Effectiveness of enzyme replacement therapy in adults with late-onset Pompe disease: results from the NCS-LSD cohort study

Establishing how much improvement in lung function and distance walked is clinically important for adult patients with Pompe disease

BACKGROUND AND PURPOSE

Pompe disease is a rare, inheritable, progressive metabolic myopathy. This study aimed to estimate the minimal clinically important difference (MCID) for an improvement in forced vital capacity in the upright seated position (FVCup) and the 6-min walk test (6MWT) after a year of treatment with enzyme replacement therapy.

METHODS

Data were obtained from two prospective follow-up studies. Between-group and within-group MCIDs were estimated using anchor-based methods. Additionally, a distribution-based method was used to generate supportive evidence. As anchors, self-reported change in health and in physical functioning, shortness of breath and a categorization of the Short-Form 36 Physical Component Summary score were used. Anchor appropriateness was assessed using Spearman correlations (absolute values ≥0.29) and a sufficient number of observations in each category.

RESULTS

In all, 102 patients had at least one FVCup or 6MWT measurement during enzyme replacement therapy. Based on the anchors assessed as appropriate, the between-group MCID for an improvement in FVCup ranged from 2.47% to 4.83% points. For the 6MWT, it ranged from 0.35% to 7.47% points which is equivalent to a distance of 2.18-46.61 m and 1.97-42.13 m for, respectively, a man and a woman of age 50, height 1.75 m and weight 80 kg. The results of the distribution-based method were within these ranges when applied to change in the outcome values.

CONCLUSION

The MCIDs for FVCup and 6MWT derived in this study can be used to interpret differences between and within groups of patients with Pompe disease in clinical trials and cohort studies.

Disease-specific therapy for the treatment of the cardiovascular manifestations of Fabry disease: a systematic review

OBJECTIVE

The cardiovascular manifestations of Fabry disease are common and represent the leading cause of death. Disease-specific therapy, including enzyme replacement therapy (ERT) and chaperone therapy (migalastat), is recommended for patients exhibiting cardiovascular involvement, but its efficacy for modulating cardiovascular disease expression and optimal timing of initiation remains to be fully established. We therefore aimed to systematically review and evaluate the effectiveness of disease-specific therapy compared with placebo, and to no intervention, for the cardiovascular manifestations of Fabry disease.

METHODS

Eight databases were searched from inception using a combination of relevant medical subject headings and keywords. Randomised, non-randomised studies with a comparator group and non-randomised studies without a comparator group were included. Studies were screened for eligibility and assessed for bias by two independent authors. The primary outcome comprised clinical cardiovascular events. Secondary outcomes included myocardial histology and measurements of cardiovascular structure, function and tissue characteristics.

RESULTS

72 studies were included, comprising 7 randomised studies of intervention, 16 non-randomised studies of intervention with a comparator group and 49 non-randomised studies of intervention without a comparator group. Randomised studies were not at serious risk of bias, but the others were at serious risk. Studies were highly heterogeneous in their design, outcome measurements and findings, which made assessment of disease-specific therapy effectiveness difficult.

CONCLUSION

It remains unclear whether disease-specific therapy sufficiently impacts the cardiovascular manifestations of Fabry disease. Further work, ideally in larger cohorts, with more standardised clinical and phenotypic outcomes, the latter measured using contemporary techniques, are required to fully elucidate the cardiovascular impact of disease-specific therapy.

PROSPERO REGISTRATION NUMBER

CRD42022295989.

Are Anti-rhGAA Antibodies a Determinant of Treatment Outcome in Adults with Late-Onset Pompe Disease? A Systematic Review

BACKGROUND

Pompe disease is a lysosomal storage disease characterised by skeletal and respiratory muscle weakness. Since 2006, enzyme replacement therapy (ERT) with alglucosidase alfa has been available. ERT significantly improves the prognosis of patients with Pompe disease. The effect of high antibody titres on treatment response in adults with late-onset Pompe disease (LOPD) remains unclear but may contribute to interpatient variation. We therefore conducted a systematic review on this subject.

METHODS

A systematic search was performed in Embase, Medline Ovid, Web of Science, Psych Info Ovid, Cochrane (Clinical Trials only), and Google Scholar (random top-200). Articles were included if they involved adults with LOPD treated with alglucosidase alfa and mentioned anti-rhGAA antibodies or antibody titres. In addition, articles mentioning dosages different from the standard recommended dosage were included.

RESULTS

Our literature search retrieved 2562 publications, and 17 fulfilled our selection criteria, describing 443 cases. Seven publications reported on anti-rhGAA antibody titres on a group level, with the percentage of patients with a high titre as defined in the included articles ranging from 0-33%. Six publications reported on the effect of anti-rhGAA antibody titre on clinical course, and four found no correlation. Two studies reported a negative effect on treatment. The first study found a greater improvement in Medical Research Council (MRC) score in patients with no detectable antibody titre. In the second study, a patient discontinued ERT due to a declining neuromuscular state as a result of high anti-rhGAA antibody titres. Seven publications reported on 17 individual patients with a high antibody titre (range 1:12,800-1:3,906,250). In only two cases were high-sustained neutralising antibodies reported to interfere with treatment efficacy.

CONCLUSIONS

No clear effect of anti-rhGAA IgG antibodies on treatment response could be established for the majority of LOPD patients with a high antibody titre. In a minority of patients, a clinical decline related to (possible) interference of anti-rhGAA antibodies was described.

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.

Home-based enzyme replacement therapy in children and adults with Pompe disease; a prospective study

BACKGROUND

Pompe disease is a lysosomal storage disease treated with life-long enzyme replacement therapy (ERT). Home-based ERT has been provided in the Netherlands since 2008 because it diminishes the burden of treatment, increases patient flexibility and autonomy, and is thus a more patient-centred approach to ERT.

METHODS

All Dutch Pompe patients receiving alglucosidase alfa infusions at home were approached to participate in a questionnaire to validate the safety of home-based ERT. Prospective data on symptoms occurring during or within 48 h after infusion and retrospective data on infusion associated reactions (IARs) in the last three months were collected four times during one year.

RESULTS

In total, 116 out of 120 eligible patients (17 classic infantile, 2 atypical infantile, 15 childhood onset and 82 adult) filled out 423 questionnaires (response rate: 88.1%). Symptoms during or after infusion were reported 27 times in 17 patients. Fatigue was the most commonly reported health complaint (in 9.5% of patients). Four health complaints were judged to be IARs and reported to the Erasmus MC University Medical Center. None of the IARs reported in this study warranted emergency clinical care.

CONCLUSIONS

Our data demonstrate that home-based ERT in Pompe disease can be safely implemented as few, mostly mild, symptoms were reported during or after infusion. Insights from this study can be used as a base for implementing home-based ERT in other countries and to further optimize patient care, as unreported mild symptoms do not pose a health risk but may still be relevant to the patient.

Association between changes in pulmonary function and in patient reported outcomes during enzyme therapy of adult patients with late-onset Pompe disease

Pompe disease is a rare, progressive, and metabolic myopathy. Reduced pulmonary function is one of the main problems seen in adult patients with late-onset Pompe disease (LOPD). We aimed to explore the association between changes over time in pulmonary function and in patient-reported outcome measures (PROMs), in these patients treated with enzyme replacement therapy (ERT). This is a post hoc analysis of two cohort studies. Pulmonary function was assessed as forced vital capacity in the upright position (FVC_up ). As PROMs, we assessed the physical component summary score (PCS) of the Medical Outcome Study 36-item Short-Form Health Survey (SF-36) and daily life activities (Rasch-Built Pompe-Specific Activity [R-PACT] scale). We fitted Bayesian multivariate mixed-effects models. In the models of PROMs, we assumed a linear association with FVC_up , and adjusted for time (nonlinear), sex, and age and disease duration at the start of ERT. One hundred and one patients were eligible for analysis. PCS and R-PAct were positively associated with FVC_up , while their relation with time was nonlinear (initial increase then decrease). A 1%-point increase in FVC_up is expected to increase PCS by 0.14 points (95% Credible Interval: [0.09;0.19]) and R-PACT by 0.41 points [0.33;0.49] at the same time point. In the first year of ERT, we expect a change of PCS and R-PAct scores by +0.42 and +0.80 points, and in the 5th year of +0.16 and +0.45, respectively. We conclude that the physical domain of quality of life and daily life activities improve when FVC_up increases during ERT.

Lentiviral gene therapy prevents anti-human acid α-glucosidase antibody formation in murine Pompe disease

Enzyme replacement therapy (ERT) is the current standard treatment for Pompe disease, a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). ERT has shown to be lifesaving in patients with classic infantile Pompe disease. However, a major drawback is the development of neutralizing antibodies against ERT. Hematopoietic stem and progenitor cell-mediated lentiviral gene therapy (HSPC-LVGT) provides a novel, potential lifelong therapy with a single intervention and may induce immune tolerance. Here, we investigated whether ERT can be safely applied as additional or alternative therapy following HSPC-LVGT in a murine model of Pompe disease. We found that lentiviral expression at subtherapeutic dose was sufficient to induce tolerance to the transgene product, as well as to subsequently administered ERT. Immune tolerance was established within 4–6 weeks after gene therapy. The mice tolerated ERT doses up to 100 mg/kg, allowing ERT to eliminate glycogen accumulation in cardiac and skeletal muscle and normalizing locomotor function. The presence of HSPC-derived cells expressing GAA in the thymus suggested the establishment of central immune tolerance. These findings demonstrate that lentiviral gene therapy in murine Pompe disease induced robust and long-term immune tolerance to GAA either expressed by a transgene or supplied as ERT.

Bioimpedance Phase Angle as a Prognostic Tool in Late-Onset Pompe Disease: A Single-Centre Prospective Study With a 15-year Follow-Up

Background: Late-onset Pompe disease (LOPD) is an autosomal-recessive metabolic myopathy caused by deficiency of the lysosomal enzyme Acid Alpha—Glucosidase (GAA), leading to glycogen accumulation in proximal and axial muscles, and in the diaphragm. Enzyme Replacement Therapy (ERT) with recombinant GAA became available in 2006. Since then, several outcome measures have been investigated for the adequate follow-up of disease progression and treatment response, usually focusing on respiratory and motor function. Prognostic factors predicting outcome have not been identified till now.

Methods: In this single Centre, prospective study, we evaluate the response to enzyme replacement therapy in 15 patients (7 males) with LOPD in different stages of disease, aged 49.4 ± 16.1, followed-up for 15 years. Treatment response was measured by the 6-min walking test, vital capacity in supine and upright position, respiratory muscle strength, muscle MRI, manual muscle testing. We investigated the usefulness of Body Impedance Vectorial Analysis for serial body composition assessment.

Results: Although most patients with LOPD benefit from long-term treatment, some secondary decline may occur after the first 3–5 years. Some nutritional (lower body mass index, higher fat free mass, higher phase angle) and disease parameters (higher creatinine and shorter disease duration at the beginning of treatment) seem to predict a better motor outcome. Lower Phase Angle, possibly reflecting loss of integrity of skeletal muscle membranes and thus treatment mis-targeting, seems to correlate with worse treatment response on long-term follow-up.

Conclusion: Body Impedance Vectorial Analysis is a fast, easily performed and cheap tool that may be able to predict long-term treatment response in patients with LOPD. Low Phase angle may serve as a marker of muscle quality and may be used to predict the response to a muscle-targeted intervention such as ERT, thus improving the identification of patients needing a closer follow-up due to higher fragility and risk of deterioration.

Six-Minute Walk Distance Is a Useful Outcome Measure to Detect Motor Decline in Treated Late-Onset Pompe Disease Patients

Late-onset Pompe disease (LOPD) is a rare, progressive disorder characterized by limb–girdle muscle weakness and/or respiratory insufficiency, caused by acid alpha-glucosidase (GAA) gene mutations and treated with enzyme replacement therapy. We studied isometric muscle strength in eight muscle groups bilaterally using a Biodex® dynamometer, as well as the Medical Research Council sum score (MRC-SS), hand grip strength, 6 min walk distance (6MWD), 10 m walk test (10MWT) and timed up-and-go test (TUG) in 12 adult, ambulatory, treated LOPD patients and 12 age-/gender-matched healthy controls, every 6 months for 2 years. The mean isometric muscle strength showed a significant decline in right and left knee extensors at 12 months in controls (p < 0.014; p < 0.016), at 18 months in patients (p < 0.010; p < 0.007) and controls (only right side, p < 0.030) and at 24 months in both groups (p < 0.035). The mean 6MWD in patients significantly decreased after 24 months, from 451.9 m to 368.1 m (p < 0.003), whereas in controls, the mean 6MWD significantly increased after 6 months (p < 0.045) and 18 months (p < 0.020) (at 24 months p = 0.054). In patients and controls, the MRC-SS, hand grip test, 10MWT and TUG did not show significant changes (p > 0.05). We conclude that the 6MWD is a useful outcome measure to detect motor decline in treated LOPD patients.

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.

Clinical efficacy of the enzyme replacement therapy in patients with late-onset Pompe disease: a systematic review and a meta-analysis

In patients with late-onset Pompe disease (LOPD), the efficacy of the enzyme replacement therapy (ERT) with recombinant human alpha-glucosidase (rhGAA) is difficult to evaluate, due to the clinical heterogeneity and the small sample sizes in published studies. Therefore, we conduct a systematic literature review and meta-analysis of the literature to evaluate the efficacy of ERT in LOPD patients considering the walking distance, respiratory function and muscle strength. Particularly, six-minute walk test (6MWT), forced vital capacity (FVC), medical research council (MRC) grading, quantitative muscle testing (QMT), and quick motor function test (QMFT) were outcomes of interest. Overall, 619 studies were identified in PubMed, EMBASE and by manual search on July 18th, 2020. After an initial assessment, 16 studies were included in the meta-analysis, containing clinical data from 589 patients with LOPD. For the 6MWT, 419 patients were analyzed. Walking distance improved on average, 32.2 m greater during the observed period (p = 0.0003), compared to the distance at the baseline. The meta-analysis did not show any improvement in FVC and only a tendency towards better muscle strength after treatment with ERT, but the difference was not statistically significant. In conclusion, the available data showed that ERT has a significant beneficial efficacy in the improvement of walking distance in LOPD patients and a non-significant improvement of muscle strength. No improvement in respiratory capacity was found. More prospective and controlled trials are needed to demonstrate a clear clinical benefit of ERT.

Long-term benefit of enzyme replacement therapy with alglucosidase alfa in adults with Pompe disease: Prospective analysis from the French Pompe Registry

Despite a wide clinical spectrum, the adult form of Pompe disease is the most common one, and represents more than 90% of diagnosed patients in France. Since the marketing of enzyme replacement therapy (alglucosidase alfa, Myozyme), all reports to date in adults demonstrated an improvement of the walking distance, and a trend toward stabilization of respiratory function, but the majority of these studies were less than 5 years of duration. We report here the findings from 158 treated patients included in the French Pompe Registry, who underwent regular clinical assessments based on commonly used standardized tests (6-minute walking test, MFM scale, sitting vital capacity, MIP and MEP). For longitudinal analyses, the linear mixed effects models were used to assess trends in primary endpoints over time under ERT. A two-phase model better described the changes in distance traveled in the 6-minute walk test and MFM. 6MWT showed an initial significant increase (1.4% ± 0.5/year) followed by a progressive decline (-2.3%/year), with a cut-off point at 2.2 years. A similar pattern was observed in total MFM score (6.6% ± 2.3/year followed by a - 1.1%/year decline after 0.5 years). A single-phase decline with a slope of -0.9 ± 0.1%/year (P < .001) was observed for FVC, and MEP remained stable over the all duration of follow-up. This study provides further evidence that ERT improves walking abilities and likely stabilizes respiratory function in adult patients with Pompe disease, with a ceiling effect for the 6MWT in the first 3 years of treatment.

Body composition and 6 minute walking ability in late-onset pompe disease patients after 9 years of enzyme replacement therapy

OBJECTIVE

Pompe disease is a rare autosomal recessive disorder caused by the deficiency of acid α-glycosidase resulting in accumulation of glycogen in the lysosomes. The late-onset form of the disease (LOPD) causes primarily progressive muscle weakness and respiratory insufficiency. Enzyme replacement therapy (ERT) introduced in 2006, showed mild improvement or stabilization of the symptoms although long-term data are limited. Aim of the study was to describe the progression of body composition and walking ability in LOPD patients receiving ERT consistently for 9 years.

METHODS

Lean body mass, bone mineral density, body fat and 6 min walking distance were assessed in three male and three female LOPD patients (height 165.8 ± 11.2 cm, age 42.3 ± 11.8yrs, body mass 71.1 ± 20.8 kg, at study entry), every three years, for 9 years since ERT initiation (T0, T3, T6, T9).

RESULTS

Total body and upper extremities' lean mass remained unchanged (p < 0.05), but it was decreased for the lower extremities (T3:13.06 ± 3.848 kg vs. T9:11.63 ± 3.49 kg, p < 0.05). Lean body mass was not significantly different after 9 years of ERT compared to before the ERT initiation (T0 to T9). Bone mineral density remained unchanged. Percent body fat increased (T0:39.1 ± 10.3%, vs. T9:43.1 ± 10.4%, p < 0.05). Six minute walking distance tended to increase after 3 years of ERT and decreased gradually thereafter, with no difference between T0-T9. Lean mass of the lower extremities adjusted for body weight was significantly correlated with 6 min walking distance (r = 0.712, p < 0.05).

CONCLUSION

The current data show that enzyme replacement therapy may preserve lean body mass, bone mineral density and walking capacity in LOPD patients.

Gene therapy with secreted acid alpha-glucosidase rescues Pompe disease in a novel mouse model with early-onset spinal cord and respiratory defects

Background

Pompe disease (PD) is a neuromuscular disorder caused by deficiency of acidalpha-glucosidase (GAA), leading to motor and respiratory dysfunctions. Available Gaa knock-out (KO) mouse models do not accurately mimic PD, particularly its highly impaired respiratory phenotype.

Methods

Here we developed a new mouse model of PD crossing Gaa KO^B6;129 with DBA2/J mice. We subsequently treated Gaa KO^DBA2/J mice with adeno-associated virus (AAV) vectors expressing a secretable form of GAA (secGAA).

Findings

Male Gaa KO^DBA2/J mice present most of the key features of the human disease, including early lethality, severe respiratory impairment, cardiac hypertrophy and muscle weakness. Transcriptome analyses of Gaa KO^DBA2/J, compared to the parental Gaa KO^B6;129 mice, revealed a profoundly impaired gene signature in the spinal cord and a similarly deregulated gene expression in skeletal muscle. Muscle and spinal cord transcriptome changes, biochemical defects, respiratory and muscle function in the Gaa KO^DBA2/J model were significantly improved upon gene therapy with AAV vectors expressing secGAA.

Interpretation

These data show that the genetic background impacts on the severity of respiratory function and neuroglial spinal cord defects in the Gaa KO mouse model of PD. Our findings have implications for PD prognosis and treatment, show novel molecular pathophysiology mechanisms of the disease and provide a unique model to study PD respiratory defects, which majorly affect patients.

Funding

This work was supported by Genethon, the French Muscular Dystrophy Association (AFM), the European Commission (grant nos. 667751, 617432, and 797144), and Spark Therapeutics.

Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review

Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness. It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure. In untreated LOPD, the most common cause of death is respiratory failure. Patients suffering from respiratory compromise may present with symptoms of sleep-disordered breathing (SDB) before overt signs of respiratory failure. Diaphragm weakness leads to nocturnal hypoventilation, which can result in sleep disruption. Both subjective and objective sleep quality can be impaired with associated excessive daytime sleepiness (EDS). Health-related quality of life worsens as sleep disturbance increases. The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure. These patients are at risk of acute deterioration due to lower respiratory tract infections; effective secretion clearance and vaccination against common pathogens is an important facet of care. Whilst disease-modifying enzyme replacement therapy (ERT) delays progression of locomotor dysfunction and prolongs life, its effect on respiratory function and SDB remains unclear. There are no data demonstrating the impact of ERT on sleep quality or SDB.

Pompe Disease: New Developments in an Old Lysosomal Storage Disorder

Pompe disease, also known as glycogen storage disease type II, is caused by the lack or deficiency of a single enzyme, lysosomal acid alpha-glucosidase, leading to severe cardiac and skeletal muscle myopathy due to progressive accumulation of glycogen. The discovery that acid alpha-glucosidase resides in the lysosome gave rise to the concept of lysosomal storage diseases, and Pompe disease became the first among many monogenic diseases caused by loss of lysosomal enzyme activities. The only disease-specific treatment available for Pompe disease patients is enzyme replacement therapy (ERT) which aims to halt the natural course of the illness. Both the success and limitations of ERT provided novel insights in the pathophysiology of the disease and motivated the scientific community to develop the next generation of therapies that have already progressed to the clinic.

Positive association between physical outcomes and patient-reported outcomes in late-onset Pompe disease: a cross sectional study

Background

Pompe disease is a rare, progressive metabolic myopathy. The aim of this study is to investigate the associations of physical outcomes with patient-reported outcome measures (PROMs) in late-onset Pompe disease.

Methods

We included 121 Dutch adult patients with Pompe disease.

Physical outcomes comprised muscle strength (manual muscle testing using Medical Research Council [MRC] grading, hand-held dynamometry [HHD]), walking ability (6-min walk test [6MWT]), and pulmonary function (forced vital capacity [FVC] in upright and supine positions).

PROMs comprised quality of life (Short Form 36 health survey [SF-36]), participation (Rotterdam Handicap Scale [RHS]) and daily-life activities (Rasch-Built Pompe-Specific Activity [R-PAct] Scale).

Analyses were cross-sectional: the time-point before, and closest to, start of Enzyme Replacement Therapy was chosen. Associations between PROMs and physical outcomes were investigated using linear regression models.

Results

RHS and R-PAct scores were better in patients with higher FVC supine and upright, HHD, MRC and 6MWT scores, accounting for the effect of sex, disease duration, use of wheelchair and ventilator support. While the SF-36 Physical Component Summary (PCS) was correlated positively with FVC upright, HHD, MRC and 6MWT scores, there was no significant relationship between the SF-36 Mental Component Summary (MCS) and any of the physical outcomes.

Conclusions

Participation, daily-life activities, and the physical component of quality of life of adult Pompe patients are positively correlated to physical outcomes. This work serves as a first step towards assessing how changes over time in physical outcomes are related to changes in PROMs, and to define the minimal change in physical outcomes required to make an important difference for the patient.

Cost-effectiveness analysis of enzyme replacement therapy (ERT) for treatment of infantile-onset Pompe disease (IOPD) in the Iranian pharmaceutical market

Infantile-onset Pompe disease (IOPD) or acid maltase deficiency is a rare metabolic disorder. It is caused by a deficiency in functioning of the enzyme acid alpha-glucosidase and leads to the accumulation of glycogen in the liver, heart, muscle, and other tissues. Myozyme is an effective drug, but it imposes a heavy financial burden on societies and healthcare systems. Therefore, this study was conducted to analyze the cost-effectiveness of Myozyme compared to conventional therapy for the treatment of IOPD. PubMed, Scopus, Web of Science, and Cochrane library databases were searched on December 2018 to identify the effectiveness of Myozyme versus conventional therapy. Then, a cost-effectiveness and a cost utility study were conducted in patients suffering from IOPD. In this cost effectiveness and cost utility analysis, Markov and decision tree models were used for modeling. Model parameters were obtained from international data, and the perspective of the payer was considered. Every cycle was one year; the model was run for 22 cycles. TreeAge pro 2011 was used for analysis. Finally, one-way and probabilistic sensitivity analyses were performed. Two papers were included and 39 patients were evaluated as the treatment group in both studies. Results revealed the effectiveness of Myozyme. Results also revealed a wide range of adverse reactions. Enzyme replacement therapy (ERT) resulted in 4.21038 quality-adjusted life years (QALY) per $381,852. The incremental cost per QALY was $96,809 and the incremental cost per life years gained (LYG) was 74,429 over a 22-year time horizon. Sensitivity analysis indicated the robustness of the results. Myozyme is effective for IOPD and could increase the life expectancy of patients significantly. However, since the calculated incremental cost per QALY was 17 times higher than the GDP per capita of Iran, Myozyme is not cost effective in Iran.

Treating lysosomal storage disorders: What have we learnt?

The first enzyme replacement therapy (ERT) for a lysosomal storage disorder (LSD) was approved in 1991 and we now have more than 25 years of experience of treating patients with type 1 Gaucher disease. Because of the remarkable success of this therapy, enormous effort and resource has gone into developing other ERTs, for Gaucher (where three different enzyme preparations have now been approved) and for other LSDs. We now have more than 10 years of clinical experience in using ERT to treat Gaucher, Fabry, Pompe and MPS I, II, and VI. This article aims to assess the real-life experience of a selection of these innovative and expensive treatments to see if they have met the high expectations which were set for them when they launched.

Large variation in effects during 10 years of enzyme therapy in adults with Pompe disease

Objective

To determine the effects of 10 years of enzyme replacement therapy (ERT) in adult patients with Pompe disease, focusing on individual variability in treatment response.

Methods

In this prospective, multicenter cohort study, we studied 30 patients from the Netherlands and France who had started ERT during the only randomized placebo-controlled clinical trial with ERT in late-onset Pompe disease (NCT00158600) or its extension (NCT00455195) in 2005 to 2008. Main outcomes were walking ability (6-minute walk test [6MWT]), muscle strength (manual muscle testing using Medical Research Council [MRC] grading), and pulmonary function (forced vital capacity [FVC] in the upright and supine positions), assessed at 3- to 6-month intervals before and after the start of ERT. Data were analyzed with linear mixed-effects models for repeated measurements.

Results

Median follow-up duration on ERT was 9.8 years (interquartile range [IQR] 8.3–10.2 years). At the group level, baseline 6MWT was 49% of predicted (IQR 41%–60%) and had deteriorated by 22.2 percentage points (pp) at the 10-year treatment point (p < 0.001). Baseline FVC upright was 54% of predicted (IQR 47%–68%) and decreased by 11 pp over 10 years (p < 0.001). Effects of ERT on MRC sum score and FVC supine were similar. At the individual level, 93% of patients had initial benefit of ERT. Depending on the outcome measured, 35% to 63% of patients had a secondary decline after ≈3 to 5 years. Still, at 10 years of ERT, 52% had equal or better 6MWT and/or FVC upright compared to baseline.

Conclusions

The majority of patients with Pompe disease benefit from long-term ERT, but many patients experience some secondary decline after ≈3 to 5 years. Individual variation, however, is considerable.

Classification of evidence

This study provides Class IV evidence that for the majority of adults with Pompe disease, long-term ERT positively affects, or slows deterioration in, muscle strength, walking ability, and/or pulmonary function.

A pattern-based approach to the interpretation of skeletal muscle biopsies

The interpretation of muscle biopsies is complex and provides the most useful information when integrated with the clinical presentation of the patient. These biopsies are performed for workup of a wide range of diseases including dystrophies, metabolic diseases, and inflammatory processes. Recent insights have led to changes in the classification of inflammatory myopathies and have changed the role that muscle biopsies have in the workup of inherited diseases. These changes will be reviewed. This review follows a morphology-driven approach by discussing diseases of skeletal muscle based on a few basic patterns that include cases with (1) active myopathic damage and inflammation, (2) active myopathic damage without associated inflammation, (3) chronic myopathic changes, (4) myopathies with distinctive inclusions or vacuoles, (5) biopsies mainly showing atrophic changes, and (6) biopsies that appear normal on routine preparations. Each of these categories goes along with certain diagnostic considerations and pitfalls. Individual biopsy features are only rarely pathognomonic. Establishing a firm diagnosis therefore typically requires integration of all of the biopsy findings and relevant clinical information. With this approach, a muscle biopsy can often provide helpful information in the diagnostic workup of patients presenting with neuromuscular problems.

Long-term follow-up of 17 patients with childhood Pompe disease treated with enzyme replacement therapy

OBJECTIVES

Pompe disease is a progressive metabolic myopathy for which enzyme replacement therapy (ERT) was approved in 2006. While various publications have examined the effects of ERT in classic-infantile patients and in adults, little has been published on ERT in children with non-classic presentations.

STUDY DESIGN

This prospective study was conducted from June 1999 to May 2015. Seventeen patients from various countries participated. Outcome measures comprised muscle function (6-minute walk test, quick motor-function test (QMFT)), muscle strength (hand-held dynamometry; manual muscle testing), and lung function (FVC sitting and supine). For each outcome measure, we used linear mixed-effects models to calculate the difference at group level between the start of therapy and 7 years of ERT. Patients' individual responses over time were also evaluated.

RESULTS

Eleven males and six females started ERT at ages between 1.1 and 16.4 years (median 11.9 years); 82% of them carried the common c.-32-13T > G GAA gene variant on one allele. At group level, distance walked increased by 7.4 percentage points (p < 0.001) and QMFT scores increased by 9.2 percentage points (p = 0.006). Muscle strength scores seemed to remain stable. Results on lung function were more variable. Patients' individual data show that the proportion of patients who stabilized or improved during treatment ranged between 56 and 69% for lung function outcomes and between 71 and 93% for muscle strength and muscle function outcomes.

CONCLUSIONS

We report a positive effect of ERT in patients with childhood Pompe disease at group level. For some patients, new or personalized treatments should be considered.

Satellite cells fail to contribute to muscle repair but are functional in Pompe disease (glycogenosis type II)

Pompe disease, which is due to acid alpha-glucosidase deficiency, is characterized by skeletal muscle dysfunction attributed to the accumulation of glycogen-filled lysosomes and autophagic buildup. Despite the extensive tissue damages, a failure of satellite cell (SC) activation and lack of muscle regeneration have been reported in patients. However, the origin of this defective program is unknown. Additionally, whether these deficits occur gradually over the disease course is unclear. Using a longitudinal pathophysiological study of two muscles in a Pompe mouse model, here, we report that the enzymatic defect results in a premature saturating glycogen overload and a high number of enlarged lysosomes. The muscles gradually display profound remodeling as the number of autophagic vesicles, centronucleated fibers, and split fibers increases and larger fibers are lost. Only a few regenerated fibers were observed regardless of age, although the SC pool was preserved. Except for the early age, during which higher numbers of activated SCs and myoblasts were observed, no myogenic commitment was observed in response to the damage. Following in vivo injury, we established that muscle retains regenerative potential, demonstrating that the failure of SC participation in repair is related to an activation signal defect. Altogether, our findings provide new insight into the pathophysiology of Pompe disease and highlight that the activation signal defect of SCs compromises muscle repair, which could be related to the abnormal energetic supply following autophagic flux impairment.

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.

Enzyme replacement therapy reduces the risk for wheelchair dependency in adult Pompe patients

Background

Pompe disease is a rare metabolic myopathy. In adult patients, progressive weakness of limb-girdle and respiratory muscles often leads to wheelchair and respirator dependency. Clinical studies have shown enzyme replacement therapy (ERT) to positively affect motor and respiratory outcomes. Here we investigate whether ERT reduces patients’ risk of needing a wheelchair or respirator.

Methods

Data were collected as part of a prospective international survey, the IPA/Erasmus MC Pompe survey, which was conducted annually between 2002 and 2016. We excluded patients who were already using a wheelchair or respirator, those under 18 at survey entry, and those who had missing information. Time-dependent Cox proportional hazard models were used.

Results

The inclusion criteria for analyzing the risk of wheelchair use were met by 189 patients (median age 47 years; range 18–75). During follow-up, 126 (67%) started ERT. Over 1120 person-years of follow-up (median 5 years), 46 became wheelchair dependent, 16 of whom used ERT. After adjustment for disease duration, sex and country, ERT reduced the risk for wheelchair use (HR 0.36; 95% CI 0.17–0.75). For analyses of respirator use, 177 patients met the inclusion criteria (median age 46 years; range 18–73). Over 1190 person-years of follow-up (median 6 years), 125 patients (71%) were treated and 48 started respiratory support, 28 of whom received ERT. We found no association between ERT and the risk for respirator use (HR 1.23; 95% CI 0.61–2.47).

Conclusions

Our study found that ERT reduced the risk for wheelchair dependency. We could not demonstrate an effect on respiratory support.

Quantification of intramuscular fat in patients with late-onset Pompe disease by conventional magnetic resonance imaging for the long-term follow-up of enzyme replacement therapy

OBJECTIVE

The objective of this study was to evaluate a quantitative method based on conventional T1-weighted magnetic resonance (MR) imaging to assess fatty muscular degeneration in patients with late-onset Pompe disease and to compare it with semi-quantitative visual evaluation (the Mercuri score). In addition, a long-term retrospective data analysis was performed to evaluate treatment response to enzyme replacement therapy with alglucosidase alfa.

METHODS

MR images of the lumbar spine were acquired in 41 patients diagnosed with late-onset Pompe disease from 2006 through 2015. Two independent readers retrospectively evaluated fatty degeneration of the psoas and paraspinal muscles by applying the Mercuri score. Quantitative semi-automated muscle and fat tissue separation was performed, and inter-observer agreement and correlations with clinical parameters were assessed. Follow-up examinations were performed in 13 patients treated with alglucosidase alfa after a median of 39 months; in 7/13 patients, an additional follow-up examination was completed after a median of 63 months.

RESULTS

Inter-observer agreement was high. Measurements derived from the quantitative method correlated well with Medical Research Council scores of muscle strength, with moderate correlations found for the 6-minute walk test, the 4-step stair climb test, and spirometry in the supine position. A significant increase in the MR-derived fat fraction of the psoas muscle was found between baseline and follow-up 1 (P = 0.016), as was a significant decrease in the performance on the 6-minute walk test (P = 0.006) and 4-step stair climb test (P = 0.034), as well as plasma creatine kinase (P = 0.016). No statistically significant difference in clinical or MR-derived parameters was found between follow-up 1 and follow-up 2.

CONCLUSIONS

Quantification of fatty muscle degeneration using the semi-automated method can provide a more detailed overview of disease progression than semi-quantitative Mercuri scoring. MR-derived data correlated with clinical symptoms and patient exercise capacity. After an initial worsening, the fat fraction of the psoas muscle and performance on the 6-minute walk test stayed constant during long-term follow-up under enzyme replacement therapy.

The impact of Pompe disease on smooth muscle: a review

Pompe disease (OMIM 232300) is an autosomal recessive disorder caused by mutations in the gene encoding acid α-glucosidase (GAA) (EC 3.2.1.20), the enzyme responsible for hydrolyzing lysosomal glycogen. The primary cellular pathology is lysosomal glycogen accumulation in cardiac muscle, skeletal muscle, and motor neurons, which ultimately results in cardiorespiratory failure. However, the severity of pathology and its impact on clinical outcomes are poorly described in smooth muscle. The advent of enzyme replacement therapy (ERT) in 2006 has improved clinical outcomes in infantile-onset Pompe disease patients. Although ERT increases patient life expectancy and ventilator free survival, it is not entirely curative. Persistent motor neuron pathology and weakness of respiratory muscles, including airway smooth muscles, contribute to the need for mechanical ventilation by some patients on ERT. Some patients on ERT continue to experience life-threatening pathology to vascular smooth muscle, such as aneurysms or dissections within the aorta and cerebral arteries. Better characterization of the disease impact on smooth muscle will inform treatment development and help anticipate later complications. This review summarizes the published knowledge of smooth muscle pathology associated with Pompe disease in animal models and in patients.

Long-term benefit of enzyme replacement therapy in Pompe disease: A 5-year prospective study

OBJECTIVE

To determine the effect of enzyme replacement therapy (ERT) after 5 years and to identify predictors for a favorable response because few data are available on the long-term efficacy of ERT in Pompe disease.

METHODS

We included 102 adult patients with Pompe disease in a nationwide, prospective cohort study. We assessed muscle strength (manual muscle testing with Medical Research Council [MRC] grading, handheld dynamometry [HHD]), muscle function (6-minute walk test, Quick Motor Function Test), daily life activities (Rasch-Built Pompe-Specific Activity [R-PAct] Scale), and pulmonary function (forced vital capacity [FVC] in upright and supine positions, maximum inspiratory and expiratory pressures) at 3- to 6-month intervals before and after the start of ERT. Data were analyzed with linear mixed-effects models for repeated measurements.

RESULTS

Median follow-up duration was 6.1 years (range 0.4-7.9 years), of which 5.0 years (range 0.2-7.3 years) were during ERT. Treated patients had better muscle strength (MRC sum score +6.6 percentage points [pp]; HHD sum score +9.6 pp, both p < 0.0001), activity levels (R-PAct +10.8 pp, p < 0.002), and pulmonary function (FVC upright +7.3 pp, FVC supine +7.6 pp, both p < 0.0003) than expected for their untreated disease course. Walking distance improved (416 vs 376 m at baseline, p = 0.03). The largest increase was seen during the first 2 to 3 years of treatment. Response to treatment was similar between groups regardless of sex, age, or disease duration.

CONCLUSIONS

Long-term ERT positively affects muscle strength, pulmonary function, and daily life activities in adult patients with Pompe disease, with a peak effect at ≈2 to 3 years of treatment.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that for patients with Pompe disease, long-term ERT positively affects muscle strength, pulmonary function, and daily life activities.

Effect of enzyme replacement therapy with alglucosidase alfa (Myozyme®) in 12 patients with advanced late-onset Pompe disease

BACKGROUND

The efficacy of enzyme replacement therapy (ERT) in patients at an advanced stage of Pompe disease has only been addressed in a few studies. Our objective was to assess the long term effects of ERT in a cohort of patients with severe Pompe disease.

METHODS

We identified patients from the French Pompe Registry with severe respiratory failure and permanent wheelchair use (assisted walk for a few meters was allowed) when starting ERT. Patients' medical records were collected and reviewed and respiratory and motor functions, before ERT initiation and upon last evaluation were compared.

RESULTS

Twelve patients (7 males) were identified. Median age at symptom onset was 24years [IQR=15.5; 36.0]. At baseline ventilation was invasive in 11 patients and noninvasive in one, with a median ventilation time of 24h [IQR=21.88; 24.00] (min 20; max 24). ERT was initiated at a median age of 52.5years [IQR=35.75; 66.50]. Median treatment duration was 55months [IQR=39.5; 81.0]. During observational period no adverse reaction to ERT was recorded, five patients (41.67%) died, three decreased their ventilation time by 30, 60 and 90min and two increased their assisted walking distance, by 80 and 20m.

CONCLUSION

Some patients at a very advanced stage of Pompe disease may show a mild benefit from ERT, in terms of increased time of autonomous ventilation and of enlarged distance in assisted walk. ERT can be initiated in these patients in order to retain their current level of independence and ability to perform daily life activities.

Effects of short-to-long term enzyme replacement therapy (ERT) on skeletal muscle tissue in late onset Pompe disease (LOPD)

AIMS

Pompe disease is an autosomal recessive lysosomal storage disorder resulting from deficiency of acid α-glucosidase (GAA) enzyme. Histopathological hallmarks in skeletal muscle tissue are fibre vacuolization and autophagy. Since 2006, enzyme replacement therapy (ERT) is the only approved treatment with human recombinant GAA alglucosidase alfa. We designed a study to examine ERT-related skeletal muscle changes in 18 modestly to moderately affected late onset Pompe disease (LOPD) patients along with the relationship between morphological/biochemical changes and clinical outcomes. Treatment duration was short-to-long term.

METHODS

We examined muscle biopsies from 18 LOPD patients at both histopathological and biochemical level. All patients underwent two muscle biopsies, before and after ERT administration respectively. The study is partially retrospective because the first biopsies were taken before the study was designed, whereas the second biopsy was always performed after at least 6 months of ERT administration.

RESULTS

After ERT, 15 out of 18 patients showed improved 6-min walking test (6MWT; P = 0.0007) and most of them achieved respiratory stabilization. Pretreatment muscle biopsies disclosed marked histopathological variability, ranging from an almost normal pattern to a severe vacuolar myopathy. After treatment, we detected morphological improvement in 15 patients and worsening in three patients. Post-ERT GAA enzymatic activity was mildly increased compared with pretreatment levels in all patients. Protein levels of the mature enzyme increased in 14 of the 18 patients (mean increase = +35%; P < 0.05). Additional studies demonstrated an improved autophagic flux after ERT in some patients.

CONCLUSIONS

ERT positively modified skeletal muscle pathology as well as motor and respiratory outcomes in the majority of LOPD patients.

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

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

GAA Deficiency in Pompe Disease Is Alleviated by Exon Inclusion in iPSC-Derived Skeletal Muscle Cells

Pompe disease is a metabolic myopathy caused by deficiency of the acid α-glucosidase (GAA) enzyme and results in progressive wasting of skeletal muscle cells. The c.-32-13T>G (IVS1) GAA variant promotes exon 2 skipping during pre-mRNA splicing and is the most common variant for the childhood/adult disease form. We previously identified antisense oligonucleotides (AONs) that promoted GAA exon 2 inclusion in patient-derived fibroblasts. It was unknown how these AONs would affect GAA splicing in skeletal muscle cells. To test this, we expanded induced pluripotent stem cell (iPSC)-derived myogenic progenitors and differentiated these to multinucleated myotubes. AONs restored splicing in myotubes to a similar extent as in fibroblasts, suggesting that they act by modulating the action of shared splicing regulators. AONs targeted the putative polypyrimidine tract of a cryptic splice acceptor site that was part of a pseudo exon in GAA intron 1. Blocking of the cryptic splice donor of the pseudo exon with AONs likewise promoted GAA exon 2 inclusion. The simultaneous blocking of the cryptic acceptor and cryptic donor sites restored the majority of canonical splicing and alleviated GAA enzyme deficiency. These results highlight the relevance of cryptic splicing in human disease and its potential as therapeutic target for splicing modulation using AONs.

Investigation on acute effects of enzyme replacement therapy and influence of clinical severity on physiological variables related to exercise tolerance in patients with late onset Pompe disease

Exercise intolerance is one of the clinical hallmarks of late-onset Pompe disease (LOPD). We studied the acute effects of ERT on the physiological variables associated with exercise tolerance in patients chronically ERT treated. Moreover, we assessed the influence of clinical severity on the investigated variables. The day before (B) and the day after (A) ERT injection, 11 LOPD patients performed on a cycle-ergometer an exercise tolerance test to voluntary exhaustion; VO₂, HR, RPE, and GAA activity were determined in B and A. The disease severity was characterized by Walton scale, 6MWT, and pulmonary function tests. No significant differences in the variables related to exercise tolerance were found in A vs B, despite a significant increase in GAA activity in peripheral lymphocytes. No differences in VO₂ peak were observed between patients with only skeletal muscle impairment and patients with both skeletal and respiratory muscle impairment. Distance walked at 6MWT was significantly higher than VO₂ peak expressed as percentage of normal values. In conclusion, in LOPD patients the exercise tolerance test is not acutely affected by ERT administration; the peripheral muscle component seems more prominent in determining the VO₂ peak decrease than the respiratory component; VO₂ peak might be more sensitive than 6MWT in estimating exercise tolerance in LOPD.

Prospective exploratory muscle biopsy, imaging, and functional assessment in patients with late-onset Pompe disease treated with alglucosidase alfa: The EMBASSY Study

BACKGROUND

Late-onset Pompe disease is characterized by progressive skeletal myopathy followed by respiratory muscle weakness, typically leading to loss of ambulation and respiratory failure. In this population, enzyme replacement therapy (ERT) with alglucosidase alfa has been shown to stabilize respiratory function and improve mobility and muscle strength. Muscle pathology and glycogen clearance from skeletal muscle in treatment-naïve adults after ERT have not been extensively examined.

METHODS

This exploratory, open-label, multicenter study evaluated glycogen clearance in muscle tissue samples collected pre- and post- alglucosidase alfa treatment in treatment-naïve adults with late-onset Pompe disease. The primary endpoint was the quantitative reduction in percent tissue area occupied by glycogen in muscle biopsies from baseline to 6months. Secondary endpoints included qualitative histologic assessment of tissue glycogen distribution, secondary pathology changes, assessment of magnetic resonance images (MRIs) for intact muscle and fatty replacement, and functional assessments.

RESULTS

Sixteen patients completed the study. After 6months of ERT, the percent tissue area occupied by glycogen in quadriceps and deltoid muscles decreased in 10 and 8 patients, respectively. No changes were detected on MRI from baseline to 6months. A majority of patients showed improvements on functional assessments after 6months of treatment. All treatment-related adverse events were mild or moderate.

CONCLUSIONS

This exploratory study provides novel insights into the histopathologic effects of ERT in late-onset Pompe disease patients. Ultrastructural examination of muscle biopsies demonstrated reduced lysosomal glycogen after ERT. Findings are consistent with stabilization of disease by ERT in treatment-naïve patients with late-onset Pompe disease.

Survival and long-term outcomes in late-onset Pompe disease following alglucosidase alfa treatment: a systematic review and meta-analysis

A number of studies have assessed the efficacy of alglucosidase alfa as an enzyme replacement therapy (ERT) on motor and respiratory endpoints in patients with late-onset Pompe disease (LOPD). A previous review evaluated the clinical efficacy and safety of alglucosidase alfa; however, it is difficult to draw inferences from individual studies due to small patient populations, particularly in evaluating the benefit on survival. To evaluate the current evidence on the long-term efficacy of alglucosidase alfa with regard to survival, motor, and respiratory function in patients with LOPD in relation to the natural progression of the disease, a new systematic literature review was performed identifying studies that assessed either mortality, percent predicted forced vital capacity (% FVC), or the 6-min walk test (6MWT) among treated and untreated LOPD patients. Patient overlap was avoided by removing smaller studies or ensuring the use of only one conflicting study per outcome. Mortality was modeled using Poisson models for each treatment group. Outcomes were modeled using first- and second-order fractional polynomial meta-analysis with fixed- and random-effects. Meta-regression was used to explore sources of heterogeneity. Twenty-two publications pertaining to 19 studies/trials were selected, including 438 patients when accounting for overlaps, with the average study duration being 45.7 months. Patients treated with alglucosidase alfa in these studies had a nearly five-fold lower mortality rate than untreated patients (rate ratio: 0.21; 95 % credible interval: 0.11, 0.41). On average, % FVC declined consistently among untreated patients, including a 2.3 % decline after 12 months follow-up and 6.2 % decline after 48 months. This is in contrast to alglucosidase alfa-treated patients, who, on average, improved rapidly, with an increase of 1.4 % FVC after 2 months, followed by a slow regression back to baseline over a three-year period. Nonetheless, the relative difference between those treated and not grew over time, from 4.5 % FVC after 12 months to 6 % FVC after 48 months. In the 6MWT, alglucosidase alfa-treated patients on average had the largest improvement over the first 20 months of treatment of approximately 50 meters increase over baseline, with its substantial stabilization in the following years. By comparison, untreated patients do not show 6MWT improvement over time. Alglucosidase alfa has a beneficial effect in LOPD patients as demonstrated by improvements in survival and ambulation maintained over time, as well as prevention of deterioration in respiratory function.

Disease models for the development of therapies for lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of rare diseases in which the function of the lysosome is disrupted by the accumulation of macromolecules. The complexity underlying the pathogenesis of LSDs and the small, often pediatric, population of patients make the development of therapies for these diseases challenging. Current treatments are only available for a small subset of LSDs and have not been effective at treating neurological symptoms. Disease-relevant cellular and animal models with high clinical predictability are critical for the discovery and development of new treatments for LSDs. In this paper, we review how LSD patient primary cells and induced pluripotent stem cell-derived cellular models are providing novel assay systems in which phenotypes are more similar to those of the human LSD physiology. Furthermore, larger animal disease models are providing additional tools for evaluation of the efficacy of drug candidates. Early predictors of efficacy and better understanding of disease biology can significantly affect the translational process by focusing efforts on those therapies with the higher probability of success, thus decreasing overall time and cost spent in clinical development and increasing the overall positive outcomes in clinical trials.

Pompe Disease: Diagnosis and Management. Evidence-Based Guidelines from a Canadian Expert Panel

Pompe disease is a lysosomal storage disorder caused by a deficiency of the enzyme acid alpha-glucosidase. Patients have skeletal muscle and respiratory weakness with or without cardiomyopathy. The objective of our review was to systematically evaluate the quality of evidence from the literature to formulate evidence-based guidelines for the diagnosis and management of patients with Pompe disease. The literature review was conducted using published literature, clinical trials, cohort studies and systematic reviews. Cardinal treatment decisions produced seven management guidelines and were assigned a GRADE classification based on the quality of evidence in the published literature. In addition, six recommendations were made based on best clinical practices but with insufficient data to form a guideline. Studying outcomes in rare diseases is challenging due to the small number of patients, but this is in particular the reason why we believe that informed treatment decisions need to consider the quality of the evidence.

Reevaluating Muscle Biopsies in the Diagnosis of Pompe Disease: A Corroborative Report

Background: Previous reports suggest that although a diagnostic muscle biopsy can confirm the presence of Pompe disease, the absence of a definitive biopsy result does not rule out the diagnosis. Methods: In this study, we reviewed patients with a limb-girdle syndrome who demonstrated nonspecific abnormalities of muscle, without evidence of the classical changes of acid maltase deficiency. These patients were rescreened for Pompe disease using dried blood spot (DBS) testing. Results: Twenty-seven patients provided blood samples for the DBS test. Four patients underwent subsequent genetic testing. Genetic analysis demonstrated that one patient tested positive for Pompe disease and one patient had one copy of a pathogenic variant. Conclusions: In conclusion, the ability of a diagnostic muscle biopsy to definitively rule out the presence of Pompe disease is limited. There is a role for a screening DBS in all patients presenting with a limb-girdle syndrome without a clear diagnosis.

Observational clinical study of 22 adult-onset Pompe disease patients undergoing enzyme replacement therapy over 5years

Pompe disease is an autosomal recessive disease resulting from deficiency of the acid alpha-glucosidase (GAA). The late-onset Pompe Disease (LOPD) patients develop muscular and respiratory complications later in life. We describe a retrospective observational cohort study including 22 patients with LOPD. The cohort was assessed at baseline before Enzyme Replacement Therapy (ERT) with alglucosidase alpha (20mg/kg biweekly) was commenced and subsequently relevant information was collected at 2, 4 and 5years later. The median age of the patients at study entry was 44years (16-64years), with median disease duration of 11.5years (4-31years). At baseline, 10 patients (45%) could walk without support, 12 (55%) could walk with unilateral or bilateral support including 3/12 were wheelchair bound. Mean predicted FVC % was 55.7 (95% CI 45-66) of predicted normal at baseline and showed no significant change after 5years (54.6 (95% CI 43-66)), (all p=0.9815). Mean FVC % supine was 41.8 (95% CI 33.8-49) of predicted normal at baseline and remained significantly unchanged at 5years (48.4 (95% CI 37-59.6)), (all p=0.8680). The overnight non-invasive ventilator dependence increased by 18.2% as compared with baseline and requirement of mobility aids increased during this period by 5.2% as compared with the baseline. Mean walking distance at 6min walk test was 411.5 (95% CI 338-485) at baseline, 266.5 (95% CI 187-346) m at 2years, 238.6 (95% CI 162-315) m at 4years and 286.8 (95% CI 203-370) m at 5years (p=0.1981; ANOVA was completed only for 14 patients). A gradual decline in FVC% predicted was noted only in four cases and a decline in FVC% supine in two other. Only one patient showed a decline in both pulmonary function tests. In all remaining cases (17/22) respiratory function remains stable. In conclusion overall pulmonary function tests and mobility remained stable for 5years in majority of patients on ERT. However, in some patients they continued to decline in spite of ERT resulting in increased number of patients requiring ventilation and increase wheel chair dependence at the end of 5years.

Role of the cardio-pulmonary exercise test and six-minute walking test in the evaluation of exercise performance in patients with late-onset Pompe disease

In patients with late-onset Pompe disease, we explored the role of the Cardiopulmonary Exercise Test (CPET) and the Six-Minute Walking Test (6MWT) in the assessment of exercise capacity and in the evaluation of the effects of enzyme replacement therapy (ERT). Eight patients affected by late-onset Pompe disease, followed up at the Centre for Neuromuscular Diseases and treated with ERT, underwent a baseline evaluation with a spirometry, a CPET and a 6MWT. Four of them were restudied after 36 months of treatment. Three patients showed a reduction in exercise capacity as evaluated by peak oxygen uptake (VO2) measured at the CPET and Distance Walked (DW) measured at the 6MWT (median % predicted: 67.1 [range 54.3-99.6] and 67.3 [56.6-82.6], respectively). Cardiac and respiratory limitations revealed by the CPET were correlated to peak VO2, but not to the DW. Nevertheless, percent of predicted values of peak VO2 and DW were strongly correlated (rho = 0.85, p = 0.006), and close to identity. In the longitudinal evaluation forced vital capacity decreased, while peak VO2 and DW showed a trend to a parallel improvement. We concluded that although only the CPET revealed causes of exercise limitation, which partially differed among patients, CPET and 6MWT showed a similar overall degree of exercise impairment. That held true in the longitudinal assessment during ERT, where both tests demonstrated similar small improvements, occurring despite deterioration in forced vital capacity.