Divergent clinical outcomes of alpha-glucosidase enzyme replacement therapy in two siblings with infantile-onset Pompe disease treated in the symptomatic or pre-symptomatic state

Muscle-specific, liver-detargeted adeno-associated virus gene therapy rescues Pompe phenotype in adult and neonate Gaa-/- mice

Pompe disease (PD) is a neuromuscular disorder caused by acid α-glucosidase (GAA) deficiency. Reduced GAA activity leads to pathological glycogen accumulation in cardiac and skeletal muscles responsible for severe heart impairment, respiratory defects, and muscle weakness. Enzyme replacement therapy with recombinant human GAA (rhGAA) is the standard-of-care treatment for PD, however, its efficacy is limited due to poor uptake in muscle and the development of an immune response. Multiple clinical trials are ongoing in PD with adeno-associated virus (AAV) vectors based on liver- and muscle-targeting. Current gene therapy approaches are limited by liver proliferation, poor muscle targeting, and the potential immune response to the hGAA transgene. To generate a treatment tailored to infantile-onset PD, we took advantage of a novel AAV capsid able to increase skeletal muscle targeting compared to AAV9 while reducing liver overload. When combined with a liver-muscle tandem promoter (LiMP), and despite the extensive liver-detargeting, this vector had a limited immune response to the hGAA transgene. This combination of capsid and promoter with improved muscle expression and specificity allowed for glycogen clearance in cardiac and skeletal muscles of Gaa-/- adult mice. In neonate Gaa-/- , complete rescue of glycogen content and muscle strength was observed 6 months after AAV vector injection. Our work highlights the importance of residual liver expression to control the immune response toward a potentially immunogenic transgene expressed in muscle. In conclusion, the demonstration of the efficacy of a muscle-specific AAV capsid-promoter combination for the full rescue of PD manifestation in both neonate and adult Gaa-/- provides a potential therapeutic avenue for the infantile-onset form of this devastating disease.

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.

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.

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.

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.

Is Newborn Screening the Ultimate Strategy to Reduce Diagnostic Delays in Pompe Disease? The Parent and Patient Perspective

Pompe disease (PD) is a rare, autosomal-recessively inherited deficiency in the enzyme acid α-glucosidase. It is a spectrum disorder; age at symptom onset and rate of deterioration can vary considerably. In affected infants prognosis is poor, such that without treatment most infants die within the first year of life. To lose a baby in their first year of life to a rare disease causes much regret, guilt, and loneliness to parents, family, and friends. To lose a baby needlessly when there is an effective treatment amplifies this sadness. With so little experience of rare disease in the community, once a baby transfers to their home they are subject to a very uncertain and unyielding diagnostic journey while their symptomology progresses and their health deteriorates. With a rare disease like PD, the best opportunity to diagnose a baby is at birth. PD is not yet included in the current newborn screening (NBS) panel in Australia. Should it be? In late 2018 the Australian Pompe Association applied to the Australian Standing committee on Newborn Screening to have PD included. The application was not upheld. Here we provide an overview of the rationale for NBS, drawing on the scientific literature and perspectives from The Australian Pompe Association, its patients and their families. In doing so, we hope to bring a new voice to this very important debate.

Training, detraining, and retraining: Two 12-week respiratory muscle training regimens in a child with infantile-onset Pompe disease

BACKGROUND

Respiratory muscle weakness is a primary cause of morbidity and mortality in patients with Pompe disease. We previously described the effects of our 12-week respiratory muscle training (RMT) regimen in 8 adults with late-onset Pompe disease [1] and 2 children with infantile-onset Pompe disease [2].

CASE REPORT

Here we describe repeat enrollment by one of the pediatric participants who completed a second 12-week RMT regimen after 7 months of detraining. We investigated the effects of two 12-week RMT regimens (RMT #1, RMT #2) using a single-participant A-B-A experimental design. Primary outcome measures were maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP). Effect sizes for changes in MIP and MEP were determined using Cohen's d statistic. Exploratory outcomes targeted motor function.

RELEVANCE

From pretest to posttest, RMT #2 was associated with a 25% increase in MIP and a 22% increase in MEP, corresponding with very large effect sizes (d= 2.92 and d= 2.65, respectively). Following two 12-week RMT regimens over 16 months, MIP increased by 69% and MEP increased by 97%, corresponding with very large effect sizes (d= 3.57 and d= 5.10, respectively). MIP and MEP were largely stable over 7 months of detraining between regimens. Magnitude of change was greater for RMT #1 relative to RMT #2.

Improvement in Cardiac Function With Enzyme Replacement Therapy in a Patient With Infantile-Onset Pompe Disease

Background

Pompe disease is a lysosomal storage disorder that results from an inborn error of metabolism involving abnormal glycogen storage. Infantile-onset Pompe disease is the most severe phenotype, and enzyme replacement therapy with alglucosidase alfa (Lumizyme) improves medical and functional outcomes in patients with infantile-onset Pompe disease.

Case Report

We report the case of a patient with infantile-onset Pompe disease who presented with severe hypertrophic cardiomyopathy, systolic and diastolic cardiac dysfunction, and hypotonia. She experienced significant improvement in cardiac systolic function while receiving enzyme replacement therapy.

Conclusion

Typically, patients with infantile-onset Pompe disease and severe hypertrophic cardiomyopathy are not as responsive to enzyme replacement therapy as patients with mild or no hypertrophic cardiomyopathy. We demonstrated the efficacy of enzyme replacement therapy in a patient with severe hypertrophic cardiomyopathy.

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

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

Long term clinical history of an Italian cohort of infantile onset Pompe disease treated with enzyme replacement therapy

Background

Enzyme replacement therapy (ERT) has deeply modified the clinical history of Infantile Onset Pompe Disease (IOPD). However, its long-term effectiveness is still not completely defined. Available data shows a close relationship between clinical outcome and patients’ cross-reactive immunological status (CRIM), being CRIM-negative status a negative prognostic factor. At the same time limited data are available on the long-term treatment in CRIM-positive infants.

Methods

A retrospective multicentre observational study was designed to analyse the long-term effectiveness of ERT in IOPD. Thirteen Italian centres spread throughout the country were involved and a cohort of 28 patients (15 females, 13 males, born in the period: February 2002–January 2013) was enrolled. IOPD diagnosis was based on clinical symptoms, enzymatic and molecular analysis. All patients received ERT within the first year of life. Clinical, laboratory, and functional data (motor, cardiac and respiratory) were collected and followed for a median period of 71 months (5 years 11 months).

Results

Median age at onset, diagnosis and start of ERT were 2, 3 and 4 months, respectively. CRIM status was available for 24/28 patients: 17/24 (71%) were CRIM-positive. Nineteen patients (67%) survived > 2 years: 4 were CRIM-negative, 14 CRIM-positive and one unknown. Six patients (5 CRIM-positive and one unknown) never needed ventilation support (21,4%) and seven (6 CRIM-positive and one unknown: 25%) developed independent ambulation although one subsequently lost this function. Brain imaging study was performed in 6 patients and showed peri-ventricular white matter abnormalities in all of them. Clinical follow-up confirmed the better prognosis for CRIM-positive patients, though a slow, progressive worsening of motor and/or respiratory functions was detected in 8 patients.

Conclusions

These data are the result of the longest independent retrospective study on ERT in IOPD reported so far outside clinical trials. The data obtained confirmed the better outcome of the CRIM-positive patients but at the same time, showed the inability of the current therapeutic approach to reverse or stabilize the disease progression. The results also evidenced the involvement of central nervous system in Pompe disease. To better understand the disease clinical history and to improve treatment efficacy larger multicentre studies are needed as well as the development of new therapeutic approaches.

The humanistic burden of Pompe disease: are there still unmet needs? A systematic review

BACKGROUND

Humanistic burden considers the impact of an illness on a patient's health-related quality of life (HRQoL), activities of daily living (ADL), caregiver health, and caregiver QoL. Humanistic burden also considers treatment satisfaction and adherence to treatment regimens. Pompe disease is an autosomal recessive, progressive, multisystemic neuromuscular disease. Approval of enzyme-replacement therapy (ERT) markedly improved prognosis for patients, but considerable morbidity and a substantial humanistic burden remain. This article characterizes the humanistic burden of Pompe disease through a systematic literature review.

METHODS

A systematic search of MEDLINE® and Embase® with back-referencing and supplementary literature searches was performed to retrieve data from interventional and non-interventional studies on the humanistic burden of Pompe disease. Publications were screened according to predefined criteria, extracted, and assessed for quality. Extracted data were narratively synthesized.

RESULTS

No publications on the humanistic burden of infantile-onset Pompe disease (IOPD) were identified. As such, of 17 publications included here, all are in patients with late-onset Pompe disease (LOPD). Thirteen publications were initiated after approval of ERT, two were initiated before, and two overlapped the approval of ERT. The review shows that LOPD patients have a significantly lower HRQoL than the general population, even if treated with ERT. On transitioning to ERT, treatment was associated with improvement in the physical component score of the SF-36 and fatigue, although the SF-36 mental component score remained stable. Physical HRQoL remained below population norms after 4 years of ERT. Significantly more ERT-treated patients reported pain than controls, and bodily pain worsened in later years following ERT initiation. Treatment-naïve LOPD patients had significantly poorer ADL functioning compared with the general population, although ERT stabilized deteriorating functioning impairment. ERT studies showed caregivers provide 17.7 h/week informal care on average. Fifty percent, 40% and <20% of caregivers reported mental health, physical health, and financial/relational problems, respectively. In ERT-naïve patients, wheelchair use and home ventilatory support was associated with lower physical HRQoL and ADL functioning. In ERT-treated patients, key factors predicting worse HRQoL and ADL functioning were higher respiratory distress, poorer sleep quality, greater pain, and more fatigue.

CONCLUSIONS

Pompe disease has a substantial humanistic burden, with strong inter-relationships among and between humanistic burden parameters and clinical progression.