internal quantitative RT-PCR for all coding exons. Application of this approach to one novel and six previously published variants in the acid-alpha glucosidase (GAA) gene causing Pompe disease enabled detection of a total of 11 novel splicing events. Aberrant splicing included cryptic splice-site usage, intron retention, and exon skipping. Importantly, the extent of leaky wild-type splicing correlated with disease onset and severity. These results indicate that this approach enables sensitive detection and in-depth characterization of variants affecting splicing, many of which are still unrecognized or poorly understood. The approach is generic and should be adaptable for application to other monogenic diseases to aid in improved diagnostics.

Urge incontinence and gastrointestinal symptoms in adult patients with pompe disease: a cross-sectional survey

OBJECTIVE

To determine the frequency and impact of gastrointestinal symptoms, and bowel and urinary incontinence, as this is currently unknown in adults with Pompe disease.

METHODS

Adult German Pompe patients and age- and gender-matched controls were asked about symptoms in the upper and lower intestinal tract as well as urinary incontinence using the Gastrointestinal Symptoms Questionnaire and the International Consultation on Incontinence Questionnaires for Bowel Symptoms and Urinary Incontinence.

RESULTS

The overall response rate was 78%; 57 patients and 57 controls participated. The mean age of the patients was 48.3 years ±14.7 (28 female, 29 male). 84% of patients were receiving enzyme replacement therapy. Stool urgency, diarrhoea, and urinary urge incontinence were reported significantly more frequently in patients compared to the age- and gender-matched controls (55%, 56%, 33% vs. 20%, 18%, 7%). 20% of Pompe patients used loperamide daily against diarrhoea. No other gastrointestinal tract-related symptoms were reported to occur more frequently in Pompe patients than in controls.

CONCLUSIONS

Compared to age- and gender-matched controls, both urinary and bowel incontinence occur in a higher frequency in adults with Pompe disease and have a major impact on daily life.