Newborn screening for Pompe disease in Japan: report and literature review of mutations in the GAA gene in Japanese and Asian patients

Efficacy and safety of avalglucosidase alfa in Japanese patients with late-onset and infantile-onset Pompe diseases: A case series from clinical trials

Background

The efficacy and safety of avalglucosidase alfa for Pompe disease (PD) have been demonstrated in a global Phase 3 trial (COMET) in patients with late-onset PD (LOPD) and a global Phase 2 trial (Mini-COMET) in patients with infantile-onset PD (IOPD). This case series examines the individual results of three Japanese patients enrolled in these trials.

Methods

Case reports were assembled from data collected in the COMET and Mini-COMET trials. Detailed methods have been reported previously. The primary endpoint of COMET was change from baseline to week 49 in upright forced vital capacity percent (FVC %) predicted. The primary endpoint of Mini-COMET was safety and tolerability of avalglucosidase alfa. In both trials, key secondary endpoints included motor function tests and other qualitative measures of improvement. Changes in biomarkers and anti-drug antibodies were also assessed in both trials.

Results

Results for Japanese patients were representative of those from the overall populations in the COMET and Mini-COMET trials. We detail results for one Japanese patient with LOPD enrolled in the COMET trial and two Japanese patients with IOPD enrolled in the Mini-COMET trial. Importantly, avalglucosidase alfa was well tolerated at doses of both 20 mg/kg and 40 mg/kg in Japanese patients with LOPD and IOPD, respectively.

Conclusions

Although the number of patients was small, avalglucosidase alfa provides an efficacy and safety profile in Japanese patients representative of the overall populations from key global clinical trials.

Global birth prevalence of Pompe disease: A systematic review and meta-analysis

BACKGROUND

Pompe disease, also known as Glycogen storage disease type II, is an autosomal recessive disorder caused by defects in alpha-glucosidase, resulting in abnormal glycogen accumulation.

METHODS

To conduct a systematic review and meta-analysis of birth prevalence of Pompe disease, the MEDLINE and EMBASE databases were searched for original research articles on the epidemiology of Pompe disease from inception until July 01, 2024. Meta-analysis was performed to estimate global birth prevalence of Pompe disease. The funnel plot was used to describe potential publication bias.

RESULTS

Twenty-two studies, screened out of 945 records, were included for data extraction. Studies that fulfilled inclusion criteria involved 15 areas/countries. Global birth prevalence of Pompe disease was 2.0 cases (95% CI: 1.5-2.4) per 100,000 live births. Global birth prevalence of infantile-onset Pompe disease was 1.0 cases (95% CI: 0.5-1.5) per 100,000 live births. Global birth prevalence of late-onset Pompe disease was 2.4 cases (95% CI: 1.8-3.0) per 100,000 live births. The main limitations are that no study was assessed as high-quality and approximately half of the studies were from Europe.

CONCLUSIONS

Quantitative data on the global epidemiology of Pompe disease could be the fundamental to evaluate the global efforts on building a better world for Pompe disease patients.

Global carrier frequency and predicted genetic prevalence of patients with pathogenic sequence variants in autosomal recessive genetic neuromuscular diseases

Genetic neuromuscular diseases are clinically and genetically heterogeneous genetic disorders that primarily affect the peripheral nerves, muscles, and neuromuscular junctions. This study aimed to identify pathogenic variants, calculate carrier frequency, and predict the genetic prevalence of autosomal recessive neuromuscular diseases (AR-NMDs). We selected 268 AR-NMD genes and analyzed their genetic variants sourced from the gnomAD database. After identifying the pathogenic variants using an algorithm, we calculated the carrier frequency and predicted the genetic prevalence of AR-NMDs. In total, 10,887 pathogenic variants were identified, including 3848 literature verified and 7039 manually verified variants. In the global population, the carrier frequency of AR-NMDs is 32.9%, with variations across subpopulations ranging from 22.4% in the Finnish population to 36.2% in the non-Finnish European population. The predicted genetic prevalence of AR-NMDs was estimated to be 24.3 cases per 100,000 individuals worldwide, with variations across subpopulations ranging from 26.5 to 41.4 cases per 100,000 individuals in the Latino/Admixed American and the Ashkenazi Jewish populations, respectively. The AR-NMD gene with the highest carrier frequency was GAA (1.3%) and the variant with the highest allele frequency was c.-32-13 T>G in GAA with 0.0033 in the global population. Our study revealed a higher-than-expected frequency of AR-NMD carriers, constituting approximately one-third of the global population, highlighting ethnic heterogeneity in genetic susceptibility.

Lysosomal Dysfunction: Connecting the Dots in the Landscape of Human Diseases

Lysosomes are the main organelles responsible for the degradation of macromolecules in eukaryotic cells. Beyond their fundamental role in degradation, lysosomes are involved in different physiological processes such as autophagy, nutrient sensing, and intracellular signaling. In some circumstances, lysosomal abnormalities underlie several human pathologies with different etiologies known as known as lysosomal storage disorders (LSDs). These disorders can result from deficiencies in primary lysosomal enzymes, dysfunction of lysosomal enzyme activators, alterations in modifiers that impact lysosomal function, or changes in membrane-associated proteins, among other factors. The clinical phenotype observed in affected patients hinges on the type and location of the accumulating substrate, influenced by genetic mutations and residual enzyme activity. In this context, the scientific community is dedicated to exploring potential therapeutic approaches, striving not only to extend lifespan but also to enhance the overall quality of life for individuals afflicted with LSDs. This review provides insights into lysosomal dysfunction from a molecular perspective, particularly in the context of human diseases, and highlights recent advancements and breakthroughs in this field.

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.

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

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

The Clinical Management of Pompe Disease: A Pediatric Perspective

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

A rapid and non-invasive proteomic analysis using DBS and buccal swab for multiplexed second-tier screening of Pompe disease and Mucopolysaccharidosis type I

PURPOSE

Current newborn screening programs for Pompe disease (PD) and mucopolysaccharidosis type I (MPS I) suffer from a high false positive rate and long turnaround time for clinical follow up. This study aimed to develop a novel proteomics-based assay for rapid and accurate second-tier screening of PD and MPS I. A fast turnaround assay would enable the identification of severe cases who need immediate clinical follow up and treatment.

METHODS

We developed an immunocapture coupled with mass spectrometry-based proteomics (Immuno-SRM) assay to quantify GAA and IDUA proteins in dried blood spots (DBS) and buccal swabs. Sensitivity, linearity, reproducibility, and protein concentration range in healthy control samples were determined. Clinical performance was evaluated in known PD and MPS I patients as well as pseudodeficiency and carrier cases.

RESULTS

Using three 3.2 mm punches (~13.1 μL of blood) of DBS, the assay showed reproducible and sensitive quantification of GAA and IDUA. Both proteins can also be quantified in buccal swabs with high reproducibility and sensitivity. Infantile onset Pompe disease (IOPD) and severe MPS I cases are readily identifiable due to the absence of GAA and IDUA, respectively. In addition, late onset Pompe disease (LOPD) and attenuated MPS I patients showed much reduced levels of the target protein. By contrast, pseudodeficiency and carrier cases exhibited significant higher target protein levels compared to true patients.

CONCLUSION

Direct quantification of endogenous GAA and IDUA peptides in DBS by Immuno-SRM can be used for second-tier screening to rapidly identify severe PD and MPS I patients with a turnaround time of <1 week. Such patients could benefit from immediate clinical follow up and possibly earlier treatment.

Outcome of Later-Onset Pompe Disease Identified Through Newborn Screening

OBJECTIVE

To determine the outcomes of patients with later-onset Pompe disease (LOPD) identified through newborn screening (NBS).

STUDY DESIGN

A prospective observational cohort study was conducted from the initiation of Pompe disease NBS by following subjects every 3-12 months for motor development and biochemical markers.

RESULTS

Between 2005 and 2018, 39 of 994 975 newborns evaluated were classified as having LOPD based on low acid α-glucosidase (GAA) activity but no cardiac involvement at the time of screening. As of December 2020, 8 of these 39 infants (21%) were treated with enzyme replacement therapy owing to persistent elevation of creatine kinase (CK), cardiac involvement, or developmental delay. All subjects' physical performance and endurance improved after treatment. Subjects carrying c.[752C>T;761C>T] and c.[546+5G>T; 1726G>A] presented a phenotype of nonprogressive hypotonia, muscle weakness, and impairment in physical fitness tests, but they have not received treatment.

CONCLUSIONS

One-fifth of subjects identified through NBS as having LOPD developed symptoms after a follow-up of up to 15 years. NBS was found to facilitate the early detection and early treatment of those subjects. GAA variants c.[752C>T;761C>T] and c.[546+5G>T; 1726G>A] might not cause Pompe disease but still may affect skeletal muscle function.

Muscle biochemical and pathological diagnosis in Pompe disease

BACKGROUND AND OBJECTIVES

Pompe disease is reportedly less prevalent in Japan than in neighbouring countries, raising a possibility that some patients may be overlooked. Therefore, all muscle biopsy samples received at our institute were screened for Pompe disease to determine the accuracy of the disease prevalence.

METHODS

The acid α-glucosidase (GAA) activity was assayed using 10 µm frozen muscle sections from 2408 muscle biopsies received between July 2015 and January 2018. Genetic analysis was performed for samples with decreased activity. The number of myopathologically diagnosed patients was retrospectively assessed.

RESULTS

The GAA activity was distributed similarly to previous results from dried blood spot screening. GAA activity measured using muscle sections corresponded to that measured using muscle blocks. Of 163 patients with GAA activity <3 nmol/hour/mg protein, 43 (26%) patients had homozygous pseudodeficiency alleles in GAA (p.G576S and p.E689K). In the retrospective analysis, the number of patients diagnosed with Pompe disease via muscle biopsies decreased to zero over time.

DISCUSSION

Muscle pathology is an accurate method to diagnose Pompe disease. It is unlikely that a significant number of patients with Pompe disease are overlooked. Pathological variants were rare, and the majority carried a pseudodeficiency allele, which further supports our conclusion.

The earliest enzyme replacement for infantile-onset Pompe disease in Japan

BACKGROUND

Infantile-onset Pompe disease (IOPD) is the most severe phenotype of a lysosomal storage disorder caused by acid alpha-glucosidase (GAA) deficiency. An enzymatic newborn screening (NBS) program started regionally in Japan in 2013 for early enzyme replacement therapy (ERT). We report the ERT responses of the first NBS-identified Japanese IOPD case and of another case diagnosed prior to NBS, to discuss the problems of promptly starting ERT in Japan.

METHODS

Acid alpha-glucosidase activity was measured by fluorometric assay in both patients. The diagnosis of IOPD was confirmed by next-generation followed by Sanger-method sequencing (patient 1) or direct sequencing of polymerase chain reaction (PCR)-amplified products (patient 2) of the GAA gene.

RESULTS

A female infant identified by NBS had a novel out-of-frame (p.F181Dfs*6) variant and a reported pathogenic (p.R600C) variant, along with two pseudodeficiency variants. Enzyme replacement therapy was started at age 58 days when the infant had increased serum levels of creatine kinase and slight myocardial hypertrophy. Clinical and biochemical markers improved promptly. She has been alive and well without delayed development at age 14 months. Patient 2, a Japanese male, received a diagnosis of IOPD at age 5 months before the NBS era. He had a homozygotic variant of GAA (p.R608X), later registered as a cross-reactive immunological material (CRIM)-negative genotype, and developed a high titer of anti-rhGAA antibodies. The patient has survived myocardial hypertrophy with continuous respiratory support for 12 years of ERT.

CONCLUSIONS

Enzyme replacement therapy should not be delayed over the age of 2 months for reversible cardiac function, although CRIM-negative cases may hamper turnaround time reduction.

Duchenne Muscular Dystrophy With Low Acidic α-Glucosidase Activity: Two Case Reports and Literature Review

BACKGROUND

Pompe disease is usually considered in children with elevated creatine kinase (CK) levels and decreased acidic α-glucosidase (GAA) enzyme activity. However, there are exceptions, such as GAA pseudo deficiency alleles, which result in lower GAA enzyme activity but do not cause Pompe disease. Here, we report two cases presenting with high CK levels and low GAA activity who were ultimately diagnosed with Duchenne muscular dystrophy (DMD).

CASE PRESENTATION

Case 1 patient was a 2-month-old boy who presented with an extremely high serum CK level (5,480∼11,880 U/L) and low GAA activity (2.72 nmol/1 h/mg). The whole-exome sequencing did not find the pathogenic GAA gene mutation, however, there was a DMD gene hemizygous variation (c. 7657C > T, p. Arg2553Ter) inherited from his mother, which was verified by the first-generation sequencing. Further genetic analysis of GAA identified two homozygous pseudo deficiency alleles (c.1726G > A, p. Gly576Ser and c.2065G > A, p. Glu689Lys), which were believed to induce the patient's low GAA activity. Therefore, the boy was diagnosed with DMD, although he had extremely low GAA activity. Case 2 patient was also a 2-month-old boy presenting with a significant increase in CK level (12,408∼24,828 U/L). His blood GAA activity (colorimetric method) was 9.02 nmol/1 h/mg. Similarly, his whole-exome sequencing did not find the pathogenic mutation of the GAA gene, but a DMD gene hemizygous variation (c.5571del, p. Lys1857AsnfsTer8), hence he was diagnosed with DMD as well. Regarding GAA activity, the case 2 patient was not as low as the case 1 patient, mainly because his two GAA pseudo deficiency alleles were heterozygous.

CONCLUSION

Pompe disease is usually screened in infants with high CK levels. We should be aware that pseudo deficiency alleles can cause low GAA activities but not Pompe disease. Genetic tests would be helpful to distinguish cases with GAA pseudo deficiency alleles from patients with some muscular disorder diseases such as DMD.

Current status of newborn screening for Pompe disease in Japan

Background

Pompe disease is an autosomal recessive inherited metabolic disorder caused by a deficiency of the acid α-glucosidase (GAA). Pompe disease manifests as an accumulation of lysosomal glycogen in the skeletal and heart muscle. We conducted newborn screening (NBS) for Pompe disease in Japan from April 2013 to October 2020 to determine the feasibility and utility of NBS for Pompe disease.

Results

From the 296,759 newborns whose enzyme activity was measured, 107 of which underwent GAA analysis, we found one patient with infantile-onset Pompe disease (IOPD) and seven with potential late-onset Pompe disease (LOPD). We identified 34 pseudodeficient individuals and 65 carriers or potential carriers. The frequency of patients with IOPD was similar to that in the United States, but significantly lower than that in Taiwan. One patient with IOPD underwent early enzyme replacement therapy within a month after birth before presenting exacerbated manifestations, whereas those with potential LOPD showed no manifestations during the follow-up period of six years.

Conclusions

The frequency of IOPD in Japan was similar to that in the United States, where NBS for Pompe disease is recommended. This indicates that NBS for Pompe disease may also be useful in Japan. Therefore, it should be used over a wider region in Japan.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02146-z.

Molecular study of Pompe disease in Egyptian infants

Background

Pompe disease (PD) is a serious genetic disorder caused by deficiency of acid α-glucosidase (GAA) and subsequent glycogen accumulation inside lysosomes. This study included a cohort of 5 Egyptian infants (1–8 months old) with far lower than average normal GAA activity and clinical signs of PD in 4 of the 5 cases. The fifth case was discovered by newborn screening (NBS). Molecular analysis of the GAA gene was performed to confirm the diagnosis and identify the underlying mutation.

Results

The study identified the causative mutations [c.1193T > C (p.Leu398Pro), c.1134C > G (p.Tyr378*) & c.1431del (p.Ile477Metfs*43)] in 4 cases. However, molecular analysis reversed the expected pathologic state in the fifth infant, where his reduced enzymatic activity was related to the presence of pseudodeficiency allele c.868A > G (p.Asn290Asp) in addition to heterozygous disease-causing mutation c.2238G > C (p.Trp746Cys).

Conclusion

This study presents the first molecular analysis of GAA gene in Egypt and has thrown some light on the importance of PD molecular diagnosis to provide precise diagnosis and enable therapeutic commencement in affected subjects.

A Systematic Review and Meta-Analysis of Enzyme Replacement Therapy in Late-Onset Pompe Disease

Pompe disease (PD) is a glycogen storage disorder caused by deficient activity of acid alpha-glucosidase (GAA). We sought to review the latest available evidence on the safety and efficacy of recombinant human GAA enzyme replacement therapy (ERT) for late-onset PD (LOPD).

METHODS

We systematically searched the MEDLINE (via PubMed), Embase, and Cochrane databases for prospective clinical studies evaluating ERT for LOPD on pre-specified outcomes. A meta-analysis was also performed.

RESULTS

Of 1601 articles identified, 22 were included. Studies were heterogeneous and with very low certainty of evidence for most outcomes. The following outcomes showed improvements associated with GAA ERT, over a mean follow-up of 32.5 months: distance walked in the 6-min walking test (6MWT) (mean change 35.7 m (95% confidence interval [CI] 7.78, 63.75)), physical domain of the SF-36 quality of life (QOL) questionnaire (mean change 1.96 (95% CI 0.33, 3.59)), and time on ventilation (TOV) (mean change -2.64 h (95% CI -5.28, 0.00)). There were no differences between the pre- and post-ERT period for functional vital capacity (FVC), Walton and Gardner-Medwin Scale score, upper-limb strength, or total SF-36 QOL score. Adverse events (AEs) after ERT were mild in most cases.

CONCLUSION

Considering the limitations imposed by the rarity of PD, our data suggest that GAA ERT improves 6MWT, physical QOL, and TOV in LOPD patients. ERT was safe in the studied population. PROSPERO register: 135102.

Newborn screening of neuromuscular diseases

Neuromuscular diseases represent an heterogenous group of more than 400 diseases, with a very broad phenotypic spectrum. Given their rarity and complexity, neuromuscular diseases are often diagnosed with a very significant delay after which irreversible muscle damage may limit the efficacy of treatments when available. In this context, neonatal screening could constitute a solution for early detection and treatment. A systematic review of the literature in PubMed up to May 1, 2021, was conducted according to PRISMA guidelines, including classical neuromuscular diseases and diseases with a clear peripheral nervous system involvement (including central nervous system disease with severe neuropathy). We found seven diseases for which newborn screening data were reported: spinal muscular atrophy (9), Duchenne muscular dystrophy (9), Pompe disease (8), X-linked adrenoleukodystrophy (5), Krabbe disease (4), myotonic dystrophy type 1 (1), metachromatic leukodystrophy (1). The future of newborn screening for neuromuscular disorders pass through a global technological switch, from a biochemical to a genetic-based approach. The rapid development of therapy also requires the possibility to quickly adapt the list of treated conditions, to allow innovative therapies to achieve their best efficacy.

Health care practitioners' experience-based opinions on providing care after a positive newborn screen for Pompe disease

The addition of Pompe disease (PD) and other conditions with later-onset forms to newborn screening (NBS) in the United States (US) has been controversial. NBS technology cannot discern infantile-onset PD (IOPD) from later-onset PD (LOPD) without clinical follow-up. This study explores genetic health care practitioners' (HCPs) experiences and challenges providing NBS patient care throughout the US and their resultant opinions on NBS for PD. An online survey was distributed to genetic counselors, geneticists, NBS follow-up care coordinators, and nurse practitioners caring for patients with positive NBS results for PD. Analysis of 78 surveys revealed the majority of participating HCPs support inclusion of PD on NBS. Almost all HCPs (93.3%) feel their state has sufficient resources to provide follow-up medical care for IOPD; however, only three-fourths (74.6%) believed this for LOPD. Common barriers included time lag between NBS and confirmatory results, insurance difficulties for laboratory testing, and family difficulties in seeking medical care. HCPs more frequently encountered barriers providing care for LOPD than IOPD (53.9% LOPD identified ≥3 barriers, 31.1% IOPD). HCPs also believe creation of a population of presymptomatic individuals with LOPD creates a psychological burden on the family (87.3% agree/strongly agree), unnecessary medicalization of the child (63.5% agree/strongly agree), and parental hypervigilance (68.3% agree/strongly agree). Opinions were markedly divided on the use of reproductive benefit as a justification for NBS. Participants believe additional education for pediatricians and other specialists would be beneficial in providing care for patients with both IOPD and LOPD, in addition to the creation of evidence-based official guidelines for care and supportive resources for families with LOPD.

Two Approaches for a Genetic Analysis of Pompe Disease: A Literature Review of Patients with Pompe Disease and Analysis Based on Genomic Data from the General Population

In this study, two different approaches were applied in the analysis of the GAA gene. One was analyzed based on patients with Pompe disease, and the other was analyzed based on GAA genomic data from unaffected carriers in a general population genetic database. For this, GAA variants in Korean and Japanese patients reported in previous studies and in patients reported in the Pompe disease GAA variant database were analyzed as a model. In addition, GAA variants in the Korean Reference Genome Database (KRGDB), the Japanese Multi Omics Reference Panel (jMorp), and the Genome Aggregation Database (gnomAD) were analyzed. Overall, approximately 50% of the pathogenic or likely pathogenic variants (PLPVs) found in unaffected carriers were also found in real patients with Pompe disease (Koreans, 57.1%; Japanese, 46.2%). In addition, there was a moderate positive correlation (Spearman's correlation coefficient of 0.45-0.69) between the proportion of certain PLPVs in patients and the minor allele frequency of their variants in a general population database. Based on the analysis of general population databases, the total carrier frequency for Pompe disease in Koreans and Japanese was estimated to be 1.7% and 0.7%, respectively, and the predicted genetic prevalence was 1:13,657 and 1:78,013, respectively.

Phenotypic implications of pathogenic variant types in Pompe disease

Newborn screening and therapies for Pompe disease (glycogen storage disease type II, acid maltase deficiency) will continue to expand in the future. It is thus important to determine whether enzyme activity or type of pathogenic genetic variant in GAA can best predict phenotypic severity, particularly the presence of infantile-onset Pompe disease (IOPD) versus late-onset Pompe disease (LOPD). We performed a retrospective analysis of 23 participants with genetically-confirmed cases of Pompe disease. The following data were collected: clinical details including presence or absence of cardiomyopathy, enzyme activity levels, and features of GAA variants including exon versus intron location and splice site versus non-splice site. Several combinations of GAA variant types for individual participants had significant associations with disease subtype, cardiomyopathy, age at diagnosis, gross motor function scale (GMFS), and stability of body weight. The presence of at least one splice site variant (c.546 G > C/p.T182 = , c.1076-22 T > G, c.2646 + 2 T > A, and the classic c.-32-13T > G variant) was associated with LOPD, while the presence of non-splice site variants on both alleles was associated with IOPD. Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features. To extend the findings of prior studies, we found that multiple types of splice site variants beyond the classic c.-32-13T > G variant are often associated with a milder phenotype. Enzyme activity levels continue to have utility for supporting the diagnosis when the genetic variants are ambiguous. It is important for newly diagnosed patients with Pompe disease to have complete genetic, cardiac, and neurological evaluations.

Dried blood spots in doping analysis

A series of dried blood spot (DBS) detection methods for doping agents have been developed in the last two decades. The DBS technique minimizes invasiveness and reduces storage and shipping costs. Recently, the World Anti-Doping Agency announced the use of DBS for the 2022 Beijing Winter Olympic Games and Paralympic Games owing to the advantages of the DBS application in routine doping control. Therefore the further development of detection methods for doping agents in DBS is important and urgent. This review summarizes five aspects of DBS application in doping analysis: sample collection, storage conditions, pretreatment, instrumentation and validation according to the Prohibited List issued by the World Anti-Doping Agency, and proposes some suggestions for future studies of DBS in doping analysis.

Carrier frequency and predicted genetic prevalence of Pompe disease based on a general population database

Background

The genetic prevalence of Pompe disease was estimated based on the proportion of individuals who have a causative genotype in a general population database. In addition, clinical severity for causative genotypes was assessed based on currently available locus-specific databases (LSDBs), which contain information on both genotype and clinical severity.

Methods

Genetic variants in the GAA gene in the Genome Aggregation Database (gnomAD) (v2.1.1) were analyzed in combination with LSDBs of ClinVar, ClinGen Evidence Repository, Pompe disease GAA variant database, and the Pompe Registry. Carrier frequency (CF) and predicted genetic prevalence (pGP) were estimated.

Results

Of 7 populations, East Asian and African showed higher proportions of pathogenic or likely pathogenic variants (PLPVs) associated with classic infantile-onset Pompe disease. Total CF and pGP in the overall population were 1.3% (1 in 77) and 1:23,232, respectively. The highest pGP was observed in the East Asian population at 1:12,125, followed by Non-Finnish European (1:13,756), Ashkenazi Jewish (1:22,851), African/African-American (1:26,560), Latino/Admixed American (1:57,620), South Asian (1:93,087), and Finnish (1:1,056,444).

Conclusions

Pompe disease has a higher pGP (1:23,232) than earlier accepted (1:40,000). The pGP for Pompe disease was expectedly wide by population and consistent with previous reports based on newborn screening programs (approximately 1:10,000-1:30,000).

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

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

Current Practices for U.S. Newborn Screening of Pompe Disease and MPSI

Two lysosomal storage disorders (LSDs), Pompe disease and Mucopolysaccharidosis type I (MPSI) were added to the Recommended Uniform Screening Panel (RUSP) for newborn screening (NBS) in 2015 and 2016, respectively. These conditions are being screened with variable practice in terms of primary and reflex analytes (either biochemical or molecular testing) as well as collection of short- and long-term follow-up elements. The goal of this study is to evaluate practices of state health departments in regards to screening methods and follow-up data collected. We conducted online surveys and phone questionnaires to determine each U.S. state's practices for screening and follow-up of positive newborn screens. We report the first snapshot of practices for NBS for the LSDs included on the RUSP. All 50 U.S. states responded to our survey. The majority of U.S. states are not currently screening for Pompe disease and MPSI as of March 2020, but this number will increase to 38 states in the coming 1-3 years based on survey results. Our survey identifies data elements used by state health departments for short-and long-term follow-up that could serve as the basis of common elements for larger, public health-based analyses of the benefits and efficacy of screening for Pompe disease and MPSI.

Pompe disease: pathogenesis, molecular genetics and diagnosis

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

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

Newborn Screening for Pompe Disease

Glycogen storage disease type II (also known as Pompe disease (PD)) is an autosomal recessive disorder caused by defects in α-glucosidase (AαGlu), resulting in lysosomal glycogen accumulation in skeletal and heart muscles. Accumulation and tissue damage rates depend on residual enzyme activity. Enzyme replacement therapy (ERT) should be started before symptoms are apparent in order to achieve optimal outcomes. Early initiation of ERT in infantile-onset PD improves survival, reduces the need for ventilation, results in earlier independent walking, and enhances patient quality of life. Newborn screening (NBS) is the optimal approach for early diagnosis and treatment of PD. In NBS for PD, measurement of AαGlu enzyme activity in dried blood spots (DBSs) is conducted using fluorometry, tandem mass spectrometry, or digital microfluidic fluorometry. The presence of pseudodeficiency alleles, which are frequent in Asian populations, interferes with NBS for PD, and current NBS systems cannot discriminate between pseudodeficiency and cases with PD or potential PD. The combination of GAA gene analysis with NBS is essential for definitive diagnoses of PD. In this review, we introduce our experiences and discuss NBS programs for PD implemented in various countries.

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

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

Long-Term Observation of the Safety and Effectiveness of Enzyme Replacement Therapy in Japanese Patients with Pompe Disease: Results From the Post-marketing Surveillance

INTRODUCTION

Alglucosidase alfa received marketing approval for the treatment of Pompe disease in Japan in 2007. We conducted a post-marketing surveillance study to monitor the long-term safety and efficacy of alglucosidase alfa therapy among Japanese patients with Pompe disease.

METHODS

The safety and efficacy outcomes were collected as real-world data for up to 9 years following the initiation of treatment with alglucosidase alfa, without any intervention to treatment strategies. The safety of the drug was assessed in 73 patients in terms of the rate of drug-related adverse events, infusion-associated reactions, and antibody titers. The efficacy was evaluated in 72 patients on the basis of subjective evaluation of their general condition after treatment, pulmonary function, 6-min walk test, and survival rate.

RESULTS

Drug-related adverse events were observed in 29 of 73 (39.7%) cases, and the cumulative adverse event rate during the 9 years of the study was 45.7%. Immunoglobulin G antibodies against alglucosidase alfa were positive in 59 of 61 cases in which the titers were not correlated with drug-related adverse events or infusion-associated reactions. After the final dosing, the treating physicians determined that the disease was at least stabilized in 62 of 72 cases (86.1%), while the results of the physical function tests suggested that disease progression was actually not stopped completely. Survival of infantile-onset cases was sustained for 9 years.

CONCLUSION

The drug was generally well tolerated, and treatment with alglucosidase alfa was able to suppress disease progression in the majority of Japanese patients with Pompe disease included in this study.

FUNDING

Sanofi.

Targeted SLC19A3 gene sequencing of 3000 Saudi newborn: a pilot study toward newborn screening

Background

Biotin–thiamine‐responsive basal ganglia disease (BTBGD) is an autosomal recessive neurometabolic disorder mostly presented in children. The disorder is described as having subacute encephalopathy with confusion, dystonia, and dysarthria triggered by febrile illness that leads to neuroregression and death if untreated. Using biotin and thiamine at an early stage of the disease can lead to significant improvement.

Methods

BTBGD is a treatable disease if diagnosed at an early age and has been frequently reported in Saudi population. Keeping this in mind, the current study screened 3000 Saudi newborns for the SLC19A3 gene mutations using target sequencing, aiming to determine the carrier frequency in Saudi Population and whether BTBGD is a good candidate to be included in the newborn‐screened disorders.

Results

Using targeted gene sequencing, DNA from 3000 newborns Saudi was screened for the SLC19A3 gene mutations using standard methods. Screening of the SLC19A3 gene revealed a previously reported heterozygous missense mutation (c.1264A>G (p.Thr422Ala) in six unrelated newborns. No probands having homozygous pathogenic mutations were found in the studied cohort. The variant has been frequently reported previously in homozygous state in Saudi population, making it a hot spot mutation. The current study showed that the carrier frequency of SLC19A3 gene mutation is 1 of 500 in Saudi newborns.

Conclusion

For the first time in the literature, we determined the carrier frequency of SLC19A3 gene mutation in Saudi population. The estimated prevalence is too rare in Saudi population (at least one in million); therefore, the data are not in favor of including such very rare disorders in newborn screening program at population level. However, a larger cohort is needed for a more accurate estimate.