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

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.

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 in India - Beyond the Caucasian phenotype

We evaluated the clinical histories, motor and pulmonary functions, cardiac phenotypes and GAA genotypes of an Indian cohort of twenty patients with late onset Pompe disease (LOPD) in this multi-centre study. A mean age at onset of symptoms and diagnosis of 9.9 ± 9.7 years and 15.8 ± 12.1 years respectively was identified. All patients had lower extremity limb-girdle muscle weakness. Seven required ventilatory support and seven used mobility assists. Of the four who used both assists, two received ventilatory support prior to wheelchair use. Cardiac involvement was seen in eight patients with various combinations of left ventricular hypertrophy, tricuspid regurgitation, cardiomyopathy, dilated ventricles with biventricular dysfunction and aortic regurgitation. Amongst 20 biochemically diagnosed patients (low residual GAA enzyme activity) GAA genotypes of 19 patients identified homozygous variants in eight and compound heterozygous in 11: 27 missense, 3 nonsense, 2 initiator codon, 3 splice site and one deletion. Nine variants in 7 patients were novel. The leaky Caucasian, splice site LOPD variant, c.-32-13T>G mutation was absent. This first study from India provides an insight into a more severe LOPD phenotype with earlier disease onset at 9.9 years compared to 33.3 years in Caucasian patients, and cardiac involvement more than previously reported. The need for improvement in awareness and diagnosis of LOPD in India is highlighted.

Genetic cause of heterogeneous inherited myopathies in a cohort of Greek patients

Inherited muscle disorders are caused by pathogenic changes in numerous genes. Herein, we aimed to investigate the etiology of muscle disease in 24 consecutive Greek patients with myopathy suspected to be genetic in origin, based on clinical presentation and laboratory and electrophysiological findings and absence of known acquired causes of myopathy. Of these, 16 patients (8 females, median 24 years-old, range 7 to 67 years-old) were diagnosed by Whole Exome Sequencing as suffering from a specific type of inherited muscle disorder. Specifically, we have identified causative variants in 6 limb-girdle muscular dystrophy genes (6 patients; ANO5, CAPN3, DYSF, ISPD, LAMA2, SGCA), 3 metabolic myopathy genes (4 patients; CPT2, ETFDH, GAA), 1 congenital myotonia gene (1 patient; CLCN1), 1 mitochondrial myopathy gene (1 patient; MT-TE) and 3 other myopathy-associated genes (4 patients; CAV3, LMNA, MYOT). In 6 additional family members affected by myopathy, we reached genetic diagnosis following identification of a causative variant in an index patient. In our patients, genetic diagnosis ended a lengthy diagnostic process and, in the case of Multiple acyl-CoA dehydrogenase deficiency and Pompe's disease, it enabled specific treatment to be initiated. These results further expand the genotypic and phenotypic spectrum of inherited myopathies.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

An update on diagnosis and therapy of metabolic myopathies

INTRODUCTION

Metabolic myopathies are a heterogeneous group of disorders characterized by inherited defects of enzymatic pathways involved in muscle fiber energetics. Diagnosing metabolic myopathies requires a thoroughly taken individual and family history, a meticulous neurologic exam, exercise tests, blood and urine tests, needle-electromyography, nerve-conduction studies, muscle biopsy, targeted genetic tests, or next-generation sequencing. There is limited evidence from the literature to guide treatment of metabolic myopathies. Treatment is largely limited to non-invasive/invasive symptomatic measures. However, promising results have been achieved with enzyme replacement therapy in Pompe disease (GSD-II). Primary coenzyme-Q deficiency responds favorably to coenzyme-Q supplementation. MNGIE responds to allogeneic hematopoietic stem cell transplantation, orthotopic liver transplantation, and carrier erythrocyte entrapped thymidine phosphorylase enzyme therapy. MADD may respond to riboflavin. Areas covered: This review aims to summarize and discuss recent findings and new insights concerning diagnosis and treatment of metabolic myopathies. Expert commentary: Except for GSD-II, coenzyme-Q deficiency, and MNGIE, treatment of metabolic myopathies is usually palliative and supportive (non-invasive or invasive). Non-invasive symptomatic treatment includes physiotherapy, diet, administration of drugs, conservative orthopedic measures, and respiratory non-invasive support. Important is the avoidance of triggers for episodic forms of fatty acid oxidation disorders. Invasive measures include orthopedic surgery and invasive mechanical ventilation.

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.

[Research advances in the diagnosis and treatment of Pompe disease]

Pompe disease, also called type II glycogen storage disease, is a rare autosomal recessive inherited disease caused by the storage of glycogen in lysosome due to acid α-glucosidase (GAA) deficiency, with the most severe conditions in the skeletal muscle, the myocardium, and the smooth muscle. Patients may have the manifestations of dyspnea and dyskinesia, with or without hypertrophic cardiomyopathy. GAA gene mutation has ethnic and regional differences, and new mutation sites are found with the advances in research. Gene analysis is the gold standard for the diagnosis of Pompe disease. Conventional methods, such as skin and muscle biopsies and dried blood spot test, have certain limitations for the diagnosis of this disease. In recent years, prenatal diagnosis and newborn screening play an important role in early diagnosis of this disease. Enzyme replacement therapy (ERT) has a satisfactory effect in the treatment of this disease, but it may lead to immune intolerance. New targeted gene therapy and modified ERT will be put into practice in the future. This article reviews the research advances in the diagnosis and treatment of Pompe disease.