Management of Confirmed Newborn-Screened Patients With Pompe Disease Across the Disease Spectrum

Successful desensitization protocol to alglucosidase and avalglucosidase alfa in a patient with infantile-onset Pompe disease

Infantile-onset Pompe disease is a lysosomal disease characterized by cardiomyopathy and muscle weakness that, without specific treatment, is fatal within the first two years of life. We present the case of an infant who developed anaphylaxia to enzyme replacement therapy with alglucosidase-alfa. We provide a desensitization protocol to alglucosidase-alfa and, for the first time, a desensitization protocol to avalglucosidase-alfa, both delivered in a reasonable time of <6 h, and without any further reactions in the patient.

Simultaneous monitoring of glycogen, creatine, and phosphocreatine in type II glycogen storage disease using saturation transfer MRI

PURPOSE

There is a need for non-invasive approaches to assess the progression of glycogen storage diseases (GSD). Here, we use saturation transfer (ST) MRI via relayed nuclear Overhauser effects (glycoNOE) to detect abnormal changes in muscle glycogen of a GSD II mouse model. In addition to glycogen, the energy metabolites phosphocreatine (PCr) and creatine (Cr) were studied to assess the muscle disease.

METHODS

Water saturation (Z-spectra) and 1H MRS were acquired at 9.4 T on the skeletal muscle of healthy control mice and homozygous acidα $$ \upalpha $$ -glucosidase (GAA) knock-out mice (ages of 2-48 weeks). The glycoNOE (-1 ppm), total creatine (tCr)* (+2 ppm, = a × [Cr] + b × [PCr]), and PCr (+2.5 ppm) from Z-spectra and the ratio between tCr and taurine signals (tCr/Tau) from 1H MRS spectra were quantified by using multi-pool Lorentzian fitting methods. The concentrations of the metabolites were also measured via tissue assays.

RESULTS

The postnatal GSD II mice (age <12 weeks) showed a continued accumulation of muscle glycoNOE signal. GlycoNOE in adult GSD II mice (age ≥12 weeks) reached a plateau, at a level above 400% of that in normal mice. PCr, tCr*, and tCr/Tau gradually decreased in GSD II mice during the postnatal stage, then stabilized at levels comparable to adult control, yet PCr in adult GSD II mice was lower than that in controls.

CONCLUSION

This study demonstrates that ST MRI of glycogen can provide in situ non-invasive biomarkers for GSD II disease progression, with the potential to study the progression and treatment response of GSDs.

Promises and challenges of genomic newborn screening (NBS) - lessons from public health NBS programs

Newborn screening (NBS) in the United States began in the 1960s to detect inborn errors of metabolism that benefited from presymptomatic treatment compared with treatment after the development of symptoms and diagnosis. Over time, it expanded to include endocrinological disorders, hematological disorders, immunodeficiencies, and other treatable diseases such as lysosomal storage diseases (LSD), cystic fibrosis, X-linked adrenoleukodystrophy, and spinal muscular dystrophy. This expansion has been driven by new technologies (e.g., tandem mass spectrometry) and novel treatments (e.g., enzyme replacement therapy and stem cell transplant for LSDs). Advances in next-generation gene sequencing (NGS) enable rapid identification of many additional conditions that might benefit from early presymptomatic intervention. We review the NGS technologies that evolved as diagnostic testing and suggest issues to be resolved before their potential application to screening the asymptomatic population. We illustrate the importance of selecting diseases to be screened and propose recommendations to follow when variants of uncertain significance are found. We address ethical issues around achieving equity in the sensitivity of genomic NBS, access to follow-up and management, especially for people from diverse backgrounds, and other considerations. Finally, we discuss the potential benefits and harms of genomic NBS to the overall health of children with monogenic diseases. IMPACT: Genomic newborn screening programs are ongoing worldwide. Public discussion is needed as to whether genomic newborn screening should be offered as a public health program and, if so, what conditions should be screened for. Providers should understand that the sensitivity of genomic newborn screening is especially low for newborns from non-European populations. Methylation, large structural variants and repeat expansion variants are not amenable to next-generation sequencing-based genomic newborn screening. The article serves as a comprehensive guide to understanding issues that need to be solved before genomic newborn screening is implemented as a public health program.

Navigating Pompe Disease Assessment: A Comprehensive Scoping Review

Pompe disease (PD) is a rare progressive autosomal recessive disorder resulting from the deficiency of acid alpha-glucosidase (GAA) enzyme activity. Due to its multisystemic involvement, PD leads to significant morbidity and impacts patients' quality of life. Despite the availability of approved disease-modifying treatments, the prompt diagnosis and management of PD, which are crucial for patient outcomes, still present several challenges. This scoping review aimed to synthesize the evidence regarding methods for screening, diagnosing, and following up PD. We searched articles in English and Spanish published from 2017 to February 8, 2022, across 11 databases (i.e., Cochrane Database of Systematic Reviews, Directory of Open Access Journals (DOAJ), Epistemonikos, Ingenta Connect, Medline/PubMed, SAGE, SciELO Citation Index, ScienceDirect, Springer Link, Virtual Health Library, and Wiley Online Library). We included primary studies (i.e., case reports, case series, cross-sectional studies, case controls, cohorts, clinical trials, and qualitative studies), reviews, and guidelines that described at least one assessment method for patients with confirmed clinical, genetic, or biochemical PD. Two independent reviewers screened and extracted data from articles, with a third reviewer solving conflicts. We synthesized data with narrative summaries and descriptive statistics. After screening 2,139 titles and abstracts, we included 96 eligible articles. Cross-sectional studies (n = 30) and guidelines (n = 1) were the most and least prevalent designs, respectively. Most studies targeted late-onset PD (LOPD, n = 48) and infantile-onset PD (IOPD, n = 21). Eleven articles described newborn screening programs, highlighting their potential to improve PD prevalence estimations and still limited availability among countries. Overall, 81 articles documented clinical manifestations of PD. Hypotonia (n = 7) and hypertrophic cardiomyopathy (n = 7) were the most documented for IOPD, while progressive muscle weakness (n = 21) and dyspnea (n = 11) were the most prevalent for LOPD. We found 26 articles reporting biochemical assays, with dried blood spots (DBS) for GAA enzyme deficiency detection being the most cited (n = 19). We also noted a lack of standardization in documenting DBS results. Additionally, 21 articles mentioned genetic studies, with next-generation sequencing emerging as the gold standard for identifying mutated alleles. Functional studies were the most utilized to follow up with patients. However, monitoring strategies for pediatric and adult PD lacked consensus, and only one article assessed patients' quality of life. This review comprehensively evaluated the literature on PD screening, diagnosis, and follow-up methods, identifying prevalent techniques within each assessment category. We emphasized the need for a more standardized approach to reporting biochemical assays, genetic testing, and clinical presentations. Our review also underscored the critical lack of standardization in PD follow-up. Addressing these gaps will enhance the comparability of future research findings and improve the quality of PD-related healthcare. Limitations of this review included restricting eligible languages and publication years to the latest five, the methodological heterogeneity of selected articles, and the lack of individual study bias assessment.

Advances in Pompe Disease Treatment: From Enzyme Replacement to Gene Therapy

Pompe disease is a neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA), hydrolyzing glycogen to glucose. Pathological glycogen storage, the hallmark of the disease, disrupts the metabolism and function of various cell types, especially muscle cells, leading to cardiac, motor, and respiratory dysfunctions. The spectrum of Pompe disease manifestations spans two main forms: classical infantile-onset (IOPD) and late-onset (LOPD). IOPD, caused by almost complete GAA deficiency, presents at birth and leads to premature death by the age of 2 years without treatment. LOPD, less severe due to partial GAA activity, appears in childhood, adolescence, or adulthood with muscle weakness and respiratory problems. Since 2006, enzyme replacement therapy (ERT) has been approved for Pompe disease, offering clinical benefits but not a cure. However, advances in early diagnosis through newborn screening, recognizing disease manifestations, and developing improved treatments are set to enhance Pompe disease care. This article reviews recent progress in ERT and ongoing translational research, including the approval of second-generation ERTs, a clinical trial of in utero ERT, and preclinical development of gene and substrate reduction therapies. Notably, gene therapy using intravenous delivery of adeno-associated virus (AAV) vectors is in phase I/II clinical trials for both LOPD and IOPD. Promising data from LOPD trials indicate that most participants met the criteria to discontinue ERT several months after gene therapy. The advantages and challenges of this approach are discussed. Overall, significant progress is being made towards curative therapies for Pompe disease. While several challenges remain, emerging data are promising and suggest the potential for a once-in-a-lifetime treatment.

Clinical insight meets scientific innovation to develop a next generation ERT for Pompe disease

Years of research into the structure, processing, and function of acid alpha-glucosidase led to the development and 2006 approval of alglucosidase alfa (recombinant human acid alpha-glucosidase, Myozyme®/Lumizyme®), an enzyme replacement therapy and the first approved treatment for Pompe disease. Alglucosidase alfa has been a lifesaving treatment for patients with infantile-onset Pompe disease and radically improved daily life for patients with late-onset Pompe disease; however, long-term experience with alglucosidase alfa unraveled key unmet needs in these populations. Despite treatment, Pompe disease continues to progress, especially from a skeletal muscle perspective, resulting in a multitude of functional limitations. Strong collaboration between the scientific and patient communities led to increased awareness of Pompe disease, a better understanding of disease pathophysiology, knowledge of the clinical course of the disease as patients surpassed the first decade of life, and the strengths and limitations of enzyme replacement therapy. Taken together, these advancements spurred the need for development of a next generation of enzyme replacement therapy and provided a framework for progress toward other novel treatments. This review provides an overview of the development of avalglucosidase alfa as a model to highlight the interaction between clinical experience with existing treatments, the role of the clinician scientist, translational research at both system and cellular levels, and the iterative and collaborative process that optimizes the development of therapeutics.

The Importance of Early Treatment of Inherited Neuromuscular Conditions

There has been tremendous progress in treatment of neuromuscular diseases over the last 20 years, which has transformed the natural history of these severely debilitating conditions. Although the factors that determine the response to therapy are many and in some instance remain to be fully elucidated, early treatment clearly has a major impact on patient outcomes across a number of inherited neuromuscular conditions. To improve patient care and outcomes, clinicians should be aware of neuromuscular conditions that require prompt treatment initiation. This review describes data that underscore the importance of early treatment of children with inherited neuromuscular conditions with an emphasis on data resulting from newborn screening efforts.

Omics-Based Approaches for the Characterization of Pompe Disease Metabolic Phenotypes

Lysosomal storage disorders (LSDs) constitute a large group of rare, multisystemic, inherited disorders of metabolism, characterized by defects in lysosomal enzymes, accessory proteins, membrane transporters or trafficking proteins. Pompe disease (PD) is produced by mutations in the acid alpha-glucosidase (GAA) lysosomal enzyme. This enzymatic deficiency leads to the aberrant accumulation of glycogen in the lysosome. The onset of symptoms, including a variety of neurological and multiple-organ pathologies, can range from birth to adulthood, and disease severity can vary between individuals. Although very significant advances related to the development of new treatments, and also to the improvement of newborn screening programs and tools for a more accurate diagnosis and follow-up of patients, have occurred over recent years, there exists an unmet need for further understanding the molecular mechanisms underlying the progression of the disease. Also, the reason why currently available treatments lose effectiveness over time in some patients is not completely understood. In this scenario, characterization of the metabolic phenotype is a valuable approach to gain insights into the global impact of lysosomal dysfunction, and its potential correlation with clinical progression and response to therapies. These approaches represent a discovery tool for investigating disease-induced modifications in the complete metabolic profile, including large numbers of metabolites that are simultaneously analyzed, enabling the identification of novel potential biomarkers associated with these conditions. This review aims to highlight the most relevant findings of recently published omics-based studies with a particular focus on describing the clinical potential of the specific metabolic phenotypes associated to different subgroups of PD patients.

Safety and efficacy of avalglucosidase alfa in individuals with infantile-onset Pompe disease enrolled in the phase 2, open-label Mini-COMET study: The 6-month primary analysis report

PURPOSE

Mini-COMET (NCT03019406; Sanofi) is a phase 2, open-label, ascending-dose, 3-cohort study, evaluating avalglucosidase alfa safety, pharmacokinetics, and efficacy in individuals with infantile-onset Pompe disease aged <18 years who previously received alglucosidase alfa and showed clinical decline (cohorts 1 and 2) or suboptimal response (cohort 3).

METHODS

During a 25-week primary analysis period, cohorts 1 and 2 received avalglucosidase alfa 20 and 40 mg/kg every other week, respectively, for 6 months, whereas cohort 3 individuals were randomized (1:1) to receive avalglucosidase alfa 40 mg/kg every other week or alglucosidase alfa (current stable dose) for 6 months.

RESULTS

In total, 22 individuals were enrolled (cohort 1 [n = 6], cohort 2 [n = 5], cohort 3-avalglucosidase alfa [n = 5], and cohort 3-alglucosidase alfa [n = 6]). Median treatment compliance was 100%. None of the individuals discontinued treatment or died. Percentages of individuals with treatment-emergent adverse events were similar across dose and treatment groups. No serious or severe treatment-related treatment-emergent adverse events occurred. Trends for better motor function from baseline to week 25 were observed for 40 mg/kg every other week avalglucosidase alfa compared with either 20 mg/kg every other week avalglucosidase alfa or alglucosidase alfa up to 40 mg/kg weekly.

CONCLUSION

These data support the positive clinical effect of avalglucosidase alfa in patients with infantile-onset Pompe disease previously declining on alglucosidase alfa.

Treatment Dilemma in Children with Late-Onset Pompe Disease

In recent years, there has been a significant increase in the diagnosis of asymptomatic Late-Onset Pompe Disease (LOPD) patients, who are detected via family screening or Newborn Screening (NBS). The dilemma is when to start Enzyme Replacement Therapy (ERT) in patients without any clinical sign of the disease, considering its important benefits in terms of loss of muscle but also its very high cost, risk of side effects, and long-term immunogenicity. Muscle Magnetic Resonance Imaging (MRI) is accessible, radiation-free, and reproducible; therefore, it is an important instrument for the diagnosis and follow-up of patients with LOPD, especially in asymptomatic cases. European guidelines suggest monitoring in asymptomatic LOPD cases with minimal MRI findings, although other guidelines consider starting ERT in apparently asymptomatic cases with initial muscle involvement (e.g., paraspinal muscles). We describe three siblings affected by LOPD who present compound heterozygosis and wide phenotypic variability. The three cases differ in age at presentation, symptoms, urinary tetrasaccharide levels, and MRI findings, confirming the significant phenotypic variability of LOPD and the difficulty in deciding when to start therapy.

Newborn screening for Pompe disease: Parental experiences and follow-up care for a late-onset diagnosis

Newborn screening (NBS) for Pompe disease (PD) was added to the Recommended Uniform Screening Panel (RUSP) in the United States in 2015 because there was compelling evidence of health benefits for early diagnosis of Infantile-onset Pompe disease (IOPD). However, one limitation of NBS for PD is its inability to distinguish IOPD and late onset forms of Pompe disease (LOPD). Management of LOPD is challenging because of uncertainty around progression of LOPD and determining the appropriate time for treatment initiation. The aims of this study were to understand the impact of LOPD identified through NBS, by exploring the differences in attitudes, emotions and opinions among parents and identify their needs for follow-up care. Study participants were recruited from states that included PD on their NBS panel. Semi-structured interviews were conducted with parents of nine children who were diagnosed with LOPD after an abnormal NBS result. Predominantly, parents reported a lack of adequate information, guidance, and psychosocial support from the very beginning and through the course of their diagnosis. This caused uncertainty, anxiety, frustration, and fear of the unknown. Parents live in a 'worry or not to worry' phase, balancing between coping methods to avoid over medicalization of their child, but also preparing concrete follow-up plans to be on the lookout for any signs of PD-related symptoms. Understanding parents' experiences allows genetic counselors and NBS programs to proactively design care plan for parents during this difficult period.

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.

Rare lysosomal disease registries: lessons learned over three decades of real-world evidence

Lysosomal storage disorders (LSD) are rare diseases, caused by inherited deficiencies of lysosomal enzymes/transporters, that affect 1 in 7000 to 1 in 8000 newborns. Individuals with LSDs face long diagnostic journeys during which debilitating and life-threatening events can occur. Clinical trials and classical descriptions of LSDs typically focus on common manifestations, which are not representative of the vast phenotypic heterogeneity encountered in real-world experience. Additionally, recognizing that there was a limited understanding of the natural history, disease progression, and real-world clinical outcomes of rare LSDs, a collaborative partnership was pioneered 30 years ago to address these gaps. The Rare Disease Registries (RDR) (for Gaucher, Fabry, Mucopolysaccharidosis type I, and Pompe), represent the largest observational database for these LSDs. Over the past thirty years, data from the RDRs have helped to inform scientific understanding and the development of comprehensive monitoring and treatment guidelines by creating a framework for data collection and establishing a standard of care, with an overarching goal to improve the quality of life of affected patients. Here, we highlight the history, process, and impact of the RDRs, and discuss the lessons learned and future directions.

The Clinical Management of Pompe Disease: A Pediatric Perspective

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

Pompe Disease: a Clinical, Diagnostic, and Therapeutic Overview

Purpose of Review

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

Recent Findings

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

Summary

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

A Qualitative Study: Mothers' Experiences of Their Child's Late-Onset Pompe Disease Diagnosis Following Newborn Screening

Pompe disease was added to the United States recommended uniform screening panel in 2015 to avoid diagnostic delay and implement prompt treatment, specifically for those with infantile-onset Pompe disease (IOPD). However, most newborns with abnormal newborn screening (NBS) for Pompe disease have late-onset Pompe disease (LOPD). An early diagnosis of LOPD raises the question of when symptoms will arise which is challenging for parents, patients, and providers managing an LOPD diagnosis. This study aimed to characterize mothers' experiences of their child's LOPD diagnosis and medical monitoring. A qualitative descriptive approach was chosen to gain an in-depth understanding of parental experiences. Eight mothers were interviewed about their experiences with positive NBS and diagnosis, experiences with living with the diagnosis, and experiences with medical monitoring. Interview transcripts were analyzed through conventional content analysis. Negative emotions like fear were more frequent with communication of NBS results. Participants expressed uncertainty surrounding age of symptom onset and the future. The medical monitoring experience increased worry but participants expressed that being vigilant with management reassured them. Parental emotions shifted to thankfulness and reassurance with time and education. These findings can provide guidance to providers about the psychosocial implications of receiving positive NBS results and an LOPD diagnosis.

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.

Assessment of Dysphonia in Children with Pompe Disease Using Auditory-Perceptual and Acoustic/Physiologic Methods

Bulbar and respiratory weakness occur commonly in children with Pompe disease and frequently lead to dysarthria. However, changes in vocal quality associated with this motor speech disorder are poorly described. The goal of this study was to characterize the vocal function of children with Pompe disease using auditory-perceptual and physiologic/acoustic methods. High-quality voice recordings were collected from 21 children with Pompe disease. The Grade, Roughness, Breathiness, Asthenia, and Strain (GRBAS) scale was used to assess voice quality and ratings were compared to physiologic/acoustic measurements collected during sustained phonation tasks, reading of a standard passage, and repetition of a short phrase at maximal volume. Based on ratings of grade, dysphonia was present in 90% of participants and was most commonly rated as mild or moderate in severity. Duration of sustained phonation tasks was reduced and shimmer was increased in comparison to published reference values for children without dysphonia. Specific measures of loudness were found to have statistically significant relationships with perceptual ratings of grade, breathiness, asthenia, and strain. Our data suggest that dysphonia is common in children with Pompe disease and primarily reflects impairments in respiratory and laryngeal function; however, the primary cause of dysphonia remains unclear. Future studies should seek to quantify the relative contribution of deficits in individual speech subsystems on voice quality and motor speech performance more broadly.

A molecular genetics view on Mucopolysaccharidosis Type II

Mucopolysaccharidosis Type II (MPS II) is an X-linked recessive genetic disorder that primarily affects male patients. With an incidence of 1 in 100,000 male live births, the disease is one of the orphan diseases. MPS II symptoms are caused by mutations in the lysosomal iduronate-2-sulfatase (IDS) gene. The mutations cause a loss of enzymatic performance and result in the accumulation of glycosaminoglycans (GAGs), heparan sulfate and dermatan sulfate, which are no longer degradable. This inadvertent accumulation causes damage in multiple organs and leads either to a severe neurological course or to an attenuated course of the disease, although the exact relationship between mutation, extent of GAG accumulation and disease progression is not yet fully understood. This review is intended to present current diagnostic procedures and therapeutic interventions. In times when the genetic profile of patients plays an increasingly important role in the assessment of therapeutic success and future drug design, we chose to further elucidate the impact of genetic diversity within the IDS gene on disease phenotype and potential implications in current diagnosis, prognosis and therapy. We report recent advances in the structural biological elucidation of I2S enzyme that that promises to improve our future understanding of the molecular damage of the hundreds of IDS gene variants and will aid damage prediction of novel mutations in the future.

Opinions of adults affected with later-onset lysosomal storage diseases regarding newborn screening: A qualitative study

Lysosomal storage diseases (LSDs) are a heterogeneous group of conditions causing substrate accumulation leading to progressive organ damage. Newborn screening (NBS) for several LSDs has become available in recent years due to advances in technology and treatment availability. While early initiation of treatment is lifesaving for those with infantile presentations, controversy continues regarding diagnosis of milder, later-onset diseases in infancy, including creation of pre-symptomatic populations of 'patients-in-waiting', the potential for medicalization, stigmatization, and/or discrimination. In-depth interviews were conducted with 36 adults [11 with Fabry disease (FD), 8 with Gaucher disease (GD), and 17 with late-onset Pompe disease (LOPD)], to determine their perspectives on NBS for their respective conditions. Thirty-four of 36 participants were in favor of NBS; both participants not in favor had GD1. Emergent themes influencing participants favorably toward NBS included earlier age of onset, a long diagnostic odyssey, less efficacious treatment, and the desire to have made different life decisions (e.g., relationships, career, or lifestyle) with the knowledge of their diagnosis. Concerns about insurance discrimination and psychological or physical burdens were associated with less favorable opinions of NBS. The ability for parents to make future reproductive decisions based their child's NBS result was considered favorably by some participants and unfavorably by others. Participants' specific condition (GD1, FD, or LOPD) contributed to these experiences differently. Participants with LOPD and FD favored NBS to initiate earlier treatment and prevent irreversible organ damage, whereas fewer patients with GD1 mentioned this benefit. Participants with LOPD had the longest diagnostic odyssey, while those with FD were more likely to report feeling misunderstood and experiencing accusations of malingering, both contributing to favorable views of NBS. Results expand prior quantitative findings by illuminating how participants' lived experiences can shape opinions about NBS. By understanding how currently affected individuals perceive the lifelong impact of a NBS result, genetic counselors can provide better anticipatory guidance to the parents of individuals diagnosed with a later-onset LSD by NBS.

Targeted Therapies for Metabolic Myopathies Related to Glycogen Storage and Lipid Metabolism: a Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Metabolic myopathies are a heterogenous group of muscle diseases typically characterized by exercise intolerance, myalgia and progressive muscle weakness. Effective treatments for some of these diseases are available, but while our understanding of the pathogenesis of metabolic myopathies related to glycogen storage, lipid metabolism and β-oxidation is well established, evidence linking treatments with the precise causative genetic defect is lacking.

OBJECTIVE

The objective of this study was to collate all published evidence on pharmacological therapies for the aforementioned metabolic myopathies and link this to the genetic mutation in a format amenable to databasing for further computational use in line with the principles of the "treatabolome" project.

METHODS

A systematic literature review was conducted to retrieve all levels of evidence examining the therapeutic efficacy of pharmacological treatments on metabolic myopathies related to glycogen storage and lipid metabolism. A key inclusion criterion was the availability of the genetic variant of the treated patients in order to link treatment outcome with the genetic defect.

RESULTS

Of the 1,085 articles initially identified, 268 full-text articles were assessed for eligibility, of which 87 were carried over into the final data extraction. The most studied metabolic myopathies were Pompe disease (45 articles), multiple acyl-CoA dehydrogenase deficiency related to mutations in the ETFDH gene (15 articles) and systemic primary carnitine deficiency (8 articles). The most studied therapeutic management strategies for these diseases were enzyme replacement therapy, riboflavin, and carnitine supplementation, respectively.

CONCLUSIONS

This systematic review provides evidence for treatments of metabolic myopathies linked with the genetic defect in a computationally accessible format suitable for databasing in the treatabolome system, which will enable clinicians to acquire evidence on appropriate therapeutic options for their patient at the time of diagnosis.

Benefits of Prophylactic Short-Course Immune Tolerance Induction in Patients With Infantile Pompe Disease: Demonstration of Long-Term Safety and Efficacy in an Expanded Cohort

Immune tolerance induction (ITI) with a short-course of rituximab, methotrexate, and/or IVIG in the enzyme replacement therapy (ERT)-naïve setting has prolonged survival and improved clinical outcomes in patients with infantile Pompe disease (IPD) lacking endogenous acid-alpha glucosidase (GAA), known as cross-reactive immunologic material (CRIM)-negative. In the context of cancer therapy, rituximab administration results in sustained B-cell depletion in 83% of patients for up to 26–39 weeks with B-cell reconstitution beginning at approximately 26 weeks post-treatment. The impact of rituximab on serum immunoglobulin levels is not well studied, available data suggest that rituximab can cause persistently low immunoglobulin levels and adversely impact vaccine responses. Data on a cohort of IPD patients who received a short-course of ITI with rituximab, methotrexate, and IVIG in the ERT-naïve setting and had ≥6 months of follow-up were retrospectively studied. B-cell quantitation, ANC, AST, ALT, immunization history, and vaccine titers after B-cell reconstitution were reviewed. Data were collected for 34 IPD patients (25 CRIM-negative and 9 CRIM-positive) with a median age at ERT initiation of 3.5 months (0.1–11.0 months). B-cell reconstitution, as measured by normalization of CD19%, was seen in all patients (n = 33) at a median time of 17 weeks range (11–55 weeks) post-rituximab. All maintained normal CD19% with the longest follow-up being 248 weeks post-rituximab. 30/34 (88%) maintained negative/low anti-rhGAA antibody titers, even with complete B-cell reconstitution. Infections during immunosuppression were reported in five CRIM-negative IPD patients, all resolved satisfactorily on antibiotics. There were no serious sequelae or deaths. Of the 31 evaluable patients, 27 were up to date on age-appropriate immunizations. Vaccine titers were available for 12 patients after B-cell reconstitution and adequate humoral response was observed in all except an inadequate response to the Pneumococcal vaccine (n = 2). These data show the benefits of short-course prophylactic ITI in IPD both in terms of safety and efficacy. Data presented here are from the youngest cohort of patients treated with rituximab and expands the evidence of its safety in the pediatric population.

A Newborn with Infantile-Onset Pompe Disease Improving after Administration of Enzyme Replacement Therapy: Case Report

Pompe disease (PD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of acid α-1,4-glucosidase enzyme (GAA). PD has two forms, namely the infantile-onset and the late-onset form. In untreated cases, infantile-onset form usually leads to cardio-respiratory failure and death in the first year of life. Herein, we report a newborn with infantile-onset PD characterized by muscular hypotonia, respiratory distress, hypertrophic cardiomyopathy, hepatomegaly, elevated serum enzyme levels of aspartate aminotransferase of 117 IU/L (three times the normal value), alanine aminotransferase of 66 IU/L (1.8 times the normal value), lactate dehydrogenase of 558 IU/L (1.2 times the normal value), and creatine kinase >5,000 IU/L (16 times the normal value). Dried blood spot testing was performed and revealed decreased GAA enzymatic activity (0.07 nmol/mL/h, normal 0.93–7.33 nmol/mL/h). GAA gene analysis performed for confirming the diagnosis showed homozygous mutation c.896T >C (p.Leu299Pro). Initiation of enzyme replacement therapy (ERT) (ERT; 20 mg/kg, once every week) at 28 days of age resulted in weaning off from respiratory support within 1 week after treatment, normalization of cardiac abnormalities, and normal neuromotor development in the 16th month of age. Early diagnosis and early treatment with ERT, especially in the neonatal period, is of great importance to improve cardiac function and motor development in infantile-onset 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.

Navigating Newborn Screening in the NICU: A User's Guide

Newborn screening (NBS) is the largest public health program in the United States, affecting every newborn. The purpose of newborn screening is to identify newborns at risk for selected disorders during the presymptomatic phase, with the hope that early intervention can prevent disease progression. NBS began in the early 1960s following the pioneering work of Robert Guthrie with phenylketonuria. Since then, NBS has expanded, with testing available for more than 50 disorders in most states. Screening tests need to be highly automated, with high sensitivity and specificity to avoid missing patients with disease, and ensuring manageable false-positive rates. Current initiatives in NBS include timeliness to ensure that results of the screen are available by 5 days after birth for a core set of critical conditions. This has resulted in the current recommendation for NBS specimens to be collected at 24 to 48 hours after birth. False-positive rates are higher in the NICU, because of the metabolic instability of sick neonates and the immaturity of premature enzyme systems. The recommended uniform screen panel (RUSP) contains the current list of disorders screened for by most states. Additional disorders continue to be added to the RUSP as medical progress allows previously untreatable disorders to be managed successfully, and thus the need to screen emerges. The costs associated with NBS continue to climb, because despite state-mandated screening, the diagnostic evaluation and treatment of these conditions has no such mandate. This is a particular concern for disorders with annual treatment costs of several hundred thousand dollars.

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.

A Newborn Screening, Presymptomatically Identified Infant With Late-Onset Pompe Disease: Case Report, Parental Experience, and Recommendations

Pompe disease is an inherited lysosomal storage disorder caused by acid alpha-glucosidase (GAA) enzyme deficiency, resulting in muscle and neuron intralysosomal glycogen storage. Clinical symptoms vary from the severe, infantile-onset form with hypertrophic cardiomyopathy, gross motor delay, and early death from respiratory insufficiency; to a late-onset form with variable onset of proximal muscle weakness and progressive respiratory insufficiency. Newborn screening programs have been instituted to presymptomatically identify neonates with infantile-onset Pompe disease for early initiation of treatment. However, infants with late-onset Pompe disease are also identified, leaving families and physicians in a state of uncertainty regarding prognosis, necessity, and timing of treatment initiation. This report presents a 31 5/7 weeks' gestational age premature infant flagged positive for Pompe disease with low dried blood spot GAA activity; sequencing identified biparental c.-32-13T>G/c.29delA GAA variants predicting late-onset Pompe disease. The infant's parents' initial reactions to the positive newborn screen, subsequent experience during confirmatory testing, and post-confirmation reflections are also reported. While uncertainties regarding natural history and prognosis of presymptomatically-identified late-onset Pompe disease infants will be elucidated with additional experience, suggestions for education of first-line providers are provided to accurately communicate results and compassionately counsel families regarding anxiety-provoking positive newborn screen results.

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.

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.

Lysosomal storage disease overview

The lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders that are caused for the most part by enzyme deficiencies within the lysosome resulting in accumulation of undegraded substrate. This storage process leads to a broad spectrum of clinical manifestations depending on the specific substrate and site of accumulation. Examples of LSDs include the mucopolysaccharidoses, mucolipidoses, oligosaccharidoses, Pompe disease, Gaucher disease, Fabry disease, the Niemann-Pick disorders, and neuronal ceroid lipofuscinoses. This review summarizes the main clinical features, diagnosis, and management of LSDs with an emphasis on those for which treatment is available.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Lysosomal storage disease overview

The lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders that are caused for the most part by enzyme deficiencies within the lysosome resulting in accumulation of undegraded substrate. This storage process leads to a broad spectrum of clinical manifestations depending on the specific substrate and site of accumulation. Examples of LSDs include the mucopolysaccharidoses, mucolipidoses, oligosaccharidoses, Pompe disease, Gaucher disease, Fabry disease, the Niemann-Pick disorders, and neuronal ceroid lipofuscinoses. This review summarizes the main clinical features, diagnosis, and management of LSDs with an emphasis on those for which treatment is available.

Pompe Disease: From Basic Science to Therapy

Pompe disease is a rare and deadly muscle disorder. As a clinical entity, the disease has been known for over 75 years. While an optimist might be excited about the advances made during this time, a pessimist would note that we have yet to find a cure. However, both sides would agree that many findings in basic science-such as the Nobel prize-winning discoveries of glycogen metabolism, the lysosome, and autophagy-have become the foundation of our understanding of Pompe disease. The disease is a glycogen storage disorder, a lysosomal disorder, and an autophagic myopathy. In this review, we will discuss how these past discoveries have guided Pompe research and impacted recent therapeutic developments.

Newborn Screening for Lysosomal Storage Diseases: Methodologies, Screen Positive Rates, Normalization of Datasets, Second-Tier Tests, and Post-Analysis Tools

All of the worldwide newborn screening (NBS) for lysosomal storage diseases (LSDs) is done by measurement of lysosomal enzymatic activities in dried blood spots (DBS). Substrates used for these assays are discussed. While the positive predictive value (PPV) is the gold standard for evaluating medical tests, current PPVs for NBS of LSDs cannot be used as a performance metric due to statistical sampling errors and uncertainty in the onset of disease symptoms. Instead, we consider the rate of screen positives as the only currently reliable way to compare LSD NBS results across labs worldwide. It has been suggested that the expression of enzymatic activity data as multiple-of-the-mean is a way to normalize datasets obtained using different assay platforms, so that results can be compared, and universal cutoffs can be developed. We show that this is often not the case, and normalization is currently not feasible. We summarize the recent use of pattern matching statistical analysis together with measurement of an expanded group of enzymatic activities and biomarkers to greatly reduce the number of false positives for NBS of LSDs. We provide data to show that these post-enzymatic activity assay methods are more powerful than genotype analysis for the stratification of NBS for LSDs.

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

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

Using Decision Analysis to Support Newborn Screening Policy Decisions: A Case Study for Pompe Disease

Background: Newborn screening is a public health program to identify conditions associated with significant morbidity or mortality that benefit from early intervention. Policy decisions about which conditions to include in newborn screening are complex because data regarding epidemiology and outcomes of early identification are often incomplete. Objectives: To describe expected outcomes of Pompe disease newborn screening and how a decision analysis informed recommendations by a federal advisory committee. Methods: We developed a decision tree to compare Pompe disease newborn screening with clinical identification of Pompe disease in the absence of screening. Cases of Pompe disease were classified into three types: classic infantile-onset disease with cardiomyopathy, nonclassic infantile-onset disease, and late-onset disease. Screening results and 36-month health outcomes were projected for classic and nonclassic infantile-onset cases. Input parameters were based on published and unpublished data supplemented by expert opinion. Results: We estimated that screening 4 million babies born each year in the United States would detect 40 cases (range: 13–56) of infantile-onset Pompe disease compared with 36 cases (range: 13–56) detected clinically without screening. Newborn screening would also identify 94 cases of late-onset Pompe disease that might not become symptomatic for decades. By 36 months, newborn screening would avert 13 deaths (range: 8–19) and decrease the number of individuals requiring mechanical ventilation by 26 (range: 20–28). Conclusions: Pompe disease is a rare condition, but early identification can improve health outcomes. Decision analytic modeling provided a quantitative data synthesis that informed the recommendation of Pompe disease newborn screening.

Moonlighting newborn screening markers: the incidental discovery of a second-tier test for Pompe disease

PURPOSE

To describe a novel biochemical marker in dried blood spots suitable to improve the specificity of newborn screening for Pompe disease.

METHODS

The new marker is a ratio calculated between the creatine/creatinine (Cre/Crn) ratio as the numerator and the activity of acid α-glucosidase (GAA) as the denominator. Using Collaborative Laboratory Integrated Reports (CLIR), the new marker was incorporated in a dual scatter plot that can achieve almost complete segregation between Pompe disease and false-positive cases.

RESULTS

The (Cre/Crn)/GAA ratio was measured in residual dried blood spots of five Pompe cases and was found to be elevated (range 4.41-13.26; 99%ile of neonatal controls: 1.10). Verification was by analysis of 39 blinded specimens that included 10 controls, 24 samples with a definitive classification (16 Pompe, 8 false positives), and 5 with genotypes of uncertain significance. The CLIR tool showed 100% concordance of classification for the 24 known cases. Of the remaining five cases, three p.V222M homozygotes, a benign variant, were classified by CLIR as false positives; two with genotypes of unknown significance, one likely informative, were categorized as Pompe disease.

CONCLUSION

The CLIR tool inclusive of the new ratio could have prevented at least 12 of 13 (92%) false-positive outcomes.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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