Prevalence of Pompe disease in 3,076 patients with hyperCKemia and limb-girdle muscular weakness

Diagnostic delay in late-onset Pompe disease among Chinese patients: A retrospective study

Surveys and retrospective studies have revealed considerable delays in diagnosing late-onset Pompe disease (LOPD) in China, where the contributing factors remain poorly represented. Our study analyzed the diagnostic journey of 34 LOPD patients seen at our neuromuscular clinic from 2005 to 2022. We defined diagnostic delay as the time from the onset of the first relevant symptoms and laboratory findings suggestive of LOPD to the eventual diagnosis, and we constructed a correlation matrix to assess relationships among these variables. The cohort consisted of 34 patients with an equal male-to-female ratio, and the mean age at diagnosis was 27.68 ± 10.03 years. We found the median diagnostic delay to be 5 years, with a range of 0.3 to 20 years, with 97.1% having been misdiagnosed previously, most commonly with "Type II Respiratory insufficiency" (36.7%). Notably, patients at earlier onset (mean age, 18.19 years vs. 31 years; p < 0.005) tended to have higher creatine kinase (CK) levels. Furthermore, 92.6% reported difficulty in sitting up from a supine position since childhood. Our research emphasizes the role of early indicators like dyspnea and difficulty performing sit-ups in adolescents for timely LOPD diagnosis and treatment initiation. The importance of early high-risk screening using dried blood spot testing cannot be overstated.

Glycogen storage diseases

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

Screening for late-onset Pompe disease in Internal Medicine departments in Spain

BACKGROUND

The screening of high-risk populations using dried blood spots (DBS) has allowed the rapid identification of patients with Pompe disease, mostly in Neurology departments. The aim of the study was to determine the prevalence of late-onset Pompe disease (LOPD) among patients not previously diagnosed or tested for this entity despite presenting possible signs or symptoms of the disease in Internal Medicine departments in Spain.

METHODS

This epidemiological, observational, cross-sectional, multicenter study included a single cohort of individuals with clinical suspicion of LOPD seen at Internal Medicine departments in Spain. The diagnosis of LOPD was initially established on the basis of the result of DBS. If decreased enzyme acid-alpha-1,4-glucosidase (GAA) activity was detected in DBS, additional confirmatory diagnostic measurements were conducted, including GAA activity in lymphocytes, fibroblasts, or muscle and/or genetic testing.

RESULTS

The diagnosis of LOPD was confirmed in 2 out of 322 patients (0.6%). Reasons for suspecting LOPD diagnosis were polymyositis or any type of myopathy of unknown etiology (in one patient), and asymptomatic or pauci-symptomatic hyperCKemia (in the other). The time between symptom onset and LOPD diagnosis was 2.0 and 0.0 years. Both patients were asymptomatic, with no muscle weakness. Additionally, 19.7% of the non-LOPD cases received an alternative diagnosis.

CONCLUSIONS

Our study highlights the existence of a hidden population of LOPD patients in Internal Medicine departments who might benefit from early diagnosis and early initiation of potential treatments.

A Comprehensive Update on Late-Onset Pompe Disease

Pompe disease (PD) is an autosomal recessive disorder caused by mutations in the GAA gene that lead to a deficiency in the acid alpha-glucosidase enzyme. Two clinical presentations are usually considered, named infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), which differ in age of onset, organ involvement, and severity of disease. Assessment of acid alpha-glucosidase activity on a dried blood spot is the first-line screening test, which needs to be confirmed by genetic analysis in case of suspected deficiency. LOPD is a multi-system disease, thus requiring a multidisciplinary approach for efficacious management. Enzyme replacement therapy (ERT), which was introduced over 15 years ago, changes the natural progression of the disease. However, it has limitations, including a reduction in efficacy over time and heterogeneous therapeutic responses among patients. Novel therapeutic approaches, such as gene therapy, are currently under study. We provide a comprehensive review of diagnostic advances in LOPD and a critical discussion about the advantages and limitations of current and future treatments.

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.

Therapeutic Options for the Management of Pompe Disease: Current Challenges and Clinical Evidence in Therapeutics and Clinical Risk Management

Pompe disease is a genetic disorder produced by mutations in the GAA gene leading to absence or reduced expression of acid alpha-glucosidase, an enzyme that metabolizes the breakdown of glycogen into glucose. There are two main phenotypes, the infantile consisting of early onset severe weakness and cardiomyopathy, and the adult which is characterized by slowly progressive skeletal and respiratory muscle weakness. Enzymatic replacement therapy (ERT) has been available for Pompe disease for more than 15 years. Although the treatment has improved many aspects of the disease, such as prolonged survival through improved cardiomyopathy and acquisition of motor milestones in infants and slower progression rate in adults, ERT is far from being a cure as both infantile and adult patients continue to progress. This fact has prompted the development of improved or new enzymes and other treatments such as gene therapy or substrate reduction strategies. Here, we review the data obtained from randomized clinical trials but also from open-label studies published so far that have assessed the advantages and limitations of this therapy. Moreover, we also review the new therapeutic strategies that are under development and provide our opinion on which are the unmet needs for patients with this disease.

Survey on the management of Pompe disease in routine clinical practice in Spain

BACKGROUND

Despite the availability of several clinical guidelines, not all health professionals use their recommendations to manage patients with Pompe disease, a rare genetic disorder involving high-impact therapy. Through several discussion meetings and a survey, the present study aimed to learn about the management of Pompe disease in routine clinical practice in Spain, to improve clinical care in a real-life situation.

RESULTS

The survey was sent to 42 healthcare professionals who manage patients with Pompe disease in their clinical practice. Although most respondents followed the clinical guidelines, clinical practice differed from the expert recommendations in many cases. Approximately 7% did not request a genetic study to confirm the diagnosis before starting treatment, and 21% considered that only two dried blood spot determinations suffice to establish the diagnosis. About 76% requested anti-GAA antibodies when there is a suspicion of lack of treatment efficacy, though a significant percentage of respondents have never requested such antibodies. According to 31% of the respondents, significant impairment of motor function and/or respiratory insufficiency is a requirement for authorizing medication at their hospital. Up to 26% waited for improvements over the clinical follow-up to maintain treatment and withdrew it in the absence of improvement since they did not consider disease stabilization to be a satisfactory outcome.

CONCLUSIONS

The results highlight the lack of experience and/or knowledge of some professionals caring for patients with Pompe disease. It is necessary to develop and disseminate simple guidelines that help to apply the expert recommendations better or centralize patient follow-up in highly specialized centers.

High-risk screening of late-onset Pompe disease: A different early portrait in China

Introduction

The lack of knowledge regarding the differences between Chinese and other ethnicities in the early manifestation of late-onset Pompe disease (LOPD) prohibits the development of an effective screening strategy. We conducted a multicenter screening study to determine LOPD prevalence in high-risk populations and define the early manifestation of LOPD in China.

Methods

Between August 2020 and April 2021, the participants were prospectively identified through medical examination at 20 centers from inpatient departments and outpatient neuromuscular clinics in China. The inclusion criteria were as follows: (1) age ≥ 1 year and (2) either one of the following conditions: (a) persistent hyperCKemia, (b) muscle weakness of the axial and/or limb-girdle muscles, or (c) unexplained restrictive respiratory insufficiency (RI). Enzymatic activity of acid α-glucosidase (GAA) was measured in a dried blood spot (DBS) using a tandem mass spectrometry (MS/MS) assay. Next-generation sequencing (NGS) was used to evaluate all samples with decreased GAA activity, searching for GAA mutations and pseudodeficiency alleles.

Results

Among the 492 cases, 26 positive samples (5.3%) were detected in the DBS test. Molecular studies confirmed a diagnosis of LOPD in eight cases (1.6%). Using MS/MS assay, GAA activities in individuals with pseudodeficiency could be distinguished from those in patients with LOPD. The median interval from the onset of symptoms to diagnosis was 5 years. All patients also showed RI, with a mean forced vital capacity (FVC) of 48%, in addition to axial/proximal muscle weakness. The creatine kinase (CK) level ranged from normal to no more than 5-fold the upper normal limit (UNL). LOPD with isolated hyperCKemia was not identified.

Conclusion

Less frequent hyperCKemia and predominant RI depict a different early portrait of adult Chinese patients with LOPD. A modified high-risk screening strategy should be proposed for the early diagnosis of Chinese patients with LOPD.

A Multidisciplinary Perspective Addressing the Diagnostic Challenges of Late-Onset Pompe Disease in the Arabian Peninsula Region Developed From an Expert Group Meeting

Pompe disease is a rare, metabolic, autosomal recessive disorder. Early diagnosis is critical for progressive Pompe disease as delays can significantly alter the clinical course of the disease. Diagnostic modalities, including dried blood spot testing and genetic testing, are available and are effective for diagnosing patients with late-onset Pompe disease (LOPD). However, clinicians face numerous clinical challenges related to the diagnosis of the disease. Two expert group committee meetings, involving 11 experts from the United Arab Emirates, Kuwait, the Kingdom of Saudi Arabia, and Oman, were convened in October 2019 and November 2020 respectively to develop a uniform diagnostic algorithm for the diagnosis of pediatric and adult LOPD in the Arabian Peninsula region. During the first meeting, the specialty-specific clinical presentation of LOPD was defined. During the second meeting, a diagnostic algorithm was developed after a thorough validation of clinical presentation or symptoms, which was performed with the aid of existing literature and expert judgement. A consensus was reached on the diagnostic algorithm for field specialists, such as neurologists, rheumatologists, general practitioners/internal medicine specialists, orthopedic specialists, and pulmonologists. This specialty-specific diagnostic referral algorithm for pediatric and adult LOPD will guide clinicians in the differential diagnosis of LOPD.

Clinico-genetic spectrum of limb-girdle muscular weakness in Austria: a multi-centre cohort study

Background and purpose

Hereditary myopathies with limb‐girdle muscular weakness (LGW) are a genetically heterogeneous group of disorders, in which molecular diagnosis remains challenging. Our aim was to present a detailed clinical and genetic characterization of a large cohort of patients with LGW.

Methods

This nationwide cohort study included patients with LGW suspected to be associated with hereditary myopathies. Parameters associated with specific genetic aetiologies were evaluated, and we further assessed how they predicted the detection of causative variants by conducting genetic analyses.

Results

Molecular diagnoses were identified in 62.0% (75/121) of the cohort, with a higher proportion of patients diagnosed by next‐generation sequencing (NGS) than by single‐gene testing (77.3% vs. 22.7% of solved cases). The median (interquartile range) time from onset to genetic diagnosis was 8.9 (3.7–19.9) and 17.8 (7.9–27.8) years for single‐gene testing and NGS, respectively. The most common diagnoses were myopathies associated with variants in CAPN3 (n = 9), FKRP (n = 9), ANO5 (n = 8), DYSF (n = 8) and SGCA (n = 5), which together accounted for 32.2% of the cohort. Younger age at disease onset (p = 0.043), >10× elevated creatine kinase activity levels (p = 0.024) and myopathic electromyography findings (p = 0.007) were significantly associated with the detection of causative variants.

Conclusions

Our findings suggest that an earlier use of NGS in patients with LGW is needed to avoid long diagnostic delays. We further present parameters predictive of a molecular diagnosis that may help to select patients for genetic analyses, especially in centres with limited access to sequencing.

Clinical and Genetic Aspects of Juvenile Onset Pompe Disease

Little is known about clinical symptomatology and genetics of juvenile onset Pompe disease (JOPD). The aims of this study were to analyze how these children are diagnosed, what clinical problems they have, and how phenotype is related to genotype. To accomplish this, we analyzed retrospectively data of 34 patients diagnosed after their first and before completion of their 18th birthday. Median age at diagnosis was 3.9 (range 1.1-17) years. Eight patients (23.5%) developed initial symptoms in the first year, 12 (35%) between 1 and 7 years, and 6 (18%) thereafter. Eight (23.5%) had no clinical symptoms at the time of diagnosis. Indications for diagnostics were a positive family history in three (9%), hyperCKemia in eight (23.5%), motor developmental delay in three (9%), and muscle weakness and/or pain in 17 (50%). Rare clinical signs were failure to thrive, recurrent diarrhea, and suspected hepatopathy with glycogen storage. Thirty-two different mutations were identified. Twenty-seven patients (79.5%) carried the milder c.32-13T > G mutation, known to be associated with a broad range of phenotypes. Three out of eight patients manifesting within the first year of life showed generalized muscle weakness, hypertrophic cardiomyopathy, and had to be ventilated during the course of disease, thereby demonstrating clinical overlap with infantile onset Pompe disease.These findings demonstrate that the phenotype of JOPD is broad and that the differential is not only restricted to neuromuscular disorders. Genotypic analysis was useful to delineate subjects with early onset JOPD from those with IOPD, but overall genotype-phenotype correlation was poor.

Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study

BACKGROUND AND OBJECTIVES

We investigated the prevalence of late-onset Pompe disease (LOPD) in patients presenting to 13 academic, tertiary neuromuscular practices in the United States and Canada.

METHODS

All successive patients presenting with proximal muscle weakness or isolated hyperCKemia and/or neck muscle weakness to these 13 centers were invited to participate in the study. Whole blood was tested for acid alpha-glucosidase (GAA) assay through the fluorometric method, and all cases with enzyme levels of ≤10 pmoL/punch/h were reflexed to molecular testing for mutations in the GAA gene. Clinical and demographic information was abstracted from their clinical visit and, along with study data, entered into a purpose-built REDCap database, and analyzed at the University of California, Irvine.

RESULTS

GAA enzyme assay results were available on 906 of the 921 participants who consented for the study. LOPD was confirmed in 9 participants (1% prevalence). Another 9 (1%) were determined to have pseudodeficiency of GAA, whereas 19 (1.9%) were found to be heterozygous for a pathogenic GAA mutation (carriers). Of the definite LOPD participants, 8 (89%) were Caucasian and were heterozygous for the common leaky (IVS1) splice site mutation in the GAA gene (c -32-13T>G), with a second mutation that was previously confirmed to be pathogenic.

DISCUSSION

The prevalence of LOPD in undiagnosed patients meeting the criteria of proximal muscle weakness, high creatine kinase, and/or neck weakness in academic, tertiary neuromuscular practices in the United States and Canada is estimated to be 1%, with an equal prevalence rate of pseudodeficiency alleles.

TRIAL REGISTRATION INFORMATION

Clinical trial registration number: NCT02838368.

Late Onset Pompe Disease with Novel Mutations and Atypical Phenotypes

BACKGROUND

Late onset Pompe disease (LOPD) is rare and generally manifests predominantly as progressive limb girdle muscle weakness. It is linked to the pathogenic mutations in GAA gene, which leads to glycogen accumulation in various tissues.

MATERIALS AND METHODS

We describe the unusual clinical, biochemical, histopathological and genetic characteristics of 5 cases of LOPD.

RESULTS

The first case had progressive anterior horn cell like disease (AHCD) that evolved later to classical limb girdle syndrome and respiratory failure, the second patient had rigid spine syndrome with gastrointestinal manifestations, the third had limb girdle weakness superimposed with episodic prolonged worsening and respiratory failure, the fourth had large fibre sensory neuropathy without primary muscle involvement and the fifth presented with classical limb girdle muscle weakness. Two homozygous missense mutations c.1461C > A (p.Phe487Leu) and c.1082C > T (p.Pro361Leu) in the GAA gene were identified in case 1 and 2 respectively. Case 3 was compound heterozygous with inframe c.1935_1940del (p.Val646_Cys647del) and an intronic splice effecting variant c.-32-13T > G. Compound heterozygous missense variants c.971C > T (p.Pro324Leu) and c.794G > A (p.Ser265Asn) were identified in case 4. Case 5 had a frameshift insertion c.1396dupG (p.Val466GlyfsTer40) and a synonymous splice affecting variant c.546G > T(p.Thr182=).

CONCLUSION

We are describing for the first time from India on LOPD with unusual phenotypes identified. A high degree of clinical suspicion and diagnosing rare phenotypes of Pompe disease is imperative to consider early initiation of Enzyme Replacement Therapy (ERT).

Recommendations for Infantile-Onset and Late-Onset Pompe Disease: An Iranian Consensus

Background: Pompe disease, also denoted as acid maltase or acid α-glucosidase deficiency or glycogen storage disease type II, is a rare, autosomal recessive lysosomal storage disorder. Several reports have previously described Pompe disease in Iran and considering increased awareness of related subspecialties and physicians, the disease's diagnosis is growing.

Objective: This guideline's main objective was to develop a national guideline for Pompe disease based on national and international evidence adapting with national necessities.

Methods: A group of expert clinicians with particular interests and experience in diagnosing and managing Pompe disease participated in developing this guideline. This group included adult neurologists, pediatric neurologists, pulmonologists, endocrinologists, cardiologists, pathologists, and physiatrists. After developing search terms, four authors performed an extensive literature review, including Embase, PubMed, and Google Scholar, from 1932 to current publications before the main meeting. Before the main consensus session, each panel member prepared an initial draft according to pertinent data in diagnosis and management and was presented in the panel discussion. Primary algorithms for the diagnosis and management of patients were prepared in the panel discussion. The prepared consensus was finalized after agreement and concordance between the panel members.

Conclusion: Herein, we attempted to develop a consensus based on Iran's local requirements. The authors hope that disseminating these consensuses will help healthcare professionals in Iran achieve the diagnosis, suitable treatment, and better follow-up of patients with infantile-onset Pompe disease and late-onset Pompe disease.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

STIG study: real-world data of long-term outcomes of adults with Pompe disease under enzyme replacement therapy with alglucosidase alfa

Background

Pompe disease is one of the few neuromuscular diseases with an approved drug therapy, which has been available since 2006. Our study aimed to determine the real-world long-term efficacy and safety of alglucosidase alfa.

Methods

This multicenter retrospective study (NCT02824068) collected data from adult Pompe disease patients receiving ERT for at least 3 years. Demographics and baseline characteristics, muscle strength, lung function (FVC), walking capability (6MWT), and safety were assessed once a year. Evaluation was done on the group and individual levels, using quantitative linear models (t test) and general univariate linear models (ANOVA).

Findings

Sixty-eight adult Pompe disease patients from four countries (Spain, Taiwan, Italy, Germany (STIG)) participated. The mean follow-up was 7.03 years ± 2.98. At group level in all outcome measures, an initial improvement followed by a secondary decline was observed. After 10 years, the 6MWT_%pred showed the most sustained positive effect (p = 0.304). The MRC_%max remained stable with a mild decline (p = 0.131), however, FVC_%pred deteriorated significantly (p < 0.001) by 14.93% over 10 years of ERT. The progression rate of FVC_%pred under ERT could be explained in most of the patients (83.5%) by the disease severity at baseline. Furthermore, our study shows a decline in the FVC combined with an increase in non-invasive and invasive ventilation requirements in adult Pompe disease patients over time.

Conclusions

The STIG real-world study confirms an initial efficacy of ERT in the first years with a secondary sustained decline in multiple outcome measures. Further efforts are required to establish a more valid long-term monitoring and improved therapies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-021-10409-9.

At-Risk Testing for Pompe Disease Using Dried Blood Spots: Lessons Learned for Newborn Screening

Pompe disease (GSD II) is an autosomal recessive disorder caused by deficiency of the lysosomal enzyme acid-α-glucosidase (GAA, EC 3.2.1.20), leading to generalized accumulation of lysosomal glycogen especially in the heart, skeletal, and smooth muscle, and the nervous system. It is generally classified based on the age of onset as infantile (IOPD) presenting during the first year of life, and late onset (LOPD) when it presents afterwards. In our study, a cohort of 13,627 samples were tested between January 2017 and December 2018 for acid-α-glucosidase (GAA, EC 3.2.1.20) deficiency either by fluorometry or tandem mass spectrometry (MS). Testing was performed for patients who displayed conditions of unknown etiology, e.g., CK elevations or cardiomyopathy, in the case of infantile patients. On average 8% of samples showed activity below the reference range and were further assessed by another enzyme activity measurement or molecular genetic analysis. Pre-analytical conditions, like proper drying, greatly affect enzyme activity, and should be assessed with measurement of reference enzyme(s). In conclusion, at-risk testing can provide a good first step for the future introduction of newborn screening for Pompe disease. It yields immediate benefits for the patients regarding the availability and timeliness of the diagnosis. In addition, the laboratory can introduce the required methodology and gain insights in the evaluation of results in a lower throughput environment. Finally, awareness of such a rare condition is increased tremendously among local physicians which can aid in the introduction newborn screening.

Is it Pompe Disease? Australian diagnostic considerations

Pompe Disease is a spectrum disorder with an evolving phenotype in which diagnostic delay is common. Contributing factors include the rarity of the disorder, its wide clinical spectrum, signs and symptoms that overlap with those of other neuromuscular disorders, variable diagnostic approaches, lack of awareness of the clinical manifestations and difficulties in completing the diagnostic inventory. International updates and recommendations have been published providing diagnostic guidelines and management criteria. However, questions remain in the Australian setting. A panel (two neurologists, one clinical geneticist) reviewed the literature, examined clinical questions of relevance to the Australian setting, and developed a framework for the guidance. A wider panel, comprising the initial panel plus eight additional members, critiqued the framework and contributed clinical guidance within the scope of their respective areas of clinical expertise. The resultant expert consensus recommendations build on currently available data to propose an appropriate management framework incorporating the diagnosis, classification, therapeutic approach, multidisciplinary care, and on-going monitoring of patients with Pompe Disease in the Australian setting. It is hoped that diagnostic delay can be reduced with appropriate recourse to evidence-based insights and practical advice on diagnosis and management tailored to the Australian setting.

The Latin American experience with a next generation sequencing genetic panel for recessive limb-girdle muscular weakness and Pompe disease

Background

Limb-girdle muscular dystrophy (LGMD) is a group of neuromuscular disorders of heterogeneous genetic etiology with more than 30 directly related genes. LGMD is characterized by progressive muscle weakness involving the shoulder and pelvic girdles. An important differential diagnosis among patients presenting with proximal muscle weakness (PMW) is late-onset Pompe disease (LOPD), a rare neuromuscular glycogen storage disorder, which often presents with early respiratory insufficiency in addition to PMW. Patients with PMW, with or without respiratory symptoms, were included in this study of Latin American patients to evaluate the profile of variants for the included genes related to LGMD recessive (R) and LOPD and the frequency of variants in each gene among this patient population.

Results

Over 20 institutions across Latin America (Brazil, Argentina, Peru, Ecuador, Mexico, and Chile) enrolled 2103 individuals during 2016 and 2017. Nine autosomal recessive LGMDs and Pompe disease were investigated in a 10-gene panel (ANO5, CAPN3, DYSF, FKRP, GAA, SGCA, SGCB, SGCD, SGCG, TCAP) based on reported disease frequency in Latin America. Sequencing was performed with Illumina’s NextSeq500 and variants were classified according to ACMG guidelines; pathogenic and likely pathogenic were treated as one category (P) and variants of unknown significance (VUS) are described. Genetic variants were identified in 55.8% of patients, with 16% receiving a definitive molecular diagnosis; 39.8% had VUS. Nine patients were identified with Pompe disease.

Conclusions

The results demonstrate the effectiveness of this targeted genetic panel and the importance of including Pompe disease in the differential diagnosis for patients presenting with PMW.

Lysosomes as a therapeutic target

Lysosomes are membrane-bound organelles with roles in processes involved in degrading and recycling cellular waste, cellular signalling and energy metabolism. Defects in genes encoding lysosomal proteins cause lysosomal storage disorders, in which enzyme replacement therapy has proved successful. Growing evidence also implicates roles for lysosomal dysfunction in more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. With a focus on lysosomal dysfunction in autoimmune disorders and neurodegenerative diseases - including lupus, rheumatoid arthritis, multiple sclerosis, Alzheimer disease and Parkinson disease - this Review critically analyses progress and opportunities for therapeutically targeting lysosomal proteins and processes, particularly with small molecules and peptide drugs.

Screening for late-onset Pompe disease in Poland

OBJECTIVES

We aimed to screen for late-onset Pompe disease using the dried blood spot (DBS) test in a cohort of patients with limb-girdle muscle weakness or persistent hyperCKemia.

MATERIALS AND METHODS

Patients with limb-girdle muscle weakness, persistently elevated CK, rigid spine syndrome, dyspnoea, myalgia or sibling of the patient diagnosed with LOPD were included in the study. Acid α-glucosidase (GAA) activity was measured on DBS by tandem mass spectrometry and followed by genetic testing when required. Study was conducted between June 2014 and May 2017.

RESULTS

A total of 337 patients aged 32.2 years (range 2-80) were included in the study. Late-onset Pompe disease was diagnosed in 10 patients (3.0% of tested cohort). All were compound heterozygotes with common c.32-13T>G mutation on one allele and missense or frameshift mutation on the other. Two of the mutations (c.1951delG and c.397T>G) were not reported previously. Seven of the patients started enzyme replacement therapy.

CONCLUSIONS

DBS test is a reliable method for screening for late-onset Pompe disease.

Cardiac Phenotypes in Hereditary Muscle Disorders: JACC State-of-the-Art Review

Hereditary muscular diseases commonly involve the heart. Cardiac manifestations encompass a spectrum of phenotypes, including both cardiomyopathies and rhythm disorders. Common biomarkers suggesting cardiomuscular diseases include increased circulating creatine kinase and/or lactic acid levels or disease-specific metabolic indicators. Cardiac and extra-cardiac traits, imaging tests, family studies, and genetic testing provide precise diagnoses. Cardiac phenotypes are mainly dilated and hypokinetic in dystrophinopathies, Emery-Dreifuss muscular dystrophies, and limb girdle muscular dystrophies; hypertrophic in Friedreich ataxia, mitochondrial diseases, glycogen storage diseases, and fatty acid oxidation disorders; and restrictive in myofibrillar myopathies. Left ventricular noncompaction is variably associated with the different myopathies. Conduction defects and arrhythmias constitute a major phenotype in myotonic dystrophies and skeletal muscle channelopathies. Although the actual cardiac management is rarely based on the cause, the cardiac phenotypes need precise characterization because they are often the only or the predominant manifestations and the prognostic determinants of many hereditary muscle disorders.

Diagnostic tools in late onset Pompe disease (LOPD)

Pompe disease is a rare metabolic disorder due to deficiency of the lysosomal acid alpha-glucosidase (GAA) that causes glycogen accumulation in all tissues with a predominant involvement of skeletal muscle. The late onset form of Pompe disease (LOPD) is characterized by a progressive weakness of proximal and axial muscles, often mimicking limb-girdle muscular dystrophies or inflammatory myopathies, with respiratory distress mainly due to a diaphragmatic weakness. Diagnostic delay is still common, and clinicians need a high index of suspicion to recognize this condition because the disorder is quite rare, the clinical spectrum is wide, and signs and symptoms are not distinguishable from those in other neuromuscular disorders that present in a similar fashion. Diagnostic laboratory tests are quite fast and reliable to detect the enzymatic deficiency. Enzyme replacement therapy has been available for several years, and other new therapeutic strategies such as gene therapy are underway. Here, we discuss the main diagnostic tools currently used for the evaluation of patients with suspected LOPD.

Identification of patients with Pompé disease using routine pathology results: PATHFINDER (creatine kinase) study

Aims

Adult-onset inherited errors of metabolism can be difficult to diagnose. Some cases of potentially treatable myopathy are caused by autosomal recessive acid α-1,4 glucosidase (acid maltase) deficiency (Pompé disease). This study investigated whether screening of asymptomatic patients with elevated creatine kinase (CK) could improve detection of Pompé disease.

Methods

Pathology databases in six hospitals were used to identify patients with elevated CK results (>2× upper limit of normal). Patients were recalled for measurement of acid α-1,4 glucosidase activity in dried blood spot samples.

Results

Samples were obtained from 812 patients with elevated CK. Low α-glucosidase activity was found in 13 patients (1.6%). Patients with neutropaenia (n=4) or who declined further testing (n=1) were excluded. Confirmation plasma specimens were obtained from eight individuals (1%) for a white cell lysosomal enzyme panel, and three (0.4%) were confirmed to have low α-1,4-glucosidase activity. One patient was identified as a heterozygous carrier of an acid α-1,4 glucosidase c.-32–13 G>T mutation. Screening also identified one patient who was found to have undiagnosed Fabry disease and one patient with McArdle’s disease. One patient later presented with Pompé’s after an acute illness. Including the latent case, the frequency of cases at 0.12% was lower than the 2.5% found in studies of patients with raised CK from neurology clinics (p<0.001).

Conclusions

Screening pathology databases for elevated CK may identify patients with inherited metabolic errors affecting muscle metabolism. However, the frequency of Pompé’s disease identified from laboratory populations was less than that in patients referred for neurological investigation.

Rehabilitation management of Pompe disease, from childhood trough adulthood: A systematic review of the literature

Pompe disease (PD) is a rare neuromuscular disorder caused by a deficiency of the enzyme acid alpha-glucosidase. There are three forms of PD depending on the age at onset and clinical severity. PD causes involvement of different organ systems, such as the heart, musculoskeletal system, and respiratory system. As of today, enzyme replacement therapy represents the main therapeutic tool for PD. Rehabilitation is an integral part of a multidisciplinary approach to this pathology. The goal of the present review is to find scientific evidence for the rehabilitative approach to PD, with respect to both the infantile- and adult-onset forms. A systematic literature review was made using the following databases: Pubmed, Pedro, Cochrane Library, EDS Base Index, Trip, and Cinhal. Randomized controlled trials or cohort studies with a sample population of at least six subjects were retrieved. The PICO method was used to formulate the clinical query. The search resulted in 1665 articles. Of these, four cohort studies were subjected to the final phase of the review. Three studies regarded inspiratory muscle training with a threshold, while the fourth study analyzed the effectiveness of therapeutic, aerobic, and reinforcement exercises. Inspiratory muscle training with a threshold increases the pressures generated during inhalation. Aerobic exercise is capable of increasing patients' muscular endurance and performance. To date, however, rehabilitative treatment for patients with PD has no validation in evidencebased medicine. Further studies, possibly with a larger sample size and higher quality are necessary to confirm the effectiveness of rehabilitation in patients with PD.

Comparison of recent pivotal recommendations for the diagnosis and treatment of late-onset Pompe disease using diagnostic nodes-the Pompe disease burden scale

Pompe disease is a rare autosomal-recessive disorder characterised by limb-girdle myopathy and respiratory weakness in the late-onset form (LOPD). Various mutations in the acid alpha-glucosidase gene lead to toxic lysosomal and extra-lysosomal glycogen accumulation in all organs due to ineffective glycogen clearance by the encoded enzyme. Only one randomized trial demonstrated beneficial effects of respiratory function and meters walked in the 6-min walking test with enzyme replacement therapy (ERT). These results were confirmed in several retrospective and prospective observations and in meta-analyses. Due to a potential lifelong therapy, moderate efficacy and high treatment costs time of ERT initiation and cessation is an ongoing matter of debate. So far, several national and international recommendations have been published with different criteria concerning diagnosis, initiation and cessation of ERT in LOPD. We therefore formally analysed recent published recommendations and consensus statements of LOPD using diagnostic nodes (DODES) as a special software tool. With DODES, an objective analysis becomes possible if the content of the recommendations is represented as algorithms using cross-compatible elements. This analysis formally disclosed both, areas of great heterogeneity and concordance for the diagnosis and management of LOPD and paved the way for a Pompe disease burden scale focussing on ERT initiation. According to this investigation further clinical research should concentrate on ERT in pre-symptomatic and severely affected LOPD patients and on cessation criteria for ERT as these issues are areas of international uncertainty and discordance.

Selective screening of late-onset Pompe disease (LOPD) in patients with non-diagnostic muscle biopsies

AIMS

As of 2016, there were five patients with Pompe in Slovenia (two infantile, one childhood and two adult onset) with a prevalence of 1:400 000; however, the prevalence of late-onset Pompe disease (LOPD) in some other countries means this ratio could be an underestimate. Since an LOPD muscle biopsy could be unspecific or even normal, the purpose of this study is to assess the prevalence of LOPD in patients with non-diagnostic muscle biopsies.

METHODS

Six hundred biopsies were recorded at the Neuromuscular Tissue Bank of the University of Ljubljana for the period 2004-2014. All adult patients with non-diagnostic muscle biopsies were invited to the National Slovenian Neuromuscular Centre for dried blood spot testing for LOPD.

RESULTS

A total of 90 patients (56% of those invited) responded. No patient with LOPD was found. A total of 49 patients (54%) had fixed muscle weakness, 31 (34%) had mild symptoms and no weakness and 10 (11%) had asymptomatic hyperCKemia. Ventilatory insufficiency associated with proximal muscle weakness was found in two patients (2%). No patients exhibited vacuolar myopathy, globular accumulations of glycogen or regions of increased acid phosphatase activity within the sarcoplasm.

CONCLUSIONS

The study results do not support the hypothesis that LOPD is underestimated in Slovenian patients with non-diagnostic muscle biopsies; this could be consistent with the fact that LOPD is of low prevalence in Slovenia, as is the case in the populations of Finland, French-speaking Belgium, west Sweden and west Denmark.

Genetic landscape and novel disease mechanisms from a large LGMD cohort of 4656 patients

Objective

Limb‐girdle muscular dystrophies (LGMDs), one of the most heterogeneous neuromuscular disorders (NMDs), involves predominantly proximal‐muscle weakness with >30 genes associated with different subtypes. The clinical‐genetic overlap among subtypes and with other NMDs complicate disease‐subtype identification lengthening diagnostic process, increases overall costs hindering treatment/clinical‐trial recruitment. Currently seven LGMD clinical trials are active but still no gene‐therapy‐related treatment is available. Till‐date no nation‐wide large‐scale LGMD sequencing program was performed. Our objectives were to understand LGMD genetic basis, different subtypes’ relative prevalence across US and investigate underlying disease mechanisms.

Methods

A total of 4656 patients with clinically suspected‐LGMD across US were recruited to conduct next‐generation sequencing (NGS)‐based gene‐panel testing during June‐2015 to June‐2017 in CLIA‐CAP‐certified Emory‐Genetics‐Laboratory. Thirty‐five LGMD‐subtypes‐associated or LGMD‐like other NMD‐associated genes were investigated. Main outcomes were diagnostic yield, gene‐variant spectrum, and LGMD subtypes’ prevalence in a large US LGMD‐suspected population.

Results

Molecular diagnosis was established in 27% (1259 cases; 95% CI, 26–29%) of the patients with major contributing genes to LGMD phenotypes being: CAPN3(17%), DYSF(16%), FKRP(9%) and ANO5(7%). We observed an increased prevalence of genetically confirmed late‐onset Pompe disease, DNAJB6‐associated LGMD subtype1E and CAPN3‐associated autosomal‐dominant LGMDs. Interestingly, we identified a high prevalence of patients with pathogenic variants in more than one LGMD gene suggesting possible synergistic heterozygosity/digenic/multigenic contribution to disease presentation/progression that needs consideration as a part of diagnostic modality.

Interpretation

Overall, this study has improved our understanding of the relative prevalence of different LGMD subtypes, their respective genetic etiology, and the changing paradigm of their inheritance modes and novel mechanisms that will allow for improved timely treatment, management, and enrolment of molecularly diagnosed individuals in clinical trials.

Vacuolated PAS-Positive Lymphocytes on Blood Smear: An Easy Screening Tool and a Possible Biomarker for Monitoring Therapeutic Responses in Late Onset Pompe Disease (LOPD)

Background: Primary aim was to investigate the diagnostic value of PAS-positive vacuolated lymphocytes on blood smear in Late Onset Pompe Disease (LOPD) patients and, secondly, to evaluate its potential utility in monitoring treatment effects.

Methods: We examined blood smear of 26 LOPD patients. We evaluated 10 treated and 16 untreated LOPD patients. Among the latter group, 7 patients later initiated ERT and were tested again 6 months after start. Blood smear was also sampled from 82 controls and 19 patients with other muscle glycogenoses (MGSDs). PAS staining was used to evaluate: (1) presence of lymphocytes with glycogen-filled vacuoles, (2) quantification of vacuolated lymphocytes.

Results: We found that PAS-positive lymphocytes were significantly higher in LOPD patients than in controls or other MGSDs (p < 0.05 and p < 0.001, respectively). ROC curve for discriminating between untreated LOPD patients and controls yielded an AUC of 1.00 (95%CI 1.00–1.00; p < 0.0001). PAS-positive lymphocyte cutoff level of >10 yielded sensitivity of 100% (95%CI 78–100%), specificity of 100% (95%CI 96–100%), and positive predictive value of 100%. Patients studied before and after ERT showed a dramatic decrease of PAS-positive vacuolated lymphocytes number (p = 0.016). In other MGSDs, PAS-positive lymphocytes were significantly lower that untreated LOPD patients but higher than controls.

Conclusions: Our data suggest that the Blood Smear Examination (BSE) for PAS-positive lymphocytes quantification could be used as a simple and sensitive test for a quick screening of suspected Pompe disease. The quantification of vacuolated lymphocytes appears to be also a valuable tool for monitoring the efficacy of treatment in LOPD patients.

Late-onset Pompe disease: what is the prevalence of limb-girdle muscular weakness presentation?

Pompe disease is an inherited disease caused by acid alpha-glucosidase (GAA) deficiency. A single center observational study aimed at assessing the prevalence of late-onset Pompe disease in a high-risk Brazilian population, using the dried blood spot test to detect GAA deficiency as a main screening tool. Dried blood spots were collected for GAA activity assay from 24 patients with "unexplained" limb-girdle muscular weakness without vacuolar myopathy in their muscle biopsy. Samples with reduced enzyme activity were also investigated for GAA gene mutations. Of the 24 patients with dried blood spots, one patient (4.2%) showed low GAA enzyme activity (NaG/AaGIA: 40.42; %INH: 87.22%). In this patient, genetic analysis confirmed two heterozygous mutations in the GAA gene (c.-32-13T>G/p.Arg854Ter). Our data confirm that clinicians should look for late-onset Pompe disease in patients whose clinical manifestation is an "unexplained" limb-girdle weakness even without vacuolar myopathy in muscle biopsy.

Low Prevalence Estimates of Late-Onset Glycogen Storage Disease Type II in French-Speaking Belgium are not Due to Missed Diagnoses

BACKGROUND

Late-onset glycogen storage disease type II is associated with variable muscle phenotypes. Epidemiological data suggest that its prevalence is lower in Belgium than in bordering countries like The Netherlands.

OBJECTIVE

We investigated whether such low estimated prevalence is due to missed diagnoses.

METHODS

We screened 100 patients with muscle phenotypes of undetermined origin using a dried blood spot test for alpha-acid glucosidase (GAA) activity. Patients with low activity at screening were re-tested by the same method and, if low activity was confirmed, GAA gene analysis was performed.

RESULTS

The screening test revealed lower than normal GAA activity in 15 patients, but in only two of them it was low enough to be considered in the disease range. Retesting confirmed lower than normal GAA activity in five patients, but in all of them it was above the disease range. A single patient carried a heterozygous known pathogenic GAA mutation, whose significance in this case remains undetermined.

CONCLUSIONS

We conclude that reported low prevalence estimates in Belgium are not likely to be due to an underdiagnosis bias. Lower prevalence compared to neighbouring The Netherlands may be due to different ethnic stratification of our patients. Diagnostic strategies should keep into account the expected prevalence of a disease in specific populations.

Update on diagnostics of metabolic myopathies

PURPOSE OF REVIEW

This review aims to highlight the most relevant clinical and laboratory findings, regarding acute and progressive metabolic myopathies, and to develop an algorithm addressing clinicians to clinical practice.

RECENT FINDINGS

Although diagnosis of metabolic myopathies remains still challenging, the recent identification of new disorders has increased the number of patients requiring specific investigations. Nowadays, a more detailed characterization of the clinical spectrum of metabolic myopathies improved awareness as well as a deeper knowledge on their natural history or multisystem involvement. Diagnostic procedures, as first-line screening tests are necessary for an earlier and more accurate diagnostic work up, not only in infantile cases, but also in adults with suspected metabolic myopathies. New generation diagnostic techniques such as NGS (Next Generation Sequencing) and whole exome/genome sequencing have emerged as innovative tools to extensively evaluate either known genes variants or new candidate genes as possible causes of metabolic myopathies.

SUMMARY

Diagnosis of metabolic myopathies is still challenging for clinicians because of rarity and clinical heterogeneity which is often overlapping with other neuromuscular disorders. Detailed algorithms supported by advanced laboratory investigations may be helpful to timely reach a diagnosis, so allowing an earlier therapeutic decision.

Vacuolated PAS-positive lymphocytes as an hallmark of Pompe disease and other myopathies related to impaired autophagy

Autosomal recessive Pompe disease is a lysosomal disorder caused by mutations of the acid-α-glucosidase (GAA) gene. Deficiency of GAA enzyme leads to glycogen accumulation and autophagy impairment in cardiac and skeletal muscles, but also in lymphocytes. Since an effective therapy is available, a rapid, sensitive, and specific test is crucial to early identify affected subjects. Number of lymphocytes containing PAS-positive vacuoles was evaluated on blood films from 72 consecutive adult patients with hyperckemia and/or muscle weakness, 13 genetically confirmed late-onset-Pompe-disease (LOPD) and 13 of their offspring. GAA activity, measured on dried blood spot (DBS) in all patients inversely correlated with number of PAS-positive lymphocytes. More than 4 PAS-positive lymphocytes were found in 11 out of the 72 patients (6 new diagnosis of LOPD, 3 different glycogen storage myopathies, 1 glucose-6-phosphate dehydrogenase deficiency, 1 caveolinopathy), in all 13 LOPD patients and in the 13 LOPD offspring. These latter resulted to have all a single GAA mutation but low GAA levels. Immunostaining with the autophagy markers LC3 and p62 confirmed the autophagic nature of lymphocytes vacuoles. ROC curve assessment of PAS-positive lymphocytes disclosed 100% of sensitivity and 94% of specificity in recognizing both compound heterozygous and heterozygous GAA carriers. The other myopathies with more than 4 PAS-positive lymphocytes appeared to be all related to impaired autophagy, which seems to be responsible of PAS-positive vacuolated lymphocytes formation. Quantification of PAS-positive lymphocytes in blood films is useful to identify autophagic vacuolar myopathies and should be routinely used as first level test for Pompe disease.

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.

Screening for late-onset Pompe disease in western Denmark

OBJECTIVE

Late-onset Pompe disease (LOPD) is a rare autosomal recessively inherited metabolic myopathy caused by reduced activity of the lysosomal enzyme alpha-glucosidase. In a previous screening study at two large neuromuscular university clinics in Denmark, three patients with LOPD were identified out of 103 patients screened. No systematic screening has been performed at the other neurological departments in the western part of Denmark. Thus, patients with a diagnosis of unspecified myopathy were screened for LOPD.

MATERIALS AND METHODS

At seven neurological departments in the western part of Denmark, medical records were evaluated for all patients registered with myopathy diagnosis codes (ICD 10 codes: G 71.0-71.9 and G 72.0-72.9) during the period January 1, 2002, to December 31, 2012. If no specific diagnosis has been reached, patients were invited for screening. Dried blood spot (DBS) test was used to analyze the activity of the enzyme alpha-glucosidase.

RESULT

A total of 654 patients were identified. From the medical records, information was obtained concerning symptoms, family history, electromyography, muscle biopsy results and creatine kinase levels. Eighty-seven patients (13.3%) (males 61%) at a mean age of 53.3 years (SD 16.5) fulfilled the criteria for screening. A DBS test was performed in 47 (54%) patients. In all patients, the enzyme activity was within reference values.

CONCLUSION

None of the screened patients had a reduced activity of the enzyme alpha-glucosidase. Although the cohort studied was small, our findings do not suggest that LOPD is underdiagnosed in patients with unspecified myopathy in western Denmark.

Metabolic myopathies: a practical approach

Metabolic myopathies are a diverse group of rare genetic disorders and their associated muscle symptoms may be subtle. Patients may present with indolent myopathic features, exercise intolerance or recurrent rhabdomyolysis. Diagnostic delays are common and clinicians need a high index of suspicion to recognise and differentiate metabolic myopathies from other conditions that present in a similar fashion. Standard laboratory tests may be normal or non-specific, particularly between symptomatic episodes. Targeted enzyme activity measurement and next-generation genetic sequencing are increasingly used. There are now specific enzyme replacement therapies available, and other metabolic strategies and gene therapies are undergoing clinical trials. Here, we discuss our approach to the adult patient with suspected metabolic myopathy. We outline key features in the history and examination and discuss some mimics of metabolic myopathies. We highlight some disorders of glycogen and fatty acid utilisation that present in adulthood and outline current recommendations on management.

Prevalence of adult Pompe disease in patients with proximal myopathic syndrome and undiagnosed muscle biopsy

We examined patients with limb-girdle muscle weakness and/or hyper-CKaemia and undiagnosed muscle biopsy for late onset Pompe disease (LOPD). Patients with an inconclusive limb-girdle muscle weakness who presented at our neuromuscular centre between 2005 and 2015 with undiagnosed muscle biopsies were examined by dry blood spot testing (DBS) including determination of the enzyme activity of acid alpha-glucosidase (GAA). In the case of depressed enzyme activity, additional gene testing of the GAA gene was carried out. Of the 340 evaluated muscle biopsies, 69 patients fulfilled the inclusion criteria and were examined with DBS. Among those patients, 76% showed a limb-girdle muscle weakness and 14% showed a hyper-CKaemia. A diagnosis of LOPD could be established in the case of two patients (2.9%) with reduced GAA enzyme activity and proof of mutations in the GAA gene. One of the two patients presents in the muscle biopsy suggestive features of Pompe disease including vacuoles with positive acid phosphatase reaction. In summary, our results show that a muscle biopsy can be helpful in identifying LOPD patients, but vacuolation with glycogen storage can also be absent. An inconspicuous muscle biopsy does not rule out Pompe disease. Consequently, all patients with limb-girdle muscle weakness should be examined by DBS before conducting a muscle biopsy.

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.

Identification of GAA variants through whole exome sequencing targeted to a cohort of 606 patients with unexplained limb-girdle muscle weakness

Background

Late-onset Pompe disease is a rare genetic neuromuscular disorder caused by a primary deficiency of α-glucosidase and the associated accumulation of glycogen in lysosomal vacuoles. The deficiency of α-glucosidase can often be detected using an inexpensive and readily accessible dried blood spot test when Pompe disease is suspected. Like several neuromuscular disorders, Pompe disease typically presents with progressive weakness of limb-girdle muscles and respiratory insufficiency. Due to the phenotypic heterogeneity of these disorders, however, it is often difficult for clinicians to reach a diagnosis for patients with Pompe disease. Six hundred and six patients from a European population were recruited onto our study. Inclusion criteria stipulated that index cases must present with limb-girdle weakness or elevated serum creatine kinase activity. Whole exome sequencing with at least 250 ng DNA was completed using an Illumina exome capture and a 38 Mb baited target. A panel of 169 candidate genes for limb-girdle weakness was analysed for disease-causing variants.

Results

A total of 35 variants within GAA were detected. Ten distinct variants in eight unrelated index cases (and four siblings not sequenced in our study) were considered disease-causing, with the patients presenting with heterogeneous phenotypes. The eight unrelated individuals were compound heterozygotes for two variants. Six patients carried the intronic splice site c.-13 T > G transversion and two of the six patients also carried the exonic p.Glu176ArgfsTer45 frameshift. Four of the ten variants were novel in their association with Pompe disease.

Conclusions

Here, we highlight the advantage of using whole exome sequencing as a tool for detecting, diagnosing and treating patients with rare, clinically variable genetic disorders.

[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.

European consensus for starting and stopping enzyme replacement therapy in adult patients with Pompe disease: a 10-year experience

BACKGROUND AND PURPOSE

Pompe disease is a rare inheritable muscle disorder for which enzyme replacement therapy (ERT) has been available since 2006. Uniform criteria for starting and stopping ERT in adult patients were developed and reported here.

METHODS

Three consensus meetings were organized through the European Pompe Consortium, a network of experts from 11 European countries in the field of Pompe disease. A systematic review of the literature was undertaken to determine the effectiveness of ERT in adult patients on a range of clinical outcome measures and quality of life. A narrative synthesis is presented.

RESULTS

Consensus was reached on how the diagnosis of Pompe disease should be confirmed, when treatment should be started, reasons for stopping treatment and the use of ERT during pregnancy. This was based on expert opinion and supported by the literature. One clinical trial and 43 observational studies, covering a total of 586 individual adult patients, provided evidence of a beneficial effect of ERT at group level. At individual patient level, the response to treatment varied, but factors associated with a patient's response to ERT were not described in many studies. Eleven observational studies focused on more severely affected patients, suggesting that ERT can also be beneficial in these patients. There are no studies on the effects of ERT in pre-symptomatic patients.

CONCLUSIONS

This is the first European consensus recommendation for starting and stopping ERT in adult patients with Pompe disease, based on the extensive experience of experts from different countries.

Targeted population screening of late onset Pompe disease in unspecified myopathy patients for Korean population

We performed targeted population screening of late onset Pompe disease (LOPD) in unspecified myopathy patients, because early diagnosis is difficult due to its heterogeneous clinical features. We prospectively enrolled 90 unrelated myopathic patients who had one or more signs out of five LOPD-like clinical findings (proximal weakness, axial weakness, lingual weakness, respiratory difficulty, idiopathic hyperCKemia). Acid alpha glucosidase activity was evaluated with dried blood spot and mixed leukocyte simultaneously. For a final diagnosis of LOPD, 16 patients with decreased enzyme activity were genotyped by GAA molecular analysis. We found two patients with LOPD (2.2%), and the remaining 14 patients had at least one G576S or E689K mutation, known as the pseudodeficiency allele. Acid alpha glucosidase activity of LOPD patients was significantly lower than that of patients with at least one pseudodeficiency allele (p = 0.017). This study is the first LOPD screening study for targeted Korean population, and more generally, an Asian population. Our findings suggest that for diagnosis of LOPD in Asian population, modified cutoff value of acid alpha glucosidase activity with dry blood spot considering that of patients having heterozygote pathogenic variants or pseudodeficiency alleles may reduce time and cost requirements and increase the comfort of patients.

The emerging phenotype of late-onset Pompe disease: A systematic literature review

BACKGROUND

Pompe disease is an autosomal recessive disorder caused by deficiency of the lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA). The adult-onset form, late-onset Pompe disease (LOPD), has been characterized by glycogen accumulation primarily in skeletal, cardiac, and smooth muscles, causing weakness of the proximal limb girdle and respiratory muscles. However, increased scientific study of LOPD continues to enhance understanding of an evolving phenotype.

PURPOSE

To expand our understanding of the evolving phenotype of LOPD since the approval of enzyme replacement therapy (ERT) with alglucosidase alfa (Myozyme™/Lumizyme™) in 2006.

METHODS

All articles were included in the review that provided data on the charactertistics of LOPD identified via the PubMed database published since the approval of ERT in 2006. All signs and symptoms of the disease that were reported in the literature were identified and included in the review.

RESULTS

We provide a comprehensive review of the evolving phenotype of LOPD. Our findings support and extend the knowledge of the multisystemic nature of the disease.

CONCLUSIONS

With the advent of ERT and the concurrent increase in the scientific study of LOPD, the condition once primarily conceptualized as a limb-girdle muscle disease with prominent respiratory involvement is increasingly recognized to be a condition that results in signs and symptoms across body systems and structures.